A two-step enzymatic approach to cheese whey valorization: Synthesis of alkyl galactoside fatty acid esters as non-ionic biosurfactants

Cheese whey is the main wastestream of dairy industry. After protein recovery, the resulting whey permeate contains a pool of carbohydrates (lactose as well as its hydrolysis products, i.e. glucose and galactose) that can be exploited as feedstock for the synthesis of Sugar Fatty Acid Esters (SFAE), non-ionic surfactants characterized by emulsifying, stabilizing, and detergency properties.1 In this work,2 an immobilization study of β-galactosidase from Aspergillus oryzae (GalAo) was carried out with the aim to develop a robust biocatalyst for lactose upcycling. Several types of binding chemistry, chemical activation of the support, and immobilization conditions were assayed. Glyoxyl-Sepabeads EC-EP resulted in good immobilization yields (immobilized protein=65% and immobilized activity=58%) and moderate activity recovery (20%). The immobilized GalAo was used for the synthesis of a library of alkyl-β-D-galactosides by reacting lactose with naturally occurring alcohols 2a-2g through a transglycosylation reaction; compounds (3a-3g) were isolated in moderate to good yields (20-45%) (Scheme 1A). n-Butyl β-D-galactopyranoside (3d) was submitted to the esterification step with palmitic acid in a solvent-free system by using Novozym 435 as the biocatalyst,3 affording 6-O-palmitoyl-1-O-butyl galactopyranoside (4d) (Scheme 1B). Scheme 1. A) Transglycosylation of lactose (1) with natural aliphatic alcohols (2a-g) catalyzed by immobilized GalAo in buffer pH 4.3/alcohol/(acetone), r.t., 6 h. B) Esterification of 3d with palmitic acid catalyzed by Novozym 435 in a solvent-free system, 80 °C, 8 h, molecular sieves. n.o.=not optimized. Interfacial features and W/O emulsifying properties of 4d together with W/O emulsion stability over time were evaluated. Acknowledgements This work was financially supported by Cariplo Foundation (Italy) (call: “Circular Economy for a sustainable future 2020”, project BioSurf, ID 2020-1094). References 1. Ortiz, M.S.; Alvarado, J.G.; Zambrano, F.; Marquez, R. J. Surfact. Deter. 2022, 25, 147-183. 2. Semproli, R. et al., manuscript in preparation 3. Sangiorgio, S.; Pargoletti, E.; Rabuffetti, M.; Robescu, M.S.; Semproli, R.; Ubiali, D.; Cappelletti, G.; Speranza, G. Colloids Interface Sci. Commun. 2022, 48 100630.