الملخص الإنجليزي
Tomato (Lycopersicum esculentum) is one of the most widely grown and consumed crop in Oman and the world. It is an important source of dietary nutrients and antioxidants, especially lycopene and vitamin C. However, little is known about the antioxidant contents of tomatoes commonly consumed in Oman. The aim of the present study was to evaluate the effect of fruit maturity, storage conditions, and natural variation of fruit size on the physico-chemical properties, proximate composition, and antioxidant components of three commercial tomato cultivars commonly grown in Oman (Lycopersicum esculentum cv. 'Monika', 'Isabella' and 'Cherry'). Significant (P < 0.05) differences were observed in the chemical composition (moisture, ash, fibre, protein, and fat), physico-chemical characteristics (pH and total soluble solids) and antioxidant contents (lycopene and ascorbic acid) among the three cultivars during maturation. 'Cherry tomato was found to contain the highest amount of fiber, ash, fat, protein and total soluble sugar compared to 'Monika' and 'Isabella'. Irrespective of cultivar, the fruit lycopene content increased rapidly during maturation; however, vitamin C content fluctuated during maturation. Among the tomato cultivars studied, "Isabella' contained the highest amount of lycopene and vitamin C at the last stage of maturation (dark red colour), compared with 'Cherry' and 'Monika', respectively.
Storage temperature and duration affected the antioxidant components and nutritive value of tomatoes; however, the magnitude of these effects depended on cultivar. Over seven day's storage duration at different temperatures, cold storage enhanced the retention of lycopene and vitamin C contents in fruit better than elevated storage temperatures. The effect of natural variation in fruit size on lycopene and vitamin C contents was investigated and found to be significant but did not follow a consistent pattern. In general, 'Isabella' fruit with large size had higher lycopene and lower vitamin C contents than very small size fruit. Large and very small sized 'Cherry tomatoes had similar antioxidant contents which were significantly different from the contents of medium and small size fruit.
Regression analysis was used to develop prediction models for lycopene and total ascorbic acid (TAA) contents of tomato fruit based on non-destructive measurement of fruit external colour indices using a portable chromameter. Overall, colorimetric index a*/b* gave a better prediction of lycopene content for 'Cherry' (y=14.7e".9833, R2=0.9573), "Isabella' (y=26.258x2+41.4x+20.856; RP=0.9784), and 'Monika? (y=41.328x2+22.912x+7.2698; R=0.9617) than vitamin C content of 'Cherry' (y=. 6.8408x +7.6425x+41.411; RP=0.8881), "Isabella' (y=-0.4094x +8.2362x+43.955; R?=0. 0.8827), and 'Monika' (y=-14.042x2+8.624x+48.483; R2=0. 0.5287). These prediction models represent new useful tools assessing the antioxidant components of these tomato cultivars during postharvest handling and nutritional planning for dietary intervention. The lycopene and vitamin C contents of tomatoes were used to demonstrate the effects of fruit maturity level, size and storage condition on the amount of fruit needed to meet the Dietary Reference Intake (DRI) of an adult. Animal models and human intervention studies are needed to assess the bioavailability of nutrients of tomato cultivars required for developing dietary guidelines in health and diseases.
