Valorization of Olive By-Products as Substrates for the Cultivation of Ganoderma lucidum and Pleurotus ostreatus Mushrooms with Enhanced Functional and Prebiotic Properties

Georgios Koutrotsios,Maria Kotsou,Georgios Bekiaris,Vasiliki Pletsa,Evdokia K Mitsou,Marianna Patsou,Petros A Tarantilis,Adamantini Kyriacou,Georgios I Zervakis

doi:10.3390/catal9060537

Abstract

The successful management of olive by-products constitutes a major challenge due to their huge volume, high organic content, and toxicity. Olive-mill wastes (TPOMW) and olive pruning residues (OLPR) were evaluated as substrates for the cultivation of Ganoderma lucidum and Pleurotus ostreatus. Chemical composition, glucans, total phenolic content, and antioxidant activity were measured in mushrooms, and their prebiotic potential was assessed by examining their effect on the growth of four intestinal bacteria. Several substrates based on olive by-products had a positive impact on P. ostreatus mushroom production, whereas only one performed adequately for G. lucidum. Increased ratios of OLPR to wheat-straw resulted in an increase of crude protein content in P. ostreatus fruit-bodies by up to 42%, while G. lucidum mushrooms from OLPR-based substrates exhibited an up to three-fold increase in α-glucan, or a significant enhancement of β-glucan content, when compared to beech sawdust (control). The mushrooms’ FTIR spectra confirmed the qualitative/quantitative differentiation detected by standard assays. In regard to prebiotic properties, mushrooms powder supported or even enhanced growth of both Lactobacillus acidophilus and L. gasseri after 24/48 h of incubation. In contrast, a strain-specific pattern was observed in bifidobacteria; mushrooms hindered Bifidobacterium bifidum growth, whereas they supported a similar-to-glucose growth for B. longum.

Highlights

The particular organoleptic and nutritional properties of olive oil, in conjunction with the need to improve human diet, have resulted at a continuous increase in olives production during the last few decades
The first part of this study aimed at determining the growth of G. lucidum and P. ostreatus in substrates consisting of olive pruning residues (OLPR) and two-phase olive mill wastes (TPOMW)
Substrates consisting of olive pruning residues (OLPR) and two-phase olive mill wastes (TPOMW) in in various various mixtures mixtureswith witheach eachother otherororwith withbeech beechsawdust sawdust (BS)

Summary

Introduction

The particular organoleptic and nutritional properties of olive oil, in conjunction with the need to improve human diet, have resulted at a continuous increase in olives production during the last few decades. Over 750 million olive trees are cultivated worldwide, 95% of which grow in the Mediterranean region, while the global production of olive oil is projected to reach 3.1 million metric tons in 2018/2019 (International Olive Council, http://www.internationaloliveoil.org). Catalysts 2019, 9, 537 the cultivation of olive trees and operation of olive mills generate huge amounts of plant residues and effluents, respectively. The annual production of pruning exceeds 15 million tons, all of which are usually burnt on farms and result in air pollution due to aerosols rich in organic compounds [1]. Are produced by two-phase olive oil mills [2]. Centralized alperujo treatment is not feasible in most countries due to the olive mills’ small capacity, seasonal operation, and scattered distribution [3]

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