Controlling soft rot of green pepper by bacteriocin paracin wx3 and its effect on storage quality of green pepper.

A bacteriocin paracin wx3 was investigated as a candidate of natural preservative to control green pepper soft rot. Firstly, paracin wx3 was heterologously expressed in Pichia pastoris X33 with an improved yield of 0.537 g/L. Its size and amino acid sequence were confirmed by Tricine-SDS-PAGE and LC-MS/MS. Then, result of antibacterial activity showed that its MIC value against Pectobacterium carotovorum was 16 µg/mL. In vitro, paracin wx3 completely killed the pathogen at high concentrations ≥8 × MIC. In vivo, disease incidence of green pepper soft rot was decreased from 90% (control) to <2% (8 × MIC). Subsequently, results of action mode showed that paracin wx3 inhibited the growth of pathogen by pore-formation on cell membrane. Last, paracin wx3 treatment reduced losses of weight, firmness, total soluble solid, Vc of green pepper during storage. It also inhibited the production of soft rot volatile p-xylene, 1-butanol, 2-methyl-2-propanol, 3-hydroxybutan-2-one-D, 2-pentyl furan, butanal, etc.

Development of antifogging double-layer film using cellulose nanofibers and carboxymethyl chitosan for white Hypsizygus marmoreus preservation.

Films with simultaneously excellent mechanical and anti-fog properties are of great importance for food packaging. A novel strategy is described here to prepare long-lasting anti-fog film with antibacterial and antioxidant capabilities via a simple, green approach. The CMC (carboxymethyl chitosan) gel was integrated with CNF/TA (cellulose nanofibers/tannic acid) composite solution based on layer-by-layer assembly to form a membrane with a bilayer structure. The anti-fog performance of the bilayer film could be adjusted by regulating the CNF/TA layer thickness. On the whole, the developed anti-fog film had high mechanical strength and excellent UV shielding properties, as well as good antibacterial and antioxidant properties, and could be non-fogging for a long time under water vapor (40 °C). The effect of double layer anti-fog film (3%CmFT-3) on the fresh-keeping effect of white Hypsizygus marmoreus was compared at room temperature (28 °C) with commercially available anti-fog PVC film. The results showed that the bilayer anti-fog film could effectively prevent the generation of fog, delay the Browning, inhibit mildew, improve the overall acceptability, and effectively extend the shelf life of white Hypsizygus marmoreus. This biomass-based anti-fog film offers great potential for the development of multifunctional green food packaging.

The effect of pulcherriminic acid produced by Metschnikowia citriensis in controlling postharvest diseases of citrus fruits.

The biocontrol effectiveness of Metschnikowia citriensis relies on its production of pulcherriminic acid (PA), which forms insoluble and stable pulcherrimin pigments by chelating iron ions, this inhibits pathogen growth by preventing their utilization of chelated Fe3+. In this study, ΔM. citriensis, which did not produce PA, was used as a control to examine changes in its biocontrol effectiveness by adding tryptophan to the medium. Tryptophan was shown to have no discernible impact on the growth and PA production of ΔM. citriensis; moreover, the PA synthesis-related genes PULs, Snf2, and leucyl-tRNA synthesis-related genes A3136 and A3022 were all down-regulated in ΔM. citriensis. The PA-free ΔM. citriensis eventually showed a much poorer inhibition zone against the pathogens in vitro, and a noticeably decreased control efficiency against postharvest diseases in citrus fruit. Tryptophan was added to the medium, which had no appreciable impact on inhibitory zone of ΔM. citriensis against pathogens in vitro, but enhanced its ability to control citrus postharvest diseases. Additionally, the control effects of culture broth of M. citriensis and ΔM. citriensis on postharvest diseases in citrus fruit were assessed. It was found that both culture broth of M. citriensis and ΔM. citriensis exhibited remarkable control effects against citrus postharvest diseases, with culture broth of M. citriensis which containing PA being more effective in controlling the disease. Last but not least, we extracted and dissolved pulcherrimin to obtain PA extracts, which were then injected to citrus fruits to assess the biocontrol effectiveness. The findings demonstrated that postharvest diseases of citrus fruit can be effectively controlled by PA extracts. This research suggested a new biological strategy for the management of citrus postharvest diseases.

Lowering glycemic levels via gastrointestinal tract factors: the roles of dietary fiber, polyphenols, and their combination.

Dietary fiber (DF) and polyphenols (DP) are typical blood sugar-lowering components, and both play distinct yet interconnected roles in exerting their blood sugar-lowering effects. We comprehensively summarized the single and combined effects of DF and DP on blood glucose homeostasis through regulating the relevant factors in the upper gastrointestinal tract (UGT) and lower gastrointestinal tract (LGT). In the UGT, DF slowed down glucose metabolism by enhancing digesta viscosity and hindering enzyme-substrate interaction. DP primarily targeted enzymes and substrates. When combined, DP enhanced the adsorption capacity of DF for glucose. DF weakened DP's inhibitory effect on enzymes. Both DF and DP disrupted glucose intestinal uptake via physical or genomic modulation, but the co-consumption of DF and DP demonstrated a lower inhibitory effect on glucose uptake than DP alone. In the LGT, DF and DP showed synergistic or antagonistic effects on gut microbiota. Remarkably, whole foods exhibited potent prebiotic effects due to their compound-rich matrix, potentially enhancing glucose homeostasis and expanding dietary options for glucose regulation research.

Fatty acid metabolism and C9 aldehyde biosynthesis are involved in ε-poly-l-lysine-induced citrus fruit resistance to Penicillium digitatum.

Citrus fruit were easily infected by Penicillium digitatum, and caused green mold rapidly, resulting in enormous post-harvest losses. ε-poly-l-lysine (ε-PL) was generally regarded as a safe (GRAS) substance. Besides, it was proved to have a dual effect on harming fungi and triggering fruit defense responses. Fatty acid metabolism is closely related to fruit defense response. However, little is known about how ε-PL affected fatty acid metabolism in citrus fruit. Here, we found that ε-PL increased the expression of CsFATA, CsACSL, CsFAD2, CsFAD3, CsLOX2S, and CsHPL in fatty acid metabolism, decreasing oleic acid levels and enhancing linoleic and linolenic acid levels. Additionally, ε-PL enriched the activities of LOX and HPL during the oxidative decomposition of fatty acids, and activating C9 aldehyde biosynthesis. Interestingly, ε-PL combined with (2E,4E)-nonadienal (C9 aldehyde) would improve the inhibitory effect against Penicillium digitatum. And the combined bio-fungicide significantly delayed the citrus green mold compared to single concentrations of the individual components. These results suggested that ε-PL improved citrus fruit defense responses through fatty acid-mediated defense responses. Combined bio-fungicide consisting of ε-PL and (2E,4E)-nonadienal have an excellent prospect for controlling citrus green mold.

Effect of L-cysteine treatment to induce postharvest disease resistance of Monilinia fructicola in plum fruits and the possible mechanisms involved.

Plum is an important stone fruit in China, but the fruit is easily perishable and susceptible to infection by pathogens. Traditionally, synthetic fungicides are used to control diseases. However, the side effects of fungicides should not be ignored. Cysteine, generally recognized as safe (GRAS) amino acid, has been reported to play roles in the plant abiotic stress response, but little is known about the role of cysteine to control postharvest diseases in fruits. Therefore, this study was designed to investigate the effect of L-cysteine treatment on control of postharvest brown rot in artificially inoculated plum fruits and the possible biocontrol mechanisms involved. Postharvest plum fruits were inoculated with 1, 10, 100 and 1000 mg L-1 L-cysteine. 100 mg L-1 L-cysteine treatment effectively controlled brown rot in artificially inoculated plum fruits by inducing resistance. Furthermore, 100 mg L-1 L-cysteine treatment increased the activities of glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase (6PGDH), enhanced the content of NADPH of the pentose phosphate pathway, as well as improved the contents of H2O2 and some amino acids in the artificially inoculated plum fruits. 100 mg L-1 L-cysteine treatment also elevated the antioxidant content (AsA, GSH) and the antioxidant enzymes activities (APX, GR, MDAR, DHAR) of the ascorbate-glutathione (AsA-GSH) pathway. The protective effects of L-cysteine treatment on postharvest plum fruits likely be due to activating some defense-related responses of the fruit against infection. L-cysteine treatment is a safe promising method for controlling postharvest brown rot in plum fruits.

Transcriptional regulatory mechanism of a variant transcription factor CsWRKY23 in citrus fruit resistance to Penicillium digitatum.

As the most productive fruit in the world, there is a lack of research on disease resistance mechanisms in citrus. WRKY transcription factors are mediators of disease resistance in plants. In this research, CsWRKY23, which could respond to exogenous salicylic acid (SA) was identified. As a variant WRKY, the transient overexpression of CsWRKY23 in citrus peel enhanced the resistance to Penicillium digitatum. The potential targets of CsWRKY23 were identified by using DNA affinity purification sequencing (DAP-seq). In combination with RNA sequencing (RNA-seq) data, 48 direct target genes of CsWRKY23 were identified. In addition, five genes for EMSA and dual-luciferase report system analysis were selected and the results showed that CsWRKY23 activate CsAAE12, CsRbohD, CsSARD1, CsWRKY22 and CsIQM6 expressions. Further analysis revealed that CsWRKY23 contributed to SA synthesis pathway, reactive oxygen species (ROS) accumulation, and cell wall strengthening. This study presented a possible regulatory network for disease resistance involving the CsWRKY23.

Activation of the phenylpropanoid pathway in Citrus sinensis collapsed vesicles during segment drying revealed by physicochemical and targeted metabolomics analysis.

Segment drying is a common internal physiological disorder in citrus fruit, and vesicles get granulated or collapsed. This study aimed to probe whether and how the phenylpropanoid metabolism changes in vesicles during collapse of blood orange (Citrus sinensis cv. Tarocco). Vesicle collapse led to a decrease in the content of nutrients and flavonoids, while an increase in lignin content. This disorder was further associated with the increasing enzyme activities and gene expression levels of both the general phenylpropanoid pathway and branch pathway of lignin synthesis, while decreasing enzyme activities and gene expression levels of branch pathway of flavonoids synthesis. Targeted metabolomics analysis of 14 metabolites of the lignin pathway revealed that lignin precursors were accumulated in collapsed vesicles. We provide solid evidence that phenylpropanoid metabolism could be activated, and, intriguingly, metabolic flux may be shuttled to lignin precursors synthesis rather than flavonoids synthesis in vesicles during collapse of blood orange.

A core epiphytic bacterial consortia synergistically protect citrus from postharvest disease.

Biological antagonists are a series of microbes that can control pathogens to reduce the incidence of disease or reduce symptoms. Herein, four varieties of citrus fruit were selected to perform an amplicon sequencing on their epiphytic microbiota to get a systematic understanding of them. Co-occurrence network, Venn, and LefSe analysis were performed to filter to 24 genera which represent the universality, specificity, and correlation among samples. Functional analysis hinted that the genes related to chitinase, which most of these 24 bacteria carry, might lead to a disease-suppressive phenotype. 115 strains of epiphytic bacteria were isolated, and the bacterial synthetic community was constructed by 8 strains. The in vivo test results indicated they were able to reduce pathogen development for a longer time than separate inoculation. Collectively, this study showed the disease control potential provided by native epiphytic bacteria of fruit and give a new strategy to sustainable agriculture.

Tryptophan enhances biocontrol efficacy of Metschnikowia citriensis FL01 against postharvest fungal diseases of citrus fruit by increasing pulcherriminic acid production.

The aim of this work was to study the capability and mechanism of enhancing the yield of pulcherriminic acid (PA) produced by Metschnikowia citriensis FL01 with the help of tryptophan for the control of postharvest diseases on citrus caused by Penicillium italicum, Geotrichum citri-aurantii and Penicillium digitatum. The adding of 10 mmol/L tryptophan to the growth medium resulted in the widest pulcherrimin pigment zone produced by M. citriensis FL01. The adding of tryptophan to the growth medium upregulated A3136 and A3022 gene expression (responsible for leucyl-tRNA biosynthesis from leucine), downregulated A1350 gene expression (responsible for the biosynthesis of leucine to branched-chain fatty acids), and decreased the content of intracellular leucine in M. citriensis FL01, speculating that the addition of tryptophan in the growth medium induced leucine conversion toward leucyl-tRNA in M. citriensis FL01. Moreover, the adding of tryptophan to the growth medium upregulated PULs (responsible PA biosynthesis) and Snf2 (transcriptional regulator) gene expression and promoted intracellular, extracellular or total PA production by M. citriensis FL01 in liquid medium. In addition, the addition of tryptophan in the growth medium showed no effect on the growth of M. citriensis FL01 itself in liquid medium, while the population dynamics in citrus fruit wounds of M. citriensis FL01 with the addition of tryptophan in the growth medium were increased compared with those of M. citriensis FL01. What's more, M. citriensis FL01 with the addition of tryptophan in the growth medium completely inhibited the growth of pathogens in vitro. The disease incidences and lesion diameters of blue mold, sour rot and green mold on citrus fruit were lower in group which treated with M. citriensis FL01 containing tryptophan in the growth medium than that treated with M. citriensis FL01 alone. Overall, the postharvest biocontrol of citrus with M. citriensis FL01 containing 10 mmol/L tryptophan in the growth medium is a promising approach to protect these fruits from blue mold, sour rot and green mold.

Phenylalanine Promotes Biofilm Formation of Meyerozyma caribbica to Improve Biocontrol Efficacy against Jujube Black Spot Rot.

During storage and transportation after harvest, the jujube fruit is susceptible to black spot rot, which is caused by Alternaria alternata. The present study aimed to evaluate the effectiveness of the yeast Meyerozyma caribbica in controlling A. alternata in postharvest jujube fruits, and to explore the biofilm formation mechanism. The results showed that M. caribbica treatment significantly reduced the A. alternata decay in jujube fruits. M. caribbica could rapidly colonize jujube fruit wounds, adhering tightly to hyphae of A. alternata, and accompanied by the production of extracellular secretions. In in vitro experiments, we identified that M. caribbica adhered to polystyrene plates, indicating a strong biofilm-forming ability. Furthermore, we demonstrated that M. caribbica can secrete phenylethanol, a quorum sensing molecule which can affect biofilm development. Phenylalanine (a precursor substance for phenylethanol synthesis) enhanced the secretion of phenylethanol and promoted the formation of M. caribbica biofilms. Meanwhile, phenylalanine enhanced the biological control performance of M. caribbica against jujube black spot rot. Our study provided new insights that enhance the biological control performance of antagonistic yeast.

Debaryomyces nepalensis reduces fungal decay by affecting the postharvest microbiome during jujube storage.

Microbial antagonists are effective and environmentally friendly in controlling postharvest diseases of fruit. The present study investigated the influence of D. nepalensis on epiphytic microbiome and postharvest decay of jujube. Results showed that D. nepalensis notably reduced fungal decay, maintained the fruit firmness and delayed discoloration. The epiphytic microbiome revealed that D. nepalensis changed the fungal communities, but few influence on bacterial communities were observed. D. nepalensis, as the dominant population in the treatment group, decreased the abundance of pathogenic fungi of Alternaria, Penicillium, Fusarium and Botrytis, while increased the beneficial bacteria of Pantoea. The canonical correspondence analysis revealed that Debaryomyces was negatively correlated with the decay rate, whereas Penicillium, Acremonium, Rhodosporidiobolus and Hansfordia were positively correlated. In conclusion, D. nepalensis altered the successional process of fungal and bacterial communities to reduce the decay rate of jujube during storage.

Low and high storage temperature inhibited the coloration of mandarin fruit (Citrus unshiu Marc.) with different mechanism.

BACKGROUND: Peel color regulated by pigment metabolism is one of the most crucial indicators affecting the commodity values of citrus fruit. Storage temperature is a vital environmental factor that regulates the fruit pigmentation. RESULTS: Results showed that the peel coloring process was significantly inhibited when mandarin fruit were stored at 5 and 32 °C with normal coloring at 25 °C as the control. However, the inhibitive mechanisms of 5 and 32 °C storage were different. At 5 °C, higher levels of CcNYC and CcCHL2 were detected, which indicated that 5 °C induces the circulation of chlorophyll rather than inhibits chlorophyll degradation. CcPSY2, CcCHYB, and CcZEP exhibited higher expression levels in fruit stored at 5 °C, which accelerated the accumulation of carotenoids. In fruit stored at 32 °C, CcNYC, CcPAO, and CcCHL2 exhibited lower expression levels than those fruit stored at 5 °C, and the expressions of CcPSY2, CcCHYB, and CcZEP were down regulated, implying the carotenoid synthesis was suppressed. CONCLUSION: Storage at 5 °C inhibited the postharvest coloring of mandarin fruit mainly by activating the cycle of chlorophyll, although it promotes the accumulation of carotenoids at the same time, but chlorophyll covers the color of carotenoids. Storage at 32 °C inhibited mandarin fruit coloring mainly by inhibiting the degradation of chlorophyll. Compared with the change of individual chlorophyll or carotenoid content, the change of the ratio of chlorophyll and carotenoid had a more important role in the coloration of mandarin fruit. This research offers valuable details for understanding the effect of temperature on the coloring process of postharvest citrus fruit. © 2022 Society of Chemical Industry.

Dietary fiber of Tartary buckwheat bran modified by steam explosion alleviates hyperglycemia and modulates gut microbiota in db/db mice.

Type 2 diabetes is a serious threat to human health. Tartary buckwheat bran dietary fiber has good hypoglycemic activity, with its modification widely studied. However, the hypoglycemic activity of steam explosion modified Tartary buckwheat bran soluble dietary fiber (SE-SDF) has not been reported. This research aimed at investigating the hypoglycemic effect with its underlying mechanism of SE-SDF on type 2 diabetic db/db mice. Results found SE-SDF decreased the levels of fasting blood glucose and glycosylated hemoglobin while improved oral glucose tolerance, insulin resistance, and injuries of liver, pancreas, and colon in diabetic db/db mice. Additionally, SE-SDF up-regulated the protein expression levels of hepatic phosphatidylinositol 3 kinase (PI3K), G protein-coupled receptor43 (GPR43), and phospho-adenosine monophosphate activated protein kinase (p-AMPK), whereas inhibited the protein expression levels of hepatic fork-head transcription factor O1 (FoxO1), phosphoenolpyruvate carboxy kinase (PEPCK) and glucose-6-phosphatase (G-6-Pase). Moreover, SE-SDF increased the production of fecal short chain fatty acids (SCFAs) and the expression of colon GPR43 and the concentration of serum glucagon like peptide-1 (GLP-1), leading to reduced ratio of Firmicutes/Bacteroidetes but increased relative abundance of Parabacteroides, norank_f_Muribaculaceae, Alloprevotella, Ruminiclostridium_9, unclassified_f_Ruminococcaceae, and Lachnospiraceae_NK4A136_group. These findings suggested that SE-SDF ameliorated type 2 diabetes via activating the liver PI3K/Akt/FoxO1 and GPR43/AMPK signaling pathways and modulating the gut microbiota-SCFAs-GPR43/GLP-1 signaling axis.

Premna microphylla Turcz pectin protected UVB-induced skin aging in BALB/c-nu mice via Nrf2 pathway.

Excessive exposure to ultraviolet B (UVB) irradiation is one of the major risk factors for skin photoaging. The aim of this study was to investigate the protective effect of Premna microphylla Turcz pectin (PMTP) against UVB-induced skin aging in BALB/c-nu mice. PMTP was characteristic of a low methoxyl RG-I pectin with Mw was 26.60 kDa, mainly composed of galacturonic acid. PMTP-containing cream efficiently inhibited the water loss, epidermal hyperplasia, matrix metalloproteinases-1 (MMP-1), and collagen destruction in UVB-induced skin injury mice. Additionally, topical administration of PMTP-containing cream significantly increased protein levels of the nuclear factor erythroid 2-related factor 2 (Nrf2), Kelch-like ECH-associated protein 1 (Keap1), macrophage-activating factor (Maf), and heme oxygenase 1 (HO-1), and the expression of antioxidant enzymes including superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px). In contrast, application of PMTP-containing cream on mice skin decreased the protein levels of nuclear factor-kappa B (NF-κB), inhibitor kappa B kinase ß (IKKß), and cyclooxygenase-2 (COX-2), and pro-inflammatory cytokines. Taken togethmier, these findings suggest that PMTP might protect UVB-induced skin aging via activating Nrf2 pathway and suppressing NF-κB pathway.

Preparation of water-soluble dialdehyde cellulose enhanced chitosan coating and its application on the preservation of mandarin fruit.

Biopolymers, e.g., polysaccharides and protein, have been employed as edible coatings for the preservation of fruits for many years and are the promising candidates for resolving the problems caused by the extensive using of synthesized polymers in recent years. Chitosan, a kind of polysaccharide with excellent antibacterial and coatings forming properties, has attracted a lot of research interests in being applied as an edible coating for the preservation of postharvest fruits. However, the applying of chitosan is restricted by its poor stability. In this study, we introduce the water-soluble dialdehyde cellulose (DAC) as the crosslinking agent for chitosan to enhance its stability. Fourier transform-infrared spectroscopy is applied to prove the happening of crosslinking and the detection of swelling ratio in water and mechanical properties of DAC-crosslinked chitosan (DAC/CS) confirms the enhanced stability. Furthermore, scanning electron microscope, thermogravimetric analysis, water contact angle, mechanical and gas barrier properties are performed to characterize DAC/CS films with different DAC contents. Finally, DAC/CS is employed as a coating agent to study the effect on the storage of mandarin fruit at room temperature. Chitosan, with enhanced stability by biopolymer, would be a promising candidate applied as a green edible coating in the preservation of fruits.

Study on the stability and oral bioavailability of curcumin loaded (-)-epigallocatechin-3-gallate/poly(N-vinylpyrrolidone) nanoparticles based on hydrogen bonding-driven self-assembly.

The biological activity and absorption of curcumin (Cur) is limited in application due to its low water solubility, poorstabilityand rapid metabolism. In this work, Cur loaded (-)-epigallocatechin-3-gallate (EGCG)/poly(N-vinylpyrrolidone) (PVP) nanoparticles (CEP-NPs) was successfully fabricated via self-assembly driven by hydrogen bonding, providing with desirable Cur-loading efficiency, high stability, strong antioxidant capacity, and pH-triggered intestinal targeted release properties. Molecular dynamics simulations further indicated the Cur was coated with EGCG and PVP in CEP-NPs and high acid prolonged release property was attribute to low ionization degree of EGCG. Besides, the enhanced intestinal absorption of Cur was related to inhibition of Cur metabolism by EGCG, enhancement of cellular uptake and higher Caco-2 monolayer permeation. Pharmacokinetic study showed that the oral bioavailability presented nearly 12-fold increment. Therefore, this study provides a new horizon for improving the Cur utilization in food and pharmaceutical fields.

Influence of arginine on the biocontrol efficiency of Metschnikowia citriensis against Geotrichum citri-aurantii causing sour rot of postharvest citrus fruit.

This study investigated the effect of arginine (Arg) on the antagonistic activity of Metschnikowia citriensis against sour rot caused by Geotrichum citri-aurantii in postharvest citrus, and evaluated the possible mechanism therein. Arg treatment up-regulated the PUL genes expression, and significantly induced the pulcherriminic acid (PA) production of M. citriensis, which related to the capability of iron depletion of M. citriensis. By comparing the biocontrol effects of Arg-treated and untreated yeast cells, it was found that Arg treatment significantly enhanced the biocontrol efficacy of M. citriensis, and 5 mmol L-1 Arg exerted the best effect. Additionally, the biofilm formation ability of M. citriensis was greatly enhanced by Arg, and the higher population density of yeast cells in citrus wounds was also observed in Arg treatment groups stored both at 25 °C and 4 °C. Moreover, Arg was shown to function as a cell protectant to elevate antioxidant enzyme activity [including catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GPX)] and intracellular trehalose content to resist oxidative stress damage, that directly helped to enhance colonization ability of yeasts in fruit wounds. These results suggest the application of Arg is a useful approach to improve the biocontrol performance of M. citriensis.