Effects of potential organic compatible sanitisers on organic and conventional fresh-cut lettuce ( Lactuca sativa Var. Crispa L)

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 multi-omics analysis strategy reveals the molecular mechanism of the inhibition of Escherichia coli O157:H7 by anthocyanins from Aronia melanocarpa and its application

Water pollution causes the propagation of pathogenic microorganisms, which poses a serious threat to human life. Escherichia coli O157:H7, as a representative organism that can directly exhibit molecular response to stress, was selected as the indicator bacteria for the study. Tandem mass tag (TMT) quantitative proteomics and non-targeted metabolomics were used to study the response of Escherichia coli O157:H7 to Aronia melanocarpa anthocyanin (AMA) treatment. The results showed that 628 proteins and 1338 metabolites changed significantly after treatment with AMAs. According to bioinformatics analysis, integrated proteomics and metabolomics analysis differentially expressed proteins (DEPs) and metabolites participate in pyruvate metabolism, glycolysis/gluconeogenesis, alanine, aspartate and glutamate metabolism and the pentose phosphate pathway. This study preliminarily proposed the inhibition mechanism of AMAs on Escherichia coli O157:H7 from the perspective of multi-omics, providing a theoretical basis for the application of natural preservatives in fresh cut vegetables.

Effects of chlorine and peroxyacetic acid wash treatments on growth kinetics of Salmonella in fresh-cut lettuce

Fresh-cut produces are often consumed uncooked, thus proper sanitation is essential for preventing cross contamination. The reduction and subsequent growth of Salmonella enterica sv Thompson were studied in pre-cut iceberg lettuce washed with simulated wash water (SWW), sodium hypochlorite (SH, free chlorine 25 mg/L), and peroxyacetic acid (PAA, 80 mg/L) and stored for 9 days under modified atmosphere at 9, 13, and 18 °C. Differences in reduction between SH and PAA were non-existent. Overall, visual quality, dehydration, leaf edge and superficial browning and aroma during storage at 9 °C were similar among treatments, but negative effects increased with temperature. These results demonstrated that PAA can be used as an effective alternative to chlorine for the disinfection of Salmonella spp. in fresh-cut lettuce. The growth of Salmonella enterica sv Thompson was successfully described with the Baranyi and Roberts growth model in the studied storage temperature range, and after treatment with SWW, chlorine, and PAA. Subsequently, predictive secondary models were used to describe the relationship between growth rates and temperature based on the models' family described by Bělehrádek. Interestingly, the exposure to disinfectants biased growth kinetics of Salmonella during storage. Below 12 °C, growth rates in lettuce treated with disinfectant (0.010-0.011 log CFU/h at 9 °C) were lower than those in lettuce washed with water (0.016 log CFU/h at 9 °C); whereas at higher temperatures, the effect was the opposite. Thus, in this case, the growth rate values registered at 18 °C for lettuce treated with disinfectant were 0.048-0.054 log CFU/h compared to a value of 0.038 log CFU/h for lettuce treated with only water. The data and models developed in this study will be crucial to describing the wash-related dynamics of Salmonella in a risk assessment framework applied to fresh-cut produce, providing more complete and accurate risk estimates.

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.

The quality and antioxidant elucidation of germinated flaxseed treated with acidic electrolyzed water

The endogenous fortification of antioxidant lipid concomitants in flaxseed was imperative to improve the oxidative stability of α-linolenic acid (ALA) in flaxseed and flaxseed oil upon processing, storage and gastrointestinal digestion. The comparative effects of acidic electrolyzed water (ACEW) and tap water (TW) on the triglyceride configuration, typical lipid concomitants, and antioxidant properties of flaxseed were conducted during 0-5 days of germination. The results showed that ACEW enhanced the germination rate of flaxseed by 18.25% and simultaneously suppressed the dynamic depletion of ALA by 5.32% when compared with TW (p < .05). The total phenolic acids, lignans, and flavonoids were effectively accumulated in flaxseed following ACEW-mediated germination with the further increase by 4.82%, 15.48%, and 8.22% in comparison with those induced by TW (p < .05). The total contents of cyclolinopeptides in flaxseed progressively dropped following either ACEW or TW treatment, a slighter decrease by 5.59% for flaxseed treated by ACEW than that by TW. Notably, the maximum accumulation of tocopherols and phytosterols had been early obtained for flaxseed treated with ACEW for 2-3 days due to the de novo synthesis or intermolecular conformational transition (p < .05). Most importantly, ACEW-mediated germination led to higher increment of the thermal oxidative stability and antioxidant properties of flaxseed and flaxseed oil in comparison to TW. In brief, the initial oxidation temperature increased by 7.09% and 3.06% (p < .05), and the antioxidant activities as evaluated by DPPH, ABTS, and FRAP values raised by 3.86%-28.07% and 4.21%-9.18% (p < .05), respectively. These findings clarify that the germination especailly mediated by ACEW could be an effective method to further optimize the nutritional and functional properties of flaxseed through reconstructing the endogenous antioxidant system.

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.

Effect of ozone, lactic acid and combination treatments on the control of microbial and pesticide contaminants of fresh vegetables

BACKGROUND

Fruit and vegetable consumption has increased due to their tremendous health benefits. However, recent studies have shown that contaminated products may serve as vehicles for foodborne pathogens and harmful chemicals. Therefore, fresh vegetables must be decontaminated before consumption to ensure food safety.

RESULTS

In this study, the combined decontamination treatment of lactic acid (2.5 mL L-1 ) and ozone (9 mg L-1 ) for 10 min showed better efficacy in the removal of contaminants from fresh vegetables as compared to individual treatments. The combined treatment resulted in a reduction of 1.5-3.5 log CFU of native mesophilic bacteria per gram and 1.6-2.9 log CFU of artificially inoculated Escherichia coli per gram from tomato, cucumber, carrot and lettuce. The combined treatment also removed spiked pesticides, which represent artificial chemical contamination (28-97% chlorpyrifos and 62-100% λ-cyhalothrin residues), from fresh vegetables. No significant difference (P > 0.05) in various sensory attributes of vegetables was observed between untreated and treated (lactic acid and ozone) vegetables.

CONCLUSIONS

The combination treatment provides a novel approach to target two groups of contaminants using a single procedure. The combination treatment can be used as an alternative to currently used decontamination techniques for the supply of safe vegetables to consumers. © 2020 Society of Chemical Industry.

Assessment of Possible Application of an Atmospheric Pressure Plasma Jet for Shelf Life Extension of Fresh-Cut Salad

Ready-to-eat salads are very perishable with quality losses within 6–7 days, and the extension of their shelf life is still a challenge. In this work, an atmospheric pressure plasma jet (APPJ) was applied for the surface decontamination of fresh-cut lettuce baby leaves. The APPJ antimicrobial efficiency on the natural microbiota and its impact on some physicochemical attributes of lettuce were evaluated as a function of the treatment duration (0–30 s). Then, the influence of plasma treatment on the salad shelf life was studied, following the growth of aerobic mesophilic bacteria in both untreated and plasma-treated samples during 9 days of storage at 4 °C, together with the plasma-induced changes in physicochemical parameters of lettuce leaves. The APPJ induced a fast (15 s) microbial decontamination (1.3 log₁₀ CFU/g) of the salad surface. Exposure time and salad-plasma plume distance were the parameters that substantially affected the microbial inactivation. APPJ treatment retarded bacterial growth during the refrigerated storage, as plasma-treated samples were noticeably less contaminated than the non-treated ones in the first 3–4 days. No significant effect were observed on electrolyte leakage, pH, and dry matter content in both the set up phase and the shelf life study.

Effect of peroxyacetic acid treatment and bruising on the bacterial community and shelf-life of baby spinach

The importance of leaf integrity, i.e. the effects of bruising (mechanical damage), and sanitisation with peroxyacetic acid (PAA) on bacterial communities of ready-to-eat baby spinach remains unclear. Two shelf-life studies were conducted at 4 °C to investigate the effect of bruising and sanitisation on the growth of spoilage microorganisms. In the first experiment, both bruising treatments (100% and 40% of leaves) halved shelf life to 12 d, whereas intact leaves had a shelf-life of 23 d. Bruising had no influence on bacterial diversity during shelf-life, though some differences in the relative abundance of minor genera were observed. Pseudomonas and Pantoea were the most dominant bacterial genera, regardless of bruising treatment. High throughput amplicon sequencing also identified other spoilage bacteria including Chryseobacterium, Stenotrophomonas, Bacillus, Sphingobacterium, Erwinia and Flavobacterium. In the second experiment, washing of intact baby spinach with a sanitiser (80 mg/L: PAA) reduced microbial load as determined by aerobic plate count but did not immediately affect the presence/relative abundance of most of the genera of spoilage bacteria observed. During shelf-life, the bacterial diversity of sanitised leaves was significantly lower than on water-washed leaves. Although sanitisation resulted in a higher initial log reduction in microbial load compared to control (portable tap water), sanitisation did not extend the shelf life of baby spinach (23 d). Sanitised spinach had reduced bacterial diversity however, by the end of shelf life, both sanitised and water-washed spinach was dominated by Pseudomonas and Pantoea spoilage bacteria. This study demonstrated for the first time that the shorter shelf life of bruised leaves was related to faster microbial growth rather than changes in bacterial diversity or community composition.

Atomic force microscopy in food preservation research: New insights to overcome spoilage issues

A higher level of food safety is required due to the fast-growing human population along with the increased awareness of healthy lifestyles. Currently, a large percentage of food is spoiled during storage and processing due to enzymes and microbial activity, causing huge economic losses to both producers and consumers. Atomic force microscopy (AFM), as a powerful scanning probe microscopy, has been successfully and widely used in food preservation research. This technique allows a non-invasive examination of food products, providing high-resolution images of surface structure and individual polymers as well as the physical properties and adhesion of single molecules. In this paper, detailed applications of AFM in food preservation are reviewed. AFM has been used to provide comprehensive information in food preservation by evaluating the spoilage with its related structure modification. By utilizing AFM imaging and force measurement function, the main mechanisms involved in the loss of food quality and preservation technologies development can be further elucidated. It is also capable of exploring the activities of enzymes and microbes in influencing the quality of food products during storage. AFM provides comprehensive solutions to overcome spoilage issues with its versatile functions and high-throughput outcomes. Further research and development of this novel technique in order to solve integrated problems in food preservation are necessary.

Effect of Basil Leaves and Wheat Bran Water Extracts on Antioxidant Capacity, Sensory Properties and Microbiological Quality of Shredded Iceberg Lettuce during Storage

The effect of basil leaf (BLE) and wheat bran (WBE) extracts (potent anti-browning agents), on the phenolic content, antioxidant potential, microbiological quality, and consumer quality of shredded lettuce during storage were studied. Treatment of lettuce with increasing concentrations of BLE proportionally increased the total phenolic content and antioxidant properties. Compared to the control, the treatment enhanced the antiradical properties. This was especially visible during the analysis of the chemical extracts, while this effect was not retained in the potentially bioaccessible fraction. In the lettuce stored for 8 days, the highest reducing potential and ability to quench radicals were observed in samples treated with 1% BLE-33 mg Trolox equivalent/g d.m. and 2.8 mg Trolox equivalent/g d.m., respectively. Compounds exhibiting antiradical properties were easily bioaccessible in vitro. There was no negative effect of the treatments on the consumer quality. Most importantly, after 8 days of storage, lettuce treated with the studied extract, except 10% WBE, had higher microbiological quality. After 8-day storage, the coliforms count was reduced by 84% and 88% in samples treated with 0.5% BLE and 10% WBE, respectively. In conclusion, treatments of shredded lettuce with BLE and WBE maintain or even improve its quality during storage.

Metabolic characterisation of eight Escherichia coli strains including "Big Six" and acidic responses of selected strains revealed by NMR spectroscopy

The metabolic diversity of Escherichia coli strains (non-pathogenic E. coli ATCC 25922, and pathogenic E. coli O157:H7, O26:H11, O45:H2, O103:H11, O111, O121:H19, and O145) was tested using nuclear magnetic resonance. Based on two representative two-dimensional ¹H-¹³C spectra, 38 metabolites were identified in E. coli intracellular samples. Principal component analysis indicated that metabolites including lysine, arginine, α-ketoglutaric acid, adenosine, and fumaric acid were responsible for the separation of E. coli ATCC 25922. Relatively large metabolic differences between ATCC 25922 and the pathogenic strains were recoded. The most varied pairwise group (ATCC 25922 vs. O26:H11) was further analysed. The screened metabolites and enrichment pathway tests revealed different amino acid metabolism and higher requirement for energy production in the pathogenic strains. The acidic responses of the selected strains were further tested. The in vitro and in vivo inactivation kinetics, morphological changes, and protein leakage showed higher acid tolerance of E. coli O26:H11. Metabolic analysis of the two strains under acidic stress revealed alternative metabolites and pathways in the two groups. Pathogenic O26:H11 was characterised by higher energy production and amino acid metabolism (lysine and glutamic acid). Real-time PCR tests confirmed that glutamic acid dependent decarboxylase/antiporter system was the major acid resistance mechanism.

Reduction of Escherichia coli O157:H7, Listeria monocytogenes, and Naturally Present Microbe Counts on Lettuce using an Acid Mixture of Acetic and Lactic Acid

Lactic acid (LA) and acetic acid (AA) are independently used to disinfect fresh leaf vegetables. LA has a higher efficacy but costs more than AA. Herein, we compared the disinfection efficacy of LA, AA, and their mixture on lettuce to determine whether the cheaper acid mixture shows similar or more efficacy than LA. Quality analysis indicated that the acid mixture and individual acids did not cause additional loss of instrument color and polyphenolic content compared with that of the control; however, visible defects were observed at AA concentrations exceeding 0.8%. Analysis of Escherichia coli O157:H7, Listeria monocytogenes, and naturally present microbes (aerobic mesophilic and psychrotrophic bacteria, coliforms, molds, and yeasts) showed that the acid mixture led to the highest reduction in microbial count during storage. 16S rRNA sequencing was further employed to understand the effects of the acid mixture and individual acids on lettuce microbial ecology. During storage, the acid mixture and individual acids significantly decreased the abundance of Massilia spp. and Alkanindiges spp. but there was a marked increase in Escherichia-Shigella abundance (LA: 0.003-58.82%; AA: 0.01-55.34%; acid mixture: undetected to 50.71%; control: 0.007-33.09%), indicating that acid disinfection altered the microbial ecology to stimulate Escherichia-Shigella growth. These results enhance our understanding of the relationship between lettuce disinfection and ecological changes.

Comparison of metabolic response between the planktonic and air-dried Escherichia coli to electrolysed water combined with ultrasound by 1H NMR spectroscopy

The antimicrobial effects of electrolysed water and ultrasound have been well reported; however, little attention was paid to their effects on the metabolite changes of bacteria in different states. In this study, the metabolomic variations of Escherichia coli ATCC 25922 in planktonic and adherent state (air-dried on stainless steel coupons) after the combination treatment of low-concentration acidic electrolysed water (AEW, free available chlorine (FAC): 4 mg/L) and ultrasound were characterised, by conducting multivariate data analysis based on nuclear magnetic resonance (NMR) spectroscopy. Overall, 43 metabolites were identified in two states of E. coli, including a wide range of amino acids, organic acids, nucleotides and their derivatives. The quantification of whole-cell metabolism in planktonic and air-dried cultures was quite different: air-dried E. coli exhibited more resistance to ultrasound and AEW treatments due to initiating a protective response against oxidative and acid stresses, which was not observed in planktonic E. coli, whose levels of all identified metabolites were decreased significantly after the combined treatment. Further pathway analysis revealed that alanine, aspartate and glutamate metabolism, glycolysis, pyruvate metabolism and tricarboxylic acid (TCA) cycle were changed significantly in planktonic culture, but to a less extent in air-dried culture, in which some shifts in glutamate decarboxylase (GAD) system and some shunts like mixed acid fermentation and pentose phosphate pathway were observed for maintaining metabolic balance. These findings suggest that NMR-based metabolomics strategy is promising in identifying different metabolic shifts in different states of bacteria. They also provide some guidance for food equipment sanitisation, especially for organic food processing.

UV-C irradiated gallic acid exhibits enhanced antimicrobial activity via generation of reactive oxidative species and quinone

A novel light-enhanced antimicrobial treatment was developed by exposing gallic acid (GA) to UV-C light. GA (15 mM) solution was exposed to UV-C for 30 min and subsequently incubated with E. coli O157:H7 for 30 min to achieve a 3.2 ± 0.2 log CFU/mL reduction. The antimicrobial activity is affected by the irradiation duration, wavelength, and pH of solution. The addition of benzenesulfinic acid (BSA) to UV-C irradiated GA lowered (P < 0.05) its antimicrobial activity, indicating that quinones contributed to its overall antimicrobial effect. In addition, the attenuated (P < 0.05) antimicrobial activity of UV-C exposed GA in the presence of reactive oxidative species (ROS) quenchers, the generation of hydrogen peroxide, and increased levels of intracellular oxidative stress detected in E. coli O157:H7 illustrated that ROS also played a role in the antimicrobial effect of UV-C irradiated GA. UV-C irradiated GA could be applied as a novel antimicrobial in food systems.

Metabolomic analysis of energy regulated germination and sprouting of organic mung bean (Vigna radiata) using NMR spectroscopy

Germination and sprouting are regulated by the energy status. In the present study, mung bean seeds were treated with adenosine triphosphate and 2,4-dinitrophenol (DNP). The metabolomic changes during development of mung beans under different energy statuses were investigated. In total, 42 metabolites were identified. Principal component analysis revealed that the featured compounds produced in seeds were oleic, linoleic, and succinic acids. Sugars, including maltose, sucrose, and glucose were related to sprouting. Mung bean seeds utilised diverse energy resources and produced higher succinic acid content. Sugars and secondary metabolites accumulated in sprouts. Nitrogen, sugar, and amino acid metabolism pathways contributed to this physiological process. DNP caused an energy deficit, which resulted in the consumption and translation of glucose. Higher contents of other saccharides and amino acids were observed. The transcriptional results further confirmed our metabolic hypothesis. In conclusion, sufficient energy supply is crucial for sprout development and nutritive metabolite synthesis.

Reduction of Escherichia coli O157:H7 and naturally present microbes on fresh-cut lettuce using lactic acid and aqueous ozone

Lactic acid (LA) is an effective sanitizer for disinfection of fresh produce. Tap water is generally used to wash disinfected fresh produce because sanitizer residues negatively affect the quality and organoleptic properties of the produce. However, tap water is ineffective for secondary disinfection compared with sanitizers. Thus, we propose a disinfection method using LA plus aqueous ozone (AO), an oxidizing sanitizer that does not lead to secondary residue. We compared the proposed method of 1% LA (90 s) plus 1 mg L⁻¹ AO (30 s) or 2 mg L⁻¹ AO (30 s) with the traditional method of 100 ppm chlorine (120 s) or 1% LA (120 s) plus tap water (30 s) and 2 mg L⁻¹ AO (150 s). Microbial analysis showed that LA plus AO led to the greatest reductions in microbes (Escherichia coli O157:H7, aerobic mesophilic counts, aerobic psychrophilic counts, moulds, and yeasts) during storage (0–5 days at 5 °C). Quality analysis (colour, sensory qualities, electrolyte leakage, polyphenolic content, and weight loss) showed that LA + AO did not cause additional quality loss compared with tap water treatment. These results indicate that the hurdle technology proposed (LA plus AO) has a good potential for use in fresh produce disinfection.

Lactic acid plus aqueous ozone is an effective hurdle technology for fresh produce disinfection.

Energy Regulated Nutritive and Antioxidant Properties during the Germination and Sprouting of Broccoli Sprouts ( Brassica oleracea var. italica)

The role of energy status in germination and sprouting of broccoli seeds was investigated by exogenous ATP and DNP treatments. With the synthesis of adenylates from 38.82 to 142.69 mg·100 g^-1 DW, the nutritive components (soluble sugar, proteins, pigments, and phenolics) and AAs were increased during germination and early sprouting (day 5). Elements of the BoSnRK2 pathway were down-regulated by more than 2 fold under the energy charge feedback inhibition. At the end of sprouting (day 7), energy depletion resulted in slowdown or reduced nutritional accumulation and antioxidant capacities. Exogenous ATP depressed the BoSnRK2 pathway by maintaining the energy status at high levels and further promoted the nutrition and antioxidant levels. It also prevented the energy depletion at day 7. On the contrary, DNP reduced the ATP contents (16.10-26.86%) and activated the BoSnRK2 pathway. It also notably suppressed the energy-consuming activities including germination, sprouts growth, and secondary metabolic synthesis.

Development of Portable Flow-Through Electrochemical Sanitizing Unit to Generate Near Neutral Electrolyzed Water

We developed a portable flow-through, electrochemical sanitizing unit to produce near neutral pH electrolyzed water (producing NEW). Two methods of redirecting cathode yields back to the anode chamber and redirecting anode yields the cathode chamber were used. The NEW yields were evaluated, including: free available chlorine (FAC), oxidation-reduction potential (ORP), and pH. The performances of 2 electrodes (RuO₂ -IrO₂ /TiO₂ and IrO₂ -Ta₂ O₅ /TiO₂ ) were investigated. The unit produced NEW at pH 6.46 to 7.17, an ORP of 805.5 to 895.8 mV, and FAC of 3.7 to 82.0 mg/L. The NEW produced by redirecting cathode yields had stronger bactericidal effects than the NEW produced by redirecting anode yields or NEW produced by mixing the commercial unit's anode and cathode product (P < 0.05). Electron spin resonance results showed hydroxyl free radicals and superoxide anion free radicals were present in the NEW produced by developed unit. The NEW generator is a promising sanitizing unit for consumers and the food industry to control foodborne pathogens.

PRACTICAL APPLICATION

Current commercial NEW-producing units are quite large and are not convenient for family using. The developed portable flow-through, NEW-producing unit has great potential in a wide range of applications, such as organic farm, households, and small food industries. The examined sanitizing treatments showed effective control of Escherichia coli O157:H7 and Listeria monocytogenes.

Combination of peracetic acid and ultrasound reduces Salmonella Typhimurium on fresh lettuce (Lactuca sativa L. var. crispa)

Salmonella outbreaks related to fruits and vegetables have been reported being lettuce one of the most contaminated. Peracetic acid (PA) at 50 mg/L, sodium dichloroisocyanurate (SD) at 100 mg/L, and the combination of SD at 100 mg/L and babaçu coconut (Attalea speciosa) oil detergent at 100 mg/L were applied to fresh lettuce. Natural contaminant microbiota, physicochemical characteristics, and sensory attributes were evaluated. PA and SD reduced mesophilic aerobic counts by 2.1 and 1.5 log cfu/g, respectively. The most efficient treatment in reducing natural microbiota (i.e., PA) was applied alone and in combination with ultrasound (US). It reduced Salmonella enterica Typhimurium counts to undetectable levels (< 1 log cfu/g). US further reduced S. Typhimurium counts by 0.6 log cfu/g in relation to PA, treatment which lessened the pH but increased the titratable acidity of lettuce, but did not cause total color difference. Therefore, the combination of PA and US holds a potential industrial application for sanitization purposes.

Metabolite profiling of Listeria innocua for unravelling the inactivation mechanism of electrolysed water by nuclear magnetic resonance spectroscopy

Bactericidal effects of low concentration electrolysed water (LcEW) on microorganisms are previously well reported; however, the inactivation mechanism of EW is not understood. The lethal and sublethal injuries of L. monocytogenes and L. innocua by EW treatments were determined and the metabolic profile changes for L. innocua were characterised using nuclear magnetic resonance (NMR). Microbial metabolomics approach combined with multivariate data analyses was used to interpret the cellular chemical fingerprints of L. innocua. The relative amount of intracellular reactive oxygen species (ROS) was assayed using 2',7-dichlorodihydrofluorescein diacetate (H₂DCFDA). The results showed that the proportion of the sublethally injured microbial cells L. monocytogenes and L. innocua increased from 40% to 70% and from 35% to 65%, respectively, when the free available chlorine (FAC) of LcEW increased from 2 to 8 mg/L. Overall, 36 low-molecular-weight metabolic compounds in L. innocua extracts were characterised by NMR spectroscopy. EW perturbation resulted in a drastic and multitude disruption across a wide range of biochemical process including peptidoglycan synthesis, nucleotides biosynthesis and amino acid metabolism. Elevated levels of α-ketoglutarate and succinate implicated the enhanced glutamate decarboxylase (GAD) system and γ-aminobutyric acid (GABA) shunt for the protection against oxidative stress. These findings provided the comprehensive insights into the metabolic response of Listeria to EW oxidative stress and can serve as a basis for better utilisation for sanitisation.

Effect of exogenous ATP on the postharvest properties and pectin degradation of mung bean sprouts (Vigna radiata)

The effects of exogenous ATP on the postharvest quality, browning and softening of mung bean (Vigna radiata) sprouts were evaluated. ATP treatment significantly alleviated the quality loss and browning events during the storage of 3 days. It also reduced the oxidant damage by inducing high activities of peroxidase (9.3-13.9%) and superoxide dismutase (8.8-10.3%) which scavenged the reactive oxygen species (ROS) effectively. Transcriptional results indicated that ATP treatment decreased VrPL1, VrPME and VrPG1 gene expression levels more than 2 folds at some time points. Furthermore, the atomic force microscope (AFM) images revealed that the pectin degradation was notably slowed by ATP treatment and the width and height of pectin backbone were better maintained (47.1% and 45.6% higher than control without ATP treatment). The cooperative effects of ROS scavenging and decreased expressions of pectin-related genes might contribute to the deferred pectin deterioration and firmness loss by ATP treatment.

Use of hydrogen peroxide, citric acid and sodium hypochlorite as sanitizer for minimally processed table grapes

The objective of this study was to explore two local table grape cultivars, one is white and the other one red colored, as a minimally processed produce, and to identify the most effective sanitizers (hydrogen peroxide, citric acid or sodium hypochlorite) to control microbial growth. The table grape cultivars indigenous to Elazig province of Turkey ‘Agin Beyazi’ and ‘Agin Kirmizisi’ were tested in the present experiment. Grape clusters were washed by dipping in tap water as control, in citric acid (20 g/L), with sodium hypochlorite (50 mg/L), or with hydrogen peroxide (20 g/L), solutions for 1 minute. Grape berries were then placed into PET clamshells and kept at 4 °C for 10 days. The berries were subject to quality assessments during the storage, and to total aerobic microbial and fungal count at the end. Washing with hydrogen peroxide- or sodium hypochlorite-diluted water was very effective controlling both aerobic microbial and fungal growth. Citric acid treatment however represented no significant effect on microbial growth. It is concluded that both hydrogen peroxide and sodium hypochlorite are strong sanitizers for table grapes tested, with no detection of undesirable effects.

Microbiological Quality of Organic and Conventional Leafy Vegetables

The aim of this study was to assess the microbiological profile of leafy vegetables from organic and conventional farming (n=70). The microbiological parameters analyzed consisted of aerobic mesophilic bacteria, yeasts and molds, coliforms at 30 and 45°C, and Salmonella ssp. A biochemical identification of the Enterobacteriaceae species was carried out. Some Enterobacteriaceae species were identified in the produce from both farming systems and Hafnia alvei was the most widespread specie observed. Salmonella spp. was not detected in the samples analyzed. The microbial counts for indicator microorganisms were, in general, higher for conventional leaves when compared to those produced by organic farming.