Drying profoundly impacts the quality of Yunnan large-leaf green tea. However, the metabolomic mechanisms underlying the quality differences between sun drying and hot-air drying have not been comprehensively elucidated. In this study, two drying methods were compared using gas chromatography-tandem mass spectrometry, ultra-performance liquid chromatography-tandem mass spectrometry, and sensory evaluation. Using widely-targeted metabolomics, 2295 metabolites were detected and 275 differential metabolites dominated by flavonoids, phenolic acids, and lipids, were screened. Furthermore, 17 of the 81 volatile compounds detected showed significantly different relative contents. Sensory evaluation revealed significant differences in taste (89 vs 81), aroma (89 vs 84), and liquor color (86 vs 84) between sun-dried green tea and hot-air-dried green tea. Notably, sun-dried tea accumulated free fatty acids contributing to floral and fruity aromas, whereas hot-air-dried tea accumulated glycerolipids and lysophospholipids. The present study reveals the metabolic basis driving flavor differentiation between sun-dried and hot-air dried green tea.
This study addresses the need to investigate high-quality lactic acid bacteria and promote the standardized development of the fermented pickle industry by formulating a process to efficiently prepare a direct-vat-set (DVS) starter culture of Lactiplantibacillus pentosus JX3 suitable for pickle fermentation. The strain JX3 was isolated from traditional fermented Jiangxi pickled peppers identified as L. pentosus via 16S rRNA sequencing. The methodology implemented in this study involved optimizing cultivation conditions by response surface methodology (total acid production as the response), systematically screening centrifugation parameters and lyoprotectant formulations, assessing the storage stability of the freeze-dried powder at −20 ± 1 °C, 4 ± 1 °C, and 20 ± 5 °C for 180 d, and comparing the fermentation performance of JX3 in pickled peppers with that of Weissella cibaria LAB1, Weissella hellenica LAB6, and spontaneous fermentation. The results revealed that the optimal cultivation conditions were an inoculum size of 33 mL/L, an initial pH of 6.0, and a temperature of 30 °C, yielding a total acid content of 18.60 g/L. A composite lyoprotectant consisting of 200 g/L skim milk and 90 g/L trehalose, mixed with the cell paste at a 1:1 ratio (w/w), achieved a freeze-drying survival rate of 89.06 %. The powder retained survival rates of 85.61 % after 30 d and 49.45 % after 180 d of storage at −20 ± 1 °C, whereas no viable cells were detected after 90 d at 20 ± 5 °C. Nitrite was detected only transiently and was undetectable in all treatments from day 20. JX3-fermented peppers appeared brighter by visual inspection. Headspace gas chromatography-ion mobility spectrometry (HS-GC-IMS) detected 76 volatile signals, of which 65 were tentatively identified; JX3 had the maximum relative signal abundance and the highest proportions of ester and aldehyde signals. Principal component analysis (PCA) and orthogonal partial least squares-discriminant analysis (OPLS-DA) separated the volatile fingerprints of the three starters. Thirty-three signals (23 compounds) had a relative odor activity value (ROAV) ≥ 1, and 11 signals had a variable importance in projection (VIP) score ≥ 1. The integrated preparation process gave a freeze-dried powder that retained part of its viability for 180 d at −20 ± 1 °C and performed well in pickled peppers, which supports further development of L. pentosus JX3 as a starter.
This study evaluates the efficiency of biodegradable bilayer packaging materials based on thermoplastic starch (TPS) and polyhydroxyalkanoates (PHAs) containing ferulic acid (F) or beer bagasse extract (E) obtained by subcritical water extraction as active agents (60 g/kg) for refrigerated pork meat preservation. Bilayers (Bilayer-F, Bilayer-E) were characterized and the physicochemical and microbiological quality of the meat packaged in these active biodegradable materials along with a free-active film and a commercial polyethylene bag, was analyzed. The results showed that the incorporation of both active agents did not significantly alter the water barrier capacity of the films but acted as plasticizers, increasing the elongation at break up to 55%. In preservation trials, all bilayers significantly inhibited microbial growth compared to commercial bags, likely due to their superior oxygen barrier capacity. Specifically, Bilayer-F exhibited the highest antimicrobial and antioxidant efficacy, achieving a 2-log reduction in total viable counts and extending pork microbiological shelf life by approximately 7 days. Conversely, Bilayer-E showed limited effectiveness due to lower bioactivity compared to pure ferulic acid. While bilayers resulted in higher weight loss than commercial bags due to their inherent water vapor permeability, Bilayer-F represents a promising sustainable alternative for maintaining fresh meat quality. Overall, these results demonstrate that TPS-PHA bilayers incorporating ferulic acid represent a highly effective active packaging system to extend the shelf life of fresh pork meat, whereas the complex beer bagasse extract was not effective in preservation.
