Nanoemulsified clove essential oils-based edible coating controls Pseudomonas spp.-causing spoilage of tilapia (Oreochromis niloticus) fillets: Working mechanism and bacteria metabolic responses.

Fish products suffer Pseudomonas-causing spoilage quickly during refrigeration storage, which could be solved by applying edible coating derived from nanoemulsified clove essential oils and fish gelatin (NCEO-FG). This study aimed to evaluate the effects and mechanism of NCEO-FG in preserving tilapia (Oreochromis niloticus) fillets that were inoculated with Pseudomonas spp. (Pseudomonas sp. strain ABa3, P. psychrophila strain ABe3, and P. fragi strain BBa3). NCEO caused remarkable leakage of proteins (198.5-252.8 µg/L) and nucleic acids (0.30-0.34 of OD260). After being incorporated into FG, NCEO-FG effectively delayed the deterioration of tilapia fillets because it significantly reduced the surviving bacteria populations (0.78 - 1.80 log CFU/g reductions) and inhibited the proteolysis and oxidation during cold storage. Further, the metabolic responses of NCEO-FG coated Pseudomonas spp. were revealed using NMR spectroscopy: the reducing levels of metabolites (e.g., pyruvate, amino acids, and betaine) suggested that the NCEO-FG disturbed energy and amino acid metabolisms of bacteria cells. However, the levels of metabolites (e.g., amino acids and osmoprotectants) were upregulated after 3 h and then back to normal concentration after 24 h, which indicated a defense system was built in bacterial cells to tolerate NCEO-FG. In short, this study confirmed that NCEO-FG could control the Pseudomonas-causing spoilage in fish fillets via elucidating the metabolisms.

Effects of electrolysed water and levulinic acid combination on microbial safety and polysaccharide nanostructure of organic strawberry.

This study aimed to better understand the effects of acidic electrolysed water (AEW, 4 mg/L) and levulinic acid (LA, food grade, 2%) combination on organic strawberry over 7 days. This combined method reduced the population of strawberry's natural microbiota by 1-2 log CFU/g and kept the level of inoculated Escherichia coli O157:H7 and Salmonella below the detection limit (2 log CFU/g) during the whole storage period. Meanwhile, AEW + LA did not affect the physicochemical qualities of strawberries significantly, maintaining most texture and biochemical attributes at an acceptable level (e.g., firmness, colour, soluble solids content and organic acid content). Atomic force microscopy further revealed that the treatment containing LA preserved the sodium carbonate soluble pectin (SSP) nanostructure best by maintaining their length and height, and slowed the breakdown of SSP chains by promoting acid-induced bonding and soluble pectin precipitation. These results demonstrated that low concentration AEW and LA combination is a promising sanitising approach for organic strawberry preservation.

Integrated metabolomics and transcriptomics reveal the adaptive responses of Salmonella enterica serovar Typhimurium to thyme and cinnamon oils.

Essential oils (EOs), such as thyme (Thy) and cinnamon (Cin) oils, present promising antibacterial properties against foodborne pathogens (e.g., Salmonella enterica serovar Typhimurium). However, the food matrix might result in sublethal EO stress, and little information about direct and/or cross-resistance development after sublethal EO exposure is available. This study revealed that S. Typhimurium under sublethal Thy and Cin (50% minimum inhibitory concentration, MIC50) treatments exhibited a lower growth rate and an extended lag phase. EO adapted cells showed direct-resistance to subsequent lethal EO treatment, and cross-resistance to thermal (58 °C) and oxidative (hydrogen peroxide, 50 mmol/L) stresses. Metabolomics analysis revealed changes of 47 significant metabolites (variable importance in projection > 1, false discovery rate (FDR) < 0.05), including lipids, oligopeptides, amino acids, nucleotide related compounds, and organic acids. Metabolic pathways, such as aminoacyl-tRNA biosynthesis, were shown to be involved in EO adaptation. Furthermore, a transcriptomics study identified 161 differentially expressed genes (DEGs, fold change > 2, FDR < 0.05) in MIC50 Thy treated cells, while more DEGs (324) were screened from the MIC50 Cin group. The integrated omics analysis allowed us to speculate on the molecular mechanisms. Under harsher Thy stress, S. Typhimurium cells adopted a conservative strategy to survive. By contrast, more radical responses were observed during Cin adaptation. In conclusion, the food industry should be more cautious in the use of EOs because sublethal EO stress might result in the development of resistance.

Effect of vacuum impregnated fish gelatin and grape seed extract on moisture state, microbiota composition, and quality of chilled seabass fillets.

The effect of fish gelatin (FG) and grape seed extract (GSE) on microbiota composition and moisture state of fish was unexplored. Herein, this study aimed to evaluate the single and combined (FGG) effects on seabass during storage (4 °C) with assistant of vacuum impregnation and to elucidate the underlying preservative mechanism. As suggested by low-field NMR and magnetic resonance imaging, FGG-treated seabass presented higher water holding capacity by controlling transformation from immobilised to free water. Moreover, the total viable count and spoilage bacteria were reduced by > 1 log CFU/g as compared to the control. Changes in microbial flora analysed using high throughput sequencing further indicated that GSE contributed to the notably suppressed growth of Pseudomonas. Also, the accumulation of biogenic amines especially putrescine was decreased (over 0.5-fold) under the combination treatment as compared to the control (P < 0.05). The results suggest that FGG is promising for seabass preservation.

Effect of chitosan coatings on the evolution of sodium carbonate-soluble pectin during sweet cherry softening under non-isothermal conditions.

The inhibiting effect of chitosan coating (2%) on the softening and sodium carbonate-soluble pectin (SSP) evolution of sweet cherries during non-isothermal storage was investigated. Chitosan coating significantly extend the softening (6.4% greater than the control group), maintained the SSP content (6.6% greater than the control group), and reduced the degradation of SSP by inhibiting the expression of the paPME1-5 genes, which regulating pectin methylesterase activity of sweet cherries under temperature variation. In addition, the results of methylation and monosaccharide composition indicated that the chitosan coating reduced demethylation of SSP and the loss of RG-I main and side chain neutral sugars. Atomic force microscopy images revealed that the coated sweet cherries contained more linked, branched, and long SSP chains and maintained the width of the pectin backbone (>140 nm). These results indicated that a chitosan coating is feasible to preserve postharvest fruit under non-isothermal conditions.

Metabolic analysis of salicylic acid-induced chilling tolerance of banana using NMR.

Banana is highly susceptible to low temperature and salicylic acid (SA) can effectively improve the chilling tolerance. The metabolic changes of SA induced chilling responses of banana were studied. Bananas normally ripened under 15 °C and dramatic metabolic difference compared with other groups was recorded. Accumulation of glucose (>1.5 folds) and consumption of unsaturated fatty acids (11.0-16.5%) were observed. The glycolysis was induced to compensate the decreased energy charge. Low temperature (6 °C) caused chilling damage and metabolites including glutamine, serine, and glucose were related to chilled bananas. Various physiological changes such as sugar metabolism and consumption of reducing substances occurred to adapt the cold stress. SA released the cold injury and the disaccharides were increased by 18.1-21.4%. Further analysis revealed the synthesis of unsaturated fatty acids, amino acids such as proline, and enhanced energy charge. Thus, SA increased the chilling tolerance via a number of different metabolic mechanisms.

Elucidating antimicrobial mechanism of nisin and grape seed extract against Listeria monocytogenes in broth and on shrimp through NMR-based metabolomics approach.

Nisin and grape seed extract (GSE) have been widely used as food preservatives; however, the mechanism against pathogens at molecular level has not been well elucidated. This work aimed to investigate their antimicrobial effect against Listeria monocytogenes and to elucidate the mechanism by NMR-based metabolomics. Nisin exhibited enhanced in vitro antilisterial effect when combined with GSE (4.49 log CFU/mL reduction). Marked change in cell membrane permeability was observed in the combination group using confocal laser scanning microscopy; this was verified by increased leakage of protein and nucleic acid. The underlying antimicrobial mechanism was revealed by NMR coupled with multivariate analysis. Significant decreases in threonine, cysteine, ATP, NADP, adenine were observed, whereas a few of metabolites such as lactic acid and γ-aminobutyric acid (GABA) increased after nisin-GSE treatment (P < 0.05). Pathway analysis further manifested that the nisin-GSE inhibited the survival of L. monocytogenes by blocking the TCA cycle, amino acid biosynthesis and energy-producing pathway. Lastly, nisin and GSE were applied to shrimp and binary combination showed remarkably antilisterial activity (1.79 log CFU/g reduction). GABA shunt and protein degradation from shrimp compensated the unbalanced glycolysis and amino acid metabolism by providing energy and carbon source for L. monocytogenes inoculated on shrimp. Thus, they were more tolerant to nisin and GSE stresses as compared to the broth-grown culture.

Effect of vacuum impregnated fish gelatin and grape seed extract on metabolite profiles of tilapia (Oreochromis niloticus) fillets during storage.

Traditional methods evaluating fish quality do not involve comprehensive qualification and quantification of quality-related components. The objective of this study was to investigate the effect of vacuum impregnated fish gelatin (FG) and grape seed extract (GSE) on metabolites of tilapia fillets during storage using nuclear magnetic resonance (NMR). Totally 42 metabolites were identified, 36 of which were quantified. The multivariate analysis results demonstrated distinct separations between fresh and stored fillets, indicating significant metabolite changes during storage. Some metabolites like choline and trimethylamine oxide were closely related to freshness while organic acids were associated with spoilage. Combined FG and GSE reduced the formation of undesirable metabolites like trimethylamine and histidine significantly (P < 0.05). Traditional freshness indexes indicated preserved quality after combined coating and further verified NMR results. This study reveals the potential of NMR to analyse metabolites that determine fish quality and to monitor their changes during storage.

Bamboo Leaf Flavonoids Extracts Alleviate Oxidative Stress in HepG2 Cells via Naturally Modulating Reactive Oxygen Species Production and Nrf2-Mediated Antioxidant Defense Responses.

In this study, bamboo leaf flavonoids extracts (BFE) were employed to alleviate oxidative stress induced by oleic acid in HepG2 cells. Biochemical indexes, intracellular reactive oxygen species production, lipid droplets accumulation, antioxidant enzymes production, and mitochondrial membrane potential were determined to show the alleviation performance of BFE intervention (P < 0.05). Importantly, the results of qRT-PCR and western blot determination indicated that BFE intervention upregulated the expression of Nrf2/HO-1/NQO1 to initiate the antioxidant defense response for counteracting oxidative stress (P < 0.05). Moreover, mitochondrial membrane potential-mediated apoptosis and FOXO signaling pathway initiation caused by BFE intervention may together contribute to oxidative stress alleviation in HepG2 cells. In conclusion, these findings suggested that BFE intervention upregulated related antioxidant defense responses for preventing cells from oxidative damage. PRACTICAL APPLICATION: In this study, bamboo leaf flavonoids extracts intervention upregulated related antioxidant defense responses for preventing cells from oxidative damage. These findings in bamboo leaf extracts antioxidants are a promising and innovative subject with practical applications to enhance the development of bamboo leaf extracts functional products in the food industry.

Vacuum impregnation of fish gelatin combined with grape seed extract inhibits protein oxidation and degradation of chilled tilapia fillets.

The present study studied the effects of fish gelatin (FG) incorporated with grape seed extract (GSE) through vacuum impregnation (VI) on refrigerated tilapia (Oreochromis niloticus) fillets over 12 days. The VI of FG-GSE significantly improved the quality of the fish by decreasing drip loss, texture changes, and microbial survival. It also delayed protein oxidation by inhibiting the formation of disulphide bonds and carbonyl groups, and maintaining a higher sulfhydryl content and Ca2+-ATPase activity. Regarding myofibril degradation, FG-GSE maintained their secondary structure by increasing the ratio of α-helices and ß-sheets (70.88-75.51%). Atomic force microscopy further revealed that the FG-GSE coating preserved the myofibril nanostructure by maintaining their length, width, and height. Overall, the synergistic effects of VI with 3% FG and 0.9% GSE suggested a promising approach for fillet preservation.

Effects of calcium and pectin methylesterase on quality attributes and pectin morphology of jujube fruit under vacuum impregnation during storage.

Calcium chloride (1% w/w, CaCl2) and pectin methylesterase (PME) (15 U/mL) were vacuum impregnated (VI) into jujubes to preserve their quality. The nanostructure of jujube pectin was investigated using atomic force microscopy (AFM) to determine the degradation mechanism of pectin. CaCl2 with PME under VI treatment (VI + Ca + PME) maintained jujubes' quality. Weight loss in VI + Ca + PME group at day 56 was only 60.36% of that in control group (CK). Firmness, soluble solids content, and ascorbic acid content of jujubes in VI + Ca + PME group were higher than those in CK. Firmness was highly positively correlated with sodium carbonate-soluble pectin (SSP) content. According to AFM results, frequencies of molecules with a width ≥60 nm of water-soluble pectin (WSP), chelate-soluble pectin (CSP), and SSP were the highest in VI + Ca + PME group at the end of storage. WSP, CSP, and SSP degradation was delayed by VI + Ca + PME treatment. The quality of jujubes was effectively maintained by VI + Ca + PME treatment.

Quantification of aflatoxin B1 in vegetable oils using low temperature clean-up followed by immuno-magnetic solid phase extraction.

In the present study, a convenient and highly efficient method was developed to quantify aflatoxin B1 (AFB1) in oil samples. Low temperature clean-up (LTC) followed by immuno magnetic solid phase extraction (IMSPE) was used to clean up oil samples. LTC assisted in freezing out the interference from the oil matrix while IMSPE further helped to preconcentrate the targeted analyte. For IMSPE, we synthesised and characterised anti-AFB1 monoclonal antibody-functionalised magnetic nanoparticles. Oil sample extraction was then carried out using LTC-IMSPE. The proposed method showed satisfactory efficiency and reproducibility with recovery rates being within the range of 79.6-117.9%, with a relative standard deviation below 11.48%. The sensitivity of the method was satisfactory with the limits of detection and quantification being as low as 0.0048 and 0.0126 ng·g-1, respectively. Real sample analysis was carried out for five kinds of different vegetable oils. The results suggest that the method developed is very sensitive and accurate.

Dispersive Solid-Phase Extraction Using Microporous Sorbent UiO-66 Coupled to Gas Chromatography-Tandem Mass Spectrometry: A QuEChERS-Type Method for the Determination of Organophosphorus Pesticide Residues in Edible Vegetable Oils without Matrix Interference.

A QuEChERS-type method without matrix interference was designed and developed to determine organophosphorus pesticide residues in edible vegetable oils, based on dispersive solid-phase extraction with cleanup using UiO-66 as sorbent. Microporous UiO-66 directly and selectively adsorbed organophosphorus pesticides and excluded interfering compounds. Clean analytes were obtained by elution and analyzed using gas chromatography-tandem mass spectrometry. The dispersive solid-phase extraction conditions (amount of adsorbent, extraction time, desorption solvent volume, and elution time) were optimized. The limits of detection of the pesticides in vegetable oils were 0.16-1.56 ng/g. Under optimized conditions, the average pesticide recoveries were 81.1-113.5%. The intraday and interday relative standard deviations for analyte recovery were <8.2 and <13.9%, respectively. Thus, the method is reliable and could detect organophosphorus pesticide residues in edible vegetable oils. Furthermore, UiO-66 can be easily recycled and reused at least 10 times, reducing the cost of analysis.

Combined effects of ultrasound and calcium on the chelate-soluble pectin and quality of strawberries during storage.

The combined effects of ultrasound and calcium on the water migration, quality, and chelate-soluble pectin (CSP) properties of strawberries were investigated using nuclear magnetic resonance (NMR), high-performance liquid chromatography (HPLC), and atomic force microscopy (AFM). The relationship among water migration, firmness, and CSP properties was also determined. Treatment with ultrasound and calcium (U + Ca) prevented the decrease in firmness of strawberries during storage (17 days). Measurements of physicochemical parameters (titratable acidity (TA), soluble solid content (SSC), CSP and Ca content) showed that U + Ca treatment maintained better fruit quality. AFM showed a larger percentage of wider and longer CSP molecules in the U + Ca group (width ≥90 nm; length ≥800 nm). These results, together with the HPLC results, confirmed that U + Ca treatment effectively inhibits CSP degradation. This study revealed that the application of ultrasound and calcium could preserve the quality of stored strawberries.

Bromelain Kinetics and Mechanism on Myofibril from Golden Pomfret (Trachinotus blochii).

Bromelain was used to tenderize golden pomfrets (Trachinotus blochii). The enzyme kinetic model was x=2.447×ln[1+(1332.21×E0S0-1.74)t], which indicated that the degree of hydrolysis (DH, x) was dependent on hydrolysis time (t), the initial concentration of myofibril (S0 ) and bromelain (E0 ). The relationship between the overall hydrolysis rate (v), S0 , E0 , and t is demonstrated as: v=(16.50(E0S0)-1.33)S0 exp {-2.447ln[1+(1332.21E0S0-1.74)t2]}. Sample of 0.40% E0 /S0 was further used to study the effects of hydrolysis time on the changes of proteins, peptides, free amino acids (FAA), and protein nanostructure. SDS-PAGE result showed that myosin heavy chain was degraded dramatically from 22.88% before treatment to 12.03% after 2 min bromelain treatment. Meanwhile, bromelain did not exhibit activity towards actin, trypomyosin, myosin light chain, and troponin C. A general increase of amino acids indicated the increased DH and the preferential cleavage sites of bromelain in the descending order of lysine, glutamic acid, glycine, ornithine, methionine sulfoxide, and alanine. Atomic force microscope images showed that the strip-like structure of myofibril was considerably degraded by bromelain, and the granulation of protein after 20 min indicated possible self-assembling of protein hydrolysate. Confocal laser scanning microscopy further confirmed the degradation of myofibril proteins and formation of protein aggregates. PRACTICAL APPLICATION: Meat of golden pomfrets is tough, thus not idea for fish balls or fish cakes. Tenderization is essential to achieve desired texture and consumer acceptance, especially for this fish meat with intrinsic hard texture. Bromelain can be extracted from pineapple processing waste. Enzymatic kinetics was studied to instruct industry to control the tenderness of the processed fish meat. The microstructural and mechanism study elucidate the process, thus could be applied to improve the quality of the seafood products correspondingly.

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.

Characterization and purification of anthocyanins from black peanut (Arachis hypogaea L.) skin by combined column chromatography.

Black peanut skins as a byproduct from peanut industry contain abundant anthocyanins, evaluated as 8.61±0.27mg/g dry black peanut skins, are currently poorly exploited. In this work, four anthocyanins and three major flavonols were detected and identified by HPLC-PDA-ESI-MS/MS from the acidified water extract of black peanut skins of Arachis hypogaea L. After preliminary removal of flavonols by ethyl acetate (EtOAc), further purification of the anthocyanins was conducted using a combination of Amberlite XAD-7HP and ODS-AQ-HG column chromatography methods. Two most abundant monomeric anthocyanins cyanidin-3-O-sophoroside (5.77±0.42mg) and cyanidin-3-O-sambubioside (4.10±0.17mg) were eventually obtained from 2g dry black peanut skins, and their purities were determined by HPLC-PDA as 97.29% and 98.28% at the yields of 87.47% and 64.27% on the basis of their total amount in the crude extracts, respectively. These sequential treatments can be easily adapted to large-scale fractionation of pure anthocyanin monomers.

Effects of calcium treatment and low temperature storage on cell wall polysaccharide nanostructures and quality of postharvest apricot (Prunus armeniaca).

Cell wall polysaccharides play an important role in postharvest fruit texture softening. Effects of calcium treatment combined with cold storage on the physical properties, polysaccharide content and nanostructure of apricots were investigated. Apricots were immersed in distilled water, 1% or 3% w/v calcium chloride, then stored at 5°C or 10°C. Storage at 5°C significantly improved apricot quality and shelf life. Significant changes in the concentration and nanostructure of cell wall pectins and hemicelluloses revealed their disassembly and degradation during apricot storage. These modifications could be retarded by 1% w/v calcium chloride treatment. Meanwhile, the basic width units of apricot cell wall polysaccharide chains were 11.7, 31.2 and 39.1nm for water-soluble pectin, 11.7, 17.6 and 19.5nm for chelate-soluble pectin, and 15.6 and 23.4nm for hemicellulose. The results suggest that texture of apricots can be effectively maintained by 1% calcium chloride treatment and storage at 5°C.

Structure and Antioxidant Activities of Proanthocyanidins from Elephant Apple (Dillenia indica Linn.).

UNLABELLED: Proanthocyanidins were isolated and purified from fruits of elephant apple (Dillenia indica Linn.) and their structural and bioactive properties were examined. Bate-Smith alcoholysis, FTIR, and (13) C NMR spectra revealed that elephant apple proanthocyanidins (EAPs) contained a dominant amount of B-type procyanidins (PC) with a minor amount of B-type prodelphinidins (PD) but no A-type interflavan linkage. (13) C NMR spectrum indicated that the cis isomer was dominant in EAPs. The electron spray ionization and matrix-assisted laser desorption ionization time of flight mass spectra of EAPs showed the clear ion peaks corresponding to B-type PC dimer to B-type PD with degree of polymerization of 11. EAPs had strong antioxidant activity, which was evidenced by the high oxygen radical scavenging capacity at 1.06 × 10(4) µmol TE/g and ferric reducing antioxidant power of 2320 µmol Fe(II)/g. The results suggest that EAPs could be extracted to be used as promising functional food materials. PRACTICAL APPLICATION: In this study, the elephant apple proanthocyanidins (EAPs) with a yield of 0.23% were identified for the first time as dominant B-type poly(catechin/epicatechin) but no A-type interflavan linkage. EAPs had higher ORAC and FRAP values compared to commercial grape seed proanthocyanidins, suggesting that EAPs may be used as promising functional food materials.

Probing starch-iodine interaction by atomic force microscopy.

We explored the interaction of iodine with three crystalline type starches, corn, potato, and sweet potato starches using atomic force microscopy. Results revealed that starch molecules aggregated through interaction with iodine solution as well as iodine vapor. Detailed fine structures such as networks, chains, and super-helical structures were found in iodide solution tests. The nanostructures formed due to iodine adsorption could help to understand the formation and properties of the starch-iodine complex.