Lawn-harvest method uses a solid medium (e.g., tryptic soy agar, TSA) to produce bacterial lawns and is widely accepted for the culture of microorganisms in microbial studies of low-moisture foods (LMFs, foods with water activity less than 0.85). It produces desiccation-tolerant cells with higher D-values in LMFs; however, little is known about the molecular mechanisms underlying bacterial resistance . Salmonella enterica Enteritidis PT 30 ( S. Enteritidis), the most pertinent pathogen in LMFs, was cultured in TSA and tryptic soy broth (TSB). Cells were harvested and inoculated on filter papers to assess their performance under a relative humidity of 32 ± 2%. Transcriptome analysis of cultured cells during long-term desiccation (24, 72, and 168 h) was conducted in TruSeq PE Cluster Kit (Illumina) by paired-end methods. Lawn-cultured S. Enteritidis cells have stronger survivability (only decreased by 0.78 ± 0.12 log after 130 d of storage) and heat tolerance (higher D/β value) than those from the broth method. More desiccation genes of lawn-cultured cells were significantly upregulated from growth to long-term desiccation. Differentially expressed genes were the most enriched in the ribosome and sulfur metabolism pathways in the lawn- and broth-cultured groups. This study tracked the transcriptomic differences between two cultured groups in response to long-term desiccation stress and revealed some molecular mechanisms underlying their different suitability in microbial studies of LMFs.
This paper highlighted the structural changes of rice starch complexed with green tea catechin and lemon peel caffeic acid under thermomechanical-assist low moisture, and their prebiotic functions during in vitro digestibility and fermentation were further explained. Extruded starch with caffeic acid, characterized by enhanced short-range order, a distinct fractal structure, and a V-amylose helical arrangement, exhibited slower glucose release due to V-type inclusion crystalline structures and strong hydrogen bondings. Additionally, extruded starch with catechin or caffeic acid changed the composition of gut microbiota by increasing the proliferation of good bacteria and reducing pathogenic microorganisms, which led to a greater synthesis of short-chain fatty acids. According to a PICRUSt2 analysis, the extruded starch with caffeic acid may trigger metabolic alterations via altering the gut flora and increasing bile acid metabolism. Thus, extruded starch with caffeic acid demonstrates significant potential as a prebiotic for developing nutritionally tailored starch-based foods.
The high temperature induces conformational changes in β-glucosidase, making it inactive and limiting its application field. In this paper, the effect of trehalose on the thermostability of β-glucosidase from low-moisture Hevea brasiliensis seeds was investigated. The results showed that the residual enzyme activities of β-glucosidase supplemented with trehalose after high-temperature treatment were significantly higher than that of the control group. The improvement of thermostability could be explained by low-field nuclear magnetic resonance (LF-NMR) and molecular dynamics (MD) simulations at the molecular level. Moreover, adding trehalose increased the water activity and water content of β-glucosidase, leading to a more stable conformation. Trehalose replaced some water and formed a stable network of hydrogen bonds with protein and surrounding water. The glass formed by trehalose also reduced molecular movement, thus providing good protection for enzymes.
危险品化学品经营许可证（带存储）