Galacto-oligosaccharides (GOS) are prebiotics that have a beneficial effect on human health by promoting the growth of probiotic bacteria in the gut, in addition to having various applications in the food industry. GOS are generally produced from lactose in a reaction catalyzed by ß-galactosidase. Synthesis of GOS from whey permeate (WP) (ultrafiltration of whey, concentrated then spray dried) using surface engineered β-galactosidase in Pichia pastoris (P. pastoris) is a novel method to convert waste into a valuable product. Cell-surface display is the expression of peptides and proteins on the surface of living cells by fusing them to functional components of cells. Surface engineered cells have many potential uses. The Flo1p flocculation functional domain, thought to be located near the N terminus, recognizes and adheres non-covalently to cell-wall components such as α-mannan carbohydrates, causing reversible aggregation of cells into flocs.

This study attempted to find an efficient method for the preparation of high-purity galactooligosaccharides (HP-GOS) using β-galactosidase and yeast fermentation. GOS prepared using Lactozym 3000L showed the greatest enhancement in total GOS of the six β-galatosidases tested. GOS alone achieved 51% conversion of initial lactose. GOS production was enhanced by fermentation with commercial yeast (Saccharomyces cerevisiae); its concentration reached 71% after 36h fermentation with 8% yeast. Component sugar analysis with HPLC indicated that HP-GOS fermented with S. cerevisiae showed significantly increased levels of 4’/6’-galactosyllactose and total GOS as well as a significantly decreased glucose level. HP-GOS facilitated the growth of Lactobacillus sp. (L. acidophilus and L. casei) and Bifidobacterium sp. (B. longum and B. bifidum). In sum, high-purity GOS has been successfully produced through both an enzymatic process and yeast fermentation. GOS encourages the growth of bacteria such as Lactobacillus and Bifidobacterium that may be beneficial to human gastrointestinal health.