A comparative evaluation of physicochemical properties of pecan (Carya illinoinensis (Wangenh.) K. Koch) husk by different drying method.

Pecan husk is the primary waste by-product of the pecan industry and accounts for about one-third of the weight of a whole pecan. However, due to the perishability of pecan husk, it is easy to cause secondary pollution to the environment. In this study, freeze-drying (FD), vacuum drying (VD), hot-air drying (HAD), and shade drying (SD) were used to determine the effects on phenolic compounds and some physicochemical properties of pecan husk. Results showed that the FD had the best effect on maintaining the uniform honeycomb structure and the color of pecan husk. The VD had the lowest residual enzymatic activity with the polyphenol oxidase (PPO) of 32.31 ± 1.32%, and the peroxidase (POD) of 34.16 ± 0.66%. The FD extract had excellent phenolic compound [total polyphenol content (TPC) of 138.84 ± 2.73 mg GAE/g DW and total flavonoid content (TFC) of 38.48 ± 3.08 mg RE/g DW], antioxidant activities (the IC₅₀ of DPPH, ABTS, and Superoxide anion were 530.41 ± 0.23, 461.53 ± 1.46, 318.07 ± 2.40 µg/mL, respectively), and antimicrobial activities decreased in the order of S. aureus (25.7 ± 0.2 mm), S. mutans (21.8 ± 0.3 mm), P.aeruginosa (18.8 ± 0.3 mm), and E. coli (16.1 ± 0.3 mm). In general, the results clarify the effect of drying methods on functional ingredients and provide guidance and suggestions for the reuse of pecan husk. [ABSTRACT FROM AUTHOR]