This study investigated the effects of hydrolysed fish and bovine collagens at 1.25%, 2.50%, and 5.00% on the fermentation kinetics, physicochemical quality, and refrigerated storage stability of fermented milk beverages enriched with vitamin C. The work addressed three linked questions: whether collagen source determines the technological response of the dairy matrix, whether these effects are dose-dependent, and whether the observed changes remain relevant during 28 days of storage at 6 °C. During fermentation at 37 °C, 1.25% fish collagen maintained acidification kinetics comparable to the control, whereas bovine collagen, especially at higher doses, prolonged the time required to reach pH 4.6. During storage, fish collagen demonstrated better technological compatibility with the fermented milk matrix, improving water-holding capacity and maintaining or increasing gel hardness, whereas bovine collagen weakened the gel structure but showed a stronger buffering effect and higher pH values. Starter culture viability was maintained throughout storage: S. thermophilus remained highly stable, whereas Lactobacillus spp. declined gradually to approximately 5.7–6.1 log CFU/g by day 28. Colour analysis showed a progressive increase in yellowness (b*) and total colour difference (ΔE*) in all samples, with the magnitude depending on collagen source, dose, and storage time. This study indicates that hydrolysed fish collagen is generally more compatible with fermented milk enriched with vitamin C when structural stability and water retention are prioritised. However, batch-specific molecular-weight distribution and amino acid composition of the hydrolysates were not determined; therefore, source-related mechanisms are interpreted as plausible technological explanations rather than direct molecular evidence.
Ziarno et al. (Mon,) studied this question.