Assessing Fermentation Quality Of Sweet Potato For Fuel Ethanol Production

Nearly117million tons of sweet potatoes are produced in China annually, accounting for85percent of worldwide production. To meet the demands for screening out sweet potatovarieties special for biofuel production at the background of the promotion of biofuelproduction currently,29species of sweet potatoes were collected from different academies ofagricultural sciences in Henan province: Shangqiu, Luohe and Zhengzhou in the present study.Based on the optimized determination method of starch content and fermentation technology,nutritional composition including moisture, crude protein, ash, starch, soluble sugars andfermentable sugars and fermentation properties were studied, and then indicators for assessingfermentation quality of sweet potato were presented according to the correlation analysisbetween quality traits and fermentation results.The major results of this study are as follows:A new determination method of starch content was developed as follows: after solublesugars of sample were removed by AACC76.13method, sweet potato flour was hydrolysedby Novozyme Liquozyme SC DS and Spirizyme Fuel instead of enzymes from Megazyme,the dosage of them were both20μL(the quantity of sample is about100mg),3mL NaAc wasadded in the liquefaction process simultaneously, and the time of liquefaction andsaccharification were20min and30min, respectively. Afterwards the hydrolysate namelyglucose content was determined by HPLC, and then it was converted to the starch content.There are significant differences in nutritional composition and their correlations amongthe tested sweet potato varieties, crude protein is weakly correlative with other ingredients,while dry matter content, starch and fermentable sugars show close correlation with otheringredients. Dry matter content is extra significantly and positively correlative with starch,significantly positively correlative with fermentable sugars, and extra significantly negativelycorrelative with soluble sugars; starch content is extra significantly and negatively correlativewith ash and soluble sugars, and extra significantly positively correlative with fermentablesugars.The correlations between dry matter content as well as starch content and other qualitytraits are all the same.Optimum fermentation condition for fuel ethanol production of sweet potato wasdetermined as follows:70mL of water per100g of sweet potato pulp,30μL of liquozyme at86℃for90min, with100μL of spirizyme, SSF was performed at30℃for60h without pHadjustment, mineral and nitrogen source. The correlation analysis between quality traits and fermentation results showed that onlydry matter content and starch content could be used as indicators for assessing fermentationquality of sweet potato. The equation between ethanol yield and dry matter was establishedfinally: Y=0.448X-1.975, in which X and Y mean dry matter content and ethanol yield,respectively, and the coefficient of determination of model was0.97.