Effects of dielectric barrier discharge plasma on the inactivation of Zygosaccharomyces rouxii and quality of apple juice

Reaction kinetics of physico-chemical attributes in coconut inflorescence sap during fermentation

The study on fermentation kinetics of the coconut inflorescence sap is important to understand its shelf life at different storage conditions and to develop suitable value added products. The coconut inflorescence sap collected by using in-house developed coco-sap chiller device is called Kalparasa. The fermentation characteristics of Kalparasa were investigated at every 1-h interval under ambient (31 ± 2 °C) and refrigerated (5 ± 1 °C) storage conditions. The results reveal that pH of the sap and total sugar content decline rapidly under ambient conditions than under refrigerated conditions. Acidity, turbidity, and reducing sugar content significantly (p < 0.001) increases for the sap stored under ambient conditions. The reaction rate constant (k) of the vitamin C and total sugar degradation increases with the atmospheric fermentation. The degradation kinetics of vitamin C and total sugar in Kalparasa during natural fermentation (ambient condition) follow second-order equation whereas the reducing sugar follows the first-order equation.

Inactivation effects and mechanisms of plasma-activated water combined with sodium laureth sulfate (SLES) against Saccharomyces cerevisiae

The present study aimed to elucidate the antifungal effect and underlying mechanism of plasma-activated water (PAW) combined with sodium laureth sulfate (SLES) against Saccharomyces cerevisiae. S. cerevisiae, initially at 6.95 log₁₀ colony-forming unit (CFU)/mL, decreased to an undetectable level following the synergistic treatment of PAW and SLES (0.50 mg/mL) for 20 min. After PAW treatment combined with SLES (2.5 mg/mL) for 30 min, the S. cerevisiae cells on polyethylene films also reduced to an undetectable level from the initial load of 5.84 log₁₀ CFU/cm². PAW + SLES treatment caused severe disruption of membrane integrity and increased lipid oxidation within the cell membrane and the intracellular reactive oxygen species levels in S. cerevisiae cells. Besides, the disruption of the mitochondrial membrane potential (∆ψm) was also observed in S. cerevisiae cells after treatment of PAW and SLES at 0.01 mg/mL for 5 min. These data suggest that the combined treatment of PAW and SLES causes oxidation injury to cell membranes and abnormal ∆ψm in S. cerevisiae, which may be eventually responsible for cell death. This study demonstrates the potential application of PAW combined with SLES as an alternative disinfection method. Key Points • PAW + SLES exhibited synergistic antifungal activity against S. cerevisiae. • PAW + SLES resulted in severe disruption of membrane integrity and permeability. • PAW + SLES induced accumulation of reactive oxygen species in S. cerevisiae cells.

Inactivation and Membrane Damage Mechanism of Slightly Acidic Electrolyzed Water on Pseudomonas deceptionensis CM2

Pseudomonas is considered as the specific spoilage bacteria in meat and meat products. The purpose of this study was to evaluate the inactivation efficiency and mechanisms of slightly acidic electrolyzed water (SAEW) against Pseudomonas deceptionensis CM2, a strain isolated from spoiling chicken breast. SAEW caused time-dependent inactivation of P. deceptionensis CM2 cells. After exposure to SAEW (pH 5.9, oxidation-reduction potential of 945 mV, and 64 mg/L of available chlorine concentration) for 60 s, the bacterial populations were reduced by 5.14 log reduction from the initial load of 10.2 log₁₀ CFU/mL. Morphological changes in P. deceptionensis CM2 cells were clearly observed through field emission-scanning electron microscopy as a consequence of SAEW treatment. SAEW treatment also resulted in significant increases in the extracellular proteins and nucleic acids, and the fluorescence intensities of propidium iodide and n-phenyl-1-napthylamine in P. deceptionensis CM2 cells, suggesting the disruption of cytoplasmic and outer membrane integrity. These findings show that SAEW is a promising antimicrobial agent.

Comprehensive studies on the properties of apple juice treated by non-thermal atmospheric plasma in a flow-through system

We present an optimized non-thermal atmospheric plasma (NTAP)-based reaction-discharge system that was applied for a continuous-flow treatment of apple juice (AJ). To optimize this system for a high-throughput production of AJ with ameliorated properties, the effect of several parameters was studied using design of experiments approach followed by the response surface methodology. Additionally, nutritional, physicochemical, microbiological and cytotoxic properties of resulting AJ were assessed. It was established that NTAP treatment of AJ led to rise in concentration of Ca, Fe, K, Mg, Na and Sr by 8–10% as well as Al, B, Ba, Cu, Mn and Zn by 11–15%. Additionally, the increased total phenolic content by ~ 11% in addition to the prolonged by up to 12 days shelf life of the product were observed. Moreover, it was found that the NTAP-treatment of AJ did not change the structure of organic compounds present in AJ, in addition to its °Brix value, color and ferric ion reducing antioxidant power. Furthermore, AJ subjected to NTAP did not show any cytotoxic activity towards non-malignant human intestinal epithelial cells but exhibited induced cell cytotoxicity in human colorectal adenocarcinoma cells. Our study provided arguments for future introduction of these types of preparations to the global market.

Possibility to extend the shelf life of NFC tomato juice using cold atmospheric pressure plasma

Cold Atmospheric pressure Plasma (CAP) is a non-thermal method used in food processing. CAP generated with the use of nitrogen in a Glide-arc device for 300 to 600 s exhibited high potential for microbial decontamination and did not induce substantial changes in the physicochemical properties of NFC tomato juice. Samples exposed to cold atmospheric plasma had mostly an intact structure, as revealed by digital microscopy. The investigations indicate that CAP can be applied for biological and chemical waste-free decontamination of food and extension of its shelf life.

Impact of pulsed magnetic field treatment on enzymatic inactivation and quality of cloudy apple juice

The effects of PMF (5-7 T, 5-30 pulses) on enzyme activity, pH, titratable acidity, soluble solids, color, ascorbic acid, total phenols and antioxidant activity (DPPH radical scavenging activity) of cloudy apple juice were evaluated. PMF inhibited activities of polyphenoloxidase (PPO), peroxidase (POD) and pectinmethylesterase (PME), but PPO was more sensitive to PMF than POD and PME. At the intensity of 6 T with 15 pulses, PPO and POD both exhibited the lowest residual activity (53.22 and 92.96%), while PME showed the lowest residual activity (83.01%) at 7 T with 30 pulses. No significant effect on soluble solids was found under all processing parameters, whereas significant decreases of ascorbic acid were observed at the intensity of 7 T with 5-30 pulses. PMF did not change pH, titratable acidity, color, total phenols and DPPH radical scavenging activity severely. These results suggest PMF can be a potential technology for enzymatic inactivation in apple juice with high retention of quality.

Effects of ultraviolet-C light-emitting diodes at 275 nm on inactivation of Alicyclobacillusacidoterrestris vegetative cells and its spores as well as the quality attributes of orange juice

Alicyclobacillus acidoterrestris is a thermoacidophilic, spore-forming bacillus. A. acidoterrestris and its spores can survive in pasteurized juices and cause microbial spoilage. In this work, the effects of ultraviolet-C light-emitting diodes at 275 nm on the inactivation of A. acidoterrestris vegetative cells and its spores in commercial pasteurized orange juice were studied. Meanwhile, the effects of ultraviolet-C light-emitting diodes on the quality attributes of the orange juice were also investigated. The quantities of A. acidoterrestris vegetative cells and its spores inoculated in orange juice were reduced by 6.04 and 2.49 log₁₀ CFU/mL after ultraviolet-C light-emitting diode treatment at 220 mJ/cm², respectively. The Weibull and Weibull plus tail models were satisfactorily fitted to estimate the reductions of A. acidoterrestris vegetative cells and its spores in orange juice, respectively. Physicochemical properties (pH, titratable acidity, total soluble solids, and clarity) of orange juice did not change significantly after exposure to ultraviolet-C light-emitting diodes. However, the total phenolic content of orange juice decreased with increasing fluence. In addition, ultraviolet-C light-emitting diode treatment at a higher fluence led to a noticeable color difference. These results indicate that ultraviolet-C light-emitting diode treatment has a potential application in the juice processing industry.

Synergistic Inactivation Mechanism of Combined Plasma-Activated Water and Mild Heat against Saccharomyces cerevisiae

ABSTRACT

This study aimed to elucidate the mechanism of synergistic inactivation of Saccharomyces cerevisiae by the combined use of plasma-activated water (PAW) and mild heat (40 to 50°C). A reduction of 4.40 log CFU/mL in S. cerevisiae was observed after the synergistic combination of PAW and mild heat at 50°C for 6 min, whereas the individual treatments of PAW at 25°C and mild heat at 50°C for 6 min resulted in a reduction of 0.27 and 1.92 log CFU/mL, respectively. The simultaneous application of PAW and mild heat caused significant increases in membrane permeability, resulting in the leakage of intracellular components (such as nucleic acids and proteins) and increased uptake of propidium iodide. The combined treatment of PAW and mild heat also resulted in significant increases in the intracellular levels of reactive oxygen species and disruption of mitochondrial membrane potential in S. cerevisiae cells. In summary, this study illustrates the potential of PAW treatment combined with mild heat to rapidly inactivate microorganisms in food products.

HIGHLIGHTS

Effects of atmospheric pressure plasma jet on the physicochemical, functional, and antioxidant properties of flaxseed protein

The aim of this study was to explore the effect of atmospheric pressure plasma jet (APPJ) on the physicochemical, functional, and antioxidant properties of flaxseed protein following APPJ treatment (0 to 240 s). The results showed that the pH value continuously dropped with the minimum value of 3.45 ± 0.15 after 240 s of APPJ treatment (-61.7%, P < 0.05). The relative protein solubility significantly declined after 15 s of APPJ treatment (-43.1%, P < 0.05), which was accompanied by the evident increase in mean particle size of flaxseed protein in aqueous solution (+157%, P < 0.05). Moreover, the surface hydrophobicity and contents of disulfide bonds gradually raised when the APPJ exposure time extended from 30 to 240 s. Notably, the foaming, emulsifying, and in vitro antioxidant properties of flaxseed protein were significantly improved following short time of APPJ treatment (5 to 15 s), which was paralleled with the changes of spatial conformation, mild protein oxidation, as well as the release of phenolic acids and flavonoids from naturally occurring protein-phenolic complex. Our findings elucidated that APPJ may be considered as an effective strategy to improve the functionality and antioxidant activities of flaxseed protein. PRACTICAL APPLICATION: We had evaluated the effect of APPJ treatment on the physicochemical, functional, and antioxidant properties of flaxseed protein, which was conducive to tailor flaxseed protein with the optimal techno-functionality and antioxidant activities as a potential nano-delivery vehicle.

Non-thermal plasma: An advanced technology for food industry

In this era of green technology, plasma technology is one of the novel techniques intended towards many industries including food industry as a principal application due to less utilization of energy, solvents, and water with minimum impact on food quality. The foremost purpose behind the utilization of nonthermal plasma processing (cold plasma) lies in the retention of freshness of food products along with furtherance of sensory properties as well as functional and nutritional composition. In addition, this technique assists in shelf life extension and carries out desirable modifications in the structure of food and packaging material. This technology has been proven to be advantageous over other technologies since all these processes are carried out at low temperature, hence is highly suitable for heat-sensitive materials. The present review summarizes the mechanism of this plasma technology along with its benefits to the industry, for example improvements in cooking quality, enhancements in enzyme activity, modification of starches, and microbial inactivation. Also, the effects of plasma treatment on characteristics of various food products have been elaborated in this review.

Factors influencing the antimicrobial efficacy of Dielectric Barrier Discharge (DBD) Atmospheric Cold Plasma (ACP) in food processing applications

Atmospheric cold plasma (ACP) is an emerging technology in the food industry with a huge antimicrobial potential to improve safety and extend the shelf life of food products. Dielectric barrier discharge (DBD) is a popular approach for generating ACP. Thanks to the numerous advantages of DBD ACP, it is proving to be successful in a number of applications, including microbial decontamination of foods. The antimicrobial efficacy of DBD ACP is influenced by multiple factors. This review presents an overview of ACP sources, with an emphasis on DBD, and an analysis of their antimicrobial efficacy in foods in open atmosphere and in-package modes. Specifically, the influence of process, product, and microbiological factors influencing the antimicrobial efficacy of DBD ACP are critically reviewed. DBD ACP is a promising technology that can improve food safety with minimal impact on food quality under optimal conditions. Once the issues pertinent to scale-up of plasma sources are appropriately addressed, the DBD ACP technology will find wider adaptation in food industry.

Effect of rosemary extract on lipid oxidation of cooked pork during simulated gastric digestion

BACKGROUND

Oxidation of food lipids occurs in the gastrointestinal tract, resulting in potential adverse health effects. Rosemary extract (RE), as one of the most popular naturally sourced antioxidants, is widely used in the food industry. However, the effect of RE on lipid oxidation during gastrointestinal digestion has not been well investigated. Therefore, this study aimed to evaluate the effect of RE on lipid oxidation of cooked pork during simulated gastric digestion.

RESULTS

Results showed that RE at 12.5, 25, 50, and 100 mg kg^-1 pork effectively decreased the formation of malondialdehyde during simulated gastric digestion of cooked pork. RE also effectively mitigated the decline of fatty acids during the simulated gastric digestion of pork. The total phenolic content in RE was calculated to be 170.67 mg gallic acid equivalent (GAE) g^-1 . RE dissolved in distilled water (pH 6.5) or potassium hydrogen phthalate-hydrochloric acid buffer solution (0.2 mol L^-1 , pH 3.0) both exhibited strong 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) and 1,1-diphenyl-2-picrylhydrazyl radical-scavenging activities as well as ferric reducing capacity. The inhibitory effects of RE on lipid oxidation of cooked pork during simulated gastric digestion may be attributed to the phenolic compounds with antioxidant properties.

CONCLUSION

The results lend support to the possible application of rosemary or RE as a rich source of natural antioxidants to inhibit the oxidation of food lipids during gastrointestinal digestion. © 2019 Society of Chemical Industry.

Genomic Insights Into Sugar Adaptation in an Extremophile Yeast Zygosaccharomyces rouxii

The osmotolerant Zygosaccharomyces rouxii is known for its trait to survive in extreme high sugar environments. This ability determines its role in the fermentation process and leads to yeast spoilage in the food industry. However, our knowledge of the gene expression in response to high sugar stress remains limited. Here, we conducted RNA-sequencing (RNA-seq) under different sugar concentrations of the spoilage yeast, Z. rouxii, which exhibit extremely high tolerance to sugar stress. The obtained differentially expressed genes (DEGs) are significantly different to that of the Saccharomyces cerevisiae, which is sensitive to extreme high sugar stress. Most of the DEGs participated in the “glucan synthesis,” “transmembrane transport,” “ribosome,” etc. In this work, we also demonstrated that the gene ZYRO0B03476g (ZrKAR2) encoding Kar2p can significantly affect the growth of Z. rouxii under high sugar stress. In addition, we combined with a previous study on the genome sequence of Z. rouxii, indicating that several gene families contain significantly more gene copies in the Z. rouxii lineage, which involved in tolerance to sugar stress. Our results provide a gene insight for understanding the high sugar tolerance trait, which may impact food and biotechnological industries and improve the osmotolerance in other organisms.

Exploring the Potential of High-Voltage Electric Field Cold Plasma (HVCP) Using a Dielectric Barrier Discharge (DBD) as a Plasma Source on the Quality Parameters of Carrot Juice

The main aim of the current investigation was to contemplate the impact of high-voltage electric field cold plasma (HVCP) on different quality characteristics (enzymes, microbial activities, coloring pigments, ascorbic acid, polyphenolic compounds, °Brix, acidity, and color index) of carrot juice in correlation with thermal processing. A carrot juice (250 mL) sample sealed in pre-sterilized food-grade bottles, which placed between two dielectric quartz plates for HVCP treatment. The gap between the plates was 30 mm, and a stable and uniform plasma dielectric barrier discharge (DBD) generated for 3 and 4 min at 60, 70, and 80 kV. Air was used as a working gas during the DBD-based plasma treatment. The observed rise in temperature was 2-5 °C during the HVCP treatment. A water bath was used to carry out thermal treatment (100 °C for 5 min). The maximum inactivation of enzymes and microorganisms was achieved with thermal treatment and then with HVCP treatment at 70 kV for 4 min. However, maximum retention of coloring compounds, ascorbic acid, total phenols, flavonoids, and tannins was found following HVCP (70 kV for 4 min) treatment compared to thermal treatment. The °Brix, pH, and acidity remained unchanged irrespective of treatments. These findings suggest that HVCP treatment at 70 kV for 4 min may be a good alternative to thermal treatment, and it may successfully be applied in carrot juice production, resulting in reduced enzymes, lower microbial activity, and improved bioactive compounds. The prospects of overcoming the existing conventional physical and chemical methods for sterilization make it a novel and more economical technique to maintain food's natural nourishment, composition, appearance, structure, and freshness.

Influence of Combined Effect of Ultra-Sonication and High-Voltage Cold Plasma Treatment on Quality Parameters of Carrot Juice

Influence of the combined effect of ultra-sonication (US) and high-voltage cold plasma treatment (HVCP) on the quality parameters of fresh carrot juice has been studied. During the treatment of ultra-sonication, carrot juice was subjected to a 0.5 inch probe for 3 min by adjusting the pulse duration 5 s on and off at 20 kHz frequency, amplitude level 80%. The ultrasound intensity was measured by using a thermocouple and was 46 Wcm⁻². The temperature was maintained at 10 °C by an automatic control unit. During the treatment of HVCP, carrot juice was then subjected to dielectric barrier discharge (DBD) plasma discharge at 70 kV voltage for 4 min. Significant increases were observed when HVCP treated carrot juice was tested against total carotenoids, lycopene, and lutein when compared to the control treatments. Moreover, this increase was raised to its highest in all pigments, chlorogenic acid, sugar contents, and mineral profile, as the results of ultra-sonication when combined with high voltage atmospheric cold plasma (US-HVCP). Whereas, a significant decreased was observed in Mg, total plate count, yeast, and mold after US-HVCP treatment. Furthermore, results indicated that the combined effect of US-HVCP treatment has improved the quality and led to a higher concentration of lycopene, lutein, chlorogenic acid, and mineral compounds (Na, K, and P). Therefore, the findings of the current study suggested that US-HVCP treatment is a novel combined technique that could provide better quality and more stability during the processing of carrot juice with better physicochemical properties and bio-available nutrients, so this novel processing technique could serve as an alternative to traditional processes.

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

The impact of cold atmospheric pressure plasma treatment on the inactivation kinetics of Bacillus cereus ATCC 14579 and the resulting quality changes was investigated in tiger nut (Cyperus esculentus L.) milk (TNM). The effect of input power (39, 43, and 46 W) and treatment time (0 to 270 s) was fitted using the Weibull model to represent the microbial kinetic inactivation in the treated TNM. Inactivation efficacy increased with an increase in treatment time and input power. A 5.28-log reduction was achieved at 39 to 46 W without significant changes in titratable acidity, whereas no reduction in titratable acidity was observed in the pasteurized sample. The inactivation kinetics was adequately described by the Weibull model. Higher input power of 43 and 46 W and 120 s of treatment resulted in marked decreases in pH, flavonoid concentration, and antioxidant activity compared with those parameters in pasteurized TNM. Increases in total color difference and phenolic concentrations also were observed. The results indicate that these changes were caused by the immanent plasma reactive species. This study provides valuable inactivation kinetics information for food safety assessment studies of B. cereus vegetative cells in TNM.

Effect of Plasma-Activated Water on the Microbial Decontamination and Food Quality of Thin Sheets of Bean Curd

Thin sheets of bean curd may serve as an excellent source of nutrition for microorganisms and are therefore prone to contamination, which can be harmful to public health. This study evaluated the influence of plasma-activated water (PAW) on the microbial load and food quality of thin sheets of bean curd. Treatment for 30 min with PAW that was activated for 90 s reduced the microbial count by 1.26 and 0.91 log10 CFU/g for total aerobic bacteria and total yeasts and molds on thin sheets of bean curd, respectively. The effect of PAW on microbial inactivation strongly depended on the activation time for PAW generation and the soaking time of the thin sheets of bean curd in PAW. Further, PAW could maintain total isoflavone content, sensory properties, and most of the textural properties of the thin sheets of bean curd. Although PAW treatments caused significant changes in color parameters of the thin sheets of bean curd, the appearance acceptance was not significantly influenced. This work highlights the potential application of PAW in the microbial decontamination of thin sheets of bean curd.

Effect of cold plasma on polyphenol oxidase inactivation in cloudy apple juice and on the quality parameters of the juice during storage

Direct cold plasma treatment has been investigated as an alternative non-thermal technology as a means of maintaining and improving quality of fresh cloudy apple juice. Process variables studied included type of plasma discharge, input voltage and treatment time on polyphenol oxidase (PPO) inactivation. Spark discharge plasma at 10.5 kV for 5 min was the best treatment, with near total inactivation of PPO achieved, although good PPO inactivation was also recorded using shorter treatment times. Residual activity (RA) of PPO was 16 and 27.6% after 5 and 4 min of treatment respectively. This PPO inactivation was maintained throughout the storage trials, but decreased with samples treated for a shorter time. Plasma treatment improved key quality parameters of Golden delicious cloudy apple juice, with retention of critical quality parameters during extended storage trials. Color was the most noticeable change, which was enhanced with retention of a greener color. An increase of 69 and 64% was obtained in the total phenolic content after 4 and 5 min of treatment, respectively. Therefore, cold plasma was demonstrated to be a good alternative to traditional heat treatments for enhanced quality retention of fresh cloudy apple juice and over its storage.

Cold Plasma for Effective Fungal and Mycotoxin Control in Foods: Mechanisms, Inactivation Effects, and Applications

Cold plasma treatment is a promising intervention in food processing to boost product safety and extend the shelf-life. The activated chemical species of cold plasma can act rapidly against micro-organisms at ambient temperatures without leaving any known chemical residues. This review presents an overview of the action of cold plasma against molds and mycotoxins, the underlying mechanisms, and applications for ensuring food safety and quality. The cold plasma species act on multiple sites of a fungal cell resulting in loss of function and structure, and ultimately cell death. Likewise, the species cause chemical breakdown of mycotoxins through various pathways resulting in degradation products that are known to be less toxic. We argue that the preliminary reports from cold plasma research point at good potential of plasma for shelf-life extension and quality retention of foods. Some of the notable food sectors which could benefit from antimycotic and antimycotoxin efficacy of cold plasma include, the fresh produce, food grains, nuts, spices, herbs, dried meat and fish industries.

Zygosaccharomyces rouxii: Control Strategies and Applications in Food and Winemaking

The genus Zygosaccharomyces is generally associated to wine spoilage in the winemaking industry, since a contamination with strains of this species may produce re-fermentation and CO2 production in sweet wines. At the same time, this capacity might be useful for sparkling wines production, since this species may grow under restrictive conditions, such as high ethanol, low oxygen, and harsh osmotic conditions. The spoilage activity of this genus is also found in fruit juices, soft drinks, salad dressings, and other food products, producing besides package expansion due to gas production, non-desired compounds such as ethanol and esters. Despite these drawbacks, Zygosaccharomyces spp. produces high ethanol and acetoin content in wines and may play an important role as non-Saccharomyces yeasts in differentiated wine products. Control strategies, such as the use of antimicrobial peptides like Lactoferricin B (Lfcin B), the use of dimethyl dicarbonate (DMDC) or non-thermal sterilization techniques may control this spoilage genus in the food industry.