Characterization of sol–gel transitions of food hydrocolloids with near infra-red spectroscopy

Near infra-red spectroscopy (NIR, 600–1100 nm) was used to characterize sol–gel transitions of food hydrocolloids including whey protein (WP), high acyl (HA) and low acyl (LA) gellan gums. Whey protein (20% w/w), LA and HA gellan (1% w/v) aqueous solutions with selected calcium concentrations (0–40 mM) were used. Principal components analysis (PCA) and principal component regression (PCR) were performed to analyze spectral data of gel dispersions at a series of controlled temperatures (20–95 °C). Gelling temperatures of gellan dispersions were determined directly based upon the PCA results without requiring for reference values. The gelling temperatures determined with the NIR method were similar to those obtained by dynamic rheological tests and dielectric property test. The PCR models showed a good predictability for temperatures of gellan dispersions with selected calcium concentrations during cooling or heating process. This study indicates that the NIR method has a great potential to detect structural change, and to monitor time and temperature dependant behaviour of food hydrocolloids during sol–gel transition period.