Combination of polyhexamethylene guanidine hydrochloride and potassium peroxymonosulfate to disinfect ready-to-eat lettuce

Development of antifouling antibacterial polylactic acid (PLA) -based packaging and application for chicken meat preservation

Microbial contamination is the leading cause of food spoilage and food-borne disease. Here, we developed a multifunctional surface based on polylactic acid (PLA) bioplastic with antifouling and antibacterial properties via a facile dual-coating approach. The surface was designed with hierarchical micro/nano-scale roughness and low surface energy. Bactericidal agent polyhexamethylene guanidine hydrochloride (PHMG) was incorporated to endow the film with bactericidal activity. The film had good superhydrophobic, antifouling and antibacterial performance, with a water contact angle of 154.3°, antibacterial efficiency against E. coli and S. aureus of 99.9 % and 99.6 %, respectively, and biofilm inhibition against E. coli and S. aureus of 63.5 % and 68.9 %, respectively. Synergistic effects of antibacterial adhesion and contact killing of bacteria contributed to the significant antibacterial performance of the film. The biobased biodegradable film was highly effective in preventing microbial growth when applied as antibacterial food packaging for poultry product, extending the shelf life of fresh chicken breast up to eight days.

The Use of Ultraviolet Irradiation to Improve the Efficacy of Acids That Are Generally Recognized as Safe for Disinfecting Fresh Produce in the Ready-to-Eat Stage

Fresh-cut produce is usually produced under standardized disinfection processes, which are unavailable at the ready-to-eat stage. Currently, chemical sanitizers are used for washing, but their disinfection efficacy is limited. In this study, UV-C (1.03 kJ/m2) was combined with organic acids that are generally recognized as safe (GRAS), including citric, malic, acetic, and lactic acids (LAs), to wash lettuce and cherry tomatoes that are contaminated with Escherichia coli O157:H7 and Salmonella Typhimurium. The results showed that LA was the most effective treatment among the single treatments, with a pathogen reduction and cross-contamination incidence of 2.0-2.3 log CFU/g and 28-35%, respectively. After combining with UV-C, the disinfection efficacy and cross-contamination prevention capacity of the four GRAS acids significantly improved. Among the combination treatments, the highest pathogen reduction (2.5-2.7 log CFU/g) and the lowest cross-contamination incidence (11-15%) were achieved by LA-UV. The analyses of ascorbic acid, chlorophyll, lycopene, antioxidant capacity, and ΔE indicated that neither the single nor combination treatments negatively affected the quality properties. These results provide a potential hurdle technology for fresh produce safety improvement at the ready-to-eat stage.

A facile strategy to fabricate antibacterial hydrophobic, high-barrier, cellulose papersheets for food packaging

As a traditionally used packaging material, natural cellulose-based paper has poor barrier properties to water and oxygen, which severely limits its wide application in food packaging. In this study, we report a new sustainable approach to producing hydrophobic, high-barrier, and antibacterial packaging materials from cellulose paper. In this process, commercially available microcrystalline cellulose was first modified by long-chain stearic acid to form hydrophobic microcrystalline cellulose ester and then mixed with stearic acid as filler in the subsequent surface coating of bagasse fibre paper. The microcrystalline cellulose ester/stearic acid-coated paper (MSP) exhibited good water repellency and oxygen barrier activity due to a continuous hydrophobic film that formed, which completely covered the pores of the original bagasse fibre paper. The coated MSP sample also showed excellent dimensional stability in water and a good wet tensile strength of 16 MPa. In addition, poly(hexamethylene guanidine) (PHMG) was chemically grafted onto the free carboxyl groups of the MSP surface layer, and the resulting MSP-g-PHMG samples exhibited excellent antibacterial activity against Escherichia coli and Listeria monocytogenes. The biodegradable cellulose-based MSP-g-PHMG sample significantly delayed the decay of raspberry during storage, indicating its potential application in food packaging.

Combination of ultrasound-peracetic acid washing and ultrasound-assisted aerosolized ascorbic acid: A novel rinsing-free disinfection method that improves the antibacterial and antioxidant activities in cherry tomato

Traditional ultrasound (US)-assisted disinfection is only effective during washing. Coating is an effective method to control microbial growth after washing; however, cross-contamination can occur during immersion in the coating aqueous solution. Tap water (TW) rinsing is generally used to remove sanitizer residues after US-assisted washing; however, the Food and Drug Administration stated that rinsing is unnecessary when the peracetic acid (PAA) concentration does not exceed 80 ppm. In this study, we proposed a novel US-assisted hurdle technology of 80 ppm PAA combined with low-frequency US (25 kHz) during washing, followed by US-assisted aerosolization processing (nonimmersion coating). Ascorbic acid (AA), a safe and low-cost agent, was selected as the aerosolization solution. Cherry tomatoes were selected as the model, and the proposed method was compared with traditional US-assisted disinfection methods (US-10 ppm free chlorine washing + TW rinsing and US-5 ppm chlorine dioxide washing + TW rinsing) to analyze the disinfection efficacy and quality changes. During storage, US-PAA + 1%AA facilitated additional 0.7-0.9, 0.6-0.8, 0.7-1.0, and 0.5-1.0 log CFU/g reductions in the counts of Escherichia coli O157:H7, Salmonella Typhimurium, aerobic mesophilic counts, and molds and yeasts, respectively, as compared with traditional US-assisted methods. Sensory properties, color index, total soluble solids, titratable acidity, and weight loss were not negatively affected by any of the treatments. Firmness was slightly reduced after all treatments; however, the firmness of the samples was maintained during storage, in contrast with the decreased firmness observed in the control. Phenolic content and antioxidant activity significantly increased after all treatments. Further analysis of two key enzymes (phenylalanine ammonia-lyase and 4-coumarate-CoA ligase) involved in phenolic synthesis showed that their levels significantly increased following all treatments, leading to an increase in phenolic content and antioxidant activity. This result also indicated that US-assisted washing could act as an abiotic elicitor to increase nutritional content. Overall, US-PAA + 1%AA treatment served as an effective method for disinfecting produce during washing and for controlling microbial growth after washing without prolonging the processing time, which is an advantage over traditional US-assisted washing.

Use of aqueous ozone rinsing to improve the disinfection efficacy and shorten the processing time of ultrasound-assisted washing of fresh produce

In minimal processing industry, chlorine is widely used in the disinfection process and ultrasound (US) increases the disinfection efficacy of chlorine and reduces the cross-contamination incidence during washing. Tap water (TW), which has no disinfection effect, is generally used to rinse off sanitizer residues on the surface of disinfected fresh-cut vegetables. In this study, aqueous ozone (AO), a low-cost and residue-free sanitizer, was used to replace TW rinsing in combination with US (28 kHz)-chlorine (free chlorine [FC] at 10 ppm, a concentration recommended for industrial use) for the disinfection of fresh-cut lettuce as a model. US-chlorine (40 s) + 2.0 ppm AO (60 s) treatment resulted in browning spots on lettuce surface at the end of storage. In contrast, US-chlorine (40 s) + 1.0 ppm AO (60 s) did not lead to deterioration of the sensory quality (sensory crispness, color, and flavor) and a change in total color difference, and the activities of browning-related enzymes were significantly lower. Moreover, US-chlorine (40 s) + 1.0 ppm of AO (60 s) treatment led to significantly lower counts of Escherichia coli O157:H7, Salmonella Typhimurium, aerobic mesophilic (AMC), and molds and yeasts (M&Y) on days 0-7 than US-chlorine (60 s) + TW (60 s) and single 1.0 ppm AO (120 s) treatments, suggesting that AO provided an additional disinfection effect over TW, while reducing the overall processing time by 20 s. Cell membrane permeability analysis (alkaline phosphatase, protein, nucleotide, and adenosine triphosphate leakage) showed that the combination with 1.0 ppm AO caused more severe cell membrane damage in E. coli O157:H7 and S. Typhimurium, explaining the higher disinfection efficacy. 16S rRNA sequencing revealed that following US-chlorine (40 s) + 1.0 ppm of AO (60 s) treatment, Massilia and Acinetobacter had higher relative abundances (RAs) on day 7 than after US-chlorine (60 s) + TW (60 s) treatment, whereas the RAs of Escherichia-Shigella was significantly lower, indicating that the former treatment has a superior capacity in maintaining a stable microbial composition. This explains from an ecological point of view why US-chlorine (40 s) + 1.0 ppm of AO (60 s) led to the lowest AMC and M&Y counts during storage. The study results provide evidence that AO has potential as an alternative to TW rinsing to increase the disinfection efficacy of US-chlorine.

Effects of ultrasound-assisted low-concentration chlorine washing on ready-to-eat winter jujube (Zizyphus jujuba Mill. cv. Dongzao): Cross-contamination prevention, decontamination efficacy, and fruit quality

Wash water is circulated for use in the minimal processing industry, and inefficient disinfection methods can lead to pathogen cross-contamination. Moreover, few disinfection strategies are available for ready-to-eat fruits that do not need to be cut. In this study, the use of chlorine and ultrasound, two low-cost disinfection methods, were evaluated to disinfect winter jujube, a delicious, nutritious, and widely sold fruit in China. Ultrasound treatment (28 kHz) alone could not decrease the cross-contamination incidence of Escherichia coli O157:H7, non-O157 E. coli, and Salmonella Typhimurium, and free chlorine treatment at 10 ppm decreased the incidence from 55.00% to 5.00% for E. coli O157:H7, 65.00% to 6.67% for non-157 E. coli, and 70.00% to 6.67% for S. Typhimurium. The cross-contamination incidence was completely reduced (pathogens were not detected in sample) when the treatments were combined. The counts of aerobic mesophiles, aerobic psychrophiles, molds, yeasts, and three pathogens in the group subjected to combination treatment (28 kHz ultrasound + 10 ppm free chlorine) were significantly lower than those in the control, chlorine-treated, and ultrasound-treated groups during storage (0-7 d at 4 °C). Analysis of weight loss, sensory quality (crispness, color, and flavor), instrument color (a*/b*), soluble matter contents (total soluble solids, reducing sugar, total soluble sugar, and titratable acid), and nutritional properties (ascorbic acid and polyphenolic contents) indicated that treatment with ultrasound, chlorine, and their combination did not lead to additional quality loss compared with properties of the control. Additionally, the activities of phenylalanine ammonia-lyase and polyphenol oxidase were not significantly increased in the treatment group, consistent with the quality analysis results. These findings provide insights into disinfection of uncut ready-to-eat fruits using a minimum dose of disinfectant for cross-contamination prevention under ultrasonication. The use of ultrasound alone to decontaminate fresh produce is accompanied by a high risk of pathogen contamination, and the use of sanitizers to decrease cross-contamination incidence is recommended.

Use of Acetic Acid to Partially Replace Lactic Acid for Decontamination against Escherichia coli O157:H7 in Fresh Produce and Mechanism of Action

Escherichia coli O157:H7 is frequently detected in ready-to-eat produce and causes serious food-borne diseases. The decontamination efficacy of lactic acid (LA) is clearly established. In this study, LA was mixed with acetic acid (AA) to reduce costs while achieving consistent or better inhibitory effects. Time-kill curves and inoculation experiments using fresh-cut spinach and arugula indicated that 0.8%LA+0.2%AA shows similar antibacterial effects to those of 1%LA. To determine whether 1%LA and 0.8%LA+0.2%AA exert antibacterial effects by similar mechanisms, proteomics analysis was used. The proteins related to macromolecule localization, cellular localization, and protein unfolding were uniquely altered after the treatment with 1%LA, and the proteins related to taxis, response to stress, catabolic process, and the regulation of molecular function were uniquely altered after the treatment with 0.8%LA+0.2%AA. Based on these findings, combined with the results of a network clustering analysis, we speculate that cell membrane damage is greater in response to LA than to 0.8%LA+0.2%AA. This prediction was supported by cell membrane permeability experiments (analyses of protein, nucleotide, ATP, and alkaline phosphatase leakage), which showed that LA causes greater membrane damage than 0.8%LA+0.2%AA. These results provide a theoretical basis for the application of an acid mixture to replace LA for produce decontamination.

Combination of ozone and ultrasonic-assisted aerosolization sanitizer as a sanitizing process to disinfect fresh-cut lettuce

Reduction of sanitizer dosage and development of non-immersion disinfection methods have become major focuses of research. Here, we examined the disinfection efficacy of combining gaseous ozone (4 and 8 ppm) with aerosolized oxidizing sanitizer [sodium hypochlorite (SH, 100 and 200 ppm)] and aerosolized organic acid [acetic acid (AA, 1% and 2%) and lactic acid (LA, 1% and 2%)]. Notably, 1% AA and 4 ppm gaseous ozone were ineffective for disinfecting Salmonella Typhimurium, and treatment with 1% AA + 8 ppm ozone caused browning of lettuce leaves and stimulated increases in aerobic mesophilic count (AMC), aerobic psychrotrophic count (APC), S. Typhimurium, and Escherichia coli O157:H7. Treatment with 2% LA + 8 ppm ozone resulted in the lowest S. Typhimurium, E. coli O157:H7, Listeria monocytogenes, AMC, APC, and molds and yeasts during storage (0-7 days at 4 °C). Quality analysis indicates that LA + 8 ppm ozone and SH + 8 ppm ozone did not negatively affect L*, a*, b*, polyphenolic content, weight loss, and sensory properties; however, the levels of two individual phenolic compounds (3,4-dihydroxybenzoic acid and vanillin), responsible for phenylpropanoid synthesis, were significantly increased after treatment with 2% LA + 8 ppm ozone. These findings provided insights into the use of LA combined with gaseous ozone for application in disinfecting fresh produce.