Enhancing bread preservation through non-contact application of starch-based composite film infused with clove essential oil nanoemulsion.

In this study, we have successfully produced a corn starch-based composite film through the casting method, formulated with clove essential oil nanoemulsion (NCEO) and corn starch. The physical and chemical changes of the composite films were investigated at various concentrations (10 %, 20 % and 40 %) of NCEO. Furthermore, the non-contact preservation effects of the composite films on bread during 15-day storage were also examined in this study. As the concentration of NCEO increased, the composite films presented a gradual thinning, roughening, and yellowing in appearance. Following this, the water content, water vapor permeability rate, and elongation at break of the films decreased, while their hydrophobicity, tensile strength, antioxidant and antimicrobial activity increased accordingly. Through FT-IR, X-ray diffraction and thermal gravimetric analysis, it was demonstrated that NCEO has strong compatibility with corn starch. Additionally, the indices' analysis indicated that utilizing the composite film incorporating 40 % NCEO can significantly boost the shelf life and quality of bread. Moreover, it was revealed that application of the non-contact treatment with composite film could potentially contribute certain preservation effects towards bread. In light of these findings, the composite film with non-contact treatment exhibits potential as an effective, safe, and sustainable preservation technique for grain products.

The biodiversity of Aspergillus flavus in stored rice grain leads to a decrease in the overall aflatoxin B1 production in these species.

Aspergillus flavus is a significant fungus that poses a threat to food safety by producing mycotoxins in various crops. In this study, A. flavus isolates were obtained from storage rice collected from seven provinces in southern China, and their AFB1 production, biosynthesis genes presence, and diversity were detected. Results showed that 56 out of the 81 A. flavus isolates produced detectable levels of AFB1, and 71 isolates (87.6 %) possessed aflR gene in their AF synthesis gene cluster, while only 41 isolates (50.6 %) had the ver-1 gene present. Genetic diversity analysis using inter-simple sequence repeats (ISSR) markers revealed seven main clusters among the isolates and the genetic similarity coefficients of 81 A. flavus isolates ranged from 0.53 to 1.00. Additionally, coculture assays were conducted using two toxigenic and two atoxigenic isolates from the same grain depot to investigate the effect of intraspecific inhibition on AFB1 production and to assess the AFB1 contamination risk of storage rice. The in situ results demonstrated that the atoxigenic isolates effectively inhibited the AFB1 contamination of toxigenic isolates. These findings provide insight into the genetic diversity of A. flavus isolates populations and highlight the potential food safety hazards of them in stored rice grain in China.

Biosurfactant from Pseudomonas fragi enhances the competitive advantage of Pseudomonas but reduces the overall spoilage ability of the microbial community in chilled meat.

Biosurfactants from Pseudomonas spp. have been reported to exhibit antibacterial and anti-adhesive properties, but their role during meat spoilage remains unclear. In this study, the biosurfactant was isolated from an isolate of Pseudomonas fragi with strong spoilage potential, and its surface tension and emulsification ability were determined. The chemical and microbial characteristics of the biosurfactant-treated meat samples were periodically analyzed. The results demonstrated that the biosurfactant produced by P. fragi could reduce surface tension and showed good emulsification properties. For the in situ spoilage trials, biosurfactant from P. fragi changed the microbial diversity on meat, helping Pseudomonas establish a dominant position in the population. However, biosurfactant treatment caused chicken meat to exhibit a weaker spoilage state, as indicated by the growth of psychrophilic microorganisms, total volatile basic nitrogen (TVBN) and meat color. These results provide practical information for understanding the role of P. fragi biosurfactant during chilled meat storage.

New insights into the persistent effect of transient cinnamaldehyde vapor treatment on the growth and aflatoxin synthesis of Aspergillus flavus.

The antimicrobial effects of continuous treatment with essential oils (EOs) in both liquid and gaseous phases have been intensively studied. Due to their rapid volatility, the effects of EOs on microorganisms after transient treatment are also worth exploring. In this work, the persistent effects of cinnamaldehyde (CA) vapor on Aspergillus flavus were detected by a series of biochemical analyses. Transcriptome analysis was also conducted to study the gene expression changes between recovered and normal A. flavus. When CA vapor was removed, biochemical analyses showed that the oxidative stress induced by the antimicrobial atmosphere was alleviated, and almost all the damaged functions were restored apart from mitochondrial function. Remarkably, the suppressed aflatoxin production intensified, which was confirmed by the up-regulation of most genes in the aflatoxin synthetic gene cluster, the velvet-related gene FluG and the aflatoxin precursor acetyl-CoA. Transcriptomic analysis also demonstrated significant changes in secondary metabolism, energy metabolism, oxidative stress, and amino acid metabolism in the recovery group. Taken together, these findings provide new insights into the mechanisms underlying the response of A. flavus to CA vapor treatment and will guide the rational application of EOs.

The Temporal Dynamics of Sensitivity, Aflatoxin Production, and Oxidative Stress of Aspergillus flavus in Response to Cinnamaldehyde Vapor.

Cinnamaldehyde (CA), a natural plant extract, possesses notable antimicrobial properties and the ability to inhibit mycotoxin synthesis. This study investigated the effects of different concentrations of gaseous CA on A. flavus and found that higher concentrations exhibited fungicidal effects, while lower concentrations exerted fungistatic effects. Although all A. flavus strains exhibited similar responses to CA vapor, the degree of response varied among them. Notably, A. flavus strains HN-1, JX-3, JX-4, and HN-8 displayed higher sensitivity. Exposure to CA vapor led to slight damage to A. flavus, induced oxidative stress, and inhibited aflatoxin B1 (AFB1) production. Upon removal of the CA vapor, the damaged A. flavus resumed growth, the oxidative stress weakened, and AFB1 production sharply increased in aflatoxin-producing strains. In the whole process, no aflatoxin was detected in aflatoxin-non-producing A. flavus. Moreover, the qRT-PCR results suggest that the recovery of A. flavus and the subsequent surge of AFB1 content following CA removal were regulated by a drug efflux pump and velvet complex proteins. In summary, these findings emphasize the significance of optimizing the targeted concentrations of antifungal EOs and provide valuable insight for their accurate application.

Effects of different carbon sources on the oxidative stress tolerance of Aspergillus niger HY2 isolated from spoiled paddies.

Fungi often experience oxidative stress in response to the environment during growth. In this study, Aspergillus niger HY2, whose presence easily results in paddy mildew, was used to investigate the effects of different carbon sources on morphological development, reactive oxygen species (ROS) metabolites, and antioxidant enzymes activities. Morphological development mainly includes the changes in conidial production and colony diameter. ROS metabolites production include the content of hydrogen peroxide (H2O2), superoxide anion (O2·-), and malondialdehyde (MDA). The results indicated that A. niger HY2 adapted to H2O2 exposure by decreasing growth and increasing the activities of some antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx). Different carbon sources also affected the expression of the developmental-specific gene flbA and the oxidative stress tolerance-related gene cat. When incubated with glucose, sucrose, and xylose as carbon sources, A. niger exhibited stronger oxidative stress tolerance, but when incubated with maltose as a carbon source, A. niger exhibited relatively poor oxidative stress tolerance. Our results can provide a theoretical basis for further understanding mechanisms of metabolic adaptation and developing targeted strategies to control the spoilage caused by A. niger.

Involvement of AprD in regulating biofilm structure, matrix secretion, and cell metabolism of meat-borne Pseudomonas fragi during chilled storage.

Pseudomonas fragi is by far one of the most threatening species in the spoilage of chilled meat that is stored under aerobic conditions. The membrane protein AprD is a well-established regulator controlling protease secretion in Pseudomonas spp. However, its exact roles in modulating metabolic pathways and spoilage potential of P. fragi at the molecular level remain undefined. Here, an in-frame deletion mutation of aprD was used to explore the impacts on their biofilm structure, matrix secretion, and cell metabolism. The results showed that ΔaprD formed relatively disorganized loose aggregation in biofilm, resulting in a thinner structure and more dead cells. Meanwhile, marked changes in the content of extracellular carbohydrates and proteins were observed. Furthermore, intracellular metabolomic profiling revealed the involvement of aprD in several cellular metabolic pathways, mostly including the carbohydrate pathway, amino acid pathway, and nucleotide pathway, while the characterization of extracellular metabolism clarified the variations in the spoilage-related metabolites (e.g., creatine, IMP, spermine, fatty acids, amino acids, and oligopeptides) could be highly correlated with aprD deletion. In this finding, we indicated that aprD could be responsible for cell reproduction and in situ spoilage potential of P. fragi NMC25 during chilled storage by controlling related metabolism and nutrients utilization. Thus, our results will contribute to an improved understanding of the regulatory mechanism of aprD gene in meat spoilage contaminated with P. fragi, which can be valuable to ensure the quality and safety of meat.

Isolation and identification of immunomodulatory selenium-containing peptides from selenium-enriched rice protein hydrolysates.

The RAW264.7 cell model was employed to screen immunomodulatory selenium-containing peptides from selenium-enriched rice protein hydrolysates (SPHs). Moreover, the selenium-containing peptides of high-activity protein hydrolysates were purified by Sephadex G-25, and identified by reversed phase ultra performance liquid chromatography coupled with triple quadrupole time-of-flight mass spectrometry. The results showed that 25 peptide sequences containing selenomethionine (SeMet) information above 90% of probability confidence were found in a fraction of alcalase hydrolysates. SeMDPGQQ and TSeMMM of 100% probability confidence were speculated as two novel selenium-containing peptide sequences. The artificially synthesized peptide TSeMMM was subsequently verified by an excellent immunomodulatory activity at a concentration of 80 µg/mL. In conclusion, the immunomodulatory activity of SPHs was correlated to SeMet sequence in the structure of selenium-containing peptides, and TSeMMM with a stronger immunomodulatory activity demonstrated potential as functional food additives for improving human health.

Analysis on Metabolic Functions of Stored Rice Microbial Communities by BIOLOG ECO Microplates.

Microbial contamination has been a pervasive issue during the rice storage and triggers extensive researches. The metabolism of microorganisms was proved as an indicator to mirror the degree of microbial contamination. It is necessary to develop a scientific method to analyze the metabolism of rice microbial communities, thereby monitoring the microbial contamination. In this study, the metabolism of rice microbial communities in different storing-year were investigated by BIOLOG ECO microplates. The three rice samples were respectively stored for 1-3 years. The related indicators of BIOLOG ECO microplates were determined, including average well-color development (AWCD) of carbon sources and three metabolic functional diversity indices. The results showed that there were significant differences in the AWCD of all carbon sources among the three rice microbial communities (p < 0.05), and the functional diversity indices except Simpson index showed significant differences (p < 0.05). Additionally, the three rice microbial communities differed significantly in the metabolic utilization of carboxylic acids and miscellaneous (p < 0.05), and there were, however, no significant differences in the other four types of carbon sources. Furthermore, principal component analysis revealed that the microbial communities of stored rice had obviously different metabolic functions in different storage period. Therefore, the study indicated that the BIOLOG ECO microplate was applicable to evaluate the metabolic functions of rice microbial communities, and carboxylic acids and miscellaneous were two crucial parameters of carbon sources to identify the metabolic differences of microbial communities, a case in which it reflected the conditions of rice microbial contamination.

The Correlation Between In Vitro Antioxidant Activity and Immunomodulatory Activity of Enzymatic Hydrolysates from Selenium-Enriched Rice Protein.

The antioxidant and immunomodulatory activities of selenium-enriched rice protein hydrolysates (Se-PH) were evaluated by a cellular antioxidant activity test and macrophage proliferation and phagocytosis assays, respectively. The results showed that trypsin hydrolysate provided the highest proliferation rate of 60.91% at a concentration of 100 µg/mL. Moreover, a remarkable rise in the phagocytosis rates for trypsin hydrolysate (64.1%) and pepsin-trypsin hydrolysate (54.5%) was observed when the sample concentrations were increased to 50 µg/mL. A positive correlation was found between the phagocytic ability of macrophages and both the selenium concentration and the degree of hydrolysis of Se-PH, and the correlation coefficients R obtained were 0.792 and 0.930 (P < 0.05), respectively. The capacity of Se-PH to inhibit the oxidation of dichlorodihydrofluorescein had a significant negative correlation with the phagocytic ability of macrophages (R = -0.840, P < 0.05). In conclusion, a positive correlation was found between the antioxidant activity and the immunomodulatory activity of Se-PH, which could be used as potential functional food additives for improving human health.

Protection mechanism of Se-containing protein hydrolysates from Se-enriched rice on Pb2+-induced apoptosis in PC12 and RAW264.7 cells.

This study aimed to investigate the protection mechanism of Se-containing protein hydrolysates (SPH) from Se-enriched rice on Pb2+-induced apoptosis in PC12 and RAW264.7 cells. Results showed that SPHs could alleviate Pb2+-induced morphological changes of apoptosis and the loss of mitochondrial transmembrane potential in both cell types. Besides this, SPHs could significantly reduce the activation of caspase-3, -8, -9 induced by Pb2+, reverse the Pb2+-induced upregulation of Bax and release of cytochrome C, and downregulate Bcl-2 in cells. HPLC-ICP-MS and SEC-HPLC assays showed that SPHs were low molecular weight peptides (229.4-534.9Da), and the major Se species found in SPHs was SeMet. Taken together, these findings suggested that SPHs could possibly protect the cells against Pb2+-induced apoptosis via a caspase-dependent mitochondrial pathway, and the primary effective constituents in SPHs were SeMet and Se-containing peptides, suggesting that SPHs might be a novel potential candidate to improve the health of people with Se deficiency or in Pb-contaminated areas.

Protective effects of Se-containing protein hydrolysates from Se-enriched rice against Pb(2+)-induced cytotoxicity in PC12 and RAW264.7 cells.

The protective capacity of Se-containing protein hydrolysates with molecular weight below 1kDa (SPHs-3), against Pb(2+)-induced damage in PC12 and RAW264.7 cells, was investigated in this study. The cell viability, levels of reactive oxygen species (ROS), lactate dehydrogenase (LDH), superoxide dismutase (SOD), nitric oxide (NO), malondialdehyde (MDA) and glutathione (GSH) in cell were analyzed. Results showed that 100µg/ml of SPHs-3 pretreatment could significantly increase cell viability by 24.9% and 23.0% in Pb(2+)-treated PC12 and RAW264.7 cells, respectively (P<0.01). The levels of ROS, NO, LDH and MDA were reduced by 32.2%, 68.2%, 79.7% and 73.7% in 100µg/ml SPHs-3 pretreated PC12 cells, respectively (P<0.01). SPHs-3 pretreatment was also associated with increases of SOD activity and GSH content in cells. In conclusion, SPHs-3 could protect cells against Pb(2+)-induced cytotoxicity, suggesting that Se-enriched rice may be a feasible candidate to improve health standard of the Pb(2+)-pollution population.

Assessment of Clostridium perfringens spore response to high hydrostatic pressure and heat with nisin.

The elimination of spores from low-acid foods presents food-processing and food-safety challenges to high-pressure processing (HPP) developers as bacterial spores are extremely resistant to pressure. Therefore, the effects of pressure (400-800 MPa), temperature (35-95 °C), and nisin (0-496 IU/mL) on the inactivation of Clostridium perfringens AS 64701 spores at various pressure-holding times (7.5-17.5 min) were explored. A second-order polynomal equation for HPP- and nisin-induced inactivation of C. perfringens spores was constructed with response surface methodology. Experiment results showed that the experimental values were shown to be significantly in agreement with the predicted values because the adjusted determination coefficient (R (Adj)²) was 0.9708 and the level of significance was P < 0.0001. The optimum process parameters (obtained by solving the quadratic polynomal equation) for a six-log cycle reduction of C. perfringens AS 64701 spores were pressure of 654 Mpa, temperature of 74 °C, pressure-holding time of 13.6 min, and nisin concentration of 328 IU/mL. The validation of the model equation for predicting the optimum response values was verified effectively by ten test points that were not used in the establishment of the model. Compared with conventional HPP techniques, the main process advantages of HPP-nisin combination sterilization in the UHT milk are, lower pressure, temperature, natural preservative (nisin), and in a shorter treatment time. The synergistic inactivation of bacteria by HPP-nisin combination is a promising and natural method to increase the efficiency and safety of high-pressure pasteurization.