ISOLATION AND SELECTION OF LOCAL YEAST STRAINS FOR THE PRODUCTION OF SWEET WINE USING PINEAPPLE AND WATERMELON JUICES
ISOLATION AND SELECTION OF LOCAL YEAST STRAINS FOR THE PRODUCTION OF SWEET WINE USING PINEAPPLE AND WATERMELON JUICES
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Date
2017-12
Authors
BASSEY, Nko Samuel
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Abstract
In developing countries like Nigeria 20-30% of fruits produced are wasted due to lack of
proper utilization, post-harvest and processing technology. By converting these fruit into
value added products like wine is a smart solution for this problem. This study was aimed at
the isolation and identification of local yeast strains from spoilt fruits and alcoholic
breverages for the production of sweet wines using pineapple and watermelon fruit juices as
substrates. The organisms obtained were isolated by spread plating 0.1ml solution obtained
from the serial dilution of 1ml of fruit juice obtained from the smashed spoilt fruit and
alcoholic breverage. The organisms obtained were characterized culturally, morphologically,
biochemically and confirmed using an API Test Kit. The organisms were further screened to
obtain the one with the best fermentative property by carrying out the Stress exclusion test,
ethanol tolerance test, temperature tolerance test, hydrogen sulfide production test and
flocculation test. The wine was then produced by cell purification by washing the yeast cell
obtained and preparation of inoculum using 400ml of water and 80g of sugar and these were
used for the wine production which lasted for 14 days. During the fermentation the microbiological analysis of the wine was carried out to ascertain the quality of wine produced
by identifying the bacteria present in the wine and these were confirmed to be safe for
consumption. Finally, sensory evaluation of the wine produced were carried out to ascertain
the organoleptic property of the wine produced. A total of seven species of yeast which
include Candida sphaerica, Pichia spp, Candida pelliculosa, Cryptococcus humicola,
Candida guilliermondii, Candida famata and Kloeckera apiculata were isolated. Candida
pelliculosa provided the best fermentative property but since it is potentially pathogenic, an
alternative yeast Kloeckera apiculata was used for the fermentation. The watermelon juice
used as substrate for wine fermentation had initial specific gravity of 1.07g/cm3
and the
fermentation ended at specific gravity of 0.01g/cm3 while pineapple juice used as substrate had its specific gravity as 1.10g/cm3
and fermentation ended at specific gravity of 1.03g/cm3
,
the total soluble solid of watermelon juice fermentation was started at 17% and ended at 3.8%
while that of pineapple juice fermentation started at 23.6% and ended at 8.2%, these showed
the gradual utilization of sugar by Kloeckera apiculata in both wines produced. The total
titratable acidity in pineapple juice fermentation was started at 0.01% and ended at 0.25%
while titratable acidity of watermelon juice fermentation was started at 0.01% and ended at
0.5%. It was observed that titratable acidity increased daily as the days increased. Also, the
alcohol content increased daily as the sugar were being utilized because the alcohol in
pineapple juice fermentation was started at 0% and ended at 12.9% while the alcohol in
watermelon juice fermentation was started at 0% and ended at 7.5%. The temperature
decreased gradually during the period of fermentation in pineapple wine from 30-180C and in
watermelon wine from 28-17 0C. The pH also decreased gradually in pineapple wine from
4.1-3.9 while in watermelon wine from 3.8-3.5. At the end of fermentation the sensory
evaluation of the wine showed that the color of the standard wine was preferred to the color
of the pineapple and watermelon wine produced, however in terms of taste and aroma the
pineapple and watermelon wine produced were preferred to the standard wine because of the
presence of glycerol produced by the organism used. Thus, through fermentation, the highly
perishable fruits can be converted into a highly nutritious wine which can be made available all year round.
Description
A THESIS SUBMITTED TO THE SCHOOL OF POSTGRADUATE
STUDIES, AHMADU BELLO UNIVERSITY, ZARIA IN PARTIAL FULFILLMENT
FOR THE AWARD OF
MASTER OF SCIENCE DEGREE IN MICROBIOLOGY
DEPARTMENT OF MICROBIOLOGY,
FACULTY OF LIFE SCIENCES,
AHMADU BELLO UNIVERSITY,
ZARIA, NIGERIA
Keywords
ISOLATION,, SELECTION OF LOCAL YEAST STRAINS,, PRODUCTION,, SWEET WINE,, USING PINEAPPLE,, WATERMELON JUICES