Physical and nutritional properties of edamame seeds as influenced by stage of development

Abstract

Changes in physical, chemical and anti-nutritional characteristics of two vegetable soybean varieties (‘Asmara’ and ‘Mooncake’) during seed development were investigated. Pods were sampled weekly for 6 weeks starting from developmental stage 5 (R5) to 8 (R8). Changes over time in measured attributes were similar but the rate of change differed among the two varieties. In both varieties seed moisture content and intensity of green color decreased as seed developed with the most significant decline observed in the last 2 weeks of sampling. Seed weight peaked at R6 then gradually decreased thereafter, while seed hardness increased throughout the sampling period with ‘Asmara’ recording significantly higher seed hardness at R8. For both varieties, protein accumulation occurred mostly in the later stages, while significant lipid accumulation was observed in the early stages of development. Among the sugars, fructose content decreased with seed development, sucrose content increased to R6 before decreasing, and there was rapid accumulation of raffinose and stachyose in the last 2 weeks of sampling. Total phenolic content decreased between R5 and R6 but increased with further seed development. Tannin and phytate content in seed increased throughout the sampling period. Changes in trypsin inhibitory activity varied with variety reaching a maximum at R6 for ‘Asmara, and closer to maturation for “Mooncake’. Our data provide physical, chemical and anti-nutritional basis for harvesting vegetable soybean at R6 namely: peak seed weight and sucrose content, lower oligosaccharide and anti-nutrients values and intense green color.