Isolation and Identification of a High-Yield Ethyl Caproate-Producing Yeast From Daqu and Optimization of Its Fermentation

Baijiu is an important fermented product in China. A yeast named YX3307 that is capable of producing a large amount of ethyl caproate (EC) was isolated from Daqu, a crude fermentation starter for Baijiu. This yeast was identified as Clavispora lusitaniae on the basis of its morphological properties, physiological and biochemical characteristics, and 26S rDNA sequence. Single-factor experiments were conducted to obtain the optimum fermentation conditions for EC production by YX3307. The highest EC yield (62.0 mg/L) from YX3307 was obtained with the following culture conditions: inoculum size 7.5% (v/v), seed cell age 30 h, sorghum hydrolysate medium (SHM) with a sugar content of 10 Brix and an initial pH of 6.0; incubation at 28°C with shaking at 180 rpm for 32 h; addition of 10% (v/v) anhydrous ethanol and 0.04% (v/v) caproic acid at 32 and 40 h, respectively, static culture at 20°C until 72 h. YX3307 synthesized more EC than ethyl acetate, ethyl lactate, ethyl butyrate, and ethyl octanoate. An intracellular enzyme or cell membrane enzyme was responsible for EC synthesis. YX3307 can produce many flavor compounds that are important for high-quality Baijiu. Thus, it has potential applications in improving the flavor and quality of Baijiu.

Influence of Ethyl Caproate on the Size of Lipid Vesicles and Yeast Cells

Ethyl caproate (EC) is a key flavor component of sake. Recently, in sake brewing, an effort has been underway to increase the content of aromatic components such as EC. However, the function of EC in yeast cells remains poorly understood. Therefore, we investigated the effects of EC using cell-sized lipid vesicles. We found that vesicle size decreases in a concentration-dependent manner when EC is contained in lipid vesicles. Furthermore, yeast experiments showed that a strain producing high quantities of EC in its stationary phase decreased in size during EC production. Given caproic acid’s (CA) status as the esterification precursor of EC in yeast, we also compared lipid vesicles containing CA with those containing EC. We found that CA vesicles were smaller than EC vesicles of the same concentration. These results suggest that EC production may function apparently to maintain cell size.

RESEARCH OF TECHNOLOGICAL PARAMETERS AND CRITERIA FOR EVALUATING DISTILLATE PRODUCTION FROM DRIED JERUSALEM ARTICHOKE

ABSTRACT In this paper, it is proposed to use dried Jerusalem artichoke as a raw material for distillate production. The purpose of the research was to develop a distillate technology from dried Jerusalem artichoke and to determine the criteria for assessing its quality. The work revealed patterns of changes in the concentrations of the main distillate volatile components, depending on the strength of the fermented wort and its composition. It was established that the increase in the strength of fermented wort by 2.0-2.5 %, leads to an increase in the yield of distillate on average by 3.0 % and enriching it with valuable volatile components. A new technical solution was proposed, based on the regulation of the strength of fermented wort from Jerusalem artichoke due to the addition of distillate. A high degree of correlation was established between the tasting evaluation of Jerusalem artichoke distillates and the concentration of 1-propanol, ethyl caproate, ethyl caprylate, the sum of enanthic ethers, the ratio of C3 and C4 alcohols, and was found the ratio of the amount of enanthic ethers to ethyl acetate. It is proposed to use the methanol concentration, the content of enanthic ethers, the total content of carbonyl compounds, the ratio of the sum of enanthic ethers to the concentration of ethyl acetate as criteria for assessing the quality of distillates from dried Jerusalem artichoke

Fermentation process of mulberry juice-whey based Tibetan kefir beverage production

Mixture of mulberry juice and whey was evaluated as a potential substrate for the production of a beverage by Tibetan kefir grains. Different mulberry juice addition was used. Acidity, pH, volatile flavour compounds as well as microbial communities were determined during 40 h of fermentation at 18°C. Gas chromatography-mass spectroscopy (GC-MS) analysis revealed that ethanol and 3-methyl-1-butanol were dominant alcohols, and ethyl caprylate, ethyl caprate, ethyl acetate and ethyl caproate were the most dominant ester compounds. The microbial communities of fermented beverage were close to kefir grains indicating that they had similar microbial communities gradually during the fermentation process. Lactococcus was frequently detected at the beginning and then Lactobacillus rapidly proliferated after acclimatizing to the fermentation environment. Acetobacter was steadily increasing during the fermentation process. For the fungi, Candida was frequently detected with the highest abundances in almost all samples.