ANTIMICROBIAL ACTIVITY OF FERMENTED KEFIR WITH A BYPRODUCTION OF GRAPE FRUIT TO Alicyclobacillus acidoterrestris

Alicyclobacillus spp. are spore-forming bacteria that deteriorate fruit-based acidic beverages, causing economic losses, being A. acidoterrestris the most studied, responsible for the alterations of the sensorial characteristics of the products. The use of natural antimicrobial agents in food may be an option to inactivate such microorganisms. Therefore, the objective of this work is to investigate the antimicrobial activity of extracts fermented by kefir, from a byproduct of grape (BPU), against A. acidoterrestris. Four extracts were prepared using BPU in water (1: 2). Extract 1: BPU + 10% kefir grains (KG); extract 2: BPU + 2% sugar (CHO) + 10% KG; extract 3: BPU (15'ultrasound) + 10% KG; extract 4: BPU (15'ultrasound) + 2% CHO + 10% KG; the 4 extracts were fermented at 28°C for 7 days. The extracts were centrifuged at 10,000 rpm for 10 min and the supernatant was subjected to membrane filtration (0.22 μm). The minimum inhibitory concentration (MIC) was determined by the serial microdilution technique of the extracts from 50 to 0.1% of the initial fermentation concentration in Bacillus acidoterrestris (BAT) medium, with initial bacterial inoculum of 104 CFU/ml. The minimum bactericidal concentration (MBC) was also determined. The structural changes of the cells after treatment were evaluated by scanning electron microscopy (SEM). The MIC value capable of inhibiting the growth of A. acidoterrestris for all extracts was 1.6%, whereas the MBC was 50% for extract 1 and 3, while for extract 2 and 4 the MBC was 25%. The results show that extracts 2 and 4 obtained a better MBC value, possibly because kefir produced more secondary metabolites with addition of CHO, in addition, the use of ultrasound did not interfere. The results of the inhibitory and/or bactericidal concentration indicate that the extracts have activity against A. acidotrrestris.