Effect of high pressure combined with temperature on the death kinetics of Alicyclobacillus acidoterrestris spores and on the quality characteristics of mango pulp

Antibacterial Activity and Transcriptomic Analysis of Hesperetin against Alicyclobacillus acidoterrestris Vegetative Cells

The aim of this research was to investigate the antimicrobial characteristics and mechanism of hesperetin against Alicyclobacillus acidoterrestris vegetative cells. The results presented show that hesperetin had effective antimicrobial activity on Alicyclobacillus acidoterrestris vegetative cells, minimum inhibition concentration (MIC) of 0.0625 g/L, and minimum bacterial concentration (MBC) greater than 2 g/L. Moreover, treatment of hesperetin caused significant damage to cell integrity, preventing the growth of Alicyclobacillus acidoterrestris vegetative cells, enhancing the leakage of nucleic acid and proteins, and destroying the vegetative cell morphology. To further investigate the mechanism, transcriptomic analysis was carried out, and 3056 differentially expressed genes (DEGs) were detected. Gene ontology (GO) enrichment analysis revealed that hesperetin inhibits Alicyclobacillus acidoterrestris by affecting the intracellular nitrogen metabolism and amino acid metabolism. The Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis explained that hesperetin was also able to prevent the growth of Alicyclobacillus acidoterrestris by affecting the processes of nutrient transport, energy metabolism, and flagella motility. These results provide new insights into the antimicrobial effects and mechanism of hesperetin against Alicyclobacillus acidoterrestris, which provides a new method for inactive Alicyclobacillus acidoterrestris in the juice industry.

The Effect of Temperature-Assisted High Hydrostatic Pressure on the Survival of Alicyclobacillus acidoterrestris Inoculated in Orange Juice throughout Storage at Different Isothermal Conditions

The purpose of this work was to investigate the population dynamics of the spores and vegetative cells of A. acidoterrestris in orange juice treated with temperature-assisted HHP and stored in different isothermal conditions. For this reason, the spores of two A. acidoterrestris strains were inoculated in commercial orange juice and subjected to HHP treatment at 600 MPa/60 °C for 5 and 10 min. Inoculated samples were subsequently stored at 4, 12 and 25 °C for 60 days. During storage, the population of A. acidoterrestris was determined before and after heat shock at 80 °C for 10 min in order to estimate the quantity of spores and any remaining vegetative cells on the Bacillus acidoterrestris medium agar. Results showed that spore populations decreased by 3.0–3.5 log cycles directly after HHP treatment. Subsequently, no significant changes were observed throughout storage regardless of temperature and bacterial strain. However, at 25 °C, an increase of 0.5–1.0 log cycles was noticed. For the remaining vegetative cells, the results illustrated that HHP treatment could eliminate them during storage at 4 and 12 °C, whereas at 25 °C inactivation was strain-dependent. Therefore, temperature-assisted HHP treatment could effectively inactivate A. acidoterrestris spores in orange juice and ensure that the inhibitory effect could be maintained throughout storage at low temperatures.

Fruit Juice Spoilage by Alicyclobacillus: Detection and Control Methods—A Comprehensive Review

Fruit juices have an important place in humans’ healthy diet. They are considered to be shelf stable products due to their low pH that prevents the growth of most bacteria. However thermo-acidophilic endospore forming bacteria of the genus Alicyclobacillus have the potential to cause spoilage of commercially pasteurized fruit juices. The flat sour type spoilage, with absence of gas production but presence of chemical spoilage compounds (mostly guaiacol) and the ability of Alicyclobacillus spores to survive after pasteurization and germinate under favorable conditions make them a major concern for the fruit juice industry worldwide. Their special characteristics and presence in the fruit juice industry has resulted in the development of many isolation and identification methods based on cell detection (plating methods, ELISA, flow cytometry), nucleic acid analysis (PCR, RAPD-PCR, ERIC-PCR, DGGE-PCR, RT-PCR, RFLP-PCR, IMS-PCR, qPCR, and 16S rRNA sequencing) and measurement of their metabolites (HPLC, GC, GC-MS, GC-O, GC-SPME, Electronic nose, and FTIR). Early detection is a big challenge that can reduce economic loss in the industry while the development of control methods targeting the inactivation of Alicyclobacillus is of paramount importance as well. This review includes a discussion of the various chemical (oxidants, natural compounds of microbial, animal and plant origin), physical (thermal pasteurization), and non-thermal (High Hydrostatic Pressure, High Pressure Homogenization, ultrasound, microwaves, UV-C light, irradiation, ohmic heating and Pulse Electric Field) treatments to control Alicyclobacillus growth in order to ensure the quality and the extended shelf life of fruit juices.