Optimization of Vacuum Impregnation for Development of Functional Dried Fruit

Abstract

Osmotic dehydration (OD) is the partial removal of water from fruits or vegetables by immersion in hypertonic solutions and utilized as a preliminary drying technique. However, the rate of mass transfer during osmotic dehydration is generally low and depends on the structure of raw materials and soaking conditions. Techniques to improve mass transfer include pulsed vacuum osmotic dehydration (PVOD).

The objective of this study was to investigate the effect of PVOD on mass transfer and antioxidant replacement in model food, fresh and dried mango cubes. Response surface methodology was used to investigate the effect of vacuum impregnation time (10-30 min), density of model food cubes (0.65-0.85 mg/mL) and sucrose concentration (30-60%w/w) on mass transfer, moisture content, total soluble solids, density, porosity and volume of pulsed vacuum osmotic dehydration (PVOD) model food. Results showed that moisture content, water loss, solids gain, weight reduction, total soluble solids and density fitted predictive multiple linear regression models, whereas porosity and volume lacked fit and were not effective. Optimization focusing on low concentration of osmotic dehydration solution with short processing time provides water loss, solids gain and total soluble solid at 10.04%, 14.09% and 14.98%, respectively. The optimum condition was 32.58% w/w sucrose solution, 14.34 min vacuum time and 0.80 g/mL sample density.

Impacts of PVOD conditions on infusion of nutritive and bioactive compounds into mango and model food cubes were also determined. Results showed that OD, PVOD and solution component (sucrose, gallic acid, ascorbic acid and calcium lactate) affected weight reduction, solids gain, water loss, color value, volume change, moisture content, water activity, pH, titratable acidity, total soluble solids and residues of ascorbic acid content, gallic acid content, sucrose content, calcium and total phenolic contents in impregnated samples. PVOD provided significantly higher contents of ascorbic acid, gallic acid, calcium, total phenolic contents and antioxidant activity in mango (958.83 mg/100 g sample, 1065.78 µg/g sample, 85.25 mg/100 g sample, 399.56 µg GAE/g sample and 0.0458 g/mL, respectively) and model food cubes (953.18 mg/100 g sample, 661.60 µg/g sample, 96.41 mg/100 g sample, 195.21 µg GAE/g sample and 0.001 g/mL respectively) when compared with OD. Mango cubes pretreated in solutions did not show any viability of mango cells.

For dried mango products, PVOD provided significantly high antioxidant properties and calcium content. Calcium contents in PVOD dried mangoes from hot air drying (373.29-388.04 mg/100 g sample) were comparable with those from freeze drying (387.44-389.69 mg/100 g sample). Therefore, PVOD offers a good choice to develop healthy dried fruit by adding physiologically active compounds which enhance antioxidant stability for longer shelf-life products.

-