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A study was carried out to determine the effect of higher shear rates (64.5 to 4835 s −1 ) on the absolute viscosities of different vegetable oils at different temperatures (26 to 90 ∘ C). The absolute viscosities of the different vegetable oils were determined using a Lamy Viscometer RM100, a rotating viscometer with coaxial cylinder. The torque of each sample at different temperatures was recorded at different shear rates. Based on the rheograms (plot of mean shear stress against shear rate), all of the vegetable oils studied were found to be Newtonian fluids. Rice bran oil was the most viscous (0.0398 Pa⋅s at 38 ∘ C) while walnut oil was the least viscous (0.0296 Pa⋅s at 38 ∘ C) among the oils studied. The higher shear range used did not significantly affect the absolute viscosities of the vegetable oils at the different temperatures. The absolute viscosities of the vegetable oils decreased with increasing temperature and can be fitted with an Arrhenius type relationship. The activation energies for the different vegetable oils ranged from 21 to 30 kJ/mole. The peanut and safflower oils had the highest and lowest activation energies, respectively. This means that greater energy was needed to effect a viscosity change in the peanut oil.

The effect of air dry bulb temperature, air relative humidity, air velocity and sample thickness on the thin-layer air drying of sweet potato slices was investigated. The drying rate curves consisted of two approximately linear falling rate periods and contained no constant rate period. Several mathematical models were fitted to the drying rates of sweet potato slices under a range of drying conditions. It was found that the modified Page equation best described the thin-layer air drying of sweet potato slices down to a moisture content of 10% dry basis. Correlations were also determined for the slope and intercept of the modified Page equation in terms of the experimental variables.

In this study, the drying characteristics, colour, oxygen reactive antioxidant capacity (ORAC) and betacarotene contents of two apricot varieties dried at different temperatures were compared. The hot air drying of apricot slices for both varieties consisted of a constant rate period (CRP) and two of falling rate periods (FRP). The CRP drying rate and the first and second FRP drying coefficients increased with drying temperature for both apricot varieties. The first and second FRP of both apricot varieties gave activation energies of 23.5-28.7 and 25.6-29.3 kJ mole )1 , respectively. The colour values (L*, a* and b*) of both dried apricot varieties decreased with increasing temperature, while the total colour change of both dried apricot varieties increased with temperature. The chroma, hue angle and browning index values of both dried apricot varieties decreased with increasing temperature, and the hydrophilic ORAC and beta-carotene contents increased with drying temperature.Effect of drying on apricots R. Ihns et al.

Fruit leathers are dehydrated fruit products which are eaten as snacks or desserts. They are flexible sheets that have a concentrated fruit flavor and nutritional aspects. Most fruit leathers are prepared by mixing fruit puree and other additives like sugar, pectin, acid, glucose syrup, color, and potassium metabisulphite and then dehydrating them under specific conditions. Various drying systems including combined convective and far-infrared drying, hot air drying, microwave drying, solar drying, and sun drying have been used to make fruit leathers. Most fruit leathers are dried at 30 to 80°C for up to 24 hours until the target final moisture content (12–20%) has been reached. Research about fruit leathers began in the 1970s. This work has reviewed published papers on fruit leathers in order to summarize useful information about fruit leathers on methods of preparation, effects of drying condition, and effects of packaging and storage, which will be useful to many in the food industry and consumers who are health-conscious.