Unveiling the potential of novel yeast protein extracts in white wines clarification and stabilization

Abstract

Fining agents derived from animal and mineral sources are widely used to clarify and stabilize white wines. Nevertheless, health and environmental problems are being raised, concerning the allergenic and environmental impact of some of those fining products. In this study, our aim is to validate the potential of yeast protein extracts, obtained from an alternative and safe source, naturally present in wine: oenological yeasts. Three untreated white wines were used in this work in order to evaluate the impact of these novel yeast protein extracts (YPE) in terms of the wine clarification and stabilization improvement. Two separated fining trials were thus conducted at laboratory scale and the yeast alternatives were compared with reference fining agents, obtained from mineral, animal and vegetable origins. Our results indicate that YPE were capable to promote (i) brilliance/color improvement, (ii) turbidity reduction (76-89% comparing with the untreated wines), and (iii) production of compact and homogeneous lees (44% smaller volume than obtained with bentonite). Additionally, after submitting wines to natural and forced oxidations, YPE treatments revealed (iv) different forms of colloidal stabilization, by presenting comparable or superior effects when particularly compared to casein. Altogether, this study reveals that YPE represent a promising alternative for white wine fining, since they are resultant from a natural and more sustainable origin, at present not regarded as potential allergenic according to Regulation (EC) No. 1169/2011.

Keywords: browning potential; clarification; fining agents; oxidation; protein content; white wine; yeast protein extracts.

Figure 1

Protein molecular weight profile. Protein samples of the fining agents used in this study by Comassie-stained SDS-PAGE (VP, Vegetable protein).

Figure 2

Final turbidity. Not treated wine, NT; Treated wine samples, Yeast protein extracts (BCV1 and BCV5); Bent, Bentonite; Cas, Casein; PVPP, Polyvinylpolypyrrolidon; VP, Vegetable protein. Bars indicate mean ± SD (n = 3).

Figure 3

Chromatic characterization using CIELab system. (A) Saturation (C^*), Brilliance (L^*); (B) Green (-a^*), and Yellow (b^*) values. Results were obtained before and after treatment of wine 1 with YPE and different fining agents. Two dosages were tested by treatment (Min, minimum; Max, maximum).

Figure 4

Aspect of the lees produced by the application YPE or fining agents. (A.1,A.2) Yeast protein extract BCV1, similar result was obtained with BCV5; (B) Casein, 100 g/hL; (C) Bentonite, 60 g/hL; (D) PVPP, 80 g/hL; (E) Vegetable polymer, 60 g/hL.

Figure 5

SDS-PAGE 12,5%, Comassie staining. Total protein was precipitated from 1 ml of each wine sample. 1, Not treated wine. Wines treated with fining agents (max. dosage); 2, BCV1; 3, BCV5; 4, Bentonite; 5, Casein; 6, PVPP; 7, Vegetable protein.

Figure 6

Heat test. Instability was measured according to the variation of absorbance at 540 nm, by spectrometry methodology (ΔA₅₄₀nm). Not treated wine, NT; Treated wine samples, Yeast protein extracts (BCV1 and BCV5); Bent, Bentonite; Cas, Casein; PVPP, Polyvinylpolypyrrolidon; VP, Vegetable protein. Bars indicate mean ± SD (n = 3).

Figure 7

Browning evaluation after natural and forced wine oxidations. (A) Yellow color (expressed as A₄₂₀nm) was measured after 0, 5, 9 months of oxidation, respectively: T0, T5, T9. (B) Oxidation was evaluated before and after oxidation using a solution of 3% (w/v) hydrogen peroxide. Different letters represent significant differences (p < 0.05). Bars indicate mean ± SD (n = 3).

Figure 8

Test of curative potential using chromatic characterization. Not treated samples were fined after 5 months oxidation and effects were compared with the previously obtained results (T0). Arrows indicate the impact obtained after the respective treatments.