| Mousse is a dairy dessert with delicate taste and unique flavor,which is popular among consumers.Due to its rich nutrition and suitable for the growth of probiotics,probiotics added to mousse can not only increase the nutritional value of mousse,but also improve its market competitiveness.However,environmental factors such as high oxygen,high osmotic pressure and low temperature during production,storage,transportation and consumption all have certain effects on the viability of bacteria.A large number of studies had shown that when bacteria are in a non-lethal stress environment,they can induce and enhance their tolerance to the same type of stress and other stresses,resulting in an interactive adaptive effect.Taking mousse as the research object,L.rhamnosus hsryfm 1301 with different pre-stressed were added to the mousse to study the growth characteristics of the strains in the mousse matrix,and to screen the pre-stress treatment conditions which is suitable for probiotic mousse production.The effects of pre-stress treatment on the quality,storage characteristics,volatile flavor substances and functional characteristics of probiotic mousse were studied.The results are as follows:1.Screening of optimal prestress treatment conditions for L.rhamnosus hsryfm 1301L.rhamnosus hsryfm 1301 was pre-stressed with different intensities of heat,acid,osmotic pressure and oxidation to determine the sublethal conditions of each stress condition on lactobacillus rhamnosus.The effects of sublethal stress on the survival rate,fermentation performance and enzyme activity of L.rhamnosus hsryfm 1301 were studied.The mousse was prepared with several strains under sublethal stress conditions,and the changes of survival rate in the mousse were compared.The results showed that the sublethal stress conditions of L.rhamnosus hsryfm 1301 were 50?-1 h,pH 2.5-3 h,3.5 mM H2O2-1 h and 1.8 M NaCl-4 h,respectively.All of the four pre-stress treatments had a certain impact on the survival rate of the strains.Among them,the logarithmic period of the pretreated strains at 50?-1 h and pH 2.5-3 h had extended 3 h compared to the control.The survival rate of the 1.8 M NaCl-4 h had no significant difference to the control(P>0.05).The adjustment period of the pretreated strains at 3.5 mM H2O2-1 h had extended 8 h compared to the control group.After pre-treated with the above four conditions,the fermentation and curd time of the L.rhamnosus hsryfm 1301 were all prolonged compared to the control.The curd time of 1.8 M NaCl-4 h was 12.5 h,which was delayed 0.5 h compared with the control group.The curd time of 50?-1 h?pH 2.5-3 h and 3.5 mM H2O2-1 h was 13 h,which was delayed 1 h compared with the control group.After four kinds of pre-stress treatment,the pH value of the pH 2.5-3 h group were significantly higher than the control,and acidity were significantly lower than the control(P>0.05).The viable counts of the four pretreated strains were lower than that of the control.In addition,all the four pretreatments improved the activity of beta-galactosidase of L.rhamnosus hsryfm 1301.Probiotic mousses were prepared with L.rhamnosus hsryfm 1301 fermented milk treated with four kinds of pre-stress.During the 21 days of storage at 4?,viable counts of the four mousse samples were all higher than 8.0 log cfu/g.The survival rate of L.rhamnosus hsryfm 1301 in the pH 2.5-3 h and 50?-1 h were higher 26.49%and 1.25%than the control group,and the survival rate of L.rhamnosus hsryfm in the 3.5 mM H2O2-1 h and 1.8 M NaCl-4 h were lower than the control.Therefore,pH 2.5-3 h and 50?-1 h were selected as the pre-stress treatment conditions for the next study.2.Effect of pre-stress treatment of L.rhamnosus hsryfm 1301 on the quality of probiotic mousseFermented milks were prepared with L.rhamnosus hsryfm 1301 treated with pH 2.5-3 h and 50?-1 h respectively,and the mousse was prepared.The effects of pre-stress on the sensory quality,acidity,pH value,texture,rheological properties and volatile flavor of probiotic mousse were studied with the mousse prepared,and L.rhamnosus hsryfm 1301 without any treatment was used as the control.The results showed that the survival rate of 50?-1 h mousse storage at-18? for 120 d was decreaseed 1.41%compared to that of the control,and the survival rate of pH 2.5-3 h mousse was increased 0.86%compared to the control.Therefore,pH 2.5-3 h was the best pretreatment condition for L.rhamnosus hsryfm 1301 compared with the control group,the sensory quality,hardness,adhesion,cohesion,mastication,elasticity,and apprarent viscosity of pH 2.5-3 h probiotic mousse had no significant difference with the control(P>0.05).The pH value of all samples were showed a downward trend,and the acidity showed an upward trend,and the postacidification of pH 2.5-3 h was lower than that of the control,and which storaged at-18? was lower than 4?.Which indicated that pH 2.5-3 h and storage at-18? would be more helpful to improve the quality of probiotic mousse.GC-MS was used to detect the changes of volatile flavor substances in mousse at different storage temperatures,and 5 kinds of major volatile components were detected,including ketones,alcohols,acids,aldehydes and esters were detected.Their relative contents were successively from high to low:acid>esters>aldehydes>alcohols>ketones.The pH 2.5-3 h treatment could reduced the formation of acid compounds in mousse,especially the content of acetic acid.3.Effects of pre-stress treatment on the gastrointestinal tolerance and drug resistance of l.rhamnosus hsryfm 1301 in mousseThe fermented milk was prepared with ph 2.5-3 h strain,and the mousse was stored at 4? and-18?,respectively.The effect of pre-stress treatment on the in vitro gastrointestinal tolerance of L.rhamnosus hsryfm 1301 in probiotics mousse was studied,using the mousse prepared with untreated strain as the control.The results showed that the survival rate of L.rhamnosus hsryfm 1301 in the artificial saliva and intestinal juice of pH 2.5-3 h group was 5.01%and 13.55%higher than that of the control group,respectively.The survival rate in the artificial gastric juice was not significantly different from that of the control group(P>0.05).The survival rate of L.rhamnosus hsryfm 1301 in artificial saliva,gastric juice and intestinal juice of pH 2.5-3 h group storage at-18? was 5.55%,4.84%and 5.46%higher than that of the control group.The results indicated that pH 2.5-3 h pretreatment could improve the tolerance of L.rhamnosus hsryfm 1 301 in the mousses to saliva and gastrointestinal environment.In addition,the results of the study on antibiotic resistance showed that the pH 2.5-3 h pretreatment had no significant effect on the antibiotic resistance of L.rhamnosus hsryfm 1301. |
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