Effect of Osmotic Dehydration with Pulsed Vacuum on Hot-Air Drying Kinetics and Quality Attributes of Cherry Tomatoes

Abstract

The effects of osmotic dehydration (OD) with or without pulsed vacuum (PV) on hot-air drying kinetics and quality attributes of cherry tomatoes were investigated. Both OD and PVOD pre-treatments were performed for 3 h at 50°C in 50 and 70^o Brix sucrose solutions with a solution-to-fruit mass ratio of 4:1, and PVOD was applied for 15 min before OD at atmospheric pressure. Samples were further dried at air temperature of 70°C. Effective moisture diffusivity (D _eff) of osmotically dehydrated samples increased gradually while the D_eff curve of fresh samples had a plateau stage during hot air drying. Lower glass transition temperature, T_g, values of osmotically dehydrated samples indicated that they needed a lower storage temperature. Both OD and PVOD pre-treatments had advantages in shortening drying cycles and improving quality of products. Compared with air drying, osmo-air drying decreased the total drying time, color change, and hardness of dried samples by 32.26%, 18.11%, and 88.21%, respectively, and increased volume ratio and vitamin C retention rate by 72.31% and 125.82%. As compared with OD, PVOD decreased color change and hardness by 28.48% and 45.17%, increased volume ratio and vitamin C retention rate by 27.41% and 17.77%, but there was no significant difference shown in drying time. Therefore, osmotic pre-treatment can shorten the total dehydration time, and improve the general quality of dried cherry tomatoes.

Keywords:

• Convective drying
• Effective moisture diffusivity
• Pre-treatment
• Vitamin C retention

ACKNOWLEDGMENTS

The study was supported by the State High-tech R&D Program of China (863 Program) (2011AA100802). It was also supported by the National Science & Technology Support Program of China in the 12th Five-year Plan Period (2012BAD36B07).

Notes

AD: hot air drying at 70°C; 50OD+AD: hot-air drying after osmotic dehydration (OD) in 50^o Brix sugar solution; 70OD+AD: hot-air drying after osmotic dehydration (OD) in 70^o Brix sugar solution.

Note: Different superscript letters (a, b, c, and d) on the data represent that the mean values were significantly different at 95% confidence level (P < 0.05). AD: hot-air drying at 70°C; 50OD+AD/50PVOD+AD: hot-air drying after osmotic dehydration (OD) or pulsed vacuum osmotic dehydration (PVOD) in 50^o Brix sugar solution; 70OD+AD/70PVOD+AD: hot-air drying after osmotic dehydration (OD) or pulsed vacuum osmotic dehydration (PVOD) in 70^o Brix sugar solution.