From Lactose to Alkyl Galactoside Fatty Acid Esters as Non‐Ionic Biosurfactants: A Two‐Step Enzymatic Approach to Cheese Whey Valorization

Abstract

A library of alkyl galactosides was synthesized to provide the “polar head” of sugar fatty acid esters to be tested as non‐ionic surfactants. The enzymatic transglycosylation of lactose resulted in alkyl β‐D‐galactopyranosides, whereas the Fischer glycosylation of galactose afforded isomeric mixtures of α‐ and β‐galactopyranosides and α‐ and β‐galactofuranosides. n‐Butyl galactosides from either routes were enzymatically esterified with palmitic acid, used as the fatty acid “tail” of the surfactant, giving the corresponding n‐butyl 6‐O‐palmitoyl‐galactosides. Measurements of interfacial tension and emulsifying properties of n‐butyl 6‐O‐palmitoyl‐galactosides revealed that the esters of galactopyranosides are superior to those of galactofuranosides, and that the enantiopure n‐butyl 6‐O‐palmitoyl‐β‐D‐galactoside, prepared by the fully enzymatic route, leads to the most stable emulsion. These results pave the way to the use of lactose‐rich cheese whey as raw material for the obtainment of bio‐based surfactants.

Chemically vs Enzymatically Synthesized Polyglycerol-Based Esters: A Comparison between Their Surfactancy

“…To further corroborate the previous outcomes, emulsifying properties and the resulting O/W emulsion stability over time were finely evaluated by turbidity tests, optical microscopy images, and rheological measurements. 22 , 27 , 28 , 32 In particular, the turbidity change over time has been already reported to be strongly linked to emulsion-breaking phenomena since this parameter decreases at each wavelength with the occurrence of destabilization. 33 , 34 Since the turbidimetric method is based on UV–vis spectroscopy, dilution was necessary to make the measurements more reliable being the starting emulsions very milky, as already reported.…”

“…To unravel the interfacial features of the PG2SAE obtained through enzymatic synthesis and to assess its performances with respect to the commercial surfactant, IFT measurements were performed at different concentrations according to the Du Noüy ring tensiometric method. , As displayed in Figure a, the trend is quite similar, showing a constant IFT decrease (down to ≈2 mN m –1 ) from 0.25 g L –1 for the C -based system and an abrupt reduction at around 0.37 g L –1 for the E -based emulsion. Literature data about IFT measurements of PGFAEs are very scarce; indeed, most of them − are related to surface tension measurements of polyglycerol esters (ranging from diglycerol to octaglycerol) having diverse saturated and unsaturated fatty tails (derived from, e.g., lauric, palmitic, oleic, and linoleic acids).…”

“…The almond oil/water interfacial tension (IFT) values were measured at (25 ± 1) °C by means of a Gibertini tensiometer following the Du Noüy ring method and by varying the amount (in the range between 0.04 and 0.40 g L –1 in oil) of PG2SAE obtained from chemical ( C ) and enzymatic ( E ) syntheses. , Data were reported as average values on three different replicates. Prior to tensiometric measurements, several parameters were introduced in the relative software to set up the method, such as liquid density, platinum ring, and wire radii, required by the Harkins–Jordan correction.…”

“…The emulsion stability within 72 h was assessed by the turbidimetric method, , following the absorbance value at 550 nm (by means of a Shimadzu UV–Vis spectrophotometer UV-2600) of both the as-prepared samples ( C and E ) and the 10-fold Milli-Q water-diluted ones ( C diluted and E diluted). Moreover, the turbidity ratio ( R ), defined as the ratio of turbidity at high and low wavelengths (800 and 450 nm), was calculated.…”

Deep Eutectic Solvents for the Enzymatic Synthesis of Sugar Esters: A Generalizable Strategy?

“…As a relevant example, the disaccharide lactose has been underinvestigated despite its large availability, being the most abundant component of cheese whey, the main waste stream of the dairy industry. This feedstock can be used as a cheap and renewable source for lactose to develop circular processes directed toward the obtainment of high-value compounds, including SFAEs. − The same may apply for many other examples of saccharides, which can be obtained from renewable resources.…”