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Extraction

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Fundamentals of Food Process Engineering

Part of the book series: Food Science Text Series ((FSTS))

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Abstract

One area in food processing that is receiving increasing attention is extraction. This separation process involves two phases. The solvent is the material added to form a phase different from that where the material to be separated originally was present. Separation is achieved when the compound to be separated dissolves in the solvent, while the rest of the components remain where they were originally. The two phases may be solid and liquid, immiscible liquid phases, or solid and gas. Solid-liquid extraction is also called leaching. In supercritical fluid extraction, gas at supercritical conditions contacts a solid or a liquid solution containing the solute. Extraction has been practiced in the vegetable oil industry for a long time. Oil from soybean, corn, and rice bran cannot be separated by mechanical pressing; therefore, solvent extraction is used for their recovery. In the production of olive oil, the product from the first pressing operation is the extra-virgin olive oil, the residue after first press may be repressed to obtain the virgin olive oil, and further recovery of oil from the cake is done by solvent extraction. Oil from peanuts is recovered by mechanical pressing and extraction of the pressed cake to completely remove the oil. One characteristic of solvent extracted oilseed meal is the high quality of the residual protein, suitable for further processing into food-grade powders. They may also be texturized for use as food protein extenders.

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Suggested Reading

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Authors and Affiliations

  1. Department of Food Science & Technology, University of Georgia, Athens, GA, USA

    Romeo T. Toledo, Rakesh K. Singh & Fanbin Kong

Authors
  1. Romeo T. Toledo
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  2. Rakesh K. Singh
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  3. Fanbin Kong
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Problems

Problems

  1. 14.1.

    Ground roasted coffee contains 5% soluble solids, 3% water, and 92% inert insoluble solids. In order to obtain an extract with high soluble solids content without having to concentrate it for spray drying, a countercurrent extraction process is to be used to prepare this extract. It is desired that the final extract contains 0.1 kg solubles/kg water and that the spent coffee grounds should have solubles not to exceed 0.005 kg/kg dry inert solids.

    1. (a)

      Determine the water to coffee ratio to be used in the extraction.

    2. (b)

      The coffee grounds carry 1 kg water/kg of soluble-free inert solids, and this quantity is constant with solute concentration in the extract. Calculate the number of extraction stages needed for this process.

  2. 14.2.

    A process for extracting sugar from sweet sorghum involves pressing the cane through a three-roll mill followed by shredding the fibrous residue (bagasse) and extracting the sugar out with water. The sorghum originally contained 20% fiber, 16% sugar, and 64% water. After milling, the moisture content of the bagasse is 55%. Because the fiber is used for fuel, after the extraction battery, the solids are squeezed to remove the absorbed solution, and the squeezed solution is added to the last stage of the extractor. The following are the constraints: The sugar recovery must be a minimum of 99%, and the concentration of sugar in the final extract must be 10%. The bagasse carries a constant amount of solution, 1.22 kg solution/kg fiber. Calculate:

    1. (a)

      The water to solid ratio needed

    2. (b)

      The number of ideal extraction stages

    3. (c)

      The final sugar content if the extract is mixed with the juice first pressed out of the cane

  3. 14.3.

    In supercritical CO2 extraction of resveratrol from grape seed and skin obtained as a by-product of the wine industry, 95% ethanol is mixed in with the CO2 entering a SCFE extraction system by injecting it into the CO2 line using a high-pressure syringe. The extraction is carried out at 48 MPa and 80 C. It is desired to use a SCFE extraction solvent containing 1 mole % ethanol in the ethanol-CO2 mixture. Assume that the mass ratio CO2/dry matter is set at 25. The grape-seed-skin material contains 60% (w/w) water. If the extraction vessel has a volume of 100 mL, and the density of the grape-seed-skin material is 900 kg/m3, calculate:

    1. (a)

      The mass of dry material in the wet grape-seed-skin material that can be extracted/batch

    2. (b)

      The volume at 101 kPa and 25 °C per minute of CO2 that will be used to set the desired mass ratio of CO2 to dry grape-seed-skin if a CO2 feed rate of 0.2 kg/h is used

    3. (c)

      The rate at which the cosolvent, ethanol, must be injected into the CO2 line to obtain the desired mole % of ethanol in the SCFE solvent.

    4. (d)

      The required extraction time

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Toledo, R.T., Singh, R.K., Kong, F. (2018). Extraction. In: Fundamentals of Food Process Engineering. Food Science Text Series. Springer, Cham. https://doi.org/10.1007/978-3-319-90098-8_14

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