The Combined Effect of UV Irradiation and Ethanol Extract from Torilis japonica Fruit on Inactivation of Bacillus subtilis Spores

The improved resistance of germinated spores to ultraviolet irradiation: Comparison with chlorine

Fungi outbreaks in water will include a series of processes, including spore aggregation, germination, biofilm, and finally present in a mixed state in the aquatic environment. More attention is paid to the control of dispersed fungal spores, however, there was little knowledge of the control of germinated spores. This study investigated the inactivation kinetics and mechanism of ultraviolet (UV) treatment for fungal spores with different germination percentages compared with dormant spores. The results indicated that the inactivation rate constants (k) of spores with 5%-45% germination were 0.0278-0.0299 cm2/mJ for Aspergillus niger and 0.0588-0.0647 cm2/mJ for Penicillium polonicum, which were lower than those of dormant spores. It suggested that germinated spores were more tolerant to UV irradiation than dormant spores, and it may be due to the defensive barrier (upregulated pigments) and some reductive substance (upregulated enoyl reductase) by absorbing UV or reacting with reactive oxygen species according to transcriptome analysis. Compared to dormant spores, the k-UV of germinated spores decreased by 18.17%-26.56% for Aspergillus niger, which was less than k-chlorine (62.33%-69.74%). A slighter decrease in k-UV showed UV irradiation can efficiently control fungi contamination, especially when dormant spores and germinated spores coexisted in actual water systems. This study indicates that more attention should be paid to germinated spores.

Bacillus spores: a review of their properties and inactivation processing technologies

Many factors determine the resistance properties of a Bacillus spore to heat, chemical and physical processing, including thick proteinaceous coats, peptidoglycan cortex and low water content, high levels of dipicolinic acid (DPA), and divalent cations in the spore core. Recently, attention has been focused on non-thermal inactivation methods based on high pressure, ultrasonic, high voltage electric fields and cold plasmas for inactivating Bacillus spores associated with deterioration in quality and safety. The important chemical sporicides are glutaraldehyde, chorine-releasing agents, peroxygens, and ethylene oxide. Some food-grade antimicrobial agents exhibit sporostatic and sporicidal activities, such as protamine, polylysine, sodium lactate, essential oils. Surfactants with hydrophilic and hydrophobic properties have been reported to have inactivation activity against spores. The combined treatment of physical and chemical treatment such as heating, UHP (ultra high pressure), PEF (pulsed electric field), UV (ultraviolet), IPL (intense pulsed light) and natural antimicrobial agents can act synergistically and effectively to kill Bacillus spores in the food industry.

Inactivation of Bacillus subtilis spores at various germination and outgrowth stages using intense pulsed light

It is important to inactivate spore-forming bacteria in foods because their spores are highly resistant to various stresses. Although thermal treatment is an effective inactivation method, the associated high temperatures can cause changes in food quality. Intense pulsed light (IPL) is a nonthermal technique that can effectively improve food safety. This study evaluated the inactivation effects of IPL at various fluences on Bacillus subtilis spores. IPL treatment at a total fluence of 7.40 J/cm² resulted in a 7 log reduction, indicating the potential of IPL to effectively inactivate bacterial spores. The sensitivity of B. subtilis spores to IPL during germination and outgrowth was also measured. The resistance to the IPL increased temporarily until 1 h after the start of incubation, and then gradually decreased for longer incubation periods. This temporary increase in resistance at the early stage of incubation was attributed to the leakage of dipicolinic acid from the spores. The results also showed that the inactivation efficiency increases after 1 h pre-incubation because the numbers of vegetative cells increased with the incubation time.