A Lactobacillus strain named SMF-L5 from traditional fermented mandarin fish was isolated using MRS medium with bromocresol green and identified as Lactobacillus sakei by morphological, physiological and biochemical assays and 16S rDNA sequence analysis. L. sakei SMF-L5 grew well in MRS liquid medium, entered the stable growth period after 14 h, and produced the highest viable cell count of 7.0 × 10⁹ CFU/mL. The production of lactic acid of the strain was 10 g/L after 24 h cultivation. The optimal culture conditions were as follows: culture temperature 30.9 ℃, initial pH 6.15 and inoculum amount 1.94%. Strain SMF-L5 had tolerance to 0.08 g/mL NaCl, and obvious inhibitory effects on Escherichia coli, Staphylococcus aureus. The fermented mandarin fish inoculated with L. sakei SMF-L5 had superior color, texture and flavor than spontaneously fermented mandarin fish. These results showed that L. sakei SMF-L5 has the potential for application as an excellent starter in the industrial production of smelly mandarin fish.

To investigate the inhibitory mechanism of small peptides on carbohydrate digestion, α-amylase and α-glucosidase inhibitory fractions from the water extract and the gastropancreatic digest of dry-cured ham muscle of Wanzhe spotted pigs were separated, purified, identified, and screened for peptide sequences. And the quantum chemical calculation was used to calculate structural and charge parameters including the distribution and energy of the frontier orbitals, electrostatic charge distribution and bond length, in order to speculate the active sites. It was found that the particle size of ham muscle decreased and its hypoglycemic activity increased after proteolysis. Two (S-Ⅰ and S-Ⅱ) and three fractions (WY-Ⅰ, WY-Ⅱ and WY-Ⅲ) were obtained from the water extract and the digest after Sephadex column chromatography, respectively. Using mass spectrometry, 104 peptide sequences consisting of 8—24 amino acids were identified from fraction WY-Ⅱ and five sequences with Peptide Ranker scores greater than 0.7 were selected. The highest occupied orbitals of the five sequences were mainly distributed in the guanidine groups of arginine and the groups close to the amino-terminal end, while the lowest unoccupied orbitals were in the carboxyl terminals and nearby groups. Sequences with lower ΔE_L-H values, GPMGPSGPR, LGFGGPSGPNAGR and APAPAPAPAPPK, might be more active. According to Coulomb’s law, the active sites of these three peptides were located at —C₁₀₆H₁₀₈ of arginine, —C₁₀H₁₂ of leucine and —C₁₇₆H₁₇₇ of lysine, respectively. This study could provide theoretical support for understanding the blood glucose-regulating mechanism of peptides and the nutritional value of local pig breeds.

We undertook this work in order to study the correlation between the microbial community composition and the characteristic flavor substances in stinky mandarin fish during the low-temperature fermentation process. 16S rDNA high-throughput sequencing was used to determine the microbial community composition. Gas chromatography-mass spectrometry (GC-MS) was used to evaluate the volatile flavor substances, and the characteristic flavor substances were identified by multivariate statistical analysis combined with odor activity value (OAV). The correlation between the microbial flora and the characteristic flavor substances was analyzed by Spearman correlation analysis. The results showed that Lactobacillus sakei, Hafnia alvei and Serratia plymuthica were the dominant microorganisms during the low-temperature fermentation process. A total of 81 volatile flavor substances were detected, and the characteristic flavor substances identified included 1-octen-3-ol, eucalyptol, linalool, hexanal, heptanal, nonanal, trimethylamine, D-limonene, and o-cymene. L. sakei showed a significant positive correlation with linalool and o-cymene (P < 0.05). H. alvei and S. plymuthica were significantly positively correlated (P < 0.05) with the aroma substances D-limonene and linalool as well as the odorous substance trimethylamine (P < 0.05). The results provide a theoretical basis for developing functional starters and regulating the flavor quality of stinky mandarin fish.