| Sweet potato and potato are mainly used as starch processing and starchy products in China,which will produce a mass of residues.These by-products still remain rich dietary fiber and starch,but are not efficiently used,just used as animal feed or wasted,which will lead to resources waste and environment pollution.In present study,the nutritional ingredients of 10 cultivars of sweet potato and 10 cultivars of potato as well as their starch processing residues were determined,and the nutritional and health-related values of these residues were investigated according to a grey relational analysis.Thereafter,egg protein powder and corn starch were mixed with the selected sweet potato/ potato residues flour to get the sweet potato/ potato compound flour(SCF and PCF),which were quite similar as sweet potato/ potato dry matter in proximate composition.Then,the physicochemical and processing properties were investigated.After that,SCF and PCF were used to replace 30% wheat flour to make steamed bread.Additionally,the nutritional,texture,sensory and flavor were measured and compared with 100% wheat and 30% whole sweet potato/ potato flake flour(SF and PF)ones.Results are as follows:The starch,total sugar,dietary fiber and protein contents were 58.46-72.14,7.45-14.01,5.88-8.44 and 3.64-8.88 g/100 g DW for starch type sweet potatoes,respectively,and those for potatoes were 63.04-72.77?3.94-9.23?4.71-7.90?4.71-10.15 g/100 g DW,respectively.The starch,total sugar and protein contents were lower in sweet potato and potato residues,but the dietary fiber could reach 20.63-31.48 and 16.68-28.57 g/100 g DW,respectively.Starch type sweet potatoes and potatoes contained rich K,Fe,Zn and Cu,but K contents decreased a lot in sweet potato/ potato residues.The vitamin C contents in sweet potatoes and potatoes were 12.80-51.87 and 20.00-70.64 mg/100 g DW,but just remained 2.00-7.86 ? 1.36-9.00 mg/100 g DW in sweet potato and potato residues,respectively.Also,the total amino acid contents were lower in residues compared with sweet potatoes/ potatoes,but the essential amino acid ratios and amino acid scores were higher.The luminance values(L values)of SCF and PCF were 91.24 and 88.19,respectively.Their total dietary fiber contents were 13.92 and 13.08 g/100 g DW,while starch and protein contents were similar as SF and PF,respectively.Their water holding capabilities were 2.13 and 1.87 g water/g sample,which were significantly lower than SF and PF.Peak viscosity of SCF and PCF were 103 and 1254 BU,respectively,and were close to sweet potato and potato lyophilized flour(112 and 935 BU).The dough with 30% SCF and PCF have higher water absorption and dough stability,lower weakness and poor extensibility compare with wheat dough.A grey relational analysis showed that the nutritional values of ‘Jishu4' at 0.7623,‘Jishu982' at 0.7135 and ‘Jishu25' at 0.6768 were the top three cultivars among the sweet potato residues,and‘LT-5' at 0.7304,‘Helan7' at 0.6938 and ‘Zhongshu5' at 0.6520 were the top three among the potato residues.According to one-factor test,the optimal parameters for 30% SCF steamed bread making were: trehalose 6%,water 75%,yeast 1%,fermentation temperature 35°C,fermentation time 75 min and vital gluten 1%,and those for PCF one were: trehalose 4%,water 70%,yeast 1%,fermentation temperature32°C,fermentation time 60 min and vital gluten 1%.In that case,the specific volumes of 30% SCF and PCF steamed bread were 2.30 and 2.04,respectively,which had no significant difference with 30% SF and PF steamed bread(2.31 and 2.07,respectively).There were no significant differences between 30% SCF/PCF steamed bread and 30% SF/PF ones in adhesiveness,springiness,chewiness,resilience,cohesiveness,but 30% SCF/PCF steamed bread showed higher hardness(4038.66 and 5652.71 g,respectively).The L value of SCF steamed bread(74.24)was higher than that of SF steamed bread(69.46),and inversely for PCF(69.19)and PF(79.64).The electronic nose showed that,the flavor of 30% SCF/PCF steamed bread were more similar as 100% wheat steamed bread than 30% SF/PF steamed bread.Taken together,sweet potato/ potato residues have a big potential to be used as novel material for sweet potato/potato staple food processing. |
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