Abstract
The effects of fish collagen on the acidification, milk protein proteolysis and organoleptic properties of plain- and Allium sativum-yogurt were investigated. Titratable acidity (TA%) increased (p < 0.05) in the presence of fish collagen in plain-yogurt (0.87-0.95%) and in A. sativum-yogurt (0.77-0.95%) compared to in the absence of fish collagen (0.79-0.84% and 0.56-0.86%) for plain- and A. sativum-yogurt respectively. Free amino acids (FAAs) in all yogurts decreased (p < 0.05) by about 1 mM during yogurt fermentation. The presence of fish collagen in plain- and A. sativum-yogurts increased the FAAs by about 4.2 and 3.5 mM respectively compared to their respective control 0.14 and 0.16 mM for plain- and A. sativum-yogurts respectively. Effects of plain- and A. sativum-yogurts in presence or absence of fish collagen on the aggregation of milk proteins in yogurt was measured by SDS-PAGE. Some milk proteins, kappa-caseins, beta-lactoglobulin and alpha-lactalbumin were reduced as a result of fermentation both in plain- and A. sativum-yogurts. The presence of fish collagen showed further proteolysis in these proteins in plain- and A. sativum-yogurts during fermentation and refrigerated storage. However, there were little changes in the degradation of alpha- and beta-caseins in all yogurts with or without fish collagen. The extent of proteolysis based upon OPA values was the highest on day 7 of refrigerated storage in A. sativum-fish collagen-yogurt (337.0 +/- 5.3 mu g/g) followed by fish collagen-yogurt (275.3 +/- 2.0 mu g/g), A. sativum-yogurt (245.8 +/- 4.2 mu g/g) and plain-yogurt (40.4 +/- 1.2 mu g/g). In addition, plain- and A. sativum-yogurts with or without fish collagen showed maximal inhibition of ACE-I on day 7 of storage which ranged between 55% and 80%. The addition of A. sativum reduced aroma and increased graininess of yogurt but these and overall consistency were improved in the presence of fish collagen. In conclusion, fish collagen increased FAAs content in yogurt and the enhanced proteolysis of certain milk proteins may be responsible for improving ACE inhibitory activity and organoleptic properties of A. sativum-yogurt. (C) 2013 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.