Optimization of fructooligosaccharides synthesis by immobilized fructosyltransferase

The optimization of fructooligosaccharides (FOS) synthesis by immobilized fructosyltransferase from Rhodotorula sp. LEB-V10 was carried out on the basis of the experimental factorial design methodology, consisting of two consecutives (24-1) Fractional Factorial Design (FFD) for the following variable factors: temperature, pH, initial sucrose concentration and immobilized enzyme activity. The main target responses were FOS yield and FOS composition. It was observed that the increase of the immobilized enzyme activity resulted not only in a significant increase of the amount of nystose (GF3) in the FOS mixture but, it also increased the residual fructose concentration in the medium over time. Based on the results from the two FFD, the best conditions for pH and enzyme activity were 6.0 and 20 Ui/mL respectively. The final study step allowed the best conditions for synthesis temperature and sucrose concentration, being 48°C and 50% (w/v), respectively. Under these optimized conditions the total synthesis time was reduced from 96 h to 24 h, the conversion of sucrose was increased by 5% (YFOS = 0.58) and the composition of GF3 by 40% (φGF3 = 0.035).