The effect of heat treatment and skimming on precipitate formation in caprine and bovine milks.

Caprine and bovine milks have a similar overall gross composition, but vary considerably in the ratios of their casein components. These differences in colloidal casein micelles could affect directly or indirectly the heat stability of caprine and bovine milks at their natural pH. In the present work, the differences in colloidal stability of caprine and bovine milk have been studied by analysing the effect of heat treatment and skimming on precipitation of proteins. Raw and heated milk samples (70 °C/5 min, 80°C/5 min and 90°C/5 min) were centrifuged at 600, 2000, and 4500  g . The amount of precipitate formed after skimming was measured and the protein composition of both precipitates and supernatants analysed using the SDS-PAGE (sodium dodecyl sulphate polyacrylamide gel electrophoresis) and densitometry. In caprine milk, the heat treatment prior to skimming had a statistically significant effect on protein precipitation. Centrifugal force had a statistically significant effect on amount of precipitate for both milks, but the amount was 2 to 4 times higher for caprine milk. When defatting the milk for electrophoresis, a centrifugal force of 600  g appeared to be the most appropriate, in order to avoid protein loss and a possible error in the interpretation of results. Results of this study could also serve as the basis for further investigations on adjusting the skimming conditions for caprine milk in industrial dairy processing environment.

Functional properties of pea (Pisum sativum, L.) protein isolates modified with chymosin.

In this paper, the effects of limited hydrolysis on functional properties, as well as on protein composition of laboratory-prepared pea protein isolates, were investigated. Pea protein isolates were hydrolyzed for either 15, 30 and 60 min with recombined chymosin (Maxiren). The effect of enzymatic action on solubility, emulsifying and foaming properties at different pH values (3.0; 5.0; 7.0 and 8.0) was monitored. Chymosin can be a very useful agent for improvement of functional properties of isolates. Action of this enzyme caused a low degree of hydrolysis (3.9-4.7%), but improved significantly functional properties of pea protein isolates (PPI), especially at lower pH values (3.0-5.0). At these pH values all hydrolysates had better solubility, emulsifying activity and foaming stability, while longer-treated samples (60 min) formed more stable emulsions at higher pH values (7.0, 8.0) than initial isolates. Also, regardless of pH value, all hydrolysates showed improved foaming ability. A moderate positive correlation between solubility and emulsifying activity index (EAI) (0.74) and negative correlation between solubility and foam stability (-0.60) as well as between foam stability (FS) and EAI (-0.77) were observed. Detected enhancement in functional properties was a result of partial hydrolysis of insoluble protein complexes.

Profile and functional properties of seed proteins from six pea (Pisum sativum) genotypes.

Extractability, extractable protein compositions, technological-functional properties of pea (Pisum sativum) proteins from six genotypes grown in Serbia were investigated. Also, the relationship between these characteristics was presented. Investigated genotypes showed significant differences in storage protein content, composition and extractability. The ratio of vicilin:legumin concentrations, as well as the ratio of vicilin + convicilin: Legumin concentrations were positively correlated with extractability. Our data suggest that the higher level of vicilin and/or a lower level of legumin have a positive influence on protein extractability. The emulsion activity index (EAI) was strongly and positively correlated with the solubility, while no significant correlation was found between emulsion stability (ESI) and solubility, nor between foaming properties and solubility. No association was evident between ESI and EAI. A moderate positive correlation between emulsion stability and foam capacity was observed. Proteins from the investigated genotypes expressed significantly different emulsifying properties and foam capacity at different pH values, whereas low foam stability was detected. It appears that genotype has considerable influence on content, composition and technological-functional properties of pea bean proteins. This fact can be very useful for food scientists in efforts to improve the quality of peas and pea protein products.