STRUCTURE OF KETCHUP.
Although the tomato pulp is broken into fine particles by the action of the cyclone, and the skin and seeds are removed by the fine sieves, pieces of the various tissues can be readily identified. The skin and seeds have characteristics which would serve to distinguish them from similar parts of other vegetables which might be used for adulteration, but particles of skin and hairs from the seeds are rarely found. The distinctive features which can be relied upon are the red, irregularly-shaped, chromoplastic bodies in the parenchyma cells, and the peculiar wavy-outlined cells of the lining layer of the chambers. As nearly all young vegetable tissues have spiral vessels in their vascular strands, these are not distinctive, except that they might differentiate similar tissues of different size. There is very little starch in mature tomatoes, and moreover, as the cooking causes the starch to swell and lose its structure, the starch could not be used for identification.
Good ketchup made from whole tomatoes, in spite of the minuteness of the particles, has a clean appearance, and can be readily distinguished from poor ketchup. All ketchup will have some micro-organisms present, as it is practically impossible to free the tomatoes from them in the washing, but the number is very small in some of the best, in the manufacture of which careful washing and sorting have been done. The poorer the ketchup, usually, the greater number of organisms—bacteria, yeasts, and molds; sometimes one form predominating, sometimes all three being in great abundance, this latter condition usually prevailing in the poorest ketchup, where more or less rotting has occurred.
As the tomato pulp is a favorable medium for certain organisms, these will develop first, and it has also been determined that while one organism is developing vigorously, others present are checked until the activity of the first ceases. Then again, as the composition of the pulp is being altered by the development of the organisms, the changes induced render it a more suitable medium for other organisms which are present but held in abeyance, so that pulp which has been allowed to stand for some time will usually have present not only a large number, but also different kinds of organisms.