Retrogradation behaviour of white and brown rice pastes during ageing

Retrogradation of gelatinised starch is the main phenomenon that influences the texture of cooked rice and the ageing behaviour of starch-containing food like gluten-free products. The rate of retrogradation is affected by several factors including amylose and amylopectin ratio, protein and fibre. Moreover, rice shows considerable differences among varieties in terms of physicochemical characteristics and retrogradation behaviour. The objective of this study was to analyze the pasting properties and the retrogradation behaviour of six traditional and five aromatic Italian rice varieties. The pasted gels, after cooling, were evaluated by dynamic rheological measurements for up to 7 days of storage at 4 °C. The samples were also analyzed by an FT-NIR spectrometer, equipped with an integration sphere. The pasting properties and the short term retrogradation behaviour of white rice flours strongly depended on the rice varieties. During gel ageing a noticeable increase of G’ and G” was observed only for the white aromatic varieties Asia, Gange and Fragrance, characterized by a high amylose content. No further hardening was found either for the other white varieties, independently of amylose concentration, or for all the brown samples. The white rice gel spectra, moreover, were correlated with the rheological parameters (G’ and G’’) and good models were obtained both in calibration and in prediction. The behaviour of gels during ageing indicates that FT-NIR spectroscopy could be used as an alternative method for the study of starch retrogradation.