APPLICATION of RESPONSE SURFACE METHODOLOGY IN PROTEIN EXTRACTION STUDIES FROM BREWER'S SPENT GRAIN

Effects of temperature of extraction, time of extraction, concentration of sodium dodecyl sulphate and Na2HPO4 in the extractant solution, particle size of grain and BSG: extractant ratio on the yield of protein soiubilized from dried brewer's spent grain (DBSG) and pressed brewer's spent grain (PBSG) were studied simultaneously using a process optimization technique termed Response Surface Methodology (RSM). the initial fractional factorial screening design indicated that time, temperature and particle size of grain were significant variables while concentration of extractant had no effect on protein yield from either DBSG or PBSG. the mean yield of protein extracted from DBSG was 28.14% compared to 9.53% for PBSG. When a central composite rotatable design was subsequently applied to four variables, temperature, time, BSG:extractant ratio and concentration of Na2HPO4 in the extractant solution, with particle size of grain held constant at 1.5mm, all variables had a significant effect on protein yield from DBSG. Using multiple regression analysis, a second order polynomial model was derived and used to predict the yield of protein extracted from DBSG under various combinations of these four variables. Generation of contour plots enabled selection of levels for each variable to give a product with a desired protein concentration. Typically, a yield of approximately 60% protein could be obtained from DBSG using a concentration of 0.6% Na2HPO4 in the extractant solution, a BSG:extractant ratio of 2.5:100 and the mixture heated at 90°C for 95 min. the observed protein yield agreed well with the predicted maximum value using a RSM approach and demonstrated RSM as a powerful and elegant research tool when several variables are to be evaluated simultaneously.