Preparation And Properties Of Amidated Low Ester Pectin

Pectin is one of high value food additive, which has wide application in food industries with fine thickening and gelling properties. There are two kinds of pectins - high ester pectin and low ester pectin, and the later including conventional low ester pectin and amidated low ester pectin. As ramification of common low ester pectin, amidated low ester pectin has improved functionalities because of its modified molecular structure: it can be used in low sugar, calorie foods; it need less calcium to gel and is less sensitive to precipitation by high amounts of calcium; their gels are claimed to be perfectly thermoreversible. As a result, amidated low ester pectin can be applied in broader fields as a new type of food additives. However, there is little research on its preparation, especially its physical-chemical properties such as the thickening and gelling properties in China. Therefore, the main purpose of the study is to prepare amidated low ester pectin, and investigate its main characteristics - viscosity and gelling properties, which can help development of improved technology for production of low ester pectin.In the experiment, the commercial high ester citrus pectin was used as raw material to study the technique of its amidation in the ammonia-ispropanol suspension. The main parameters during the reaction including amidation and acid-precipitation process were analyzed and the optimal parameters were decided finally. In addition, the parameters effect the viscosity and gel breaking strength were also studied and their changing rules were gained under different conditions.Reaction of high ester citrus pectin with ammonia in isopropanol suspension: The amidated low ester citrus pectins were prepared in ammonia-isopropanol suspension under different conditions, including ammonia concentration, temperature, reaction time and isopropanol concentration, and then precipitated in acid-isopropanol suspension. The kinetics of de-esterification, viscosity, degree of esterificaiton, degree of amidation of amidated low ester citrus pectin were studied to determine the best procedures during amidation.Precipitation in acid-isopropanol suspension: The high ester pectin was first treated in ammonia-isopropanol suspension under the same condition, and then precipitated in acid-isopropanol suspension under different parameters, including concentration of isproponal, pH value and time during the precipitation. In the study, the yield, viscosity, degree of esterificaiton, degree of amidation of amidated low ester citrus pectin. were studied to determine the best procedures during precipitation.Therefore, the optimal parameters for preparing amidated low ester pectin during the amidation and precipitation process were treating high ester pectin under 4mol/L ammonia-60%ispropanol suspention for 40 min at 5℃,and then, the amidation solution was precipitated in acid-60%ispropanol for 20min at pH4.0.Properties of amidated low ester citrus pectin:Inflence of pectin concentration, temperature, heat, pH, sugar content and calcium on viscosity of amidated low ester citrus pectin: Increasing the pectin concentration increases the viscosity of pectin solution, especially at 1.0%-1.6% range of pectin concentration, in which a linear relationship was found between viscosity and pectin concentration; The viscosity of pectin solution shows not completely elasticity recovery during increasing and decreasing of temperature steps; The linkage of pectin chain was destroyed by heating but only happening at the beginning; The changes of pH value would lead up to the decrease of viscosity of pectin solution; Increasing the sugar content increases viscosity of pectin solution but finally approaches a constant value; Viscosity reaches its maximum value when adding 25mg Ca²⁺ /g pectin.Inflence of setting temperature and time, pectin concentration, pH, sugar content, calcium and buffer solvent on viscosity of amidated low ester citrus pectin: Decreasing the temperature of setting time increases the gel breaking strength; A linear relationship between pectin concentration and gel breaking strength is found as the pectin concentration was larger than 0.8%; Relatively stable gel will be gained at pH2.8-3.4 ; Gel breaking strength increase while the sugar content increasing from 10% to 30%, but decreases when as the sugar content exceeds 30%; Excellent gel will be gained in salt-free water in a narrow range of Ca²⁺ concentration while good gel will be gained in a much wider range; The gels formed by amidated low ester citrus pectin are thermoreversible, which would lose much less breaking strength with the optimal buffer salts.