As a famous fruit worldwide, citrus is susceptible to green mold caused by Penicillium digitatum, which causes large economic losses every year. ε-Poly-L-lysine (ε-PL) is a novel preservative with strong inhibitory effects on fungi, and has the capacity to induce disease resistance in fruit, but the mechanism has been reported rarely, especially in citrus. In the present study, 800 μg/mL ε-PL and P. digitatum spores were inoculated in two different wounds on the citrus pericarp at an interval of 24 h. The results revealed that ε-PL inhibited that the development of green mold without direct contact with P. digitatum, indicating that the disease resistance of citrus was activated. Transcriptome analysis revealed that ε-PL activated amino acid metabolism and phenylpropanoid biosynthesis. Besides, the accumulation of glutamic acid, proline, arginine, serine, lysine, phenylalanine, and tyrosine were changed during storage. In phenylpropanoid biosynthesis, ε-PL increased phenylalanine ammonia-lyase (PAL), cinnamate 4-hydroxylase (C4H), and 4-coumarate:coenzyme A ligase (4CL) activities and total phenolic and flavonoid contents. Importantly, among these phenolic compounds, ε-PL promoted the accumulation of individual phenolic compounds including ferulic acid, chlorogenic acid, p-coumaric acid, caffeic acid, gallic acid, catechins, epicatechin, and narirutin. In conclusion, ε-PL enhanced the resistance of citrus through amino acid metabolism and accumulation of phenolic compounds. These results improved the knowledge of the mechanism of ε-PL–induced disease resistance and provided a fresh theoretical basis for the use of ε-PL in postharvest citrus preservation.

Refrigeration is considered a prime technology for preserving meat products. Temperature alterations are commonly ignored by industry during refrigeration, which have impacts on product quality. Thus, we conducted research on pork loin and salmon fillets that were preserved for 0, 5, 9, 12, and 15 d, where different temperature fluctuations and shocks were established on 4 °C. Data revealed that several meat parameters such as total volatile basic nitrogen, total viable count, and lipid oxidation were significantly changed in the ±2 °C fluctuations group compared with the constant temperature group. Additionally, both the temperature fluctuations and shocks groups had accelerated myofibril protein degradation, while desmin expression and species richness/diversity of bacteria were significantly reduced in the ±2 °C fluctuations group compared with the constant temperature group. Briefly, temperature fluctuations and shocks accelerated the destruction of muscle structural integrity. Furthermore, both conditions accelerated meat spoilage by progressively expanding the water-loss channels, which can reduce meat edibility. This study provides a new theoretical basis for the proper use of refrigerated temperatures for storing meat products.

Seed-borne bacterial pathogens cause severe yield loss and biotoxin contamination in rice, leading to increasing concern on the global food supply and environmental safety. Plant native microbes play an important role in defending against diseases, but their actions are often influenced by the chemical fungicides applied in the field. Here, Bacillus licheniformis mmj was isolated from rice spikelet, which uniquely showed not only fungicide-responsiveness but also broad-spectrum antimicrobial activity against major rice bacterial pathogens including Xanthomonas oryzae pv. oryzae, Burkholderia plantarii and Burkholderia glumae. To understand the hallmark underlying the environmental adaptation and antimicrobial activity of B. licheniformis mmj, the genome sequence was determined by SMRT and subjected to bioinformatics analysis. Genome sequence analysis enabled the identification of a set of antimicrobial-resistance and antibacterial activity genes together with an array of harsh environment-adaptive genes. Moreover, B. licheniformis mmj metabolites were analyzed with gas chromatography coupled to triple quadrupole mass spectrometry, and the volatile components that were linked with the antimicrobial activity were preliminarily profiled. Collectively, the present findings reveal the genomic and metabolic landscapes underlying fungicide-responsive B. licheniformis, which offers a new opportunity to design harsh environment-adaptive biopesticides to cope with prevalent bacterial phytopathogens.

Although surface-enhanced Raman spectroscopy (SERS) substrates have achieved high sensitivity, it is still difficult to apply these SERS protocols to the on-site detection of real samples due to the SERS substrate being fabrication-complexed, unstable, reproducible, or unable to be applied in batch production. Here, a large-scale ordered two-dimensional array of Au nano-hemispheres was developed through electron beam vaporization of Au onto the easy-available commercialized anodic aluminum oxide (AAO) template with two-layer nanostructures of different diameters. The uniform Au nano-hemisphere is reliable for SERS detection of malachite green (MG) due to the relative standard deviation (RSD) of the SERS intensities at different locations less than 10%. With the optimized excitation wavelength, solvent effect and pH environment, the linear range of MG detection spans from 10–10 to 10–6 mol/L with a limit of detection (LOD) of 4×10–10 mol/L. The enhancement factor can reach 1.2×106. After extraction with acetonitrile and dichloromethane, MG in the spiked tilapia was detected with satisfactory recovery. The results indicate that the Au nano-hemisphere array can be expected to greatly facilitate SERS practical applications in detecting harmful food additives and chemicals due to the advantages of chemical inertness, physical robustness, simple fabrication, controllability, large-area uniformity, and large-batch production.

Polycarboxylic acids (PACs) are important metabolic products in almost all living bodies, yet current analytical methods for detection of PACs in tea beverages are still unsatisfactory due to the complex matrix and physicochemical properties of PACs. In this work, a rapid method was developed for the simultaneous determination of 7 PACs, including tartaric acid, α-ketoglutaric acid, malic acid, malonic acid, cis-aconitic acid, succinic acid, and fumaric acid, in beverages, based on selective removal of the matrix in combination with liquid chromatography–mass spectrometry (LC-MS) analysis. By stirring with activated carbon and the Na2CO3 solution, the matrix in beverages was selectively removed, and PACs were almost retained in the supernatant of diluted Na2CO3 solution. Under optimized parameters, the limit of quantitation for the PACs was in the range of 1–50 ng/mL, and the content of the PACs in 8 beverages was determined with the recovery range of 72.2%–122.5%. The contents of malic acid, malonic acid, and succinic acid in tea beverages were found to be greater than those in non-tea beverages. Moreover, the concentration of these PACs in beverages was found to be multiplied many times in their deterioration period, especially for fumaric acid and α-ketoglutaric acid. These results indicated that PACs can be selected as a criterion to differentiate qualified tea beverages from spoiled beverages.