Yeast Characteristics And Effects Of Them On The Storability And Quality Of Frozen Dough And Steamed Bread

The paper was aimed to find out the yeasts which made the characteristics of fermentation and the quality of steamed bread made by fresh dough better by studying the effects of different dry yeasts from the market of domestic and foreign on the fermentation ability and stability of fresh dough,compared with the fresh yeast,baking powder,jiaozi and mixed leavenings.The flavor substances of steamed bread made by 6 kinds of leavenings was analyzed and compared by gas chromatography-mass spectrometry(GC-MS)and electronic nose,including low sugar dry yeast(DY1),high sugar dry yeast(DY2),fresh yeast(FY),baking powder(BP),jiaozi(SS)and mixed leavenings(MIX).The differences of fermentation characteristics and frost resistance of 25 kinds of leavenings were studied to find out the yeasts which had stronger ability of fermentation and better frost resistance than others.The effects of different yeasts which had stronger ability of fermentation or better frost resistance on the characteristics of the fermentation and rheology of frozen dough and the texture,color,specific volume and sensory quality of steamed bread during frozen storage were studied to find out the yeasts which made the quality of frozen dough and steamed bread better and more stable.The results were as follows:1.The correlation analysis showed that in the gas production it was extremely significant correlation between cylinder method and Rheofermentometer F3 instrument.And the gas production of Rheofermentometer F3 instrument and scores of sensory evaluation had a positive correlation,but not significantly.The largest expansion height of dough(Hm),the gas maximum height of release curve(H,m),the gas production and gas holding capacity of the fresh dough made by Tailong dry yeast(3~#),Angel low-sugar high-activity dry yeast(6~#),Chuibao low-sugar high-activity dry yeast(7~#),Guoguang low-sugar high-activity dry yeast(10~#),Actis Mali Apple instant high-active dry yeast(12~#),Pinyi high-activity dry yeast(15~#),and Angel high-sugar-intolerance high-activity dry yeast(25~#)made were all higher.The cylinder method showed that the fermentation rate of 3~#,6~#,10~#,12~# and 25~# was relatively more stable.The sensory quality of steamed bread made by 6~#,Mali high-sugar instant high-active dry yeast(8~#),Actis Mali Yanshan high-sugar dry yeast(9~#),10~#,the swallow brand instant dry yeast(14~#),Aoli low-sugar high-active dry yeast(16~#),New-Aoli high-sugar high-active dry yeast(18~#)and 25~# were better.The fermentation performance of 10~#was not only better,but also the quality of steamed bread made with 10~# was better.In the production of steamed bread,10~# was preferred,followed by 6~# and 25~#.2.The results of electronic nose and GC-MS are basically consistent.GC-MS showed that the flavor compounds of steamed bread made by different types of leavenings were similar,however their composition and quantities were different.21,48,39,38,47 and 42 kinds of volatile compounds were detected in the steamed bread made by DY1,DY2,FY,BP,SS and MIX,respectively.Steamed bread made by the six kinds of leavenings all contained n-tridecane,n-tetradecane,7-methyl-pentadecane and benzaldehyde in common.Ethyl palmitate was examined in DY2,SS and MIX bread;ethanol was only found in DY1 bread;the eighteen alkyl vinyl ether was detected only in DY2 bread;a little linoleic acid was examined both in SS and MIX bread;anethole containing fennel aroma was detected only in SS and MIX bread,which suggested the anethole was produced by SS.Steamed bread made by baking powder could be differentiated rapidly from the steamed bread made by other leavenings using PCA method of electronic nose.The flavor components of MIX and SS steamed bread overlapped too much to differentiate.The principal components of DY2 were closer to FY than DY1.3.The correlation analysis showed that the yeast cells had an effect on frost resistant force;fermenting power after frozen and trehalose contents had a positive correlation,but not significantly.The results of yeasts fermentation characteristics and frost resistance showed that the fermenting power and H'm of both fresh-made and frozen dough produced by 10~#,12~# and 15~# were higher,frost resistant force was general,but resistance to fermentation was poor.And 8~#,Danbaoli high-sugar instant high-active dry yeast(20~#)and 25~#had stronger frost resistant force,higher gas holding proportion,general fermenting power.Steamed bread of both fresh-made and frozen dough made by 15~#,20~# and 25~# had good sensory quality,and 8~#,9~# and 10~#had better sensory quality relatively.After comprehensive comparison,yeasts whose fermenting power was stronger and had weaker frost resistant relatively.4.The quality of frozen dough and steamed bread made by different yeasts was significantly different.The elastic and viscous modulus were in turn higher in dough made by 10~#,25~#and 20~#,when the dough was frozen for 35 days,of which the rheological properties of the dough made by 20~# was the most stable.10~# and 12~#whose frost resistant force was general and fermenting power was stronger always maintained higher fermentation activity during the frozen storage of 35 days,followed by 25~# whose all fermentation characteristics were quite stable.And the yeasts whose frost resistant force was general and fermenting power was stronger was superior to the yeasts whose fermenting power was general and frost resistant force was stronger.The steamed bread made by the frozen dough of 10~# and 25~# always had better texture and sensory quality and larger specific volume during frozen storage,followed by 12~#.The steamed bread made by the frozen dough of 10~#had higher brightness value,lower red-green value and yellow-blue value,and relatively had better and more stable color,followed by 25~#.After comprehensive comparison,10~# made the quality of frozen dough and steamed bread and stability better in the production of frozen dough,followed by 25~#.