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Prof Jennie Brand-Miller and Dr Alan Barclay answer 5 of the most common questions we are asked about starch.

Starch structure
WHAT IS STARCH? Starch is found naturally in grains, legumes (beans, peas and lentils), potatoes and other starchy vegetables (e.g., parsnip, potato, pumpkin, squash), nuts and seeds. It’s the plant’s reserve energy supply that it stores in seeds and tubers. In fact, there are two types of starches which are part of the large group of polysaccharides – chains of glucose joined together by chemical bonds. 

  • Amylose is a straight chain of glucose molecules that tend to line up in rows like a string of beads and form tight, compact clumps that are harder for our bodies to gelatinise and digest. 
  • Amylopectin is a string of glucose molecules with lots of bushy looking branching points, such as you see in some types of seaweed or a tree. Amylopectin molecules are larger and more open and the starch tends to be easier for our bodies to gelatinise and digest. 

 WHAT IS GELATINISATION? Ever tried to eat raw rice or dried beans or raw potato? Not a good experience. Possibly mission impossible. That’s because the starch in these foods is stored in hard, compact granules that make it virtually impossible for our starch-digesting enzymes (amylases in our saliva and intestinal digestive juices) to attack and digest. And that’s why we cook these foods. It makes the difference called gelatinisation. It softens them up you might say.

Let’s take rice. The cooking instructions for the absorption method tell us to throw 1 cup of rice into the pot with 1½ cups of water and bring to the boil. Reduce the heat and simmer, covered, for 20 minutes or until the water has evaporated. Remove from heat, keep covered and set aside for 5 minutes. So, what happens? The starch granules absorb the water, swell up and some burst, freeing the thousands of individual starch molecules. We now have fluffy rice and a food we have no difficulty digesting because our highly specialised starch-digesting enzymes (amylases) have a lot more accessible surface area to attack.

WHAT IS GLYCOGEN? Glycogen is very similar to starch in its chemical structure. Our bodies make it from glucose and store it as backup in the liver and muscles (we can store about 1500 to 1900 calories worth). It comes from the carb foods (starches and sugars) we consume and provides energy we can draw on when our carb stores run low with fasting or intense exercise. When carb stores run low, our bodies convert the glycogen back to glucose to power our muscles and brains.

WHAT IS RESISTANT STARCH? Many scientists categorise resistant starch as another form of dietary fibre these days because of what it does. It actually is starch that resists digestion and absorption in the small intestine and zips through to the large intestine largely intact to be fermented into short chain fatty acids, like acetate, propionate and butyrate by those good gut bacteria we have down there (our microbiome). Research in recent years suggests it may well be as important as fibre in helping reduce the risk of colorectal cancer, so it has a lot of fans. It’s found naturally in unprocessed cereals and whole grains, firm (unripe) bananas, beans and lentils. But you can create it in your own kitchen too when you make potato salad, rice salad or pasta salad – starchy foods that you cook and then cool. The same goes for old-fashioned oatmeal if you cook up a pot one day and reheat individual portions the next.

WHAT ARE MALTODEXTRINS? Maltodextrins don’t occur naturally in foods, they are chains of glucose molecules ranging from three to nine glucose units long produced by processing corn (maize), potato, rice, tapioca, or wheat to break down the starch in a factory. We call them highly refined carbohydrates. As they are flavourless and only slightly sweet, they are commonly added to processed foods to provide bulk and texture and to help blend ingredients together. You will also find them in the single-serving, tabletop packets of some intense sweeteners and in pharmaceuticals.

Are they gluten-free? In the United States and Canada, maltodextrins are most often made from corn, potato, or rice but in Europe, Australia, and New Zealand, wheat is widely used. It seems to be generally accepted that the source may not matter, since the original grain or starchy vegetable is highly processed to remove all the gluten-containing protein. However, dietitian Dr Kate Marsh, always recommends people with celiac disease avoid maltodextrin derived from wheat as there is a possibility it may contain small amounts of gluten. She says: “Wheat will appear on the label when it has been used to make maltodextrin. If you have celiac disease and are concerned about a particular product, your local celiac society should be able to help. Alternatively, check with your doctor or dietitian.”

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