During industrial handling, Lactococcus lactis needs to adapt to different culture conditions by regulating its metabolic pathways. Modifying culture conditions may be an important way to control the biomass and functional metabolites of lactic acid bacteria. In this study, we identified the differentially expressed genes and proteins of L. lactis under different culture conditions by integrating transcriptomics and proteomics. We also analyzed the data using a bioinformatic approach to reveal the regulatory mechanisms affected by culture conditions. The transcriptome and proteome studies indicated that different culture conditions (fructose, calcium ion, palmitic acid, low pH) affected gene and protein expressions. The levels of differentially expressed proteins did not significantly correlate with the expression levels of their corresponding genes. Our results highlight the importance of comparative transcriptomics and proteomics analyses. In this study, fructose and pH significantly affected sugar metabolism of L. lactis. When lactose was replaced by fructose, fructokinase expression was promoted, and fructose metabolism was accelerated, whereas starch and sucrose metabolism and galactose metabolism system were inhibited. Low pH may be beneficial to homofermentation of L. lactis, which may also metabolize galactose through the tagatose pathway and the Leloir pathway. Fatty acid metabolism and fatty acid biosynthesis were significantly downregulated under calcium ion and palmitic acid. The purine metabolism was upregulated under fructose treatment and downregulated under palmitic acid treatment.
Physalis pubescens L. is rich in natural pigments but has not yet been fully utilized. Ultrasound-assisted extraction of yellow pigment from Physalis pubescens L. was investigated by response surface methodology in this study. Optimal parameters were ultrasonic power of 29.21%, ultrasonic time of 14.41 min, and ultrasonic interval time of 10.55 s. The yield was 0.193% under optimal parameters. FRAP, ABTS, and superoxide radical scavenging activity of the yellow pigment were 6.11 ± 0.22 mmol/g, 2.80 ± 0.27 mmol/g, and 57281.5 ± 2749.5 U/g, respectively. The results showed that the yield of yellow pigment could be improved by ultrasonic-assisted extraction and the yellow pigment extracted by ultrasound had antioxidant activity.
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