Influence of the addition of transglutaminase on the immunoreactivity of milk proteins and sensory quality of kefir

Traditionally prepared kefir was enriched by the addition of transglutaminase (m-TG) to milk used for fermentation. Following multiplication of lactic acid bacteria and yeasts, milk proteins were hydrolysed to short chain peptides. Results of a chromatographic analysis demonstrated significant changes in protein profiles observed at 214 nm and 280 nm absorbance. The addition of m-TG to fresh kefir evoked the formation of protein aggregates. Two distinct fractions (at 50–55 ml and 135–155 ml) were observed at 280 nm, which may suggest the formation of aromatic acids. After storage, the first fraction (50–55 ml) observed in the chromatographic analysis and the second one (135–155 ml) tended to divide into two peaks, both the kefir with m-TG and that without m-TG. Two-dimensional electrophoresis proved the formation of the protein aggregates as an effect of transglutaminase action. The ELISA results obtained during the reaction of kefir proteins with specific antibody against individual milk proteins (β-lactoglobulin, α-lactalbumin and α-casein, β-casein and κ-casein) indicated differences in the level of proteins as a result of m-TG addition as well as storage. The reaction between immunoreactive β-lg and specific antibodies was not detectable in any of the kefir samples under the adopted conditions of the ELISA assay. The kefirs were evaluated for their sensory quality using a quantitative descriptive analysis (QDA). The results showed that both the addition of the m-TG enzyme and storage had significant effects on the sensory quality of the kefir samples. The kefirs with m-TG obtained higher scores for overall quality than the control one. The results indicated that this type of kefir can be offered especially to those consumers who are searching for foodstuffs with low immunoreactivity.