Valorization of Olive Pruning Residues through Bioconversion into Edible Mushroom Pleurotus ostreatus (Jacq. Ex Fr.) P. Kumm. (1871) of Improved Nutritional Value

Abstract

In several Mediterranean countries, olive pruning residues (OLPRs) are abandoned or burned leading to several environmental problems. Valorization of these agrowastes could be a challenge for the primary decomposer Pleurotus ostreatus, turning them into edible biomass. The OLPR was used alone (OLPR), or in mixtures with wheat straw (WS : OLPR 1 : 3 v/v and WS : OLPR 3 : 1 v/v). Mycelial colonization was hastened by 3.7 days in WS : OLPR 1 : 3 (v/v). Yields were comparable to control (WS) in WS : OLPR 3 : 1 (v/v). Organic matter loss decreased with increasing proportions of OLPR in substrates. The nutritional value of mushrooms was improved by lower fat and sodium contents, in WS : OLPR 1 : 3 (v/v) and WS : OLPR 3 : 1 (v/v), and higher total protein, crude fiber, iron, and total carbohydrates contents in WS : OLPR 3 : 1 (v/v), compared with those of control. Polyunsaturated fatty acids, mainly linoleic acid, were the most abundant in mushrooms. Monounsaturated fatty acids increased in mushrooms of the substrates containing OLPR. A good predictive model of partial least square regression analysis showed different relationships of mushroom palmitic, oleic, linolenic, palmitoleic, and stearic acids with substrate composition. Findings suggested the use of OLPR as a supplement to commercial wheat straw and as a tool to reduce the negative impacts of their hazardous disposal on the environment.

Figure 1

Relation between organic matter loss (OML) and proportions of olive pruning residues (OLPRs) (OML = −0.32 × OLPR + 75.76) (r² = 0.85).

Figure 2

Physical characteristics of mushrooms obtained in tested substrates (SD: stipe diameter, PD: pileus diameter, SL: stipe length, PD/SL: pileus diameter/stipe length, and ns: no significance).

Figure 3

Correlations between mushroom fatty acids and substrates chemical composition: C14 : 0: myristic acid, C16 : 0: palmitic acid, C16 : 1: palmitoleic acid, C18 : 0: stearic acid, C18 : 1: oleic acid, C18 : 2: linoleic acid, C18 : 3: linolenic acid, C20 : 0: arachidic acid, and M: mushroom.

Figure 4

Regression coefficients and significant indications (shown in streaked bars) for substrate chemical composition variable: C16 : 0: palmitic acid, C16 : 1: palmitoleic acid, C18 : 0: stearic acid, C18 : 1: oleic acid, C18 : 2: linoleic acid, C18 : 3: linolenic acid, C20 : 0: arachidic acid, and M: mushroom. (a) C14 : 0 M/standardized coefficients (95% conf. interval). (b) C16 : 0 M/standardized coefficients (95% conf. interval). (c) C16 : 1 M/standardized coefficients (95% conf. interval). (d) C18 : 0 M/standardized coefficients (95% conf. interval). (e) C18 : 1 M/standardized coefficients (95% conf. interval). (f) C18 : 2 M/standardized coefficients (95% conf. interval). (g) C18 : 3 M/standardized coefficients (95% conf. interval).