Abstract
A study was designed to produce evaporator-concentrated juice from Al-Nokel grapes and to contrast the proximate, physical and elemental composition of the fresh fruits (edible portion), single strength juice and the concentrate. Also, changes during storage in physicochemical (reducing sugars, sucrose, ascorbic acid and acidity), microbial and sensory characteristics were studied to determine the effect of storage time and storage temperature on the quality. The Al-Nokel grape cultivar is grown on a commercial level in the Al-Nokel area in Al-Madina Al-Monawara City, the South-Eastern region of Saudi Arabia. Proximate analysis indicated that the protein, lipid and ash contents of the edible portion of Al-Nokel grapes found in this study were approximately in agreement with the literature values (FAO, (1982)
Food Composition Tables for the Near East. FAO, Rome; Paul & Southgate, (1978)
The Composition of Foods. Elsevier/North-Hall, New York) but the total sugar content was higher than those reported in the literature and by Wall & Merrill (1975)
Composition of Food, Agricultural Handbook no. 8. Consumer and Food Economics Institutes. Agricultural Research Service, US Department of Agriculture, Washington, DC. The edible portion of the fruit was found to be rich in potassium and magnesium while the fresh extracted juice was a fair source of potassium, magnesium and iron. The decrease in sucrose and ascorbic acid and the increase in reducing sugars were linearly related to the storage time. The increase in the reducing sugars was due to the hydrolysis of the sucrose under these conditions.
The results of sensory evaluation indicated that panellists were not able to detect any significant changes in the quality attributes after 2 months of storage at various temperatures. However, after 6 months of storage there was a significant difference (
p < 0.05) in colour, flavour and overall acceptability between samples stored at 25°C and those stored at 1 and 5°C. Microbial analysis revealed that the concentrates stored at the three various temperatures were microbially stable through the storage period, and showed the absence of aerobic plate counts, coliforms, sporeformers and yearsts and moulds.