Modeling the Inactivation of Bacillus cereus in Tiger Nut Milk Treated with Cold Atmospheric Pressure Plasma

Oxygen and air cold plasma for the inactivation of Bacillus cereus in low-water activity soy powder

Cold plasma (CP) technology is a promising alternative to thermal treatments for the microbial decontamination of foods with low-water activity. The aim of this work is study the application of low-pressure CP (0.35 mbar) for the inactivation of Bacillus cereus in a soybean powder matrix using O₂ and synthetic air as ionizing gases. The parameters tested were an input power of 100, 200 and 300 W and an exposure time of 10 to 30 min. The excited reactive species formed were monitored by optical emission spectroscopy, and survival data were analyzed using the Weibull mathematical model. Treatments with both gases were effective in inactivating B. cereus. Air plasma resulted in a maximum 3.71-log reduction in bacterial counts at 300 W and 30 min, while O2 plasma showed the strongest inactivation ability, achieving levels higher than 5 log cycles at 300 W and > 25 min. This is likely due to the strong antimicrobial activity of oxygen-derived radicals together with carbon monoxide as an oxidation by-product. In addition, the Weibull distribution function accurately modeled the inactivation of B. cereus. Cold plasma technology is a promising approach for the decontamination of bacteria in low-water activity foods.

Plant-based milk: unravel the changes of the antioxidant index during processing and storage - a review

As a nutrient rich emulsion extracted from plant materials, plant-based milk (PBM) has been the latest trend and hot topic in the food industry due to the growing awareness of consumers toward plant-based products in managing the environmental (carbon footprint and land utility), ethical (animal well-fare) and societal (health-conscious) issues. There have been extensive studies and reviews done to discuss the distinct perspective of PBM including its production, health effects and market acceptance. However, not much has been emphasized on the valuable antioxidants present in PBM which is one of the attributes making them stand apart from dairy milk. The amounts of antioxidants in PBM are important. They offered tremendous health benefits in maintaining optimum health and reducing the risk of various health disorders. Therefore, enhancing the extraction of antioxidants and preserving their activity during production and storage is important. However, there is a lack of a comprehensive review of how these antioxidants changes in response to different processing steps involved in PBM production. Presumably, antioxidants in PBM could be potentially lost due to thermal degradation, oxidation or leaching into processing water. Hence, this paper aims to fill the gaps by addressing an extensive review of how different production steps (germination, roasting, soaking, blanching, grinding and filtration, and microbial inactivation) affect the antioxidant content in PBM. In addition, the effect of different microbial inactivation treatments (thermal or non-thermal processing) on the alteration of antioxidant in PBM was also highlighted. This paper can provide useful insight for the industry that aims in selecting suitable processing steps to produce PBM products that carry with them a health declaration.

Stability, nutritional composition, and antioxidant properties of surfactant-assisted enzymatically extracted tiger nut milk

This study evaluated the effect of surfactant-assisted enzymatic extraction on the quality of tiger nut milk (TNM). TNM was extracted from tiger nuts using different concentrations of xylanase (0.010–0.100%) and Tween 20 (0.005–0.010%). The yield, stability, nutritional, antioxidant, and sensory properties of the samples were determined. The yield of TNM significantly increased, by 32.72–50.67%, following surfactant-assisted enzymatic extraction. Optimum yield and stability of TNM were obtained using 0.010% xylanase and Tween 20. Enzymatic extraction significantly increased total sugar and flavonoids, however, starch, dietary fibre, protein, carotenoids, lycopene, total phenolic content, and antioxidant properties reduced significantly. The incorporation of Tween 20 stabilised these parameters. There was no significant difference in panellists' preference for the control (sample extracted without enzyme and surfactant), enzymatically-extracted, and surfactant-assisted enzymatic extracted samples in mouthfeel and aroma, however, the surfactant-assisted enzymatic extracted sample was most preferred in colour, consistency, taste, and overall acceptability. Using surfactant-assisted enzymatic extraction could prove invaluable for the production of TNM.

Stress Resistance and Pathogenicity of Nonthermal-Plasma-Induced Viable-but-Nonculturable Staphylococcus aureus through Energy Suppression, Oxidative Stress Defense, and Immune-Escape Mechanisms

The occurrence of viable-but-nonculturable (VBNC) bacteria poses a potential risk to food safety due to failure in conventional colony detection. In this study, induction of VBNC Staphylococcus aureus was conducted by exposure to an atmospheric-pressure air dielectric barrier discharge-nonthermal-plasma (DBD-NTP) treatment with an applied energy of 8.1 kJ. The stress resistance profiles and pathogenicity of VBNC S. aureus were further evaluated. We found that VBNC S. aureus showed levels of tolerance of heat, acid, and osmosis challenges comparable to those shown by culturable S. aureus, while VBNC S. aureus exhibited enhanced resistance to oxidative and antibiotic stress, relating to the mechanisms of cellular energy depletion, antioxidant response initiation, and multidrug efflux pump upregulation. Regarding pathogenicity, NTP-induced VBNC S. aureus retained the capacity to infect the HeLa host cells. Compared with the culturable counterparts, VBNC S. aureus caused reduced immune responses (Toll-like receptor [TLR], nucleotide-binding oligomerization domain [NOD]) in HeLa cells, which was attributed to suppression of biosynthesis of the recognized surface ligands (e.g., peptidoglycan). Additionally, the proteomic analysis revealed that upregulation of several virulence factors (ClfB, SdrD, SCIN, SasH, etc.) could ensure that VBNC S. aureus would adhere to and internalize into host cells and avoid the host attack. The camouflaged mechanisms described above led to VBNC S. aureus causing less damage to the host cells, and their activity might result in longer intracellular persistence, posing potential risks during NTP processing.IMPORTANCE The consumer demand for freshness and nutrition has accelerated the development of mild decontamination technologies. The incomplete killing of nonthermal (NT) treatments might induce pathogens to enter into a viable-but-nonculturable (VBNC) status as a survival strategy. The use of nonthermal plasma (NTP) as a novel food decontamination technology received increased attention in food industry during recent decades. Our previous work confirmed that the foodborne pathogen S. aureus was induced into VBNC status in response to NTP exposure. This work further revealed the development of stress resistance and virulence retention of NTP-induced VBNC S. aureus through the mechanisms of energy suppression, oxidative stress defense, and immune escape. The data provide fundamental knowledge of the potential risks posed by NTP-induced VBNC S. aureus, which require further parameter optimization of the NTP process or combination with other techniques to avoid the occurrence of VBNC bacteria.