Abstract:
This research aimed to investigate the physicochemical properties of flours and starch from chestnut (Sterculia monosperma Vent.), and their uses in food products. Two milling methods (dry-milling and wet-milling) were studied and found that the yield and fiber content of the dry-milled and wet-milled flours were not significantly different (p>0.05). Flour from dry-milling had higher protein, fat and ash and lower carbohydrate and amylose contents than those from wet-milling. The starch granules of both flours were round and half cut oval shape. The dry-milled flour granules were found to lose their birefringence partially and had more other components or damaged starch attached on the surface than the wet-milled flour granules. From the color measurement it was found that the dry-milled flour had lower L, a values and white index, but higher b values than the wet-milling. The dry-milled flour were found to have higher damaged starch, water binding capacity, solubility, onset temperature (T [subscript o], peak temperature (T [subscript p]) and pasting temperature but lower swelling power, peak viscosity, breakdown, enthalpy of gelatinization ( AH [subscript gel]) and retrogradation than the wet-milled flour. Type and concentration of extracted solution (water, 0.3-0.7% NaHSO[subscript 3] and 0.1-0.5% NaOH) were studied. The results showed that starch isolated by using 0.5% NaOH had the lowest protein content (.028%db). The starch obtained had carbohydrate, protein, fiber and amylose contents of 99.55%, 0.28%, 0.15% and 36.63%db, respectively, and trace amounts of ash and fat. Clear birefringence of starch granules ws observed under the polarized light. The china-chestnut starch granules had the average sizes of 9.10 um and exhibited a C-type X-ray diffraction pattern. The gelatinization temperature of china-chestnut starch was 70-81 degree Celsius and AH [subscript gel] was 18.19 J/g. The pasting properties of starch as measured by RVA at concentration of 7% showed to be pasting temperature of 82.37% degree Celsius, peak viscosity, breakdown and setback of 150.53, 17.58 and 63.36 RVU, respectively. In addition, the starch had low freeze-thaw stability. From the study on the effect of pH (3-9) on pasting properties of china-chestnut flour and starch pastes, it was found that the pastes at pH 9 had the highest viscosity. The application of the wet-milled flour and starch showed that they could be used as thickener in acidic food such as chilli sauce but were not suitable for rice noodles.