Effects Of Physical Structure Of Potato Cell Wall On In Vitro Starch Digestion Properties

Potato is the fourth staple food only after rice,wheat and maize,and also an important glycemic carbohydrate in the human diet.Many studies indicated that intact cellular structure provides a physical barrier to limit the access/binding of digestive enzymes to the intracellular starch substrates,thus slowing down the starch digestibility.However,during cooking or processing,the gelatinization and swelling of starch and pectin solubilization destroy cell wall structures,resulting in increased cell wall permeability and accessibility of amylase to intracellular starch.Hence,most potato-based foods are considered to be medium or high glycemic index(GI)food,and their long-term consumption is potential contributors to obesity and type 2 diabetes.In this paper,intact parenchyma potato cells were successfully isolated as a whole food model through soaking with mild acid and alkali solutions,and followed by hydrothermal treatment under excess and controlled water conditions,and chemically cross-linked treatment,respectively.The morphology of potato cells,structure and in vitro digestion kinetics of intracellular starch were investigated to study the effects of physical structure of potato cell wall on starch digestion properties.The results will be helpful to provide theoretical guidance and technical support for the development of low-GI potato food and further promote the potato staple strategy in China.Potato cells were hydrothermally treated under excess water condition and the morphology of intracellular starch and cell wall,crystalline structure changes and in vitro starch digestion kinetics were investigated to study the effects of incubation temperature on in vitro entrapped starch digestion properties.The results showed that three classes of starch digestion of potato cells are identified:(1)when incubation temperature was set at 55°C or 60°C,the efficient physical cell wall barrier significantly reduced the starch digestion rate and extent;(2)within the gelatinization temperature range(i.e.,65°C),the cell wall structures apparently reduced the digestion rate but only slightly reduced the final extent compared to the starch counterpart,due to a weaker physical barrier caused by swelling pressure from gelatinized starch;(3)at above gelatinization temperature(i.e.,?70?),starch swelling pressure and pectin solubilization could have largely increased the cell wall permeability,resulting in that the damaged cell wall decreased the digestion rate,but did not reduce the final extent.Potato cells were hydrothermally treated under controlled water condition to prepare a set of potato cell samples with various DG values from 0 to 100%.The morphology of intracellular starch and cell wall,crystalline structure changes and in vitro starch digestion kinetics were investigated to study the effects of degree of gelatinization on in vitro entrapped starch digestion properties.The results indicated that the digestion rate and extent of intact and broken cells were positively correlated with the degree of gelatinization(R~2>0.9).Under the same gelatinization degree,the digestibility rate and extent of intact cells were apparently lower than that of broken counterparts,indicative of physical cell wall barrier limiting access/binding of digestive enzymes to starch substrates.However,the inhibition effect of cell wall structures on starch digestion weakened as a function of increasing gelatinization degree,due to the fact that starch gelatinization and swelling increased the permeability and thus weakened the physical barrier.Potato cells were cross-linked with different amounts of crosslinking agents.The phosphorus content,swelling power and starch leaching content of cross-linked cells were determined and the morphology of intracellular starch and cell walls,crystalline structure changes and in vitro starch digestion kinetics were investigated to study the effects of cross-linked cell wall structure on in vitro entrapped starch digestion properties.The results indicated the cross-linking reaction could slow down the digestion rate of starch in both intact and broken cells.Under the same cross-linking degree,the digestibility rate and extent of intact cells were apparently lower than that of broken counterparts,indicated that after cooking,cross-linked cell wall structures could still act as physical barrier limiting diffusion of digestive enzymes to starch substrates.The inhibition effect of cell wall barrier on starch digestion increased as cross-linking degree increased,which is attributed to that formation of covalent bonds between starch or cell wall polysaccharide chains via phosphate groups limited starch swelling and pectin solubilization during boiling processing,thus protecting cell wall structure and decreased cell wall permeability.