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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.

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.

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.

This study aimed to investigate the protection mechanism of Se-containing protein hydrolysates (SPH) from Se-enriched rice on Pb

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 (P0.05), 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, P0.05). 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.

The stability and isomerization of lycopene by high hydrostatic pressure (HHP) were evaluated. Lycopene standard in hexane and tomato puree were pressurized at 100, 200, 300, 400, 500 and 600 MPa for 12 min at controlled temperature (20 ± 1 °C). After application of pressure, samples were stored at refrigerator temperature (4 ± 1 °C) and ambient laboratory temperature (24 ± 1 °C) under lightproof conditions. HPLC and spectral analysis were employed to analyze lycopene and its cis-isomers in samples after HHP and after 2, 4, 8 and 16 days of storage. High pressure affected the content of total lycopene and the percentage of the presumptive 13-cis isomer, both in lycopene solution and tomato puree. Furthermore, the higher the storage temperature, the greater was the loss of total lycopene and the higher the percentage of 13-cis isomer. However, the pressure effects were widely different in lycopene solution and tomato puree. 500 and 600 MPa led to a significant (P < 0.05) loss of lycopene while 400 MPa retained the maximal stability of lycopene in solution. The highest stability of lycopene was found when tomato puree was pressurized at 500 MPa and stored at 4 ± 1 °C.

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

China is the predominant paddy grower in the world. Annual paddy output is 166.20 million tonnes which is approximately 36.9% of the world output. China's total output ranks first among more than 100 paddy-cultivating countries. Paddy is a seasonal crop, and China is a country, with 1.3 billion people, As a consequence, paddy, and milled rice storage and reserves are extremely significant in China. There are three major types of storage facilities: horizontal warehouses of Soviet Union origin, bins, and silos. China has large territory and its climate, field and drainage conditions are quite varied. Appropriate paddy storage facilities must be chosen to ensure the safe storage of rice under different ecological conditions. The overall losses for paddy and rice during storage are the same though the degree is varied. There are two types of losses, namely quality and quantity. China's grain (including paddy, wheat, and maize) storage loss is about 0.2% at national reserve level, while rural household storage losses amount to 7-13%. The keeping qualities of the abovementioned grains, from the best to the worst, are wheat, paddy, and maize. The main causes of grain storage loss in China can be summarized as insects in the south and moisture in the north. Moisture content and temperature are the most important parameters affecting the stability of the stored rice. To ensure the safe storage of rice, storage techniques such as conventional storage, low-temperature storage, controlled-atmosphere storage and chemical storage are all practiced in China. China's paddy storage loss is low in terms of quantity. The cost of China's paddy storage is relatively low, at about 80 PBY RMB per tonne.