| Brown rice is rich in nutritional components,such as linoleic acid,GABA and inositol.Due to rough texture and un-easy digesting absorption,it has been eaten in the form of refined rice,which results in human nutrition imbalance in some regions of China.Germination can improve the rough and stiff mouth-feel sensation,nutrition and processing characteristics of brown rice.In this thesis,three brown rice varieties,namely normal brown rice(WYJ),waxy rice(W-55)and sweet rice(DHX)were used as the experimental materials.The composition,physiochemical properties and carbohydrate profile of aforementioned brown rice varieties during different periods of germination were investigated.Specifically,the morphological structure,thermodynamics and rheology of brown rice starch during germination,as well as the effect of pressure treatment on textural properties of gel was studied.Furthermore,the feasibility of replacement of fat by brown rice starch in low-fat sausage was also explored.The main results are summarized as follows:The chemical composition,changes of main physiological properties and cabohydrate metabolism of the three brown rice varieties during different gerimination stages were studied.To be exact,WYJ was characterized by highest contents of amylase and free amino acids while there was no significant difference between W-55 and DHX.The water content,1000 kernel weight and reducing sugar content in W-55 was highest.There was no significant difference in crude fat and ash among the three varieties.During brown rice germination,the shoot length,germination rate increased gradually,while the dry matter decreased simultaneously.The amylase activity and respiratory intensity of the three brown rice varieties fluctuated during germination.However,?-amylase activity was significantly higher than that of a-amylase.With the effect of amylase,the starch and amylase content decreased,while reducing sugar content increased gradually.Reducing sugar content reached maximum after 60 h germination.According to the compositon of and germination characteristics of the three brown ric varieties,WYJ was germinated and the starch inside was extracted and used in the following studies.The effect of germination on the processing properties of brown rice starch was studied.SEM images indicated that after 24 h germination,the size of starch granules decreased and tended to be uniform.Pits and holes appeared after 48 h germination.More fragment cracks were found in the end of germination.The original appearance-related characteristics did not change significantly,indicating that germination within 120 h did not destroy the structure of BR starch.After 24 h germination,starch paste's transparency,retro gradation and freeze-thaw stability increased significantly,and kept steadily within 24 h to 72 h.These properties increased again in the following period of germination and reached maximum at the 96th hour.After that,they decreased until the end of germination.Furthermore,the emulsion stability enhanced.Germination had little effect on the water binding capacity,while oil holding capacity was improved.The texture-properties of starch gel changed according to the germination time.Gel strength,hardness,springiness,gumminess and chewiness reached a maximum value at 72 h germination.The effect of germination on the functinal properties of brown rice starch was explored.Along with the increase of germination time,the peak values of G' and G" increased,denaturation temperature dropped and the elasticity and viscosity were improved.Static rheological results showed that apparent viscosity and shear stress were lower than that of control sample,which reached minimum after 48-h germination.DSC scanning map showed that germination had little effect(P>0.05)on phase transition temperature(TO,TP,TC)of starch.Moreover,the gelatinization enthalpy increased and the stability and the crystallinity were improved.In addition,the changes of starch's structure and properties during 120 h germination at 32.9? were revealedAfter germination,the effects of ultra high pressure(UHP)treatment on textural properties of gel from brown rice were studied.The adhesiveness,cohesiveness,resilience and gumminess of starch were affected by pressure level,dewelling time and pH.The optimal conditions of UHP treatment to improve the textural properties of starch were:pressure 200 MPa,dwelling time 20 min and pH 6.RVA results exhibited that after UHP treatment for 20 min,peak viscosity of starch gel was higher than that of control sample,whereas hot paste viscosity,final viscosity,setback,attenuation value increased.Furthermore the peak time and pasting temperature decreased after pressure processing.The effects of pressure and pH on RVA were insignificant,reflecting that pressure-treated starch had a higher pressure and pH stability.After pressure treatment at 200 MPa and pH 5 or 8 for 10 min,the freezing-thawing stability of starch was also improved.The feasibility of utilization of brown rice starch as an alternative to fat in low-fat sausage was explored.The addition of brown rice starch(B),germinated brown rice starch(C),pressure-treated germinated brown rice starch(D)to the enema resulted in the improvement of adhesiveness,cohesiveness,chewiness,sensory evaluation and freeze-thaw stability of final products.Moreover,cooking lose rate also decreased.In general,the addition of pressure-treated germinated brown rice starch led to the highest enhancent of enema quality.The optimal substitution rate of fat was found to be 25%. |
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