Bakri H. Hassan

Flow properties of Roselle (Hibiscus sabdariffa L.) extract

Flow properties of water extract of Roselle calyces were determined using a concentric cylinders rotational viscometer for extract concentration range of 5–65% TS, temperature range of 20–60 °C, and shear rate range of 2·5–979 s−1. Measured shear stress was within the range 0·5 to 49·7 Pa, corresponding to an apparent viscosity range of 0·0015–1·55 Pa s. Within the tested ranges of concentration, temperature, and shear rate, the extract exhibited a pseudoplastic behaviour, and was adequately described by the simple power law model. The flow behaviour index was consistently below unity (0·76–0·97), with the consistency index varying between 0.007 and 1.6 Pa sn. Activation energy of flow varied from 18·74 to 42·80 (kJ/kmol) for the extract concentration range of 5–65% TS, at a shear rate of 100 s−1. The experimental results were fitted by mathematical models to allow prediction of apparent viscosity as a function of concentration, temperature, and shear rate.

Water sorption isotherms of date pastes as influenced by date cultivar and storage temperature

Abstract The water sorption isotherms of pastes of three date cultivars – Ruziz, Khudari, and Khlass – were determined using the static method of saturated salt solutions at three storage temperatures: 5°C, 25°C and 40°C. The effect of temperature on sorption behavior was more pronounced than the effect of date cultivar. Equilibrium moisture content decreased with increasing temperature at water activities below 0.45–0.55. However, above 0.45–0.55, equilibrium moisture content increased with increase in temperature, mainly due to the additional dissolution of sugars at higher temperatures. The experimental data fitted well with GAB, Iglesias and Chirife, and Halsey equations, suitable for high sugar foods.

Freezing of fresh Barhi dates for quality preservation during frozen storage

Fresh harvested dates are perishable and there is a need for extending their shelf life while preserving their fresh like quality characteristics. This study evaluates three different freezing methods, namely cryogenic freezing (CF) using liquid nitrogen; individual quick freezing (IQF) and conventional slow freezing (CSF) in preserving the quality and stability of dates during frozen storage. Fresh dates were frozen utilizing the three methods. The produced frozen dates were frozen stored for nine months. The color values, textural parameters, and nutrition qualities were measured for fresh dates before freezing and for the frozen dates every three months during the frozen storage. The frozen dates’ color values were affected by the freezing method and the frozen storage period. There are substantial differences in the quality of the frozen fruits in favor of cryogenic freezing followed by individual quick freezing compared to the conventional slow freezing. The results revealed large disparity among the times of freezing of the three methods. The freezing time accounted to 10 min for CF, and around 80 min for IQF, and 1800 min for CSF method.