Dehydration of Kiwi Fruit (Actinidia deliciosa) by Consecutive Osmotic Dehydration and Freeze-Drying

Objectives: In this study, a highly nutrient food rich in vitamins and minerals, kiwi fruit (Actinidia deliciosa), is dehydrated effectively at a faster rate keeping almost all its original properties. Methods/Analysis: A new methodology, consecutive Osmotic Dehydration (OD) and Freeze Drying (FD), was developed and applied. This technique was found to be very effective with respect to drying time, cost and quality. The OD was performed using sucrose solution at three concentrations (40°B, 55°B, and 70° B), three temperatures (40°C, 45°C, 50°C) and three time spans (2, 3 and 4 h). OD parameters were optimized by “Taguchi orthogonal design” methodology. Findings: Optimal time for OD was found to be 3 h, at 40°B, 50°C corresponding to 60.75% water loss and 9.86% solute gain. Notably, at optimal OD conditions, application of fructose solution resulted unfavorable result. In FD of osmotically dehydrated kiwi fruit, the thermal energy was supplied by an innovative Silver Coated Steel Heater (SCSH), which was found to be much more efficient (required only 2.5 h drying time) compared to an equal power conventional steel heater (SH) (required 3.82 h drying time) to achieve a final kiwi fruit moisture content ≤ 5% (w/w). At both optimal OD and FD, the drying kinetics was assessed using four models. The values of effective diffusivity (D_eff) and activation energy indicated higher energy-efficiency for SCSH compared to SH. The proximate nutritional analyses for fresh and dehydrated kiwi samples indicated very good quality of the processed product. Novelty/Improvement: The uniqueness and novelty of this research work is less drying time and almost no nutritional loss as compared with other conventional techniques.