Grape is the largest fruit crop in the world, and most (80%) of the harvested fruit is used to make wine. The main by-product of the wine industry is called grape marc, which consists of the stalks, skin, pulp and seeds that remain after pressing the grapes. The aim of this study was to evaluate whether grape marc could be processed by vermicomposting on an industrial scale to yield both a high-quality organic, polyphenol-free fertiliser and grape seeds (as a source of bioactive polyphenols). Vermicomposting reduced the biomass of grape marc substantially (by 58%), mainly as a result of the loss of volatile solids. After 2 weeks, the process yielded a nutrient-rich, microbiologically active and stabilised peat-like material that was easily separated from the seeds by sieving. Although the polyphenol content of the seeds was considerably reduced, this disadvantage was outweighed by the ease of separation of the seeds. Separation of the seeds also eliminated the polyphenol-associated phytotoxicity from the vermicompost. The seeds still contained useful amounts of polyphenols, which could be directly extracted for use in the pharmaceutical, cosmetic and food industries. The procedure described is effective, simple and economical, and could easily be scaled up for industrial application.

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Wild Scotch broom ( Cytisus scoparius (L.) Link) shrubs are widely distributed throughout the world and, in some countries, are considered to be a threat to other plant species. The use of plant biomass from Scotch broom as a fertiliser seems to be the optimum solution for its disposal because it contains considerable amounts of macronutrients. However, its direct application to soils may cause phytotoxicity due to the release of polyphenols, which could negatively affect crop growth. This study evaluated the efficiency of vermicomposting in processing this leguminous plant on an industrial scale. Vermicomposting substantially reduced the biomass of Scotch broom (by 84%), mainly as a result of the loss of volatile solids. Simultaneously, the initial population of earthworms ( Eisenia andrei) increased remarkably throughout the process, offering the possibility of obtaining earthworm protein for animal feed. A nutrient-rich and stabilised peat-like material without polyphenol-associated phytotoxicity was obtained after 42 days of vermicomposting. Lower values of microbial biomass and activity, indicative of stabilised materials, were recorded at the end of the trial. These findings suggest that vermicomposting is an environmentally sound management system for Scotch broom and could easily be scaled up for industrial application.

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