Testing synthetic zeolites obtained from recycled waste materials for oenological applications

Zeolites are tectosilicates characterized by high microporosity and cation exchange capacity. Due to their adsorption properties and attitude to act as molecular sieves, these aluminosilicates are employed in a number of industrial and agricultural applications. Besides natural zeolites, several processes have been developed in the last decades to synthetize zeolites with useful chemical and structural properties. A simple procedure based on the alkaline hydrothermal treatment of glass and aluminum recovered from food and drink packaging to produce Na and K zeolites (Zeo-Na, Zeo-K) has been recently published by our research group. The objective of this work is to evaluate the potential applications of Zeo-Na and Zeo-K for the removal of riboflavin (RF), a molecule responsible for the light-struck taste of white and rosé wines when present at concentrations higher than 100 μg L-1. Only few studies have been published about the application of zeolites to improve the stability and shelf-life of wines, none of these adopting synthetic zeolites. Preliminary experiments were performed using a model wine solution (5 g L-1 tartaric acid, 12% ethanol (v/v), pH adjusted to 3.2 with NaOH). RF was added at the concentration of 300 μg L-1 in the model solution. Each zeolite, previously characterized by X-ray powder diffraction and for physico-chemical properties, was added to the RF-enriched solution at the concentrations of 1 g L-1 (Zeo-K1, Zeo-Na1) and 10 g L-1 (Zeo-K10, Zeo-Na10). For comparison, two bentonites were also tested at the concentration of 1 g L-1. A control without zeolites nor bentonites was also run. The samples were stirred in the dark at 25°C up to 24 h, then filtered at 0.45 μm and analyzed by HPLC (C18 column, DAD detector at λ= 440 nm). All the treatments were replicated three times. The diffraction analysis revealed that Zeo-K contained 16% edingtonite, and Zeo-Na contained 30% zeolite-A. The remaining fraction consisted of amorphous phases. The HPLC analyses revealed that RF concentration remained unvaried in the control, whereas it decreased from 4% (Zeo-K1) to 37% (Zeo-Na10) in the treatments. Both zeolitic materials appeared less efficient than bentonites at the same concentration. Nevertheless, synthesizing zeolites with higher crystallinity is likely to lead to materials with higher efficiency, almost comparable to bentonites. Efforts are being undertaken to produce more effective zeolites from waste materials for oenological applications.