Clarification of Apple Juice - Springer Link

126 downloads 12648 Views 2MB Size Report
84 Processed Apple Products. Table 4-1. Materials Causing .... zation of insoluble pectin was the first important step in the course of clarification. Experiments ...
4 Clarification of Apple Juice Arun Kilara and Jerome P. Van Buren

Consumer preference for a totally clear, shining apple juice has made clarified apple juice much more popular than unclarified natural apple juice. The production of clear apple juice requires the removal of suspended material and prevention of the development of turbidity after juice bottling. Freshly pressed juice contains suspended solids that are deliberately precipitated prior to filtration. This precipitation step is' called clarification. Other measures often are taken to remove soluble materials that have the potential to form after-bottling hazes. These measures are often called fining. Fining methods, which can remove haze particles as well as soluble materials, are discussed in chapter 5. Table 4-1 lists materials that may cause turbidity in apple juice and their relative sizes. Apple juice from a press or extractor contains not only discrete solid particles but also unstable compounds that can be coagulated by heat or by enzyme action. Depending on pressing or extraction conditions, the amount of solids in the juice may vary from 0.5 to 8% as determined by centrifuge test. The largest solids are normally removed as the juice comes from the press by rotating or vibrating stainless-steel screens. In some installations a continuous self-cleaning centrifuge is used for this purpose.

SUBSTRATES CONTRIBUTING TO TURBIDITY Pectic (Greek-congealing) substances are a group of complex colloidal plant carbohydrates made up primarily of (1,4)-a-D-polygalacturonic acid (fig. 4-1). This polygalacturonic acid exists in widely varying states ofmethoxylation and neutralization. Pectic acid is almost pure, colloidal polygalacturonic acid practically free from methyl groups. 83

D. L. Downing (ed.), Processed Apple Products © Van Nostrand Reinhold 1989

84 Processed Apple Products Table 4-1. Materials Causing Turbidity in Apple Juice.

Size 100 micrometer

10 micrometer

1 micrometer 100 nanometers

Material Plant cell crystals and coag· ulatedprotoplasm Mold Yeast Plant cell fragments Bacteria Spores Protein-tannin complexes Retrograded starch Gums Polymeric carbohydrates

10 nanometers

Proteins Polyphenols (tannins)

1 nanometer

Acids, sugars, alcohol

COOH

Settling behavior

}

Settle quickly

}

Settle slowly

} }

Colloidal, stay in suspension True solutions

1)';, ' Jl~--t/ n OH

POLYGAlI>CTURONIC ACID t 0( h~4I;nk.g