Solar drying Eggplants impregnated with Ca and Zn

Abstract

Eggplant (Solanum melongena L.) has bioactive compounds with healthy properties. The objective of the work was to obtain dehydrated eggplants with high nutritional value and excellent rehydration capacity. The eggplants were cut into 5 mm slices, dehydrated in a solar dryer, some of them were subjected to a pre-treatment of osmotic dehydration / impregnation (OD/I) to fortify them with calcium and zinc and the others to compare their structural and nutritional quality. The dehydrating solution consisted of 40% m / m sucrose, 5% m / m calcium chloride, 5% m / m ascorbic acid and 1% m / m citric acid (55 ° Brix) at a temperature of 40 ° C. A mass ratio of solution to mass of eggplants of 4 and a stirring level of 120 rpm were used. During drying, samples were taken to determine the content of calcium and zinc by atomic absorption spectrophotometry, humidity, weight loss and color. Likewise, the drying kinetics and subsequent rehydration were modeled.
After solar drying for 6 h, the eggplants without OD / I reached a concentration of 600 mg Ca / kg while the pretreated ones, reached a value of 18000 mg Ca / kg. Fresh eggplants have a humidity range of 91-94% on a humid basis, after a pretreatment (OD/ I) of 1his reached a value of 64-67% (h.b.) and the posterior solar drying for 7h achieves a value of 30-21%. After solar for 7 h drying without pretreatment a humidity of 66-63% (h.b.) was obtained.
The pretreated product presented lower luminosity L *: 49.7 ± 0.7 compared to the non-pretreated L *: 71.7 ± 3.1, higher a * values with a difference of 50% and quite similar b * values. To model the drying kinetics, the Page and Crank models were used. The parameters of the Page model obtained were: C: 1 ± 0.25; K: 0.078 ± 0.004 and n: 1.7 ± 0.3 for an adjustment (R2: 0.995), for the samples that were subjected to pretreatment by osmotic dehydration and C: 2.65 ± 0.50; K: 0.0047 ± 0.00024, n: 2.75 ± 0.48 (R2: 0.998) for the rest of the samples. The effective diffusion coefficient obtained by the Crank model was 2.44 ± 0.33. 10 -10 m2 / s and 1.87 ± 0.25. 10-10 m2 / s for samples with and without osmotic dehydration pretreatment, respectively. Rehydration was better in pretreated eggplant. After 4 hours of rehydration at 20 ° C, a humidity of 89% (h.b.) was reached. This phenomenon showed that osmotic dehydration / impregnation preserve the structure of the food