| The disadvantages of brown rice in cooking quality and processing characteristics,and the nutrition loss during processing,not only restrict the development of its products,but also cause a waste of resources.In this study,high pressure(HP)treatment was combined with traditional modification methods(milling or germination pretreatment)to develop a brown rice modification technology considering both taste and nutrition.The effects of high pressure based modification technology(HPMT)on gelatinization,rheological and digestive properties as well as retrogradation characteristics of brown rice were studied.The observation of ultrastructure and the study of water migration characteristics were used to explore the mechanism of above changes in physicochemical properties.The main results are as follows:1.HPMT facilitated the gelatinization of starch granules of brown rice,reduced the initial swelling temperature(from around 60 ℃ to around 50 0C)and inhibited the excessive swelling at higher temperatures.The decreased setback and breakdown values after HPMT indicated a higher cooking quality,while the higher pasting temperatures(PT)indicated that the HPMT resulted in brown rice with better thermal stability.2.HPMT increased the diversity of rheological properties and could carry out directional modification.Except for long time germination(GBR9),HPMT could result in thicker paste with enhanced shear thinning behavior.Among them,HP treatment combined with long time germination(GBR9)obtained pastes with different shear structure recovery ability,which may be used to adjust the operation time.3.HPMT with milling pretreatment enhanced the gel texture and improved its storage stability,while HPMT with germination pretreatment had the opposite effects.Desired taste may be achieved by adjusting the ratio of these two treatments.4.HPMT promoted the digestibility and retarded its change associated with long-term retrogradation.Among them,the digestion rate constant(k)of stored gel(7 d)from HPMT-treated samples increased up to 2.2 times,as compared to the one from Control samples.5.Milling and germination pretreatments reduced the water binding capacity of rice paste,while HPMT showed the opposite effects.Besides,HPMT could effectively retard the changes in water migration characteristics associated with retrogradation.6.HP had a marginal effect and could reduce the pretreatment level required for modification.This is conducive to the nutrition preservation during processing,the simplification of production processes and the improvement of its efficiency.Among them,the threshold modification conditions(400 MPa,10 min)was found to be the most desirable HP condition.7.Results demonstrated that HP(400 MPa-10 min),combined with partial milling(MR)and short time germination(GBR5),were enough to obtain gels with target taste,easy digestibility,strong water retention and stable nutritional quality.In addition,according to the correlation among different retrogradation parameters,hardness and slowly digestible starch(SDS)content could be selected as quality evaluation indicators for gels during retrogradation.This provides a theoretical basis for the research and development of gel foods.8.Results of ultrastructure observation showed that the bran layer was removed gradually by milling pretreatment.As for the germination pretreatment,the seedcase and internal structure of rice grain became loose,with its starch granule size decreased,both of which would reduce the amount of connection parts in the rice flour network.All these might be responsible for the different physicochemical properties among samples,and would influence the modification effect of HP.Besides,HP modification maintained the integrity of starch granules. |
