Study On Technology And Quality Of Quick-frozen Baked Sweet Potato

Sweet potato's resources are rich,baked sweet potato is one of the most common processing methods.However,due to the limitation of seasons,the traditional baked sweet potatos were mainly supplied in winter,and most of them are produced and sold on the spot.The baking conditions,raw materials and flavors are different,which cannot guarantee the quality and edible safety of the products.In this project,fresh sweet potato as material for baked,quick-frozen and storage.Analyzed the physicochemical indexes and volatile components and the varieties of baked sweet potato were selected.The baking process,quick freezing method and microwave reheating conditions were optimized and studied the quality changes of baked sweet potato during frozen storage,which provided theoretical basis for the development of quick-frozen baked sweet potato.The main results are as follows:(1)Comparative study on physicochemical quality and volatile components of different baked sweet potato varieties:reducing sugar,crude fiber,VC,carotene and sensory score of yam 25 was significantly higher than 161603 and 173307(p<0.05);water content,protein,fat,starch,L*value,H~ovalue and maximum shear force of161603 was significantly higher than that of two varieties(p<0.05);a*value,b*value and c*value of 173307 was significantly higher than that of two varieties(p<0.05).There was no significant difference in adhesion,elasticity,adhesiveness and chewiness(p>0.05).(2)Comparative study on volatile components:a total of 84 volatile components were identified from three baked sweet potatoes,including 18 aldehydes,11 alcohols,10 ketones,4 esters,1 phenol,13 diluents,16 alkanes and 11 other compounds,among which alcohols,esters and alkenes were the most abundant.Through OAV analysis,a total of 29 aroma components were identified,including 23,18 and 16 aroma components in yam 25,161603 and 173307,respectively.Among them,aldehydes accounted for the highest proportion.Damascone,?-ionone,p-vinylguaiacol,2-nonenal,isophorone,caryophyllene,2-Acetylfuran and nonanal makes significant contributions to the composition of baked sweet potato's aroma.In conclusion,Yam 25is more suitable for baking sweet potato.(3)Determination of the best baking technology of sweet potato:Single factor experiment was used to determine the optimal baking technology level of sweet potato,which was 90?100 min baking time and 200?220?baking temperature;the optimal baking technology through orthogonal test was 210?baking for 100 min,which reducing sugar content of sweet potato was 14.43%,and sensory evaluation score was88.7.(4)Effects of freezing rate on the quality of roasted sweet potato:the time through the maximum ice crystal formation area were 192min,159min,57min,5s,respectively,when frozen at-18?,-25?and-60?refrigerator and liquid nitrogen.Compared with fresh baked sweet potato,the moisture content,soluble solids,reducing sugar,VC,L*value,b*value,elasticity and cohesiveness increased significantly(p<0.05),carotene,a*value,hardness,adhesiveness and chewiness decreased significantly(p<0.05).Compared with different freezing rates,liquid nitrogen freezing rate was the highest,juice loss rate was the lowest,which was 1.14%,and soluble solid content was the highest,which was 39.97%;the content of reducing sugar frozen at-60?was the highest,which was 14.60%;the content of carotene frozen at-25?was the highest,which was 18.25 mg/100g;the content of VC frozen at-18?was the highest,which was 2.16 mg/100g.Considering comprehensively,liquid nitrogen quick-frozen was selected as the pre-freezing method of quick-frozen baked sweet potato(5)Effects of microwave reheating conditions on the quality of baked sweet potato:with the increase of microwave power and reheating time,the surface temperature,central temperature and sensory score increased significantly(p<0.05);the juice loss rate and water content decreased significantly(p<0.05).The best reheating process of quick-frozen roasted sweet potato was microwave high fire reheating for 4 min.Under this condition,the quality of roasted sweet potato was better.(6)Effects of different frozen storage temperatures(-18?,-25?,-60?,-80?)on the quality of baked sweet potato:the juice loss rate gradually decreased with the decrease of frozen storage temperature(p<0.05);the soluble solid content,water content and reducing sugar content of roasted sweet potato frozen at-25?were the highest,which were 31.57%,33.56%and 17.39%respectively,and significantly higher than other frozen storage(p<0.05);the total sugar content frozen at-60?was significantly higher than that of other frozen storage temperatures.There were significant differences in carotene content and sensory score between frozen at-80?and other frozen storage temperatures(p<0.05),and tne highest sensory score was82.6;the crude fiber content of frozen storage at-18?was highest,which was 1.72%.Considering the economic and cost,the best-frozen storage temperature of roasted sweet potato was-25?.(7)Effects of frozen storage period on physicochemical properties of baked sweet potato:with the increase of frozen storage period,the juice loss rate,total color difference(35)E and total number of colonies increased significantly(p<0.05);soluble solids,moisture,reducing sugar,total sugar content and chewiness showed increased first and then decreased(p<0.05);crude fiber,b*value,hardness and sensory score significantly decreased(p<0.05).In considering the changes of quality indexes during frozen storage,these results suggest that 120 days should be chosen as the most optimal frozen storage period.