It is doubtless true that foods when they can be had fresh are to be preferred to those which have been sterilized. It is also true that many unsterilized foods from unsanitary environments are more dangerous in the fresh state than when they have been exposed to a high temperature. Taking into consideration all the circumstances in the case, it must be conceded that the process of sterilization, first practiced by Appert and afterward placed on a scientific basis by Pasteur, has proved of almost immeasurable advantage to mankind. Thus for this greater reason the character and quality of foods thus preserved should be wholly above suspicion, and no adulteration or sophistication of any kind should be practiced therewith. The manufacturer is quite as much interested as the consumer in placing the whole output of sterilized foods on a plane above suspicion.
PART VII.
VEGETABLE OILS AND FATS, AND NUTS.
VEGETABLE OILS AND FATS.
The production of a substance known as fat or oil, composed of oxygen, hydrogen, and carbon in the form of a fatty acid and combined with glycerine, is a function of almost every plant. The fat acids are usually in combination with glycerine, which plays the part of a base and in so far as its proportion by weight is concerned is much less important than the fatty acid itself. In round numbers it may be said that nine-tenths of all glycerids or fats are composed of a fatty acid and one-tenth of glycerine. When at ordinary temperature this combination is in a liquid form it is called an oil, and when at ordinary temperature it is in a solid or semi-solid condition it is known as a fat. The term “ordinary temperature” means in this connection that of an ordinary living room and not the extremes of outside temperature. In general terms it may be said that the temperatures referred to are included between the minimum of 50 degrees and the maximum of 85 degrees F. In so far as chemical composition and dietetic properties are concerned, there is no distinction between the oils and the fats. The names are simply a means of ordinary discrimination which has assumed importance by reason of common usage.
There are three of the fatty acids which are particularly important from a dietetic point of view which go to make up the greater part of these fatty and edible vegetable oils and fats. These three acids are oleic, stearic, and palmitic. Of the three, oleic acid is by far the most important, as it constitutes the greater part of nearly all these bodies, especially of oils. In fact the term “olein” and oil are of common origin. Palmitic acid exists chiefly in certain forms of vegetable oil and fats, while stearic acid is a very important constituent of animal oils and fats.
These three acids uniting with glycerine form the glycerids which make up the great body of edible and animal oils and fats, and these principal glycerids are known as olein, palmitin, and stearin, respectively.
Chemical Characteristics.
—The chemical composition of these bodies has been pointed out above. There is, however, in almost all cases, some free acid present in the compound, that is, an acid which is present uncombined with the glycerine. This free acid is usually present in small quantities and is more abundant in the overripe and older plants than in the freshly matured parts. The natural oil also contains certain other ingredients which may be regarded as impurities, and which it is necessary to remove from the oils by a process of purification or refining before they are ready for the table. These impurities may be of a mechanical nature, that is, consisting of parts of the material itself from which the oil is expressed or of certain juices not oils which are found in the animal tissue, portions of protein and other forms of nitrogenous matter, and traces of carbohydrates and gums. The oils have certain definite chemical reactions which are common to them as a class. Among these may be cited, principally, the faculty of absorbing, under certain conditions, the halogens, namely iodin, bromin, and chlorin.
Without entering into any technical description of this process it is sufficient to say here that the degree of absorption of iodin is in a measure the test for the varieties of oil. The different vegetable oils have, as a rule, certain definite relations to the absorption of iodin by means of which they may be to a certain extent identified or separated from similar bodies. The degree of absorption is expressed in the percentage by weight of the oil itself and is known as the iodin number. If, for instance, a gram of any particular oil absorbs one gram of iodin, it is said to have an iodin number of 100. Many oils absorb more than their own weight of iodin, while many others absorb very much less. Another characteristic of oil is found in the fact that with certain reagents, such as an acid either in a dilute state or in a concentrated state, definite colors are produced which are characteristic of the variety of oil in question. As an example of this may be cited the faculty which cottonseed oil has of reducing nitrate of silver to the metallic state, leaving the silver in that finely divided form which has a black color. This is the only oil in common use which has this faculty, and hence it may be regarded as a characteristic test.
Another characteristic chemical property of cottonseed oil is the color which is produced in the Halphen reaction, which has already been described.