Olive Mill Wastes: A Source of Bioactive Molecules for Plant Growth and Protection against Pathogens

From antiquity to contemporary times: how olive oil by-products and waste water can contribute to health

Since antiquity, numerous advantages of olive oil and its by-products have been recognized in various domains, including cooking, skincare, and healthcare. Extra virgin olive oil is a crucial component of the Mediterranean diet; several of its compounds exert antioxidant, anti-proliferative, anti-angiogenic and pro-apoptotic effects against a variety of cancers, and also affect cellular metabolism, targeting cancer cells through their metabolic derangements. Numerous olive tree parts, including leaves, can contribute metabolites useful to human health. Olive mill waste water (OMWW), a dark and pungent liquid residue produced in vast amounts during olive oil extraction, contains high organic matter concentrations that may seriously contaminate the soil and surrounding waters if not managed properly. However, OMWW is a rich source of phytochemicals with various health benefits. In ancient Rome, the farmers would employ what was known as amurca, a mulch-like by-product of olive oil production, for many purposes and applications. Several studies have investigated anti-angiogenic and chemopreventive activities of OMWW extracts. The most prevalent polyphenol in OMWW extracts is hydroxytyrosol (HT). Verbascoside and oleuperin are also abundant. We assessed the impact of one such extract, A009, on endothelial cells (HUVEC) and cancer cells. A009 was anti-angiogenic in several in vitro assays (growth, migration, adhesion) and inhibited angiogenesis in vivo, outperforming HT alone. A009 inhibited cells from several tumors in vitro and in vivo and showed potential cardioprotective effects mitigating cardiotoxicity induced by chemotherapy drugs, commonly used in cancer treatment, and reducing up-regulation of pro-inflammatory markers in cardiomyocytes. Extracts from OMWW and other olive by-products have been evaluated for biological activities by various international research teams. The results obtained make them promising candidates for further development as nutraceutical and cosmeceutical agents or dietary supplement, especially in cancer prevention or even in co-treatments with anti-cancer drugs. Furthermore, their potential to offer cardioprotective benefits opens up avenues for application in the field of cardio-oncology.

Chromium(VI) Toxicity and Active Tolerance Mechanisms of Wheat Plant Treated with Plant Growth-Promoting Actinobacteria and Olive Solid Waste

The present study aimed to assess the potential of plant growth-promoting Actinobacteria and olive solid waste (OSW) in ameliorating some biochemical and molecular parameters of wheat (Triticum aestivum) plants under the toxicity of high chromium levels in the soil. With this aim, a pot experiment was conducted, where the wheat plants were treated with a consortium of four Actinobacterium sp. (Bf treatment) and/or OSW (4% w/w) under two levels of nonstress and chromium stress [400 mg Cr(VI) per kg of soil] to estimate the photosynthetic traits, antioxidant protection machine, and detoxification activity. Both Bf and OSW treatments improved the levels of chlorophyll a (+47-98%), carotenoid (+324-566%), stomatal conductance (+17-18%), chlorophyll fluorescence (+12-28%), and photorespiratory metabolism (including +44-72% in glycolate oxidase activity, +6-72% in hydroxypyruvate reductase activity, and +5-44% in a glycine to serine ratio) in leaves of stressed plants as compared to those in the stressed control, which resulted in higher photosynthesis capacity (+18-40%) in chromium-stressed plants. These results were associated with an enhancement in the content of antioxidant metabolites (+10-117%), of direct reactive oxygen species-detoxifying enzymes (+49-94%), and of enzymatic (+40-261%) and nonenzymatic (+17-175%) components of the ascorbate-glutathione cycle in Bf- and OSW-treated plants under stress. Moreover, increments in the content of phytochelatins (+38-74%) and metallothioneins (+29-41%), as markers of detoxification activity, were recorded in the plants treated with Bf and OSW under chromium toxicity. In conclusion, this study revealed that the application of beneficial Actinobacteria and OSW as biofertilization/supplementation could represent a worthwhile consequence in improving dry matter production and enhancing plant tolerance and adaptability to chromium toxicity.

Combining Ultrafiltration and Nanofiltration to Obtain a Concentrated Extract of Purified Polyphenols from Wet Olive Pomace

Despite the environmental concerns raised every year by the generation of high volumes of wet olive pomace, it contains valuable phenolic compounds that are essential for the valorization of this by-product. In this work, an integrated process to recover phenolic compounds from wet olive pomace is proposed. It consists of ultrasound-assisted solid-liquid extraction, followed by ultrafiltration and nanofiltration. Several commercial membranes were studied at different operational conditions. The ultrafiltration stage allowed the purification of biophenols, which were obtained in the permeate stream. Regarding organic matter, satisfactory rejection values were obtained with both commercial UH030 and UP005 membranes (Microdyn Nadir), but the latter provided more efficient purification and higher values of permeate flux, above 18 L·h^-1·m^-2 at 2.5 bar and 1.5 m·s^-1. Later, this permeate stream was concentrated by means of a nanofiltration process, obtaining polyphenol rejection values that surpassed 85% with the commercial NF270 membrane (DuPont), then achieving the concentration of the previously purified polyphenols.

Treatment technologies for olive mill wastewater with impacts on plants

Olive mill wastewater (OMW), produced during olive oil production, contains high levels of salt contents, organic matter, suspended particles, and toxic chemicals (particularly phenols), which all result in increased biological and chemical oxygen demand. Olive Oil Mills' Wastes (OMW), which have dark brown color with unpleasant smell, consist mainly of water, high organic (mainly phenols and polyphenols) and low inorganic compounds (e.g. potassium and phosphorus), as well as grease. OMW components can negatively affect soil's physical, chemical, and biological properties, rendering it phytotoxic. However, OMW can positively affect plants' development when it's applied to the soil after pretreatment and treatment processes due to its high mineral contents and organic matter. There are various approaches for removing impurities and the treatment of OMW including chemical, biological, thermal, physiochemical, and biophysical processes. Physical techniques involve filtration, dilution, and centrifugation. Thermal methods include combustion and pyrolysis; biological techniques use anaerobic and aerobic techniques, whereas adsorption and electrocoagulation act as physiochemical methods, and coagulation and flocculation as biophysical methods. In contrast, combined biological treatment methods use co-digestion and composting. A comparison of the effects of both treated and untreated OMW samples on plant development and soil parameters can help us to understand the potential role of OMW in increasing soil fertility. This review discusses the impacts of untreated OMW and treated OMW in terms of soil characteristics, seed germination, and plant growth. This review summarizes all alternative approaches and technologies for pretreatment, treatment, and recovery of valuable byproducts and reuse of OMW across the world.

Sustainable vs. Conventional Approach for Olive Oil Wastewater Management: A Review of the State of the Art

The main goal of this review is to collect and analyze the recently published research concerning the conventional and sustainable treatment processes for olive mill wastewater (OMW). In the conventional treatment processes, it is noticed that the main objective is to meet the environmental regulations for remediated wastewater without considering the economical values of its valuable constituents such as polyphenols. These substances have many important environmental values and could be used in many vital applications. Conversely, sustainable treatment processes aim to recover the valuable constituents through different processes and then treat the residual wastewater. Both approaches’ operational and design parameters were analyzed to generalize their advantages and possible applications. A valorization-treatment approach for OMW is expected to make it a sustainable resource for ingredients of high economical value that could lead to a profitable business. In addition, inclusion of a recovery process will detoxify the residual OMW, simplify its management treatment, and allow the possible reuse of the vast amounts of processed water. In a nutshell, the proposed approach led to zero waste with a closed water cycle development.

Biological activities and phenolic compounds of olive oil mill wastewater from Abani, endemic Algerian variety

The current study aimed to determination of cytotoxicity, antioxidant, anti-inflammatory, anti-hemolytic, and anticoagulant activities of phenolic compounds extracted from olive oil mill wastewater (OMW) issue from the cold extraction of olive oil from Khenchela eastern in Algeria. The LC–MS (liquid chromatography–mass spectrometry) results were revealed the presence of 20 phenolic compounds in the extract of OMW and mostly consisted of Kaempferol, 4,5-di-O-caffeoyquinic acid, quinic acid, and caffeic acid. The extracts possessed effective reducing power (FRAP) and high radical scavenging activity against DPPH (2,2-diphenyl-1-picrylhydrazyl), ABTS + (2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) free radicals, and it inhibited cytochrome c reduction in a dose-dependent manner. They exert a protective effect on red blood cells, and they were found to exhibit the highest inhibitory effect anti-inflammatory activity using inhibition of protein denaturation (IPD) and membrane stabilizing potential (MSP) tests (80.46 ± 3.81 µg/mL and 87.43 ± 0.66 µg/mL) more than the standard used. The extract also showed the greatest anticoagulant activity in both the endogenous and exogenous routes (44.77 ± 0.25 s and 15.84 ± 0.12 s, respectively). Based on these findings, it is reasonable to infer that OMW is a good source of natural phenolic compounds with potential antioxidant, anti-inflammatory, and anticoagulant properties.

Preliminary Studies on Suppression of Important Plant Pathogens by Using Pomegranate and Avocado Residual Peel and Seed Extracts

Potential synergistic action of aqueous extracts of pomegranate peel (PP), avocado peel (AP), and avocado seed (AS) wastes isolated by microwave-assisted extraction were assessed in in vitro and in vivo assays as biocontrol agents against several plant pathogenic fungi. The study findings contribute to the utilization of a value-added industrial byproduct and provide significant value in advancing the development of new plant protecting compositions that benefit from the synergistic effects between two important plant species that contain several natural bioactive compounds. More specifically, the in vitro results proved that the use of 100%-pure (PP) extracted waste affected the mycelium growth of Penicillium expansum. Furthermore, mycelium growth of Aspergillus niger was decreased by 10.21% compared to control after 7 days of growth in medium agar containing 100% AP and extracted waste. Moreover, mycelium growth of Botrytis cinerea was affected by equal volume of avocado extraction wastes (50% peel and 50% seed) only at the first 3 days of the inoculation, while at the seventh day of the inoculation there was no effect on the mycelium growth. Equal volumes of the examined wastes showed decreased mycelium growth of Fusarium oxysporum f.sp. lycopersici by 6%, while Rhizoctonia solani mycelium growth was found to be the most sensitive in PP application. In addition, the in vivo assay shown that PP extract suppresses damage of tomato plants caused by R. solani followed by extracted wastes from AP. Based on the research findings, it can be argued that PP and AP extracts can be used as natural antifungals instead of dangerous synthetic antifungals to effectively treat phytopathogens that cause fruit and vegetable losses during cultivation.

Evolution of the Olive Oil Industry along the Entire Production Chain and Related Waste Management

The production of olive oil involves the sustainable management of the waste produced along the entire production chain. This review examines the developments regarding cultivation techniques, production technologies, and waste management, highlighting the goals to be achieved and the most reasonable prospects. The results show that cultivation and production technology have evolved to an almost final solution to meet economic feasibility, keeping the oil’s high quality. Continuous horizontal decanters will coexist with traditional mills in many countries with old olive oil production and consumption traditions. High-quality products have conquered markets, especially in the wealthiest countries. At the same time, the exploitation of dried pomace by solvent extraction is increasingly an obsolete practice. However, waste management is still looking for one or a few reasonable solutions that meet modern society’s constraints. The enhancement of some experienced technologies and the full-scale application of emerging technologies and strategies should solve this problem in the short–medium term. A short discussion is reported on the possibility of unifying the nature and the quality of the waste, whatever the olive oil production method is. Furthermore, modern thermochemical treatment for solid wet organic waste disposal is examined and discussed.

Available Pathways for Operationalizing Circular Economy into the Olive Oil Supply Chain: Mapping Evidence from a Scoping Literature Review

Circular economy (CE) is increasingly seen as a promising paradigm for transitioning agri-food systems towards more sustainable models of production and consumption, enabling virtuous and regenerative biological metabolisms based on strategies of eco-efficiency and eco-effectiveness. This contribution seeks to provide a theoretical and empirical framework for operationalizing the CE principles into the olive oil supply chain, that plays a central role in the agroecological systems of the Mediterranean region. A scoping literature review has been conducted in order to identify the available pathways so far explored by scholars for reshaping the olive oil supply chain from a circular perspective. The analyzed literature has been charted on the base of the circular pathway examined, and according to the supply chain subsystem(s) to which it refers. Results are discussed highlighting the main issues, the technology readiness level of the available pathways, the prevailing approaches and knowledge gaps. A synthetic evidence map is provided, framing visually the scrutinized pathways into the Ellen MacArthur Foundation’s CE ‘butterfly’ graph. The work is intended to be a valuable baseline for inquiring how circularity can be advanced in the specific supply chain of olive oil, and which are the strategic opportunities, as well as the barriers to overcome, in order to foster the transition.

Olive Oil Dregs as a Novel Source of Natural Antioxidants: Extraction Optimization towards a Sustainable Process

Olive oil dregs (OOD), which are an underutilized by-product from oil mills, were used for the extraction of antioxidant compounds. The residues from three oil mills located in Campania (Southern Italy) were extracted with acidified methanol, and hydroxytyrosol (HT) was the main phenolic compound detected. Total phenolic content (TPC) and HT amount were measured. EVO Campania oil mill provided the residue with the highest TPC and HT quantities: 6.801 ± 0.159 mg Gallic Acid Equivalents (GAE)/g OOD and 519.865 ± 9.082 μg/g OOD, respectively. Eco-friendly extractions at different temperatures and times were performed on EVO Campania OOD, obtaining 9.122 ± 0.104 mg GAE/g OOD and 541.330 ± 64.087 μg/g OOD for TPC and HT, respectively, at 121 °C for 60 min. Radical Scavenging Activity (RSA), Superoxide Scavenging Activity (SSA), and Ferric Reducing Antioxidant Power (FRAP) were measured in OOD aqueous extracts. Extract prepared at 37 °C for 60 min showed the greatest RSA and SSA values (44.12 ± 1.82 and 75.72 ± 1.78, respectively), whereas extract prepared at 121 °C for 60 min exhibited the highest FRAP value (129.10 ± 10.49 μg Ascorbic Acid Equivalents (AAE)/mg). OOD extracts were able to protect sunflower oil from oxidation for 4 weeks at 65 °C. The overall results suggest that this novel residue can be usefully valorized by providing HT-rich extracts to use as antioxidant agents.