Suchergebnisse

From the beginning of time, the history of man has been his struggle to obtain food. After many thousands of years, this is still a major problem which confronts the peoples of the earth. Although much food is available on earth, a great deal never benefits mankind because of deterioration and spoilage. Various kinds of spoilage cause a million tons of grain to be wasted each year. Man has learned to control and overcome some of these destructive forced through a variety of methods of food preservation. Some forms of preservation such as drying, salting, and so forth, probably have been known since the beginning of civilization. The most ancient method of food preservation, drying, was copied from nature. Early man gathered dried fruits, berries, nuts, legumes, and grains which had matured and dried on the plants. Later they used their shelters to dry food, and pre-Columbus American Indians used the heat from their fires. However, it was not until about the latter part of the eighteenth century that a hot air dehydration room was used. Much of the drying done for modern consumers is in the form of dehydration, which means artificially dried. About the same time that dehydration came into being, Nicholas Appert began work on another process of preserving food, which came to be known as canning. He received an award from Napoleon when he proved that food heated in sealed containers would not spoil if the containers were not reopened or the seal was not broken. For half a century there was no correct explanation for the success of this process until Pasteur discovered that microscopic growth caused food to spoil. It then became clear that Appert had destroyed micro-organisms by heat, and excluded their re-entry by sealing the containers. The invention of a pressure steam retort, social legislation of the Food and Drug Act, use of the common "sanitary" tin can, and research devoted to the study of nutrients in relation to the canning process have all aided significantly in creating our modern canning industry. Desrosier (7) has aptly said that food preservation practices prior to the discovery of canning were copied from nature. Canning, which has no counterpart in nature, has changed the eating habits of the western world. Although freezing was used as a method of preserving foods for centuries, the invention of a successful refrigerator in the late 1800's marked the beginning of the vast field of the modern method of refrigeration and freezing. Fish was frozen commercially as early as 1880; meats, in 1891; fruits, in 1905; and vegetables, in 1929. However, int he 1930's when modern homes contained a refrigerator, frozen foods began to find their place in commerce. It was not until 1940 that freezing assumed its rightful place as a means of preservation. To preserve foods as nearly as possible in their natural state has long been an aim of man. Each method of preservation has obvious advantages, but not one has wholly accomplished this aim. If a method could be found that preserved food without marked change in its natural characteristics, it would mean man was close to achieving his goal. Fruits and vegetables, which are very perishable, make up 40 percent of the total food consumption. Twenty-five to 50 percent of the fruits and vegetables produced to be eaten fresh, spoil before they can be consumed (45). A new method of food preservation was made possible in 1945 when the Congress of the United States passed the Atomic Energy Act. Several divisions of the Atomic Energy Commission were concerned with the application of the peaceful uses of atomic energy. In 1953, considerable research on radiation preservation of food was started on a large scale. Subjecting food to ionizing radiation has been accepted by many as an effective means of preservation. Because of the many complex problems associated with radiation sterilization, preservation by this means is not as feasible at this time as that accomplished by the low doses of radiation for pasteurization. However, there are a number of areas in these low dose treatments which show great promise for use of radiation processing of foods. 1. Conservation of grain and certain packaged products by the destruction of insect infestation. 2. The inhibition of sprouting in potatoes and other root crops. 3. The destruction of trichinae in pork and pork products. 4. The inactivation of Salmonella in egg products. 5. The extension of shelf-life of fresh fruits and vegetables, cut meats, and fresh fish. The first four areas are approaching the stage at which commercial exploitation might be considered. However, considerable research must still be pursued toward the improvement of certain radiation-treated fresh foods in regard to wholesomeness, nutritive value, color, texture, flavor, and odor. The studies presented in this thesis were conducted on the acceptability and refrigerated-life of strawberries, and sweet cherries in relation to gamma radiation dose, variety and maturity of crops and physical changes.