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  Greening of Puree

A Research Note

Factors Governing the Greening of Garlic Puree

T. M. Lukes
Journal of Food Science, Volume 51, No 6, 1986.


Storing garlic bulbs for a month at or above 23°C, prior to processing, prevented the production of a green pigment in the garlic puree. The amino acid S-(1-propenyl) cysteine sulfoxide was necessary for the development of the green color.


GARLIC PUREE has been a commercial food product for over forty years, produced by breaking garlic bulbs into cloves, cleaning and then grinding them. The grinding is done in a manner that results in a skin-free garlic puree. Sodium chloride is usually added and citric acid is always added. The final pH value is near 4. The temperature is then raised in a heat exchanger to inactivate the enzymes and reduce the number of microorganisms. Ideally, the final product should have a light tan to cream color. Some lots of garlic bulbs produce purees which are dark green to blue-green instead of cream (Sano, 1950; Shannon, 1961). This product is unsaleable because of the green color, the cause of which is unknown. The object of this study was to find a method of preventing the development of the green pigment.

Materials and Methods

Testing for puree color

Garlic cloves were hand peeled and pureed in a food blender with twice their weight of water and enough citric acid to reduce the pH value to between 4.0 – 4.3. This puree was held over night at 45°C, filtered and the amount of green color was determined at 590 nm.

Amino acid analysis

The garlic was prepared for analysis by peeling the cloves and then slicing them in half lengthwise. Twenty grams of the halves were ground in a kitchen blender for 2 min with 60g of water containing 1.6 ml of 5N HCl and 40 mg of cysteic acid, as an internal standard. The HCl was added to reduce the pH value to 1.8 to 2.0. At this value the allinase was not able to react with the sulfoxides. It was assumed that unheated solutions at pH 2 would not cause these amino acids to hydrolyze to any great extent. The puree was filtered, and an aliquot was placed directly on a 0.9 by 40 cm column packed with Dowex 50-X8. The solvent was 0.2M sodium citrate buffer (pH 2.9) with 10% methanol added. After the first 40 ml of buffer was run through the column, the pH was slowly raised by adding increasing amounts of 0.2M, pH 3.2 sodium citrate buffer to the reservoir. The amino acids were separated by the above ion exchange chromatography with post column analysis with ninhydrin (Moore et al., 1958)

Storage tests

Commercially grown California Late and California Early cultivars, purchased in a local market, were stored at four different temperatures; 3°C, 12°C, 23°C and 28°C. Periodically, samples were withdrawn and tested for the amount of green pigment that would develop when pureed.

Effect of S-(1-propenyl) cysteine sulfoxide (PECSO) on color

Ten ml of puree were mixed with various amounts of a solution of PECSO in pH 4.0, 0.2M citric acid buffer. More buffer was added to make a final volume of 15 ml. The mixture was held overnight at 45°C, filtered and the green pigment measured at 590 nm in 1 cm cells with a Bausch and Lomb Spectronic 21 spectrophotometer. PECSO was prepared from onion by the method of Carson et al (1966).



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