Biochemical characterization of two cellobiose 2-epimerases and application for efficient production of lactulose and epilactose

John Kristian Jameson,Phillip B Pope,Bjørge Westereng,Sabina Leanti La Rosa,Geir Mathiesen

doi:10.1016/j.crbiot.2021.02.003

Abstract

Lactose is the most abundant by-product of the dairy industry and is increasingly recognized as an important feedstock to produce value-added compounds. Lactulose and epilactose are valuable prebiotics that can be generated from lactose with cellobiose 2-epimerases (CEases). Here we describe the characterization of the two CEases CbCEP and RfCEP, originated from the thermophilic microorganism Caldicellulosiruptor bescii and the mesophilic microorganism Roseburia faecis, respectively. CbCEP showed exceptional pH and temperature stability, with maximal activity at pH 7.5 and 70 °C. RfCEP exhibited maximum activity at 50 °C and pH 8. Under optimal conditions in small-scale experiments with commercial lactose, CbCEP produced both lactulose and epilactose with yields of 29.8% and 21.6%, respectively, while RfCEP produced only epilactose with a yield of 19.3%. Furthermore, we evaluated the application of CbCEP for lactulose and epilactose production in stirred fermenters at two different temperatures (70 and 30 °C) at a scale of 5 L volume and a concentration of cheese-whey permeate of 50 g/L. At 70 °C, lactulose was the predominant product of CbCEP-mediated lactose conversion, with a final yield of 30% (12.8 g/L) lactulose and 24.7% (10.6 g/L) epilactose. At 30 °C, lactose was mainly converted into epilactose, with a final yield of 35% (14.9 g/L), and a minor amount of lactulose (final yield of 4.3%, 1.8 g/L). The findings presented here may guide the design of an industrial strategy, based on the temperature-tunable activity of CbCEP, for production of valuable lactose derivatives at high yields directly from whey permeate.

Highlights

Cheese whey is a by‐product of the dairy industry that causes significant disposal and environmental pollution problems (Smithers, 2008)
We evaluated the use of the cellobiose 2‐epimerases (CEases) from the thermophile Caldicellulosiruptor bescii (CbCEP) and the mesophile Roseburia faecis (RfCEP) for the efficient conversion of lactose directly from whey permeate to obtain lactulose and epilactose at high yields
Results showed that CbCEP initially favors the production of epilactose that is likely converted to the more stable product lactulose over time (Fig. 1C), as indicated by the increase of the concentration of lactulose in the reaction mixture

Summary

Introduction

Cheese whey is a by‐product of the dairy industry that causes significant disposal and environmental pollution problems (Smithers, 2008). Just in Norway, about 100,000 tons of milk are processed each year, which generates about 85,000 tons of whey and about 4250 tons of lactose (Marquer, 2013). Prebiotics are non‐digestible food ingredients that beneficially affect the host by selectively stimulating the growth of desirable bacteria, mostly Firmicutes, Bacteroidetes and Bifidobacterium spp., in the gastrointestinal tract, eventually improving host health (Gibson et al, 2017). Fermentation of the prebiotic carbohydrates by beneficial bacteria results in production of short chain fatty acids (SCFAs), leading to the acidification of the colon, and other metabolites that influence the gut function and beyond (Louis and Flint, 2017). Gut microbial dysbiosis is the leading cause of numerous chronic (Murphy et al, 2015) and metabolic diseases (Cani and Delzenne, 2009)

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Results

Conclusion