Comparative content and antioxidant nutritional quality of some bioactive compounds in commonly consumed fresh fruits in South--Western Nigeria.
Plant--based food items are rich in bioactive compounds, many of which are beneficial to man. These compounds serve as flavourants, colourants and antioxidants, thereby influencing the quality, acceptability and stability of such foods. Fresh fruits in particular are good sources of antioxidants which are first line of defence against free radical damage (Duthie et al., 2000). Antioxidant compounds like phenolic acids, polyphenol and flavonoids scavenge free radicals such as peroxides, hydroperoxide or lipid peroxyl and thus inhibit the oxidative mechanism that lead to degenerative diseases (Eberhadt et al., 2000). Epidemiological studies show that a diet high in fruits and vegetables can significantly reduce the risk of cancer, cardiovascular disease, ashthma and diabetes probably due to polyphenol antioxidant and anti-inflammatory effects (Wolfe et al., 2003). Phenolic compounds in fruits and vegetables are the secondary metabolites in plants that are derived from the metabolism of phenylalanine and tyrosine (Van Sumere, 1989). They are anticarcinogenic and they have been shown to reduce the bioavailability of carcinogens and inhibit the metabolic activation of carcinomas (Huang and Ferraro, 1992).
Fruits have organoleptic properties and are commonly enjoyed by many cultures and research is continuously being conducted on their health effects [6,7](Aprikian et al., 2001; Breinholt et al., 2003) which are functions of their inherent bioactive phytochemicals. Many factors affect the phytochemical profile of fruits and phytochemical concentrations vary greatly between different fruits and cultivars. The level of some phytochemicals varies during maturation of the fruits in response to available light, stage of fruit development, some types of fertilisation (Vinson et al., 2001) and exogenous bioregulator application (Olaiya et al., 2010). This study was conducted to analyse seven commonly consumed fresh fruits in South-Western Nigeria for basic bioactive phytochemicals of importance to human health. The results are described in this paper, along with data on certain biochemical indices of their palatability.
Materials and Methods
Plant Material: Seven different fruits were selected for this research. The fruits include mangoes (Magnifera indica), tomatoes (Solanum lycopersicon), watermelon (Citrulus lanatus), pineapple (Ananas comosus), oranges (Citrus sinensis), Apples (Malus sieversii), Avocado pears (Persea Americana). The fresh fruits were purchased at Bodija market in Ibadan, Nigeria.
Preparation of sample homogenate
The fruits were washed with distilled water; peeled, chunked, and about 200g of each sample was weighed with a calibrated weighing balance. The weighed samples were then macerated in a pestle and mortal with 800ml of distilled water to get the homogenate.
pH determination: About 20g of each sample were macerated with 80ml of distilled water. The samples were then homogenized for 2 minutes at maximum speed (Steinkraus et al., 1960) and pH of the homogenate were read at 25[degrees]C directly on a scholar pH meter, model 425.
Determination of titratable acidity: The AOAC (1999) official method of analysis  was used to determine the titratable acidity. Samples of the homogenate were directly titrated against 0.1M NaOH and the titratable acidity values were expressed as percent citric acid.
Determination of total anthocyanins: 1ml of each sample was diluted with 2ml of potassium chloride (0.025M) at pH 1.0 and sodium acetate (0.04M), pH 4.5. The diluted samples were held for 15minutes before taking the reading. The absorbance was measured at two different wavelengths 530nm and 700nm and at pH 1.0 and 4.5 using:
A = (A530nm - A700nm) pH 1.0 - (A530nm - 700nm) pH 4.5
The monomeric anthocyanin pigment concentration was calculated using the equation:
A x Mw x DF x 1000 / ([epsilon] - l)
where A = absorbance; Mw = molecular weight; DF = dilution factor; [epsilon] = molar absorptivity of cyanin-3- glucoside; l = path length.
Determination of total phenolics: 1ml of hydrophilic sample was diluted with distilled water fivefold, after 0.5ml of Folin-Ciocalteu reagent was added and allowed to react for 3minutes, followed by addition of 1ml of sodium carbonate and the sample were vortexed for 15seconds. Sample were been incubated for 1hour. The absorbance was measure at 725nm using camspec spectrophotometer. Distilled water was used as blank. The phenolic content was recorded as milligram tannic acid equivalent per 100g fresh weight of sample (mg TAE/100mg fw).
Determination of total flavonoids: 1ml of hydrophilic extract was added to each test-tube and the volume was made up to 5ml with distilled water. 0.3ml of 50g/L sodium nitrite was added and the tube was allowed to stand for 5minuts. Then 0.6ml of 100g/L alluminium chloride was added. After six minutes of mixing, 2ml of 1mol/L sodium hydroxide was added, followed by 2.1ml of distilled water. The absorbance was read at 510nm against the blank (distilled water).
Determination of total soluble solids (0Brix): Portions of the sample homogenate were rapidly heated to 80[degrees]C in a waterbath with constant stirring and stored at 70[degrees]C (Paredes-Lopez et al, 1987). The homogenate were then centrifuged at 6000 rpm at 10-12[degrees]C for 50minutes and filtered through Whatman No.1 filter paper to obtain the soluble extract. Total soluble solids were determined for each sample by drying 5ml of the filtrate at 70[degrees]C for 48 hours and were expressed as percent TSS.
The data obtained were expressed as the mean + standard error of three replications. The student t-test was used to determine the significant differences between means at 95% confidence level (Steele and Torrie, 1991).
Results and Discussion
The results revealed that the fruits show a wide range of antioxidant potential. Fruits from temperate regions are good sources of natural dietary antioxidants (Lees et al., 1995) which have been reported to have an important role in combating pathological states such as cardiovascular disease, diabetes and cancer, as they fight against free radical damage to cellular constituents. The total phenolic content varied from 0.60 to 2.17mg/100gfw, with watermelon fruit juice (WFJ) and avocado fruit juice (AvFJ) having the least and highest concentrations respectively. Interestingly, mango fruit juice (MFJ) exhibits a significantly higher (p<0.05) content of anthocyanin (8.026mg/100gfw) while AvFJ had no anthocyanin (Table 1). These results are consistent with that of Luximon-Rama et al., 2003 who reported similar findings in some Mauritian exotic fruits. Different fruits have varied anthocyanin content and this variation has been attributed to environmental conditions, and in some cases, to the analytical method (Hong et al., 2009).
Kalt et al.  1998 reported that phenolic composition, anthocyanin and antioxidant capacities in strawberries and highbush and lowbush blueberries changed during postharvest storage and the antioxidant capacity was correlated with the level of phenolics and anthocyanins. The phenolic content correlation does not seem to be restricted to fruits, as similar observation have been made for medicinal plants, beverages, vegetables, juice, wine and fresh and processed edible seaweed (Gul et al., 2000).
It is noteworthy that fruit anthocyanin content was much higher than those of any other phenolic subclass analysed and therefore appear to contribute significantly to antioxidant capacity of fruits. It has been shown that anthocyanin which comprises Pdimers and their derivatives and oligomers are strong antioxidants because of the hydroxyl group attached to the ring structure (Plumb et al., 1998).
The pH is an index of the eating quality of fruits as it contributes effectively to the taste. The low pH values of the fruits ranging from 3.94 to 5.96 (Table 2) would inhibit the proliferation of microorganisms thereby affecting the keeping quality. The moderate acidity values obtained for the fruits gives an indication of the level of organic acids in the juice. These organic acids are mostly responsible for the flavour of fruits and AvFJ gave a statistically higher (p<0.05) value of 0.73 in comparison with others (Table 2). The soluble solids content of the fruits was between 0.1 and 1.0 0Brix, with the highest value recorded in AFJ (Table 2). The soluble solids content is also an important criterion in the determination of fruit quality (Alobo, 2000).
MFJ had a significantly higher (p<0.05) brix = to - acid ratio relative to the other fruit juices (Table 3). This therefore suggests that mango will exhibit the highest degree of sweetness since this ratio has been linked with fruit sweetness (Fawcia et al., 1999).
Flavonoid level in the fruits ranged between 0.070mg/100gfw and 0.95mg/100gfw, with AFJ recording the highest amount while PFJ had the least (Table 3). Flavonoids therefore seem to exert less effect on the antioxidant potential of the fruits when compared with anthocyanins and phenolics that are present in greater proportions. As free radical scavengers, flavonoids are known to inhibit lipid peroxidation, enhance vascular relaxation and help prevent atherosclerosis (Hollman and Katan, 1997). They also inhibit cyclooxygenases which may reduce thrombosis (Formica and Regelson, 1995).
This study shows the potential antioxidant properties of Nigerian fruits, notably mango, orange, avocado pear, watermelon, tomato, pineapple, and apple that could be used as supplement in a balanced diet within existing nutrition programmes. This could prove to be a more effective and economic means of protecting the body against various oxidative stresses than supplementation with individual antioxidants, thereby serving to ameliorate diseases ascribed to free radical damage and promoting the health of the populace.
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C.O. Olaiya * and M.A. Bello
Department of Biochemistry, University of Ibadan, Ibadan, Nigeria.
* Corresponding Author E-mail: email@example.com
Table 1: Total phenolic and anthocyanin content of fruit juices Fruit sample Phenolic content mg/100gfwb % AFJ 0.92 [+ or -] 0.02 9.87 AvFJ 2.17 [+ or -] 001 23.25 MFJ 1.88 [+ or -] 0.02 20.06 OFJ 1.54 [+ or -] 0.03 16.47 PFJ 1.05 [+ or -] 0.01 11.26 TFJ 1.19 [+ or -] 0.01 12.68 WFJ 0.60 [+ or -] 0.02 6.41 Fruit sample Anthocyanin content mg/100gfwb % AFJ 0.836 [+ or -] 0.015 5.77 AvFJ 0.000 [+ or -] 0.000 0.00 MFJ 8.026 [+ or -] 0.015 * 55.43 * OFJ 4.100 [+ or -] 0.010 28.32 PFJ 0.650 [+ or -] 0.011 4.49 TFJ 0.813 [+ or -] 0.011 5.61 WFJ 0.053 [+ or -] 0.005 0.37 AFJ = Apple fruit juice, AvFJ = Avocado pear fruit juice, MFJ = Mango fruit juice, OFJ = Orange fruit juice, PFJ = Pineapple fruit juice, TFJ = Tomato fruit juice, WFJ = Watermelon fruit juice * Significantly different from others in the column (p<0.05). Table 2: pH, titratable acidity and total soluble solids content of fruit juices Fruit pH Titratable acidity sample (%) AFJ 4.10 [+ or -] 0.07 0.24 [+ or -] 0.17 AvFJ 5.96 [+ or -] 0.10 * 0.73 [+ or -] 0.14 * MFJ 4.08 [+ or -] 0.03 0.22 [+ or -] 0.17 OFJ 4.48 [+ or -] 0.06 0.11 [+ or -] 0.06 PFJ 3.94 [+ or -] 0.03 0.23 [+ or -] 0.09 TFJ 4.46 [+ or -] 0.05 0.41 [+ or -] 0.11 WFJ 4.89 [+ or -] 0.03 0.40 [+ or -] 0.07 Fruit Total soluble sample solids ([sup.0]Brix) % AFJ 1.00 [+ or -] 0.09 * AvFJ 0.10 [+ or -] 0.06 MFJ 1.10 [+ or -] 0.03 OFJ 0.10 [+ or -] 0.07 PFJ 0.11 [+ or -] 0.02 TFJ 0.50 [+ or -] 0.08 WFJ 0.51 [+ or -] 0.07 * Significantly different from others in the column (p<0.05). Table 3: oBrix/Acid Ratio and Total Flavonoids content of fruit juices Fruit sam[sup.o]Brix/Acid ** Ratio Total flavonoids mg/100gfwb % AFJ 4.17 [+ or -] 0.20 0.95 [+ or -] 0.02 49.53 * AvFJ 0.14 [+ or -] 0.05 0.24 [+ or -] 0.01 12.66 MFJ 5.00 [+ or -] 0.12 * 0.07 [+ or -] 0.01 3.80 OFJ 0.91 [+ or -] 0.08 0.25 [+ or -] 0.02 13.03 PFJ 0.48 [+ or -] 0.07 0.07 [+ or -] 0.02 3.64 TFJ 1.22 [+ or -] 0.16 0.21 [+ or -] 0.01 10.74 WFJ 1.28 [+ or -] 0.14 0.13 [+ or -] 0.01 6.56 * Significantly different from others in the column (p<0.05). ** Titratable acidity
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|Author:||Olaiya, C.O.; Bello, M.A.|
|Publication:||International Journal of Biotechnology & Biochemistry|
|Date:||Nov 1, 2011|
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