Unlike brewers and bakers yeast, torula yeast made its entry into foods and feeds very late: during World Wars I and II. The best explanation for this is that torula yeast is not used to make breads or beer and wines; it made its debut when there was a shortage of protein and to utilize the by-product containing larger amounts of pentoses.

The name "torula" is derived from its original name: Torulopsis utilis. Later it was re-classified as Candid utilis. There is lot of confusion about torula yeast, some think it is a nutritional yeast; others think that it is used only in animal feeds; few think it is grown to reduce the biological oxygen and chemical oxygen demand of the by-product that is obtained from the paper mills; yet some others think that it is used to replace MSG and as a flavor enhancer. However, not many are aware that it is also used for honey production, aquaculture, as a media additive in industrial fermentation and insect cell culture, or as an attractant for the management of the olive fruit fly. All of these applications are accurate, but it is important to have a clear understanding about the differences of torula yeast that is grown on a by-product and primary grown torula yeast that is grown on a refined sugar feed stocks such as corn syrup, glucose, or alcohol.

The quality of torula yeast is very much dependent on the substrates and production methods employed. For example, sometimes it may have fungus Pichia jadinti, which may be grown on wood sugars from paper mill wastes. The quality and concentration of protein and vitamins is superior when torula yeast is grown on the wood hydrolysate containing pure sugars as a substrate compared to by-products such as spent sulfite liquor and molasses.See the table below for composition of torula yeast that is grown on various substrates:

It is interesting to note that the first commercial production of torula yeast was started in Germany during WWI from the by-product spent sulfite liquor (SSL; for more information see the NF Wiki). Prof. Fink in Germany first reported that torula yeast could be grown on SSL, which has significant amounts of pentoses that are not easily metabolized by S.cerevisiae. The process for commercial manufacturing of torula yeast is known as Waldhof process (using Waldhof fermentor) and has been used in United States also. Several scientists all over the world including the Forest Products Laboratory, later modified this process. If you would like more information about the process or references for the applications listed below, please contact the Site Administrator.

As the applications of torula yeast have gone beyond the feed industry, modern manufacturers in US and other countries are producing primary grown torula yeast utilizing refined sugar feed stocks or alcohol ensuring pure yeast and consistency batch after batch, unlike that of torula yeast made using by-products.

Why is torula yeast so much in use when brewers and bakers yeast are available?

• Torula yeast is relatively easy to maintain, grow quickly, has the ability to utilize pentose sugars, excellent nutritional properties, and has been accepted all over the world as a safe and wholesome food and feed.
• Torula Yeast contains relatively higher amounts of nucleotides, especially RNA, that help to enhance flavors. Some companies have isolated torula yeast strains to make extracts with exceptionally high amounts of 20% IMP+GMP (Inositol Mono Phosphate and Guanosine Mono Phosphate). Since it is all naturally occurring, it can be labeled as yeast extract while still providing the powerful flavoring effect of nucleotides.
• Torula yeast has a very clean flavor profile and does not come with bitter/strange taste like regular yeast extract. It can be used without tainting your overall flavor as it reaches the threshold of flavor enhancement.
• Because of its high nucleotide content, torula is a good source for pet foods, especially for cats.
• Torula yeast was found to be the most palatable feed when fed individually into one beehive at a time.
• Torula yeast was superior to the soybean meal or brewers' yeast for chick growth when fed on a ten percent level in the feed.
• One study observed that when torula yeast is supplemented with methionine the results were almost comparable to that of casein when fed to the adult rats:

  Net protein digestibility and growth promoting values of Bakers, Brewers and Torula Yeast
  
  Adapted from J. Nutrition, 517-526, 1949

• In another study the results suggest that it is possible to replace up to 65% of animal protein with a mixture of plant proteins, including 30% from torula yeast, in tilapia fry diets without adverse effects on fish performance and culture profit.
• The two most important factors to be considered in animal feeds are: the protein hydrolysis (degradability) and their digestion in the intestine. One study found that the protein hydrolysis into peptides and amino acids of torula yeast is much higher (70%) compared to that of soybean meal (59%) bone & meat meal (50%) and fish meal (50%). However, the intestinal digestibility is relatively lower for torula yeast (87%) compared to that of soybean meal (98%) bone & meat meal (70%) and fish meal (94%):

  

• Torula yeast provides nutritional benefits, enhances flavor as well as improves palatability and is economical to use.
• Torula Yeast is used in dry and canned pet foods, moist pet treats and animal feeds.
• Torula yeast is used Foods: Gravies, soups, sauces,
• The most important aspect one should consider in manufacturing torula yeast is the strain and media as they greatly influence the flavor profile and palatability.

To learn more about yeast extract flavors in the food industry follow this link

In closing, I must say that based on the scientific studies the digestibility of torula yeast is relatively higher compared to soybean, fish meal, bone and meat meal. Absorption of the digested proteins (peptides and amino acids) is closer to that of the fish meal and higher than bone and meat meal products. Further, the unique characteristics of torula yeast (by itself neutral in flavor) give it the potential to enhance flavors in any applications, unlike brewers yeast which is bitter and astringent. Torula yeast is highly palatable and not thoroughly exploited in the feed industry.

Comments (3)
Vijai Pasupuleti,   March 17th, 2008