Effects of Infrared Pre-Drying on Phenolic Profile and Hypoglycemic Potential of Free and Bound Phenolics in Pecan...

To investigate the effects of infrared radiation (IR) pre-drying on the phenolic profiles and hypoglycemic activities of free and bound phenolics (FP, BP) in pecan kernels, fresh in-shell pecans were subjected to IR at 500 W, 600 W, and 700 W for 2 min, respectively, and then dried with 70°C hot air (HA) until their moisture contents reached about 4%. Results of HPLC-Q-Orbitrap-MS/MS indicated that detected FP accounted for more than 60% of the total phenolics in fresh or dried pecan kernels and that IR pre-drying reduced the contents of FP and BP in pecans (except IR₆₀₀-FP) and changed their phenolic composition, as evidenced by the appearance of ferulic acid in FP and BP and vanillic acid in FP. With the increase of IR pre-drying power, the time required for HA drying of pecans to 4% moisture content, as well as the IC₅₀ values of FP and BP against α-amylase and α-glucosidase, decreased; however, no significant differences were observed in the contents of FP and BP, while certain variations emerged in their phenolic compositions (e.g., rutin was absent in IR₇₀₀-FP, and catechin hexoside was detected in IR₇₀₀-BP). In vitro, the hypoglycemic activity of BP from IR pre-dried pecans was higher than that of their FP; oppositely, in vivo, the down-regulation of blood sugar level of BP was lower. Pecan phenolics may regulate blood glucose levels by inhibiting digestive enzyme activities via competitive, noncompetitive, and mixed inhibition. To ensure the bioactivities of pecan phenolics, optimal IR conditions are needed.