Abstract:
The first part of this thesis aimed to study the chemical composition of rice flour and investigate the amount and type of amino acids and fatty acids that are the composition of rice protein and rice lipid, respectively. The second part aimed to study the effects of protein and lipid on gelatinization and retrogradation of rice starch paste using thermal property and mechanical property investigation. Rice flour composed of 8.06% protein, 0.69% fat, 1.11% ash, 0.35% fiber, and 89.79% carbohydrates (w/w dry basis). Rich protein consisted of 88.73% glutelin, 2.07% albumin, 7.58% globulin, and 1.63% prolamin. The major amino acid of all protein fractions was glutamic acid. Rice lipid comprised 55.45% non-starch lipid and 44.55% starch lipid. The main fatty acids in both non-starch lipid and starch lipid were palmitic acid, oleic acid, and linoleic acid. It was found that the ratio of palmitic acid : oleic acid : linoleic acid in non-starch lipid and starch lipid was 30.6: 28.2:33.9 and 50.4 : 13.2 : 27.3, respectively. An addition of commercial rice protein Remypro N80+[Registered sign] at 6% to 18% resulted in an increase in onset temperature (T[subscript o]) peak temperature (T[subscript p]), and conclusion temperature (T[subscript c]), a decrease in the enthalpy of gelatinization ([Delta]H[subscript gel]) and the enthalpy of melting of retrograded paste ([Delta]H[subscript ret]). Two fatty acids; palmitic acid (PA) that is the major saturated fatty acid in rice lipid, and linoleic acid (LIN) that is the major unsaturated fatty acid in rice lipid, were chosen for the investigaion of their effect on starch gelatinization and retrogradation. An addition of PA and LIN at 0.5% and 1% (w/w) had no effect on T[subscript o], T[subscript p] , and T[subscript c] of starch gelatinization, but increased T[subscript o], T[subscript p] , and T[subscript c] of melting endotherm of retrograded starch paste. The lowest [Delta]H[subscript gel] was resulted when adding 0.5% LIN and 0.5% PA to 10-20% starch paste. An addition of LIN at [is more than or equal to] 0.5% and PA [is less than or equal to] 0.5% yielded a starch paste with reduced [Delta]H[subscript ret]. The peak complex viscosity ([eta]*[subscript peak]) of starch paste during gelatinization was reduced when protein was added to 10% starch paste, but increased when protein was added to 15% and 20% starch pasted. The complex modulus (G*) of gelatinized starch paste, which had been heated at 90 ํC, increased with increasing starch concentration but was not affected by protein addition. The [eta]*[subscript peak] of the starch pastes was found to increase with an addition of PA and LIN at [is more than or equal to] 0.5%. The same level of addition of PA and LIN also resulted in a decrease in G* of gelatinized starch pastes at all starch concentrations.