This study was conducted to examine the utilization potential of grape stems as nutritional supplements, and the physiological functionalities of 70% ethanol extracts from grape fruit stem (GFS) were investigated. Each experimental group was prepared with different methods and included GFSF (GFS prepared with freeze drying), GFSI (GFS prepared with infrared drying), GFSH (GFS prepared with heat air drying), and GFSS (GFS prepared with sun drying). The respective yields of freeze-dried powders for the GFSF, GFSI, GFSH, and GFSS were 59.27%, 57.13%, 58.57%, and 58.87%, respectively. Total polyphenol contents in the GFSF were significantly greater than those in the other extracts, whereas total flavonoid contents in the GFSI were higher than those in the other extracts. The contents of proanthocyanidin-related substances were ranked in the order of GFSF > GFSI > GFSH > GFSS. The thin layer chromatograph (TLC) analysis of catechin showed that the GFSF, GFSI, GFSH, and GFSS were detected in the same band. The electron donating ability with 500 μg/mL (w/v) solutions of GFSF, GFSI, GFSH, and GFSS amounted to 93.14%, 93.07%, 92.64%, and 86.95%, respectively, and the reducing powers (OD 700) were 1.933, 1.765, 1.455, and 1.200 absorbance units, respectively. Additionally, the ABTS radical scavenging ability showed the same tendency that was observed with the electron donating ability and reducing power. The angiotensin-converting enzyme (ACE) inhibitory activity and tyrosinase inhibitory activity with 500 μg/mL (w/v) solutions of GFSF and GFSI were higher than those of GFSH and GFSS. In conclusion, the infrared drying technique is the superior method for the enhancement of biological activity for by-product utilization.

• Kwang-Sup Youn | 윤광섭 Corresponding author