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From: Food Quality & Safety magazine, April/May 2011

A Key Figure in Food Safety

Louis Pasteur discovered that microorganisms spoil wine and milk

by Lori Valigra

A Key Figure in Food Safety

Mention the name Louis Pasteur (1822-1895), and most people think of the pasteurization process he invented to prevent beverage spoilage. But Pasteur was a true renaissance man, researching, teaching chemistry and physics, and ultimately making discoveries that revolutionized fields such as agriculture, hygiene, and industry.

Often seen as the first modern microbiologist, Pasteur produced the first rabies vaccine, contributed to the founding of medical microbiology with his germ theory of disease, helped solve the mystery of diseased silkworms in mid-19th century France, and invented lab instruments to advance his research. He’s even credited with disproving the outdated theory of spontaneous generation, in which living organisms were thought capable of springing forth from nonliving matter. But, most importantly to the food and beverage industries, Pasteur’s discoveries of the roots of food spoilage and pasteurization helped to bring food safety to where it is today.

“This was a revolutionary idea,” according to Purnendu Vasavada, PhD, food safety specialist in the University of Wisconsin-River Falls Department of Animal and Food Science. “He made an unparalleled contribution in the history of food safety.”

Pasteurization, the process named after Pasteur, applies heat for a specified time to destroy human pathogens in foods and beverages to prevent spoilage.

“Pasteur found that microorganisms were the cause of spoilage in milk and other products such as wine and beer,” said Aaron L. Brody, PhD, president and CEO of the consultancy Packaging/Brody Inc., Duluth, Ga. “Pasteur used a microscope to identify the fact that microorganisms were present. Not much was known in the body of science at that time.”

Dr. Brody called Pasteur the foundation stone in the food safety industry. “If we didn’t know microorganisms were there and that they were the cause of a large percentage of food spoilage, then there would have been no further movement [in the field],” he added. “Nicolas Appert [a confectioner who worked 100 years before Pasteur and discovered that heat and airtight bottles could preserve food—see “The Father of Food Preservation,” Food Quality, February/March 2011] blindly did it without knowing why it worked. Pasteur figured out why it worked. It was seminal work, the microbial theory.”

Later, in 1894, Samuel Cate Prescott and William Lyman Underwood recognized that surviving microorganisms were the cause of spoilage in canned food. “I have a hunch Pasteur’s work was used as the basis for Prescott’s work,” said Dr. Brody. His research also influenced canning and other packaging research and use—and continues to do so.

“The diversity of his research, the brilliance of his intuitions, the rigor of his experimentations, and the importance of the results he obtained dramatically advanced both science and its techniques,” said a document produced by the Pasteur Foundation in New York.

Nonetheless, he didn’t apply his germ theory to all products, according to Dr. Brody, but only to those that were commercially valuable products in France at the time, like wine.

He tackled the theory of spontaneous generation in 1859, and in 1861 discovered anaerobic life. By this time, Pasteur was deeply into the study of fermentation. In 1863, Emperor Napoleon III asked Pasteur to study diseases that spoil wine; he set up a lab in 1864 in Arbois near a vineyard to conduct research.

A Storied Career

Pasteur was born in Dole, France, on Dec. 27, 1822, to a poor tanner. When he was 5, his family moved to Arbois. In 1839, he attended high school at the College Royal in Benancon and received a baccalaureate in letters in 1840 and a baccalaureate in science in 1842, according to information provided by the Pasteur Foundation. In 1843, he was admitted to the Ecole normale supérieure, and he attended the chemistry courses of noted chemist Jean-Baptiste Dumas at the Sorbonne. In 1844, German scientist Eilhard Mitscherlich found that tartaric and paratartaric acids have the same chemical composition and form but affect polarized light differently, a discovery that started Pasteur’s scientific research career, according to the Pasteur Foundation.

In 1847, he defended his theses in chemistry and physics and was awarded his doctor of sciences. His first major discovery, molecular asymmetry, came in 1848. In 1849, the same year as the California Gold Rush, he became acting professor of chemistry at the University of Strasbourg and married Marie Laurent, the university rector’s daughter. Two daughters and one son were born from 1850 to 1853, followed by two more daughters in 1858 and 1863. In 1854, Pasteur was appointed professor of chemistry and dean of the Faculty of Sciences in Lille, France. The following year, according to the Pasteur Foundation, he started his research on fermentation.

He tackled the theory of spontaneous generation in 1859, and in 1861—the year the U.S. Civil War began—he discovered anaerobic life, which does not require oxygen to grow. By this time, Pasteur was deeply into the study of fermentation.

In 1863, Emperor Napoleon III asked Pasteur to study diseases that spoil wine, an important economic product in France, and in 1864 he set up a lab in Arbois near a vineyard to conduct that research. Only a few years later, in 1867, he won the Grand Prize of the Exposition Universelle for what became known as pasteurization, his method of preserving wine by heating it, after publishing a book on the subject the year before.

In 1868, Pasteur suffered a stroke that left him paralyzed on his left side. He opened a new lab in Arbois in 1875 to study fermentation, and the following year tried his hand at politics by entering a Senate race, which he lost. It was in that same year that Alexander Graham Bell invented the telephone in the United States.

After that, Pasteur turned to medical studies, with research on infectious diseases and rabies, and, in 1884, publicized the general principle of vaccinations against infectious diseases, according to the Pasteur Foundation. In December 1885, his rabies vaccination was given to four American boys who traveled to Paris and subsequently returned to the United States in good health. In that same year, the Statue of Liberty was inaugurated in New York.

On his 75th birthday, in 1892, he was honored at the Sorbonne. Pasteur died at Marnes-la-Coquette on Sept. 28, 1895, from complications of a series of strokes, in the same year the Limiere Brothers projected the first moving picture before a public audience in France and Wilhelm Roentgen discovered the X-ray in Germany. Pasteur was a devout Catholic who died with a crucifix in his hand, according to a paper written by University of Memphis Professor King-Thom Chung, PhD, and University of Illinois Professor Deam Hunger Ferris, PhD, titled “Louis Pasteur: The True Master of Microbiology.” His remains are at the Institut Pasteur in Paris.

Pasteur won many awards, including the Grand Croix of the Legion of Honor. Institut Pasteur in Paris and Louis Pasteur University in Strasbourg are named after him. Many streets are named in his honor, including Avenue Louis Pasteur near Harvard Medical School in Boston, and there is a Pasteur Institute in India that is involved in vaccine trials and rabies diagnosis.

H. Daillion (french sculptor, 1854-1937) and G. Débrié (french architect): Louis Pasteur, statue erected in 1901, Arbois, Jura, France.
H. Daillion (french sculptor, 1854-1937) and G. Débrié (french architect): Louis Pasteur, statue erected in 1901, Arbois, Jura, France.

Microorganisms and Spoilage

Pasteur is credited with being the first to understand and show scientifically that fermentation is caused by specific microorganisms, a discovery that also led him to the conclusion that microbes caused diseases. He showed that heat destroyed the microbes that caused spoilage in wine and beer. Pasteur and English surgeon Joseph Lister began corresponding, and Lister based his sterile surgical procedures on Pasteur’s work.

“It’s hard to say if the medical studies or the food work came first,” said Dr. Vasavada. “What causes spoilage? What causes infections? Before Pasteur, it was explained by spontaneous generation. But we would not be where we are in terms of food quality if we did not have Pasteur. He had vision and was ahead of his time.”

Pasteur held public experiments at the University of Paris to show that bacteria caused spoilage, according to a November 1956 article published in Engineering and Science magazine titled “The Origin of Life: A colorful account of the studies man has made in his attempt to discover the fundamental characteristics of living matter,” by Norman H. Horowitz, a Caltech geneticist.

In the first of the three experiments, Pasteur showed that boiling and destroying bacteria in a flask and then letting only sterile air enter it resulted in no bacterial growth. The second experiment showed that bacteria would grow in a medium exposed to dust from the air. The third experiment, perhaps his most famous, used the gooseneck flasks he had invented. For the test, he prepared broth in a regular flask that he had in a flame, from which he pulled it to create a thin gooseneck. He boiled the medium in the flask for several minutes until steam rose in the gooseneck. He then put that flask into an incubator without sealing it and showed that nothing would grow in it.

According to Horowitz, Pasteur explained that when the broth is boiled, the steam rising through the gooseneck drives the air out. When the flame is then turned off, air does come back into the flask, but it is exposed to liquid almost at its boiling point, which can kill the bacteria. As the broth cools, less air comes into the flask because it is trapped in the moist gooseneck, so it never reaches the cool broth. Horowitz noted that the experiments showed that bacteria were not spontaneously generated, as had previously been believed.

“What he did goes to the crux of food spoilage,” said Dr. Vasavada.

Valigra is a freelance writer based in Cambridge, Mass. Reach her at lvaligra@gmail.com.

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