Food Drying

The performance of the rotary bed desiccant dehumidifier was evaluated for different air mass flow rates of 0.32, 0.63, 0.95 and 1.30 kg s-1 and different reactivation temperatures of 60, 70, 80, 90, 100, 110 and 120 °C, respectively. Obtained experimental data including temperature and absolute humidity at both process and reactivation side via random factorial scheme are analyzed. Comparison of data average is carried out with the help of the multi amplitude test of Tukey. Statistical analysis of experimental data shows that reactivation temperature (RT) and air mass flow rate (AMFR) have a reasonable impact on the process and reactivation out temperature and absolute humidity. However, a combined effect of reactivation temperature (RT) and air mass flow rate (AMFR) on process and reactivation out temperature and absolute humidity is not meaningful (p>0.05). Process air inlet moisture content affects outlet moisture, if air is more humid entering the dehumidifier, it will be more humid leaving the unit. More moisture is removed from the process air as inlet humidity ratio increases. Process air mass flow rate through the desiccant bed strongly affects leaving moisture. Outlet humidity ratio is less if process air flow rate is less. Thus, more moisture is removed when the air mass flow rate is less. Results shows that by controlling air mass flow rate and reactivation temperature, a good range of temperature can be attained which is suitable for drying of agricultural crops at low humidity. Low temperature food drying enhances the product quality, drying rate and retention of nutrients.

This study was conducted with a view to find out the most suitable concentration of sugar for the preparation of aonla candy. In this research, six sets of aonla candy samples were made with varying syrup concentration (80 %, 70 %, 60 %, 50 % and 40 %) using sucrose and fresh aonla candy was used as control. The shelf-life stability of aonla candy was studied for 0 to 120 days at ambient temperature. The results obtained from the study revealed that moisture and total fiber content of aonla candy decreased with storage time while protein, fat, ash, total carbohydrate were increased. Ascorbic acid and total phenol content was found to decrease with increasing storage period. However, sufficient amount of ascorbic acid was retained in all samples. Titrable acidity was also increased with progressive increase of storage. Reducing sugar and total sugar was found to increase while non-reducing sugar decreased with the advancement of storage time. Almost all samples had good sensory in terms of colour, flavour, texture, taste and overall acceptability. On the basis of the results obtained in the present investigation, it can be drawn that application of various concentration of sugar syrup significantly affected the quality parameters of aonla candy.

The level of applied microwave power is a critical parameter for the quality of the dried product in microwave drying. It is impossible to assess the applied power of the dried product with the naked eye. This work aimed to predict the applied power of black carrot powders using a chromameter and near-infrared reflectance spectroscopy with partial least squares regression. A good correlation was found between applied power, color parameters, and near-infrared reflectance. The near-infrared spectroscopy predicted the applied power with better performance (R 2 ¼ 0.99) and can be utilized to appraise the applied power of black carrot powders with acceptable accuracy.

Experiments were carried out to evaluate the performance of a hot-air supplemented solar dryer for drying white yam (Dioscorea rotundata) over indirect solar dryer. The effect of parameters such as; drying temperatures, yam slice thicknesses and drying air velocity were investigated for hot-air supplemented solar dryer and an indirect solar dryer. Three temperatures (40, 60 and 70 °C), yam slice thickness of 2 and 4 mm and drying air velocity of 0.8 m/s were used for the experiments. The initial moisture content of the white yam was 73.1 % wet basis (w.b.) while moisture loss was determined hourly. After the experiment, it was deduced that the total drying time used to reduce the samples initial moisture to safe storage moisture content (SSMC) differs for the two different drying conditions. It was 18 hours for solar dryer and 13 hours for hot-air supplemented solar dryer. In both methods, drying rate increases with the increasing temperature and decreases with the increasing slice thickness. The machine efficiency was calculated for different drying conditions. Also the incorporation of the hot-air section aids the stability of the temperature in the drying chamber throughout the drying period. The average thermal efficiencies were 31.45 %, 13.97 %, 42.10 % and 55.91 % for solar drying, hot-air supplemented solar drying at 40, and 70 ºC respectively and also the solar collector highest efficiency was calculated to be 83.28 % at solar radiation intensity of 1199.46 W/m 2 and lowest efficiency of the solar collector was 23.89 % at solar radiation intensity of 300.40 W/m 2 .