Local manufacture of yeast, a viable proposition

By Dr. Tilak Nagodawithana

In a country like Sri Lanka where rice has been the staple food for centuries, it is not surprising to find that the per capita consumption of bread and for other bakery goods has remained low over the years, relative to those of developed nations.

Yeast, as we know, is the key ingredient needed to provide the flavour nuances and the leavening power to provide the familiar bread matrix. With dwindling bread consumption, the disappointing market potential it has created for yeast in Sri Lanka, is thus understandable.

Following the end of 30 years of terrorism, a handful of entrepreneurs showed interest in filling this void by exploring the possibility of building production facilities. But all such surveys carried out stopped in their tracks primarily due to the limited captive markets in Sri Lanka.

In recent years this situation has worsened with the increase of wheat prices in the world market. An additional issue which can be less important but nevertheless critical is a possible shortage for locally produced molasses. This is the substrate for making yeast and is being used extensively for making alcoholic drinks which ironically, in Sri Lanka has immediate payback.

Currently, the entire supply of yeast and yeast related products are imported. As a result, there is a substantial foreign exchange drain which can easily be avoided by investing on yeast production facilities in areas where sugar cane plantations are expanding.

Discovered by Egyptians

This report, therefore, is to bring the reader's attention to other far reaching goals yeast manufacturers in the developed world already have in place, for increasing their product lines and thereby improving their profitability.

Yeast is, without doubt, the most important group of microorganisms commercially exploited and safely consumed by mankind today.

Many authorities believe that Egyptians discovered the extraordinary properties of yeast 6,000 years ago when some freshly crushed grapes left exposed to air turned into a pleasant and intoxicating beverage which they subsequently named as wine.

The early 'Oenologists' quite accidentally found out that when they carefully scraped the white sediment that fell to the bottom of every batch of wine and added to the next batch of fresh juice, the wine made second time was as good as the previous batch. After these humble beginnings, production of wine and subsequently beer developed as an art and craft in complete absence of scientific know-how.

Legend has it that it did not take too long before some enterprising baker of flatbread, added a portion of a primitive wine sediment to his dough, looking to improve its quality. To his surprise, the dough leavened (puffed) and improved the flavour and texture of flatbread. The twin art of baking and wine making and subsequently brewing then became profitable ventures within communities at the time without any understanding of the basic principles associated with such processes.

The very existence of the microbial world was unknown to mankind until the microscope was invented by a Dutch lens grinder, A van Leeuwenhoek in 1680. He first observed the microbial world when he examined a drop of fermenting beer through a handmade single lens microscope. However, the work he brilliantly began was not extended for over a century.

Finally, in 1850s, Louis Pasture discovered that these changes in composition of 'wine' are as a result of metabolic changes in sugary media, caused by the action of live yeast.

These painstaking studies by Pasteur followed by his brilliant interpretations of his results gave the world the basic knowledge upon which most of our modern industrial biotechnology has been built.

Yeasts are represented by numerous strains that were chosen and adapted for specific industrial fermentation. They include Baker's yeast, wine yeast, top and bottom fermenting brewer's yeast and distiller's strains used for alcohol production from molasses and other sugary materials.

Strain improvement

Strain improvement by conventional methods, genetic manipulation and protoplast fusion has contributed superior strains for the aforementioned processes.

Earliest commercial production of Baker's yeast probably occurred in Holland around the early 1780s. In their process, sugar solution was slowly fed to an aerated suspension of yeast and the process was named as Zulaufer/fahren.

This process was widely accepted by not only the yeast manufacturers but the entire fermentation industry as an incremental feeding or fed-batch process.

Thus the baker's yeast industry has contributed greatly to the entire fermentation industry by the introduction of the fed-batch process which now has wide application in the production of organic acids, amino acids, enzymes, vitamins, and in the antibiotic industry.

In general, there are five to seven stages of propagations, progressively getting larger in volume with every change of stage, in the production of Bakers' yeast: the laboratory stage in which the pure culture from slants is transferred to growth flasks; then to two to three stages of set batch (substrate and nutrients all in) where the contents of the preceding stages are transferred through sterile piping to the succeeding stages of increasing volume; then to two stages of fed-batch (incremental sugar feeding) fermentations and finally the commercial stage which often carries 50,000 gallons of fermenting liquid.

The final content is eventually centrifuged, and the separated cream is pressed and sold as pressed cake or turned to noodles and dried in air-lift dryers to produce Active Dry Yeast (ADY). Yeast production is important not only for baking, brewing and distillery fermentation but also for the production of a variety of value added products.

Lucrative market

In this category, the most important segment is the flavour and flavour enhancing yeast extracts which are gaining immense popularity in the vastly expanding food industry. There is a high demand for yeast extracts in the fermentation industry as a cost effective microbial growth nutrient.

Adding yeast extracts to complex media to improve their nutritional properties is way to reduce the cost of production of a variety of products such as in the manufacture of drugs, antibiotics, enzymes, hormones, citric acids, and other important organic chemicals, where microbial fermentation is the standard production procedure.

Yeast extract is a concentrate of soluble material derived from yeast following hydrolysis of the cell material, particularly the proteins, soluble carbohydrates, and nucleic acid. This is generally carried out by use of its own hydrolytic enzymes (autolysis) or added enzymes to release the cell contents in a highly degraded form.

As in the case of fermentation industries, different quality and varying composition yeast extracts are now available in the market to meet the complex needs of food industries. Such extracts made through reaction flavour technology are capable of producing beafy, chickeny, cheesy, or fish-like flavours without ever adding the animal source and are in high demand for making food formulations to vegetarians.

Driving force

From the 1950s taste has continued to be the driving force in the food processing industry. Therefore, the success of the food products will be largely influenced by the correct choice of the flavour deliver system. Monosodium glutamate (MSG originated in Japan) has for some time, been the principle flavour enhancer used in the formulations of soups, sauces and gravies.

However, in the 1960s, when certain small percentage of the population was beginning to report certain health problems following the use of MSG, scientists developed two other products called 5'-inosine monophosphate and 5'-guanosine monophosphate (5'-IMP and 5'-GMP) that could provide the same or even higher flavour enhancing properties without causing health problems.

The negative publicity against MSG in the media created an increased demand for 5'- nucleotide-rich, natural flavour enhancers. Yeast being typically high in RNA content which is the prerequisite for 5'-nucleotide production, became an obvious choice for the production of natural 5'- nucleotides-rich yeast extracts.

Today, the market is flooded with yeast extracts containing different levels of 5'-nucleotides, thereby gradually replacing the once popular MSG among food formulators.

In the meantime, the medical community has begun to show that high consumption of salt or sodium is largely responsible for the cardiovascular diseases among many.

The food industry has reacted to this by requesting flavour ingredient suppliers to supply salt or sodium replacers. Currently, 5'-nucleotide rich yeast extracts are extensively used not only as a savoury flavour enhancer but also in food formulations to reduce salt or sodium or as bitter blockers.

In case where salt (NaCl) is replaced by Potassium chloride (KCl), the bitter and metallic taste of potassium (K) is generally masked by yeast extracts made to contain high levels of Adenosine monophosphate (AMP).

Yeast based ingredients project a natural ingredient label appeal and in this era of food label concerns, yeast-based products serve as a relief for many food formulators and the public.

Dietary fibre

Another product made from yeast is a dietary fibre isolated and purified from the yeast cell wall. .

The therapeutic effect of beta glucan has primarily been due to the stimulation of the reticular endothelial system (RES), which in turn produces increased amounts of antibodies against invading pathogens which is the key role in the body's natural immune system.

Hence, it prepares the body to fight infections by acting like a broad spectrum antibiotic. With banning of four antibiotics used in poultry feed in EU countries, beta glucan has now taken their place as a replacement to control the common pathogenic bacteria to improve and maintain the health of livestock.

The yeast flavour may be pleasant to some, or indifferent or less than desirable to others. However, it is not used as a flavour but because of their nutritional contributions of protein, and vitamin B1.

In such cases, the yeasts are killed by pasteurisation, made into a powder by spray drying and often tableted for convenient use. Research done more than six decades ago, reveals that certain nutritional deficient diets showed impaired tolerance to blood sugar (as in type 2 diabetics).

Today, there are yeast products with organically bound Selenium in the form of Selenomethionine, produced per this writer's US Patent, for use as nutritional supplements. In this regard, it must be mentioned that high levels of elemental Selenium is toxic to human.

Biochemistry

Modern biochemistry and molecular biology, related to the study of enzymes, among other things, was also born off yeast.

In 1978 came the first breakthrough in yeast genetic with the introduction of a technique called transformation. The molecular biologists responsible for this pioneering work managed to insert a foreign gene into the yeast genome through the use of a vector (transport carrier called plasmid) containing the foreign gene.

Yeast is helping immensely to uncover the biochemistry and regulation of human genes and it is fairly straightforward to predict where along the biochemical pathways to intervene. It is still premature to predict that yeast will show the way to the cure of life threatening human diseases. But given the role that yeast has played thus far in identifying human health problems, it is not safe to count out that possibility.

With yeast technology advancing in leaps and bounds, we see that the yeast which was once only good for baking bread is now fast becoming a force to be reckoned with.

We, as Sri Lankans, should jump into the band wagon even at this late stage to get familiarised with what is progressing in biotechnology and molecular biology with special emphasis on yeast. If we fail to do so, we could miss some lucrative business opportunities in this competitive world.

The writer is the President of Esteekay Associates Inc., Milwaukee.