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

Glucose

Ethanol

Carbon dioxide

Results indicated that theoretically, the yield of ethanol was about 65%

(v/w)ȱofȱtheȱinitialȱglucoseȱcontent,ȱbutȱtheȱactualȱconversionȱefficiencyȱ

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

increasingȱpresenceȱofȱethanol,ȱtheȱanaerobicȱconditions,ȱtheȱuseȱofȱsulfitesȱ

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

highȱimpactȱonȱtheȱflavourȱprofileȱofȱfermentedȱbeverages.ȱTheȱstudiesȱ

revealed that during fermentation of apple juice, the rate and content of

ethanol, sugars, tannins, esters, methanol and volatile acids were some of

theȱqualityȱcharacteristicsȱthatȱcouldȱbeȱaffectedȱbyȱtheȱspecificȱyeastȱstrain.

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.

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