Winery–distillery composts as partial substitutes of traditional growing media: Effect on the volatile composition of thyme essential oils

Abstract

The purpose of the experiment was to study the effects of the use of three different types of winery–distillery composts as substrate components for thyme (Thymus vulgaris) cultivation on the yield and composition of the essential oils present in this herb. A major component of the composts was exhausted grape marc combined with different quantities of one of the following co-composting wastes: citrus juice waste (for compost C1), tomato soup waste (for compost C2) or cattle manure (for compost C3). The substrates were prepared by mixing traditional peat–perlite mixture (PP) with increasing proportions of each respective compost (0%, 25%, and 50% by volume) and the physical and physico-chemical properties of the substrates were analyzed. The best results for the cultivation of thyme were obtained with the growing media prepared using composts derived from exhausted grape marc mixed with citrus juice waste (C1) or cattle manure (C3). Essential oils were extracted by hydrodistillation and analyzed using GC–MS and GC–FID. Forty-six volatile compounds were tentatively identified, with thymol, p-cymene, carvacrol, linalool and 1,8-cineole (eucalyptol) being the major compounds. The total concentration of volatiles in the control samples (29.6gkg−1) was significantly increased in treatment B (to 34.6gkg−1), consisting of compost C1 at the proportion 50% by volume, and treatment E (to 37.6gkg−1), made from compost C3 at the proportion 25% by volume, showing that the characteristics of the composts used as components of the growing media strongly affected the production of essential oils in the thyme plants.