Master of Science (MS)
School of Nutrition and Food Sciences
Amino acids were previously found to modify starch functionalities and potentially increase starch utilization. The effect of amino acids at different pH levels on the pasting properties, thermal characteristics, and resistant starch (RS) formation of rice starch was investigated. Prior to the analyses, pretreatment of starch was done by adding amino acid (aspartic acid, leucine, lysine and tyrosine) at 6% dry weight basis and dispersing the mixture in distilled water, solutions adjusted with HCl and NaOH to pH 4, 7 and 10, and buffers of acetate, phosphate and carbonate at the same pH levels, respectively. Samples in HCl/NaOH solutions were mixed at room temperature and at 40+2oC. The slurries were stored at -80oC and lyophilized. Lysine and aspartic acid raised the breakdown (BD) and reduced the total setback (TSB) at all pHs using HCl/NaOH, with aspartic acid exhibiting the greater effect. Lysine shortened the pasting time (PTime) without affecting the peak temperature (PT) and increased the peak and conclusion temperatures with or without pH adjustment. Tyrosine in pH 10 solution reduced the PTime. In buffers, lowering of the peak viscosity, PTime and PT was observed, but was mainly attributed to the buffers. Heating at 40+2oC likewise decreased the paste viscosities and gelatinization temperatures, but raised the PTime and PT, with lysine having the most profound effect. Samples added with aspartic acid and leucine generally caused substantial increases in RS yields. No conclusive results on RS formation were obtained based on effect of charges. Therefore, charges in additives played an important role in altering pasting and thermal properties of rice starch, but not in controlling RS formation. To determine effect of hydroxyl-containing amino acid, starch was added with tyrosine, gelatinized, and lyophilized. The sample in pH 10 solution (HCl/NaOH) had higher BD and TSB than native starch. RS yields of gelatinized samples were negatively correlated to treatment in pH 10 solution. Compared to pretreated samples, gelatinized samples had higher paste viscosities and RS values. In conclusion, amino acids in combination with pH treatments can be used to alter rice starch functionalities, and may consequently enhance formation of RS.
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Manaois, Rosaly Vallejo, "Modification of rice starch properties by addition of amino acids at various pH levels" (2009). LSU Master's Theses. 2074.
Joan M. King