Proteolytic degradation of ewe milk proteins during fermentation of yoghurts and storage

Abstract

Yoghurts are mostly produced from cow milk and to a very limited extent from ewe milk. The evolution of caseins and whey proteins in ovine milk submitted to different thermal treatments (63 degrees C/30 min; 73 degrees C/15 min; 85 degrees C/10 min or 96 degrees C/5 min) was followed during fermentation of yoghurts and during their storage up to 14 days, using two different sets of starters. One set of starter LAB was a "ropy" culture (YC-191), which is a well-defined mixed strain culture containing Streptococcus thermophilus ST-143 and Lactobacillus delbrueckii subsp. bulgaricus (LB-18 and LB-CH2). The other set of starter bacteria (YC-460) was a standard yoghurt culture("non-ropy") containing mixed strain culture of Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus. Contents of free amino groups in produced yoghurts increased gradually during the fermentation, up to a maximal value obtained after 4 h fermentation, then they did not change significantly during storage of yoghurt produced with YC-191 starter. In contrary, a large drop in the amount of free amino groups was observed in the first 24 h of storage in the case of yoghurt made with YC-460 indicating that microorganisms continue still to grow in low temperatures. During fermentation and storage of both yoghurt types, alpha-lactalbumin was hydrolyzed to a slightly bigger extent than beta-lactoglobulin. During fermentation, beta-casein was slightly more degraded than alpha(s)-caseins; however, the opposite was observed during storage up to 14 days. Generally, a more intense heat pretreatment led to a higher degradation of whey proteins and caseins during fermentation and storage. Differences in proteolytic activity between the two starters used (whey proteins more degraded by YC-191; caseins more degraded by YC-460) may lead to improvement in production and formulation of yoghurts differing in their physicochemical and rheological properties.

Farklı Tür Sütlerden Üretilen Yoğurtların Bazı Kalite Özellikleri ve Mineral İçerikleri Üzerine Karşılaştırmalı Bir Araştırma

“…Furthermore, buffaloes' milk is the second most produced milk in the world with 82 billion liters produced each year (12.5% of milk produced in the world), after cows' milk (84% with 551 billion liters) 5 , although it is the least produced milk in Turkey. Ewes' milk, the other milk type, contains higher amount of proteins than cows' milk (58 g/kg and 33 g/kg, respectively) and does not require fortification of the milk in the production of yoghurt 6 . Besides, ewes' yoghurt has a pleasant creamysour flavour, considered by many to be better than cows' yoghurt 7 .…”

Changes in peptic digestibility of bovine β-lactoglobulin as a result of food processing studied by capillary electrophoresis and immunochemical methods

“…Even though digestibility of ␤LG upon processing has already been studied by different analytical and biochemical methods (SDS-PAGE, RP-HPLC, chemical characterisation), no quantitative data were given about the proteolytic degradation or kinetics of the digestion assay [27][28][29].…”

Formation and Degradation of Beta-casomorphins in Dairy Processing

“…In yoghurt production, secondary heating in addition to pasteurization is commonly performed at 90-95 C for five minutes (EFSA, 2009) causing denaturation of whey proteins, and promotion of the interaction between caseins and whey proteins; particularly k-casein and b-lactoglobulin. The formation of this complex influences proteolysis during fermentation (El-Zahar et al, 2003). Furthermore, heat treatments contribute to the breakdown of parent proteins to form lower molecular weight peptides (Gaucheron et al, 1999).…”