JWSS - Journal of Water and Soil Science

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Physicochemical characteristics of potato (Solanum tuberosum L.) are very important for storage and processing qualities. The amount of reducing sugars (glucose and fructose) and organic acids at harvest, during and after storage is the most important factor. In this study, three potato cultivars (Moran, Marfona and Agria) were collected, dry cleaned and graded into three sizes. They were analyzed for specific gravity and dry matter content. Potato tubers were stored at 4°C and about 85% R. H. for 15 weeks and then reconditioned at room temperature (25±l)°C for 4 weeks. During the storage period of tubers, sugars (sucrose, glucose and fructose) were analyzed on a weekly basis, but citric, D-malic and D-pyroglutamic were analyzed on a monthly basis by high performance liquid chromatography (HPLC). Data were analyzed statistically in a completely randomized design with sampling and Duncans multiple range test.

The total sugar and organic acid contents of tubers significantly increased during the 15 weeks of storage at 4°C and decreased after reconditioning at room temperature. The size of tubers did not affect the accumulation of total sugars. Dry matter content and specific gravity of Agria tubers were higher than those of both Moran and Marfona. Also accumulation of reducing sugars was lower in Agria than in Moran and Morfona initially and after the storage and reconditioning periods. Therefore, Agria must be suitable for processing into chips or dry powder.

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Resveratrol (5,3,4'- trihyroxystilbene) is a valuable polyphenolic compound which prevents cancer, heart and vascular diseases in human. In this research, the compound was extracted from leaf and fruit tissues of two Iranian grape cultivars (Rajabie Sefide Shiraz and Keshmeshie Ghermez) using a general extraction method with some modification, and analyzed quantitatively by High Performance Liquid Chromatography (HPLC). Resveratrol content in leaf and fruit of Rajabie Sefide Shiraz cultivar was higher than Keshmeshie Ghermez and its amount in the fruits of both cultivars was observed to be greater than their leaves. The accumulation of Resveratrol at the early stage of fruit growth (4 weeks after full bloom) was higher than the subsequent stages of fruit growth and development (8 weeks after full bloom and ripened fruit) in both cultivars. This compound gradually decreased from the beginning of fruit set to the complete stage of growth and development and reached the lowest level when the fruits were ripe. Leaves and fruits of both cultivars were treated with methyl jasmonate (1 mM), then the rate of resveratrol was measured after treatments. It was observed that the amount of this compound was significantly increased in treated samples when compared with the control however, the difference diminished later. The fruits of both cultivars responded better to the treatments 4 weeks after full bloom.