Effects of Deep Sea Water (DSW) Nigari on the Alcohol Production of Yeasts Fermented in Acidic Roselle Extract

Abstract

The effects of deep sea water (DSW) nigari refined from DSW pumped from a depth of 400 m off Hualien, Taiwan, on the brewer's yeasts used in making a beverage based on roselle extract (pH 2.57) were investigated. Experimental results showed that the addition of DSW nigari (300 mg/L) produced a higher alcohol yield with yeast strains B1 (4.13% [vol/vol]), B6 (4.97% [vol/vol]), and Saccharomyces bayanus BCRC 21673 (3.00% [vol/vol]), in marked contrast to not adding DSW nigari to the three yeast strains (2.23, 1.77, and 0.77% [vol/vol] for B1, B6, and BCRC 21673, respectively). The results also indicated that the increase in alcohol yield was dose dependent when DSW nigari was used at 0, 150, 300, and 450 mg/L with strain B6. Although the addition of DSW nigari resulted in higher levels of viable cells than those in the control samples, they did not significantly differ from each other. A concentration of four individual metal chlorides (CaCl2, KCl, MgCl2, and NaCl) or a mixture of these metals equivalent to 300 mg of DSW nigari per L was added to investigate which major components of DSW nigari affect strain B6 with regard to growth and the production of alcohol and flavor compounds. The results revealed that Mg and Ca did not affect yeast growth, whereas K, Na, and the metal mixture did, although they were still less effective than DSW nigari. Furthermore, DSW nigari produced the highest yield of alcohol, followed by the metal mixture. No significant differences were observed between the individual metals and the control group. Addition of DSW nigari increased the amounts of ethyl acetate, isoamyl alcohol, and isobutanol produced; however, this phenomenon was not directly due to stimulation from alcohol acetyltransferase activity but was caused mainly by an increase in yeast growth.