PROJECT TOPICS ON 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 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.
Wine is a popular drink being enjoyed all over the world. Historians believe that wine started in the Caucasuses and Mesopotamia as early as 6000 BC (Robinson, 2006). Rigveda Amply testified that the wine is perhaps the oldest fermented product known to man. However, the actual birth place of wine is still unknown, although it had been prepared somewhere in 350 BC. (Joshi and Devender, 2005). Wine has been made in India for as many as 5,000 years. It was the early European travallers to the courts of the Mughal emperors Akbar, Jehangir and Shah Jahan in the sixteenth and seventeenth centuries who reported tasting wines from the royal vineyards (Philip, 2000).
Grapes (berries) are the main fruit that has been used for wine production. Though, the suitability of fruits other than grapes have been investigated all over the world, the amount of wine produced from non-grape fruits are insignificant. In many countries, other fruit wines from apple (Spain, France, Belgium, Switzerland and England), plum (Germany) and cashew (India) are in high demand.
Fruit is a structural part of plant that contains seeds, normally fleshy, sweet and edible in the raw states, and examples include: oranges, grapes, strawberries, juniper berries, pineapple, and water melon (Mauseth, 2003). They are ripe ovaries or carpels that contain seed (McGee, 2004). Most fruits are eaten as desserts and they can be processed into liquid products which include fruit juices, wines and other preserves like; marmalade, jams and jellies.
The pineapple and watermelon fruits are popular fruits wildly consumed in Nigeria. They are generally grown in the southern and some eastern parts of the country. Typically, pineapple is flavored and eaten fresh by consumers because of its unique characteristics (Sarah et al., 1997). Its flesh is a deep yellow color with good firmness and has a delicious taste characterized by sweetness and a little acidity. Additionally, it has very intense fruity fragrance and aromatic flavour. Pineapple as a fruit crop has a lot of economic, nutritional, medicinal, and industrial importance (Sarah et al., 1997).
On the other hand, watermelon (Citrullus Lanatus) is grown for its large edible fruit, which is a special kind of berry with a hard rind and no internal division. Botanically it is called a pepo. The fruit has a smooth hard rind which is usually green with dark green stripes or yellow spots on it and a sweet, juicy interior flesh which is usually deep red to pink in color, but sometimes orange, yellow, or white depending on the variety with many seeds, which can be soft and white or hard and black. Watermelon fruit supplies 30 calories of energy and low amounts of essential nutrients. Only vitamin C is present in appreciable content at 10% of the daily value. Watermelon fruit is 91% water, contains 6% sugars (sucrose, fructose and glucose), and is low in fat. Wonderfully delicious and juicy melons are the great source of much-needed water and electrolytes to tame tropical summer temperatures. It quenches thirst while reboosting our body with the anti-oxidant lycopene and vitamin-A (Zohary & Hopf, 2000).
Yeasts are without doubt the most important group of microorganisms exploited by man. No other group of microorganisms has been associated with the progress and wellbeing of humans like yeasts (Anna, 2003). Yeasts are simple eukaryotic and unicellular organisms classified in the kingdom Fungi with over 1,500 species known (Kurtzman & Robnert, 1998).
In wine and beer making, yeast is the ―ingredient‖ that converts the simple sugars into ethanol and carbondioxide. The most common species used are Saccharomyces species. However, other species are also used. It has been known for a long time that freshly crushed grape juice harbours a diversity of yeast species, principally within the genera Hanseniaspora (anamorph Kloeckera), Pichia, Candida, Metschnikowia, Kluyveromyces and Saccharomyces. Occasionally, species in other genera such as Zygosaccharomyces, Saccharomycodes, Torulaspora, Dekkera and Schizosaccharomyces may be present (Graham, 2008). It is also well known that many of these non-Saccharomyces species (especially species of Hanseniaspora, Candida, Pichia and Metschnikowia) initiate spontaneous alcoholic fermentation of the juice (Graham, 2008).
A typical wine contains ethyl alcohol, sugar, acids, higher alcohols, tannins, aldehydes, esters, amino acids, minerals, vitamins, anthocyanins, and minor constituents like flavouring compounds (Swami et al., 2014). The wines are classified as natural wines (9-14 % alcohol), dessert and appetizer wines (15-21 % alcohol). If fermentation stops before the sugars have all been metabolized by the yeast, the finished product is a sweet wine. If all the sugars have been metabolized, the wine is said to be dry wine. Dry wine, sweet table wine, specialty wine, champagne, muscat and burgundy wines are natural wines while sweet wine, cherries, vermouth and port wines are regarded as dessert and appetizer wines. (Swami et al., 2014)
Red wine is made from red grapes, which are actually closer to black in colour. There are many different types of red wines. This is considered to be the most classic in the kingdom of wines, mixing the delicious red grapes with a wide range of aromas, from oak to eucalypti, chocolate or even mint hints. The juice from most black grapes is greenish-white; the red colour comes from anthocyan pigments present in the skin of the grape. (Swami et al., 2014).
White wine on the other hand is not exactly white; it is often yellow, gold or straw coloured, depending on whether it includes the skin of the grape or just the juice. White wine can be made by the alcoholic fermentation of the non-coloured pulp of green or gold coloured grapes or from selected juice of red grapes. It is treated so as to maintain a yellow transparent colour in the final product. White wines often taste lighter, crispier and more refreshing than red wine (Swami et al., 2014).
According to FAO (1998) fermentation is one of the most ancient and most important food processing technologies which had been neglected by scientists and policy makers especially in traditional fermented products from developing countries. Fermentation is a relatively efficient, low energy preservation process which increases the shelf-life and decreases the need for refrigeration or other form of food preservation technology. It is therefore a highly appropriate technique for use in developing countries and remote areas where access to sophisticated equipment is limited. Fermented fruit wines are popular throughout the world, and in some regions it makes a significant contribution to the diet of millions of individuals (Jolly et al., 2003).
Individual yeast strains that carry out fermentation possess different physiological traits. There are several traits that are highly desired in wine strains of Saccharomyces (Jolly et al., 2003). The most important characteristic is that the strain be able to complete the fermentation, leaving little or no residual sugar. It is also critical that the strain display a steady rate of fermentation. It is problematic if the rate is too fast as well as too slow. A slow rate of fermentation becomes difficult to distinguish from problem fermentation. If the rate is too fast, the fermentation may reach too high a temperature due to the rate of heat released from metabolism. Rapid fermentations may also lead to increased loss of volatile components (Jolly et al., 2003).
1.1 Statement of Research Problem
The pineapple and watermelon industry in Nigeria is faced with lots of challenges ranging from fruit rejections from export markets to inadequate storage and processing facilities, as well as tropical temperature that causes fruit spoilage, coupled with unavailable markets. Also poor handling and transportation of the fruits contribute significantly to high post-harvest losses. According to (Appert, 1997) losses in pineapple fruits harvest could be as hig as 50%. Research institutions and other private companies are trying hard to reduce these losses by processing the fruits into drinks and fresh cut fruits for the local market. Little work however is done on processing the fruits into other products such as wine (Jolly et al., 2003).
According to Adams and Moss (1995) maize and cassava dough are fermented and maize, millet, and other cereal grains are brewed into local drinks such as ‗pito‘ and ‗brukutu‘ in Nigeria and in other Sub-Saharan African countries. Very little however is known about fermentation of pineapple, cashew, mango, and orange juices into wine (Au Du., 2010).
The highly perishable nature of fruits especially watermelon and pineapple lead to insecurity in fruit growers and fruit sellers because of the fear of money loss instead of profit making. The high perishability of theses fruits contribute to the seasonality of the fruits thus making it available only during a particular season which is usually very short.
1.2 Justification of the Study
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 fruits into value added products like wine is a smart solution for this problem. (Nwachukwu et al., 2006). Thus, wine production should be promoted for adding value to local fruits, imported wine reduction, job creation, income generation and rural development.
FAO (2002) and ―ComisiónVeracruzana de Comercialización Agropecuaria‖ (COVECA, 2002) reported that there are several pineapple and watermelon varieties commonly grown in Africa, and for that matter Nigeria, that have favourable pH (4.5-6.5) and sufficient sugar levels for fermentation to occur. Keller et al. (2010) also noted that pineapple juice could be converted into wine in the presence of yeast. Thus, through fermentation, the highly perishable pineapple fruit could be converted into a highly nutritious wine which can be made
available all year round. Marketing of this product will ensure security for pineapple growers as wine and other alcoholic beverages will be in high demand throughout the country and the world as a whole. Thus ensuring a secure source of income for both the farmers and the investors. Wine production from other sources other than the traditional fruits has been successfully done on carrot, banana and cashew (Au Du, 2010). A little is done on watermelon and pineapple.
The possibility and the use of pineapple and watermelon for the production of wine will create employment, income generation for farmers and address the post-harvest losses associated with glut on the local market in Nigeria. The findings of this study will provide information with regards to the preservation and storage of pineapple and watermelon in particular and fruits in general. This will ultimately ensure a secured source of income for both the farmers and the investors.
1.3 Aim of the Study
The aim of this study is to isolate and identify local yeast strain for the production of sweet wine from pineapple and watermelon juice.
1.4 Objectives of the Study
The specific objectives of this work were to:
- Isolate and identify yeast species from fruits and a local alcoholic beverage (Brukutu).
- Screen and select yeast species with the best fermentative potentials.
- Produce wine from watermelon and pineapple juices using the selected yeast specie.
- Determine the microbiological and physicochemical profile of the wine produced
- Evaluate the sensory quality of the wine produced.