OSMOTIC DEHYDRATION OF KIWIFRUIT (Actinidia deliciosa) AND ITS EFFECTS ON PHYSICOCHEMICAL PROPERTIES AND DRYING TIME
Osmotic dehydration is a gentle pre-process of water removal which can be applied to fruits and vegetables. This process can remove a great quantity of water using low temperature, reducing drying time and preserving more of the nutritional and sensorial characteristics. The aim of this study was to evaluate the osmotic dehydration of kiwifruit (Actinidia deliciosa), to estimate drying time and to assess the impact of pre-processing on physicochemical properties of the fruit. Osmotic dehydration was studied by 2^3 Central Composite Rotable Design to evaluate: osmotic solution concentration (30-60° Brix), ratio fruit:osmotic solution (1:3 to 1:5) and CaCl2 (0 to 2% w/w) using 0.5 cm thickness slices, room temperature without stirring for 2 hours. Physicochemical properties were measured (pH, acidity, humidity, ash, and vitamin C) and drying was evaluated in oven at 60°C for 15 hours. The best condition for osmotic dehydration was osmotic solution of 45°Brix and ratio fruit:osmotic solution 1:4. A second order codified model was adjusted to water loss with 96% of confidence: [PA = 25,03 + 6,36 S + 0,74 S^2 – 0,09 R + 2,17 R^2 -0,77 C + 3,92 C^2 – 1,45 (S.R) – 1,35 (S.C) – 1,48 (R.C.)] where S = saccharose concentration, R = ratio fruit:osmotic solution, C = calcium chloride concentration. The results were validated with triplicate trials in the best condition, which led to (24±2)% weight loss, (11,8 ± 0,7)% solids gain and (36 ± 1)% water loss in relation to the initial mass of kiwi. Drying time of osmotically dehydrated kiwifruit was estimated at 40 hours and there was reduction in the concentration of organic acid and vitamin C of 52% and 40% (total) and 37% and 21% (by portion), respectively. The dehydration and vitamin C reduction were 100% and 29% higher compared to literature, respectively.