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Nutritional Yeasts and Yeastophobia: An interview with Dr Seymour Pomper
By Richard A. Passwater, Ph.D.
Letters. We got letters. The recent interview with cancer researcher Dr. Larry Clark and yeast expert Dr. Lon Baugh sparked many letters asking about nutritional yeasts in general. In this column, we'll address many of these issues, including a comparison of yeasts that are appropriate for human use and those that may be harmful.
There are "good" yeasts and "bad" yeasts in much the same manner as there are "good" and "bad" bacteria, "good" and "bad" fats and "good" and "bad" cholesterol. In the case of the first example, we use probiotics-"good" bacteria-to replenish and/or maintain the population of the "good" bacteria in our gut that help maintain the healthy intestinal environment and reduce the chances of overpopulation by "bad" bacteria.
Although the yeast scenario is not exactly parallel to that of bacteria, suffice it to say that there are indeed both "good" and "bad" yeasts, the former offering numerous benefits to human health, while the latter often are the cause of pesky, even dangerous, infections.
We always should remember that nutritional yeasts, along with wheat germ and wheat germ oil, black strap molasses and yogurt, were once one of the four cornerstones of the health food movement. They were the reliable super-foods of the "good old days." Nutritional yeasts (brewer's yeast and baker's yeast) were a primary source of B-vitamins and minerals in the days before vitamin concentration, and today several important nutritional yeast products are available.
In 1996, there came dramatic news. Dr. Clark had conducted a clinical study indicating that an organically bound high selenium yeast supplement (SelenoPrecise) cut the cancer death rate in half. Once again, great interest arose in nutritional yeasts. More recently, reports that Chinese red yeast grown on rice reduces blood cholesterol levels have spurred this renewed interest in nutritional yeasts to even higher levels.
To answer the many questions that I received about nutritional yeasts, I have called upon yeast expert Dr. Seymour Pomper. He will share some of his broad knowledge of yeasts with us. Dr. Pomper is a well-known and respected authority on yeast with approximately 40 years of experience working with industrial food applications of yeast (Saccharomyces cerevisiae). Dr. Pomper received his B.S. in bacteriology from Cornell University and his M.S. and Ph.D. in microbiology and genetics from Yale University He now is retired and lives in Stamford, CZ: While at the Oak Ridge National Laboratory in Tennessee, he conducted radiation studies on yeast and researched yeast genetics and yeast mutants.
Dr. Pomper holds 10 U.S. patents and has published some 20 research papers on yeast. He has written yeast-related chapters in two books and has lectured widely on yeast technology. He also served as the research director of Fleischmann's Yeast while it was a division of Standard Brands.
Passwater: Dr. Pomper, in order to understand the benefits of using yeasts in industry and, in particular, in nutraceutical products, it may be helpful for everyone to understand what yeasts are. Can you provide us with a general understanding of yeasts?
Pomper: Yeasts are unicellular, non-photosynthetic fungi. So, in the broad sense, they belong to the plant kingdom. A typical baker's yeast cell measures about 5 x 7 microns. Yeasts typically reproduce by budding. Yeasts are everywhere in nature. So called wild yeasts, i.e. not cultured yeasts, can be found on fruits, plants, vegetables, etc.
The strains of yeast used commercially, e.g. in the baking industry or the nutraceutical industry, represent, in many cases, generations of selection for particular properties. The species of yeast used in baking and, in many instances nutraceutical, is Saccharomyces cerevisiae. There are many strains of this yeast, again selected over many years for particular properties of fermentation, yield, etc. The strains of yeast used today are direct descendants of the yeast first introduced into the baking industry in the U.S. more than 100 years ago.
Taxonomically, yeasts can be divided into two broad categories-those that can form ascospores and those that cannot. While yeasts usually reproduce by budding (an asexual form of reproduction), sonic have the ability to reproduce sexually through the formation of ascospores. Saccharomyces cerevisiae is an example of an ascosporogenous yeast, while Candida utilis is representative of anascosporogenous yeasts. This is a very fundamental taxonomic difference. Some yeasts, such as Candida, also are characterized by forming mycelial type growth under appropriate conditions, very much like their cousins, the true Molds.
Passwater: Many people are not clear on the difference between yeasts and molds, yet these two organisms are distinctly different from each other. Can you help us understand some of the differences?
Pomper: Both yeasts and molds belong to the kingdom of the fungi. To that extent, yeasts and molds are related. The principal difference between yeasts and molds is that the true yeasts, such as S. cerevisiae, reproduce asexually solely by budding. Molds, on the other hand, reproduce asexually by forming strands of growth called hyphae or mycelia. Saccharomyces cerevisiae reproduces sexually by forming enclosed spores (ascospores), whereas molds typically reproduce sexually by forming external spores.
Passwater: Can you provide a brief history on the production and utilization of yeast?
Pomper: The action of yeast in the fermentation of wine and beer and in the leavening of dough has been known for 4,000 to 5,000 years, or perhaps more. The role of an active leavening principle already was known in ancient Egypt-witness the exodus of the Jews from Egypt with unleavened bread. Also, it is referred to in ancient mythology, e.g. the "mead" of the gods. In the 17th century, Leeuwenhoek, using a crude microscope, was able to describe and draw yeast cells in fermenting liquid. In the 18th century, Krunitz published an encyclopedia on yeast, and recognized the importance of culturing the yeast for best results. In the 19th century, Fleischmann's introduced the use of pure yeast cultures in the U.S. baking industry. Today, pure culture yeast (strains of Saccharomyces cerevisiae) are used in the baking and brewing industries worldwide. An authoritative reference on yeast technology in various fermentation industries (wine making, cider-making, brewing, distillery practice, baking) is The Yeasts, volume :1, edited by A.H. Rose and J.S. Harrison.
Passwater: In the nutraceutical industry we are aware of the use of inactive yeast (Saccharomyces cerevisiae) as a carrier liar minerals, vitamins and other compounds. Call you discuss what characteristics make yeast so versatile in its traditional uses?
Pomper: Saccharomyces cerevisiae is the organism used in the baking and brewing industries. Different strains of this species have slightly different characteristics that make them uniquely suitable for different applications.
Thus, a strain with a higher than normal tolerance for ethanol would be used in the brewing and distillery industries, and a strain with a higher than normal tolerance for high concentrations of sugar might be used in the production of sweet baked goods.
Passwater: Many of our readers are familiar with the term "common yeast." Unfortunately, this term tends to leave the general public with the impression that all yeasts are the same. Can you draw any distinctions between the various yeast strains and the misnomer related to the term "common yeast?"
Pomper: There are variations among strains of S. cerevisiae, as indicated in my previous answer. There are wide differences among different genera and species of yeasts. Differences in the ability to utilize different carbohydrate sources or nitrogen sources, as well as in the end products of metabolism, are common among the various yeast genera.
One of the interesting differences between Saccharomyces cerevisiae and Candida utilis lies in the issue of potential human pathogenicity. I am not aware of any strains of S. cerevisiae that have ever been shown to be pathogenic for humans. Whereas some strains of Candida utilis have been implicated in disease. This serves to illustrate why the term "yeast" should not be applied too broadly, not when one "yeast" (S. cerevisiae) has been a servant of mankind for thousands of years and another "yeast" (Candida utilis) may cause disease.
Passwater: In the nutraceutical supplement industry there are many products that contain yeast. Most of the high-quality products are marketed as primary grown yeast while others say they are secondary yeast products. Would you please take a moment to explain what the difference is between these two types of yeast?
Pomper: Primary y grown yeast refers to yeast that hits been grown for the sake of its cell mass. Baker's yeast is a perfect example of primary grown yeast. The cells are harvested and used in the baking process.
Some yeast grown for the nutraceutical market also is an example of primary grown yeast. This yeast is grown from a pure culture slant specifically to be used as a carrier of supplemented items, such as minerals. An example of is secondary, or by-product yeast is that used in the brewing industry. In this application, the yeast cell mass is not of importance per se, but rather the characteristics of the mash in which the yeast fermented. The conditions of fermentation are set to favor production of an end product rather than that of producing the yeast itself.
Passwater: When reviewing the labels of many products that contain yeast, one finds that the term "inactive yeast" is very common. Would you please tell the readers what inactive yeast is and how it is different from active yeast?
Pomper: When one refers to yeast as being active it means that is has its full complement of enzyme activities and is able to grow in a suitable environment. An inactive yeast product is one that no longer has the ability to reproduce or ferment. An active yeast may be rendered inactive by several methods, one of which is heat used in the pasteurization and spray drying processes. Another example of this is the bread baking process, in which active yeast is rendered inactive by the heat of the oven.
Passwater: When we consume yeast (Saccharomyces cerevisiae) in breads, alcohols or nutraceuticals, is it dead or alive?
Pomper: Unequivocally, the yeast in bread and alcohol-containing beverages such as wine or liquor is (lead. The yeast in nutraceuticals also is dead, since the yeast manufacturing process involves a high-temperature, short-dwell sterilization of the cream yeast immediately prior to spray drying. This can be confirmed by a simple microbial analysis for specifications established by the government.
Passwater: As you have already discussed, Saccharomyces cerevisiae is inactive when it is consumed in breads, alcohols, and nutraceuticals. How does inactive Saccharomyces cerevisiae differ from the pathogenic genera of Candida?
Pomper: S. cerevisiae belongs to the group of ascosporogenous yeasts; i.e. these yeasts have the ability to form ascospores. Candida belongs to tile group described its anascosporogenous Yeasts, i.e. those that do not form ascospores.
In addition to this fundamental taxonomic difference, there are many metabolic differences including such things as the ability of many Candida strains to use sources of nitrogen and carbon that S. cerevisiae cannot. Candida is basically an aerobic organism, and under appropriate conditions may develop mycelia. S. cerevisiae is a facultative anaerobe; i.e. it can metabolize either in the presence or absence of oxygen, and it does not have a mycelial growth pattern. Strains of Candida tend to produce a greater variety of end products than do strains of S. cerevisiae (which basically produces ethanol and carbon dioxide under anaerobic conditions, and carbon dioxide and water under aerobic conditions).
Passwater: Over the course of history, have we learned anything about consuming large quantities of live yeast? Has the government issued warnings about consuming live yeast?
Pomper: Years ago, eating live yeast was promoted as beneficial in terms of nutrients and laxative effects. More recent medical research indicated that the ingestion of large amounts of live yeast was not only not beneficial, but might have a deleterious effect. There was an indication that the ingestion of live yeast led to the scavenging of B-vitamins by the yeast, so that there was no benefit to the body.
Passwater: Can inactive Saccharomyces cerevisiae yeast products propagate in the human body?
Pomper: No. By definition, an inactive yeast is dead and has lost its ability to reproduce in or out of the human body.
Passwater: Are there any known diseases caused by active or inactive S. cerevisiae?
Pomper: I would say no. In almost 40 years in the yeast industry I have never encountered a confirmed case of anyone suffering a disease from S. cerevisiae.
Passwater: Is S. cerevisiae considered Generally Regarded As Safe (GRAS)? Also, does this status apply to C. albicans?
Pomper: I believe that use of S. cerevisiae precedes the notion of GRAS, and the issue never was raised in the industry. I do not know about C. albicans. There may be a reference in the Federal Register or the US Pharmacopoeia on this.
Passwater: The yeast used in nutraceuticals is tested to meet all United States Department of Agriculture/Food and Drug Administration (USDA/FDA) requirements. Can you explain this?
Pomper: I do not have available current USDA/FDA requirements. However, in the past these have dealt primarily with issues of cleanliness, e.g. freedom from contaminating pathogens such as Salmonella.
Yeast intended for nutritional purposes has to meet whatever standards of composition the regulations specify. For example, moisture, protein and phosphate contents must be within a certain range. I would expect that for nutraceuticals the specifications would call for a product essentially free of live yeast cells. For selenium-containing yeast products, I would expect that chemical analysis of every batch would confirm the presence of at least the specified amount of selenium. The results of these laboratory analyses typically are reported in the certificate of analysis supplied by the raw material manufacturer.
Passwater: Dr. Pomper, I would like to thank you for taking the time to provide your expertise related to the varied historical uses of Saccharomyces cerevisiae and
their versatile nutritional and industrial purposes. This review has given us a broader understanding of yeast and reminded us that nutritional yeast products are still an excellent source of nutrition today. In preparation for next month's column, I would like to call special attention to your discussion of the genetic and physical differences between Saccharomyces cerevisiae and Candida.
Next month, we will continue on the subject of "Nutritional Yeast and Yeastophobia" through an interview with Dr. Tack Sobel of Wayne State University. Dr. Sobel is an expert on infectious disease, with an emphasis on Candida-related illnesses. Dr. Sobel will discuss Candida, Saccharomyces cerevisiae and their frequently misunderstood interrelationship as regards their functional utilization and disease status. WF
© 1999 Whole Foods Magazine and Richard A. Passwater, Ph.D.
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