Antimicrobial activity of grape seed extract on Alicyclobacillus acidoterrestris DSM 3922 vegetative cells and spores in apple juice

- Antimicrobial activity of grape seed extract (GSE) against Alicyclobacillus acidoterrestris cells and spores were evaluated.
- The Weibull model produced best fit to the cell inactivation data.
- Damage to the cell structure and cellular components was observed by scanning electron microscopy.
- Antimicrobial activity against spores was dependent on sporulation media.
- GSE may prevent the development of spores into vegetative cells.

The present study evaluated the antimicrobial activity of grape seed extract (GSE) against Alicyclobacillus acidoterrestris vegetative cells and spores in apple juice (pH 3.82, °Brix 11.3) during storage at 37 °C. After 336 h, reductions in the cell numbers were 3.14, 3.55, 3.8, 4.1, and 4.63 log CFU/mL in the apple juice with 0.23, 0.45, 0.9, 1.8, and 3.6% of GSE, respectively. The Weibull was found to be the best fitted model for cell inactivation kinetics (R2 > 0.988). Moreover, the spores produced on different sporulation media (potato dextrose agar, malt extract agar, Bacillus acidoterrestris agar, and Bacillus acidocaldarius agar) were treated with GSE (0-1.9%, v/v). While control spores in apple juice without GSE increased by 2.2-2.6 log CFU/mL within the first 48 h, 0.9% and 1.8% of GSE inhibited the growth from all spore suspensions. Finally, scanning electron microscopy (SEM) indicated that the main target of the GSE may be the membrane of A. acidoterrestris cells leading to leakage of cellular constituents and may prevent the development of spores into vegetative cells. This study highlights the potential use of the by-products of the fruit juice/beverage industry as natural antimicrobials to inhibit the growth of A. acidoterrestris.