Content area
Full Text
ABSTRACT
This study was conducted to examine the characteristics of oxidation reaction on the primary alcohol groups in corn starch, when 2,2,6,6tetramethyl-1-piperidinyl oxoammonium ion (TEMPO) was used, and to determine the optimum conditions for the preparation of oxidized corn starch (OCS). Applicability of the OCS in the food system was also investigated. The effects of TEMPO, sodium bromide (NaBr), and temperature on oxidation reaction time, yield, and selectivity for primary alcohol groups were examined by response surface methodology. As the temperature and the levels of TEMPO and NaBr increased, reaction time and selectivity decreased. Yield decreased with increased NaBr and
selectivity decreased with the increased temperature and NaBr. Selectivity increased with higher TEMPO levels up to a certain point and then decreased. Optimum levels of TEMPO, NaBr, and temperature for the preparation of OCS were determined as 0.6 mM/100 mM of anhydroglucose unit (AGU), 45 mM/100 mM AGU, and 7 deg C, respectively. Water binding capacity, emulsion stability, and viscosity of starch increased significantly by oxidation. Corn starch containing OCS had decreased initial pasting temperature, setback, and gelatinization and retrogradation enthalpy ((Delta)H). Corn starch gel containing OCS showed delayed staling during storage.
Sodium hypochlorite (NaOC1) is the most frequently used oxidizing agent for oxidation of starch, while sodium bromide (NaBr), gaseous chlorine, calcium hypochlorite, hydroperoxide, potassium pemranganate, and ammonium persulfate are used less frequently (Wing 1994). These agents randomly attack the secondary alcohol groups at C2, C3, and C4 as well as the primary alcohol groups at C6 in glucose units (Brouch 1985; Floor 1989). Oxidation of secondary alcohol groups is accompanied by the hydrolysis of glycosidic bond and opening and cleavage of monomeric rings. Consequently, there is a loss of polymer properties and decreased viscosity (Chang and Cho 1997). It is hard to control this oxidation reaction and to obtain the desired degree of oxidation.
Selective oxidation of the primary alcohol groups in the presence of secondary group has gained interest during the last few years since a novel method using a stable organic nitroxyl radical, 2,2,6,6-tetramethyl-l-piperidinyl oxoammonium ion (TEMPO), NaBr, and NaOC1 was presented by De Nooy et al (1994, 1995). In TEMPO-mediated oxidation, NaOC1 and NaBr were used as regenerating oxidants, and water was used as a solvent....