Evaluation of the metabolic response of Escherichia coli to electrolysed water by 1 H NMR spectroscopy

The Effect of Coating Incorporated with Black Pepper Essential Oil on the Taste Quality of Jinhua Ham After Storage for Four Months

In this study, ¹ H NMR and multivariate data analysis were used to investigate the effect of coating incorporated with black pepper essential oil (CIBPEO) on the taste of Jinhua ham after 4 months of storage; four treatments of control check (CK), base formula coating (BC), BC + 0.05% BPEO, and BC + 0.1% BPEO were used for the coating of hams. Results showed that the metabonome was dominated by 23 metabolites, including amino acids, sugar, organic acids, alkaloids, nucleic aides and their derivatives, and others. BPEO decreased the intensity of sourness, sweetness, bitterness, aftertaste, and the relative nonvolatile taste metabolites compared to CK and BC; the decrease of intensity was not dependent on the BPEO contents. These findings demonstrated that CIBPEO could give a new taste balance to Jinhua ham and be beneficial to a group of people with a particular sensory preference, who are sensitive to undesirable sourness and bitterness, and prefer a light overall taste. PRACTICAL APPLICATION: The coating incorporated with black pepper essential oil during storage could give a new taste balance to Jinhua ham and be beneficial to a group of people with a particular sensory preference, who are sensitive to undesirable sourness and bitterness, and prefer a light overall taste.

Culture fermentation of Lactobacillus in traditional pickled gherkins: Microbial development, chemical, biogenic amine and metabolite analysis

Fermented cucumber pickles are the lactic acid fermentation products formed through the influence of microorganisms present in the environment. This study investigated the impacts of starter cultures, namely, Lactobacillus plantarum, Lactobacillus pentosus and Lactobacillus paraplantarum, typically utilized for the fermentation of traditional pickled gherkins, on fermentation process. The chemical (pH, total acidity and salt) and microbiological (total mesophilic aerobic bacteria, lactic acid bacteria and yeast-mould) changes were observed against the control sample during fermentation process. Moreover, the amounts of biogenic amines (BAs) and metabolites formed as a consequence of fermentation were determined using HPLC. It was found that the chemical analyses provided similar results for all the samples. The amount of total mesophilic aerobic bacteria and yeast-mould colonies in pickle sample containing L. plantarum 49 strain appeared to reduce significantly. The amount of BAs was the lowest for the pickle samples where L. plantarum strains were added. The amount of BAs was below the toxic value that could affect human health. More BAs were synthesized as the fermentation period increased. Lactate was seen to exist in the samples when pyruvate was present, and acetoin was converted into 2.3-butanediol during the fermentation period. It was concluded that the pickle sample for which L. plantarum 49 strain was used displayed a better fermentation profile (i.e., metabolite and biogenic amines) than the remaining samples. Producing a more delicious and reliable product using such characteristics of L. plantarum strains in pickled gherkins is believed to significantly contribute to the food industry.

Emerging chemical and physical disinfection technologies of fruits and vegetables: a comprehensive review

With a growing demand for safe, nutritious, and fresh-like produce, a number of disinfection technologies have been developed. This review comprehensively examines the working principles and applications of several emerging disinfection technologies. The chemical treatments, including chlorine dioxide, ozone, electrolyzed water, essential oils, high-pressure carbon dioxide, and organic acids, have been improved as alternatives to traditional disinfection methods to meet current safety standards. Non-thermal physical treatments, such as UV-light, pulsed light, ionizing radiation, high hydrostatic pressure, cold plasma, and high-intensity ultrasound, have shown significant advantages in improving microbial safety and maintaining the desirable quality of produce. However, using these disinfection technologies alone may not meet the requirement of food safety and high product quality. Several hurdle technologies have been developed, which achieved synergistic effects to maximize lethality against microorganisms and minimize deterioration of produce quality. The review also identifies further research opportunities for the cost-effective commercialization of these technologies.

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.

The Antifungal Potential of Carvacrol against Penicillium Digitatum through 1H-NMR Based Metabolomics Approach

Carvacrol (5-Isopropyl-2-methylphenol), a volatile oil constituent, mainly exists in Labiaceae family plants. Carvacrol has long been studied for its natural antifungal potential and food preservative potential. However, its exact mode of action, especially against Penicillium digitatum (P. digitatum), remains unexplored. Herein, a 1H-NMR-based metabolomic technique was used to investigate the antifungal mechanism of carvacrol against P. digitatum. The metabolomic profiling data showed that alanine, aspartate, glutamate, and glutathione metabolism were imbalanced in the fungal hyphae. A strong positive correlation was seen between aspartate, glutamate, alanine, and glutamine, with a negative correlation among glutathione and lactate. These metabolic changes revealed that carvacrol-induced oxidative stress had disturbed the energy production and amino acid metabolism of P. digitatum. The current study will improve the understanding of the metabolic changes posed by plant-based fungicides in order to control citrus fruit green mold caused by P. digitatum. Moreover, the study will provide a certain experimental and theoretical basis for the development of novel citrus fruit preservatives.

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.

1H NMR-based metabolic characterization of Chinese Wuding chicken meat

The aim of this study was to evaluate the chemical composition of precursor flavor substance of Wuding chicken with the age of 110, 140, 170, 200 and 230 days. The metabolic composition of chicken meat was studied using ¹H nuclear magnetic resonance (NMR) spectroscopy. Compared with 110 days, the total metabolite content was significantly higher in other four periods for the chicken breast and leg meat (P < 0.01). Organic acid and small peptides were the two most metabolites for the chicken breast and leg meat. Comprehensive multivariate data analysis showed significant differences about precursor substance between the chicken samples of 230 days and other four ages including lactate, creatine, IMP, glucose, carnosine, anserine, taurine and glutamine (P < 0.05). These results contribute to a further understanding of changes in chicken meat metabolism as chicken ages, which could be used to help assess the quality of chicken meat.

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.

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.

The Efficacy of an Electrolysed Water Formulation on Biofilms

Electrolysed water is a basic process whereby an electric current is passed through deionised water containing a low concentration of sodium chloride in an electrolysis chamber, which results in a more complex chemistry resulting in the production of a strong bactericidal and fungicidal solution at the anode. This microbicidal solution contains hypochlorous acid that is fast-acting and environmentally safe, as upon bacterial killing, the equilibrium shifts from hypochlorous acid back to salt and water. Other antimicrobial agents produced in this process include sodium hypochlorite and chlorine. The use of electrolysed water formulations in wound care to control wound bioburden is underway. However, there is limited evidence of the efficacy of electrolysed water on the control of biofilms, which are renowned for their tolerance to a variety of antimicrobials. Therefore this study aimed to assess a new electrolysed water formulation on in vitro Staphylococcus aureus and Pseudomonas aeruginosa biofilms. Results showed that the electrolysed water formulation effectively reduced biofilm in all models following a 15 min contact time. Microbial cell counts confirmed the reduction biofilm bacteria. Additional cytotoxicity using L929 fibroblasts confirmed that a 50% and 25% dilution of the electrolysed water formulation was non-cytotoxic to cells. In conclusion, this study has confirmed that the application of a new electrolysed water product effectively removed biofilm after a short exposure time. The use of this technology as a wound cleanser may help to control existing biofilms in complicated, non-healing wounds.

Effect of high-pressure treatment on taste and metabolite profiles of ducks with two different vinasse-curing processes

The effect of high-pressure (HP) (0.1, 150 and 300MPa, 15min) on taste profiles of vinasse-cured ducks was investigated; the metabolite profiles were determined using ¹H NMR. HP at 150MPa increased the taste intensity of products compared with the controls, while HP at 300MPa did not further improve their taste compared with 150MPa treated samples. The metabonome of vinasse-cured ducks was dominated by 27 metabolites. HP increased amino acids, glucose, alkaloids and organic acids, but decreased inosine monophosphate and its derivatives, compared with the controls. The increments of metabolites in vinasse-dry-cured duck were higher than those in vinasse-wet-cured duck. The change of metabolites could be related to the enzyme activity, the degradations of proteins, sugars and nucleotides, and the permeation from vinasse-curing agents to duck meat. These findings suggest that 150MPa treatment was effective to improve the taste of vinasse-cured duck.

Effect of high pressure treatment on metabolite profile of marinated meat in soy sauce

Marinated meat in soy sauce was produced using hind leg by washing, rubbing salt, marinating with soy sauce and spices, and air dry-ripening for 15d. The effect of high pressure (HP) (150 and 300MPa for 15min) on the metabolite profiles of products was characterized using ¹H NMR and multivariate data analysis. The results showed that the metabonome was dominated by 26 metabolites, including amino acids, sugars, organic acids, nucleic aides and their derivatives. PC1 and PC2 explained a total of 75.4 and 11.9% of variables, respectively. HP treatments increased most of the metabolites, especially PC1, glutamate, sugars, nucleotides, anserine, lactate and creatine compared to the control. The increase of metabolites under HP was not dependent on pressure level except for alanine, lactate, acetate, formate, fumarate, glucose and 5'-IMP. These findings demonstrated that HP treatment at 150MPa was economical to improve the taste of marinated meat in soy sauce.