Effect of heating time and temperature on partially gelatinized starch-fatty acid interactions

- Crystallites are formed on the surface of starch granules under controlled conditions.
- Long chain fatty acids inhibit granule swelling of starch heated up to 85 °C.
- Amylose-fatty acid complexes crystallites are formed at temperatures as low as 75 °C.

A series of samples of aqueous dispersions of high amylose (70%) maize starch were prepared in the presence of fatty acid potassium salts. The samples were heated at either 75 or 80 or 85 °C for 30 or 60 or 90 min. The fatty acids used were myristic, palmitic and stearic and they were added to starch dispersions either before the commencement of heating or after the heating was completed at the predetermined temperature and heating time. Flow behavior studies revealed that the temperature of heating but not the time of heating affected the flow properties of the samples. X-ray diffraction studies showed that at temperatures below 85 °C the degree of amylose-fatty acid complexation was fatty acid chain length dependent i.e. the shorter the fatty acid chain length the more the available amylose interacted with the fatty acid when the addition of the acid was done prior to heating. Scanning Electron Microscopy revealed that spherulites were formed on the surface of the thermally treated starch granules, at temperatures as low as 75 °C, which could be due not necessarily only to the amylose-fatty acid complexes but to retrograded amylose aggregates as well.