Selection of Salt-Tolerance and Ester-Producing Mutant Saccharomyces cerevisiae to Improve Flavour Formation of Soy Sauce during Co-Fermentation with Torulopsis globosa.

Soy sauce, as a traditional seasoning, is widely favoured by Chinese and other Asian people for its unique colour, smell, and taste. In this study, a salt-tolerance Saccharomyces cerevisiae strain HF-130 was obtained via three rounds of ARTP (Atmospheric and Room Temperature Plasma) mutagenesis and high-salt based screening. The ethanol production of mutant HF-130 was increased by 98.8% in very high gravity fermentation. Furthermore, ATF1 gene was overexpressed in strain HF-130, generating ester-producing strain HF-130-ATF1. The ethyl acetate concentration of strain HF-130-ATF1 was increased by 130% compared to the strain HF-130. Finally, the soy sauce fermentation performance of Torulopsis globosa and HF-130-ATF1 was compared with T. globosa, HF-130, HF-130-ATF1, and Torulopsis and HF-130. Results showed ethyl acetate and isoamyl acetate concentrations in co-fermentation of T. globosa and HF-130-ATF1 were increased by 2.8-fold and 3.3-fold, respectively. In addition, the concentrations of ethyl propionate, ethyl caprylate, phenylethyl acetate, ethyl caprate, isobutyl acetate, isoamyl alcohol, phenylethyl alcohol, and phenylacetaldehyde were also improved. Notably, other three important flavour components, trimethylsilyl decyl ester, 2-methylbutanol, and octanoic acid were also detected in the co-fermentation of T. globosa and HF-130-ATF1, but not detected in the control strain T. globosa. This work is of great significance for improving the traditional soy sauce fermentation mode, and thus improving the flavour formation of soy sauce.

Multiple headspace solid-phase microextraction using a new fiber for avoiding matrix interferences in the quantitative determination of ethyl carbamate in pickles.

Multiple headspace solid-phase microextraction (HS-SPME) using a novel fiber coated with anilino-methyl triethoxy silicane-methacrylic acid/terminated silicone oil has been introduced as a useful pretreatment technique coupled to gas chromatography-flame ionization detector for the detection of ethyl carbamate in pickles. Anilino-methyl triethoxy silicane and methacrylic acid are put into use simultaneously with the aim to increase the hydrogen interaction strength between ethyl carbamate and the coating. In addition, the new fiber exhibits high thermal stability, good reproducibility, and long lifetime. Extraction temperature, extraction time, amount of desiccant, and amount of sample were well optimized to guarantee the suitability of multiple HS-SPME. Significant matrix interference was observed among various types of pickles and the multiple HS-SPME procedure was proved to be effective in avoiding the matrix effect by a complete recovery of the analyte. The method showed satisfactory linearity (0.1-100 mg kg(-1)), precision (4.25%, n = 5), and detection limit (0.038 mg kg(-1)). The accuracy of the method was evaluated by comparison with standard addition method and the results were statistically equivalent. The study indicates that the multiple HS-SPME procedure is simple, convenient, accurate, and low-cost, and most of all, can be used for quantitative analysis in complex matrix without matrix effect.