Retrogradation behaviour of milled and brown rice pastes during ageing

Retrogradation of gelatinised starch is the main phenomenon that influences the texture of cooked rice. The rate of retrogradation is affected by several factors including amylose and amylopectin ratio, protein and fibre. The objective of this study was to analyse 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 analysed by a NIR spectrometer. The pasting properties and the retrogradation behaviour of milled rice flours strongly depended on the rice varieties. During gel ageing, a noticeable increase of G' and G'' was observed only for the milled rice varieties Asia, Gange, Fragrance and Vialone Nano, characterised by a high amylose content. No further hardening was found either for the other milled varieties or for all the brown samples. The methods used in this work (dynamic oscillatory rheometry and FT-NIR spectroscopy) turned out to be very useful in the definition of rice starch gels ageing.