Abstract
Alicyclobacillus acidoterrestris (A. acidoterrestris), a spore-forming bacterium, has become a main challenge and concern for the juices and acid beverage industry across the world due to its thermo-acidophilic characteristic. Thymoquinone (TQ) is one of the active components derived from Nigella sativa seeds. The objective of this study was to investigate antibacterial activity and associated molecular mechanism of TQ against A. acidoterrestris vegetative cells, and to evaluate effects of TQ on A. acidoterrestris spores and biofilms formed on polystyrene and stainless steel surfaces. Minimum inhibitory concentrations of TQ against five tested A. acidoterrestris strains ranged from 32 to 64 μg/mL. TQ could destroy bacterial cell morphology and membrane integrity in a concentration-dependent manner. Field-emission scanning electron microscopy observation showed that TQ caused abnormal morphology of spores and thus exerted a killing effect on spores. Moreover, TQ was effective in inactivating and removing A. acidoterrestris mature biofilms. These findings indicated that TQ is promising as a new alternative to control A. acidoterrestris and thereby reduce associated contamination and deterioration in the juice and acid beverage industry.
Highlights
A. acidoterrestris, a gram-positive, thermo-acidophilic, and spore-forming spoilage bacterium, is mainly responsible for the deterioration of acid products especially fruit juice, vegetable juice, and other relevant beverages (Keiichi and GOTO, 2006; Smit et al, 2011)
The results revealed that TQ at 1 × Minimum inhibitory concentrations (MICs) and 2 × MIC exerted a bactericidal effect on A. acidoterrestris cells
The results revealed that TQ at 1 × MIC and 2 × MIC destroyed the cell morphology of A. acidoterrestris
Summary
A. acidoterrestris, a gram-positive, thermo-acidophilic, and spore-forming spoilage bacterium, is mainly responsible for the deterioration of acid products especially fruit juice, vegetable juice, and other relevant beverages (Keiichi and GOTO, 2006; Smit et al, 2011). This bacterium is extensively distributed in almost all components of the production and processing chain including the orchard, picking basket, fruit granary, fruit surface, cleaning water, pipeline water, production line, concentrated juice, semi-products, and final products (Chen et al, 2006; Driks et al, 2013; Huang et al, 2015). The off-flavors of these compounds undermined the quality of the products (Pornpukdeewattana et al, 2020), which led to unaccepted products and substantial economic losses for the beverage industry
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