| This study was to investigate the effect of low temperature (4°C and-20°C) onthe retrogradation of milling degree (0,3,6, and9%, based on brown rice) of riceflour during storage and elementary exploration of the mechanism, in order to providesome theoretical guidance for retarding the retrogradation of rice flour inindustrialized production, the results are as follows:(1) Indica rice “Zaoxian167” were dehulled using a Satake rice machine. Afterdehulling, the brown rice was milled using a Satake Rice Test Mill to various degreesof milling (0,3,6, and9%, based on brown rice). Samples were placed into therefrigerator at4°C (-20°C) for1,3,7,12and20d. The retrogradation properties ofrice flour gels with different milling degrees during storage at low temperature wereinvestigated by DSC, Texture profile analysis, FT-IR, XRD and SEM.Results showed that rice flour gels with the same DOM stored at4°C retrogradefaster than those stored at-20°C. Also, higher milling degree leads to a fasterretrogradation in the same temperature. Texture profile analysis demonstrated thatsamples showed a lower hardness but higher adhesiveness during storage at-20°Cand under the same conditions, brown rice had a lower hardening rate and changingrate of adhesiveness. Differential scanning calorimetry (DSC) revealed that the higherthe milling degree, the higher retrogradation index (ΔHr/ΔHg) at4°C or-20°C andsamples stored at-20°C expressed lower (ΔHr/ΔHg). X-Ray diffraction (XRD)analysis indicated that storage at-20°C decreased the degree of crystallinitycompared with storage at4°C. Fourier Transform infrared spectroscopy (FT-IR)revealed that higher milling degree leads higher absorbance ratio(A1047/A1022cm-1).Scanning electron microscopy (SEM) confirmed that samples stored at-20°C canhold more water and brown rice had the best abilities to keep water compared withthe others. Water is higher, retrogradation is lower.(2) The effect of dietary fiber of rice bran on the retrogradation of rice starchwere investigated by Texture profile analysis, RVA, FT-IR and XRD. Results have shown that rice starch gels with different amount of dietary fiberadded at4°C storage condition, increase of hardness, pasting temperature, setbackvalue, degree of crystallinity and infrared of absorbance ratio(A1047/A1022cm-1) wereobserved while the viscosity decreases. This means that dietary fiber have a certaindelaying effect on rice starch aging and the effect of the amount added to10%wasbetter than the amount added to5%of the experimental group.(3) The effects of insoluble dietary fiber component (cellulose, hemicelluloseand lignin) on the retrogradation of rice starch during the storage.Results showed that those three elements all delayed the retrogradation of ricestarch. Among them, the best effect was hemicellulose, cellulose second, and ligninwas the worst. RVA expressed that the addition of insoluble dietary fiber had lowerbut more stable pasting temperature and setback. Texture profile analysisdemonstrated that the addition of insoluble dietary fiber had a lower hardness buthigher adhesiveness. XRD analysis indicated that the addition of insoluble dietaryfiber had no change in crystalline structure but had a lower degree of crystallinity.FT-IR revealed that addition of them had an interaction with starch by hydrogen-bondand a lower absorbance ratio(A1047/A1022cm-1). SEM confirmed that cellulose, ligninand hemicellulose will associate with starch, through reducing the chances of starchchains combining with themselves so as to retard staling. |
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