As we just enjoyed the holidays, good food, music, movies and alcoholic and non-alcoholic drinks I thought it would be appropriate to look at yeast, yeast varieties used for foods and drinks, and their use in animal feeds.
History and Types of Yeast
In Egypt as early as 4000 B.C. yeast has been used in the preparation of food and drink but it was only in the 19th century that the role of yeast in fermentation was clearly established by Pasteur, and only in the past few decades that yeast has been genetically modified to make value added chemicals, pharmaceutical drugs, etc.
There are several types of yeast available in the market, such as brewers yeast, sake yeast (Japanese alcoholic beverage made from rice sometimes referred to as "rice wine"), wine yeast, bakers yeast, and distillers yeast (obtained after ethanol by wet mill process). All of these are S.cerevisiae, Torula yeast (Candida utilis) and Lactic yeast (Kluyveromyces lactis). There are several other yeasts (for example methylotrophic yeast) that do not need glucose feedstock but can be easily grown on methane or methanol. However, methylotrophic yeast is typically used to modify the yeast cells to produce chemicals, drugs and enzymes. An interesting development with yeast is that they can be grown with chromium and selenium (antioxidant) so that these minerals are delivered biologically more effectively through yeast.
Yet another category of yeast called "osmophilic yeast" such as Zygosaccharomyces rouxii, Pichia farinos can tolerate higher concentrations of salt and sugars and can survive in low water activity environments such as jelly and jams. There are also some pathogenic yeasts which bring the bad press and commonly referred to as "yeast infection".
Yeast Uses
There are countless uses for yeast, however, the majority of the yeast and yeast extracts are used in a variety of foods such as baking, brewing, or used as flavor enhancers (an essential ingredient in replacing MSG), bioremediation, production of biochemicals, drugs, as probiotics, or as nutritional supplements. In other words we are dependent on yeast for our delicious food, drinks, and good nutrition for human beings and animals.
Manufacturing of Yeast
I am not detailing the manufacturing process of yeast here but would like to highlight the sources of yeast and their effect on consistency. Most yeast products are made from the by-products with the exception of some bakers and torula yeast. The yeast that are grown on glucose feedstock are known as the "primary grown" in other words the yeast is primarily grown for food/feed applications. The whole process starting from the raw materials are well controlled therefore, the yeast is expected to be more consistent unlike brewers yeast.
Brewers yeast is a by-product of alcohol fermentation and may not be consistent (not all brewers yeast are same, varies from brewery to brewery or sometimes within the same brewery depending on the type), and so is the yeast and yeast extracts made from them.
The feedstock for yeast varies and it is important because some of the constituents are carried along with the yeast and to the yeast extracts. For example:
- Brazil pretty much uses sugarcane molasses.
- Brewers yeast carries with it some of the metabolites from hops.
- Distillers yeast carries some of the metabolites from corn steep (wet milling process).
- Kluyveromyces carries soluble constituents from whey.
- Torula yeast is manufactured from the by-product of paper companies brings along some sulfites. However, a very few companies grow torula yeast on a glucose feedstock as "Primary Grown".
I will be discussing in detail about the yeast autolyzates, yeast extracts and yeast cell walls and their applications in the near future.
- Follow this link for one of the earlier reports of yeast feeding to lactating cows. Not a positive one but it is interesting to see scientific papers on yeast in animal feeds from 1924. http://jds.fass.org/cgi/reprint/8/2/89.pdf
- Follow this link as how yeast is contributing to the modern medicine. http://nobelprize.org/nobel_prizes/chemistry/laureates/2006/illpres/2_yeast.html
- Follow this link as how a Nobel Laureate used yeast cells http://nobelprize.org/nobel_prizes/medicine/laureates/2001/press.html
Vijai Pasupuleti, January 7th, 2008