Red Color in Tomatoes. The red coloring matter in tomatoes is in the form of irregularly shaped crystal-like chromoplasts, which occur in masses of various sizes. They are present in largest amounts usually in the protoplasm which lies close to the ectoplasm and in that surrounding the nucleus. They vary from sharp, bright-colored forms to those more or less blunt in outline, and dull in color. They may be situated largely in the periderm, the soft parenchyma beneath the periderm, or through the whole mass of the parenchyma with the exception of the matrix surrounding the seeds in the loculi. In tomatoes having the color in the periderm a considerable amount is lost by adherence to the skin. The chromoplasts are not affected by rotting to the same extent as are the other constituents of the cell; they can be found floating free in the debris from rotted cells, still retaining considerable color. They lose their color gradually, in some varieties much more rapidly than in others. In stored pulp which has fermented, the color may be faded to a dull yellowish brown. In tomatoes intended for ketchup where a bright red color is desirable, care should be used in the selection of a variety having the chromoplasts bright, properly oriented, and in sufficient quantity.
Vascular Bundles. In the pulp of the tomato are found strands of vascular tissue, entering from the stem, and dividing and ramifying through the soft pulp. These consist of long tubes with thin walls, some of which have a strengthening band in spiral form on their interior walls, the associated cells being without any special marking. The strands vary in size from those having a few tubes to those having a large number.
Seeds. The seeds of the tomato are small, flattened, yellow bodies covered by a clear gelatinous membrane. Their peculiar characteristic is the out-growth of hairs of varying lengths. The seeds constitute about 2.5 per cent of the weight of the tomato.
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.
CHANGES PRODUCED IN PULP BY ROTTING.
When tissue is held and allowed to rot spontaneously, the pulp is decomposed into a granular, watery mass. The cells beneath the epidermis are the finest and driest in the sound tomato, considerable pressure of the cover-glass being required to separate them for examination. Even when forced apart, the cells retain their shape. They contain a delicate semi-transparent protoplasm with a rather large nucleus surrounded by protoplasm and having strands from this mass connect with the protoplasm lining the wall. Pieces of the same tissue, on having the skin removed so as to expose the broken tissue to the air, were covered with mold in one day and in three days so badly disorganized that the cells separated with the weight of the cover-glass. The cells were transparent, the walls collapsed into a wrinkled mass, the protoplasm had disappeared, except a skeleton of the nucleus, but the red chromoplastic masses were intact. The middle lamella of the cells is the part which dissolves first, allowing the cells to separate and causing the walls to become thinner. The cell cavity is often filled with bacteria, so that the effect of the rotting can not be seen until the cells have been washed thoroughly. These bacteria have been mistaken for the particles left by the decomposition of the cell contents. The vascular bundles are surrounded usually by small parenchyma cells which do not separate readily from the strand in the healthy tissue, but in the decayed tissue the vessels can be seen clearly, free from other tissue. In advanced stages of rottenness the walls of the vessels may be dissolved, leaving only the spiral thickening, and the parenchyma tissue crumbled into powder-like fragments. The parts of the tomato which resist rotting the longest are the skin, which may be washed clean of adhering particles, the spirals of the vessels, and red particles of the chromoplasts.
The conditions found in the rotted sections and pieces of tomato can be distinguished in the poor ketchup and these factors, together with the large number of organisms present, serve for purposes of differentiation.