High level production of a β-fructofuranosidase in Aspergillus niger for the preperation of prebiotic bread using in situ enzymatic conversion

Abstract

Fructooligosaccharides (FOS) are applied in food, pharmaceutical, and cosmetics. The large scale production of FOS through enzymatic conversion is limited by the expression level and properties of β-fructofuranosidases. A β-fructofuranosidase (AnFTase70) gene from Aspergillus niger was successfully overexpressed in A. niger FBL-B (ΔglaA, ΔamyA, Δaamy, ΔpyrG). The highest β-fructofuranosidase activity of 15,006 U/mL was produced by high–cell density fermentation in a 200 L fermentor, and is so far the highest value ever reported. AnFTase70 was most active at 55 °C and pH 5.5, respectively. It showed high specific activity of 812.0 and 91.8 U/mg towards sucrose and raffinose. AnFTase70 efficiently produced melibiose and FOS with a yield of 55.7 % and 60.6 %, respectively. The membrane filtration system significantly increased the FOS content from 56.1 % to 95.3 % (w/w) with a FOS yield of 69.1 %. Moreover, AnFTase70 was added into bread making to produce a rich prebiotic bread with the highest FOS content of 3.3 g/100 g by in situ enzyme conversion. This study provides a promising way for efficient production of β-fructofuranosidase in A. niger as well as in situ synthesis of FOS in foods.