Study On Rice Starch And Protein Extraction And Development Of Gluten-free Rice Starch Bread

Rice has properties, such as the absence of gluten, low levels of sodium, protein, and fat, and ahigh amount of easily digested carbohydrates, which are desirable for certain special diets.The main objectives of this research was to optimize the extraction process of starch and proteinfrom polished rice;to evaluate the effect of the extraction procedure on the properties of theextracted starch;and to use the extracted starch as raw material for gluten free rice starch bread.Long grain polished rice was the raw material used in this research work.In the starch and protein extraction procedures, sodium hydroxide and flavourzyme 500 MG wereused for alkali and enzymatic methods respectively.A 3 factor, 3 levels Box-Behnken experiment design was used to optimize the experimentalconditions for each method.Sodium hydroxide concentration, time and temperature were chosen as independent variables(experimental factors) in the alkali method. Amount of flavourzyme, pH and time were theindependent variables in the enzymatic method.For each experiment 3 dependent variables (responses) including protein yield, starch yield, andprotein residual were measured.The response surface methodology was chosen to graphically express the relationship betweenthe independent variables with the dependent variables.The optimum conditions determined by the experimental design were:1) in alkali extraction method— NaOH concentration (0.05mol/L), time (5 hours) and temperature(50 °C);2) in enzymatic extraction method—amount of enzyme (0.55g/100g flour), time (5 h.32min.) andpH (8).The results of the simultaneous optimization experiments were:1) in alkali extraction method: 75.99% protein yield, 89.31% starch yield, and 0.39% residualprotein;2) in enzymatic extraction method: 85.68% protein yield, 93.74% starch yield, and 0.645%residual protein.Starch extracted by the enzymatic method showed slight lightness in color compared to the starchextracted by alkali method. Data of amylose content, granule shape, swelling power, solubility,turbidity, syneresis did not show significant difference between the starches extracted by bothmethods. The flavourzyme extracted starch had lower peak and conclusion temperatures ofgelatinization than the alkali extracted starch.The enzymatic evaluation of the degree of retrogradation of starch stored at -20°C (frozen), +4°C(refrigerated), and +25°C(room temperature) for 1, 2 and 3 days increased in the following order:refrigerated>room temperature>frozen.The % of nitrogen soluble of rice protein extracted by the alkali method was minimum at pH values4.0 to 5.0 and increased gradually below pH 4.0 and above pH 6.0. Maximum solubility (80.12%)was observed at pH 11.5.Emulsifying properties of bovin serum albumin were significantly higher than those of rice proteinextracted by the alkali method.The enzymatic extracted starch was used as raw material to make gluten free rice starch bread.Whole rice starch bread was made by the no-time method.Hydroxypropylmethylcellulose (60RT, viscosity 4000 for 1% aqueous solution at 25° C) was usedas substitute of gluten.Three main ingredients including hydroxypropylmethylcellulose (HPMC), water and sugar werefound to be critical with regard to bread quality. Their optimum levels in formula for 100g flour were:4 g HPMC, 110 g water, and 8 g sugar.Such levels produced a bread of appreciable volume and acceptable quality as judged by panelist.The food action rating score for rice starch bread was 7.31 on a 9-point scale, against 8.42 forwheat bread.In conclusion, the enzymatic extraction method produced both starch and protein with higher yield,and lower protein contamination (residual protein). A part from the gelatinization characteristic, allproperties were similar.Hydroxypropylmethylcellulose (60RT viscosity 4000) gave dough with the viscoelastic propertynecessary to trap fermented gases, and also to develop a good loaf volume.Such product is useful for patients with celiac disease or others who require diets low in proteinand sodium.Additionally, the result suggests that bread made with rice starch and HPMC contain 27.09% ofslowly digestible starch against 8.23 % in the original rice starch.Economic benefit is also manifested by substituting rice starch for wheat flour in breadmaking forcountries where wheat is not a native crop.