English abstract
Dates could be considered probably the most important fruit cultivar in the Middle East and especially Arab countries such as Oman. This fruit received abundant care from tanate government since it represents about 50% of the total agricultural land and 83% of fruit trees in the Sultanate. The fruit production in 2014 reached 316200 MT. The fruit is very nutritive as it is rich in many important nutrients and provide good source of rapidly available energy due to their high sugar content (70–80%). Dates' color is playing an important role in determination of date value and quality, Dates' darkening is a natural phenomenon which has adverse effect on the fruits color. The color changes from the natural accepted golden color to dark brown color. The change takes place at room temperature due to action of polyphenol oxidase and peroxidase enzymes and formation of melanin especially in tamer stage during storage. This defect causes loss up to 50%. on fruits and vegetables. In this project, the effect of different preservation methods on preserving the color and the relation between dark color and melanin pigment were investigated Dates samples were preserved by Modified Atmosphere Packaging (air was replaced by N2 gas), Cold Storage (4°C), Sulfur Dioxide gas, and blanching by steam (~100°C) for three minutes and one sample was kept as Control. After the treatment, the samples were stored for four months at room temperature; except the samples in the treatment Cold storage. During the storage, browning enzymes (polyphenol oxidase (PPO) and Peroxidase (POD)) activity, color, moisture content, water activity and melanin concentration were assessed in the treated samples as well as the control samples. The results showed that polyphenol oxidase (PPO) was active in all treatments except the samples treated with sulfur dioxide gas where no activity was noticed throughout the entire period of storage. On the other hand, peroxidase was found active in all samples where the sulfated samples had the lowest activity compared with the rest of the samples. Moreover, sulfated samples have shown improvement in color (lighter yellow color) compared with all other treatments, whereas, the steamed samples showed more color deterioration. Significant differences in water activity and moisture content were found between all treated dates (P value<0.05), the highest level was found in the steamed samples. Melanin content increased in all samples over the period of storage except in the sulfated samples. The results obtained from melanin measurements correlate positively with that obtained from color measurements. In conclusion, the obtained results demonstrate effectiveness of sulfation treatment to limit browning enzymes action and improve dates' color during storage at room temperature (25-27°C). Keywords: Polyphenol oxidase, Peroxidase, Melanin, Blanching, Dates, Sulfur Dioxide gas, Modified Atmosphere Packaging, Cold Storage.
