Solubility of cellulose derivatives is a limited indicator of their function on retarding starch digestion

Cellulose and its derivatives have been utilized as additives and functional fibers in food industries. The solubility has been traditionally used to categorize cellulose derivatives, whilst their complex effects within food matrix are less understood. In this study, insoluble forms i.e., cellulose and ethyl cellulose (EC), and soluble forms i.e., methylcellulose (MC) and sodium carboxymethylcellulose (Na-CMC) were selected to investigate the mechanisms by which the two groups of cellulose ingredients regulate in vitro digestibility of starch-based foods. In the Michaelis-Menton analysis, the addition of insoluble cellulose or EC as inhibitors tended to decrease the V_max of α-amylase at a non-significant level compared to the value without inhibitors (p > 0.05). Starch-based matrix with insoluble cellulose or EC became less porous, but did not consistently resulting in an increased level of resistant starch content. Soluble MC and Na-CMC as inhibitors not only significantly reduced the V_max (decreased from 1.0 to 0.8 and 0.9 mg/min, respectively) and k_cat/K_m (catalytic efficiency, decreased from 30.9 to 22.2 and 23.3, respectively) of α-amylase (p < 0.05), but the formed matrices had higher level of short-range ordering (R_1047/1022). The soluble forms of cellulose derivatives resulted in higher level of resistant starch (up to 6 %), compared to insoluble cellulose. In summary, this study provides new insights into the complexity in the effects of cellulose derivatives on the digestion of food matrix, and suggests that solubility is a limited indicator of their function on retarding starch digestion. The structural changes in starch-based food matrix induced by cellulose derivatives should be considered in the development of functional foods with low glycemic index.