Process Intensification for Enzyme Assisted Turmeric Starch Hydrolysis at Hydrotropic and Supercritical Condition

Abstract

The turmeric rhizome (Curcuma longa) contains curcuminoids embedded in the starch matrix. It is important to target starch removal by hydrolysis to enhance the rate and extent of extraction of curcuminoids. Enzymes are green catalysts and their activity can be enhanced by working on certain parameters. In the case of starch hydrolysis, α- amylase is more efficient when the starch is in the gelatinized form than when it is in its natural form. α-Amylase activity improves under supercritical carbon dioxide (scCO2) conditions. Certain surfactants improve α- amylase activity. Hydrotropes are a mild form of the surfactants. However, there are no reports on hydrolysis of turmeric starch in hydrotropic or supercritical (SFC) conditions. The work in this report shows beneficial effect of hydrotrope on the enzymatic reactions. There is marked enhancement in the diffusion coefficient (De) for curcuminoid extraction. The increased starch hydrolysis also improves the solid filtration rates after hydrotropic extraction of the curcuminoids. In the case of hydrotropic extraction of curcuminoids alone otherwise the filtration rate decreases due to the sticky nature of the extraction mass, caused by swelling of the starch. The present work includes hydrolysis of turmeric starch in its natural and gelatinized forms using α-amylase in hydrotrope solution (HS) and scCO2.The starch hydrolysis parameters include α-amylase concentration, solid loading concentration, scCO2 flow rate, presence of modifier in scCO2, residence time and scCO2 backpressure. The optimum hydrolysis parameters are 200 IU.cm-3 of α-amylase, at 328 K, 10 % (w/w) of turmeric loading concentration, 6.5 reaction pH, 900 rpm agitation speed for hydrotropic hydrolysis while the optimum conditions are 5 % w/w turmeric loading concentration, 40 min of scCO2 residence time, 15 cm3 of scCO2 phase modifier and 15 MPa as the scCO2 backpressure. The De for hydrolysis in the HS for turmeric starch in gelatinized form (A) was 4.1 x 10-11 m2s-1 and De for starch hydrolysis methods including in HS for turmeric starch in natural state (B), SFC condition for turmeric starch in natural state (C) and SFC for turmeric starch in gelatinized (D) were approximately 4.1 x 10-12 m2s-1. De for native turmeric starch in the absence of hydrotrope and SFC (E), and in case of gelatinized turmeric starch hydrolysis in absence of SFC and hydrotrope were 4.1x 10-14 and 4.1x 10-13 m2s-1, respectively. The filtration rates for (A), (D), (B), (C), (E) were 2 x 10-4, 1.25 x 10-11, 1.4 x 10-11, 7.3 x 10-11, 8.2 x 10-11 kgm2s-1 respectively. The De and filtration rate were noted in order (A) > (D) > (B) > (C) > (E) > (F). The 2.5 h SFC and 2.15 h HS enzyme treated turmeric powder gave 6.56 and 2.44 x 106 times increased filtration rate for curcuminoid extraction compared to untreated turmeric powder.