Non-thermal inactivation of Alicyclobacillus acidoterrestris and guaiacol production in orange juice by using silica microparticles functionalised with essential oil components

Abstract

[EN] Alicyclobacillus acidoterrestris is an acidophilic, spore-forming bacterium that is particularly notable for its ability to spoil fruit juice and other acidic beverages. It produces guaiacol, a compound that confers these products a smoky, medicinal or phenolic off-flavour, which results in consumer rejection and significant economic losses for the beverage industry. This microorganism is also known for its high thermal resistance, which poses challenges in traditional thermal preservation methods. This work aimed to assess the effect of silica microparticles functionalised with essential oil components on controlling the growth of vegetative cells of different A. acidoterrestris strains and subsequent guaiacol production capacity in orange juice. Immobilised essential oil components were applied following two different approaches: contact with juice in uniform dispersion; filtering juice through a layer of functionalised microparticles. Firstly, the potential of the different pure essential oil components was evaluated by in vitro experiments in culture medium by determining microbial counts and guaiacol production by HPLC. These tests revealed that eugenol and thymol were the most effective antimicrobials, while vanillin and geraniol displayed moderate or minimal effectiveness, respectively. The orange juices inoculated with A. acidoterrestris were treated by contact or filtration with both the free and immobilised forms of eugenol and thymol. In the first approach, the juice incubation with MIC × 0.5 of free or immobilised eugenol and thymol for 24 h lowered A. acidoterrestris counts and inhibited guaiacol production. In the second approach, the inoculated juices were also filtered through eugenol and thymol particles, and this fast process was able to inhibit guaiacol production. These findings highlight the potential of harnessing the antimicrobial properties of immobilised essential oil components to mitigate A. acidoterrestris contamination risks during juice production. By these approaches, juice producers can meet consumer demands for safe, premium-quality products, while ensuring extended shelf life and minimising flavour defects and, thus, food waste.