E: Food Engineering & Materials Science Membrane-Filtered Olive Mill Wastewater: Quality Assessment of the Dried Phenolic-Rich Fraction Ivana Sedej, Rebecca Milczarek, Selina C. Wang, Runqi Sheng, Roberto de Jes´ us Avena-Bustillos, Lan Dao, and Gary Takeoka Abstract: A current trend in olive mill wastewater (OMWW) management is to not only decrease environmental pollution but also to extract and utilize valuable by-products. Therefore, the objectives of this study were to explore different techniques for drying a phenolic-rich membrane filtration fraction of OMWW and compare the techniques in terms of the dried product quality and feasibility of the process. The OMWW from 2 (3-phase and 2-phase) California mills was subjected to a 2-step membrane filtration process using a novel vibratory system. The reverse osmosis retentate (RO-R) is a phenolic-rich coproduct stream, and the reverse osmosis permeate is a near-pure water stream that could be recycled into the milling process. Spray-, freeze-, and infrared-drying were applied to obtain solid material from the RO-R. Drying of the RO-R was made possible only with addition of 10% maltodextrin as a carrier. The total soluble phenolics in dried RO-R were in the range 0.15 to 0.58 mg gallic acid equivalents/g of dry weight for 2-phase RO-R, and 1.38 to 2.17 mg gallic acid equivalents/g of dry weight for the 3-phase RO-R. Spray-dried RO-R from 3-phase OMWW showed remarkable antioxidant activity. Protocatechuic acid, tyrosol, vanillic acid, and p-coumaric acid were quantified in all dried RO-R, whereas 3-hydroxytyrosol was found in 3-phase dried RO-R. This combination of separation and drying technologies helps to add value and shelf-stability to an olive oil by-product and increase environmental sustainability of its production. Keywords: drying, membrane filtration, olive mill wastewater, phenolics Practical Application: The results show the possibility to obtain a dried, phenolic-rich product after olive mill wastewater membrane filtration, and drying. This will lead toward better usage of by-products from olive oil production, an increase in the feasibility of the production, and lowering of the environmental impact. Introduction During olive oil production, large quantities of wastewaters and solid wastes are generated. The characteristics of olive oil waste are variable, depending on method of extraction, type and maturity of olives, region of origin, climatic conditions, and associated cul- tivation/processing method (Paraskeva and Diamadopoulos 2006; Rahmanian and others 2014). Nowadays, 2 processes are used for the extraction of olive oil: 3-phase and 2-phase systems. Waste produced by the former is composed of 2 main byproducts: an aqueous liquid known as olive mill wastewater (OMWW) and a solid waste (pomace; Obied and others 2005). The newer 2-phase system produces semisolid waste known as alperujo (Fern´ andez- Bola˜ nos and others 2002) or sludge (Celma and others 2007), and small amounts of OMWW from the secondary centrifugation, generated during the washing and purification of virgin olive oil (Borja and others 2006). OMWW is a dark, acidic matrix made up of water (83% to 94%), organic substances including carbohydrates, pectins, mu- cilage, lignin, tannins, lipids, and inorganic substances (Rahmanian and others 2014). However, from the perspectives of both human MS 20151255 Submitted 7/23/2015, Accepted 2/12/2016. Authors Sedej, Wang, and Sheng are with Univ. of California, Davis, Olive Center, 392 Old Davis Rd., Davis, CA 95616, U.S.A. Authors Milczarek, Avena-Bustillos, Dao, and Takeoka are with United States Dept. of Agriculture – Agricultural Research Service, Healthy Processed Foods Research Unit, 800 Buchanan Street, Albany, CA 94710, U.S.A. Direct inquiries to Author Sedej (E-mail: ivana.sedej@ars.usda.gov). health and environmental impact, the most important compo- nents of OMWW are phenolic compounds, most of which are hydrophilic in nature, and thus remain in the water when por- tioned during olive oil processing (Rodis and others 2002). The concentration of phenolic compounds in OMWW ranges from 0.5 to 2.4 g/L (Paraskeva and Diamadopoulos 2006); many of these phenolic compounds are formed by the action of hydrolytic enzymes on olive secoiridoids, oleuropein, and ligstroside, during oil extraction (Angelino and others 2011). The phenolic composition of OMWW has been widely stud- ied, and today more than 50 phenolic compounds have been isolated from olive mill waste (Obied and others 2007). Among them, hydroxytyrosol and tyrosol are the most abundant com- pounds in OMWW (Obied and others 2005; Comandini and oth- ers 2015) followed by 4-methylcatechol, p-hydroxybenzoic acid, vanillic acid, syringic acid, gallic acid (GA), catechin, apigenin, kaempferol, luteolin, quercetin, cyanidin, peonidin, n¨ uzhenide, ligstroside, verbascoside, and some polymeric compounds (tannins and catecholmelanins) (Cardinali and others 2011). OMWW is considered a highly polluting effluent due to its high organic load and phytotoxic/antibacterial phenolic substances, which are resistant to biological degradation (Cassano and others 2013). Thus, management, treatment, and disposal of produced waste raise serious environmental concerns. At the same time, ex- traction of the phenolic substances from OMWW has become an important target since benefits of their bioactivity have been shown at all levels of in vitro, ex vivo, and in vivo studies (Jerman C  2016 Institute of Food Technologists R  doi: 10.1111/1750-3841.13267 Vol. 81, Nr. 4, 2016  Journal of Food Science E889 Further reproduction without permission is prohibited