Variations in functional components in seeds among black cowpea lines traditionally cultivated in Miyako Islands, Okinawa, Japan

Abstract

With increasing interest in regionally unique functional food ingredients, this study focuses on black cowpea (Vigna unguiculata) traditionally cultivated in the Miyako Islands of Okinawa, Japan. These landraces are often confused with black-seeded kidney beans (Phaseolus vulgaris), resulting in a lack of genetic and compositional knowledge essential for their conservation. Here, we analyzed the genetic diversity and seed composition of five black cowpea lines using SSR markers and chemical assays. The PCR-based SSR analysis revealed that all five lines were genetically distinct from black-seeded kidney beans and adzuki beans (Vigna angularis), and also showed polymorphism among themselves, indicating the presence of genetically diverse landraces. Functional seed components, including total anthocyanins, total polyphenols, ferric reducing antioxidant power (FRAP), and DPPH radical scavenging activity, were measured. Overall, black cowpea lines exhibited higher levels of these components compared to the other legumes, with the Tarama-jima line showing the highest values. Fatty acid analysis revealed lower oleic acid but higher linoleic and linolenic acids in the Tarama-jima line. Furthermore, significant differences in total carbon, sucrose, and protein contents were observed among lines, with the Tarama-jima line consistently exhibiting the highest levels. These findings highlight the genetic and biochemical uniqueness of black cowpea lines from the Miyako Islands, supporting their potential as valuable local genetic resources.

Keywords

• Antioxidant activity
• black cowpea
• fatty acid
• genetic resources
• local foods