Effect Of Short-range Order Of Non-Crystalline Starch On Its Functional Properties And Bread Quality

Starch is the main source of carbohydrates in the human diet and is an essential source of energy for humans.The complex multi-scale structure of native starch is mainly determinant for its functional properties.Starch and starch-based foods are usually undergone thermal processed before being eaten by consumers,resulting in the disruption of the multiscale structure of starch and consequently in changes in its functional properties.As is well known,the structural change of condensed structure of starch during thermal processing is closely related to its functional properties and digestibility.Previous studies have focused on the effect of changes in the crystalline structure of starch(with both long-range and shortrange order)on its functional properties and digestibility during thermal processing,while little information about the effect of the change of amorphous aggregates(with only shortrange order)on the functional properties and digestibility of starch during the later stages of thermal processing.As a result,it is difficult to analyze the structural changes of starch during the complete food processing and its influence on the final food quality.Therefore,the aim of this thesis is to systematically investigate the effects of short-range order of non-crystalline starch during thermal processing on starch retrogradation,the formation starch-lipid complex,starch digestibility and on bread quality.The main contents and conclusions are as follows:(1)The mechanism of the effect of short-range order of non-crystalline starch on starch retrogradation and the functional properties of retrograded starch were investigated.A series of non-crystalline starches were prepared by differential scanning calorimetry and water bath heating,and then stored at 4℃ for 7 days to study their retrograded behaviour.The results showed that with the increase of moisture content,heating temperature and heating time reduced the short-range order of non-crystalline starch to different extent and affected the starch retrogradation.The potential mechanism is that,within a certain range,the short-range order reduction would enhance the mobility of starch chains and promote the formation of double helix of amylopectin and starch retrogradation.Further reduce the short-range order will lead to less entanglement of starch chains,reduce the nucleation ability and thus slow down the retrogradation.Higher degree of starch retrogradation and better structural order of retrograded starch result in lower digestibility and higher gel strength.(2)On this basis,the effect of short-range molecular order of non-crystalline starch on the formation of amylose-lipid complexes was investigated.A series of non-crystalline starches and starch-lipid complexes were prepared by modulating water content and heating time using Rapid Visco Analyser(RVA).By characterizing the short-range order in noncrystalline starches,it was found that the increase of moisture content and heating time will decrease the short-range order of non-crystalline starches and affected the formation of starch-lipids complex.The results show that higher short-range order of non-crystalline starch would restrict the mobility of amylose and reduce the access of starch to lipids.However,when the short-range order in non-crystalline starch was disrupted excessively,the starch chains was too disordered to reduce the ability of amylose to encapsulate lipids.(3)Non-crystalline starches with different short-range order were prepared by water bath method at different temperature,moisture content and heating time.The gel properties of non-crystalline starches and their in vitro enzyme digestibility were investigated by Texture Analyzer as well as an in vitro digestion model.The results showed that the decrease of short-range ordered of non-crystalline starch led to the decrease of starch gel strength and the increase of gel surface adhesiveness.The correlation between the gel properties and in vitro enzyme digestibility of amorphous starch with different starch short-range order was constructed by mathematical and statistical analysis.The mechanism of the influence of short-range order of non-crystalline starch on its digestibility was proposed,namely,the higher adhesiveness makes it difficult for α-amylase to diffuse into the internal matrix,thus inhibiting the hydrolysis of starch.(4)Based on the above results,a series of baking temperatures and baking times were designed to prepared bread,and the changes of short-range order of non-crystalline starch in bread and their effects on bread quality were further investigated.The results showed that the crystalline structure of the starch in the bread had completely disappeared after thermal processing.After analyzed by Raman spectroscopy,it was found that the short-range order of non-crystalline starch in bread decreased with the increase of baking temperature and time.A comprehensive analysis of the hardness,texture structure and color property of the bread showed that higher and lower short-range order of non-crystalline starch was not good for the quality of the bread.The best baking condition was 25 min at 170°C.The fresh bread prepared under this condition had excellent hardness,more uniform and internal pores,good color,and less aging and hardening after storage.In summary,this paper presents an in-depth study on the changes of short-range order of non-crystalline starch during thermal processing and the control of starch retrogradation,formation of starch-lipid complex,starch digestibility and bread quality,which enriches the theories related to the transformation of condensed structure of starch and functional properties,and the results and conclusion are of great theoretical significance for the quality control of starch-based foods.