β mercaptoethanol

(1) Enterococcus lactis S-15: A strain with a potent acid-producing ability and a weak proteinase-producing ability was isolated from the traditional fermented food, sour fish, in our laboratory. The strain was cultured twice in MRS medium at 37 °C for 12 h each time. After centrifugation (4 °C, 8000 × g, 5 min), the bacterial suspension was collected. The collected suspension was washed twice with sterile physiological saline solution (0.85% NaCl) and the optical density of the bacterial solution was adjusted to 10⁹ CFU/mL using a UV spectrophotometer (UV-1800, Shimadzu Co., Kyoto, Japan) to prepare the fermentation inoculum, which was used on the same day.
(2) Frozen green shrimp meat was purchased from the official flagship store on JD.com (https://item.m.jd.com). The shrimp meat was stored at -20 °C, ensuring that the same batch of materials was used for each experiment. Food-grade sodium chloride (NaCl) was purchased from a local supermarket in Zhenjiang, Jiangsu, China. Analytically pure chemicals including sodium dodecyl sulfate (SDS) and β-mercaptoethanol were supplied by Sinopharm Chemical Reagent Co., Ltd. in Shanghai, China.

D-(+)-glucose (C₆H₁₂O₆, MW 180.16), L-(+)-arabinose (C₅H₁₀O₅, MW 150.13), and D-(+)-xylose (C₅H₁₀O₅, MW 150.13) (All 99% purity) were purchased from Shanghai Macklin Biochemical Co., Ltd. (Shanghai, China). O-phthalaldehyde (OPA), disodium hydrogen phosphate, sodium dihydrogen phosphate, methanol, sodium dodecyl sulfate (SDS), borax, and β-mercaptoethanol were of analytical reagent grade and supplied by Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China).