Properties Of β-D-galactosidase And The Key Technology Of Preparation Of High Purity Galacto-oligosaccharides

As novel prebiotic, galacto-oligosaccharides(GOS) are functional foods which areapproved by Chinese Ministry of Health as new resources foods. GOS are becoming moreand more important in food industry. The demand of GOS is very large, especially in Japanand Europe. Currently on the market there’s no high-purity GOS on sale, and the ordinarygrade of GOS’s concentration are27%to65%. Usually, the method of purifying GOS iscomplicated to operation, with galactose and lactose remained. In China, there’s no methodfor producing commercial high-purity GOS.GOS are synthesized from lactose using the transgalactosidation of β-D-galactosidase,transfering glycosyl to lactose. The goal of this research was to produce GOS from lactosecatalyzed by β-D-galactosidase of Kluyveromyces marxianus SK16.001screened bylaboratory. The GOS syrups were subjected further to the fermentation by the same yeastwhereby galactose, glucose and lactose were depleted, resulting in GOS content up to93.07%(w/w) of total sugar.Kluyveromyces marxianus SK16.001β-D-galactosidase has both hydrolysis andtransgalactosidation. After purification, the optimum pH of K. marxianus SK16.001β-D-galactosidase for transgalactosidation and hydrolysis was7.0and its optimumtemperature was40oC and35oC, respectively. The enzyme was stable in the pH range of6.5-7.0. The Kmand Vmaxvalues for lactose were0.56mmol/L and0.31μmol/(mg proteinï¹'min). The hydrolytic activity of the enzyme could be inhibited by Na+while thetransgalactosidation was unaffected. Mg2+could improve both the hydrolytic andtransgalactosidase activity of the enzyme. Using lactose as substrate, the hydrolytic activitywas significantly inhibited by galactose and the transgalactosidase activity was inhibited byglucose.High pressure homogenious is the best instrument for cell disruption in industryprocess. The maximum GOS yield was42%(w/w) of total sugar after24h crude enzymereaction under the optimal conditions: lactose concentration400g/L, enzyme addition1U/glactose, pH7.0,0.1mol/L sodium phosphate buffer,0.04mol/L MgSO4.High purity GOS were produced by K. marxianus SK16.001fermentation. K.marxianus SK16.001has strong ability to consume glucose, galatose and lactose. Theculture conditions of K. marxianus SK16.001were the same as producingβ-D-galactosidase. The initial syrup concentration was20%and the additional amount fromof K. marxianus SK16.001was15%of total sugar. The initial pH was7.0and pH wascontrolled at6.0-7.0by2mol/L NaOH. After20h fermentation by K. marxianus SK16.001,the glucose, galactose, lactose and other disaccahrides were depleted, resulting in GOScontent up to93.07%.