Abstract | Keywords | Export | Availability | Bookmark

Choose an application

• Reference Manager
• EndNote
• RefWorks (Direct export to RefWorks)

Starch, found in many plants, is a complex carbohydrate that serves as a source of energy. Next to the two main components: amylose (AM) and amylopectin (AP), it also has noncarbohydrate components present such as lipids, proteins, ... AM is a linear polymer containing α-(1,4)-glycosidic linkages that can form inclusion complexes with lipids or salicylic acid (obtained from sodium salicylate (NaSal)). AP, which is highly branched, also contains α-(1-6)-glycosidic linkages. Native maize starch has A-type crystallinity through the AP chains that are crystallized in a monoclinic lattice. The presence of these inclusion-complexes leads to V-type crystallinity. Upon heating starch in the presence of water, starch gelatinization occurs in which starch granules absorb water, swell, and burst, releasing AM and AP molecules into the medium. This will lead to the loss of their semi-crystalline structure which can be observed with small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD). The gelatinization temperature (Tgel) can change due to the amount of water present or certain additives, like glucose or NaSal. These changes can be monitored with differential scanning calorimetry (DSC). Glucose is known for increasing Tgel while the hydrotrope (NaSal), an organic molecule that enhances solubility, decreases it. The amount of water will change the shape of the DSC peaks. In excess water, only one peak is formed, G endotherm, while in limited water, two peaks are formed, G and M1 peaks. An M2 peak is seen in the presence of AM-inclusion complexes. This research can be interesting as starch is crucial in the food industry but also in e.g. medicines, glue, etc. The search for less sugar in food and baked goods is nowadays a ‘hot topic’, but the amount of sugar influences the gelatinization temperature which can alter the final baked product. For glues and the other mentioned industries, it can be beneficial to lower the gelatinization temperature (e.g. addition of NaSal) so no heating is required. This research shows transient gelatinization stages in excess and limited water conditions in which part of the semicrystalline blocklets are converted to fully gelatinized starch while others remain as layered stacks in which the dense layers are ordered like smectic liquid crystals. In excess water conditions granules in the transient stage rapidly convert into fully gelatinized starch. However, in limited water conditions, the gelatinization process is arrested up to when gelatinization is resumed at higher III temperatures. At first sight, the involvement of a liquid crystalline state aligns with the side-chain liquid crystalline polymer (SCLP) model. However, unlike the SCLP model, the G and M1 endotherms do not seem to be strictly coupled with a helix-helix dissociation and a subsequent helix-coil transition. The double melting behaviour under limited water conditions thus seems to be related to a temporary arrest rather than to a split into two mechanistically different gelatinization steps (dissociation and helix unwinding). As expected, glucose indeed raises the gelatinization temperature while NaSal decreases it down to room temperature when enough NaSal is added. The glucose molecules, that are dissolved in water, seem to penetrate the starch granules when the granules are submerged into the aqueous glucose solution.