Effect of Ripening on Eating Quality of ‘Keitt’ Mango Chips

F. Appiah, P. Kumaha, I. Idun and J.R. Lawson Department of Horticulture Faculty of Agriculture College of Agriculture and Natural Resources Kwame Nkrumah University of Science & Technology Kumasi Ghana

Keywords: ‘Keitt’ mango, chips, physico-chemical changes, eating quality, sensory evaluation

Abstract Mango (Mangifera indica) is consumed, among other reasons, for its pleasant taste and flavour. Mango fruits are rich sources of vitamins A, B and C. They are being increasingly processed into products such as dried mango slices (chips). These products have longer shelf life than fresh fruit and therefore assure all year round availability of mango in various forms. Mango at different stages of ripening possesses different physico-chemical properties. A study was carried out to determine the effect of stage of ripening of fruits on eating quality of ‘Keitt’ mango chips. Physico-chemical changes were monitored in fruits during ripening. There were increases in levels of Total Soluble Solids and pH while titratable acidity and vitamin C content declined with ripening. Chips showed increased levels of protein and crude fiber with ripening whereas the levels of carbohydrates declined. Magnesium levels in chips increased with ripening whereas the levels of phosphorus, potassium, calcium and sodium declined. Sensory analysis revealed that chips produced from fully ripe ‘Keitt’ mango fruits were more acceptable than half ripe and unripe in appearance (1.37), taste (1.27), flavour (1.38) and mouth feel (1.45). Texture of chips produced from fully ripe mangoes performed satisfactorily (2.64).

INTRODUCTION Mango (Mangifera indica L.), a fruit native to the tropics and sub-tropics belonging to the family Anacardiaceae (Pamplona-Roger, 2003), is usually consumed worldwide for its pleasant taste and flavour (USDA, 2006). It is a rich source of vitamins A and C as well as dietary fibers (Pal, 1988). According to Litz (1998), mango is commonly utilized for processing of juice, nectars, fruit leather, and frozen pulp as well as for flavouring product for baked goods, ice cream or yoghurt. Dried pieces may be added to salads and fruit cocktail as well (Nakasone et al., 1999). Global production of mangoes is forecasted to reach 30.7 million tons (Mt) by 2010 (FAO, 2003), with India maintaining the lead with 12.3 Mt. Mango is a non- traditional export produce in Ghana where the industry is employing many workers. Ghana produced 4,000 t of mangoes in 2003 (Deng and Janssens, 2004). Mangoes produced in Ghana include, (the local cultivar), ‘Palmer’, and ‘Keitt’; ‘Keitt’ alone represents 85% of the total export value (Asiedu et al., 2007). Mango is a delicate perishable fruit (Temple, 1999) which must be handled with care. Recent developments at the international market have necessitated the need to research into promoting local consumption and utilization of processed mangoes. This study assessed the effect of stage of ripening on eating quality of ‘Keitt’ mango chips.

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Proc. First All African Horticultural Congress 547 Eds.: J. Wesonga and R. Kahane Acta Hort. 911, ISHS 2011 MATERIALS AND METHODS

Experimental Design and Sample Preparation The experiment was carried out at the laboratory of the Department of Horticulture, Kwame Nkrumah University of Science and Technology, KNUST, Kumasi, Ghana. Fresh fully mature ‘Keitt’ mango fruits were harvested from Dormehsco Farm at Somanya in the Greater Accra Region of Ghana and transported immediately to the laboratory for analysis. Mature mango fruits were plucked from the same tree and 180 selected for the study. Selected fruits were uniform and undamaged with no visible symptoms of infection. Fruits were cleaned and randomly grouped into 3 (60 mangoes per group). Each group was subdivided into 3 subgroups (replicates) with each subgroup having 20 fruits. Fruits were allowed to ripen under room conditions (20-33°C). The first group (60 fruits) was analyzed unripe, the second analyzed half-ripe and the third fully- ripe. Fruits were considered unripe when firm with no depression when thumb-pressed. Fully ripe fruits had strong perfume, and indented upon pressing with the thumb (Mamiro et al., 2007). Five mango fruits per replicate of 20 were used for the analyses whilst 10 were used for chip production. This procedure was repeated for all treatments.

Chips Production Fresh ‘Keitt’ mango fruits were washed, peeled and sliced into slices (2.0×4.0× 0.5 cm3) and spread evenly on trays lined with aluminum foil. Trays were then placed in a Wagtech oven (Model GP120SSE300HYD) at temperature of 60°C for 24 h. The slices were periodically turned to ensure uniform drying. The dried slices were allowed to cool for about 30 min in a dessicator before analysis. Mango fruits were analyzed for moisture content, pH, Total Soluble Solids (TSS), titratable acidity (TA), and vitamin C. Standard procedures recommended by AOAC (1990) were followed for proximate parameters, pH, TSS, titratable acidity and vitamin C content. pH was measured using a Suntex electronic pH meter (model FF 701). TSS were determined with a Bellingham and Stanley Delta refractometer (20-60). Potassium and sodium were determined by flame emission photometry (Jenway PFP-7), calcium and magnesium by EDTA titration while phosphorus was measured by Ammonium Molybdate method (AOAC, 1990).

Sensory Evaluation Sensory evaluation was carried out on the mango chips using 30 untrained panelists. Sensory attributes assessed were appearance, taste, aroma, crispness, mouth feel and overall acceptability. A hedonic scale of 1-5 (1 - like very much; 2 - like slightly; 3 - neither like nor dislike; 4 - dislike slightly; 5 - dislike very much) was used for the assessment. All data were analyzed using GENSTAT (Discovery edition 3) and graphs were plotted to show trends. Least significant difference (LSD) test was used to determine differences between means.

RESULTS AND DISCUSSIONS

Chemical Characteristics of Fruits during Ripening Moisture content of the fruits increased from 79.75 to 83.11% during ripening (Fig. 1). There were significant differences at P>0.05 between all the stages of ripening. The increase in moisture content of the fruits during ripening could be attributed to hydrolysis of storage carbohydrates into simple sugars that increased osmotic transfer of moisture from peel to pulp (Kays, 1991; Izonfuo and Omuaru, 1988). During ripening TSS content increased significantly at P<0.05 in the mango pulp (Fig. 2) and rose from 7.00 to 15.95% in unripe and fully ripe mangoes respectively. Gill et al. (2000) and Ihekoronye and Ngoddy (1985) reported that the major sugar in ripe mango was sucrose. Vazquez-Salinas and Lakshminarayana (2006) reported spectacular increases in sucrose content of mango during ripening. However, Favier et al. (1993) reported that the soluble sugars of mango pulps were mainly composed of fructose, with about 30% sucrose and

548 20% glucose. Mitra and Baldwin (1997) and Selvaraj (1989) attributed the increase in TSS during ripening to transformation of starch (long chain carbohydrates) into soluble sugars as the carbohydrates in the ripening fruit were broken down into simple sugars under the action of phosphorylase enzymes. Fuchs et al. (1980) associated the hydrolysis of starch in the ripening mango fruit with amylase activity. This is in agreement with higher osmolality attracting more moisture in the flesh of the fruit. Titratable acidity content in the mango fruits showed significant decline (at P>0.01) with ripening (Fig. 3). According to Dadzie and Orchard (1997) titratable acidity gives a measure of the amount of acid present. Ihekoronye and Ngoddy (1985) identified citric acid as the major acid in mango. Vazquez-Salinas and Lakshminarayana (2006) reported sharp decline in acidity of ‘Kent’ mango fruits during ripening. The decline in acidity could be due to susceptibility of citric acid to oxidative destruction as impacted by ripening environment (Aina, 1990). There was significant change in pH from 2.47 to 3.90 during ripening at P>0.01 (Fig. 4). This trend was already reported by Tovar et al. (2000). They reported increase in titratable acidity was associated to decreased pH. The observed decline in pH could be due to utilisation of acids as respiration substrates (Dadzie and Orchard, 1997). The decline in acidity during ripening was reported as a consequence of starch hydrolysis leading to increasing total sugars and acidity reduction (Fuchs et al., 1980). There was a rapid significant (P>0.05) decline in vitamin C content with mango fruit ripening (Fig. 5). Vitamin C content declined from 29.08 to 3.45 mg 100 g-1. Similar trends were reported by Mamiro et al. (2007) and Vazquez-Salinas and Lakshminarayana (2006) during ripening of different mango cultivars. This decline could be attributed to susceptibility of vitamin C to oxidative destruction (Aina, 1990).

Nutritional Composition of Mango Chips There was insignificant decline in protein and carbohydrates contents of mango chips with ripening (Table 1). However, fat, crude fibers and ash contents increased. Decline in energy during ripening was not significant. Phosphorus, calcium and sodium levels declined significantly (P>0.05) with ripening with the exception of potassium which showed insignificant decline (Table 2). Increase in magnesium content was insignificant. FAO recommended dietary allowances for calcium is 0.4 g, what a mango per day could almost cover.

Sensory Evaluation Crispness of the mango chips produced from unripe fruits was most preferred (1.72) to that of the half (2.29) ripe and full ripe (Table 3). The crispness of chips from full-ripe mangoes was the least preferred with a mean sensory score of 2.64. The declining acceptance of crispness with ripening could be attributed to softness of the pulp, high moisture and TSS contents with ripening. These differences in crispness at different stages of ripening were all significant at P>0.05. Taste of chips produced from the full-ripe mango fruits were most preferred (1.27) as compared to unripe (2.91) and half ripe (2.52) mango fruits (Table 3). There were significant differences in chips produced from the three ripening stages (P>0.05). Acids are known to be responsible for the taste in most fruits with low pH. Taste is due to the sensations one feels on the tongue that is whether sweet, salty, acidic or bitter. As starch in mango fruits were transformed into sugars during ripening, the taste became sweet due to increased contents of short chain sugars (fructose, sucrose) contributing to the sweetness of the fruit. Full-ripe chips performed better probably due to their sweetness. The panelist did not like the taste of chips made from the unripe fruits probably due to their sourness (acidity not balanced by sweet sugars). The aroma of a fruit is usually derived from the production of plenty different volatile compounds (Seymour et al., 1993). Aroma of mango chips produced from full- ripe fruits was most preferred (1.36) followed by half-ripe (2.41) and unripe (2.89) (Table 3). The characteristic aroma of mango could not be solely attributed to any single

549 component. However, the typical green-aroma of the unripe mango might be attributed to cis-ocimene and b-myrcene (Engel and Tressl, 1983). Fruit metabolism changes during ripening and this explains why the aroma of mango chips produced from the full-ripe mango fruits was preferred by the panelist to the others. Appearance is the most important factor consumers take into consideration in purchasing a produce. Chips produced from full-ripe mango fruits scored highest for appearance (1.37) as compared to those from unripe (2.61) and half-ripe mangoes (2.33) (Table 3). Intensity of yellow colour increased with fruit ripening. This contributed significantly to the attractiveness of full-ripe chips. Mouth feel gives an indication of the sensation when food is in the mouth. Mature- green, half-ripe and full-ripe chips scored 3.09, 2.49 and 1.45 respectively (Table 3). Chips from full-ripe mango fruits were significantly (P>0.05) most preferred while those from unripe were least preferred. Preference for full-ripe chips could be attributed to its high sugar content and lower acidity. Overall acceptability gave the overall preference of the sensory panelists. Mean score for overall acceptability for the chips ranged 3.13, 2.56 and 1.38 for unripe, half- ripe and full-ripe mangoes respectively (Table 3). Panelists preferred chips produced from the full-ripe ‘Keitt’ mango fruits to those made from the mature-green mangoes or half- ripe mangoes. This was probably due to the high sugar contents of full-ripe fruits. Although differences in overall acceptability of mango chips produced from the unripe and half-ripe mangoes were not significant (P<0.05), differences between unripe and full- ripe as well as half-ripe and full-ripe were significant.

Correlation between Chemical Properties of Fruit and Sensory Attribute of Chips We have been able to evidence a strong inverse correlation between pH-taste, pH- flavour, pH-overall acceptability, TSS-taste, TSS-flavour and TSS-overall acceptability (Table 4). Taste, flavor, mouth-feel and overall acceptability increased with declining TA.

CONCLUSION This project was initiated to process ‘Keitt’ mango fruits at different ripening stages into chips and to establish the effects of ripening on the eating quality of the mango chips. During ripening of ‘Keitt’ mango fruits moisture content of pulp, pH, TSS increased while TA and vitamin C content decreased. Phosphorus, calcium and sodium contents in mango chips declined with ripening while magnesium content increased. These changes had significant effects on the sensory evaluation of the mango chips. Chips produced from ripe mango fruits were most preferred although they were not crispy. High sugar content and reduced acidity of chips from full-ripe mangoes contributed significantly to their acceptance.

Literature Cited Aina, J.O. 1990. Physic-chemical changes in African mango (Irvingia gabogensis) during normal storage ripening. J. Food Chem. 36:205-212. AOAC. 1990. Official methods of analysis of Association of Official Analytical Chemists. 15th Edition, Association of Official Analytical Chemists, Arlington VA. p.1058-1059. Aurore, G., Parfait, B. and Fahrasmane, L. 2009. Banana, raw materials for making processed food products. Trends in Food Science and Technology 20:78-91. Dadzie, B.K. and Orchard, J.E. 1997. Routine Post Harvest Screening of Banana/Plantain Hybrids: Criteria and Methods. Technical Guidelines 2. INIBAP (International Network for the Improvement of Banana and Plantain); IPGRI (International Plant Genetic Resources Institute, Rome, Italy); Montpellier, France; CTA (ACP-EU Technical Centre for Agricultural and Rural Cooperation), Wageningen, The Netherlands (Pubs). Favier, J.C., Ireland-Ripeit, J., Luussuc, C. and Feinberg, M. 1993. Répertoire général des aliments. Tome 3: Table de composition des fruits exotiques, fruits de cueillette

550 d’Afrique. INRA, France (ed.). p.55-59. Fuchs, Y., Pesis, E. and Zauberman, G. 1980. Changes in amylase activity, starch and sugar contents in mango fruit pulp. Scientia Horticulturae 13:155-160. Gil, A., Duarte, I., Delgadillo, I., Colquhoun, I., Casuscelli, F., Humpfer, E. and Spraul, M. 2002. Study of the compositional changes of mango during ripening by use of nuclear magnetic resonance spectroscopy. J. Agric. Food Chem. 48:1524-1536. Ihekoronye, A.I. and Ngoddy, P.O. 1985. Integrated Food Science and Technology for the Tropics. Macmillan Publishers Ltd. 303p. Kansci, G., Koubala, B.B. and Lape, I.M. 2003. Effect of ripening on composition and the suitability for jam processing of different varieties of mango (Mangifera indica). African Journal of Biotechnology 2(9):301-306. Kays, S.J. 1991. Postharvest Physiology of Perishable Plant Products. Van Nostrand Reinhold N.Y. 247p. Litz, R.E. 1997. The mango: Botany, Production and Uses. CAB International, N.Y. 425p. Mitra, S. and Baldwin, E.A. 1997. Mango. p.85-122. In: Post harvest physiology and storage of tropical and subtropical fruits. CAB International, N.Y. Mamiro, P., Fweja, L., Chove, B., Kinabo, J., George, V. and Mtebe, K. 2007. Physical and chemical characteristics of off-vine ripened mango (Mangifera indica L.) fruit (Dodo). African Journal of Biotechnology 6(21):2477-2483. Pal, R.K. 1998. Ripening and rheological properties of mango as influenced by ethereal and carbide. J. Food Sci. Technol. 35(4):358-360. Pamplona-Roger, G.D. 2003. Healthy Foods. Editorial Safeliz, Madrid. p.326-329. Shashirekha, M.S. and Patwardhan, M.V. 1976. Changes in amino acids, sugars and non volatile organic acids in a ripening mango fruit (Mangifera indica, Badami Variety) Lebesmittel Wissenchaft Technologie 9:369-370. Selvaraj, Y., Kumar, R. and Pal, D.K. 1989. Changes in sugars, organic acids, amino acids, lipid constituents and aroma characteristics of ripening mango (Mangifera indica L.) fruit. J. Food Sci. Technol. 26:308-313. Temple, L. 1999. Le marché des fruits et légumes au Cameroun. Bulletin technique. CIRAD-IRAD (ed.). Yaoundé, Cameroun. 163p. Tovar, B., Ibarra, L.I., Garcia, H.S. and Mata, M. 2000. Some compositional changes in Kent mango (Mangifera indica) slices during storage. J. Appl. Hortic. 2(1):10-14. USDA. 2006. Nutrient Database for standard reference. http://www.thefruitpages.com/ chartmango.shtml. Vazquez-Salinas and Lakshminarayana. 2006. Compositional changes in mango fruit during ripening at different storage temperatures. J. Food Sci. 50(6):1646-1648.

551 Tables

Table 1. Proximate composition of ‘Keitt’ mango chips (in % of dry weight).

Crude Crude Carbo- Moisture Crude fat Ash Energy Stage protein fibers hydrates (%) (%) (%) (Cal) (%) (%) (%) Unripe 8.74 4.90 0.09 1.52 5.80 78.95 336.21 Half-ripe 9.74 4.46 0.15 1.73 8.37 75.55 321.39 Full-ripe 11.43 4.01 0.27 1.80 8.58 73.91 314.11 Lsd 2.72 0.92 0.19 0.31 0.63 5.19 22.50

Table 2. Mineral composition of ‘Keitt’ mango chips (in % of dry weight).

Phosphorus Potassium Calcium Magnesium Sodium Stage (%) (%) (%) (%) (%) Unripe 0.134 0.780 0.480 0.384 0.660 Half-ripe 0.122 0.720 0.480 0.624 0.640 Full-ripe 0.092 0.670 0.320 0.624 0.560 Lsd 0.020 0.182 0.095 0.026 0.081

Table 3. Panelists scoring for sensory parameters of ‘Keitt’ mango chips.

Mouth Overall Stage Crispness Taste Aroma Appearance feel acceptability Unripe 1.72 2.91 2.89 2.67 3.09 3.13 Half-ripe 2.29 2.52 2.41 2.33 2.49 2.56 Fully ripe 2.64 1.27 1.38 1.37 1.45 1.38 Lsd 0.81 0.61 0.61 0.59 0.67 0.62

Table 4. Correlation between chemical characteristics of ‘Keitt’ mango fruits and sensory attributes of mango chips.

Parameters Mouth Overall Crispness Taste Flavour Appearance studied feel acceptability pH -0.93 0.98 0.99 0.99 0.99 0.99 TSS -0.99 0.96 0.98 0.96 0.99 0.98 TA 0.98 -0.98 -0.99 -0.98 -0.99 -0.99

552 Figures

Fig. 1. Changes in moisture content of mango fruit during ripening.

Fig. 2. Changes in Total Soluble Solids of mango fruit during ripening.

Fig. 3. Changes in titratable acidity of mango fruit during ripening.

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Fig. 4. pH changes in mango fruit during ripening.

Fig. 5. Changes in vitamin C content of mango fruits during ripening.

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