Enzyme-assisted processing increases antimicrobial and antioxidant activity of bilberry

Abstract

The effects of nine cell wall-degrading enzymes on the antimicrobial and antioxidant activities of bilberry were studied. Antimicrobial activity was measured using the human pathogens Salmonella enterica sv. Typhimurium and Staphylococcus aureus as test strains. Enzyme treatments liberated phenolics from the cell wall matrix, which clearly increased the antimicrobial activity of berry juices, press cakes, and berry mashes on the basis of plate counts. Antibacterial effects were stronger against Salmonella than against Staphylococcus bacteria. In general, the increase in activity measured as colony-forming units per milliliter was 3-5 logarithmic units against Salmonella and 1-2 units against Staphylococcus bacteria. Increase in antimicrobial activity was observed only in acidic conditions, which is also the natural environment in various berry products, such as juices. The activity profile of the pectinase preparation affected the chemistry of the phenolics due to the presence of deglycosylating activities in some preparations. The difference in phenolic profiles was reflected in the antimicrobial effects. Bilberry mashes treated with Pectinex Ultra SP-L, Pectinex 3 XL, and Pectinex BE XXL were most efficient against Salmonella bacteria, whereas mashes treated with Pectinex Smash, Pectinex BE 3-L, and Biopectinase CCM showed the strongest antimicrobial activity against Staphylococcus bacteria. Due to the liberation of phenolics from the cell wall matrix the antioxidant activity measured as radical scavenging activity was also increased on average about 30% by the enzymatic treatments. The highest increase in phenolic compounds was about 40%. Highest increases in anthocyanins and in antioxidant activity were observed in berry mash treated with Pectinex Smash XXL enzyme, and the lowest increase was observed after treatment with Pectinex BE 3-L. Enzyme-assisted processing is traditionally used to improve berry and fruit juice yields. However, enzymatic treatments also have an impact on the functional properties of the products. The increased liberation of phenolics from the cell wall matrix can prolong the shelf life of berry products by limiting the growth of contaminants during processing or storage. The increased amount of phenolic compounds may also have a positive effect on gut well-being.