Sweeping-frequency ultrasonic preprocessing improves removal rate and stability of pigment removed from okra powders by different drying and sieving methods.

Decolorization is a necessary step before the extraction of okra pectin, and the reapplication of removed pigment will benefit hierarchical utilization of resources. Based on sweeping-frequency ultrasonic preprocessing (SFUP), effects of drying methods (hot air drying (HD), freeze-drying (FD)), sieves (of 60, 80, and 120 mesh) on removal rate and stability of okra pigment (OPI) were investigated. Color deepening caused by the formation of enzymatic products within 1 h of OPI degradation was explained. The extracted OPI was finally applied to noodles to check its stability further. Results showed that compared with non-ultrasonic treatment, SFUP increased removal rate of OPI with the maximum value of 49.32%, and further enhanced the stability of OPI when applied to noodles. OPI through sieves of 80 mesh owned brighter color and more excellent stability, and colored noodles with OPI through SFUP and FD had a small total color difference and strong stability. [ABSTRACT FROM AUTHOR]