physicochemical

SCREENING OF YEAST ISOLATES AND PRODUCTION OF ALCOHOL
fermentation bottles containing 200 ml of sucrose
medium, two g of yeast extract powder and 100 ppm
of KMS at the rate of 5% under aseptic conditions.
The fruits of Kallipatti variety used in the
experiment were collected from local market of
Hyderabad, Andhra Pradesh, India. Over ripened fruits
with uniform quality were selected for the pulp
preparation. Sapota fruits washed with potable water
were used for preparation of pulp. Pulp was prepared
by removing peel and deseeding. Further, this pulp
was homogenized in a mixer and then diluted by using
water. Then the Brix which was 19.45, was adjusted
to 23 0 B by adding sugar solution to the pulp and
used in various treatments. The composition of
homogenized pulp was determined before starting of
fermentation - Reducing sugars: 7.62 g 100g -1 , Total
sugars: 11.85 g 100g -1 , TSS: 19.50 0 B and pH 5.4.
The standard culture Saccharomyces
cerevisiae (MTCC-172) obtained from the Institute
of Microbial Technology, Chandigarh (IMTECH) and
one of the best local isolate, AMY-2, were maintained
on Sabouraud Dextrose Agar slants. Inoculum was
built up by transferring pure culture inoculating into
the Sabouraud broth. Each of the mother culture was
used for inoculation of the pulp as per the
experimental plan and allowed for fermentation. Batch
fermentation of the inoculated pulp was carried out
in a number of reagent bottles with cultures
(Saccharomyces cerevisiae MTCC-172 &
Saccharomyces cerevisiae AMY-2), with different
pH’s (4.0, 4.5 & 5.0) and incubating at different
temperatures (ambient temp.- 30-38.6 0 C & controlled
temp.- 26 0 C), for a period of 3 days. Samples were
collected at 24 h intervals and centrifuged in a
centrifuge (Sigma) at 15,000 rpm for 10 min. They
were analysed for the alcohol content, total and
reducing sugars.
All the chemicals and reagents used in the
experimentation and analysis were of A.R. grade,
purchased from standard chemical companies. The
dehydrated media and chemicals of Himedia were
used for screening, growing and maintenance of yeast
cultures.
Reducing and Total sugars in the sapota pulp
was estimated by DNS method (Sadashivam and
Manickam, 2008). The total soluble solids content of
the pulp was determined by using ERMA hand
refractometer and expressed in Brix (Ranganna,
1986). pH of the fruit pulp was determined by digital
pH meter. Alcohol content in fermented pulp was
estimated by using spectrophotometer at 600 nm as
per the procedure given by Natu et al.,(1986).
RESULTS AND DISCUSSION
Yeast isolates (AMY-1 to AMY-10) obtained
from different sources were purified and maintained
on Sabouraud Dextrose Agar medium. Based on the
morphological, cultural and alcohol producing ability
of all yeast pure cultures, it was concluded that they
belonged to Saccharomyces cerevisiae.
All pure yeast isolates including MTCC-172
were screened for alcohol production with sugar
medium for 24 h fermentation period. Alcohol content
ranged from 29.80 to 67.85 g L -1 among the local
isolates and MTCC-172. Alcohol content after
fermentation was found to be the highest and nearly
equal with MTCC-172 (67.85 g L -1 ) and pure isolate
AMY-2 (67.80 g L -1 ). These two cultures were
significantly different from other isolates in terms of
alcohol production
Table 1. Screening of yeast isolates and standard culture for alcohol production
Yeast Isolates Alcohol Content (g L -1 ) Yeast Isolates Alcohol Content (g L -1 )
AMY-1 43.50 AMY-7 29.80
AMY-2 67.80 AMY-8 58.40
AMY-3 59.40 AMY-9 44.10
AMY-4 55.50 AMY-10 49.80
AMY-5 62.30 MTCC-172 67.85
*values presented are mean of three replications
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