Quality attributes, processing, and selection of vegetable soybean

Vegetable soybean is a crop harvested immature when seeds completely fill the pod, but are still bright green, large, and sweet. Vegetable soybean acreage would increase if new and improved varieties were developed, and post-harvest management of the crop was optimized. The overall objective of this research was to characterize the changes in quality attributes of vegetable soybean under different processing and selection practices. In the first area of research we identified optimum blanching and cooking times based upon the changes in color, texture, enzymatic activity, and chemical composition of three vegetable soybean lines subjected to six different boiling times and processed either in pods or shelled using a steam-jacketed kettle or an electrical-resistance stove. Also, we studied heat-sterilization times and brine compositions, and developed a protocol for canning vegetable soybean that produced a product with acceptable safety and organoleptic properties. On the other hand, a series of field studies were conducted to test the feasibility of indirect selection for important but difficult-to-measure breeding traits. First, we evaluated the correlation of important vegetable soybean quality traits between immature (R6) and mature (R8) stages using 4 genotypes. We observed positive and moderate-to-high correlation coefficients between the R6 and R8 stages for yield, sucrose, texture, and protein; in contrast, no significant correlations were observed for glucose, fructose, raffinose, stachyose, and verbascose contents. Therefore, vegetable soybean lines could be evaluated at the R8 stage and indirectly selected for high yield, soft texture, and high protein and sucrose contents at the R6 stage. Additionally, a marker-assisted-selection approach was conducted for seed sucrose content in a population of 125 lines derived from the cross between a conventional soybean variety and a high-sucrose soybean line. Using 102 single-sequence repeat markers in the region of previously-reported quantitative trait loci we identified two markers with minor effect on seed sucrose content in the population. Additionally, we observed a possibly new single-gene mutation that conferred a high-sucrose low-raffinose low-stachyose phenotype. In conclusion, as an outcome of this research we have optimized vegetable soybean post-harvest management and processing protocols, and we have identified interrelationships of quality traits, molecular markers, and a single-gene for sucrose content that will be helpful in breeding vegetable soybean.