Mechanisic Study For The Structure Features And Digestion Properties Of Starches In Intact Pinto Bean Cotyledon Cells Influenced By Heating Process

Pulse is an important part of daily diets.The study showed that the low digestibility of starch can effectively reduce postprandial blood sugar response,lowering the risk of the incidence of chronic diseases such as obesity,and type II diabetes mellitus and so on.The relationship between starch structure and digestibility of pulse was discussed in order to provide theoretical guidance for the processing method of pulse healthy food,which could effectively meet the needs of different consumer groups.In this paper,the complete cotyledon cells were isolated from pinto bean,a representative pulse variety in China,as a research model to study the pulse whole food.The effects and mechanisms of high temperature baking(dry heat treatment),autoclaving,boiling and oil frying on the structure and digestibility of starch in cotyledons of pinto bean were studied.This paper further explored from the following two aspects:Pinto bean cells were treated at 120,140,160,180? for 4 hours.The morphology of cells was observedof by microscopy and scanning electron microscope;the crystalline structure of cells was analyzed by X-ray diffraction and differential scanning calorimeter;and the digestion kinetics were analyzed based on the first-order kinetic model.The results showed that the epidermis of cotyledon cells of pinto bean shrinked,the volume of cotyledon cells decreased slightly,and the polarizing cross decreased slightly after being treated at different dry heating temperatures.X-ray diffraction patterns showed that the crystalline type of the cells was still C-type and the crystallinity of the cells decreased.Compared with the untreated starch,the gelatinization enthalpy of untreated cells decreased by about 4.61 J/g,and the gelatinization enthalpy of cells decreased by 11.70 J/g under dry heating treatment at 140?.The digestibility of cotyledon cells treated at 180? was 3.02% higher than that of untreated cells.However,the hydrolysis rate of cells at 360 min(~8%)was significantly lower than that of pinto bean starch(~60%).Although dry heating treatment increased the pore size of cell wall,the cytoplasmic matrix formed a barrier to starch granules,and ?-amylase could not bind to starch effectively,which leads to low starch digestion rate and extent in vitro.The effects of high temperature baking(dry heating treatment),autoclaving,boiling and oil frying on the structure and digestibility of starch in pinto bean cells were studied by using pinto bean starch as control.The digestion rate and extent of pinto bean starch was much higher than that of cells under the same heat treatment.This may be due to the barrier of cell wall to amylase and the adsorption of intracellular protein to ?-amylase,which results in the digestibility of starch in cotyledon cells much lower than that of pure starch.Under different heat treatment conditions,the digestibility of cotyledon cells was as follows: Autoclaved(89.45%)>Boiled(47.77%)> Baked(3.15%)?Fried(2.31%)? Untreated(1.80%).After oil-frying and high-temperature baking,the morphology of the starch and the intensity of polarizing cross did not change significantly,but the crystallinity and gelatinization enthalpy decreased by about 5% and 0.6 J/g,respectively.This may because starch cannot be fully gelatinized,and was less digested due to low moisture content.After autoclaving and boiling,the polarizing cross of starch weakened significantly and the crystallinity decreased about 12%.The starch gelatinization peak could not be detected by DSC,and the digestibility of the cells was significantly higher than that of baked and oil fried cells.Compared with boiling treatment,autoclaving treatment can break up the whole cell wall,leading to the starch granules gelatinized,and digestibility of the cells increased.