By Mortin Satin
Posted: Friday, October 10, 2003
ARTICLES
Publication Date: October 10, 2003
There are parallels between the objections now made to food irradiation and objections, long since discredited, to pasteurization. The idea of preserving foods through the reduction or destruction of the microorganisms they harbor is centuries old. In the 18th century, boiling was used to preserve meat extracts (1765-Spallanzani) and vinegar (1782-Scheele).[i] One of the greatest advances in food technology, canning, resulted from the work of a French confectioner by the name of Nicholas Appert in 1804. Napoleon had put forth a prize-winning challenge to come up with new methods for the improved preservation of foods for use by the French army. Appert found that by heating food in a metal container, and sealing it off from air, the food could be kept in an edible condition for a very long time. Appert submitted his technology and won the prize in 1809. He deeply believed in his work and promptly invested the prize money in the world's first food canning plant.
Although it was known these methods worked well to preserve foods, the reasons were not understood. A similar situation existed in the field of medicine at the time. Although it was possible to control the symptoms of certain diseases, physicians did not know their precise causes. Microorganisms and their effects were virtually unknown.
The work of Pasteur changed all that. Following the Italians, Spallanzani and Fabroni, he instinctively felt that there was a close link between diseases and the fermentation which so often accompanies food spoilage. In his push "to arrive at the knowledge of the causes of putrid and contagious diseases" he carried out in-depth studies on the causes of spoilage in wine. These studies eventually led to the investigation of disease in silkworms and ultimately to his researches on animal and human diseases. Pasteur's efforts revolutionized our world and were probably the single most important scientific work providing us with a means of controlling the effects that microorganisms have upon us.
From 1860-1864, Pasteur's research clearly demonstrated that spoilage in wine was caused by simple microorganisms. In order to handle the problem, he recommended a level of heat treatment that was sufficient to inactivate the spoilage microorganisms (50-60oC), but not great enough to destroy the quality or character of the products processed.[ii] This was, in fact, the key to his process. He could easily have boiled the wine in order to kill off all the microorganisms, but that would have destroyed the wine's taste as well. He therefore determined the minimum processing required to do the job without impairing the product's overall acceptability. The technique turned out to be very successful and he soon after applied it to beer as well.
Thus, for the first time, a method became available to prevent the spoilage that had always been accepted as an unavoidable fact of life. Consumers no longer had to tolerate wine or beer that spoiled prematurely. Not only was the shelf-life of a product extended, but the very basis of its untimely spoilage was finally understood. Even though the commercial significance of this technology was the primary consideration at the time of its development, its greatest impact was ultimately to be felt in the area of public health. The drinking of wine or beer may not have been generally recommended for health, but the consumption of milk by children was, and it was in the dairy industry that Pasteur's had the greatest impact. His technique was a genuine breakthrough that saved the lives of thousands and changed the course of our eating habits forever. Curiously, there are no records of Pasteur himself employing the new method on milk. However, when the same process was eventually applied to milk, it was aptly named "pasteurization" in recognition of his enormous contribution to science and to our everyday lives.
Commercial Pasteurization
The pasteurization of milk did not become a commercial reality for many years after Pasteur's initial work. The idea of applying the pasteurization method to milk was first commercially tested in Germany in 1880 but was focused solely upon the preservation of milk in order to improve its shelf-life rather than its health characteristics.[iii] The first recommendation to employ pasteurization to improve the health-related properties of milk came from the German chemist Soxhlet in 1886. Even before it was generally accepted that milk carried diseases such as diphtheria, typhoid, tuberculosis, and scarlet fever, both Soxhlet and the American pediatrician, Jacobi, advocated only heat-treated milk for infant feeding.[iv]
Figure 1: American Medical Association Criticism of Milk
A debate then evolved around the value of pasteurization compared to sterilization (extended boiling), with Europeans generally favoring the latter technique for infant feeding. Additional work was carried out on the canned sterilization and condensation of milk, but it became obvious that these products had flavors and consistencies so different from fresh milk that they would never be accepted for general consumption. The eventual success of pasteurized milk occurred in America when it was demonstrated that full boiling was neither necessary nor desirable. Pasteurized milk was safe and practical and fit the needs of most urban consumers. It was very similar in taste and color to fresh milk and required no change in consumption or cooking habits. Yet, even though these advantages were obvious, it still was a struggle to establish pasteurized milk on the market. The defensive posturing of the dairy industry-together with the outspoken remonstrations of conservatives who espoused the peerless qualities of natural, raw milk-significantly delayed the adoption and commercialization of the new methods.
Figure 2: Chicago Health Department Recommendation to Mothers
As milk became more and more associated with the transmission of disease, however, public health officials and the medical community became more direct in their condemnation of the dairy industry and its products. These criticisms varied from harsh, graphic associations of raw milk and death to more sober endorsements of breast-feeding.[iv]
The dairy industry soon realized that their historic belief in the purity of raw milk was becoming passé and, in response to growing public criticism, slowly began to clean up its act. In collaboration with the State Medical Associations, certain dairies made an effort to place their operations under a much higher degree of hygienic control. Much greater attention was paid to cleanliness of animals, barns, and milking utensils. Workers had to be healthy, and the operating procedures were subject to rigid inspection. Milk that was produced under the specified conditions received the endorsement of the State Medical Milk Commissions and was categorized as "Certified" milk. Certified milk was considered to be the purest and safest raw milk possible to produce.
Figure 3: Certified Milk Seals
Even though Certified Milk was a great step forward in the cleanliness and hygienic quality of milk, it quickly became evident that the procedures involved were no guarantee against milkborne infections. There was no step anywhere in the process to actually destroy any contaminating bacteria. Certified milk was found to be responsible for several outbreaks of diphtheria, tuberculosis, and scarlet fever. In some cases, the infections were traced to dairy employees who carried the diseases but had no outward signs of suffering from them. As a result, the notion that raw milk was dangerous, whether Certified or not, began to gain ground. The growing public awareness of the risks of milkborne disease pointed to the need for new technology. The weight of evidence began to tip the balance away from the old belief that fresh, raw milk was the best milk.
This change in attitude toward raw milk brought forth other approaches to the problem of milk safety aside from pasteurization. Among the most curious methods proposed were chemical treatments of milk. Some of the chemicals recommended were hydrogen peroxide, salicylic and benzoic acids, and potassium dichromate. Recommended substances, often used commercially, included borax, boracic acid, and formaldehyde! Such compounds were sold to dairies under such trade names as "Freezine" or "Aseptine."[iv] All this was an effort to get around the need to pasteurize.
Pasteurization Finally Succeeds
The early history of pasteurized milk was fraught with difficulty. The process was criticized for destroying the "essential quality" of milk. But, because the practical problems of providing an adequate and reliable supply of safe milk to consumers in large cities was an almost insurmountable technical barrier, milk pasteurization was often done secretly. In New York City, the secret pasteurization of milk was outlawed in 1906, and a city ordinance required that all pasteurized milk be so labeled. Demands were made by many to devise tests to determine if milk was pasteurized. People who believed in the local farmer or even the idea of the family cow felt that raw, untreated milk was better and posed no health risk. Despite the growing public health information regarding the potential for milk to transmit diseases such as tuberculosis, many influential consumers still believed raw milk to be the best. Many people still believe it.
The often-emotional debate over the risks and benefits of pasteurization long delayed its introduction. The overwhelming body of scientific knowledge clearly demonstrated the benefits of pasteurization in the extension of shelf life and the prevention of foodborne diseases.[v] There is little doubt that the spread of this knowledge through the popular press provided both the pressure and incentive for manufacturers and legislators to finally ensure that pasteurized milk was made available to the public. For the first time in history, the food industry, or more correctly, the dairy industry was able to provide consumers with products that were virtually as tasty and nutritious as the fresh, raw product but without the risks associated with their spoilage. By the 1920s, pasteurized milk was common throughout the United States and Canada and was compulsory in most large cities. Unfortunately, the benefits it held for the reduction of disease took considerably longer to be realized in most other parts of the world.
Some Countries Still Do Not Have Pasteurized Milk
One of the very last countries in Europe to enact mandatory pasteurization laws was Scotland. Prior to the enactment of this legislation in 1983, the rate of milkborne Salmonellosis in Scotland was the highest in Europe. A year after pasteurization was made compulsory, Scotland's rate was one of the lowest. A study was then carried out on the remaining incidence of milkborne Salmonellosis in the three-year period following compulsory pasteurization. Of the fifteen outbreaks that occurred, all were in the rural farming communities and none in the general urban population. This was attributed to the fact that milk consumed in the remote farming districts was exempt from the compulsory pasteurization legislation that applied to the rest of the country.[vi]
The Relationship between Pasteurization and Food Irradiation
The historic coincidence in timing between the work on pasteurization and irradiation was not accidental. Once the relationship between spoilage and disease was known, efforts were put in motion to eliminate both menaces. The use of heat was natural for liquids because it could be evenly distributed simply by mixing or stirring. Unfortunately, the problem was not quite so straightforward in the case of solid foods. Heat cannot be transferred and distributed so easily through solids. If you want to use heat to kill salmonella in poultry, you have to cook them completely in order to ensure that any bacteria in the geometric center of the birds are also destroyed. If you want to destroy the sprouting enzymes in potatoes with heat, you have to cook them thoroughly for the same physical reason. This alters the product to such an extent as to make them unmarketable to the general public. Therefore conventional heating techniques could not be applied to solid foods in the same way as they were to liquids. However, any technology that ultimately allowed energy to be transferred quickly and evenly throughout a solid food without appreciably altering it could finally provide the same degree of freedom from foodborne diseases that pasteurization does to liquid foods.
Although the food irradiation technique worked well on solid foods almost a hundred years ago, it was simply not feasible at the time because there were no cheap and practical irradiation sources available then. Had there been, there is no doubt that irradiation would have become as well established a food process as pasteurization. As it happened, when practical irradiation sources finally became available and economically feasible, the public perception of the process was more closely identified with the military rather than the peaceful uses of nuclear energy.
Irradiated Milk
The milk industry provides us with another interesting parallel to food irradiation. The process of milk irradiation was used during the 1930s in order to increase the vitamin D content of milk. By 1935, there were an estimated 35,000,000 consumers of irradiated milk in North America. In addition, over half of the entire production of evaporated milk, which represented 1,000,000 tons of fluid milk, was irradiated. The difference between milk irradiation of the 1930s and food irradiation of today was only the wavelength of the electromagnetic spectrum chosen to carry out the work. Milk irradiation was carried out using ultraviolet (UV) light as the source of ionizing energy rather than gamma rays.
The idea to use this type of irradiation on milk to increase its vitamin D activity derived from the natural action of sunlight upon plants. Sunshine does the same to our skin. The UV radiation in sunlight works by a mechanism of ionization and free radical formation to change a natural steroid called 7-dehydrocholesterol into vitamin D. Rickets is a disease of infancy and childhood where bone hardening is delayed because calcium metabolism is deficient due to a lack of vitamin D. In view of the common occurrence of rickets, it was felt there was a legitimate need for a convenient source of an antirachitic (anti-rickets) factor in foods commonly consumed by children. Although it was theoretically possible to add vitamin D to milk, the available sources were neither cheap nor convenient. Earlier work carried out in the 1920s revealed that certain foods or their original sources, after exposure to light energy of particular wavelengths, had a greater ability to prevent rickets.[vii,viii]
There were also some flavor problems initially, but these were overcome to a point where they were not considered a problem for consumers. (The same flavor problems, which are due to oxidation and not souring, occasionally occur today when bottled milk is left too long on the doorstep exposed to the sun, even if it is cold outside.) Not surprisingly, irradiation of milk with gamma rays comes up against the same flavor problems as with ultraviolet rays and has been solved in the same way. In 1930, inert nitrogen gas was used to eliminate oxidation resulting from ultraviolet irradiation, and the same approach was used almost sixty years later for the irradiation of milk with gamma rays.[ix]
The case of irradiated milk is as close to food irradiation as one can get. The decisions to employ this technology were based upon rational scientific studies and nothing else. It served its purpose until a better technology came along to replace it. Perhaps many readers of this article would have been spared bowed legs if irradiated milk were available to them when they were young. Unfortunately, they were not given the option to have greater protection from disease. And perhaps that is the greatest parallel with food irradiation.
Endotes:
i. Sommer, H.H., Market Milk and Related Products, 3rd Edition, Published by Author, Madison, Wisconsin, 1952.
ii. Pasteur, L., Études Sur Le Vin, L'Imprimerie Impériale, Paris, 1866.
iii. Kilbourne, C.H., The Pasteurization of Milk, John Wiley and Sons, New York, 1916.
iv. Rosenau, M.J., The Milk Question, Haughton Mifflin Company, Boston, 1913.
v. Wiley, H.W., Foods and their Adulteration, 3rd Edition, P. Blakiston's Son and Co., Philadelphia, 1917.
vi. Forbes, G.I., Sharp, J.C.M., Collier, P.W., Reilly, W.J., and Paterson, G. M., Food Epidemiology-Milk Borne Salmonellosis Affecting Farming Communities in Scotland, Environmental Health, 94(10), 269, (1986).
vii. Steenbock, H., The Induction of Growth Promoting and Calcifying Properties in a Ration by Exposure to Light, Science, 60, 224, (1924).
viii. Hess, A.F., Weinstock, M., Antirachitic Properties Imparted to Inert Fluids and to Green Vegetables by Ultra-Violet Radiation, Journal of Biological Chemistry, 62, 301, (1924).
ix. Searle, A.F.J., and McAthey, P., Treatment of Milk by Gamma Irradiation-Effect of Anoxia on Lipid Peroxidation and the Survival of Pseudomonas aeroginosa, Journal of the Science of Food and Agriculture, 48, 361, (1989).
