Characterization of Nopal cactus cladode flours regarding dietary fiber and starch content, and their effects on postprandial glycemic regulation

Abstract: Background: Previous study found that 2 batches of Nopal flour supplied by the same suppliers at different time was performing different results in in vitro studies and the quality of Nopal flour might thus be different. Besides, investigation on whether the soluble or the insoluble fraction of the Nopal flour suspensions contributed to the glycemic modulation was still necessary. Method: Composite wheat/nopal breads were made by including different batches of Nopal flour and soluble and insoluble fractions of the water suspension of one batch Nopal flour. The contents of available starch and dietary fiber were measured. The chewing/digestion method, an in vitro procedure mimicking intestinal hydrolysis and absorption of starch, was performed to calculate the hydrolysis index, which can be used to predict the actual glycemic index, for comparisons between batches and fractions with white bread as control. A pilot meal study with the participation of 7 healthy subjects was performed to investigate the postprandial glycemic and insulinemic modulation of different fractions and the Nopal flour breads. In the meantime, subjective appetite variables were also evaluated. Result: Breads made from 3 batches of Nopal flour showed different results in the in vitro experiment, although their dietary fiber contents were similar. Thus, there were differences among the 3 batches of Nopal flour and the contents of dietary fiber were unlikely the reason for the different results in the in vitro experiment. Breads made for comparison of soluble and insoluble fractions of Nopal flour had little influence on the starch hydrolysis rate or hydrolysis index of this in vitro experiment. Although no significant difference could be found between these two breads, it is still reasonable to believe that the bread made from the soluble fraction contained higher amount of soluble dietary fiber. The pilot meal study provided no statistical evidence to prove that the selected batch of Nopal flour had any effect on postprandial glycemic and insulinemic modulation, though differences on the averages could be found among their mean values of the glycemic and insulinemic peaks and sectional incremental area under curve (iAUC). Differences among 3 Nopal sample breads could hardly be found in the result of 3 appetite-related variables, fullness, hunger and desire to eat. This lack of statistical power could result from the limited number of subjects. Due to the little performance on these experiments, the conclusion on whether soluble or insoluble fraction contributes to the modulating effect on glycemic and insulinemic responses and appetite variables could not be drawn.