Optimized Conditions of Trichloroacetic Acid Precipitation for the Determination of Free Amino Acids in Fermented Soybean Paste

In this study,trichloroacetic acid precipitation for protein removal coupled with biuret colorimetry was applied to determine protein in fermented soybean paste.The influence of three factors such as precipitant dosage and concentration,temperature and centrifuge speed was examined,and aa mathematical model was established by Box-Behnken design for statistical optimization of the factors by response surface analysis.The results showed that the optimal conditions for trichloroacetic acid precipitation were TCA concentration 8.3 g/100 mL,precipitation temperature 47 ℃,and centrifugal speed 1726 r/min and had the smallest effect on the determination of free amino acids.The precipitate obtained under these conditions contained 23.29 g/100 g prtoein.