SUITABILITY OF CARAMBOLA (AVERRHOA CARAMBOLA) FRUIT JUICE AS A SUBSTRATE FOR WINE FERMENTATION

Grace Anim and Kwaku Tano-Debrah*,

ABSTRACT

The physico-chemical characteristics of carambola (Averrhoa carambola) fruit juice were determined to assess the suitability of the fruit as raw material for local wine production. Fresh ripe fruits of the carambola tree (Averrhoa carambola) were processed into a fruit juice. The juice was analysed to determine moisture, fat, total solids, soluble solids, total sugars, and vitamin C content, the types of sugars present, titratable acidity and pH.  The fruit had a characteristic soft, fragile and thin skin, relatively few and tender seeds, and a high water content (94%) which made its processing into a fruit juice fairly simple and easy. A juice yield of about 76% was observed. The juice was yellowish in colour. Some physico-chemical characteristics of the fruit juice were: pH 2.2, total solids 5.9%, soluble solids 5.0%, titratable acidity 0.66, fat 0.25% and total sugars 2.55%. The analysis of the sugars showed glucose, fructose and sucrose as the predominant sugars present. Vitamin C content was substantially high (35 mg/100 g), but fat content was low (0.25%).  The total sugars content and pH were very low. Most brewer's yeasts require a pH range of 4-6; and for adequate alcohol production to form a wine, the sugar content should be about 10%.  The physico-chemical characteristics of the juice suggest the feasibility of modifying the juice into a suitable must that could yield adequate amount of alcohol to form a wine.  The carambola fruit is, therefore, considered as a suitable raw material for wine production locally.

 Key words: Carambola (Averrhoa carambola), carambola fruit juice, wine production

INTRODUCTION

The carambola fruit is a large indehiscent berry borne by the carambola tree, Averrhoa carambola. The tree, a member of the Averrhoaceae, grows to about 5-10 m high [1]. It bears compound leaves composed of 2-5 pairs of ovate or ovate lanceolate leaflets, and small white or purplish flowers in short racemes from the back of branches. The tree bears fruits continuously throughout the year. The fruit is typically 7-12 cm long, oval to elliptical in outline with 3,4 or 5 longitudinal ribs giving it a characteristic cross-sectional star shape.  The ripe fruit has a thin, smooth translucent yellowish orange to brown skin colour and it is waxy in texture. Unripe fruits are green and firmer. Two carambola fruit varieties have been described: one, smaller in size with strong sour taste, and the other, larger in size with mild sweet taste [2]. Several cultivars of the tree exist which are described as sweet types or sour types [3,4].

The carambola fruit is an economically important commodity. Most carambola fruits are marketed in processed forms. It is edible and has numerous uses. The ripe fruit may be processed into fermented or unfermented drinks, preserves, jam or jelly, or eaten fresh as dessert [5].  The unripe fruit may also be eaten as a vegetable [5].The sweet type is processed into wine in Surinam [6]. In Southern China, carambola fruits are preserved in thin packages and exported to other countries. The fruit is a potential source of pectin. The fruits are recommended for use as a febrifuge, and especially effective against polydipsia [7]. The fruits have narcotic and emetic potentials which are exploited in infusion to alleviate asthma and various colics [8].   Among the major importers are The United Kingdom, Germany, Hong Kong, Singapore, France, Belgium, Denmark and Switzerland [9]. Several countries produce the fruits for export and they include Thailand, Israel, the Philippines, Indonesia, Trinidad-Tobago and Surinam [9]. In Ghana the tree seems to do very well. However, the economic potentials have not been fully exploited. Apparently, it is only planted for ornamental purposes. The few trees available may only be found in parks and gardens.

Among the possible reasons for the non-commercial exploitation of the fruits in Ghana may be the unavailability of local technologies for processing the fruits into edible products. The fruits are also not very familiar to the majority of Ghanaians. This work forms part of a study investigating the local processing of the fruits into wine; with the objectives of producing and characterizing the carambola fruit juice, studying the fermentation characteristics of the juice, and collating information for increasing the awareness on the fruit in the country. The data presented here determines the suitability of the carambola fruit as a raw material for wine production.

MATERIALS AND METHODS

Carambola  fruits. Ripe carambola fruits were harvested from a tree at the Department of Crop Science, University of Ghana, Legon.

 Processing of fruits into juice. The fruits after cleaning were blended in a Hobart cutter (model 84142 PED, Hobart Mfg. Co. Ltd. Ontario) and strained through a piece of white nylon cloth previously sterilized in 1% potassium metabisulphite solution. The extract was termed as the carambola fruit juice.

Characterization of the carambola fruit juice. The pH, moisture, total solids, soluble solids, total sugars, titratable acidity, fat contents, and specific gravity of the juice were determined. The types of sugars and the vitamin C content were also determined. The pH was determined using a pH meter (model HM-30S, Tokyo, Japan).  Moisture and total solids were determined by the Sand Plan Technique [10]. About 20 g of clean, dry fine sand and a glass stirring rod were added into a moisture dish. The dish was oven-dried (at 105 EC) to constant weight, cooled in a dessicator and weighed. Three grams of the juice was then weighed into the sand and mixed with the rod. The dish containing the mixture and the rod was similarly dried and weighed. The moisture and total solids content were then calculated. Soluble solids content was determined using an Abbe refractometer, [11]. The total reducing sugar content was determined using the Lane and Eynon method [12]. The titrable acidity was determined by titrating 10 g of the juice diluted in 30 ml distilled water against standardized 0.1N NaOH, using phenolphthalein as an indicator. The acidity was calculated as citric acid of equivalent weight of 70.05. Specific gravity was determined using a hydrometer, with the juice in a 100 ml measuring cylinder.     

The component sugars were determined by thin layer chromatography. Ethanol-extracted solution was used for the analysis. Glass plates (15 cm x 15 cm) of Kieselgur gel plates, 2.5 Fm thick were used. Glucose, fructose, sucrose, maltose and D-galactose standards in isopropanol (10%) were also spotted alongside the juice extract for identification. The plates were developed in a solvent system composed of ethyl acetate, isopropanol, water and pyridine (in a ratio of 26:14:7:2, respectively) to a solvent front of about 12 cm, starting from a baseline of 2 cm,  by an ascending chromatography. They were dried and sprayed with  a colour developing solvent composed of 10% aniline in acetone, 10% diphenylamine in acetone and 85% orthophosphoric acid (in a ratio of 5:5:1, respectively). The plates were dried in an oven at 100 EC for 5-10 minutes for colour to develop and the retention factors calculated with reference to glucose (Rg).

Vitamin C content was determined using the method of Chichilo et al. [13]. Aliquots of the clarified juice in oxalic acid were titrated with standardized 2,6-dichloroindophenol dye to a faint pink colour that persisted for 5-10 minutes. The vitamin C content, calculated as mg ascorbic acid, was then determined. Fat was determined using the Rose Gottlieb modification method [14] as follows: 100 g of the fruit juice was extracted with 50 ml of hexane in a separatory funnel. The extraction was repeated 3 times, each with 50 ml of hexane. The hexane layers were pooled into a weighed flask and 3 g of anhydrous sodium sulphate added to liberate the trapped water. The hexane was then evaporated on a water bath, after which the flask was placed in an air-oven at 105 EC for 1 hour to dry. The flask was again weighed to determine the fat extracted. The fat content of the juice was then determined.   

RESULTS

A 76% juice yield was observed. The juice extraction process looked simple and easy, but effective. The juice was yellowish in colour. The physico-chemical characteristics of the carambola fruit juice are shown in Table 1. The moisture content of the juice was high. Conversely the total solids content was low. Hough et a.l reported moisture content of 87.4% [15]. Abdullah and Ragab [16], Campbell and Kock [17] and Mathews [18] also independently, reported a value of 90%. These all confirm the juiciness of the fruit.  The juice was acidic, having a low pH. Varieties with pH of 3.8-4.1 are described as sweet and those with pH 2.2-2.6 are described as tart [6]. The pH values observed suggest that the variety analyzed is a tart cultivar.

The total solids content was low, but most of the total solids appeared to be soluble solids (Table 1). There was correspondingly low total sugar content.  Fat content was typically low. Hough et al. [15] reported a fat content of 0.3%. The fruit seems to be a good source of vitamin C. Consuming 100 g of the juice a day could supply the daily requirement of an individual [19].

Table 2 shows the Rg of the standard sugars and the unknown sugars in the fruit extracts.  The spot of the fruit juice extract resolved into 3 different bands with different Rgs, indicating the presence of 3 different sugars. Comparing the Rgs of the unknown to the standard sugars, it was observed that the predominant sugars in the fruit juice are fructose, glucose and sucrose. These are common fermentable sugars for most ethanol fermentation microorganisms.

DISCUSSION

The data obtained generally indicated that the carambola fruits are suitable raw materials for wine production. It was possible to process the fruit into a fruit juice using a fairly simple process.  The characteristic soft, fragile and thin skin, relatively few and tender seeds and the juicy nature of the fruit all make its processing into a fruit juice simple and easy. The juice also contains fermentable sugars (fructose, glucose and sucrose) which could support the growth of ethanol fermenting microorganisms. The amounts of these sugars present, (Table 1) are however, too low for adequate alcohol production, to call the product a wine. Acceptable wine should contain a minimum alcohol concentration of 8% by volume [20]. This requires sugar content of about 10% w/v [21].  It would thus be necessary to supplement the sugar content of the fruit if it should be used for wine production.  Again, the pH of the fruit is relatively low. By this pH, the fruit type processed would be described as a tart variety [8].  Most brewer's yeast shows optimum pH in the range of 4-6. The low pH, thus suggests the need for pH adjustment if the juice is to be fermented into wine. The fat content of the juice is extremely low and would, thus, make modification of the juice feasible.  With the high water content, the low soluble solids content could be increased by adding the desired sugars for the fermentation, making the wine production possible. Lewis and Grocizam (1989) reported the use of the sweet types in wine making in Surinam [6]. Whether the juice is modified or not before fermentation was not reported. However, some cultivars of carambola are said to have high carbohydrates (specifically glucose) content, [15-18] and pH around 4, which make their processing into wine more feasible.  The variety of the fruits processed in this study is not known, but from the characteristics, it may be the sour tart type. This suggests that the juice from the tart fruit type needs some modification before it can be processed into a wine. On the other hand it can be simply modified and thus, used as a raw material for wine production.  

CONCLUSION

The study demonstrated the feasibility of producing carambola fruit juice. The juice has a low pH, low soluble solids and low sugar contents all of which need to be modified before the juice could be suitable for wine production. The sugars present are, however, fermentable sugars, meaning the juice could support some microbial growth and undergo some fermentation. The carambola juice could thus be used as a base for the production of wine. 

Table 1
Characteristics of Carambola fruit juice

Water (%) Total solids (%) Soluble solids (%) Total Sugars (%) Crude fat (%) Vitamin C (mg)                                 pH Titratable acidity (%)

94.1 5.90 5.0 2.55 0.25 35 2.20 0.66

Table 2
Rg of standard sugars and unknown sugars of the carambola fruit juice

Sample                                               Rg*                                            Plate 1                Plate 2 Fructose                               140                      114 Glucose                                100                      100 D-Galactose                           84                        40 Sucrose                                   60                        37 Maltose                                 156                      126 Unknown 1                           140                      114 Unknown 2                           100                       97 Unknown 3                             60                       37  *Rg – retention factor in reference to glucose Unknown 1, 2, 3 - the component sugars of the carambola fruit juice. Plate 1, 2 – sampled replicate TLC plates run in the analysis

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