Starch is broken down into glucose in the mouth and small intestine. To date, the focus on its metabolic activity has largely been restricted to the glycaemic response and consequent glycaemic index. However, this is only a reflection of the influx rate of exogenous glucose, glucose produced in the liver and its distribution in tissues. Accordingly, scientists from the EU funded project 13C-STARCH investigated other important features of carbohydrate metabolism involved such as digestion time, internal transit time and gastric emptying. The fate of glucose not absorbed by the small intestine is that it enters the colon and undergoes fermentation. The products include short chain fatty acids (SCFAs). Some of these enter the portal circulatory system and they then pass into the liver where they are thought to influence the organ's metabolism. Furthermore, they may be ligands (binding signallers) for protein receptors that are expressed in adipose or fatty tissue. Interestingly, these have a wide range of effects like feeding behaviour and insulin sensitivity. Partners at the University Medical Centre, Groningen, conducted research into glucose kinetics after a meal. The first step was to grow wheat and barley using a 13C carbon dioxide source and then prepare food like bread using the cereals that had sufficient 13C. The dual isotope technique was used so D-[6,6-2H2]glucose was also administered. During the period after the meal, the team were able to measure glucose concentrations in test subjects and determine its source, exogenous or endogenous. They could then obtain the net rate of intestinal absorption of glucose. Other 13C products produced for tracking starch metabolism included 13C barley for acetate production and 13C lactulose which is an important substrate for colonic fermentation. The ability to grow 13C enriched crops for traceable food in vivo offers a huge opportunity to study the effects of starch fermentation and its metabolic effects in other tissues and organs. As such, it may provide further insight into obesity, type II diabetes and cardiovascular disease. For the food industry in particular, this provides evidence of advantages of the production of food that incorporates modified, slowly digestible and resistant starch.
Stable isotope applications to monitor starch digestion and fermentation for the development of functional foods.
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30 April 2020