Measurement of Color Changes In Foods E. J. EASTMOND
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on June 2, 2015 | http://pubs.acs.org Publication Date: June 17, 1950 | doi: 10.1021/ba-1950-0003.ch002
Western Regional Research Laboratory, U. S. Department of Agriculture, Albany, Calif.
Methods are described for determining the extent to which original natural color is preserved in processing and subsequent storage of foods. Color differences may be evaluated indirectly in terms of some physical characteristic of the sample or extracted fraction thereof that is largely responsible for the color characteristics. For evaluation more directly in terms of what the observer actually sees, color differences are measured by reflectance spectrophotometry and photoelectric colorimetry and expressed as differences in psychophysical indexes such as luminous reflectance and chromaticity. The reflectance spectrophotometry method provides time-constant records in research investigation on foods, while photoelectric colorimeters and reflectometers may prove useful in industrial color applications. Psychophysical notation may be converted by standard methods to the colorimetrically more descriptive terms of Munsell hue, value, and chroma. Here color charts are useful for a direct evaluation of results.
C o l o r is a significant factor in the consumer acceptability of foods. The consumer's reaction may be simple dislike for a certain color or, more likely, a reaction based on association of certain color characteristics with fresh and wholesome quality. More fundamental is the fact that color is often directly related to nutritive factors such as carotene (nutritionally important as provitamin A). Some degree of correlation has been found between color and general quality in certain industrial products such as vegetable oils, but the problem is more complicated with fresh and processed foods. Regardless of the degree to which color is a true indication of palatability or nutritional quality, it is a very evident characteristic of foods and is recognized as important in quality grading. Many quality standards, including a color factor, have already been officially established. Fresh and processed fruits and vegetables, fats and oils, meats, dairy products, poultry, and eggs are among the foods in which color is important in quality standards. Factors affecting the color of foods include hereditary varietal differences, maturity, growing conditions (temperature, moisture, locality), and processing procedures. The first three operate in a complex way on the raw product and result in an original natural color over which the food processor has control only in so far as he can select his raw material. However, the extent to which this original natural color is preserved during processing and in subsequent storage is one important criterion of processing procedures. This discussion is devoted to some of the methods that may be used to characterize differences in natural color of food products and to detect and specify changes in reflection or absorption characteristics that occur as a result of processing treatment and storage conditions, even though no associated change i n visual color is perceptible. 3
In ANALYTICAL METHODS IN THE FOOD INDUSTRY; Advances in Chemistry; American Chemical Society: Washington, DC, 1950.
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ADVANCES IN CHEMISTRY SERIES
Measurement of Physical Characteristics Related to Color
Downloaded by UNIV OF CALIFORNIA SAN DIEGO on June 2, 2015 | http://pubs.acs.org Publication Date: June 17, 1950 | doi: 10.1021/ba-1950-0003.ch002
The objective indication of color differences in foods has usually been attempted in a simplified, indirect way that involves a comparison of some physical characteris tic of the samples or, more often, an extracted fraction that is assumed or has been proved to be largely responsible for the associated color characteristics. Although such a method does not measure the actual visual color of the samples, a measure of relative amounts of color-characteristic pigments or a comparison of physical proper ties of extracts of color-critical fractions (which may be mixtures of several pigments) may prove to be very sensitive indications of differences that are closely related to color.
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