Measuring Color

Visual color is closely related to perceptions. Consumer perception or purchase decision is made even prior to tasting food. Color is defined as the impact of wavelength in the visual spectrum from 390 to 760 nanometers (nm) of the human retina. Reflected light is perceived as color. To detect the color, either the human eye or the instrument used must be capable of recognizing the object and translate the stimuli into a perception of color.

Various manufacturers of colorimeters and spectrophotometers market their equipment as portable, benchtop, and in-process equipment. In food, effect of color is very important to “determine effects of raw ingredients to the finished product; its shelf life or changes due to processing; ensure suppliers are guaranteeing a consistent colored material; and determine if the final product meets internal quality standards established,” says Cliff Walsh, operations director at American Licorice Company.

Subjective Evaluation of Colors

Color in raw materials or in finished goods is important to a food processor. Easier said than done is the quick approach to check colors with the naked eye. “There are disadvantages associated with visual examination,” comments Ramon Navoa, the director of innovation at American

Licorice Company. “Judgment is influenced by lighting, visual deficiencies of the eye, or in a trained panel based on repeatability. All these affect variability,” he adds.

A subjective evaluation system can include matching the colors, Pantone color matching system, and actual photos of finished or raw materials. Another system called Munsell is used by the USDA. The color system divides hue into 100 equal divisions around the color circle. Applications include dairy products such as milk, cheese, egg yolk, beef fruits, and vegetables. Food manufacturers use Royal Horticultural Society’s color charts to standardize food colors. The Natural Color System Digital Atlas also has more than 1,950 colors that can be used to compare colors. Any visual examination or comparing of colors has inherent constraints and are product dependent.

Agricultural commodities may have batch to batch variation and getting a consistent supply may be more critical. For example, cinnamon’s flavor may be perceived to be meeting the aroma specification, but the color is variant based on the region the cinnamon is harvested, bark color, age of the bark, intentional contamination, and country of origin. Knowing variability exists with the color is hard to explain to a consumer who has expectations on the end-product’s visual appearance. Some naturally occurring colors also degrade based on exposure to heat, sunlight, processing conditions, and storage. This adds complexity to the color consistency expectations.

Artificial colors added to food have their inherent drawbacks. Colors are added to food to offset color loss due to light, air, extreme temperatures, storage, and moisture. Others use artificial colors to mask natural variations in color or enhance naturally occurring color. Artificial colors provide identity to the product, protect flavors and vitamins from damage, or are used for decorative purposes.

Colors, either natural or synthetic lakes or dyes, have inherent properties and applications. Applications dictate if the measurement of color becomes critical to monitor in process samples for color degradation or conformance to a standard. The product appearance may be a subjective phenomenon, but when it comes to color there are instruments available in the market. Many instrument manufacturers can provide assistance in providing equipment for specific applications.

The Instruments and Their Applications

Common colorimeters are Konica Minolta’s chroma meter, HunterLab colorimeters, and Hach Lange colorimeters. Colorimeters use sensors and simulate how a regular person views an object and quantifies the color differences between a standard and a production sample. Colorimeters employ three photocells as receptors, just like a human eye. The same wavelength is used to measure, and hence, measurement conditions do not change. A light source and a microprocessor convert colors to internationally accepted numeric values. Colorimeters feature a wide range of apertures and illumination for specific applications and various levels of data processing. They are good for measuring and comparing color differences between two specimens, strength determination, fastness determination, and shade sorting.