Measurement and characterization of external oil in the fried waxy maize starch granules using ATR-FTIR and XRD

- Surface oil contents in fried starch was determined by ATR-FTIR.
- The peak at 1743 cm−1 can be used as fingerprint for oil determination.
- The effect of moisture on the oil absorption of starch was investigated.
- The majority of absorbed oil was located near the surface layer of starch granules.
- The external oil was found to interact with starch to form the V-type complex.

Concerns regarding increased dietary oil uptake have prompted efforts to investigate the oil absorption and distribution in fried starchy foods. In the present study, attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, together with a chloroform-methanol method, was used to analyze the external and internal oil contents in fried starchy samples. The micromorphology of fried starchy samples was further investigated using scanning electron microscope (SEM), polarized light microscope (PLM) and confocal laser scanning microscopy (CLSM). The results indicated that large amounts of oil were absorbed in or within waxy maize starch, but the majority of oil was located near the surface layer of the starch granules. After defatting, the internal oil was thoroughly removed, while a small amount of external oil remained. As evidenced by the changes of the crystalline characteristics with the help of X-ray diffraction (XRD), the interaction between starch and lipids on the surface was confirmed to form V-type complex compounds during frying at high moisture.