Distribution of Cell Envelope Proteinases Genes among Polish Strains of Lactobacillus helveticus.

Most of the lactic acid bacteria (LAB) are able to grow in milk mainly due to the activity of a complex and well-developed proteolytic system. Cell envelope-associated proteinases (CEPs) begin casein hydrolysis and allow for releasing the peptides, enclosed in the structure of native milk proteins that are essential for growth of Lactobacillus helveticus. The biodiversity of genes encoding CEPs among L. helveticus strains can have an effect on some technological parameters such as acid production, bacterial growth rate in milk as well as liberation of biologically active peptides. The study reveals significant differences in the presence of various variants of CEPs encoding genes among ten novel Polish strains and indicates the intraspecific diversity exhibited by L. helveticus. In terms of distribution of CEPs genes, four different genetic profiles were found among the microorganisms analyzed. Furthermore, the strains exhibited also various levels of proteolytic activity. Molecular analysis revealed that prtH3 is the most abundant CEPs-encoding gene among the strains investigated. The results indicate also that ecological niche and environmental conditions might affect proteolytic properties of L. helveticus strains. The greatest variety in terms of quantity of the detected CEP encoding genes was noticed in L. helveticus 141, T105 and T104 strains. In these strains, the combination of three nucleotide gene sequences (prtH/prtH2/prtH3) was identified. Interestingly, T104 and T105 exhibited the highest proteolytic activity and also the fastest dynamic of milk acidification among the tested strains of L. helveticus.

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

BACKGROUND: 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. METHODS: 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). RESULTS: 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 fermented by L. helveticus T105 (64.82 ±0.013%), while in the case of α-lactoalbumin (α-la), the strongest free radical scavenging activity (66.67 ±0.020%) was noted for unfermented samples (control). CONCLUSIONS: The greatest increase in DPPH scavenging activity (% of inhibition) was noted for fermented SMP solutions. The highest values of the parameter measured were recorded for SMP fermented by the reference strain (85.98 ±0.009%) and T80 (81.66 ±0.013%). Strain T105 demonstrated the most desirable properties with respect to milk acidifying dynamic and texture properties of fermented skim milk products, while the reference strain (L. helveticus DSMZ 20075) and L. helveticus T80 seem to be more desirable in terms of the possibility of obtaining fermented protein preparations with the best antioxidant properties. The Polish strains analyzed here might find application in dairy products and also in developing functional food products. Furthermore, the preparations of milk protein that were fermented by the strains being tested may be a natural source dietary antioxidants.