The Effect And Its Mechanism Of Chickpea Flour Fortification On The Starch Digestibility And Texture Of Biscuits

With the development of society and people’s growing concern about nutrition and health,the meal replacement biscuits with slow starch digestion developed for special groups such as diabetes patients have more market development potential.Pulses have the potential to reduce the starch digestibility of foods.However,most of the related products and existing researches on delayed digestion properties in biscuits mainly focused on cereal fortification.The effect and mechanism of using chickpea flour to enhance starch digestion of biscuits were still unclear.Therefore,the reasons of the partial replacement of chickpea flour for wheat flour on reducing the in vitro starch digestibility of biscuits were analyzed in this paper.On this basis,the effect of chickpea thermal treatments on further regulating the starch digestibility in fortified biscuits were investigated.The mechanism of the differences in starch digestibility and texture quality of thermal-treated chickpea flour fortified biscuits were revealed from the perspective of microstructures change and the interaction between starch and other components.Based on color,texture,sensory properties,and in vitro starch digestibility of biscuits,the effect of chickpea flour replacement on the biscuit was studied.It was found that the partial replacement of chickpea flour for wheat flour(10%-40%)helped to improve the color of biscuits.Starch digestibility and estimated glycemic index decreased with the increase of chickpea flour.However,a high replacement amount(40%)caused high hardness,reduced taste and flavor qualities,and affected the overall sensory acceptability of the chickpea flour fortified biscuits.Combining the results of texture,sensory quality and digestibility,the 30% of wheat flour was replaced by chickpea flour,which not only reduced the starch digestibility and estimated glycemic index(e GI=69.60)of biscuits,but also maintained the good sensory acceptability.Based on composition analysis,gelatinization characteristics,thermal characteristics,and microstructure,the mechanism of chickpea flour affecting the starch digestibility of biscuits was investigated.It was found that partial substitution of chickpea flour increased the water solubility and decreased the swelling power of mixed powder,which made starch more difficult to gelatinize completely due to insufficient water absorption.Furthermore,the incorporation of chickpea flour increased the content of protein and fat in the biscuits and reduced the proportion of starch,which promoted the formation of a compact network structure in the matrix and enhanced the entrapment effect on the starch in the biscuits.This resulted in a barrier to hinder the contact between amylase and starch,and reduced the action area of starch particles.As a result,the digestion rate of starch in chickpea flour fortified biscuits was decreased.The effects of chickpea thermal treatments on starch digestibility and the mechanism were investigated.The results showed that roasting and heat-moisture treatment significantly reduced the in vitro starch digestibility of chickpea flour fortified biscuits to 50.5% and 48.4%,respectively.After analyzing the conditions of heat-moisture treatment,it was found that the e GI could be reduced to 60-61 after heat-moisture treatment at 120℃ or 130℃ for 2 hours with water content 30%.This is because the heat-moisture treatment of chickpea made the chickpea flour fortified biscuit have a higher gelatinization temperature,enhanced the intermolecular hydrogen bond and the short-range order of starch molecules,and thus inhibited the enzymatic hydrolysis rate.Scanning electron microscope observation showed that the surface and interior of chickpea flour fortified biscuits prepared by roasting and heat-moisture treatment formed the denser microstructure,which hindered the contact between enzymes and starch.The postprandial blood glucose response of mice also demonstrated that the GI values of chickpea flour fortified biscuits after baking and heat-moisture treatment were 66 and 61,respectively.The thermal treatments of chickpea could delay the appearance of blood glucose peaks and decrease the peak value obviously,which achieved the effect of delaying starch digestion in biscuits and reducing starch digestibility.The effects of chickpea thermal treatments on the texture of biscuits were further evaluated by means of functional properties of the mixed flour,kneading and rheological properties of the dough.Meanwhile,the relationship between the texture,starch digestibility and the starch structure was also preliminarily analyzed by partial least squares regression.Heat-moisture treatment of chickpea significantly increased the hardness and chewiness of flour fortified biscuits and reduce the crispness,which was related to the improvement in the water holding capacity,oil holding capacity,storage modulus,loss modulus,gel network structure and viscoelastic structure.Partial least squares regression indicated that the hardness of the biscuit was significantly positively correlated with the short-range order and relative crystallinity of the starch,while the in vitro digestibility of starch and the glycemic index in biscuits were negatively correlated with the two structural parameters of starch.The biscuits fortified with chickpea flour were stored at 25℃,40℃ and 55℃,respectively,and the changes in the degree of fat oxidation,microbial growth and sensory evaluation during storage were investigated.The results showed that the degree of fat oxidation deepened with the increase of temperature and the prolongation of time.The microorganisms did not exceed the maximum value specified by the national standard,and the sensory score of biscuits showed a downward trend during the storage.Moreover,the peroxide value was used as an indicator to predict the shelf life of biscuits and the Arrhenius equation showed that they could be stored at 25℃ for 156d.