Combining osmotic–steam blanching with infrared–microwave–hot air drying: Production of dried lemon (Citrus limon L.) slices and enzyme inactivation

ABSTRACT

The different pretreatments were given to lemon slices to inactivate pectinesterase and peroxidase enzymes and to dry the product rapidly using infrared–microwave hot air combination. Osmotic pretreatment followed by 1-min steam blanching was found to reduce moisture in the product, increase solid content, and inactivate enzymes in lemon slices while maintaining negligible dry matter and juice sac loss. The infrared hot air was found effective in partial drying of pretreated lemon slices up to 1 hour without entering in drastic falling-rate period. Therefore, after 1 h microwave hot air was used to complete the drying process. The optimum infrared drying condition was found at 3000 W/m² radiation intensity, 90°C air temperature, 100 mm distance between lamp and product, and 1.5 m s⁻¹ air velocity. In microwave finish drying, the power density of 0.30 W g⁻¹, 89.9°C air temperature, and 0.5 m s⁻¹ air velocity were found to result in the best product. The hybridization of osmotic–steam blanching and the two drying methods overcame the problems of browning, extended falling-rate periods, improper power distribution, and quality deterioration. Also, the higher values of moisture diffusivities were observed during hybrid drying.

KEYWORDS:

• Blanching
• enzyme inactivation
• hybrid drying
• optimization
• osmotic pretreatment

Additional information

Funding

The authors are thankful to Ministry of Food Processing Industries [Grant Number SERB/MOFPI/030/2015] and Ministry of Human Resource Development (MHRD), Government of India for providing facilities to this research work.