# Glycaemic Index of Bakery Products and Possibilities of Its Optimization
### Rapidly Digestive, Slowly Digestive and Resistant Starch
A physical barrier (in particular the seed or grain envelope) is the cause of the low glycaemic index of the food concerned [43; 44]. Resistant starch type 2 (RS2) is a native starch contained in the starch grains of raw potatoes, green bananas, legumes and high-amylose corn starch. The reason for RS2 resistance is the native conformation of the starch grain, or the presence of a higher proportion of a tightly 'packed' crystalline amylose structure (either in native form or as ungreased parts of the starch grain). During the appropriate heat treatment of foods, RS1 and RS2 starch types undergo gelatinization and become partially digestible components [43; 44]. Resistant starch type 3 (RS3) is formed as a result of certain technological processes, by the action of heat and moisture on the material being processed. It is a form of retrograded starch, retrograded amylose and amylopectin. During the gelatinization of the starch (suspension of the starch in water), the amylose chains are released into solution, and after the mixture has cooled, the amylose chains (ordered double helices stabilized by hydrogen bonds) are reconnected. This is the process of retrogradation of amylose (the retrogradation of amylose is much faster than the retrogradation of amylopectin). The resulting solid helices of amylose prevent amylolytic enzymes from accessing the glycosidic bonds, and this type of amylose is resistant to enzymatic hydrolysis. The retrogradation of amylopectin is much slower due to the complex structure of amylopectin. Type RS3 (retrograded starch) is found in large quantities in foods such as aged breads and pastries, chilled cooked potatoes, chilled cooked pasta, sterilized peas, sterilized beans, etc. One option for increasing the RS3 content in starch (in the laboratory or in industry) is to use starch gelatinization under various physical and physicochemical conditions of hydrothermal treatments, including extrusion [44; 45; 46]. Resistant starch type 4 (RS4) is a modified starch--a chemically or physically modified starch that does not occur naturally. The RS4 content of the starch can be increased by, for example, acid hydrolysis of the starch isolated from high-amylose barley followed by repeated heating and cooling of the mixture (suspension). Chemical modification of the starch consists of cross-linking the starch, e.g., after reacting the starch with phosphate and other reagents. Resistant starch type 5 (RS5) is a thermally stable starch fraction containing an inclusion of the hydrophobic part of the lipid into the helical cavity of the amylose helix. Fats and oils and monoacylglycerollycerols used as emulsifiers form inclusion compounds with the amylose, thus retarding the swelling of the starch and reducing the extent of starch gelatinization [44; 47; 48; 49]. It should also be mentioned that other factors that hinder starch digestion are the presence of \(\alpha\)-amylase inhibitors, a high content of non-starch polysaccharides (fibre) in the food, higher viscosity of the food, etc. In a general context, it is the slowing down of the access of enzymes to the substrate and the creation of a certain resistance, a barrier, that limits the digestion of starch [43; 50; 51]. During the processing of cereals and other raw materials, the digestibility of starch varies depending on the technological processes used; in addition, RS2, RS3 and RS4 types can be added to food as a functional ingredient (additive). An important source of resistant starch is cooked foods/feeds made from legumes, potatoes and cereals. Cooked and cooled (or stored) foods/feeds have higher RS contents than freshly cooked ones [40; 51].