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

Abstract

Purpose Olive oil industry is a growing industrial sector in Mediterranean countries. Unfortunately, about 30–35% 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 fiber 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-8281 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 fiber was decreased by 8.56%, while crude
protein, fat and carbohydrate contents were increased by 2.74, 2.63 and 3.57%, respectively. Moreover, the effect 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 96.75% with 2.8 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.