Genotypic variation for phenolic compounds in developing and whole seeds, and storage conditions influence visual seed quality of yellow dry bean genotypes

Citation

Xiong, M., Zhao, M., Lu, Z.X., Balasubramanian, P. (2020). Genotypic variation for phenolic compounds in developing and whole seeds, and storage conditions influence visual seed quality of yellow dry bean genotypes, 100(3), 284-295. http://dx.doi.org/10.1139/cjps-2019-0153

Plain language summary

Naturally occurring phenolic compounds in seed affect seed quality of yellow dry bean. Consumers perceive seed lots with dark seed coat as poor quality both visually and nutritionally, and such seed lots are sold at a discount. New yellow bean varieties developed in Canada have visually appealing, bright seed coat compared to older varieties. Therefore, a laboratory study was conducted to identify i) differences in naturally occurring phenolic compounds in the seed coat, and ii) storage temperature and duration on brightness of yellow bean seed. Two yellow bean varieties, CDC Sol and AAC Y073 with a bright yellow seed coat had low levels of naturally occurring phenolic compounds such as condensed tannin, phenolic acids and flavonoid in both developing and mature seed. Whereas, the older variety Arikara Yellow with a dark seed coat had high levels of the above compounds. Phenolic compounds in seeds increased between two and four months of storage, and with increase in storage temperature from 6 to 30 °C. The increase in phenolic compounds in the seed coat was accompanied by darkening of seed coat, indicating a strong relationship between seed brightness and phenolic compounds. Seeds stored for two months and at a lower temperature of 6 °C retained their colour compared to those stored for longer duration and at higher temperatures. The results of this study will enable the development of future dry bean cultivars with improved seed coat colour preferred by consumers, and to store seeds in appropriate conditions to ensure marketable seed quality.

Abstract

Seed coat colour is an important determinant of the visual quality of dry beans, as seeds are sold as a dry commodity. Phenolic compounds have a major effect on the colour of bean seeds. The objectives of the study were to determine the changes in phenolic compounds during seed development and in whole seeds of yellow bean genotypes with contrasting seed coat colour, and the effects of storage temperature and duration on seed phenolics and colour. Condensed tannin, phenolic acid, flavonoids, and antioxidant activity were observed as early as 10 d after flowering in the developing seeds of Arikara Yellow, which darken at harvest and during postharvest storage. In contrast, for CDC Sol and AAC Y073 seeds which remain yellow, phenolic compounds and antioxidant activity were consistently low. Seed brightness (L*) and yellow colour (b*) were negatively correlated with phenolic compounds and antioxidant activity, and conversely seed redness (a*) was positively correlated with phenolic compounds, confirming a negative influence of phenolic compounds on seed coat colour. Yellow bean genotypes had low anthocyanin but were high in β-carotene. Storage temperature influenced condensed tannin and seed coat colour, whereas the duration of storage influenced phenolic compounds, antioxidant activity, and seed coat colour. Higher temperatures (20 or 30 C) and longer storage duration (120 or 180 d) generally resulted in darker seeds with increasing redness compared with seeds stored at 6 °C or for 60 d. AAC Y073 and CDC Sol with improved seed coat colour may increase consumer preference, value, and marketability of yellow beans. °