Studies On The Processing Quality Evaluation Of Sweetpotato Soluble Proteins

Sweet potato (Ipomoea batatas Lam. ), a member of Convolvulaceae family, is ranked as the world seventh most important food crop. More than 117 million tons of sweet potatoes are produced in China annually, accounting for 85 percent of worldwide production. In the present study, 62 species of sweet potatoes were collected from Beijing,Hebei,Jiangsu and FuJian provinces for analysis. Based on data from nutritional composition and soluble protein extractability, the composition of soluble protein of various sweet potatoes and their functional properties were investigated. By analyzing statistically the sensory characteristics and physico-chemical properties of soluble proteins of sweet potatoes, indexes for evaluating the quality soluble proteins from sweet potatoes, as well as methods for screening species suitable for processing are presented.There were significant differences in the composition between species and location of cultivation of the sweet potatoes. Based on chemical composition and application of the sweet potatoes, they can be divided into various types, namely the starchy type, the multi-functional type; the food type and the colorant type (Beta-carotene and antocyanin types). Results of correlation showed that drying of sweet potatoes was positively correlated with starch contents. The relationships between protein and other constituents in sweet potatoes were affected by the condition during cultivation.The compositions (crude protein, fiber, fat, moisture, total ash and sugar), extractability, molecular structures and colors for soluble proteins from various sweet potatoes were determined. Results showed that sweet potatoes from Beijing and Heibei areas were suitable for protein extraction, due to its high purity and extractibility. The protein molecule components from different sweet patatoes were similar. In the absence of reducing reagent, SDS-PAGE produced bands of 22kDa, 31kDa and 50kDa. In contrast, one protein band of 25kDa was detected in the presence of reducing reagent.The functional properties including solubility, water holding capacity(WHC), oil holding capacity (OHC), foaming capacity(FC) and stability,emulsifying activity index (EAI) and stability of SSP were determined. SSP possess good solubility, normally exceeding 80ï¼…. There was positive relationship between WHC and protein content, but no significant relationship between WHC and solubility in the samples. The SSP of starchy and multi-functional type of sweet potatoes possessed high WHC and OHC than the others. With the increase in soluble protein concentration, the turbidity value,FC and foaming stability tended to increase. Changes in foaming property of sweetpotato Soluble Protein depended on pH of solution. In general, SSP possess better functional properties than soybean and peanut proteins.Indexes used for evaluating the quality of sweet potatoes includes 1) sensory properties: color L*,a* and b*; 2) Physico-chemical properties: fat and protein contents; 3) functional properties: solubility, FS, EAI and OHC. Results showed that the quality indexes of SSP were correlated positively to the contents of protein and dry matter in sweet potato but negatively with fat and fiber contents. Sweet potato species with higher content of dry matter and protein and lower amount of crude fiber, fat and ash were suitable for the extraction of soluble protein. Based on the method, 10 sweet potatoes species were screened, among them, Yz-1å’ŒYz-2 were found to be suitable for the processing of starch and protein.