Eric F. Greenberg
Attorney and partner, Bullwinkel Partners, Ltd., Chicago, Illinois, USA
The legal status of a food article or food component is a crucial part of the evaluation of any new product development project. Questions such as whether it will require pre-approval, timing to market, and how it may be labeled and advertised, are an essential part of development strategy.
Matching the explosive growth of the industries, rapid changes are occurring
in the regulatory treatment of functional foods, medical foods, foods for
special dietary use, dietary supplements, and even conventional foods.
Enormous changes have also been made recently, and continue, in the legal
treatment of substances considered to be Generally Recognized As Safe,
indirect food additives, and direct food additives.
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Investigating the molecular origins of protein structure and function at interfaces
Michelle K. Bothwell and JOSEPH McGUIRE
Biological Engineering, Oregon State University, Corvallis, Oregon
An understanding of the relationship between a protein's structure and its function at interfaces is important in a number of areas relevant es is important in a number of areas relevant to food, pharmaceutical and biomedical technology. We know much about surface and solution influences on interfacial behavior, but relatively little about how protein properties affect adsorption phenomena. One way to gain a better understanding of the molecular origins of protein surface activity is by comprehensive study of sets of molecules varying only in a single property considered relevant to their interfacial behavior. We have been studying the interfacial behavior of charge- and structural stability mutants of bacteriophage T4 lysozyme (T4L). The T4L mutants constitute the largest, most well-characterized set of synthetic mutants of a single protein available anywhere in the world. Numerous variants of this protein have been synthesized and characterized with respect to their deviations in crystal structure and thermodynamic stability from the wild type.
The isoleucine at position 3 (Ile 3) in T4L has been replaced with 13 different amino acid residues by site-directed mutagenesis. In that work, thermodynamic measurements of stability, along with high resolution X-ray structural analyses were used to unambiguously illustrate the contribution of hydrophobic interaction at the site of Ile 3 to the overall structural stability of the protein. In the case of charge mutants, selected lysine residues were replaced with glutamic acid to produce proteins varying in net charge from +5oteins varying in net charge from +5 to +9. We have used both types of T4L mutants to quantify the influence of these properties on adsorption at solid-water and air-water interfaces using a number of techniques. We completed several studies using in situ ellipsometry and surfactant-mediated elution, and recently performed spectrophotometric assays of enzymatic activity of T4L mutants bound to colloidal silica [1]. In addition, ring tensiometry, the interferometric surface force technique [2], and circular dichroism [3] have recently been applied to T4L stability mutants. Sequential and competitive adsorption from mixtures of T4L variants have been recorded at both air-water and solid-water interfaces, using 14C and 125I labels. From an engineering standpoint, we believe the most important result of our past work is that T4L adsorption can be modeled as occurring such that molecules adopt specific structural "states" at the interface. These states are distinguished by differences in binding strength, occupied area, and function, with differences in behavior among protein variants attributable to the relative amounts adsorbed in each state.
For modeling purposes, the simplest adsorption mechanism consistent with the fact that adsorbed proteins can exist in multiple states would include two adsorbed states. Figure 1 shows such a mechanism. Rate constants k1 and k2 gover k1 and k2 govern adsorption into states 1 and 2, respectively. If adsorption of practically relevant proteins can be adequately described in this way, extension to the case of competitive protein adsorption would be straightforward. Figure 2 shows a mechanism for competitive adsorption (between two proteins, A and B) based on Fig. 1. In each case, all associated rate constants can be determined a priori. The protein-specific, surface-coverage dependent k1C and k2C of Fig. 2 can be obtained from single-component kinetic data and the various exchange constants can be determined through sequential adsorption experiments. It is a simple matter to simulate the adsorption kinetics associated with each fractional surface coverage, and these simulated patterns can be compared to experimental kinetic data for adsorption from binary mixtures [4]. Figure 2 can be easily redrawn to depict competitive adsorption ocompetitive adsorption of three proteins A, B, and C. So long as we have sequential adsorption data for each pair permutation of A, B and C, we will have an a priori estimate of all rate constants and their competition can be simulated.
Figure 1 A simple mechanism for protein Figure 2. A mechanism for competitive
adsorption from single-component solutions. adsorption between two proteins A and
B, based on Fig. 1.
Structural changes are believed to be one of the driving forces for protein adsorption. Several mechanisms and models for protein adsorption at solid surfaces have been described in the literature and most include some kind of structural alteration in the adsorbed protein. Motivation for development of such models is their potential for quantifying protein interfacial behavior in real circumstances. Understanding the role of structural stability in adoption of multiple adsorption states is thus needed to understand and eventually control events at an interface. Much current effort is focused on study of structure and function of the nonenzymatic, protein antimicrobial nisin, in regard to applications in drug formulation. As we have met with success in describing protein-specific differences in adsorption behavior in terms fferences in adsorption behavior in terms of protein-specific tendencies for adsorbing into different structural states, and we expect to describe protein-specific differences in interfacial function (i.e., biological activity) in the same mechanistic sense.
Cited references:
- Bower, C.K., Xu, Q., McGuire, J. (1998). Activity losses among T4 lysozyme variants after adsorption to colloidal silica particles. Biotechnol. Bioeng., 58, 658-662.
- Fröberg, J.C., Arnebrant, T., McGuire, J., Claesson, P.M. (1998). Effect of structural stability on the characteristics of adsorbed layers of T4 lysozyme. Langmuir, 14, 456-462.
- Tian, M., Lee, W.-K., Bothwell, M.K., McGuire, J. (1998). Structural stability effects on adsorption of bacteriophage T4 lysozyme to colloidal silica. J. Colloid Interface Sci., 200, 146-154.
Lee, W.-K., McGuire, J., Bothwell, M.K. (1999). A mechanistic approach to modeling single protein adsorption at solid-water interfaces. J. Colloid Interface Sci., in press.
ANTIMUTAGENIC AND / OR ANTICARCINOGENIC PROPERTIES OF MILK PROTEINS COMPARED TO SOY PROTEINS
Pirkko T. Antilaa and Hannu J. Korhonenb
-
Professsup>and Hannu J. Korhonenb
- Professor Emeritus, University of Helsinki
- Prof., Agricultural Research Centre of Finland, Food Research Institute, FIN-31600, Finland
Research in this area has been carried out under both in vitro and in vivo conditions in animals and also using human cancer cell lines. The anticarcinogenic properties of milk proteins are mostly elucidated by colorectal and mammary gland models.The antimutagenicity of the whole milk proteins (skim milk powder) and casein have been indicated. Compared to soy proteins and some other food proteins (meat, wheat), milk proteins, especially casein, have shown to to be highly antimutagenic. On the other hand, whey protein concentrates do not have much antimutagenic activity. Of the individual whey proteins serum albumin and lactoferrin are more antimutagenic than other whey proteins. Enzymatic digestion improves antimutagenecity of both milk and soy proteins. Latest results indicate that heat treatments do not destroy antimutagenic activity of caseinnot destroy antimutagenic activity of casein.
The anticarcinogenicity of milk proteins is more connected with the whey proteins than caseins. In this respect, whey proteins belong to the most active protein sources. Also casein has anticarcinogenic activity which is stronger than in meat, wheat and soy protein. According to many studies pure soy protein has the lowest activity. On the other hand, soy protein isolates containing phytoestrogens (isoflavonoids) have indicated to posses anticarcinogenic properties.The most studied of them is genistein. Recent studies have given promising results from the chemoterapeutic properties of isoflavonoids retarding especially hormone derived breast and prostate cancers. Another very potential anticarcinogenic agent in soy beans is the Bowman –Birk protease inhibitor (BBI). It is a protein of a molecular weight of 8000. Its concentrations in soy products e.g. in tofu have been postulated to be high enough to cause therapeutic effects in cancer prevention. . To the other proteins with direct or indirect anticarcinogenic properties belong different binding proteins; iron binding lactoferrin and folate-, B12- and retinol- binding proteins representing minor whey proteins. Different growth factors isolated from whey have also indicated anticarcinogenic activities e.g. peptide growth factor TGF-b and basic fibroblast growth factor bFGF.
The structure and amino acir bFGF.
The structure and amino acid composition of proteins as well as the infuences of peptides released during the digestion of proteins are factors determining their cancer preventing properties. The most anticarcinogenic whey proteins are rich in sulphur containing amino acids. Their inhibition impact on the carcinogenesis has been explained e.g. by glutathione and methylation hypotheses. Also, the immunomodulating peptides may confer anticarcinogenic effects.
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Structure-function relationship of whey proteins: A review
JOYCE I. BOYEa, Inteaz Allib, Chin -Y. Mac
a. Agriculture & Agri-Food Canada, 3600 Casavant West, St. Hyacinth, QC, Canada J2S 8E3
b. Department of Food Science, McGill University, Ste Anne de Bellevue, QC, Canada H9X 3V9
c. Department of Botany, University of Hong Kong, Pokfulam Road, Hong Kong
Physicochemical properties of the three major whey proteins ( beta-lactoglobulin -lg; alpha-lactalbumin, -lac; bovine serum albumin, BSA) play a significant role in the overall functionality of whey protein concentrates and isolates [1-4]. Expression of a specific functional property, may be directly correlated with molecular changes occurring at the primary, secondary and tertiary structural levels [mary, secondary and tertiary structural levels [4]. -lg, is an 18 Kda protein which consists primarily of antiparallel -sheets and exists as a dimer under physiological conditions. Genetic polymorphism is a characteristic of this protein. Seven variants have been identified which vary in their amino acid composition. Various studies have shown that the seemingly minor differences in the primary structure of these variants have significant effects on their physicochemical properties [3]. Understanding the functional implication of these differences is imperative to the accurate selection of particular variants for specific use in foods. -Lac, is a low molecular weight calcium-binding protein with remarkable renaturability. In solution, it undergoes a series of intermolecular interactions leading to varying degrees of polymerization [1]. Although the protein does not easily form a gel by itself, its presence has been shown to enhance the gelling capacity of -lg. Blling capacity of -lg. BSA is a large globular protein consisting of 580 amino acid residues that has also been shown to enhance the aggregation and gelation of -lg. Effective utilization of these proteins in food formulation requires detailed knowledge of the changes occurring at their molecular level when processed. Results from differential scanning calorimetry, Fourier transform infrared spectrometry, size exclusion HPLC, mass spectrometry, electron microscopy and rheological studies showing the relationship between secondary structure, thermal stability and functional properties of these proteins will be reviewed.
Cited references
1. Boye, J. I., Alli, I., Ismail, A. (1997). Use of differential scanning calorimetry and infrared spectroscopy in the study of thermal and structural stability of -lactalbumin. J. Agric. Food Chem., 45, 1116-1125.
2. Boye, J. I., Alli, I., Ismail, A. (1996). Interactions involved in the gelation of bovine serum
albumin. J. Agric. Food Chem., 44, 996-1004.
3. Boye, J. I., Ma, C. -Y., Ismail, A. A. (1998). Thermal denaturation and gelation characteristics of -lactoglobulin genetic variants. In "Functional properties of food components," ed. J. R. Whitaker. Am. Chem. Soc., Washington DC, USA, pp. 168-183.
4. Boye, J. I., Ma, C. -Y., Harwalkar, V. R. (1997). Thermal denaturation and coagulation of proteins. In "Food proteins and their applications. In "Food proteins and their applications," ed. S. Damodaran and A. Paraf. Marcel Dekker Inc., New York, USA, pp. 25- 56.
BACK TO INDEXMartin Beaulieu* and Sylvie L. Turgeon
Centre de Recherche en Sciences et Technologie du Lait, UniversitŽ Laval, Quebec, Canada.
Gelation and phase separation in food biopolymer mixtures are active research areas. Previous studies have shown the great potential of these blends for the improvement of food texture and the development of new products [1]. However, little has been done regarding whey proteins and low-methoxyl (LM) pectin systems. Whey proteins are used as functional ingredient in a variety of foods. When heated, whey proteins can gel via disulfide cross-links and the resulting gel can be affected by the pH and the mineral phase [2]. Pectin is an important polysaccharide, which has a variety of applications in the food and pharmaceutical industries. In LM pectins, gelation results from ionic linkage via calcium bridges between two carboxyl groups belonging to two different chains. Pectin gel formation is mainly dependent on the structural conformation of the pectin used, the calcium concentration, and the pH [3].
In this study, geltration, and the pH [3].
In this study, gelation of single and mixed solutions of whey protein isolates and LM pectins (DE=28, 35, 40, and 47) has been investigated using the penetrometry method. Ratios were adjusted to keep whey protein concentrations constant at 8%. Pectin and calcium concentrations were respectively fixed at 0.1, 0.5, 1.0, 1.5% and 0, 5, 10 mM. Heat treatment was used to induce whey protein gelation and the pH was adjusted to 6.0.
Gelation of single biopolymer solutions was not observed, except for protein solutions with 10 mM calcium, whereas mixed solutions allowed gel formation. Gel hardness was affected by the type and proportion of pectin, as well as the calcium concentration. Increasing the amount of pectin and the calcium concentration made mixed gels firmer. White gels were observed when calcium was added, indicating aggregation of whey proteins. This aggregation was modulated by the type of pectin used. Finally, results suggest that the gelation of whey proteins and LM pectin systems occurs through a competition between biopolymers for the binding of water and calcium.
Tolstoguzov, V.B. (1991). Functional properties of food proteins and role of protein-polysaccharide interaction. Food Hydrocolloids, 4, 429-468.
Aguilera, J.M. (1995). Gelation of whey proteins. Food Technology, 49, 83-89.
Voragen, A.G.J., Pilnik, W., Thibault, J.F., Axelos, M.A.V., Renard, C.M.G.C. (1995). PectinsM.A.V., Renard, C.M.G.C. (1995). Pectins. In ‘Food polysacchrides and their applications’ ed. A.M., Stephen. Marcel Dekker, New York, U.S.A., pp. 287-339.
BACK TO INDEX Functional Properties of Whey Proteins Fractionated by Complex Formation
LEORGES M. FONSECA and Robert L. Bradley Jr.
Department of Food Science, University of Wisconsin-Madison
1605, Linden Drive-Madison-WI 53706
Whey protein concentrate (WPC) and other whey protein derivatives are proteins with different functional properties. Desirable functionality of these proteins in food applications can be limited if a mixture is present, instead of pure fractions. We investigated a process to obtain different whey protein fractions by reacting WPC and dialysed WPC with complex carbohydrates at specific conditions. WPC and dialysed WPC were reacted with equal volumes of pectin, sodium alginate, propylene glycol alginate, carboxymethyl cellulose (CMC) and xanthan gum solutions. Reactions were done in the range of pH 2.0 to 6.0. The product was centrifuged at 1200 X G for 30 minutes, and the supernatant was analysed for protein composition. Protein and non-protein nitrogen were assayed using the Kjeldahl method. Assessment of specific proteins was done by SDS-PAGE electrophoresis with electronic recording of the gel images. Banlectronic recording of the gel images. Bands of proteins were measured by computer-assisted densitometry, viscosity measurements were made using the Brookfield method, and complex sizes were analysed by gel permeation chromatography. Other gravimetric analyses were done using AOAC methods.
Precipitation of up to 95% total protein was obtained with sodium alginate, CMC and xanthan gum in specific conditions. Less protein precipitation was obtained in low concentration CMC:WPC solutions due to formation of molecular compounds too small to precipitate. Fractions containing more than 95% of alpha-lactalbumin in the total protein were obtained with the use of xanthan gum and dialysed WPC in specific conditions. Protein precipitation was influenced by the ionic strength of salts in the WPC solutions. An increase in the ionic strength of sodium chloride or calcium chloride resulted in a decrease in the amount of precipitated protein. Fractions obtained after selective precipitation were concentrated by ultrafiltration or microfiltration, and their functional properties were studied. These experiments show the effect of using these complex carbohydrates to fractionate whey proteins, functional properties of the fractions obtained, conditions influencing yield, and carbohydrate-protein interactions and their effect on food systems.
Key words: Fractionation, Proteins, Whey protein concentrate
BACKr>BACK TO INDEXMicro-meat product models: tools to study meat and non-meat protein functionality
Randolph P. Happea, Stef. J. Koppelmana*, Riek Vlooswijka, Gerrit Wijngaardsa and Alard A. van Dijkb
a. TNO Nutrition and Food Research Institute, Zeist, The Netherlands
b. DSM Gist-Brocades, Food Specialties Division, Delft, The Netherlands
The performance of (non-meat) protein ingredients in meat product is usually judged by performing application tests, being an inevitable step in the track of developing and testing of new protein ingredients. Such application tests are time consuming and expensive, and require relatively large amounts of the ingredient. Th amounts of the ingredient. Therefore, easy and reliable small-scale tests (micro-meat product models) are favorable if many protein ingredients are to be tested. On basis of the outcome of such small-scale screening tests a deliberate decision can be made if it is worth the effort of evaluating a particular ingredient (e.g. a vegetable protein) in application tests.
Here the development of micro models for two types of meat products (I) cooked hams, and (II) cooked emulsified sausages is reported. The recipes of the models were intensively investigated. We varied meat source and type, the amount of added water, processing aids (e.g. polyphosphate), and processing steps. In the case of models for sausages, various vegetable oils and fats of animals sources were added. Either a meat extract, meat batter or ground meat was included in the model. Finally this led to models of a scale of 30 grams and lower.
Testing and evaluation of the products prepared in the models was mainly performed by means of a Lloyd load instrument in combination with the ‘Texture Profile Analysis software for data collection and mathematical processing. These tests were carried out in either a destructive mode (large-deformation) or a less-destructive mode (25 % deformation). They reveal information on hardness, fracture force and/or elastic properties. The back-extrusion test (method of Harper [1]) was used if very small scale products]) was used if very small scale products had to be tested (1-5 g). When it was of interest, estimates were made of the cooking loss (separated fat or water) [2].
The models were validated by comparison with the respective real meat products, either with or without added non-meat proteins. In a series of experiments we substituted part of the intrinsic meat proteins by commercially available protein ingredients (e.g. soy, milk proteins, plasma protein). The models compared well with the real products. Consequently, the required amount of a to be evaluated non-meat protein ingredient, can hereby be decreased to sub-gram scale. The fast processing procedure and rapid testing method lead to a significant gain in time.
Acknowledgments: This work was in part financed by the Dutch Ministry of Economical Affairs.
Cited references:
[1] Harper, J.P., Suter, D.A., Dill, C.W. and Jones, E.R. (1978), J. Food Sci. 43, 1204-1209.
[2] Hall, G.W., ed. (1996), Methods of testing protein functionality, Blackie Academic & Professional, London
BACK TO INDEXFunctional and Structural Characteristics of Acid-Hydrolyzed Whey Protein Concentrate
NOOSHIN ALIZADEH-PASDARa* & Inteaz. Allib
a. Department of Food Science, The University
a. Department of Food Science, The University of British Columbia, 6650 NW Marine Drive, Vancouver, B.C. Canada V6T 1Z4
b. Department of Food Science and Agricultural Chemistry, Macdonald Campus of McGill University, 21111 Lakeshore, Ste-Anne-de-Bellevue, Quebec, Canada H9X 3V9
Proteins, especially milk proteins, represent a very important class of functional ingredients in many foods. By intentional modification of physicochemical properties of a protein, the functional properties can be altered [Kinsella, 1976]. Modification of proteins can be achieved by chemical, enzymatic [Babiker et al., 1996], or physical [Nakai and Li-Chan, 1985] means. It has been shown that acidic modification of proteins can improve their functional properties [Matsudomi et al., 1985]. However, this method of modification is not used for improving whey proteins functionality.
The objective of this study was to investigate the effects of acid hydrolysis (AH) on whey protein concentrate (WPC). The products of the hydrolysis were identified by electrophoresis, reverse phase-high pressure liquid chromatography (RP-HPLC) and mass spectrometry (MS), and the functional properties of the hydrolysates were determined.
Dispersions of WPC in organic acids (0.5 N, 1 N and 1.5 N acetic acid, citric acid, phosphoric acid and mixture of these acids were subjected to acid hydrolysis (6, 18 and 48 h) and the effects of this modification onh) and the effects of this modification on functional properties were assessed. The degrees of hydrolysis were measured and freeze-dried hydrolysates were evaluated for their foam capacity and stability, emulsifying activity and stability index and toughness.
Highest foam capacity was found in the hydrolysate obtained using 0.5 N acetic acid. AH increased foam stability, in general. In addition, AH did not affect emulsifying activity index but gave higher emulsifying stability index and toughness of prepared gels. Results of electrophoresis indicated that a -lactalbumin was the most sensitive protein with significant degradation after 6 h hydrolysis. RP-HPLC analysis of peptides identified three major peaks in the unhydrolyzed WPC and three other peptides after 18 h hydrolysis. The molecular weight of peptides were identified using MS.
Cited References:
Babiker, E.F.E.; Fujisawa, N.; Matsudomi, N. and Kato, A. (1996). Improvement in the functional properties of gluten by protease digestion or acid hydrolysis followed by microbial transglutaminase treatment. J. Agric. Food Chem. 44, 3746-3750.
Kinsella, J.E. (1976). Functional properties of proteins in foods: a survey. CRC Crit. Rev. Food Sci. Nutr. 76, 219-225.
Matsudomi, N. Sasaki, T. Kato, A. and Kobayashi, K. (1985). Conformational changes and functional properties of acid-modified soy protein. Agric. Biol. Chem. 49, 1251d soy protein. Agric. Biol. Chem. 49, 1251-1256.
Nakai, S. and Li-Chan, E. (1985). Structure modification and functionality of whey proteins. J. Dairy Sci. 68, 2763-2772.
BACK TO INDEXProtein gel induction by chemical and physical means
Alfonso Totosausa*, Gerardo Montejanob and Isabel Guerreroa.
- Departamento de Biotecnología, UAM-Iztapalapa, Apdo. Postal 55-535, México City, México.
- ITESM-campus Querétaro, Apdo. Postal 37, Querétaro 76000, Qro., México.
Heat-induced gelling occurs in two steps: first, partial denaturation of the protein molecule followed by gradual association or aggregation of molecules in order to form a matrix [1]. As sol-gel transition of proteins is affected by mainly by pressure [2], high pressure is also applied to form protein gels. Here, high pressure is also applied to form protein gels. Here, portions of covalent bonds are involved although hydrophobic and ionic forces are also responsible of the matrix formation [3]. High-pressure gel induction is not as efficient as gel induction by heating, and a less rigid matrix is formed; a combination of pressure and heating produces a more stable gel [4, 5, 6].
Acid-induced gelling is achieved by a slow lowering of pH. Glucolactone addition to a protein solution promotes acidification resulting in gel formation [7, 8]. Transglutaminase (E.C.2.3.2.13) is obtained from strains of Streptoverticillium mobaraense, it is a non-Ca2+ dependent enzyme used to enhance "setting" of surimi paste [9]. It induces covalent cross-links among different protein chains, hence forming a gel matrix [10]. Calcium-induced gelling occurs in two steps: the first one consists in globular protein denaturation and polymerization by heating so they form high molecul so they form high molecular weight aggregates; this step is followed by cooling and a calcium salt addition resulting in a lattice formation due to Ca2+-mediated interactions [11, 12]. Urea-induced gels are formed via intermolecular disulphide linkages caused by oxidation of thiol groups to disulphide bonds, and to SH-SS interchange reactions. Urea causes protein dissociation and thiol groups exposure due to protein unfolding, facilitating extensive intermolecular SH-SS interchange and resulting in lattice formation and gelling [13].
Anyone of these mechanism depends on a number of factors and process conditions, such as protein concentration, pH, ionic strength and temperature as well as on characteristics of the protein such as molecular weight, amino acid composition, heating/denaturation rate and aggregation rate to forma protein matrix. Studies on protein gelation processes suggest the used of combined processes.
- Matsumura, Y., Mori, T. (1996). Gelation. In "Methods to testing protein functionality", ed. G. M. Hall, Blackie Academic & Professional, Suffolk, U.K., pp. 76-81.
- Balny, C., Masson, P. (1993). Effects of high pressure on proteins. Food Review Int., 9, 611-628.
- Pérez-Mateos, M., Lourenco, H., Montero, P., Borderias, A.J. (1997). Rheological and biochemical characteristics of high-pressure and heat- induced gels of whiting (Micromesistius poutassou) muscle proteins. J. Agric. Food Chem., 45, 44-49.
- Fernandez, P., Cofrades, S., Solas, M.T., Carballo, J., Jimenez Colmenero, F. (1998). High pressure-cooking of chicken meat batters with starch, egg white, and iota carrageenan. J. Food Sci., 63, 267-271.
- Montero, P., Pérez-Mateos, M., Solas, T. (1997). Comparison of different methods using washed sardine (Sardina pilchardus) mince: effects of temperature and pressure. J. Agric. Food Chem., 45, 4612-4618.
- Pérez-Mateos, M. (1998). Estudio de hidrocoloides en la gelificación del músculo de bacaladilla (Micromesistius poutassou, Risso) inducida térmicamente y por alta presión. Ph.D. Thesis, Universidad de Alcalá de Henares, Spain.
- Ngapo, T.M., Wilkinson, B., Chong, R. (1996) 1,5-glucono-d-lactone- induced gelation of myofibrillar proteins at chilled temperatures. Meat Sci., 42, 3-13.
- Totosaus, A., Gault, N.F.S., Guerrero, I. (1998) Comportamiento reológico de geles de proteína muscular inducidos por acidez. Avan. Ing. Quím. In press.
- Lee, H.G., Lanier, T.C., Hamann, D.D., Knopp, J.A. (1997). Transglutaminase effect on low temperature gepp, J.A. (1997). Transglutaminase effect on low temperature gelation of fish proteins sols. J. Food Sci., 62, 20-23.
- Kuraishi, C., Sakamoto, J., Yamazaki, K., Susa, Y., Kuhara, C., Soeda, T. (1997). Production of restructured meat using microbial transglutaminase without salt or cooking. J. Food Sci., 62, 488-490, 515.
- Hongsprabhas, P., Barbut, S. (1997). Protein and salt effect on Ca+2-induced cold gelation of whey protein isolate. J. Food Sci., 62, 382-385.
- Ju, Z.Y., Kilara, A. (1998). Textural properties of cold-set gels induced from heat-denatured whey protein isolates. J. Food Sci., 63, 288-292.
- Xiong, Y.L., Kinsella, J.E. (1990). Mechanism of urea induced whey protein gelation. J. Agric. Food Chem., 38, 1887-1891.
Table 1: Different protein gels induced chemically and physically . Protein Gelation Physical Heat- induced Two step procedure: initial unfolding and subsequent a"4">Two step procedure: initial unfolding and subsequent aggregation in an ordered protein matrix High-pressure- induced High-pressure (200-500 mPa) induce hydrophobic and ionic interactions between protein molecules Chemical Acid- induced Gluconolactone hydrolysis produced a slow pH reduction, forming strand-like gel structures Enzymic- induced Tgase catalyses an acyl transfer reaction between a g-carboxyamide of protein-bond glutamine and a primary amine Calcium- induced Network formation via calcium ions between protein strand in the cooling process after heating Ured> Urea- induced Thiol groups oxidation forming SH-SS bonds Functionality of honey in fermented milk.
Z. USTUNOL. Department of Food Science and Human Nutrition. Michigan State University E. Lansing.
Due to its >healthy= and >natural= image there has been an increased interest in incorporating honey into various foods. Honey has been used in the manufacture of food products such as health beverages, cereals, frozen desserts, beer and processed meats among others. Honey has a unique composition which imparts important functional properties to foods which sets honey apart from other sweeteners. In this presentation properties of honey will be reviewed and functional properties of clover honey in a fermented strawberry flavored yogurt drink containing probiotic cultures Lactobacillus acidophilus and bifidobacteria will be discussed. The functional properties of honey in the fermented yogurt drink include 1) enhanceney in the fermented yogurt drink include 1) enhancement of perception of viscosity and strawberry flavor intensity 2) enhancement of growth and activity of bifidobacteria 3) enhancement of viability of bifidobacteria during refrigerated storage. The functional properties of honey will be compared to that of sucrose and discussed as it relates to their compositional differences.
Acknowledgments: This work was supported by National Honey Board and Michigan Agricultural Experiment Station.
Key words: Honey, milk, viscosity, sweetness, bifidobacteria
Cited References:
Crane, E. and P. Walker. 1984. Composition of honeys from some important honey sources. Bee World 65:167-174.
Lee, Y.K. and S. Salminen. 1995. The coming age of probiotics. Trends in Food Sci. and Tech.
6:241-245.
V
Vachon, H. 1998. Development and properties of a drinkable yogurt shake sweetened with honey. M.S. Thesis, Michigan State University, E. Lansing.
White, J.W. 1975. Composition of honey In: Honey: A comprehensive survey. Heinemann. London, UK p. 157-206.
Zumla, A. and A. Lulat. 1989. Honey - a remedy rediscovered. J. Roy. Soc. Med. 83:384-385.
BACK TO INDEXM.A.S.KHAN, E.E.Babiker, H.Azakami and Akio Kato
Department of Biological Chemistry, Yamaguchi University,Yamaguchi shi -753, Japan
The molecular mechanism for the excellent emulsifying properties of egg yolk phosvitin was investigated here. The emulsifying properties, particularly the emulsion stability, of phosvitin was found to be higher than those of other food proteins. The emulsifying properties were greatly decreased by protease and phosphatase treatment. The protease digestion of phosvitin resulted in the peptide cleavage of large fragment (phosphorylated core region, 50 to 210 peptide) and small fragments (N-terminal 1 to 49 and C-terminal 211 to 217 peptides) . The large fragment lacking the small fragments did noarge fragment lacking the small fragments did not show the excellent emulsifying properties, suggesting that small fragments of protein moiety play an important role in emulsifying properties. On the other hand, the effect of phosphatase treatment showed that electrostatic repulsive force of phosphate in phosvitin has a significant affect on its emulsifying properties[1]. To further elucidate the molecular mechanism of phosvitin, the emulsifying properties of native and N- and C-terminal-deleted phosvitin (protease digests) were compared after conjugation with galactomannan. The emulsifying properties of Maillard-type phosvitin-galactomannan conjugates were greatly improved, while those of the protease-digested phosvitin-galactomannan conjugates were not so dramatically improved. Phosvitin was highly glycosylated with galactomannan, while the protease-digested phosvitin conjugates consisting of highly phosphorylated core peptide fragment was not. The results suggest that both N- and C-terminals of the peptide moiety, digested by protease, were essential for the improvement of emulsifying properties of phosvitin-galactomannan conjugates. In addition, the role of N and C-terminals as anchors in oil droplets was supported from the comparative studies of native phosvitin, phosvitin-galactomannan conjugates and protease-digested phosvitin-galactomannan conjugates [2].
Key words:
Phosvitin, emulsifying properties, chymotrypsin, emulsifying properties, chymotrypsin, pepsin, trypsin and galactomannan
References:
Khan, M.A.S., Babiker, E.E., Azakami, H., Kato,A. (1998). Effect of protease digestion and dephosphorylation on high emulsifying properties of hen egg yolk phosvitin. J. Agri. Food Chemistry, 46 (12), 4977-4981.
Khan, M.A.S., Babiker, E.E., Azakami, H., Kato,A. (In press). Molecular mechanism of excellent emulsifying properties of phosvitin-galactomannan conjugate. J. Agri. Food Chemistry.
BACK TO INDEXCurrent progress in the development of immune milk products
H. Korhonen and P. Marnila
Agricultural Research Centre of Finland, Food Research, FIN-31600 Jokioinen, Finland
The importance of colostrum to the growth and health of a new-born offspring is well known. In bovine colostrum, the naturally occurring antibodies (immunoglobulins) provide a major antimicrobial effect against a wide range of microbes and confer a passive immunity until the calf’s own immune system has matured [1,2]. The underlying mechanisms of passive immunity, however, were only recognized as late as the 1960’s when the chemical structure of immunoglobulins was identified [3]. In particular, the identificans was identified [3]. In particular, the identification of the mucosal or secretory immune system in the 1970’s has provided new insights into the role of colostral antibodies in the prevention or treatment of enteric infections in mammals [4]. The concentration of specific antibodies in mammary secretions can be raised by immunizing cows with certain immunogens or microbial vaccines. Such hyperimmune colostrum or antibodies isolated from it provide an increased specific protection against different enteric diseases in calves and pigs [5]. In many countries, colostral Ig supplements designed for farm animals are commercially available. Also, "health products" based on natural bovine colostrum are available in a few European countries.
The historical concept of "immune milk" dates back to the 1950’s [6]. Despite a few promising clinical studies in humans relatively little attention was paid on the commercialization of immune milk products until the late 1980’s. Since then, renewed interest has been focused on the possibilities of exploiting bovine colostral antibodies for passive immunotherapy or prophylaxis of human gastrointestinal diseases. Indeed, bovine colostrum-based immune milk preparations have proven effective against various human microbial diseases [7,8,9,10]. Most encouraging results have been obtained with products targeted against rotavirus, Shigella, E. coli, C. difficile, S. mutans and Crcile, S. mutans and Cryptosporidium infections. A few commercial products are already on the market. Currently, clinical studies are in progress in many countries to evaluate the potential of immune milk products for prevention of treatment of various hospital infections, especially those caused by antibiotic resistant bacteria and Helicobacter pylori, the causative agent of chronic gastritis [11].
Immune milk products may be considered as prominent examples of health-promoting functional foods. This review summarizes the recent progress made in the development of immune milk products and evaluates their potential as functional foods.
Cited references:
[1] Butler, J.E. (1994). Passive immunity and immunoglobulin diversity. In: Indigenous Antimicrobial Agents of Milk – Recent Developments. International Dairy Federation Special Issue 9404, 14-50.[2] Pakkanen, R. & Aalto, J. (1997). Growth factors and antimicrobial factors of bovine colostrum. Int. Dairy J. 7, 285-297.
[3] Larson, B.L. (1992). Immunoglobulins of the mammary secretions. In: P.F. Fox (Editor), Advanced Dairy Chemistry – 1: Proteins. Elsevier, London, New York, pp. 231-254.
[4] Goldman, A.S. (1993). The immune system of human milk: antimicrobial, anti-inflammatory and immunomodulating properties. Pediatr. Infect. Dis. J. 12 (8), 664-672.
[5] Schaller, J.P., Saif, L.J., Cordle, C.T., Candler, E., Jr., W Saif, L.J., Cordle, C.T., Candler, E., Jr., Winship, T.R. & Smith, K.L. (1992). Prevention of human rotavirus-induced diarrhea in gnotobiotic piglets using bovine antibody. J. Infect. Dis. 165, 623-630.
[6] Campbell, B. & Petersen, W.E. (1963). Immune milk – a historical survey. Dairy Sci. Abstr. 25, 345-364.
[7] Facon, M., Skura, B.J. & Nakai, S. (1993). Potential for immunological supplementation of foods. Food Agric. Immunol. 5, 85-91.
[8] Hammarström, L., Gardulf, A., Hammarström, V., Janson, A., Lindberg, K. & Smith, C.I.E. (1994). Systemic and topical immunoglobulin treatment in immunocompromised patients. Immunol. Rev. 139, 43-70.
[9] Ruiz, L.P., Jr. (1994). Antibodies from milk for the prevention and treatment of diarrheal disease. In: Indigenous Antimicrobial Agents of Milk – Recent Developments. International Dairy Federation Special Issue 9404, 108-121.
[10] Davidson, G.P. (1996). Passive protection agai96). Passive protection against diarrheal disease. J. Pediatr. Gastroenterol. Nutr. 23, 207-212.
[11] Korhonen, H. (1998). Colostrum immunoglobulins and the complement system – potential ingredients of functional foods. Bulletin of the IDF No 336, 36-40.
BACK TO INDEXMeasurement of surface hydrophobicity of proteins using anionic versus uncharged fluorescent probes
EUNICE C. Y. LI-CHAN, Nooshin Alizadeh-Pasdar and Eugene S. Y. Cheng
Food, Nutrition & Health, Faculty of Agricultural Sciences, University of British Columbia, Vancouver, BC, Canada. Food protein functionality is related to specific structural characteristics of the protein molecules. Charged groups and hydrophobic patches on the surface of the protein molecule are influential in intermolecular interactions between proteins, other food components such as lipids, carbohydrates or salts, and solvent molecules. Processing and ingredient formulation can alter the distribution of charged and hydrophobic regions on the surface versus interior of protein molecules.Methods based on fluorescent probes are being widely used to monitor changes in surface hydrophobicity of protein molecules as a function of different processing treatments or conditions. The quantum yield of fluorescs or conditions. The quantum yield of fluorescence and wavelength of maximum emission of these probes depend on the polarity of their environment. The popularity of these probes arises from the simplicity and speed of the assay, and many reports have appeared correlating the hydrophobicity values thus measured with functionality of proteins in various food systems.
Two commonly used probes in food protein systems are 1,8-anilinonaphthalenesulfonate (ANS) and cis-parinaric acid (CPA), containing aromatic and aliphatic hydrocarbon moieties, respectively [1]. For some proteins, conflicting results have been reported on hydrophobicity measured by the two probes. The discrepancies may in part be due to differences in the binding sites for aromatic versus aliphatic probes, but are further complicated by the possible contributions of charge to the probe-protein interactions. The sulfonate and carboxylate groups on ANS and CPA, respectively, suggest that in addition to binding through hydrophobic interactions, anionic fluorescent probes may also be involved in either attractive or repulsive electrostatic interactions with the protein surface, depending on pH and ionic strength.
Recently we have used uncharged fluorescent probes such as diphenylhexatriene (DPH) and 6-propionyl-2-(N,N-dimethylamino)naphthalene (PRODAN), for the measurement of surface hydrophobicity, including studies on the effects of ionic strength (0.01M - 1. effects of ionic strength (0.01M - 1.0 M NaCl), pH (3-9) and interactions with an anionic polysaccharide (k -carrageenan) [2-5]. The results of these studies, which will be reviewed in this presentation, emphasize the need to consider the nature of the fluorescent probe used in evaluating surface hydrophobicity of food proteins.
Acknowledgements: This work was supported by NSERC (Canada).
Cited references:
[1] Nakai, S., Li-Chan, E. Arteaga, G. (1996) Measurement of surface hydrophobicity. In "Methods of testing protein functionality." Ed. G. M. Hall. Blackie Academic. pp. 226-259. [2] Haskard, C. A., Li-Chan, E. C. Y. (1998) Hydrophobicity of bovine serum albumin and ovalbumin determined using uncharged (PRODAN) and anionic (ANS-) fluorescent probes. J. Agric. Food Chem. 46, 2671-2677. [3] Alizadeh-Pasdar, N., Li-Chan, E. C. Y. (1998) Comparison of protein surface hydrophobicity measured using three different fluorescent probes. IFT Annual Meeting, Poster 20B-24. [4]Alizadeh-Pasdar, N. Li-Chan, E. C. Y. (1999). Application of PRODAN fluorescence probe to measure surface hydrophobicity of proteins interacting with k -carrageenan. IFT Annual Meeting, Poster 65A-22. [5] Cheng, E. S. Y, Li-Chan, E. C. Y. (1999). Comparison of protein surface hydrophobicity measured using PRODAN and ANS fluorescent probes. IFT Annual Meeting.
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Molecular Elasticity of High Molecular Weight Glutenin Subunits and Breadmaking Potential of Hard Wheats
William E. Barbeau
Department of Human Nutrition, Foods and Exercise, Virginia Polytechnic Institute and State University, Blacksburg Virginia 24061-0430
Glutenins are defined as those proteins in the wheat kernel that are soluble in dilute acids and alkalies [ 1] . The breadmaking potential of hexaploid wheats is believed to be conferred in part by the presence of certain high molecular weight (HMW) glutenin subunits [ 2,3] . CD-spectroscopy has revealed that HMW glutenin subunits are composed of three domains, an interior domain rich in B -reverse turns and devoid of cysteine residues, and N- and C-terminal domains that contain a -helices and all of the proteins’free sulfhydryl groups [ 4] . Scanning tunneling microscopy images indicate that the repetitive B -reverse turns in the interior of HMW glutenins combine to form a B -spiral [B -spiral [ 5] . This B -spiral may change its length and its shape in response to external forces such as kneading, accounting for the known elastic behavior of these proteins. The proteins’ N- and C-terminal domains may also play an important role in their functionality by their participation in sulfhydryl-disulfide interchange reactions. The breakage and reformation of disulfide linkages occurring during free sulfhydryl-disulfide interchange reactions are believed to be instrumental in relieving stresses and strains in wheat flour doughs in response to various internal and external perturbations.
Cited References:
1. Osborne, T.B. and Voorhees, C.L. 1894. Proteids of the wheat kernel. J. Amer. Chem. Soc. 16: 524-535.
2. Payne, P.I., Corfield, K.G., and Blackman, J.A. 1979. Identification of a high-molecular-weight subunit of glutenin whose presence correlates with bread-making quality in wheats of related pedigree. Theor. Appl. Genet. 55: 153-159.
3. Payne, P.I., Nightingale, M.A., Krattiger, A.F. and Holt, L.M. 1987. The relationship between HMW glutenin subunit composition and bread-making quality of British-grown wheat varieties. J. Sci. Food Agric. 40: 51-65.
4. Tatham, A.S., Miflin, B.J., and Shewry, P.R. 1985. The beta-turn conformation in wheat gluten proteins: relationship to gluten elasticity. Cereal Chem. 62:p to gluten elasticity. Cereal Chem. 62: 405-412.
5. Miles, M.J., Carr, H.J., McMaster, T.C., I’Anston, K.J., Belton, P.S. et al. 1991. Scanning tunneling microscropy of a wheat seed storage protein reveals details of an unusual supersecondary structure. Proc. Natl. Acad. Sci. USA. 88: 68-71.
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Factors affecting the potency of guar gum glycemia blunting effect
CHRON-SI LAI
Abbott Laboratories, Ross Product Division, Clumbus, Ohio
The effect of guar gum on glycemic response has been extensively studied. The majority of literature reports indicate that inclusion of guar gum in the diet blunts glycemia. The effectiveness of this serum glucose blunting effect has been reported to be a function of guar gum level (up to 3%). The literature suggevel (up to 3%). The literature suggests guar gum blunts glycemia by imparting a high viscosity to the digesta which results in slower stomach emptying and reduces glucose absorption rate in the small intestine. This viscosity theory seems to contradict to the fact that some researcher's finding that guar gum is not functional in blunting glycemia or that the potency of the guar gum on blunting glycemia is not a function of guar gum molecular weight (viscosity) or particle size. We reviewed literature and propose hypothesis that may explain the discrepancies between the viscosity theory and those clinical findings.
BACK TO INDEX Uses of enzymatically modified components of rice bran in preparation of value-added products
Jamel S. Hamada*
Southern Regional Research Center, USDA-ARS, New Orleans, LA 70179
Typically, defatted rice bran is sold as feed despite its relatively high protein content and the presence of health-promoting components including dietary fiber, minerals, vitamins and phytic acid [1]. The low value of rice bran makes its conversion to new value-added products with high quality exceptionally desirable.
Large portions of rice protein cannot be solubi>Large portions of rice protein cannot be solubilized by ordinary solvents [2] but proteases have been used to enhance protein solubility and to obtain a wide range of protein hydrolysates for many food applications [3]. Improvement in functional properties of hydrolysates was dependent on the degree of hydrolysis. Proteolysis reversed the dramatic reduction in protein solubility and functional properties caused by extrusion of rice bran. Using exoprotease along with endoprotease led to a substantial improvement in protein recovery, flavor and functional properties [4]. Preparative HPLC was used to isolate value-added peptides with flavor enhancing potential to replace monosodium glutamates in foods [5].
An alkaline phytase capable of hydrolyzing phytic acid to functional inositol phosphates for the food and pharmaceutical industries has been recently identified in rice bran [6]. This alkaline phytase activity was optimal at 40-45oC and appeared to be thermostable.
Cited References:
1. Saunders, R.M. (1990). The properties of rice bran as a foodstuff. Cereal Foods World, 35 (7), 632-635.
2. Hamada, J.S. (1997). Characterization of protein fractions of rice bran to devise effective methods of protein solubilization. Cereal Chem., 74, 662-668.
3. Hamada, J.S. (1999) Use of proteases to enhance solubilization of rice bran proteins, J. Food Biochem. (In press).
4. Hamada, J.S. (1998). Functional p).
4. Hamada, J.S. (1998). Functional properties of rice bran proteins modified by commercial exoproteases and endoproteases, Abstr. 59th Annual Mtg., Inst. Food Technol., Chicago, IL.
5. Hamada, J.S., Spanier, A.M., Bland, J.M., and Diack, M. (1999). Preparative separation of value-added peptides from rice bran proteins by high performance liquid chromatography. J. Chromatogr. A (In press).
6. Liu, H. (1996). Isolation and identification of phytases, phytic acid and inositol phosphate from rice bran, MS Thesis, Department of Food Science, Louisiana State University.
BACK TO INDEXHeat-induced gelation of beta-lactoglobulin and myosin: Enhancing the use of whey proteins in processed meat products
DENISE M. SMITH* and Manee Vittayanont
Department of Food Science and Human Nutrition, Michigan State University, East Lansing, MI 48824-1224
The formation of a firm protein gel is necessary to maximize the yield and quality of many processed meat and poultry products, especially of reduced fat comminuted products, such as frankfurters and bologna. If the endogenous muscle proteins cannot form adequate gels, starches, gums or non-meat proteins are generally used to obtain the desired gelling properties in these meat products. Whey proteins merties in these meat products. Whey proteins may be added to improve yield, texture or color of meat and poultry products and to reduce costs. However, the effect of whey proteins on the textural attributes of meat products is highly variable and whey proteins are often not used to their fullest potential in these products. Commercially available whey proteins do not form gels at cooking temperatures used by meat processors, thus their influence on meat product texture is due to other factors.
Although native whey proteins do not gel until temperatures above about 80EC are reached, cold-set whey proteins can form gels at or below typical meat processing temperatures. The optimum conditions for initial aggregate formation and cold-set gelation of whey proteins have been extensively studied. In this process, soluble aggregates are formed by heat-induced denaturation of protein in dilute solutions. To initiate cold-induced gelation, the solution conditions and protein concentration are changed to induce cross-linking by the soluble aggregates. Cold-gelation of whey proteins can be induced by increasing the ionic strength through the addition of salts. Recently, cold-set whey protein has been used in processed meat products cooked between 68 and 71EC to improve product texture and cooking yields. To better understand how cold-set whey proteins function in meat products, model eins function in meat products, model systems were used to elucidate changes in the denaturation, aggregation and gelation properties of mixtures of heat-denatured soluble aggregates of $-lactoglobulin (dLG), the major whey protein, and myosin, the major functional meat protein.
This presentation will review the conditions necessary for the production of cold-set whey protein gels and provide an update on the use of cold-set whey protein in meat products. Interactions between dLG and myosin during heat-induced gelation will be described. A better understanding of interactions between whey proteins and meat proteins may allow for increased use of whey products in meat products, and in a variety of other applications, where protein gelation at low temperatures is desirable.
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Protease induced gelation of proteins from whey and other sources
RICHARD IPSEN, Jeanette Otte and Karsten B. Qvist
Department of Dairy and Food Science, Royal Veterinary and Agricultural University, Rolighedsvej 305, DK-1958 Frederiksberg C, Denmark
Gelation of whey protein isolate (WPI) can be induced enzymatically by a protease from Bacillus licheniformis (BLP) upon incubation at neutral pH and 40°C [1,2]. Relaion at neutral pH and 40°C [1,2]. Relatively strong gels are formed at a protein concentration of 9%, at which concentration heating at 80°C for 30 min. does not induce gelation of native whey protein. A thermal pre-treatment has been shown to have a major impact on the enzyme-induced gelation as well as on the microstructure and appearance of gels made from WPI by the action of BLP [3] and there are striking differences in the mechanism of gelation of thermally pre-treated and unheated WPI.
The individual whey proteins can be induced to gel with BLP. b-Lactoglobulin, the major whey protein gels with BLP at a concentration of 5%. However, as b-lactoglobulin also possesses good thermal gelation properties, it is perhaps more interesting that the other major whey protein, a-lactalbumin, which has poor thermal gelling ability, can produce strong, transparent gels ie strong, transparent gels if treated with BLP. We have also recently showed that it is possible to induce gelation in soy protein isolate, pea protein isolate and in wheat protein by using BLP.
We believe that enzyme induced gelation is an additional tool for design of protein ingredients with specific functionality, especially when gelation is needed at neutral pH in products where thermal processing at temperatures above 50oC is unwanted.
Cited references:
Ju, Z.Y., Otte, J., Madsen, J.S. and Qvist, K.B. (1995). Effects of limited proteolysis on gelation and gel properties of whey protein isolate. J. Dairy Sci., 78, 2119-2128.
Otte, J., Ju, Z.Y., Færgemand, M., Lomholt, S.B. and Qvist, K.B. (1996). Protease induced aggregation and gelation of whey proteins. J. Food Sci., 61, 911-915,923.
Ju, Z.Y., Otte, J., Zakora, M. and Qvist, K.B. (1997). Enzyme-induced gelation of whey proteins: Effect of protein denaturation. Int. Dairy J., 7, 71-78.
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Physical Stability Concerns with Shelf Stable Nutritional Beverages
Steven R. Dimler
Product Research and Development, Ross Producst Division Abbott Laboratories, Columbus, Ohio
Shelf stable, liquid, nutritional beverages can have different emulsion instnutritional beverages can have different emulsion instability issues over time. Instability is defined as creaming, gelation, whey separation, and sedimentation. Emulsion stability can be associated and affected by the type and level of protein, carbohydrate, minerals, emulsifiers, stabilizers, pH, and processing conditions. Various scenarios will be explored and compared to the reported literature. The need to have means of predicting emulsion stability in complex food systems will be emphasized.
BACK TO INDEX Interactions of proteins in mixed food gels
Nazlin K. Howell
University of Surrey, School of Biological Sciences, Guildford, Surrey GU2 5XH, UK
Protein-protein interactions can result in interesting phenomena such as synergistic interactions, precipitation and phase separation which affect the processing of foods and the texture of food products (1,2). In a MAFF-Industry LINK project supported by the Ministry of Agriculture, Fisheries and Food as well as four industrial partners the interactions between food proteins including whey, meat, wheat gluten and soya were probed by analytical, microscopical and rheological techniques (3).
The studies showed that mixtures of soya and whey; meat and soluble wheat protein (SWP); SWP and b meat and soluble wheat protein (SWP); SWP and bovine serum albumin (BSA) and SWP and whey isolate phase separated and formed separate networks on heating; this generally led to lower gelling properties (4,5). The exception to this was when only small amounts of one protein were added to the main protein component which can result in gel enhancement. For example, on the addition of small amounts of SWP to salt soluble meat proteins (SSMP), the shear modulus, fracture stress and strain increased together with the water holding capacity (6). Transmission electron microscopy/immunocytochemistry indicated linking of the SSMP strands by SWP and filling in of the SSMP porous network by the SWP, confirming the view that the distribution and bridging of the proteins in the network influences the network structure and strength; however electrostatic and hydrophobic interactions at specific sites cannot be ruled out. It was also apparent from rheological studies on soya-whey mixtures that the protein which gelled first namely whey isolate, formed the continuous phase even when present in small amounts (4).
Acknowledgements
Funding from the MAFF Link Scheme and from the industrial partners is gratefully acknowledged.
References
1. Howell, N.K. (1992). Protein-protein interactions. In Biochemistry of Food Proteins.Ed.B.J.F.Hudson. Elsevier Applied Science Publ.Ltd., Essex, pp 35-74.
2. Howell, N.K. (1995). Synergism and Interactions in Mixed Food Protein Systems. In Biopolymer Mixtures, Ed. S.E. Harding, S.E.Hill and J. Mitchell. University of Nottingham Press, UK. pp 329-347.
3. Howell, N.K. (1999). Protein-protein and protein-polysaccharide interactions in food gels. Food Ingredients and Analysis International.(2),
4. Comfort, S and Howell, N.K.(1999). Interaction of soya protein isolate with whey protein isolate. Food Hydrocolloids. Submitted.
5. Friedli, G.L.and Howell, N. (1996). Gelation properties of deamidated soluble wheat protein. Food Hydrocolloids 10, 255-261.
6. Comfort, S and Howell, (1999). Interaction of soluble wheat protein and meat proteins in mixed gels. Food Hydrocolloids. Submitted.
Effect of High-Pressure Processing on Protein–Protein
and Protein–Polysaccharide Interactions in EmulsionsEric Dickinson
Procter Department of Food Science, University of Leeds,
Leeds LS2 9JT, U.K.The influence of static high-pressure processing on the emulsifying properties of milk proteins has been investigated under neutral pH conditions. Wherinvestigated under neutral pH conditions. Whereas treating ?-casein or sodium caseinate before homogenization has negligible effect on droplet-size distribution or stability, the emulsifying efficiency of ?-lactoglobulin is sensitive to both treatment pressure and duration. High-pressure treatment of whey protein-stabilized emulsions after formation can induce significant levels of flocculation, and at high oil volume fractions this leads to the formation of a viscoelastic emulsion gel. In high-pressure-treated emulsions containing a mixture of ?-lactoglobulin and sodium caseinate, the degree of flocculation of the droplets is dependent on the time-dependent competitive adsorption behaviour of the two different milk proteins.
In emulsions containing both protein and polysaccharide, there may additional effects of high-pressure treatment on protein–polysaccharide interactions. This is especially the case with highly charged polysaccharides such as dextran sulfate or ?-carrageenan which form electrostatic complexes with globular proteins such as bovine serum albumin and ovalbumin at pH values above the protein’s isolectric point. Size exclusion chromatography of mixed protein + polysaccharide solutions show that the balance of protein–protein and protein–polysaccharide interactions is affected by high-pressure treatment. Interfacial complexation between added polysaccharide and adsorbed protein in emulsionide and adsorbed protein in emulsions causes bridging flocculation and leads to large changes in emulsion rheology at high volume fractions. As this type of complexation is mainly electrostatic, it is extremely sensitive to changes in pH and ionic strength.
Key Words: Emulsions; protein interactions; high-pressure processing; complexationReferences
E. Dickinson and K. Pawlowsky. 1996, ‘Effect of high-pressure treatment of protein on the rheology of flocculated emulsions containing protein and polysaccharide’, J. Agric. Food Chem., 44, 2992.
V. B. Galazka, D. A. Ledward, I. G. Sumner and E. Dickinson. 1997.‘Influence of high pressure on bovine serum albumin and its complex with dextran sulfate’, J. Agric. Food Chem., 45, 3465.
E. Dickinson and J. D. James 1998. ‘Rheology and flocculation of high-pressure-treated ?-lactoglobulin-stabilized emulsions: comparison with thermal treatment’, J. Agric Food Chem., 46, 2565.
K. Pawlowsky and E. Dickinson 1998. ‘Protein–polysaccharide interactions in emulsions containing high-pressure-treated protein’, in High Pressure Food Science, Bioscience and Chemistry (ed. N. S. Isaacs), Royal Society of Chemistry, Cambridge, UK, p. 214.
Quality of Tropical Fruits Irradiated for Disinfestation PurposeJames H. Moy*, Ryan Chung, and Xing Bian
Department of Food Science and Human Nutrition
University of Hawaii, Honolulu, Hawaii 96822 U.S.A.
Most of the tropical fruits grown in Hawaii and other subtropical regions are prone to infestation by fruit flies and other insect pests. One of the most useful applications of gamma-radiation is to disinfest these fruits with a low dose [1]. The function of the radiation treatment is to render the insect eggs and larvae on the fruits to lose their viability through cleaving of the DNA. With the minimum dose of 0.25 kGy required by USDA [2], most fruits can tolerate radiation with no changes in quality. However, in a commercial irradiator, the dose rates are not uniformly distributed. As a result, some fruits would receive doses as high as 2.5 to 3.0 times of the minimum dose. Knowing the tolerance dose of each fruit is very important to an exporter [3]. Sensory and chemical qualities o very important to an exporter [3]. Sensory and chemical qualities of carambola, litchi, mango, papaya, and rambutan were extensively studied in our laboratory between non-irradiated control and those irradiated to 0.75 and 0.90 kGy. Results show that only the pulp color of three varieties of litchi were different at p=0.05 between control and irradiated samples. No differences were found in vitamin C content, total soluble solids, and titratable acidity between the control and all five irradiated fruits. Results suggest that these tropical fruits can retain their qualities when treated in a commercial irradiator with the required quarantine dose.
[1] Moy, J.H. (Ed.) (1985) Radiation Disinfestation of Food and Agricultural Products. Proc. Intl. Conf., Honolulu, Hawaii, Nov. 1983. Haw. Inst. Trop. Agri. & Human Resources, U. of Hawaii, 424 pp.
[2] United States Department of Agriculture, Animal and Plant Health Inspection Service. [1996] The application of irradiation to phytosanitary problems - Notice of policy. U.S. Fed. Regis. 61(95) May 15, 24433-24439.
[3] Moy, J.H. and Wong, L. (1994) Current interest in and prospect for adopting irradiation as a quarantine treatment procedure in Hawaii. Proc. Workshop on Irradiation as a Quarantine Treatment for Fruits and Vegetables. USDA-ARS-APHIS, Gainesville, FL. U.S.A., Feb. 2-4, 61-65.
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The Effects of Milk Storage Time and Temperature on the Rheological Properties of Rennet Induced Skim Milk GelsJody Renner-Nantz and Charles F. Shoemaker Department of Food Science & Technology, University of California, Davis
Fundamental dynamic rheological tests were used to measure the rigidity (|G*|) and viscoelasticity (tan ?) of gels made from skim milks that were 1) never cooled, 2) stored at 4?C, and 3) stored at 4?C and then rewarmed to 25?C._ Milks cooled and held at 4?C prior to gel formation produced gels with significantly lower |G*| 's and higher tan ?'s than fresh milk gels._ Chilled milks that were rewarmed to 25?C for 16 h prior to gel formation produced gels with rheological properties similiar to fresh milk gels._ The solubilization of ?-casein during cold storage was thought to influence the observed differences in gel rheology.
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