Importance of starch
Starch, along with crude fat, is one of the most important energy sources in pigs’ rations. That is why Duynie Feed finds it important to extensively and accurately measure the starch content in co-products.
Optimum digestion of starch
Starch is a carbohydrate and generally consists of long and uninterrupted chains of glucose units. During digestion in the pig, these long chains need to be broken down into smaller absorbable parts with the aid of enzymes. The enzymes to break down starch are produced by the pig and added to the feed at various points in the digestive tract.
Optimum digestion of starch
Starch digestion already starts in the pig’s mouth. By chewing the food, the pig adds saliva which naturally contains the Amylase enzyme, which breaks down the starch structure into smaller chunks. The feed travels via the oesophagus to the stomach, where the pH is very low. After the stomach, the pH of the feed is neutralised and enzymes are added by the pancreas. The starch chunks are then broken down to absorbable glucose units by enzymes in the small intestine. These glucose units are absorbed into the bloodstream in the small intestine, to support all sorts of bodily processes (maintenance and production). Starch is digested optimally by pigs when absorption occurs in the small intestine.
Ewers starch determination
Starch content is normally determined using the Ewers method. Starch is not water soluble but can be broken down by hydrochloric acid hydrolysis, in a process that is stricly standarised in terms of acid strength, time and temperature. The resulting products cause an optical rotation, this rotation can be quantified using a polarimeter.
A second sample from the same batch is treated with 40% ethanol and rotation measured with the polarimeter. The difference in the results is multiplied by a known factor to give the starch content. However the acid hydrolysis can also produce some resistant carbohydrates, not-enzymatically decomposable and also not soluble in 40% ethanol, but that do cause optical rotation, these resistant carbohydrates are also beneficial to gut health as they pass through the small intestine intact and are then fermented in the large intestine, producing short chain fatty acids (SCFA) which serve as an energy source for colonic cells.
When starch rich products are heated (during processing or at a later stage), the starch structure is broken up. This heating process is referred to as the gelatization of the starch. This makes the starch accessible to the digestive enzymes, so that the starch can be digested optimally in the pig’s small intestine.
Raw, insufficiently heated starch products are not broken down in the small intestine. It ends up unbroken in the large intestine, where it is decomposed by microbes in a fermentation process.
Starch that is broken down through a fermentation process has a (slightly) lower energy value than starch that is digested by enzymes.
Fermentatively degradable potato starch can be used in the large intestine to form organic acids and thereby contribute to an optimum intestinal health. However, an excess of fermentatively degradable starch can upset the microbial balance.