Emulsifying and foaming properties of mannoprotein-rich extracts obtained by treating wine lees with Natural Deep Eutectic Solvents.

Wine lees is a by-product obtained from wine production, rich in dead yeast cells. This biomass can be considered a source of valuable molecules such as cell wall’s mannoproteins, currently studied as emulsifiers and foaming agents for food applications. In this study we focus on the extraction and characterisation of mannoproteins-rich extracts obtained by treating wine lees in autoclave using 3 different Natural Deep Eutectic Solvents (NADES): (Citric acid-Betaine (CA), Tartaric acid-Betaine (TA), Choline chloride-urea (UR)). A fourth autoclave extraction, conducted using pH 3.4 McIlvaine buffer (MC), was taken as control. Extraction yield was generally higher when NADES were applied even if, in at least one case (TA) the NADES was included in the final extract thus reducing the mannoproteins presence. The extracts were tested for their emulsifying activity by using them to produce oil-in-water emulsions at 3 different pH values (3.4, 5.4, 7.0) and by monitoring the emulsions’ stability over a period of 7 days. Among them, UR extracts had the highest emulsifying activity along with longer stability of the emulsion followed by CA extract. Emulsions made with these two extracts also reported the highest viscosity after 7 days. Conversely, TA extract yield emulsions with poor stability that disappeared within 2 days. Foaming activity was conducted with a sonicator at 45% power for 5 seconds, at a concentration of 1mg/mL for 24 hours, MC had the highest foaming activity and higher stability, whereas TA showcased the lowest. This suggests that CA and UR could hold potential for further applications, while TA appears to have the least activity, probably due to the presence of NADES in the extract. All in all, the study indicates that the use of NADES can improve the yield and efficiency of mannoproteins-rich extracts that can be obtained from wine lees.