Vacuum Steam Pulsed Blanching and Refractance Window Drying of Fresh Spinach

Abstract

In the present work, the effect of blanching and drying on the quality characteristics of fresh spinach was evaluated. Vacuum steam pulsed blanching (VSPB) was used as a novel pre-treatment method on fresh spinach, to analyze the impact of different cycles (1 - 5), on the enzyme inactivation, drying characteristics, and quality changes. The results showed that VSPB inactivated peroxidase and polyphenol oxidase activities to 11 % and 8 % within four cycles, respectively. The chlorophyll content, total phenolic content, and antioxidant activity were enhanced compared to fresh leaves whereas the ascorbic acid was decreased with the treatment cycles. The blanched and untreated spinach paste was further subjected to refractance window drying. The VSPB aids in enhancing the drying rate by opening the pores resulting in faster moisture evaporation and lesser drying time. Page model showed the best fit to the drying kinetics. The better retention of the color, phenolic content, and antioxidant activity of the dried spinach powder was observed. The functional properties of the dried powder showed a better water absorption index, percentage solubility, dispersibility, and swelling capacity.