Efeitos da desidratação osmótica e desidratação osmótica assistida por ultrassom na secagem convectiva de cenoura (Daucus carota L.).

Abstract

Carrot ( Daucuscarota L.) is among the most cultivated and consumed vegetables in the world. This is mainly due to its high content of β - carotene, precursor of vitamin A, which makes t he carrots to be considered the best plant source of this vitamin. Carrots are highly perishable crops which naturally deteriorate few days after harvest due to its high moisture content. An alternative to reduce post - harvest losses is drying, a method of preservation that enables an extension of shelf life by reducing the water content of the product, reducing the costs of storage and transportation. However, drying also causes unpleasant effects such as reduced nutritional value and changes in color, tast e and texture of food. Therefore, the osmotic dehydration and ultrasound has been used as pre - treatments to minimize losses in quality, as processing time and drying temperature are reduced. This study aimed to evaluate the effects of ultrasound and osmoti c dehydration pretreatments followed by air - drying of carrots. The osmotic solutions used were: sucrose (25 - 50 ° Brix), sodium chloride (1 - 5%) and distilled water. The immersion times were: 10, 20 and 30 minutes. The forced circulating air - drying oven was set at 60°C with air moisture content at 18%. Control assays, without pre - treatment. W ater loss, solid gain, weight reduction, drying rate, water activity and effective diffusivity of water were evaluated. The higher water loss was obtained for 50°Brix su crose sonicated for 20 and 30 minutes (11.79% ± 0.23 and 14.09 ± 0.29%, respectively) and sodium chloride 5% sonicated during 30 minutes (8.34% ± 0.28). The highest values of effective diffusivity of water were found when 25 ° Brix sucrose was used as os motic agent and the samples were sonicated for 30 and 20 minutes (4.80 x 10 - 10 m 2 /s, 4.50 x 10 - 10 m 2 /s respectively). The shortest time necessary to reduce water activity of carrot to 0.6 was found when 50° Brix sucrose was used as an osmotic agent for a sonication time of 20 minutes (5 hours of drying). Reductions in water activity were also observed for treatments with sodium chloride 5% and 20 minutes of sonication (6 hours of drying) and 25 ° Brix sucrose for 30 minutes of sonication. The osmotic dehyd ration combined with ultrasound used as pre - treatment was a viable alternative to reduce drying time and process costs