| The dietary structure and disease spectrum have undergone major changes with the rapid development of social economy.The high intake of carbohydrates is one of the reasons for the significant increase in the prevalence of metabolic diseases such as diabetes.Rice is the staple food consumed by Chinese,the main component of rice is starch.The crystal structure of rice starch could be destroyed during thermal processing,resulting in a high sugar release during digestion.In order to regulate the hydrolysis properties of rice starch,the structure of starch should be controlled through adjusting the processing conditions.In real food systems,starch can form different structural complexes with other food ingredients.Ester emulsifiers and edible oils are widely used in starch-based foods,however,the relationships between the formation conditions,structure and digestibility of rice starch-lipid complexes has not been clarified.In this paper,Indica rice starch(IS),different chain length fatty acids and the correspondent monoglycerides were used as raw materials to prepare IS-lipids complexes,and the structure characterization and digestion properties of the complexes were studied.Firstly,the effects of preparation conditions such as lipids addition,complexing temperature,recombination time and heating rate on the complex index(CI)and pasting properties were investigated and their bivariate correlation was studied.Secondly,fourier transform infrared spectrometer(FT-IR),differential scanning calorimeter(DSC),X-ray diffraction analyzer(XRD)and scanning electron microscope(SEM)were used to investigate the effects of chain length of lipids and processing conditions on the structure of IS-lipids complexes.Afterwards,the digestion properties of the complexes were characterized by in vitro combined with first order kinetic model.Lastly,the correlation between the complex index(CI),crystallinity(X_c)and digestion properties was also investigated.The main results are shown as follows:(1)With the decrease of chain length of fatty acids,complex index(CI)of IS-fatty acids complexes was increased at 95?,and easier to form a viscosity peak during cooling.However,the IS-monoglycerides complexes exhibited opposite changes.The IS-lauric acid complex reached the highest complex index(CI)value of 30.8%.The increase of heating time reduced the degree of complexation of IS-lipids complexes,but had no significant effect on pasting trend.Temperature and heating rate had different effects on the degree of complexation of different IS-lipids complexes.The CI and pasting properties of IS-glycerol monostearin complexes and IS-lauric acid complexes were highly correlated(p<0.05).(2)The transformation of the rice starch's crystal structure was promoted from type A to from type(A+V)and V by the addition of lipids,and the crystal form conversion was affected by the lipid types and preparation conditions.The conversion can be promoted with a higher complexing temperature,which resulted in a certain degree of decrease in the crystallinity of the complexes.With the increase of carbon chain length of fatty acids,the crystal structure regularity of the IS-fatty acid complexes was decreased.IS-glycerol monopalmitin complex had a highest crystallinity and a most regular crystal structure among the IS-monoglycerides complexes.(3)Compared with monoglycerides,fatty acids were more likely to form type II complexes with regular structures and higher crystallinities.The dissociation temperature was increased with the increase of fatty acid carbon chain length,while the lipid addition amount and recombination time had little effects on the dissociation characteristics.The stability of the complexes was increased with the increase of complexing temperature.IS-lipids complexes were mostly stacked in the form of spherulites,tending to aggregate and accumulate into sheets in the form of flakes.The surface of the IS-monoglycerides complexes was more rough with the increase of the carbon chain,and shown in the form of a plate.(4)The crystallinity of IS-fatty acids complexes was significantly positively correlated with the resistant starch content.The complex index and crystallinity of IS-monoglycerides complexes were significantly negatively correlated with the rapidly digestible starch(RDS)content.The starch digestion rate and the predicted glycemic index were reduced to some extent when the IS-lipids complexes were formed.With the decrease of carbon chain length of fatty acids,the digestion rate of the complexes was decreased.The influence of monoglycerides on the digestion rate of the IS from large to small was glycerol monopalmitin>glycerol monostearin>glycerol monolaurin.What'more,IS-lauric acid complex had the strongest effect on inhibiting digestion rate among the six kinds of complexes,which was reduced by about 69%compared with IS. |
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