Research and Application of Osmotic Dehydration Technique in Preservation of Fresh Guavas (Psidium guajava L.)

摘要

The consumer demand for high quality products with fresh-like characteristics has promoted the development of a new technology of osmotic dehydration. Osmotic dehydration done only as soaking process requires long time for osmotic equilibrium achievement. Vacuum pulse technique, solutions temperature and concentration can enhance mass transfer process of solution's solids. The effects of those parameters on mass transfer of different geometrical shapes of minimally processed Guavas (plate slices, cylinder and sphere) were investigated. Weight reduction, water loss and gain solids were obtained using sucrose solutions at 45, 57 and 65 °Brix at solution's temperatures of 30, 48 and 58 ℃ and vacuum pulse of 0, 50 and 100 mbar for 10 and 20min at the process beginning. Higher solutions concentrations, temperatures and the vacuum pulse application caused an increase on water loss of osmotically dehydrated Guavas. The highest water loss reached was 69.17 % at 65 °Brix, 58 ℃ and 100 mbar at 20 min. The gain solids was reduced by the increase in osmotic solutions concentration; and raised up by vacuum pulse application and solutions temperature. Maximum gain solids achieved was 25.93 % at 45 °Brix, 48 ℃ and 100 mbar at 20min. Osmotic dehydrated Guavas' plates have the optimum mass transfer characteristics of gain solids and water loss due to its higher surface area to volume ratio of 520 m~(-1). Kinetics diffusion model of Fick's law, for the three different geometrical shapes, was tested obtaining diffu-sivity and to compare favored shape. The effective diffusivity determined by the model well represented the effect of osmotic dehydration process treatments on mass transfer and showed a better agreement to the experimental data. The quality of investigated Guavas {Psidium guajava L.) pulsed osmotically dehydrated and packaged under passive modified atmosphere conditions, was evaluated during four weeks of storage. Passive modified atmosphere applied with polyethylene terephthalate containers had the highest potential on preserving and maintaining weight loss of 13 % and respiratory quotient of 1.40 ±0.97.