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

English. 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.

English. Nopal is a cactus cultivated in tropical and subtropical areas and its green parts (cladodes) have been found to possess various health beneficial properties. This degree project would focus on the antidiabetic property of Nopal cladodes. Based on results of previous studies in our lab, this degree project aimed to answer two main questions. The first question was whether there is quality difference among different commercial Nopal flour batches regarding their effects on blood glucose immediately after a meal. This question would be answered by means of digestion experiments with wheat breads containing 3 batches of Nopal flour. The second question was which of the fractions separated from Nopal cladode flour i.e., the water soluble or the water insoluble one, contributes to the beneficial effect of the flour on postprandial blood sugar regulation and hunger-related sensations. This question would be answered by performing both digestion experiment and a meal study in seven healthy volunteers. The result of the digestion experiment for the first question indicated that there was quality difference among the 3 Nopal batches, since they differed in their ability to decrease the rate of starch digestion of bread. The quality difference was not related to the content of soluble dietary fiber or insoluble dietary fiber. The digestion experiment for the second question indicated that neither the soluble nor insoluble fraction of Nopal flour had any impact on the predicted blood sugar modulating effect. The meal study showed that Nopal flour and its two fractions might favor the regulation of postprandial glucose levels by retarding the postprandial concentration peak and also modulating insulin levels. However, a larger experimental group of volunteers would be required for providing a clear picture of these effects, supported by statistical evidence. Similarly, more subjects would also be required for conclusively identifying the effect of Nopal flour and its two fractions on postprandial sensations of fullness, hunger and desire to eat. Further studies on the effects of Nopal flour and its different fractions, including larger number of volunteers and different focuses are necessary to reveal the mechanism of the plant antidiabetic property.