Improving the nutritive value of olive pomace by solid state fermentation of Kluyveromyces marxianus with simultaneous production of gallic acid

Purpose Olive oil industry is a growing industrial sector in Mediterranean countries. Unfortunately, about ۳۰–۳۵% of total olive weight is discarded as olive pomace (OP), a highly environmental-polluting solid waste.OP is mostly used for composting and production of animal feed; nevertheless, the high oil content, phenolic compounds and fber contents in addition to its low protein content represent major obstacles for both applications. So, the present study was conducted to evaluate the role of solid state fermentation (SSF) in OP using Kluyveromyces marxianus NRRL Y-۸۲۸۱ yeast on the chemical composition and tannin content of OP in a trial for its bioconversion into a value-added animal feed. Methods Chemical composition, nutritive and energetic values, tannin and gallic acid contents of unfermented and fermented olive pomace were investigated. Results The fermentation altered the chemical composition of OP, so that crude fber was decreased by ۸.۵۶%, while crude protein, fat and carbohydrate contents were increased by ۲.۷۴, ۲.۶۳ and ۳.۵۷%, respectively. Moreover, the efect of fermentation on cell wall constituents, gross energy, digestible energy, total digestible nutrients and digestible crude protein was evaluated. Furthermore, HPLC analysis revealed that K. marxianus mediated fermentation of OP resulted in a sharp decrease in tannin content by ۹۶.۷۵% with ۲.۸ times increase in gallic acid concentration. Conclusion SSF of OP by K. marxianus does not only eliminate the environmental pollution resulting from its accumulation, but also presents a new eco-friendly valorization technique which leaves OP with an altered chemical composition allowing its use as animal feed or compost.