2018 ASHS Annual Conference

Edamame, a vegetable soybean [Glycine max (L.) Merr.] known for larger seeds or beans and sweet flavor, is harvested and consumed in the R6 growth stage prior to reaching full maturity. Consumers in the U.S. have increasing interest in edamame because of its protein content and beneficial health properties; however, the buttery flavor and crispy texture is responsible for the desirability with American consumers. Sulfur (S) is a component of the amino acids cysteine and methionine which are the building blocks of proteins, but also contributes to bitter flavors in many vegetable crops. Little is known about how S fertility influences protein and carbohydrate content in the beans of edamame. As result, a solution culture experiment was conducted to evaluate the effect of S fertility levels on protein and carbohydrate content in edamame beans. Seeds of ‘Chiba’ edamame were germinated under greenhouse conditions at 22°C day/14°C night in the fall of 2016. Fifteen days after germination, seedlings were transferred to twenty 30 L tubs holding five plants each and filled with a modified Hoagland’s nutrient solution containing S treatment levels of 4, 8, 16, 32, and 64 mg S L^-1. Sulfur treatments were delivered as magnesium sulfate (MgSO₄) and sodium sulfate (Na₂SO₄) to balance the other essential nutrients. Treatments were arranged in a randomized complete block design with four replications. Nutrient solutions were replaced to their original nutrient concentrations every 2 weeks and the photoperiod was reduced to 10 h on 8 Nov 2016 to induce flowering. Plants were harvested approximately 60 days after planting when they reached the R6 maturity stage and weighed for fresh biomass. Fresh samples were either frozen at -20°C for carbohydrate analysis or oven dried at 60°C for protein content analysis. Elemental S concentrations were measured in oven-dried bean tissue using ICP-MS. Manipulating S fertility concentrations showed no significant effect on bean accumulation of crude protein (P=0.171), adjusted protein (P=0.171), acid detergent fiber-neutral protein (P=0.409), acid detergent fiber dry matter (P=0.707), or amylase neutral detergent fiber (P=0.271). Edamame bean sucrose (P=0.009) and fructose (P=0.001) increased linearly in response to decreasing S fertility, but bean glucose (P=0.416) levels were not affected. The results showed that increasing the S concentration from 4 to 64 mg S L^-1 in nutrient solution culture did not affect the protein composition in beans of ‘Chiba’ edamame, but did significantly affect bean carbohydrate levels.