Isolation And Selection Of Local Yeast Strains For The Production Of Sweet Wine Using Pineapple And Watermelon Juices

In developing countries like Nigeria 20-30% of fruits produced are wasted due to lack ofproper utilization, post-harvest and processing technology. By converting these fruit intovalue added products like wine is a smart solution for this problem. This study was aimed atthe isolation and identification of local yeast strains from spoilt fruits and alcoholicbreverages for the production of sweet wines using pineapple and watermelon fruit juices assubstrates. The organisms obtained were isolated by spread plating 0.1ml solution obtainedfrom the serial dilution of 1ml of fruit juice obtained from the smashed spoilt fruit andalcoholic breverage. The organisms obtained were characterized culturally, morphologically,biochemically and confirmed using an API Test Kit. The organisms were further screened toobtain the one with the best fermentative property by carrying out the Stress exclusion test,ethanol tolerance test, temperature tolerance test, hydrogen sulfide production test andflocculation test. The wine was then produced by cell purification by washing the yeast cellobtained and preparation of inoculum using 400ml of water and 80g of sugar and these wereused 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 producedby identifying the bacteria present in the wine and these were confirmed to be safe forconsumption. Finally, sensory evaluation of the wine produced were carried out to ascertainthe organoleptic property of the wine produced. A total of seven species of yeast whichinclude Candida sphaerica, Pichia spp, Candida pelliculosa, Cryptococcus humicola,Candida guilliermondii, Candida famata and Kloeckera apiculata were isolated. Candidapelliculosa provided the best fermentative property but since it is potentially pathogenic, analternative yeast Kloeckera apiculata was used for the fermentation. The watermelon juiceused as substrate for wine fermentation had initial specific gravity of 1.07g/cm3and thefermentation ended at specific gravity of 0.01g/cm3 while pineapple juice used as substrate had its specific gravity as 1.10g/cm3and 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 showedthe gradual utilization of sugar by Kloeckera apiculata in both wines produced. The totaltitratable 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 at0.5%. It was observed that titratable acidity increased daily as the days increased. Also, thealcohol content increased daily as the sugar were being utilized because the alcohol inpineapple juice fermentation was started at 0% and ended at 12.9% while the alcohol inwatermelon juice fermentation was started at 0% and ended at 7.5%. The temperaturedecreased gradually during the period of fermentation in pineapple wine from 30-180C and inwatermelon wine from 28-17 0C. The pH also decreased gradually in pineapple wine from4.1-3.9 while in watermelon wine from 3.8-3.5. At the end of fermentation the sensoryevaluation of the wine showed that the color of the standard wine was preferred to the colorof the pineapple and watermelon wine produced, however in terms of taste and aroma thepineapple and watermelon wine produced were preferred to the standard wine because of thepresence of glycerol produced by the organism used. Thus, through fermentation, the highlyperishable fruits can be converted into a highly nutritious wine which can be made available all year round.

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