Sugar and dietary fibre components of tamarind

Full Research Article

32

Sugar and dietary fibre components of tamarind (tamarindus indica l.) fruits from Nigeria 1

2

Abiodun Aderoju Adeola and Ogugua Charles Aworh 1 Department of Home Economics, Emmanuel Alayande College of Education, Oyo, Oyo State, Nigeria. E-mail:[email protected] 2 Dept. of Food Technology, University of Ibadan, Ibadan, Oyo State, Nigeria

ABSTRACT Tamarind (Tamarindus indica L.), a fruit tree belonging to the Ceasalpinicae family, grows naturally in many tropical and subtropical regions. It grows wild on wastelands, backyards and roadsides in the Savannah region of Nigeria. Tamarind fruit, though, has considerable industrial potential, is largely underutilised in Nigeria. Mature tamarind fruits, collected from nineteen randomly selected major towns of the twenty states in the Savannah region on Nigeria, were analysed for their sugar and dietary fibre components, using standard methods. Sugars

identified in tamarind fruits included glucose (1.1-4.4 %), galactose (0.1-0.4 %), fructose (0.7-3.2 %), arabinose (0.1-0.3 %) and xylose (0.2-0.4 %). Dietary fibre components of tamarind fruits were 4.4-5.4 % NDF, 6.0-7.4% ADF, 2.6-3.7 % lignin, 1.52.2 % hemicellulose and 2.8-4.2 % cellulose. Consumption of tamarind fruits could lead to improved health of Nigerians, especially diabetic and heart patients. Key words: underutilized fruit, tamarind, nutrients, sugar, dietary fibre

INTRODUCTION Food insecurity in Africa will remain if efforts are not made towards finding alternative and cheaper sources of food such as the underutilised indigenous wild plants. Underutilised or little-known food plants are good sources of protein, fat, minerals and vitamins, and are available at certain critical periods of the year when the common food sources are very scarce or completely unavailable (Okigbo, 1986; Salih et al., 1991; Tewari, 1993; Martinello et al., 2006). Several studies (Onyechi et al., 1998; Sandhya and Vijayakshmi, 2000; Mbofung et al., 2002; Ella Missang et al., 2003; Ojewole, 2003; Oboh and Akindahunsi, 2004; Ayodele, 2005; Dicko et al., 2005; Ngondi et al., 2005; Dahiru et al., 2006) on African indigenous plants confirm both their richness in nutrients and their health promoting and protecting properties.

al., 2005; Martinello et al., 2006). Tamarinds grow naturally in many tropical and sub-tropical regions (Gunasena and Hughes, 2000; BAIF, 2002; Sudjaroen et al., 2005; Martinello et. al., 2006). It is found in the savannah region of Nigeria where it grows wild in backyards, roadsides or wastelands. Tamarind tree is most well known for its fruits, which have one of the highest levels of protein and carbohydrate of any fruit (BAIF, 2002). It can produce an annual fruit yield in the range of 150-500 kg/tree (BAIF, 2002). The ripe fruit is filled with a sticky pulp, which has a versatile use. Tamarind pulp is high in potassium, phosphorus and calcium, and contains vitamin C and β- carotene (Morton, 1987; BAIF, 2002). The seeds are gaining importance as a rich source of protein, with favourable amino acid composition. Tamarind is available when other food supplies are low (Gunasena and Hughes, 2000). Tamarind could Tamarind (Tamarindus indica L.) is a fruit tree, therefore contribute significantly to the nutrition w h i c h b e l o n g s t o t h e l e g u m i n o s e a / of low-income rural households, especially caesalpiniceae family (Gunasena and Hughes, children, in Nigeria. However, information in the 2000; Luengthanaphol et al., 2004; Sudjaroen et literature on Nigerian tamarind is few and too NIGERIAN FOOD JOURNAL, VOL. 28,NO 2 2010 (www.ajol.info/journals/nifo) ISSN 0189-7241

Chemical properties of Nigerian tamarind fruits………….Adeola & Aworh

33 scanty for any meaningful conclusion on its 5µl of 10% reference sugar standards. One-way quality attributes and possible adoption for descending chromatography was run for 20hr industrial exploitation. using n-butanol-toluene-pyridine-water (5:1:3:3v/v). After air-drying the chromatogram, Furthermore, carbohydrates in fruits are the sugar spots were located with saturated important in that fruits containing high AgNO3 in acetone and 0.5M alcoholic NaOH proportions of free sugars are not good for solutions. In quantifying the sugars, about diabetic patients (Nahar et al., 1990). However, 0.01ml of each concentrated sample extract was polymeric carbohydrates forming the major part spotted in quadruplicate on Whatman No.1 of the dietary fibre (DF) are beneficial to patients chromatography paper at 5cm interval. The suffering from diabetes and coronary heart chromatograms were run for 20hr. After drying disease. This is due to the fact that DF lowers the chromatogram in air, one of the quadruplicate both sugar and serum cholesterol (Nahar et al., strips was cut out and the sugar spots on it located 1990). Fruits are a very convenient source of DF. with AgNO 3 in ethanol. Next, the areas containing the spots were marked out and the It is therefore the aim of this paper to evaluate corresponding areas on each of the remaining and compare the sugar and dietary fibre triplicates were removed and eluted with 5ml of components of some tamarind fruits that grow distilled water for 1hr (Faparusi, 1970; 1981). wild in Nigeria. The amount of sugar in the eluates was determined colorimetrically, according to the MATERIALS AND METHODS method of I.I.T.A. (1991). About 0.01g of DSources of raw materials glucose was weighed into a 100ml volumetric Mature tamarind fruits were collected between flask. The flask was made up to 100ml mark with the months of March and May from nineteen distilled water to form the stock solution towns, which were randomly selected from the (100µg/ml). 0, 0.1, 0.2, 0.3, 0.4 and 0.6ml of major towns of the twenty Savanna states of the stock solution was pipetted into test Nigeria. To minimise problems caused by insect tubes and each was made up to 1.0ml with infestation, fruit pulp was hand-scraped from the distilled water to correspond to 0, 10, 20, 30, seeds, cleaned to remove non-plant materials and 40 and 60 µg glucose per ml. Colour insect-infested parts, and stored in an industrial development was carried out by adding to each of 0 freezer at 20 C prior to analyses. the test tubes 0.5 ml of 5% phenol and mixing each test tube thoroughly. Thereafter, 2.5 ml of Analytical methods H2SO4 was added and the mixture cooled in a beaker containing cold water. The absorbance Sugar analysis was read at 490nm with a spectrophotometer Sugars in tamarind pulp samples were extracted (Unicam Heλlios-γ). A standard graph was with 70% aqueous methanol, using a soxhlet plotted with values of absorbance obtained and extractor. This was followed by concentration of the slope determined. extract to remove the solvent. Sugar standards consisting of glucose, galactose, fructose, xylose About 0.02g of pulp sample was weighed into a and arabinose were separately prepared by centrifuge tube and 1.0ml of absolute ethanol weighing 1.0g of each sugar into five added. About 2.0 ml distilled water and 10 ml hot beakers and adding 10ml of 50% aqueous absolute ethanol were successively added methanol (Sherma and Zweig, 1971; followed by mixing. The resultant mixture was Harbone, 1991). 5µl of extract was spotted centrifuged at 2000rpm for 10 minutes. The on Whatman No.1 chromatography paper supernatant was decanted and made up to 20 ml (46cm x 57cm) at 5cm intervals along with with absolute ethanol, from which 0.2 ml was NIGERIAN FOOD JOURNAL, VOL. 28,NO 2 2010 (www.ajol.info/journals/nifo) ISSN 0189-7241


34 transferred into a test tube and 0.8 ml distilled water added. Colour development was thereafter carried out as was done for the sugar standards. Dietary fibre components:

away and the crucible was refilled with 720g/l d, 0 dried overnight at 100 C and weighed. The acid detergent lignin was taken as the difference in weight.

Neutral detergent fibre (NDF) The method of Hopkins et al. (1995) was used. About 1 g pulp was placed in 200ml roundbottomed flask, to which was added 100ml neutral detergent (sodium lauryl sulphate at pH 7.0). The round-bottomed flask was linked to a condenser and refluxed for 1hr. The suspension was filtered through a weighed glass fibre filter paper, rinsed successively with 100ml hot water 0 (approximately 60 C), 100ml methanol and 100ml acetone. The glass fibre filter paper containing the residue was then air-dried overnight at room temperature and weighed. The weight of the filter paper was subtracted from the total weight to obtain the weight of the residue (NDF).

Cellulose The method of Silva et al. (2005) was used. The principle of the procedure is that the ADF residue is primarily lignocellulose, of which the cellulose is dissolved by concentrated H2SO4. The remaining residue consists of lignin and acidsoluble ash. Thus the cellulose was estimated from the difference between ADF and lignin.

Acid detergent fibre (ADF) The method of Saura-Calixto et. al. (1983) was used. About 1 g of the pulp was weighed into 250ml flask containing 100ml acid detergent solution (40g of cetyl trimethyl ammonium bromide in 2l of 0.5ml H2SO4) and the condenser fitted. The flask was gently boiled and refluxed for 1hr after which the solution was filtered, using gentle suction. The residue was then washed with three 50ml aliquots of boiling water, followed by washing with acetone until the wash solution was clear. The residue was sucked dry by vacuum and then dried in the oven 0 for 4hr at 105 C, cooled in a dessicator and weighed. The acid detergent fraction was taken as the difference in weight. Acid detergent lignin The method of A.O.A.C. (1990) was used. The final residue obtained from the ADF determination was put in a pre-weighed crucible. The content of the crucible was then covered 0 with cool (5 C) 720g/l H2SO4 and stirred to a smooth paste. The acid was allowed to drain

Hemicellulose The difference between the NDF and ADF was estimated as hemicellulose (Silva et al., 2005). Statistics: All data were assessed by analysis of variance (ANOVA) and Duncan Multiple Range Test. RESULTS AND DISCUSSION Table 1 shows the sugar contents of tamarind fruits from various locations in Nigeria as glucose, galactose, fructose, arabinose and xylose. There were significant differences (p? 0.05) in the glucose, galactose and fructose contents of the fruits. The range in values was between 1.1-2.8%, 0.1-0.4%, 0.7-3.2%, 0.10.2% and 0.2-0.4% for glucose, galactose, fructose, arabinose and xylose respectively. Thus, the total sugar content of tamarind pulp comprises mainly glucose and fructose. Various authors (Hassan and Ijaz, 1970; Feungchan et al., 1996: Gunasena and Hughes, 2000) have reported wide variations in the sugar contents of tamarind fruits, ranging from 5.0 to 47.7 %, probably due to such factors as season, maturity, storage time, cultivar, extraction procedure, horticultural practices and environmental conditions. The sugar contents of tamarind fruits are much lower than some tropical fruits such as mango (Mangifera indica L.) which contain 7-12 % (Nahar et al., 1990; Medicott and Thompson, 2006), pineapple (Ananas comosus L.) which contain 5.8 % (Nahar et al., 1990) and dates which contain 45-85 % on dry weight basis

NIGERIAN FOOD JOURNAL, VOL. 28,NO 2 2010 (www.ajol.info/journals/nifo) ISSN 0189-7241


35 (Barreveld, 1993). Ibrahim et al. (2004) reported that tamarind seeds contained glucose, galactose, arabinose, xylose and uronic acid. The results of the fibre analyses are as shown in Table 2. Significant differences (p? 0.05) occurred in the dietary fibre components of the fruit samples. The acid detergent fibre (NDF) ranged from 4.4 for Maiduguri sample to 5.8% for Oyo sample. The range in values for neutral detergent fibre (ADF), lignin, hemicellulose and cellulose was 6.0 (Maiduguri sample) - 7.5% (Oyo sample), 2.6 (Sokoto sample) - 4.5% (Oyo sample), 1.5% (Minna sample) - 2.2% (Kano sample), 1.3% (Shaki sample) 2.5% (Sokoto sample), respectively. NDF values were consistently higher than ADF values, suggesting that more dietary fibre components were solubilised by acid detergent. Belo and de Lumen (1981) and Silva et al. (2005) reported similar observation. According to Kuhnlein (1989), NDF is closer to total dietary fibre than are ADF and crude fibre. The hemicellulose contents of the tamarind pulp are lower than the lignin and cellulose contents. Nutritionally, this could be important, since hemicelluloses have been shown to be degraded much more than cellulose by the intestinal microflora, and this would result in a decreased production of volatile fatty acids (acetic and lactic acids) that are thought to have a laxative effect or even cause diarrhea (Southgate and Durnin, 1970; Whistler and Daniel, 1985). According to AACC (1983), NDF determination is considered the method of choice for assessing the insoluble dietary fibre content of food crops. Insoluble and soluble fibres are of great importance in the well-being of the body.

where it may set the stage for high blood pressure, heart diseases and stroke (Chemiron Newsletter, 2001). The findings of VidalValverde (1992), Ezeagu (1997), Vijayakumari et al. (1997) and Ketiku and Adepoju (2004) on little-known legumes showed much higher values of dietary fibre components than the results of the present study. CONCLUSION Tamarind fruits are low in free sugars but moderate in DF. The major sugars in tamarind fruits are glucose and fructose, with neutral and acid detergent fibres being more abundant than other dietary fibre components. The consumption of tamarind fruits should help to alleviate the problem of diabetes and coronary heart disease among the Nigerian populace. Industrial utilisation of tamarind fruits should also help to alleviate the problem of malnutrition and increase the food choices of people living in developing countries. Efforts should therefore be made by various governments, especially those in regions where tamarinds are growing wild, to improve the local varieties and increase public awareness about the nutritional importance of tamarind fruits.

Insoluble fibre provides roughages that speed up the elimination of faeces, thus decreasing the time that the body is exposed to harmful substances. Soluble fibre, on the other hand, mixes with food in the stomach to prevent or reduce the absorption by the small intestine of potentially dangerous substances from food. Soluble fibre also binds dietary cholesterol and carries it out of the body thereby preventing it from accumulating in the inner walls of arteries



36 Table 1: Sugar contents of tamarind (Tamarindus indica L.) Fruits from various locations in Nigeria

Location

Glucose (%)

Galactose (%)

Arabinose (%)

Xylose (%)

Fructose (%)

Abuja

2.1±0.67

0.2±0.08

1.8±0.64

0.1±0.06

0.2±0.03

Azare

1.7±0.61

0.3±0.04

1.5±0.44

0.2±0.06

0.2±0.07

Bauchi

1.1±0.02

0.1±0.04

0.7±0.55

0.1±0.02

0.4±0.42

Bichi

2.5±0.38

0.2±0.09

1.8±0.59

0.1±0.02

0.2±0.08

Birni Kebbi

1.9±0.72

0.3±0.06

1.7±0.54

0.3±0.01

0.3±0.05

Funtua

1.4±0.31

0.3±0.09

1.1±0.01

0.1±0.04

0.2±0.04

Gombe

2.7±0.30

0.4±0.01

1.7±0.56

0.2±0.14

0.3±0.03

Gwarzo

2.4±0.37

0.2±0.03

1.7±0.56

0.1±0.04

0.2±0.05

Jega

2.0±0.77

0.2±0.10

1.6±0.53

0.2±0.03

0.3±0.07

Jos

2.6±0.96

0.3±0.05

1.8±0.54

0.2±0.11

0.2±0.03

Kaduna

1.4±0.29

0.2±0.03

1.0±0.02

0.1±0.10

0.2±0.05

Kano

2.5±0.36

0.2±0.04

1.8±0.64

0.1±0.04

0.2±0.13

Kastina

1.2±0.19

0.2±0.03

0.7±0.31

0.1±0.05

0.2±0.02

Langtang

2.0±0.46

0.2±0.03

1.6±0.51

0.1±0.01

0.2±0.08

Maiduguri

1.5±0.40

0.3±0.15

1.2±0.11

0.2±0.07

0.2±0.12

Mallamsidi

2.4±0.35

0.2±0.04

1.8±0.65

0.1±0.04

0.2±0.02

Minna

2.0±0.84

0.2±0.04

1.7±0.42

0.2±0.01

0.4±0.12

Oyo

4.4±0.25

0.3±0.02

3.2±0.23

0.2±0.02

0.3±0.11

Sokoto

1.1±0.14

0.2±0.05

0.7±0.27

0.1±0.03

0.4±0.43

Each result expresses the mean ±SD



37

Table 2: Dietary fibre components of tamarind (Tamarindus indica L.) fruits from various locations in Nigeria Location Acid Neutral Lignin (%) Hemicellulose Cellulose detergent detergent (%) (%) fibre (%) fibre (%) Abuja

4.9±0.21

6.6±0.29

3.1±0.25

1.7±0.16

1.8±0.33

Azare

5.1±0.14

6.7±0.22

3.4±0.1

1.6±0.08

1.7±0.08

Bauchi

4.9±0.22

7.0±0.14

3.4±0.3

2.1±0.14

1.5±0.08

Bichi

5.4±0.14

7.2±0.16

3.7±0.2

1.8±0.16

1.7±0.24

Birni-kebbi

5.0±0.08

6.9±0.08

3.5±0.2

1.9±0.14

1.5±0.16

Funtua

5.3±0.14

7.2±0.24

3.3±0.4

1.9±0.14

2.0±0.45

Gombe

5.0±0.08

6.8±0.14

3.3±0.1

1.8±0.08

1.7±0.08

Gwarzo

5.2±0.22

7.2±0.16

3.4±0.4

2.0±0.14

1.8±0.16

Jega

5.3±0.14

7.1±0.08

3.4±0.4

1.8±0.08

1.9±0.22

Jos

4.7±0.16

6.5±0.45

2.9±0.2

1.8±0.16

1.8±0.22

Kaduna

4.6±0.08

6.3±0.14

3.1±0.3

1.7±0.16

1.5±0.22

Kano

4.8±0.14

7.0±0.24

3.7±0.3

2.2±0.16

1.1±0.29

Katsina

5.3±0.14

7.4±0.14

3.3±0.2

2.1±0.14

2.0±0.14

Langtang

4.5±0.41

6.5±0.45

2.9±0.2

2.0±0.014

1.6±0.29

Maiduguri

4.4±0.22

6.0±0.16

3.2±0.2

1.6±0.08

1.2±0.36

Mallamsidi

4.9±0.22

6.9±0.16

3.1±0.1

2.0±0.14

1.7±0.33

Minna

4.9±0.22

6.4±0.14

3.0±0.2

1.5±0.14

1.9±0.24

Oyo

5.8±0.24

7.5±0.24

4.5±0.3

2.4±0.08

1.3±0.29

Sokoto

5.1±0.14

6.8±0.24

2.6±0.3

1.7±0.16

2.5±0.33

Each result expresses the mean ±SD



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