Abstract
The review will discuss the methods that have been optimized so far for the enzymatic hydrolysis of soapstock into enriched mixtures of free fatty acids, in order to offer a sustainable alternative to the procedure which is currently employed at the industrial level for converting soapstock into the by-product known as acid oil (or olein, i.e., free fatty acids removed from raw vegetable oil, dissolved in residual triglycerides). The further biocatalyzed manipulation of soapstock or of the corresponding acid oil for the production of biodiesel and fine chemicals (surfactants, plasticizers, and additives) will be described, with specific attention given to processes performed in continuous flow mode. The valorization of soapstock as carbon source in industrial lipase production will be also considered.
Highlights
Raw vegetable oil, obtained from seeds by a combination of pressing and solvent extraction, is a complex mixture of fatty acids, mono, di, and triglycerides, phosphatides, pigments, sterols, tocopherols, trace amounts of metals, flavonoids, tannins, and glycolipids.The recovered crude oil is necessarily submitted to a multi-step procedure, usually referred to as refining process, for removing non-triglyceride fatty materials, making it suitable for human consumption, and improving its organoleptic properties
Soapstock is submitted to a so-called splitting procedure, with the aim of stabilizing it Soapstock is submitted to a so-called splitting procedure, with the aim of stabilizing and reducing weight for shipment
Much effort is devoted to investigating the use of this edible oil processing byproduct in the production of second-generation biofuels, which are considered greener alternatives to fossil fuels and to conventional first-generation biofuels, i.e., those obtained directly from edible feedstocks in competition with food industry [9]. Specific applications in this field are represented by the use of soapstock as biomass for anaerobic digestion to produce biogas, or its conversion into fatty acid methyl esters (FAMEs) or ethyl esters (FAEEs) for biodiesel production
Summary
Raw vegetable oil, obtained from seeds by a combination of pressing and solvent extraction, is a complex mixture of fatty acids, mono-, di-, and triglycerides, phosphatides, pigments, sterols, tocopherols, trace amounts of metals, flavonoids, tannins, and glycolipids. The degummed oil is treated with an alkaline solution, typically diluted NaOH, to neutralize free fatty acids and any excess of phosphoric acid present from the previous step In this process a modest loss of oil occurs, and a small quantity of triglycerides is hydrolyzed by the alkaline treatment. The separated soapy material is referred to as soapstock, i.e., a heavy alkaline aqueous emulsion of lipids, containing usually water fatty acids leads to the formation of soap. The separated soapy material is referred to (nearly 45%, but the percentage varies according to the operating conditions), fatty acid as soapstock, i.e., a heavy alkaline aqueous emulsion of lipids, containing usually water sodium salts (10%, determined free according acids), triacylglycerols and diacylglycerols (12%),.
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