Document Type : Original Article
Authors
1
The Central Laboratory of Date Palm Research and Development, Agricultural Research Center, Giza, 12619, Egypt
2
Food Science Department, Faculty of Agriculture, Cairo University, Giza 12613, Egypt
Abstract
During this study, the effect of pH levels on the quality of nectar produced by soft date (Barhi, Samani and Zaghloul) and semi-dry date (Siwi) cultivars after processing and during the storage period was investigated. The nectar (15.5 Brix) at different pH levels 6, 5.5., 5.0, and 4.5 and the initial 6:5.5 pH was organoleptically evaluated. The highest sensory assessments for date nectar samples were analysed physically, chemically, and microbiologically after processing and during storage at 4˚C for 6 months. The high taste, colour, Odor, consistency, and overall acceptability score was observed at a pH 6 for Barhi, Samani, and Zaghloul date nectar samples. At the same time, the high score for Siwi date nectar was at pH 5.5 (control sample). The results indicated no significant difference among four date nectar samples in the TSS, pH, TSS/acid ratio, titratable acidity, crude fibre and protein. There were significant differences among four date fruits nectar with the highest value of lightness (L) ordered as follows Barhi (20.5) >Samani (17.7) > Zaghloul (13.7) >Siwi (12.4). Also, the highest redness (a) value was in Siwi date nectar (0.47) followed by Zaghloul (0.42), Samani (0.28) and Barhi (0.25). The highest yellowness (b) value was observed in Barhi (1.87) compared to Samani (1.76) >Zaghloul (1.69) >and Siwi (1.56). The sucrose content of date nectar samples was ordered as follows Samani) 7.35% < (Zaghloul (6.23%) < Barhi (5.03%) < Siwi (1.88%). Reducing sugar (fructose, and glucose) were ordered as follows Siwi< Barhi< Zaghloul< Samani. The total phenolic content and flavonoids of date nectar samples were ordered as follows Siwi > Zaghloul > Barhi> Samani. On the other hand, antioxidant values were consistent with total phenolic and flavonoid values. Total soluble solids of date nectar were slightly decreased during storage at 4⁰C for 6 months. The percentage decrease of TSS ranged between 0.6 to 1.26% from the initial value. The same trend of pH value slightly declined to 5.9 for three soft date nectar samples and to 5.45 for Siwi nectar sample. The (L and b) values were decreased during the first 3 months of storage while a clear deficiency was observed in the second 3 months of storage period. A little gradual increase in a value was observed till 6 months of storage. The acidity of date nectar was slightly decreased during storage period. Reducing sugars was slightly increased, while total sugars were slightly decreased during storage. Total phenolic content, total flavonoids and antioxidant activity of date nectar samples gradually decreased, especially during the second 3 months of storage period. Total bacterial counts and Yeast and Mold were slightly increased during storage but were within specification range. The overall acceptability score was slightly decreased at the end of storage compared to zero time. Therefore, producing nectar from different Egyptian types of dates will increase the economic value of these dates, which have a limited shelf life.
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