The effects of fish collagen on the proteolysis of milk proteins, ACE inhibitory activity and sensory evaluation of plain- and Allium sativum-yogurt

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, κ-caseins, β-lactoglobulin and α-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 α- and β-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 μg/g) followed by fish collagen-yogurt (275.3 ± 2.0 μg/g), A. sativum-yogurt (245.8 ± 4.2 μg/g) and plain-yogurt (40.4 ± 1.2 μg/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.

► Fish collagen in Allium sativum- and plain-yogurt effect on titratable acidity compared to in the absence of fish collagen.
► The presence of fish collagen in plain- and A. sativum-yogurts increased the free amino acids.
► Little changes in the degradation of α- and β-caseins in all yogurts with or without fish collagen.
► Fish collagen in yogurt enhanced proteolysis of milk proteins and organoleptic properties of A. sativum yogurt.
► Fish collagen did not effect on ACE inhibitory activity of yogurt.