Bhat et al.
2009). Further the studies revealed that yeasts had high tolerance to acidity
that facilitated their survival and growth in fruit juices that have pH values
below the tolerance level for several other microorganisms. The substrate
used for yeast metabolism was mainly monosaccharides like glucose,
fructose and mannose that were metabolised into two molecules of
pyruvate in the glycolysis, also called Embden-Meyerhof-Parnas pathway
(EMP pathway). The pyruvate was further reduced to ethanol (C 2 H 5 OH)
and carbon dioxide by the enzymes pyruvate decarboxylate and alcohol
dehydrogenase. The overall chemical reaction is presented as:
C 6 H 12 O 6 2
CH 3 CH 2 OH +2CO 2 + 55 Kcal
Carbon dioxide
Results indicated that theoretically, the yield of ethanol was about 65%
was reduced to about 60% due to loss of glucose for production of minor
compounds and growth.
Fleet et al., (2003) explored that the Saccharomyces genus was most
commonly used in beverage industry due to their higher capacity to
ferment sugars which allowed them to colonize sugar-rich media over
other yeasts, which were not tolerant to alcohol. They reported that the
imposition of Saccharomyces cerevisiae along the AF was associated with the
during harvesting and the high concentration of sugar in the must.
Joshi et al., (2002) studied that for cider production, the strains commonly
used belonged to the species Saccharomyces cerevisiae or Saccharomyces
bayanus andthe choice of yeast strain as starting culture could have a
revealed that during fermentation of apple juice, the rate and content of
ethanol, sugars, tannins, esters, methanol and volatile acids were some of
Kocher et al., (2006) studied the conversion ofsugarcane juice to ethanol
by Saccharomyces cerevisiae . This ethanol was used for vinegar production
using adsorbed (bagasse, corn cobs and wood shavings) and entrapped
(calcium alginate) cells of Acetobacteraceti NRRL 746. All the three adsorbed
carrier materials were statistically similar for acetic acid production and
produced acidity from 5.9 to 6.7% after 28 days of submerged fermentation.