Tomatoes, color specifications

By contrast, we have a series of local markets for canned fruits and vegetables. Even though standards prevail on a nationwide basis, these are not always adequately defined. A concerted attempt is being made, therefore, to improve color specifications. This is especially true for tomato products. 

The Production and Marketing Administration of the United States Department of Agriculture promulgated standards of identity, including color specifications based on the Munsell system for tomato pulp (pur e), juice, paste, and catsup. We shall consider the specifications for pulp, the grade of which is determined by a numerical point score, 60 for color and 40 for absence of defects. (The color score for catsup is only 25% and for juice, 30% of the total score.) The appropriate section of the specification is quoted below ... 

Other organic fiber products which are mostly used in foods as dietary ballast additives are made from wheat, oats, tomato, apples, and citrus. Such dietary fibers are non-starch polysaccharides obtained from cell walls only, which can not be broken down by the digestive enzymes of the human organism and, therefore, constitute inert ballast materials. Color, taste, and odor relate to the fiber source. Unlike cereal brans or dietary fibers derived from, for example, sugar beets, which are often rejected by consumers because of their specific taste, wheat, oat, tomato, apple, and citrus fibers offer physiological properties that are much more readily accepted. 

There are, necessarily, limitations to the above. Normally, the specular component of the reflected light is eliminated, and since the color matches are metameric, viewing conditions must be specified. Also, the greatest usefulness lies in the measurement of surface colors. The object should be opaque and nonfluorescent. The nature of the surface of tomato pur4e is far from ideal. Although many difficulties arise in borderline cases, and the result is dependent on the skill and color vision of the observer, the method has served a useful purpose. If however we examine the wording of the PMA specification, a sample shall contain as much or more red than that produced by spinning the specified Munsell discs. . . , it... 

Chemical processes that are triggered by photons are also understood using the kinetics concepts mentioned in this chapter. The chemistry of vision is one example. The currently accepted mechanism for vision involves a compound called rhodopsin, which is composed of a protein molecule (opsin) attached to a colored polyene molecule called c/s-retinal. (C/s-retinal is chemically related to a class of molecules called carotenes, which are highly colored compounds responsible for the colors of carrots and tomatoes. Eating carrots does help vision, specifically in low light.) The vision process begins when the c/s-retinal absorbs a photon and is isomerized about one of its double bonds to make frans-retinal ... 

---