Antioxidative properties of milk protein preparations fermented by Polish strains of Lactobacillus helveticus

The increasing significance of food products containing substances with antioxidative activi- ties is currently being observed. This is mainly due to the fact that pathogenic changes underlying some diseases are related to the carcinogenic effects of free radicals. Antioxidative compounds play an important role in supporting and enhancing the body's defense mechanisms, which is useful in preventing some civili- zation diseases. Unfortunately, it has been already proved that some synthetic antioxidants pose a potential risk in vivo. Therefore, antioxidant compounds derived from a natural source are extremely valuable. Milk is a source of biologically active precursors, which when enclosed in structural protein sequences are inactive. The hydrolysis process, involving bacterial proteolytic enzymes, might release biopeptides that act in various ways, including having antioxidant properties. The objective of this study was to determine the antioxidant properties of milk protein preparations fermented by Polish strains of L. helveticus. The research also focused on evaluating the dynamics of milk acidification by these strains and analyzing the textural properties of the skim milk fermented products obtained. The research studied Polish strains of L. helveticus: B734, 141, T80 and T105, which have not yet been used industrially. The antioxidant properties of 1% (w/v) solutions of milk protein preparations (skim milk powder, caseinoglycomacropeptide and α-lactoalbumin) fermented by these strains were determined by neutralizing the free radicals with 2,2-diphenyl-1-picrylhydrazyl (DPPH˙). Moreover, solutions of skim milk powder (SMP) fermented by the microorganisms being tested were analyzed on gel electrophoresis (SDS-PAGE). The dynamics of milk acidification by these microorganisms was also analyzed L. helveticus strains were used to prepare fermented regenerated skim milk products that were subjected to texture profile analysis (TPA) performed using a TA-XT2i (Stable Micro Systems, Godalming, UK). The results suggest that the antioxidant activity of fermented milk protein preparations depended on the type of milk protein preparation and was also related to the strain that conducted the fermentation process. The process of caseinoglycomacropeptide (CGMP) fermentation by DSMZ 20075, T105 and 141 signifi- cantly (p < 0.05) influenced the increase in the antioxidant activities of the protein preparation, the highest values of parameter were obtained in samples fer