Tamarind seed polysaccharide isolation from tamarind kernel powder by protease enzyme and high-intensity ultrasound

Abstract

Tamarind seed polysaccharide, xyloglucan (XG), is obtained from Tamarind Kernel Powder (TKP). In food industry, XG is widely used as a thickener, stabilizer, fat replacer, or starch modifier to improve rheological and thermal properties of many products. The TKP composes of polysaccharide, protein, oil and others 69.84, 18.82, 8.00 and 3.34%, respectively. Isolation of tamarind seed polysaccharide from TKP by using protease enzyme and high-intensity ultrasound in this research was divided into three parts; the de-oiled processing, the isolation of tamarind seed polysaccharide processing and the purification of isolated tamarind seed polysaccharide using dialyzer. For the de-oiled processing, isopropanol and hexane have similar extraction efficiency on the basis of extraction time, extraction temperature and solvent to solid ratio. The water content in 95% ethanol decreased the effective of oil removal. The use of high-intensity ultrasound in the 95% ethanol extraction increased the percentage of oil removal but reduced the size of TKP and the average molecular weight of polysaccharide. The decreasing of oil content in DTKP (de-oiled TKP) made the good dispersions in water. The oil extraction using isopropanol at the solvent to solid ratio of 3:1 ml g-1, extraction time 10 min and the temperature of 30°C was a suitable condition for DTKP production. The obtainable product compositions are 75.40, 20.32, 0.65 and 3.63% for polysaccharide, protein, oil and others, respectively. For tamarind seed polysaccharide isolation process, the experiment was divided into three parts. The use of protease, high-intensity ultrasound and combination of protease and high-intensity ultrasound were studied. The solely utilization of protease digestion for 3 to 5 hours and 0.3 to 0.5% enzyme concentrations produced low protein ITSP (isolated tamarind seed polysaccharide) with good thermal properties. The kinetics of protein digestion could be fit with Michaelis-Menten equation. The high-intensity ultrasound could not decrease the protein contamination in ITSP. The increasing of amplitude level and sonication time was declining the average molecular weight of polysaccharide. The Schmid polymer degradation model was used to fit the kinetics of molecular weight of polysaccharide decay as a function of time. A combination of protease and high-intensity ultrasound treatment has a potential to produce ITSP in high yield and low protein contaminated in short time. A 0.3% protease and 50% amplitude level at 30 min sonication time gave the 93.49% protein eliminated and 60.12 % yield for ITSP. ITSP composes of polysaccharide, protein and others at 95.86, 2.06 and 2.08 respectively. The last experiment, MTSP (modified tamarind seed polysaccharide) was the purification of ITSP by using dialyzer. The increase of feed flow rate increased the dialysance (D, the performance of dialyzer) and the overall mass transfer coefficient (kOV) and also decreased the rejection coefficient (R) of protein. The highest purity of polysaccharide, 99.13%, at 63.12% yield was achieved at 250 ml min-1 feed flow rate and 1500 ml min-1 dialysate flow rate. The MTSP could rapidly dissolve in water at low temperature. So, the initial viscosity was higher than that of other polysaccharides. The increase of polysaccharide purity could increase the viscosity and the pasting properties of product. It was also found that the powder could be rapidly dissolved in water at low temperature