Roasting and Cryogenic Grinding Enhance the Antioxidant Property of Sword Beans ( Canavalia gladiata)

The objective of this study was to optimize the conditions to enhance the antioxidant property of sword bean (Canavalia gladiata) as a coffee substitute in two processing methods, roasting and grinding. The optimum condition to remove off-flavor of the bean and maximize functionality and efficiency was light roasting and cryogenic grinding (<53 μm). In this condition, extraction yield was 16.75%, total phenolic content (TPC) was 69.82 ± 0.35 mg gallic acid equivalents/g, and total flavonoid content (TFC) was 168.81 ± 1.64 mg quercetin equivalents/100 g. The antioxidant properties were 77.58 ± 0.27% for DPPH radical scavenging activity and 58.02 ± 0.76 mg Trolox equivalents/g for ABTS radical scavenging activity. The values of TFC and ABTS radical scavenging activity were significantly higher (p<0.05) than in other conditions, and TPC and DPPH radical scavenging activity were second highest in lightly roasted beans following raw beans. HS-SPME/GC-MS analysis confirmed that the amino acids and carbohydrates that are the main components of sword bean were condensed into other volatile flavor compounds such as derivatives of furan, pyrazine, and pyrrole during roasting. Roasted and cryogenic-ground sword beans showed higher functionality in terms of TFC, DPPH, and ABTS radical scavenging activities compared to those of coffee. Overall results showed that light roasting and cryogenic grinding are the most suitable processing conditions for enhancing the bioactivity of sword beans.

Keywords: Canavalia gladiata; antioxidant; cryogenic grinding; roasting; sword bean.