| Starch is an important source of carbohydrates and blood glucose in the diet,and its gelation behavior during food thermal processing is closely related to digestion characteristics.Miscellaneous beans play an important role in the diversified and balanced dietary structure of Chinese residents due to their rich protein,resistant starch and dietary fiber.In the process of food thermal processing,the cell wall structure of miscellaneous beans affects the gelation process of starch and the hydrolysis of enzymes by limiting water migration and steric hindrance.The molecular structure changes and the correlation mechanism with digestion characteristics are still lack of systematic research.In this paper,chickpeas were used as raw materials,and the separation of cells and the grinding of whole powder were used as research objects to simulate the different food particle sizes induced by processing.The effects of cell wall structure on starch gelation behavior and digestion characteristics were investigated by accurately controlling water content and heating conditions.The main conclusions are as follows:(1)Complete chickpea isolated cells were obtained by weak shear without gelation of starch.The intact cells and partially broken cells were hydrothermally processed by controlling different water content and heating time,and the changes of multi-scale structure and functional properties of starch were characterized.The results showed that with the increase of water content,the degree of starch gelation in intact cells was significantly lower than that in broken cells,and the residual crystal content and short-range order after heating were higher than those of broken cell samples,and the solubility(or intracellular leachate content)was much lower than that of broken cell samples.In vitro digestion experiments showed that the starch digestion rate k of intact cell samples was always lower than that of broken cell samples,but there was no significant difference in the final digestion degree.Laser confocal microscopy showed that most of the cell walls in the intact cell samples maintained the basic morphology without rupture,and the relatively complete starch swelling granules in the cells could still be observed.In summary,cell wall integrity can limit water migration and starch swelling,resulting in a very limited degree of gelation and retaining more ordered starch structures.The ordered structure of starch in intact cells can affect the hydrolysis rate of starch,but it does not affect the final digestion degree of starch compared to broken cell samples.The possible reason is that the intact cell wall structure only delays the migration process of enzyme and substrate starch.(2)The grinding whole powder of chickpea with different particle sizes was taken as the research object,and the thermal processing was carried out under a series of water contents.The changes of multi-scale structure and functional properties of starch in each grinding component were studied.The results showed that at 20 %(w/v)moisture content,with the decrease of particle size,the gelation degree and crystal content of starch increased gradually,which was related to the retention degree of cell wall structure in different ground whole powders.The available water required for starch swelling under cell clusters was more limited,and the steric hindrance effect was greater,resulting in limited gelation degree.At the same time,the particle size was negatively correlated with the formation of starch-lipid complexes,which may be related to the spatial distribution of starch and other food components.However,at 40～60 %(w/v)moisture content,no residual gelatinization enthalpy was detected in each component,indicating complete gelation occurred.The relative crystallinity and short-range order decreased with the increase of moisture content,especially at 40 %(w/v),the larger particle size components retained more short-range order.The results of in vitro digestibility showed that the starch digestion rate of the larger particle size components under low moisture heating was positively correlated with the degree of gelatinization,but the complete gelatinization occurred with the increase of moisture,and the digestibility difference between the particle size components was not significant.The results of electron microscopy showed that the morphology of starch granules in the whole powder with larger particle size was well preserved,indicating that the starch under the cell wall was limited swelling and gelation.(3)Chickpea powder with different particle sizes(0.25～0.8 mm,0.15～0.25 mm,<0.15mm)was used as raw material.Based on the quality of mixed powder,20% chickpea powder and wheat flour were added for compounding.The effects of particle size on the farinographical and pasting properties of composite flours,as well as the extensibility,fermentation performance and dynamic rheological properties of composite doughs were investigated.The results showed that with the increase of the particle size of chickpea powder,the peak viscosity of the compound powder decreased and the gelatinization temperature advanced.The formation time and stability time of dough showed a decreasing trend,and the water absorption and weakening degree increased gradually.The extensibility and fermentation performance of the compound dough decreased with the increase of particle size,but the fermentation stability did not change significantly.The elastic modulus G′ and viscous modulus G′′ of the dough gradually increased,showing an increase in solid properties.With the increase of the particle size of chickpea powder,the hardness,chewiness and adhesiveness of steamed bread increased significantly,while the specific volume,color difference and sensory evaluation decreased.The digestion rate and degree of starch digestion decreased with the increase of particle size,and there were significant differences among samples with different particle sizes.The results of this study can provide a theoretical basis for the rational processing and utilization of chickpea and the evaluation of dietary nutrition and health. |
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