21.2: Objectives of Food Processing

Preparation

One function of processing is the preparation of food for eating. More and more of what used to be done entirely in the home kitchen is now also done by food companies. We can buy entire dinners that only need heating. Much of food processing is really industrialized cookery.

Most of this work centers about two general concepts, just as our home cooking does. First, we select the part of the food we want to eat, and separate it from the part we don’t want—as in taking peas from a pod, a banana from its skin, or meat from the bone. And second, we modify the food for a specific eating purpose. Milk may be heated and flavored with chocolate at breakfast, or made into yogurt for lunch, or used to make a pudding for dessert at dinner. Of course, most of this sort of processing has to do with sensory values.

Some processing has to do with consumer demand for “healthier” foods, often at a sacrifice of sensory pleasure. These include low-fat or fat-free modifications (e.g., fat-free salad dressings), low-sodium modifications (e.g., low-sodium cheese), and “fabricated foods” (e.g., margarine).

Preservation

Unlike the home cook who can serve dinner right after making it, the food company must preserve whatever it has prepared, whether a bag of peas out of their pods, a pint of “light” sour cream, or a four-compartment plate of meat, gravy, potatoes, green beans, and apple cobbler.

Preservation has two broad aspects. The first is to combat deterioration—changes occurring within the food itself. It may be entirely the result of the food’s own chemistry, or it may be caused partly by such outside influences as light, oxygen, heat, and so on. Stale bread and rancid oil are examples of deteriorated food.

To shield foods from light, we use opaque or tinted packaging. (An age-old method is to store foods in the dark—as in the cellar). We do this with the oily potato chips and the mostly-fat bacon, to prevent light-induced rancidity of the fat. We do this with milk, to prevent the destruction of its riboflavin by light. We do this with sacks of potatoes, to lessen light-induced formation of solanine (a nerve toxin found when a green layer forms under potato skin).

To keep oxygen from doing damage, we use vacuum packs and antioxidants. To stop the food’s own deterioration-causing enzymes, we blanch (quickly heat) the food. To further slow the food’s chemistry, we lower the temperature by refrigeration or freezing.

Sometimes, substances are removed from the food to preserve freshness. Removing the oily wheat germ (the part that goes rancid) to make white flour increases the shelf life of the flour— an especially important factor in the days when flour was stored for a long time, its transport slow, and when bread was our “staff of life.” (There was also an esthetic preference for white flour then, as now. White bread is still the most popular bread. Bread, noodles, and pastries made with whole wheat flour aren’t much of a hit.

The second general aspect of preservation is really a part of our age-old competition with other life forms for food. For just as we must defend our berries from the crows, and our grain from the rats and insects, so must we compete with the microbes which would flourish in our food. Spoilage is the term used by food technologists to denote the damage wrought by microbes. Soured milk and moldy bread are examples.

Preventing spoilage is an aspect of microbial chemistry. Preventing deterioration is an aspect of plant chemistry. The chemistry, whether of food or microbes, is similar. Preservation from spoilage will be discussed further in the section on microbial food hazards.