Membrane-based extractions, food

Application of Membrane-Based Extraction Techniques to Food and Agricultural Samples... 

Table I. Major membrane-based extraction techniques used for food and...

Membrane based extractions are capable of complementing conventional techniques (liquid-liquid and solid phase extractions) in food and agricultural sample preparation. Their attractiveness in sample preparation is based on their selectivity and ability to tolerate samples with high organic content and/or dissolved solid. They can also be easily automated and interfaced to other separation techniques. However, despite these advantages, membrane based extractions especially SLM extraction and MMLLE techniques have not been applied much to food and agricultural samples as compared to PME techniques. 

Membrane-based separation processes are recognized as environmentally friendly alternatives to conventional separation techniques such as distillation or extraction. The field of large-scale applications covers the range of drinking water processing, potable water production, waste-water treatment, application in the food and pharmaceutical industries, recovery of aroma and active substances as well as sterile filtration of pharmaceuticals and clarification of beverages. 

Several standard DNA isolation kits are commercially available, including the QIAamp DNA Stool Mini Kit and the DNeasy Plant Mini Kit made by Qiagen. Both of these products are based on silica gel membrane technology and allow for the extraction of total DNA from processed foods and raw foodstuffs, respectively. In... 

In the domain of food industries, EED was used to reduce oxygen in fruit juice [46], to extract cytoplasmic proteins from alfalfa [47,48], to coagulate proteins [49], and to reduce disulfide bonds in proteins [50]. These applications are based on the electrode redox reactions coupled with monopolar membrane action. 

Two other methods have been approved by AOAC for determination of sulfites in food. One is a quantitative assay based on malachite green decolorization using flow injection analysis. Sulfite is released from a sample slurry with alkali, then the test stream is acidified to produce sulfur dioxide gas which diffuses across a Teflon membrane into a flowing stream of malachite green, and the extent of decolorization is measured at 615 nm. The other method is based on ion exclusion chromatography with sulfur dioxide being released by alkali extraction, and the diluted filtrate is injected onto an anion exclusion column linked to an electrochemical detector. 

The mode of extraction for PAHs is highly dependent on the matrix. For solid-based matrices such as food samples, sediments, soil, marine organisms, etc. extraction methods such as Soxhlet extraction with nonpolar solvent [35 6], hollow fiber membrane solvent microextraction (HFMSME) [10], pressimzed hquid extraction (PLE) [37,38], sonication extraction [3], microwave-assisted extraction (MAE) [3], supercritical fluid extraction, (SEE) [39], accelerated solvent extraction (ASE) [40], cold extraction [41], soxtec extraction [42], microwave-assisted alkaline saponification (MAAS) [43], dynamic microwave-assisted extraction (DMAE) [44], add-induced cloud point extraction (ACPE) [45], methanolic saponification extraction (MSE) [7], etc. are employed. Of all these, Soxhlet extraction is the most common for solid samples and has achieved excellent extraction with high-level recovery but its setback is the high consmnption of solvent and time associated with it. 

Membrane separation processes can be used for a wide range of applications and can often offer significant advantages over conventional separation such as distillation and adsorption since the separation is based on a physical mechanism. Compared to conventional processes, therefore, no chemical, biological, or thermal change of the component is involved for most membrane processes. Hence membrane separation is particularly attractive to the processing of food, beverage, and bioproducts where the processed products can be sensitive to temperature (vs. distillation) and solvents (vs. extraction). 

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