Intactness of cell wall structure controls the in vitro digestion of starch in legumes

Abstract

Increasing the level of starch that is not digested by the end of the small intestine and therefore enters the colon ('resistant starch') is a major opportunity for improving the nutritional profile of foods. One mechanism that has been shown to be successful is entrapment of starch within an intact plant tissue structure. However, the level of tissue intactness required for resistance to amylase digestion has not been defined. In this study, intact cells were isolated from a range of legumes after thermal treatment at 60 °C (starch not gelatinised) or 95 °C (starch gelatinised) followed by hydrolysis using pancreatic alpha amylase. It was found that intact cells, isolated at either temperature, were impervious to amylase. However, application of mechanical force damaged the cell wall and made starch accessible to digestive enzymes. This shows that the access of enzymes to the entrapped swollen starch is the rate limiting step controlling hydrolysis of starch in cooked legumes. The results suggest that a single cell wall could be sufficient to provide an effective delivery of starch to the large intestine with consequent nutritional benefits, provided that mechanical damage during digestion is avoided.

High‐Amylose Starches to Bridge the “Fiber Gap”: Development, Structure, and Nutritional Functionality

“…Previous studies have reported a reduction of glycemic responses (C. H. Edwards et al., ) and excretion of undigested macronutrients (Ellis et al., ; Noah et al., ; Tovar, Bjorck, & Asp, ) on consumption of whole grains or cooked legumes in humans and rats. The in vitro digestion rate of starch and lipids was reduced due to the intact cell walls (Dhital, Bhattarai, Gorham, & Gidley, ; C. H. Edwards, Warren, Milligan, Butterworth, & Ellis, ), whose roles in macronutrients encapsulation have been reviewed recently (Grassby, Edwards, Grundy, & Ellis, ; Grundy et al., ). The intactness of cell walls is related to particle size, which is dependent on mastication habits and processing conditions, for example, milling and heating.…”

Comparison between microwave‐cooking and steam‐cooking on starch properties and in vitro starch digestibility of cooked pigmented rice

“…In contrast, in the homogenized slurry samples (Figure c and d), approximately 50% of the starch was digested in the first 5 min of simulated small intestinal digestion, an increase of around 10‐fold that of the grain samples. Generally, the pericarp and aleurone layers of brown rice grain would be a barrier against enzyme accessibility to the internal grain, whereas the amorphous nature of the homogenized slurry samples would decrease the particle size of cooked rice, thereby increasing the susceptibility of the starch to amylase enzyme (Dhital, Bhattarai, Gorham, & Gidley, ; Ogawa et al, ). Similarly, Tamura, Singh, Kaur, and Ogawa () demonstrated that the starch particles of the homogenized slurry were unpacked and easily accessible to digestive enzymes, and consequently, most of the starch was degraded in the first 5 min of simulated small intestinal digestion.…”

The cotyledon cell wall and intracellular matrix are factors that limit iron bioavailability of the common bean (Phaseolus vulgaris)

“…The role of storage in prolonging the cooking time has been studied extensively in beans and is related in part to the separation of the middle lamellar regions between the cotyledon cell walls. 27 Such observations cast further doubt on the accuracy of the Fe absorption measurement in studies using extrinsic labeling. 25 The cotyledon cell walls may also be a major factor preventing the proper equilibration of the extrinsic labelling of Fe in beans.…”