Occurrence of Alicyclobacillus acidoterrestris in pasteurized and high hydrostatic pressure-treated fruit juices and isolates' characterization.

In recent years, acidophilic, heat-resistant, and spore-forming spoilage bacteria have been identified in pasteurized or treated by high hydrostatic pressure (HPP) fruit juices. Alicyclobacillus acidoterrestris is the bacteria more frequently linked to the spoilage of this type of product because its spores can survive conventional pasteurization and HPP treatments. Under favourable conditions, such as an acidic pH, its spores can germinate and multiply, with the consequent production of guaiacol. Guaiacol is a compound with an undesirable odour ("medicinal", "smoked" or "antiseptic"). In this context, our objective was to determine the prevalence of A. acidoterrestris in 150 Spanish pasteurized and HPP-treated fruit juices purchased from supermarkets or received from manufacturers. Then, the isolates and the reference strain (CECT 7094 T) were characterized to establish differences in terms of (i) growth capacity at different pH and temperatures, and in (ii) guaiacol production capacity. The results showed a high incidence of A. acidoterrestris (18.0 %) in the analysed juices. The 44.4 % of the isolates came from blends of fruit juices. Within juice blends, 9 juices contained apple juice among their ingredients. This represents a 18.8 % of incidence with respect to the total of blended juices with apple. A high incidence in monovarietal apple juices was also observed (3 out of 14 samples). Regarding the characterization of the isolates, EC1 (isolated from an apple concentrate) showed the highest growth capacity at pH 4.0 at temperatures from 20 to 55 °C. Besides, three strains (R42, EC10, and EZ13, isolated from clementine, plum and white grape juice, respectively) could grow at room temperatures (20 and 25 °C). For pH, only EZ13, isolated from white grape juice, was able to grow significantly at pH 2.5. Finally, the production of guaiacol ranged from 74.1 to 145.6 ppm, being the isolate EC1 the one that produced more guaiacol after 24 h of incubation at 45 °C (145.6 ppm). As we have observed, there is a high incidence of A. acidoterrestris in marketed juices and intermediate products despite the treatments received (pasteurization or HPP). Under favourable conditions for the development of this microorganism, it could produce enough guaiacol to spoil the juices before their consumption. Therefore, in order to improve the quality of fruit juices it is necessary to investigate in more detail the origin of this microorganism and to find strategies to reduce its presence in final products.

Bacterial Spore Inactivation in Orange Juice and Orange Peel by Ultraviolet-C Light.

Spore-forming bacteria are a great concern for fruit juice processors as they can resist the thermal pasteurization and the high hydrostatic pressure treatments that fruit juices receive during their processing, thus reducing their microbiological quality and safety. In this context, our objective was to evaluate the efficacy of Ultraviolet-C (UV-C) light at 254 nm on reducing bacterial spores of Alicyclobacillus acidoterrestris, Bacillus coagulans and Bacillus cereus at two stages of orange juice production. To simulate fruit disinfection before processing, the orange peel was artificially inoculated with each of the bacterial spores and submitted to UV-C light (97.8-100.1 W/m2) with treatment times between 3 s and 10 min. The obtained product, the orange juice, was also tested by exposing the artificially inoculated juice to UV-C light (100.9-107.9 W/m2) between 5 and 60 min. A three-minute treatment (18.0 kJ/m2) reduced spore numbers on orange peel around 2 log units, while more than 45 min (278.8 kJ/m2) were needed to achieve the same reduction in orange juice for all evaluated bacterial spores. As raw fruits are the main source of bacterial spores in fruit juices, reducing bacterial spores on fruit peels could help fruit juice processors to enhance the microbiological quality and safety of fruit juices.