Control of Alicyclobacillus spp. vegetative cells and spores in apple juice with rosemary extracts

In this study, we initially investigated the antimicrobial activities of two commercial rosemary extracts (V20, V40) against Alicyclobacillus strains, with the ultimate purpose to determine whether these can be used in apple juice for the control of growth of alicyclobacilli. Minimum inhibitory concentrations (MICs) were first determined, and put through sensory analysis. Addition of the rosemary extracts to apple juice at their MICs did not change the colour, odour, taste or opacity of the apple juice. Growth kinetics studies with these rosemary extracts indicated a reduction in vegetative cells for Alicyclobacillus acidoterrestris, Alicyclobacillus hesperidum and Alicyclobacillus cycloheptanicus in Bacillus acidoterrestris broth and in apple juice. Further studies with A. acidoterrestris spores showed that the MICs of these rosemary extracts had relatively low effects on spore numbers in B. acidoterrestris broth, but had a spore number inhibition index >15% in apple juice. A four-fold increase in the rosemary extract concentrations showed the opposite effects: greater reduction in spores in B. acidoterrestris broth (inhibition index, >60%) than in apple juice (inhibition index, <10%). These data indicate that at their MICs, the V20 and V40 rosemary extracts allow outgrowth of spores but reduce vegetative cells, acting together with the low pH or other particular constituents of the apple juice. Rosemary extracts applied at their MICs thus represent an alternative method for the control of A. acidoterrestris in apple juice.