The preservative efficacy ofnspri multipurpose dryer on ascorbic acid and polyphenol content of Lycopersicum esculentum (Tomato)

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1 Bioscien'ce Research Communications Vol. 14. No, 6. December Printed in Nigeria /2002 $ Klobex Academic Publishers The preservative efficacy ofnspri multipurpose dryer on ascorbic acid and polyphenol content of Lycopersicum esculentum (Tomato) O. B. Oloyede l and 1. S. Afolabi 2 IDepartment of Biochemistry, University of!lorin, P.M.B !lorin, Kwara State. Nigeria. 2Nigerian Stored Product Research Institute, P.M.B !lorin, Kwara State, Nigeria. ABSTRACTS: The effect of NSPRl Multipurpose dryer on the Ascorbic acid and spolyphenol content of Lycospersicum esculentum (tomato) has been studied. NSPRl Multipurpose drying (50-60 C) significantly (P<0.05) reduced the ascorbic acid concentration at moisture content of 18.28%. A significant (P<0.05) increase in polyphenol concentration was observed at moisture content of 11.10%. The increase in polyphenol content (an antioxidant) which is desirable may indicate that NSPRI dryer will be adequate for drying tomato provided a moisture level of tomato fruit is not more than 18.28% to retain the major concentration of ascorbic acid. Tomato fruits (Lycopersicum esculentum) belongs to the fruits and vegetables class, it is consumed locally in Nigeria for the provision of vitamins (e.g. ascorbic acid and ~-carotene). It is a highly perishable food due to its high moisture content 94.1 % (Jay, 1986), it therefore requires a special attention for its preservation and storage. The conventional drying method (i.e. sun-drying) aimed at reducing its moisture level so as to minimise storage loss is locally used for tomato preservation, a process usually accompanied by unhygienically spreading the fruits to sun-radiation either on the ground or on a platform; thus making it an easy prey to mould, bacteria, dust, rats and insect infestation. Moreso, the method is faced with problems of seasonal changes (rainfall and high humidity). Attempt to eliminate these associated problems led to the development of an economically cheap NSPRI Multipurpose dryer as described by Williams (1999) for drying varieties of food products including tomato. Ascorbic acid and the phenolic group (consisting of phenolic acid like p-coumaric acid, ferulic acid. chlorogenic acid. cathecols, Isof1avones, etc.) are particularly important in fruits and vegetables where they both act as a synergist to the natural antioxidants (Davidek et ai., 1990; Maillard and Bersert. \995: Swanson. 1995: Vinson et ai., 1998). In addition. ascorbic acid is commonly known to prevent disease like scurvy (Lehninger. 1982). Polyphenol has also been reported to be of long term benefit to human health in

2 the prevention of diseases like cancer, cardiovascular diseases etc. (Soleas et ai., 1997; Wiseamn, 1995). This work was therefore designed to assess the efficacy of the NSPRl dryer using its effect on the ascorbic acid and polyphenols content of the tomato fruits. Ripe Roma type tomatoes (1. esculentum) were purchased fresh from Ipata local market, Ilorin, Nigeria. The fruits that were free from bruise and infection were selected, washed and dried. NSPRl Multipurpose dryer was used for drying (50-60 C drying temp.) and the drying of samples was commenced at least 30mins after the heating chamber was ignited, as described by Williams (1999). The tomato samples were weighed and arranged in sets into the dryer with each of the sets having its own corresponding sets as control were arranged under ambient temperature (23 _ 28 C). Analysis were done at 0.5hr, 1.0hr, 1.5hrs, 2.5hrs and 3.5hrs on the first day of drying and then 24.0hrs and 48.0hrs after the last analysis was done on the first day. At this stage, drying had been completed and the product ready for storage. The ascorbic and extraction method of Tono and Fujita (1982) was used g of fresh tomato was taken after drying and was homogenised with 60ml of 0.5M sodium phosphate buffer, ph 7.0 for 1.0min. The homogenate was then centrifuged at 3500g x 15mins. The resulting supernatant was used as ascorbic acid assay solution. Ascorbic acid concentration was determined by the method of Jagota and Dani (1982). An aliquot of 0.5ml of the ascorbic acid extract was added to 1.5ml of distilled water, Folin - Cocalteau reagent (0.2ml) was thereafter added to the sample test tube to produce a blue colour (which is stable for l8hrs). A mixture of 0.2ml distilled water and 0.2ml Folin-Ciocalteau reagent was used as the blank, the mixrures were shaken vigorously and left to stand for 10mins. After which the absorbances were read at 760nm wavelength. The absorbances were read off from prepared standard graph to obtain the ascorbic acid concentration. The extraction method of Swain and Hills (1959) was used. Dried tomato (1 OOg fresh wt.) was homogenised in 50ml of 2M HC1, the homogenate was boiled in a water bath for 30mins. The boiled homogenate was cooled down to ambient temperarure and then filtered through a double layered cheese cloth, the residue obtained was made-up to 500ml using distilled water. The method of Swain and Hills (1959) was used to assay for polyphenol concentration. An aliquot of O.5ml of the polypheno extract was added to 5.5ml distilled water, and thereafter Folin-Ciocalteau reagent (O.5ml) was also added. After standing for 30mins, 0.5ml of saturated sodium carbonate solution (0.164g1ml) was aqded and the mixture was then incubated at 37 C for 60mins. The reference sample contained the same proportion of all the mixtures with the exception of the polyphenol extract. The absorbance readings were taken at 700nm wavelength and the corresponding concentration were extrapolated from a prepared standard graph.

3 The moisture levels obtained in both the fresh samples and the drying samples during the drying period is as shown in Table 1, the drying method had no significant effect up to 3.5hrs on ascorbic acid concentration of L. esculentum. However, significant reduction (P<0.05) was manifested in the ascorbic acid concentration drying proceeded for 2 days (Fig. 1), as at this period, the ascorbic acid concentration reduced to 1I6 th of the value of the sample exposed to ambient temperature (when moisture content was 18.28%). The concentration reduced to 117 th of the value of the sample exposed to ambient temperature (when moisture content was 11.10%) on the third day of drying. There was no significant difference (P>0.05) in the polyphenol concentration (Fig. 2) for the 2 days of drying (when moisture content was 18.28%) but a significant increase (P<0.05) in polyphenol concentration representing about 3 times the value for the control was obtained on the 3 days drying period (when moisture content was 11.10%). Table I: Moisture content levels in fresh Lycopersicum esculentum and the sample subjected to drying at C using NSPRl dryer. Time (hr) Dryed Samples (%) Fresh Samples (%) ± ± ± ± ± ± ± ± 1.021? ± ± _.) ± ::t: ± ::: :i: ± The significant reduction of ascorbic acid concentration during drying is expected because ascorbic acid is a water soluble vitamin. To avoid any severe effect on ascorbic acid concentration, drying of tomato with NSPRl dryer should not exceed a moisture level of 18.28%. Ascorbic acid losses in fruilsivegerables could occur during storage even at 2.5% moisture content (Davidek et ai., 1990), hence stabilizing the ascorbic acid content under low temperature storage (Akinlua and Bamgbose, 1998) is essemial IO minimise further losses. The significant increase in polyphenol concentration in the dried sample as observed in the present study over that of the sample exposed to ambient temperature agrees with the report of Vinson et al (1988). The temperature of C employed in the NSPRl Multipurpose dryer could be responsible for the release of insoluble bound phenolic compounds in the tomato fruits as the linkages between the phenolates and lignins are broken (Maillard and Bersert, 1995). Also, the increase in phenolic content cannot be attribmed IO de novo synthesis as phenylalanine ammonia lyase (PAL), a key enzyme in phenolic biosynthesis is reported to lose its activiry Jrouno the temperature (50-60 C) used in this study (Maillard and Bersen. 1995).

4 Fig. I: Ascorbic acid concentration in Lycopersicum esculentum exposed to ambient temperature (x----x) and the sample subjected to drying at C (e e) using NSPRI multipurpose dryer. Fig. 2: Polyphenol concentration in L\ copersicllm esculentum exposed to ambient temperature (x----:-.:).1nd the sample subjected ro drying at C (e e) using 1 SPRl multipurpose dryer.

5 The NSPRl multipurpose dryer may successfully conserve the ascorbic acid content provided the tomato is not dried below 18.28%, drying beyond this moisture level significantly reduced ascorbic acid content but the reduction is compensated for by the release of similarly health beneficial membrane bound' polyphenols. Akinlua, O. and Bamgbose, A. (1998). The effect of home storage conditions on vitamin C content of cooked peppers.. Proceeding of nnd Annual NIFEST Conference, vol. I, Davidek, J.; Velisek, J. and Porkomy, J. (1990). Chemical changes during food processing: In development in food science, vol. 21, Jagota, S.K. and Dani, H.M. (1982). A new colorimetric technique for estimation of vitamin C using Folin reagent. Anal. Biochem. 127( 1), Jay, J.M. (1986). Spoilage of fruits and vegetables; In Modem Food Microbiology, Third edition, pp , CBS Publisher and Distributors, New-Delhi, (India). Lehninger, A.L. (1982). Principle of Biochemistry textbook, 2 nd edition. Worth Publisher Inc., South N.Y., 10016, pp Maillard, M. and Bersert, C. (1995). Evolution of antioxidant activity during kilning; role of insoluble bound phenolic acids of barley and malts. J. Agric. Fd. Chern., 43(7), Soleas, CoJ.; Tomlinson, G.; Diamandis, E.P. and Goldberg, D.M. (1997). Relative contributions 0: ~')lvphenolic constituents to the antioxidant status of wines. J. Agric. Fd. Chern. 45(10), Swain, T. and Hills, W. E. (1959). Phenolic constituents of prums domestica. 1. Sci. Fd. Agric. IO( I), Swanson, B.G. (1995). Tannins and polyphenols; In encyclopaedia of Food Science, Food Tech. and Nutrition (1st edition), vol. 7, pp Tono, T. and Fujita, S. (1982). Spectrometric determination based on difference spectra of L. ascorbic acid in plant and animal foous. Agric. BioI. Chern. 46( 12), Vinson, 1.:\.: Hao, Y.: Su, X. and Zubik, L. (1998). Phenol antioxidant quantity and qualitv In foods, vegetal,!es. J. Agric. Fd. Chern. 46( I0), Williams, J.O. (1999). Post-harvest technology; training of artisans and small holders farmers in selected communiries. NSPRliUNDP Project. 9 th - 11 th Nov., pp Wiseman. H. (1995). Dierary influences on membrane function: importance in prorecrion againsr OXidatIve damage and diseases. Nutr. Biochem. 7( 1), 2-15.