Fruit and vegetable drying to make leather, pestil or powder products is a challenging task. Traditional drying adversely affects the taste, colour, nutritional qualities and preservation of bioactive compounds due to high-temperature exposure of the product. The substitute for traditional drying processes is consequently necessary to impart superior quality and preserve greater nutritional value in processed foods. Refractance window (RW) drying is a thin film drying system having high heat and mass transfer rates that speeds up the rate of drying. Polyester (Mylar), an infrared transparent plastic sheet transmits radiative heat to food during the RW drying process with higher drying rate, more retention of nutrients and low aroma and flavour loss. RW drying is reported to be affected by the thickness of puree or slices and temperature of drying, as thick samples need longer drying time, generate higher water activity, bring changes in colour parameters, experience higher effective diffusion coefficient (D ) and result in lower solubility of powder. RW drying was compared with different drying processes and was observed to have more retention of nutrients and be more economical. RW dried samples were better in terms of colour and textural quality when compared with other traditional drying methods. © 2018 Society of Chemical Industry.

Refractance window (RW) drying of mango pulp has shown good quality retention compared to conventional drying methods. Different pulp thickness (2, 3 and 4 mm) and drying temperature (85, 90 and 95 °C) were optimized for RW drying of mango pulp for responses as drying time, ascorbic acid, total phenolics content (TPC) and hardness of mango leather. Face-centered central composite design was performed for optimization using Design-Expert software. RW drying of 2 mm thick mango pulp took the shortest drying time, however lower ascorbic acid and TPC were determined as compared to 3 mm and 4 mm thick pulp mango leather. Hardness of RW dried mango leather was determined to be in the chewable range as 3.62-5.33 N. The optimum solution generated for RW drying temperature and pulp thickness was 95 °C and 2.49 mm, respectively. The drying time was 22.5 min with high quality retention in terms of ascorbic acid, TPC and hardness as 62.33 mg/100 g DW, 7.72 mg GAE/g DW and 4.60 N respectively of dried product with desirability function obtained was 0.969. More nutrients were preserved in mango leather as well as microstructure of mango powder was observed as smooth and flaky with uniform thickness of powder particles with RW drying process when compared with tray and oven drying at 95 °C drying temperature and 2.50 mm mango pulp thickness.

The present study was aimed at optimizing the enzyme assisted aqueous extraction (EAAE) process for extraction of maize germ oil. The different EAAE process parameter viz., pH of the slurry, seed to water ratio, the temperature of incubation and time of hydrolysis were optimized for improving oil recovery and oil quality. The combined effect of independent variables on recovery of oil, time taken for oil extraction and various quality parameters were studied using response surface methodology. The designed experimental runs were conducted to obtain the optimal conditions as 5.85 pH of slurry, 1:6.92 seed to water ratio, 45.12 °C temperature of incubation and 1 h time of hydrolysis. Oil extracted under these conditions was light yellowish in color and had a pleasant nutty taste, with maximum oil recovery of 70 %. The extraction variables viz., pH of slurry, seed to water ratio, the temperature of incubation had a significant effect on recovery of oil and various quality characteristics, however the time of hydrolysis had a non significant effect.

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