| Funing rice cake is a traditional Chinese snake,the taste of which is soft,glutinous and sweet.Funing rice cake,originating from Yancheng City,Jiangsu,has a history of more than 400 years.However,Funing rice cake can be easily aged and polluted by molds during delivery and storage.In this thesis,the mechanism of starch aging in Funing rice cake during storage was studied.Meanwhile,the effects of different ameliorants on the quality of Funing rice cake were investigated.Moreover,the inactivation kinetics of Escherichia coli and Penicillium citreoviride under ozone treatment were studied.The quality evolution of Funing rice cake after ozone treatment during storage was also studied.The main findings are shown as follows:1.The quality of Funing rice cake during storage was monitored.Specifically,the cakes were packaged in plastic bags made of polyethylene terephthalate and then stored at ambient temperatures for 8 weeks and the moisture content,water activity,texture,thermodynamic parameters,water status were analyzed every week.The results showed that water content first decreased and then increased.After storage for 4 weeks,water content decreased from 17.71%to 14.78%.After that,it increased gradually,reaching 17.45%in the end of storage.Water activity exhibited a similar trend with water content.To be exact,water activity decreased to 0.806 after 4-week storage and then increased to 0.811 after 8-week storage.The texture profile analysis(TPA)provided the information about hardness,springiness,cohesiveness,chewiness and resilience of Funing rice cake.Meanwhile,the DSC analysis showed the retrogadation enthalpy(?H)of amylopectin.The hardness,chewiness and ?H all increased gradually during storage.In the end of storage,the values of hardness,chewiness and AH were 63.80 kg,53.04 kg and 2.86 J/g,respectively.Furthermore,transverse relaxation time includes deep bound-water relaxation time(T21)and half bound-water time(T22)were obtained through nuclear magnetic resonance analysis.T21 and T22 evolved similarly during storage and there was no significance difference in T21 and T22.In addition,the content of half-bind water first decreased then increased.According to PCA analysis,it was found that both starch aging and water content affected the quality of Funing rice cake.2.Nine ameliorants,including potato hydroxypropyl starch,?-cyclodextrin,mycose,sorbitol,ssl,polyvinyl alcohol ester,?-dextran,carrageenan and distilled monoglyceride were added to Funing rice cake,separately.The quality of resulting Funing rice cake was analyzed after 1 and 14 days of storage.It was found that the aforementioned 9 ameliorants changed the water content,water activity,texture,thermodynamic properties and water status of Funing rice cake.Among them,potato hydroxypropyl starch and polyvinyl alcohol ester had high water absorption ability,thus affecting the water content of rice cake.The water content in the cakes containing potato hydroxypropyl starch increased from 16.11%to 18.11%after 14-day storage,while the corresponding content in the cakes with polyvinyl alcohol ester increased from 16.67%to 18.00%.Moreover,?-dextran had a high ability to retain water in rice cake.Water activity of rice cake containing ?-dextran decreased from 0.836 to 0.812 after 14-day storage.Distilled monoglyceride and mycose significantly decreased the aging rate of Funing rice cake(p<0.05).After 1-day storage,?H of rice cake containing dstilled monoglyceride was the lowest,being 1.59 J/g.After 14day storage,AH of rice cake containing mycose was the lowest,being 1.76 J/g.In addition,?-dextran and carrageenan significantly decreased the hardness of Funing rice cake(p<0.05).After 1-day storage,the hardnesses of rice cakes containing ?-dextran and carrageenan were 12.98 kg and 14.69 kg,while the corresponding value of control sample was 16.19 kg.Similarly,the hardness of both samples were also lower that of control sample after storage.In summary,all the mentioned ameliorants can improve the quality of Funing rice cake in different aspects and ?-dextran was regarded as the best ameliorant.3.The effect of ozone treatment on the inactivation kinetics of Escherichia coli and Penicillium citreo-viride on the surface of Funing rice cake,as well as its effect on the quality of rice cake was studied.Exactly,Funing rice cake was treated by ozone at 10,20 and 30 ppm for 2.5,5,10,20 and 30 min,respectively.It was found that more Escherichia coli were inactivated by ozone with the increase of processing time.After ozone treatment at 20 ppm for 2.5 min,the number of Escherichia coli decreased by 0.82 log cfu/g,while another 0.21 log cfu/g was decreased after 5 min of ozone treatment.As for Penicillium citreoviride,the inactivation effect increased with the increase of ozone concentration and processing time.After 2.5-min ozone treatment,the number of Penicillium citreoviride decreased by 0.74 log cfu/g at 10 ppm,1.59 log cfu/g at 20 ppm and 1.56 log cfu/g at 30 ppm,implying that ozone had a significant inactivation effect on Penicillium citreoviride.Next,the quality evolution of Funing rice cake treated by ozone at 20 ppm for 20 min during 3-month storage was studied.Generally,water content decreased gradually,while the values of ?H,hardness,chewiness,aerobic plate count and mold number increased.Compared with control sample,water content,aerobic plate count and mold number of ozone-treated samples were significantly lower than of control sample,while there were no significant differences in other parameters. |
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