Protein Gel Formation Research Articles

Actual problems of research in food science.

Starting from the necessary trend towards development in the field of food production, the author outlines, on the basis of current knowledge, the problems to be solved in food science. A general research conception is deduced for the essential nutrient "protein" (as an example) which is illustrated by results from studies on protein fibre and protein gel formation.

The formation and structure of milk protein gels

The formation of gels from milk proteins is irreversible. Most are not suitable for optical or rheological approaches. Various gels from milk products are discussed: those made by the action of rennet on whole milk, yoghurt, those from heated milk and by the storage of heated milk and gels made from whey protein of very high nutritional quality.

A sugar-dependent increase in red cell stability

The effects of several monosaccharides on the resistance of human erythrocytes to hypotonic stress have been examined. By using probit analysis to determine the 50% response, it is shown that d-glucose reduces cell fragility as a linear function of concentration and that the glucose-dependent increase in cell stability decreases rapidly when the temperature is raised aboe 20°C. d-Fructose also reduces cell fragility, but this effect is not sensitive to temperatures in the range 0–37 °C. K + loss from cells is insufficient to account for the sugar-dependent cell stabilization. Cell sizing by a multi-channel cell volume analyser shows that the critical haemolytic volume is unaffected by glucose. By measurement of the relaxation time of cell fragility the bulk visco-elastic moduli can be calculated (see Appendix). It is shown that at 0 °C, glucose increases both the cell elastic and viscous moduli ( E A increased by 1.2 · 10 5–3.3 · 10 5 nM −2, whilst ν A increased by 1.8 · 10 7–9.0 · 10 7 nM −2 · s −1). Proton magnetic resonance studies suggest that glucose, water and intracellular protein form a ternary complex, below 20 °C the ratio of bound water : glucose is 10 : 1. These changes in cell water structure and the cell bulk visco-elastic moduli are consistent with the view that intracellular glucose promotes protein gel formation.

Role of the sulphydryl group in the formation of alkaline protein gels.

COMMENTING on an account1 from this laboratory of the gelation of alkaline casein dispersions, Wormell2 has suggested that the sulphydryl group is the specific one concerned in gelation and that its oxidation to the disulphide bond provides the most likely cross-linkage. In, work as yet unpublished, we have also considered the possibility of non-methionine sulphur being involved in gelation. The results shown in Table 1 represent the amounts of alkalilabile sulphur liberated from the system lactic casein–sodium hydroxide–water at 25° C. when the ratio of air-dry casein to water is 2:5. At the end of the period of reaction, the glues were dispersed in their own volume of water and 1 N hydrochloric acid added, in excess of that required for precipitation. The appearance of the protein precipitated after treatment at high pH. was distinctly fibrous; milder treatments yielded flocculent precipitates. The hydrogen sulphide evolved was passed through N/10 iodine solution, the protein dispersions being boiled until a negative sulphide test was given by lead acetate. The liberated sulphur was determined by back-titration against N/100 sodium thiosulphate.