ArticlePDF Available

Production of Food Grade Yeasts



Summary Yeasts have been known to humans for thousands of years as they have been used in traditional fermentation processes like wine, beer and bread making. Today, yeasts are also used as alternative sources of high nutritional value proteins, enzymes and vitamins, and have numerous applications in the health food industry as food additives, conditioners and flavouring agents, for the production of microbiology media and extracts, as well as livestock feeds. Modern scientific advances allow the isolation, construction and industrial production of new yeast strains to satisfy the specific demands of the food industry. Types of commercial food grade yeasts, industrial production processes and raw materials are highlighted. Aspects of yeast metabolism, with respect to carbohydrate utilization, nutri- tional aspects and recent research advances are also discussed.
ISSN 1330-9862 review
Production of Food Grade Yeasts
Argyro Bekatorou*, Costas Psarianos and Athanasios A. Koutinas
Food Biotechnology Group, Department of Chemistry, University of Patras, GR-26500 Patras, Greece
Received: January 30, 2006
Accepted: March 20, 2006
Yeasts have been known to humans for thousands of years as they have been used in
traditional fermentation processes like wine, beer and bread making. Today, yeasts are also
used as alternative sources of high nutritional value proteins, enzymes and vitamins, and
have numerous applications in the health food industry as food additives, conditioners
and flavouring agents, for the production of microbiology media and extracts, as well as
livestock feeds. Modern scientific advances allow the isolation, construction and industrial
production of new yeast strains to satisfy the specific demands of the food industry. Types
of commer cial food grade yeasts, industrial production processes and raw materials are
highlighted. Aspects of yeast metabolism, with respect to carbohydrate utilization, nutri-
tional aspects and recent research advances are also discussed.
Key words: food grade yeasts, single cell proteins (SCP), raw materials, propagation, baker’s
yeast, brewer’s yeast, distiller’s yeast, Torula, whey, kefir, probiotics
Yeasts are a group of unicellular microorganisms most
of which belong to the fungi division of Ascomycota and
Fungi imperfecti. Yeasts have been known to humans for
thousands of years as they have been used in fermenta
tion processes like the production of alcoholic beverages
and bread leavening. The industrial production and com
mercial use of yeasts started at the end of the 19th cen
tury after their identification and isolation by Pasteur. To
day, the scientific knowledge and technology allow the
isolation, construction and industrial production of yeast
strains with specific properties to satisfy the demands of
the baking and fermentation industry (beer, wine, cider
and distillates). Food grade yeasts are also used as sources
of high nutritional value proteins, enzymes and vitamins,
with applications in the health food industry as nutri
tional supplements, as food additives, conditioners and
flavouring agents, for the production of microbiology me
dia, as well as livestock feeds. Yeasts are included in start
er cultures, for the production of specific types of fer
mented foods like cheese, bread, sourdoughs, fermented
meat and vegetable products, vinegar, etc.
The significance of yeasts in food technology as well
as in human nutrition, as alternative sources of protein
to cover the demands in a world of low agricultural pro
duction and rapidly increasing population, makes the
production of food grade yeasts extremely important. A
large part of the earth’s population is malnourished, due
to poverty and inadequate distribution of food. Scien
tists are concerned whether the food supply can keep up
with the pace of the world population increase, with
the increasing demands for energy, the ratio of land area
required for global food supply or production of bio
energy, the availability of raw materials, as well as the
maintenance of wild biodiversity (1–4). Therefor e, the pro
duction of microbial biomass for food consumption is a
main concern for the industry and the scientific commu
The impressive advantages of microorganisms for
single cell protein (SCP) production compared with con
ventional sources of protein (soybeans or meat) are well
known. Microorganisms have high protein content and
short growth times, leading to rapid biomass production,
which can be continuous and is independent from the
environmental conditions. The use of fungi, especially
A. BEKATOROU et al.: Food Grade Yeasts, Food Technol. Biotechnol. 44 (3) 407–415 (2006)
*Corresponding author; Phone: ++30 2610 997 123; Fax: ++30 2610 997 105; E-mail:
yeasts, for SCP production is more convenient, as they
can be easily propagated using cheap raw materials and
easily harvested due to their bigger cell sizes and floc
culation abilities. Moreover, they contain lower amounts
of nucleic acids than bacteria (5–7).
Yeast Metabolism
Yeasts are facultative anaerobes, and can grow with
or without oxygen. In the presence of oxygen, they con
vert sugars to CO
, energy and biomass. In anaerobic con
ditions, as in alcoholic fermentation, yeasts do not grow
efficiently, and sugars are converted to intermediate by-
-products such as ethanol, glycerol and CO
. Therefore,
in yeast propagation, the supply of air is necessary for
optimum biomass production. The main carbon and
energy source for most yeasts is glucose, which is con
verted via the glycolytic pathway to pyruvate and by the
Krebs cycle to anabolites and energy in the form of ATP.
Yeasts are classified according to their modes of further
energy production from pyruvate: respiration and fermen
tation. These processes are regulated by environmental
factors, mainly glucose and oxygen concentrations. In res
piration, pyruvate is decarboxylated in the mitochond
rion to acetyl-CoA which is completely oxidized in the
citric acid cycle to CO
, energy and intermediates to pro-
mote yeast growth. In anaerobic conditions, glucose is
slowly utilized to produce the energy required just to
keep the yeast cell alive. This process is called fermen-
tation, in which the sugars are not completely oxidized
to CO
and ethanol. When the yeast cell is exposed to
high glucose concentrations, catabolite repression occurs,
during which gene expression and synthesis of respira-
tory enzymes are repressed, and fermentation prevails
over respiration. In industrial practice, catabolite repres-
sion by glucose and sucrose, also known as Crabtree ef-
fect, may lead to several problems, such as incomplete
fermentation, development of off-flavours and undesirable
by-products as well as loss of biomass yield and yeast
vitality (8–10).
Yeasts can metabolize various carbon substrates but
mainly utilize sugars such as glucose, sucrose and malt
ose. Sucrose is metabolized after hydrolysis into glucose
and fructose by the extracellular enzyme invertase. Mal
tose is transferred in the cell by maltose permease, and
metabolized after hydrolysis into two molecules of glu
cose by maltase. Some yeasts can utilize a number of
unconventional carbon sources, such as biopolymers,
pentoses, alcohols, polyols, hydrocarbons, fatty acids and
organic acids, which is of particular interest to food and
environmental biotechnologists. For example, lactose can
be utilized by yeasts that have the enzyme b-galactosi
dase. The yeasts of genera Kluyveromyces and Candida can
grow e.g. in whey, yielding biomass under certain condi
tions, with applications in food production. Biopolymers
like starch, cellulose, hemicellulose and pectin can be
metabolized by some yeasts directly, or after hydrolysis
by non-yeast enzymes. Some yeast species of Hansenula,
Pichia, Candida and Torulopsis are also able to grow on
methanol as sole energy and carbon source. The inabil
ity of yeasts to ferment certain sugars can be overcome
by r-DNA technology, introducing genes of the corre
sponding enzymes from other species (8,11). Finally, ele
ments like N, P, S, Fe, Cu, Zn and Mn are essential to all
yeasts and are usually added to the growth media. Most
yeasts are capable of assimilating directly ammonium
ions and urea, while very few species have the ability to
utilize nitrates as nitrogen source. Phosphorus and sul
phur are usually assimilated in the form of inorganic
phosphates and sulphates, respectively.
Food Grade Yeasts
Various microorganisms are used for human con
sumption worldwide as SCP or as components of tradi
tional food starters, including algae (Spirulina, Chlorella,
Laminaria, Rhodymenia, etc.), bacteria (Lactobacillus, Cellulo
monas, Alcaligenes, etc.), fungi (Aspergillus, Penicillium, etc.)
and yeasts (Saccharomyces, Candida, Kluyveromyces, Pichia
and Torulopsis)(6,7). Among the yeast species, Saccharo
myces cerevisiae and Candida utilis are fully accepted for
human consumption, but very few species of yeast are
commercially available.
The most common food grade yeast is Saccharomyces
cerevisiae, also known as baker’s yeast, which is used
worldwide for the production of bread and baking pro
ducts. S. cerevisiae is the most widely used yeast species,
whose selected strains are used in breweries, wineries
and distilleries for the production of beer, wine, distil-
lates and ethanol. Baker’s yeast is produced utilizing mo-
lasses from sugar industry by-products as a raw mate-
rial. Commercial S. cerevisiae and other yeast products
available to cover the needs of the baking and alcoholic
fermentation industries or for use as nutritional supple-
ments for humans and/or animals are described in the
following paragraphs.
Bakers yeast
Fresh baker’s yeast consists of approximately 30–33 %
of dry materials, 6.5–9.3 % of nitrogen, 40.6–58.0 % of
proteins, 35.0–45.0 % of carbohydrates, 4.0–6.0 % of lipids,
5.0–7.5 % of minerals and various amounts of vitamins,
depending on its type and growth conditions. Commer
cial fresh baker’s yeast includes products in liquid, creamy
or compressed forms and active dry yeast. Compressed
baker’s yeast is the most commonly used product, con
sisting of only one yeast species, S. cerevisiae. Special
strains of S. cerevisiae can be used for the production of
dry yeast products, like active dry yeast or instant dry
yeast. Active dry yeast consists of grains or beads of live
dried yeast cells with leavening power, while instant
dry yeast usually comes in the form of fine particles that
do not require rehydration before use. Unlike active dry
yeast, inactive dry yeast is a product without leavening
properties, used for the conditioning of dough proper
ties in baking or the development of characteristic fla
Brewer’s yeasts
Pure brewer’s yeast cultures are produced industrial
ly to supply the brewing industry. Usually two Saccharo
myces species are used: S. uvarum, formerly known as S.
carlsbergensis, which is used for the production of several
types of beer with bottom fermentation (lager yeasts),
and S. cerevisiae, which conducts top fermentation (ale
A. BEKATOROU et al.: Food Grade Yeasts, Food Technol. Biotechnol. 44 (3) 407–415 (2006)
yeasts). Due to recent reclassification both ale and lager
yeast strains are considered S. cerevisiae species. Top-fer
menting yeasts are used for the production of ales, porters,
stouts, wheat beers, etc., and bottom-fermenting yeasts
are used for lager beers like Pilsners, Bocks, American
malt liquors, etc. (12). Inactive brewer’s yeast prepara
tions, made from inactive yeast and other special ingre
dients, are produced commercially to be used as nutrients
to reinitiate or avoid sluggish and stuck fermentations.
Nutritional brewer’s yeast
Commercial, nutritional brewer’s yeast is inactive yeast
(dead yeast cells with no leavening power), remaining
after the brewing process. Brewer’s yeast is produced by
cultivation of S. cerevisiae on malted barley, separated
after the wort fermentation, debittered and dried. It is
an excellent source of protein and it is used as a nutrient
supplement rich in B vitamins. Brewer’s yeast products are
usually found in the form of powders, flakes or tablets,
or in liquid form. Liquid yeast contains enzymatically
digested yeast for better digestion, absorption and utiliza
tion. Brewer’s yeast should not be confused with »bre
wer’s type yeasts«, which are pure yeasts usually grown
on enriched cane or beet molasses under controlled pro
duction conditions, and are not by-products of the brew
ing process.
Brewer’s yeast is an excellent source of B vitamins,
Ca, P, K, Mg, Cu, Fe, Zn, Mn and Cr and has been stu-
died extensively for its medicinal properties. It is often
used for the treatment of diabetes (regulation of insulin
levels), loss of appetite, chronic acne, diarrhoea, etc.(13–
15). It is also recommended as a dietary supplement for
healthy hair and nails. Nevertheless, according to some,
brewer’s yeast is suspected of causing various problems,
like chronic fatigue, memory disorders, immunodefi-
ciency, irritable bowel syndrome, allergies, etc., mainly
due to the presence of yeast antigens and high amounts
of Cr and salicylates (16,17).
Wine yeasts
A wide variety of pure yeast cultures, mainly Sac
charomyces (S. cerevisiae, S. bayanus, S. uvarum, S. oviformis,
S. carlsbergensis, S. chevalieri, S. diastaticus, S. fructuum, S.
pasteurianus, S. sake, S. vini, etc.) are produced industrial
ly for the use in induced wine fermentations, according
to the industrial demands for fermentation efficiency and
productivity. The suitable type of yeast is selected with
respect to the geographical area, climate, type of grapes
and desirable organoleptic quality of the product (taste,
aroma, colour, tannin and glycerol content, etc.). Pure yeast
cultures are also used to conduct specific types of fer
mentations, like bottle fermentation of Champagne and
sparkling wines, or to treat stuck and sluggish fermen
Distillers yeasts
Distiller’s yeasts are used for the industrial produc
tion of alcohol and spirits (brandy, whiskey, rum, tequila,
etc.). They are usually isolated from industrial fermen
tations of fruit pulps and beet or sugar cane molasses.
Their selection depends on the desired product proper
ties, including flavour, alcohol yield, productivity, and
other technological features. Generally, distiller’s yeasts
must exhibit low foam formation, high stress-tolerance
and high alcohol yields. They must also form controlled
amounts of ethyl esters, aldehydes, fatty acids and high
er alcohols, which is an important prerequisite for the
production of fine quality distillation products. Distiller’s
yeasts must be able to ferment various substrates, such
as corn, barley, wheat, potato, etc. after hydrolysation in
fermentable sugars. They must be able to conduct fast
fermentations with high productivities and low produc
tion costs, and tolerate high temperatures, osmotic pres
sures and alcohol concentrations (18–20).
Probiotic yeasts
»Probiotics are live microbial feed supplements which
beneficially affect the host animal by improving its in
testinal microbial balance«, or by a wider definition »pro
biotics are microbial cell preparations or components of
microbial cells that have a beneficial effect on the health
and well-being of the host« (21). Probiotic properties of
yeasts, like S. cerevisiae, have been reported and display
ed as the ability to survive through the gastrointestinal
(GI) tract and interact antagonistically with GI pathogens
such as Esherichia coli, Shigella and Salmonella. Specifically,
S. boulardii, a thermophylic, non-pathogenic yeast, has been
used for more than 50 years as a livestock feed probiotic
supplement as well as therapeutic agent for the treat-
ment of a variety of gut disorders like diarrhoea. This
yeast is safe, it is resistant to antibiotics, achieves high
cell numbers in the intestine in short time, does not per-
manently colonize the intestine and is quickly cleared
after the cease of administration. Its probiotic effects are
also enhanced by its ability to produce polyamines, which
are compounds that strongly affect cell growth and dif-
ferentiation (22–24). S. boulardii is widely used and is
available in various commercial formulations. Other yeasts
allowed and commonly used in animal feeds as probio
tic additives are Candida pintolopesii, C. saitoana and S.
cerevisiae (25,26).
Yeast extract
Yeast extract is the product of enzymatic digestion
of the yeast cell constituents by endogenous and exoge
nous yeast enzymes. It is rich in peptides, amino acids,
nucleotides and vitamins, therefore it is good for use as
supplement in culture media. It is also used in pharma
ceuticals, as well as flavour and taste enhancer (replac
ing glutamates and nucleotides) in many canned foods.
Although brewer’s yeasts contain residual beer flavour
compounds (mainly constituents of hops), they are com
monly used for commercial food grade yeast extract pro
duction, which is destined for use as supplement in both
human and animal foods, and as flavour enhancer (27).
Torula yeast
Torula or Candida yeast refers to products containing
Candida utilis, which have been used commercially for
more than 60 years as nutritional supplements in animal
feeds. Food grade Torula yeast is cultivated in mixtures
of sugars and minerals, usually containing molasses, cel
lulosic wastes (e.g. spruce wood) or brewing by-prod
ucts. After cultivation the yeast is harvested, washed,
A. BEKATOROU et al.: Food Grade Yeasts, Food Technol. Biotechnol. 44 (3) 407–415 (2006)
thermolyzed and dried. Thermolysis renders the yeast
cells inactive, losing their fermentation ability. The yeast
is then usually spray-dried into a fine powder with
slight yeasty and meaty flavours. It is a highly digestible
and nutritious food, containing more than 50 % of pro
tein (rich in lysine, threonine, valine and glutamic acid),
minerals and vitamins (mainly niacine, pantothenic acid
and B vitamins). Torula yeast can be used as a meat sub
stitute or food additive in many processed foods, in sea
sonings, spices, sauces, soups, dips, etc. It is also used in
vegetarian and diet food, in baby food, meat products,
doughs, etc.(28–31).
Whey yeasts
A variety of microorganisms, especially those pre
sent in milk microflora, are able to utilize whey, the main
by-product of the dairy industry, but only a few are ap
proved as GRAS by the USFDA for use in food industry
(32). The yeasts most widely studied and used at indu
strial scale for the production of yeast biomass from whey
are the lactose fermenting Kluyveromyces yeasts K. lactis
and K. marxianus (formerly classified as K. fragilis). Kluy
veromyces yeasts can efficiently grow on lactose as sole
carbon source, although it has been reported that under
aerobic conditions (like those used in biomass produc
tion) some K. marxianus strains present a mixed type me-
tabolism, with intermediate metabolite production (alco-
hol, aldehydes, esters, etc.) and low yields of biomass
Lactose fermenting yeasts are also found in kefir, a
natural mixed culture found in the Caucasian milk drink.
It contains various microorganisms, sharing symbiotic re-
lationships, including species of lactose-fermenting yeasts
such as Kluyveromyces, Candida, Saccharomyces, Debaryo-
myces, Zygosaccharomyces, lactic acid bacteria and occasio-
nally acetic acid bacteria (34). Kefir yeasts have been used
at semi-industrial scale for whey lactose utilization and
production of value added products such as ethanol, bio
mass, lactic acid and alcoholic beverages (35). Kefir pro
duced using whey has also been evaluated as starter
culture in bread making and maturation of cheeses with
good results (36–38).
Sourdough starters
Sourdough is a mixture of flour and water, contain
ing yeasts and lactic acid bacteria, used as starter culture
to leaven bread. The use of sourdough has a number of
important advantages over baker’s yeast, such as the de
velopment of characteristic flavour (39) and texture (40),
as well as extension of preservation time through the in
situ production of antimicrobial compounds (e.g. bacte
riocins) (41). Therefore, sourdoughs are produced at com
mercial level using various combinations of yeasts and
bacteria, and are used for the conditioning of dough,
improvement of preservation time and the development
of breads and baking products with special organoleptic
properties (38).
Nutritional Aspects
Today yeast SCP are considered a potential protein
source for humans as well as animals. Food grade yeasts
can provide proteins, carbohydrates, fats, vitamins (main
ly the B group), minerals, essential amino acids (mainly
lysine) (6,42). Generally, the lysine content in yeasts is
higher than in bacteria or algae. Moreover, yeasts con
tain low amounts of nucleic acids (6–12 % on dry mass
basis) (6,7). The acceptability of a particular microorga
nism as food or feed depends on its nutritional value and
safety (including nucleic acid content, presence of toxins
and residual undesirable compounds such as heavy me
tals). SCP for human consumption should be free from
nucleic acids as purine bases are metabolized to uric
acid, creating problems to humans that do not possess
the enzyme uricase (6). Nucleic acid content in SCP can
be reduced by chemical treatment and autolytic me
thods (precipitation, acid or alkaline hydrolysis and/or
enzymatic treatment). Generally, the processes involved
in SCP production include mechanical disruption of cell
walls, removal by centrifugation, precipitation and ex
trusion of proteins to form the textured products (6).
Today, the only species fully acceptable as food for humans
is S. cerevisiae (baker’s and brewer’s yeasts). Novel SCP
sources demand extensive quality controls and should
be purified to meet international safety standards.
Yeasts may cause common food intolerances, although
in smaller frequency than other foodstuffs such as milk,
eggs, nuts, fish, shellfish, meat, chemical additives, etc.
Salicylates occurring naturally or added in foods as fla-
vouring agents (benzyl, methyl, ethyl, isoamyl, isobutyl
and phenethyl salicylates) may be present in yeast and
yeast extracts and may be associated with food intole-
rance symptoms in susceptible people (43,44). Also, the
foreign protein in yeasts may cause allergic reactions to
humans. Finally, digestibility is an important factor that
should be considered when SCP is used as food sup-
Yeast Production: Established Technology and
Raw materials
The raw materials used as substrates for industrial
yeast biomass production are usually agricultural, fores
try and food waste by-products. There are two types of
raw materials depending on the grown microorganism:
conventional materials like starch, molasses, distiller’s
wash, whey, fruit and vegetable wastes, wood, straw, etc.,
and unconventional ones like petroleum by-products,
natural gas, ethanol and methanol (6).
The most widely used substrate for baker’s yeast pro
duction is cane or beet molasses, the main by-product of
the sugar industry. Molasses contain 45–55 % ferment
able sugars including sucrose, glucose, fructose, raffinose,
melibiose and galactose. The use of molasses for the
production of food grade yeast is determined by their
availability and low cost, their composition and absence
of toxic substances and fermentation inhibitors (45). The
fermentation mixture for optimum yeast biomass produc
tion is usually fixed to pH=4.5–5.0 and enriched by the
addition of extra nutrients (N, P, Mg, Ca, trace amounts
of Fe, Zn, Cu, Mn, and vitamins, usually biotin), depend
ing on the initial composition of molasses. Molasses
A. BEKATOROU et al.: Food Grade Yeasts, Food Technol. Biotechnol. 44 (3) 407–415 (2006)
contain approx. 40 % (dry mass) of nonfermentable sub
stances that are eventually rejected and constitute a sig
nificant cause of pollution and increase of production cost
due to required waste treatment operations. The nonfer
mentable substances are usually collected and used as
animal feed or as fertilizers.
Whey is the main waste of the dairy industry. It is
produced worldwide in large amounts and its disposal
causes serious environmental problems due to its high
organic load (COD 35 000–68 000), which makes its full
treatment impossible (5). On the other hand, whey has a
significant nutritional value since it contains respectable
amounts of proteins, lactose, organic acids, fat, vitamins
and minerals. Therefor e, its conversion to products of ad
ded value is a major concern for science and industry.
The composition (high salt concentrations) and tempera
ture of whey at the moment of its production in the fac
tory do not allow easy microbial utilization. Lactose, the
main sugar constituent in whey, can be metabolised
only by a few species of the Kluyveromyces and Candida
yeasts. The yeast S. cerevisiae cannot utilize lactose be
cause it lacks the enzyme b-galactosidase and lactose per
mease. K. marxianus is the only strain used for biomass
production from whey on a commercial scale.
S. cerevisiae can utilize starch, only after its conver-
sion to fermentable sugars, glucose and maltose. Hydro-
lysis of starch to glucose can be done either by treatment
with acid or non-yeast enzymes. Enzymatic treatment in-
cludes three different processes: gelatinisation by heat-
ing, liquefaction by thermostable a-amylases, and saccha-
rification by mixed enzyme activities (46). Nevertheless,
processes like these imply considerable costs, which is
the main limiting factor in industrial utilization of starch
for yeast biomass production. Starch can be utilized by
mixed cultures of yeasts and amylolytic fungi like Asper
gillus species for SCP or ethanol production (6,46).
Residues of forestry and agriculture
Wastes of agriculture and forestry are rich in cellu
lose, hemicellulose and lignin. Their enzymatic conver
sion to fermentable sugars requir es chemical pretreatment
that leads to various polymer fragments. S. cerevisiae does
not have the variety of enzymes required to hydrolyse
these polymers. As a result, yeast biomass production
on lignocellulosic wastes implies a high economic cost.
A solution to this problem could be the use of mixed
cultures of S. cerevisiae and cellulolytic microorganisms,
but this process is today applied for ethanol production
in pilot plants only (47).
Propagation processes
Industrial propagation of yeast is done on abundant
ly available and cheap agricultural and industrial wastes,
mainly molasses, by successive submerged fermentations.
After fermentation, the yeast biomass is harvested and
may be subjected to downstream processing steps like
washing, cell disruption, protein extraction and purifica-
Industrial yeast production generally involves the fol-
lowing stages as described below: propagation, involv-
ing a number of fermentation processes, harvesting, con-
centration and/or drying, packaging and shipment. Fig. 1
presents a commercial baker’s yeast propagation scheme
A. BEKATOROU et al.: Food Grade Yeasts, Food Technol. Biotechnol. 44 (3) 407–415 (2006)
Fig. 1. Description of a propagation scheme for the production of baker’s yeast (adapted from Randez-Gil et al. (48) and industrial data)
Yeast cells are grown in a series of fermentation bio
reactors, which are operated under aerobic conditions to
promote yeast growth. Initially, cells from a pure yeast
culture are grown on a suitably adjusted mixture of mo
lasses in the laboratory and the produced biomass is trans
ferred aseptically into one or more bioreactors, which
operate in batch mode without air supply. The next bio
reactor usually operates in fed batch mode with air sup
ply, and the produced biomass is used to pitch the stock
bioreactor. The biomass produced in this bioreactor is
harvested by centrifugation and used in the next stage,
the pitch fermentation. Both these stages operate in fed
batch mode with vigorous aeration and incremental ad
dition of nutrients. The biomass produced in the pitch
bioreactor is used to pitch the final trade fermentations.
At the end of the process the content in the trade bio
reactors is aerated for an additional time period, and this
is the maturation stage. The amount of yeast biomass
produced increases from stage to stage, and the sequence
and the number of fermentation stages vary among ma
nufacturers. Food grade yeast biomass can also be pro
duced as by-product of industrial ethanol production on
molasses (e.g. Vogelbusch technology) (49).
Treatments and packaging
The yeast in the final trade bioreactor is concentrat
ed by centrifugation and finally harvested by a filter press
or a rotary vacuum filter, until it contains 27–33 % of dry
cell mass. The yeast cake is blended with suitable amounts
of water and emulsifiers and cutting oils (soybean or cot
tonseed oil) to obtain its extrudable form. The yeast is
then packaged and shipped as compressed fresh baker’s
yeast, or thermolysed and dried to form various types
of dry yeast. The dried yeast is packed under vacuum
or nitrogen atmosphere. The packaging method varies
among manufacturers and depends on the type of yeast
Recent advances and research
Various by-products of the food industry and agri
culture have been proposed for the production of food
grade yeast biomass. Some of these efforts are summa
rized in Table 1 (50–77). Species of Candida, Saccharomyces,
Kluyveromyces, Pichia, Rhodotorula, etc., alone or in mixed
cultures with other yeasts, have been grown on vegeta
A. BEKATOROU et al.: Food Grade Yeasts, Food Technol. Biotechnol. 44 (3) 407–415 (2006)
Table 1. Production of yeasts using alternative, low cost waste by-products of the food and agricultural industries
Microorganism Raw material Ref.
Rhodotorula rubra, Candida tropicalis, C. utilis, C. boidinii,
Trichosporon cutaneum
salad oil manufacturing wastewater (50)
Candida arborea rice straw hydrolysate (51)
Candida halophila, Rhodotorula glutinis glutamate fermentation wastewater (52)
Saccharomyces cerevisiae extracts of cabbage, watermelon, green salads and tropical fruits (53)
Candida utilis defatted rice polishings (54)
Candida versatilis, Kluyveromyces lactis, Kluyveromyces
whey (55)
Candida utilis, Pichia stipitis, Kluyveromyces marxianus,
Saccharomyces cerevisiae
waste chinese cabbage (56)
Candida utilis apple pomace (57)
Saccharomyces cerevisiae virgin grape marc (58)
Saccharomyces sp., Pichia sp., Rhodotorula sp., Candida sp.,
Kluyveromyces sp. and Trichospora sp.
lettuce brine (59)
Candida langeronii cane bagasse hemicellulosic hydrolyzate (60)
Torulopsis cremoris, Candida utilis, Kluyveromyces fragilis whey (61)
Pichia guilliermondii waste brine from kimchi production (62)
Geotrichum candidum orange peel (63)
Candida, Rhodotorula, Leucosporidium prawn shell waste (64)
Hansenula sp. sugar beet stillage (65)
Candida utilis pineapple cannery effluent (66)
Saccharomyces cerevisiae waste date products (67)
Saccharomyces cerevisiae hydrolyzed waste cassava (68)
Saccharomyces cerevisiae, Torula utilis, Candida lipolytica deproteinized leaf juices of turnip, mustard, radish and cauliflower (69)
Saccharomyces cerevisiae shrimp shell waste (70)
Candida krusei, Saccharomyces sp. sorghum hydrolysate (71)
Candida rugosa sugar beet stillage (72)
Kluyveromyces fragilis cheese whey (73)
Cellulomonas flavigena, Xanthomonas sp. sugarcane bagasse pith (74)
Candida spp. (utilis, tropicalis, parapsilosis and solani) molasses and sugar beet pulp (75)
Kluyveromyces, Candida, Schizosaccharomyces sp. jerusalem artichoke (76)
Pichia pinus mango waste or methanol (77)
ble processing wastewaters, hydrolysates and pulps
(rice, cabbage, apple, lettuce, pineapple, radish, cauliflow
er, turnip, sorghum, etc.), on dairy wastes (whey), sugar
and ethanol industry by-products (molasses, vinasse, stil
lages, bagasses, sugar beet pulps), fishery by-products
(prawn-shell waste), etc. The need to design feasible and
financially viable processes and the utilization of low cost
industrial wastes as raw materials for edible yeast biomass
production is extremely important, as it gives a solution
to the management of these wastes and the environmen
tal pollution caused by their disposal. Moreover, apart
from providing alternative sources of food for humans
or animals and reducing pollution, food grade yeast pro
duction using waste materials is attractive to manufac
turers as it leads to increased profits from the use of low
cost raw materials, production of added value and re
duction of waste treatment costs.
Today, modern techniques like DNA recombination,
induced mutations, and selection methodologies can also
be employed to obtain new specialized yeast strains with
improved properties, according to the manufacturer’s de
mands for fermentation efficiency and productivity (48,
78–80). For example, the modern baking industry demands
the production of more stable yeast strains, tolerant of
pH and temperature variations and high osmotic pres
sures. Especially, probiotic yeasts must be able to sur-
vive food production conditions, the presence of antimi-
crobial agents and storage.
Industrial strains should be improved to face prob-
lems related to glucose repression when mixed carbohy-
drate substrates are used, to avoid the production of un-
desirable by-products like ethanol and glycerol under
aerobic conditions (10). Genetic engineering has made pos-
sible the creation of such yeast strains, with new or en-
hanced enzymatic properties for maximum utilization of
various problematic raw materials, like cheese whey,
starch, sugar cane bagasses, lignocellulosic materials,
etc., for bioremediation purposes and optimum biomass
yields. Finally, strains have been constructed to increase
the nutritional value of foods, such as, for example, ami
no acid overproducing baker’s yeast for more nutritious
bread (42). Therefore, genetic engineering can lead to the
reduction of yeast production costs by increasing the avail
ability of the raw material, and avoiding the traditional
chemical reatment methods for their conversion. In the
frame of these efforts, new rapid methods for DNA ana
lysis have been introduced for the identification of speci
fic industrial yeast strains, and novel aerobic bioreactor
designs have been proposed to enable optimum produc
tion of yeast biomass, maximum utilization of the raw
material, reduction of cost and simultaneous reduction
of environmental pollution. Nevertheless, despite the tre
mendous progress in the genetic engineering of yeasts
achieved at the end of the 20th century (establishment
of genetic transformation of yeast in 1978 and determi
nation of the complete genome sequence in 1996), the
genetically modified (GM) yeasts have not yet been used
commercially. Only two GM yeast strains have been offi
cially approved for commercial use in 1990 (baker’s yeast)
and 1994 (brewer’s yeast), but none has been used com
mercially (81).
1. D. Pimentel, R. Harman, M. Pacenza, J. Pecarsky, M. Pi
mentel, Natural resources and an optimum human popu
lation, Popul. Environ. 15 (1994) 347–369.
2. D. Pimentel, J. Morse, Malnutrition, disease, and the de
veloping world, Science, 300 (2003) 251.
3. B. Gilland, World population and food supply: Can food
production keep pace with population growth in the next
half-century?, Food Policy, 27 (2002) 47–63.
4. J. Wolf, P.S. Bindraban, J.C. Luijten, L.M. Vleeshouwers, Ex
ploratory study on the land area required for global food
supply and the potential global production of bioenergy,
Agr. Syst. 76 (2003) 841–861.
5. A.M. Martin: Bioconversion of Waste Materials to Industrial
Products, Elsevier Applied Science, London, UK (1991).
6. J.M. Jay: Modern Food Microbiology, Chapman and Hall, New
York, USA (1996).
7. A.P. Ravindra, Value-added food: Single cell protein, Bio
technol. Adv. 18 (2000) 459–479.
8. H. Feldmann: Yeast Molecular Biology. A Short Compen
dium on Basic Features and Novel Aspects, Adolf Butenandt
Institute, University of Munich, Munich, Germany (2005)
9. K.J. Verstrepen, D. Iserentant, P. Malcorps, G. Derdelinckx,
P.V. Dijck, J. Winderickx, I.S. Pretorius, J.M. Thevelein, F.R.
Delvaux, Glucose and sucrose: Hazardous fast-food for in
dustrial yeast?, Trends Biotechnol. 22 (2004) 531–537.
10. K. Ringbom, A. Rothberg, B. Saxén, Model-based automa
tion of baker’s yeast production, J. Biotechnol. 51 (1996) 73–
11. G. Gellissen, C.P. Hollenberg, Application of yeasts in gene
expression studies: A comparison of Saccharomyces cerevi-
siae, Hansenula polymorpha and Kluyveromyces lactis Are-
view, Gene, 190 (1997) 87–97.
12. T. Goldammer: The Brewers’ Handbook. The Complete Book to
Brewing Beer, Apex Publishers, Clifton, V irginia, USA (2000).
13. Y. Sinai, A. Kaplun, Y. Hai, B. Halperin, Enhancement of
resistance to infectious disease by oral administration of
brewer’s yeast, Infect. Immun. 9 (1974) 781–787.
14. M. McCarty, High-chromium yeast for acne, Med. Hypothe
ses, 14 (1984) 307–310.
15. S.M. Bahijiri, S.A. Mira, A.M. Mufti, M.A. Ajabnoor, The
effects of inorganic chromium and brewer’s yeast sup
plementation on glucose tolerance, serum lipids and drug
dosage in individuals with type 2 diabetes, Saudi Med. J.
21 (2000) 831–837.
16. B.A. Baldo, R.S. Baker, Inhalant allergies to fungi: Reac
tions to bakers’ yeast (Saccharomyces cerevisiae) and iden
tification of bakers’ yeast enolase as an important allergen,
Int. Arch. Allergy Appl. Immunol. 86 (1988) 201–208.
17. D.L. Smith, Brewer’s yeast as a cause of infection, Clin.
Infect. Dis. 22 (1996) 201.
18. G.I. de Becze, Reproduction of distillers’ yeasts, Biotechnol.
Bioeng. 6 (1964) 191–221.
19. K. Laube, J. Wesenberg, P. Lietz, Selection of distiller’s yeasts
with particular respect to non-Saccharomyces strains, Acta
Biotechnol. 7 (1987) 111–118.
20. S.I. Ibragimova, D.G. Kozlov, N.N. Kartasheva, N.I. Suntsov,
B.D. Efremov, S.V. Benevolensky, A strategy for construc
tion of industrial strains of distillers yeast, Biotechnol. Bio
eng. 46 (1995) 285–290.
21. S. Salminen, A. Ouwehand, Y. Benno, Y.K. Lee, Probiotics:
How should they be defined?, Trends Food Sci. Technol. 10
(1999) 107–110.
22. A. Lourens-Hattingh, B.C. Viljoen, Growth and survival of
a probiotic yeast in dairy products, Food Res. Int. 34 (2001)
A. BEKATOROU et al.: Food Grade Yeasts, Food Technol. Biotechnol. 44 (3) 407–415 (2006)
23. C. Costalos, V. Skouteri, A. Gounaris, S. Sevastiadou, A.
Triandafilidou, C. Ekonomidou, F. Kontaxaki, V. Petrochilou,
Enteral feeding of prematur e infants with Saccharomyces bou
lardii, Early Hum. Dev. 74 (2003) 89–96.
24. L.V. McFarland, Meta-analysis of probiotics for the preven
tion of traveler’s diarrhea, Travel Med. Infect. Dis. (in press).
25. R. Bovill, J. Bew, S. Robinson, Comparison of selective me
dia for the recovery and enumeration of probiotic yeasts
from animal feed, Int. J. Food Microbiol. 67 (2001) 55–61.
26. R.G.K. Leuschner, J. Bew, P. Fourcassier, G. Bertin, Valida
tion of the official control method based on polymerase
chain reaction (PCR) for identification of authorised pro
biotic yeast in animal feed, Syst. Appl. Microbiol. 27 (2004)
27. H.J. Chao, H. Joo, M.J. In, Utilization of brewer’s yeast cells
for the production of food-grade yeast extract. Part 1: Ef
fects of different enzymatic treatments on solid and pro
tein recovery and flavor characteristics, Bioresour. Technol.
76 (2001) 253–258.
28. W.M. Weatherholtz, G.C. Holsing, Evaluation of Torula yeast
for use as a food supplement, Fed. Proceed. 34 (1975) 890.
29. L. Kuzela, J. Masek, V. Zalabak, J. Kejmar, Some aspects of
biomass of Torula in human nutrition New protein source,
Bibl. Nutr. Dieta, 23 (1976) 169–173.
30. FAO: ADCP/REP/83/18 Fish feeds and feeding in de
veloping countries An interim report on the ADCP feed
development programme, Aquaculture Development and
Coordination Programme, United Nations Development
Programme, Food and Agriculture Organization of the
United Nations, Rome, Italy (1983).
31. P. Lezcano, Development of a protein source in Cuba: To
rula yeast (Candida utilis), Cuban J. Agric. Sci. 39 (2005) 447–
32. M. Rubio-Texeira, Endless versatility in the biotechnologi-
cal applications of Kluyveromyces LAC genes, Biotechnol. Adv.
24 (2006) 212–225.
33. C.L. Flores, C. Rodríguez, T. Petit, C. Gancedo, Carbohy-
drate and energy-yielding metabolism in non-conventional
yeasts, FEMS Microbiol Rev. 24 (2000) 507–529.
34. E. Simova, D. Beshkova, A. Angelov, T. Hristova, G. Fren
gova, Z. Spasov, Lactic acid bacteria and yeasts in kefir
grains and kefir made from them, J. Ind. Microbiol. Biotech
nol. 28 (2002) 1–6.
35. A.A. Koutinas: Kefir Yeast Technology. In: New Horizons in
Biotechnology, S. Roussos, C.R. Soccol, A. Pandey, C. Augur
(Eds.), Kluwer Academic Publishers, Dordrecht, The Neth
erlands (2003) pp. 297–310.
36. O. Harta, M. Iconomopoulou, A. Bekatorou, P. Nigam, M.
Kontominas, A.A. Koutinas, Effect of various carbohydra
te substrates on the production of kefir grains for use as a
novel baking starter, Food Chem. 88 (2004) 237–242.
37. A.A. Koutinas, A. Bekatorou, Kefir starter culture in food
production, Current Topics on Bioprocesses in Food Industry:
Proceedings of the International Congress on Bioprocesses in
Food Industries (ICBF-2004), Asiatech Publishers Inc., New
Delhi, India (2006).
38. S. Plessas, L. Pherson, A. Bekatorou, P. Nigam, A.A. Kouti
nas, Bread making using kefir grains as baker’s yeast, Food
Chem. 93 (2005) 585–589.
39. A. Hansen, P. Schieberle, Generation of aroma compounds
during sourdough fermentation: Applied and fundamen
tal aspects, Trends Food Sci. Technol. 16 (2005) 85–94.
40. B. Meignen, B. Onno, P. Gélinas, M. Infantes, S. Guilois, B.
Cahagnier, Optimisation of sour dough fermentation with
Lactobacillus brevis and bakers yeast, Food Microbiol. 18 (2001)
41. W. Messens, L. De Vuyst, Inhibitory substances produced
by Lactobacilli isolated from sourdoughs A review, Int. J.
Food Microbiol. 72 (2002) 31–43.
42. A.M. Rincón, T. Benítez, Improved organoleptic and nutri
tive properties of bakery products supplemented with
amino acid overproducing Saccharomyces cerevisiae yeasts,
J. Agric. Food Chem. 49 (2001) 1861–1866.
43. W.K. Webb, W.H. Hansen, Chronic and subacute toxicol
ogy and pathology of methyl salicylate in dogs, rats, and
rabbits, Toxicol. Appl. Pharm. 5 (1963) 576–587.
44. S. Bischoff, S.E. Crowe, Gastrointestinal food allergy: New
insights into pathophysiology and clinical perspectives,
Gastroenterology, 128 (2005) 1089–1113.
45. P. Skountzou, M. Soupioni, A. Bekatorou, M. Kanellaki, A.A.
Koutinas, R. Marchant, I.M. Banat, Lead uptake during ba
ker’s yeast production by aerobic fermentation of molas
ses, Process Biochem. 38 (2003) 1479–1482.
46. P. Nigam, D. Singh, Enzyme and microbial systems in
volved in starch processing, Enzyme Microb. Technol. 17
(1995) 770–778.
47. J.C. Cuzens, J.R. Miller, Acid hydrolysis of bagasse for etha
nol production, Renew. Energ. 10 (1997) 285–290.
48. F. Randez-Gil, P. Sanz, J.A. Pietro, Engineering baker’s yeast:
Room for improvement, Trends Biotechnol. 17 (1999) 237–
49. J. Modl, Jilin fuel ethanol plant, Int. Sugar J. 106 (2004) 142–
50. S. Zheng, M. Yang, Z. Yang, Biomass production of yeast
isolate from salad oil manufacturing wastewater, Bioresour.
Technol. 96 (2005) 1183–1187.
51. Y.G. Zheng, X.L. Chen, Z. Wang, Microbial biomass pro
duction from rice straw hydrolysate in airlift bioreactors, J.
Biotechnol. 118 (2005) 413–420.
52. S. Zheng, M. Yang, Z. Yang, Q. Yang, Biomass production
from glutamate fermentation wastewater by the co-culture
of Candida halophila and Rhodotorula glutinis, Bioresour. Tech-
nol. 96 (2005) 1522–1524.
53. O. Stabnikova, J.Y. Wang, H.B. Ding, J.H. Tay, Biotransfor-
mation of vegetable and fruit processing wastes into yeast
biomass enriched with selenium, Bioresour. Technol. 96 (2005)
54. M.I. Rajoka, M.A.T. Kiani, S. Khan, M.S. Awan, A.S. Hash
mi, Production of single cell protein from rice polishings
using Candida utilis, World J. Microbiol. Biotechnol. 20 (2004)
55. H. Moeini, I. Nahvi, M. Tavassoli, Improvement of SCP pro
duction and BOD removal of whey with mixed yeast cul
ture, Electron. J. Biotechnol. 7 (2004) U36–U42.
56. M.H. Choi, Y.H. Park, Production of yeast biomass using
waste Chinese cabbage, Biomass Bioenerg. 25 (2003) 221–
57. S.G. Villas-Boas, E. Esposito, M.M. de Mendonca, Biocon
version of apple pomace into a nutritionally enriched sub
strate by Candida utilis and Pleurotus ostreatus, World J. Mi
crobiol. Biotechnol. 19 (2003) 461–467.
58. R.B. Lo Curto, M.M. Tripodo, Yeast production from virgin
grape marc, Bioresour. Technol. 78 (2001) 5–9.
59. W. Suntornsuk, Yeast cultivation in lettuce brine, World J.
Microbiol. Biotechnol. 16 (2000) 815–818.
60. J.N. Nigam, Cultivation of Candida langeronii in sugar cane
bagasse hemicellulosic hydrolyzate for the production of
single cell protein, World J. Microbiol. Biotechnol. 16 (2000)
61. E. Cristiani-Urbina, A.R. Netzahuatl-Munoz, F.J Manriquez-
Rojas, C. Juarez-Ramirez, N. Ruiz-Ordaz, J. Galindez-May
er, Batch and fed-batch cultures for the treatment of whey
with mixed yeast cultures, Process Biochem. 35 (2000) 649–
62. M.H. Choi, Y.H. Park, Growth of Pichia guilliermondii A9,
an osmotolerant yeast, in waste brine generated from kim
chi production, Bioresour. Technol. 70 (1999) 231–236.
A. BEKATOROU et al.: Food Grade Yeasts, Food Technol. Biotechnol. 44 (3) 407–415 (2006)
63. R. Lo Curto, M.M. Tripodo, U. Leuzzi, D. Giuffrè, C. Vac
carino, Flavonoids recovery and SCP production from
orange peel, Bioresour. Technol. 42 (1992) 83–87.
64. R. Rhishipal, R. Philip, Selection of marine yeasts for the
generation of single cell protein from prawn-shell waste,
Bioresour. Technol. 65 (1998) 255–256.
65. S.A. Shojaosadati, R. Khalilzadeh, H.R. Sanaei, Optimizing
of SCP production from sugar beet stillage using isolated
yeast, Iran. J. Chem. Chem. Eng. 17 (1998) 73–80.
66. J.N. Nigam, Single cell protein from pineapple cannery ef
fluent, World J. Microbiol. Biotechnol. 14 (1998) 693–696.
67. N. Nancib, A. Nancib, J. Boudrant, Use of waste date pro
ducts in the fermentative formation of baker’s yeast bio
mass by Saccharomyces cerevisiae, Bioresour. Technol. 60 (1997)
68. A.O. Ejiofor, Y. Chisti, M. Moo-Young, Culture of Saccharo
myces cerevisiae on hydrolyzed waste cassava starch for pro
duction of baking-quality yeast, Enzyme Microb. Technol. 18
(1996) 519–525.
69. S. Chanda, S. Chakrabarti, Plant origin liquid waste: A re
source for single cell protein production by yeast, Biore
sour. Technol. 57 (1996) 51–54.
70. J. Ferrer, G. Paez, Z. Marmol, E. Ramones, H. Garcia, C.F.
Forster, Acid hydrolysis of shrimp-shell wastes and the pro
duction of single cell protein from the hydrolysate, Biore
sour. Technol. 57 (1996) 55–60.
71. S. Konlani, J.P. Delgenes, R. Moletta, A. Traore, A. Doh,
Optimization of cell yield of Candida krusei SO1 and Sac
charomyces sp. LK3G cultured in sorghum hydrolysate, Bio
resour. Technol. 57 (1996) 275–281.
72. K.Y. Lee, S.T. Lee, Continuous process for yeast biomass
production from sugar beet stillage by a novel strain of
Candida rugosa and protein profile of the yeast, J. Chem.
Technol. Biotechnol. 66 (1996) 349–354.
73. A.E. Ghaly, R.M. Ben-Hassan, N. Ben-Abdallah, Effect of
ambient temperature on the heating/cooling requirement
of a single cell protein batch reactor operating on cheese
whey, Biomass Bioenerg. 3 (1992) 335–344.
74. R. Rodriguez-Vazquez, G. Villanueva-Ventura, E. Rios-Leal,
Sugarcane bagasse pith dry pretreatment for single cell pro
tein production, Bioresour. Technol. 39 (1992) 17–22.
75. P. Nigam, M. Vogel, Bioconversion of sugar industry by-
products Molasses and sugar beet pulp for single cell
protein production by yeasts, Biomass Bioenerg. 1 (1991) 339–
76. P.K. Bajpai, P. Bajpai, Cultivation and utilization of Jerusa
lem artichoke for ethanol, single cell protein, and high-
fructose syrup production, Enzyme Microb. Technol. 13 (1991)
77. M.M. Rashad, S.A. Moharib, E.W. Jwanny, Yeast conver
sion of mango waste or methanol to single cell protein and
other metabolites, Biol. Wastes, 32 (1990) 277–284.
78. A.I. Angelov, G.I. Karajov, Z.G. Roshkova, Strains selection
of baker’s yeast with improved technological properties,
Food Res. Int. 29 (1996) 235–239.
79. I. Petsas, K. Psarianos, A. Bekatorou, A.A. Koutinas, I.M.
Banat, R. Marchant, Improvement of kefir yeast by muta
tion with N-methyl-N-nitrosoguanidine, Biotechnol. Lett. 24
(2002) 557–560.
80. L. Olsson, J. Nielsen, The role of metabolic engineering in
the improvement of Saccharomyces cerevisiae: Utilization of
industrial media, Enzyme Microb. Technol. 26 (2000) 785–792.
81. F. Akada, Genetically modified industrial yeast ready for
application. Review, J. Biosci. Bioeng. 94 (2002) 536–544.
A. BEKATOROU et al.: Food Grade Yeasts, Food Technol. Biotechnol. 44 (3) 407–415 (2006)
FTB 44 (3) 407-415.
Proizvodnja prehrambenih kvasaca
Kvasci su poznati čovjeku već tisućama godina jer se koriste u tradicionalnim
fermentacijskim procesima dobivanja vina, piva i kruha. Danas se oni koriste i kao
alternativni izvori visokovrijednih proteina, enzima i vitamina, imaju brojnu primjenu u
proizvodnji zdravstveno korisne hrane kao aditivi, regulatori i sastojci arome, u proizvodnji
mikrobioloških podloga i ekstrakata, te kao krmivo. Suvremena znanstvena dostignuća
omogućuju izolaciju, izradu i industrijsku proizvodnju novih sojeva kvasaca koji ispunjavaju
posebne zahtjeve prehrambene industrije. U radu su istaknuti tipovi industrijskih
prehrambenih kvasaca, procesi njihove proizvodnje i sirovine. Također se raspravlja o
metabolizmu kvasca, s obzirom na utrošak ugljikohidrata, hranjiva te nova dostignuća u
njihovu istraživanju.
... In addition to the individual process steps, which can influence the end product, one of the major media components used during yeast production also plays a decisive role. For the fermentation of yeast, molasses is often used as a source of carbon, nitrogen and several other nutrients [28][29][30]. Molasses is a side product of sugar production and, hence, subject to variation [31,32]. Although producers try to partially compensate for the lack of nutrients in specific molasses, this does not seem to fully compensate for the differences in the nutrient portfolio between different batches of yeast extract [28,29]. ...
... Molasses is a side product of sugar production and, hence, subject to variation [31,32]. Although producers try to partially compensate for the lack of nutrients in specific molasses, this does not seem to fully compensate for the differences in the nutrient portfolio between different batches of yeast extract [28,29]. Furthermore, producers state that they use different yeast strains depending on the customer's desires, which can additionally increase the variation of the final product [33]. ...
Full-text available
Background In research and production, reproducibility is a key factor, to meet high quality and safety standards and maintain productivity. For microbial fermentations, complex substrates and media components are often used. The complex media components can vary in composition, depending on the lot and manufacturing process. These variations can have an immense impact on the results of biological cultivations. The aim of this work was to investigate and characterize the influence of the complex media component yeast extract on cultivations of Azotobacter vinelandii under microaerobic conditions. Under these conditions, the organism produces the biopolymer alginate. The focus of the investigation was on the respiration activity, cell growth and alginate production. Results Yeast extracts from 6 different manufacturers and 2 different lots from one manufacturer were evaluated. Significant differences on respiratory activity, growth and production were observed. Concentration variations of three different yeast extracts showed that the performance of poorly performing yeast extracts can be improved by simply increasing their concentration. On the other hand, the results with well-performing yeast extracts seem to reach a saturation, when their concentration is increased. Cultivations with poorly performing yeast extract were supplemented with grouped amino acids, single amino acids and micro elements. Beneficial results were obtained with the supplementation of copper sulphate, cysteine or a combination of both. Furthermore, a correlation between the accumulated oxygen transfer and the final viscosity (as a key performance indicator), was established. Conclusion The choice of yeast extract is crucial for A. vinelandii cultivations, to maintain reproducibility and comparability between cultivations. The proper use of specific yeast extracts allows the cultivation results to be specifically optimised. In addition, supplements can be applied to modify and improve the properties of the alginate. The results only scratch the surface of the underlying mechanisms, as they are not providing explanations on a molecular level. However, the findings show the potential of optimising media containing yeast extract for alginate production with A. vinelandii, as well as the potential of targeted supplementation of the media.
... Cyberlindnera jadinii (C. jadinii), previously classified as Candida utilis, is an inactivated yeast product that can be cultivated on local-based lignocellulosic biomass (Bekatorou et al., 2006). The high crude protein content (50−58%) and favorable amino acid profile make C. jadinii an interesting and promising alternative protein source. ...
Full-text available
The effect of dietary graded levels of Cyberlindnera jadinii yeast (C. jadinii) on growth performance, nutrient digestibility, and gut health of broilers was evaluated from 1 to 34 d of age. A total of 360 male broiler chicks were randomly allocated to 1 of 4 dietary treatments (6 replicate pens each) consisting of a wheat-soybean meal-based pelleted diet (Control or CJ0), and 3 diets in which 10% (CJ10), 20% (CJ20), and 30% (CJ30) of the crude protein were supplied by C. jadinii, by gradually replacing protein-rich ingredients. Body weight and feed intake were measured at d 1, 11, 22, and 32. Pellet temperature, durability, and hardness increased linearly (P < 0.05) with C. jadinii inclusion, with highest (P < 0.05) values for CJ30. Up until d 22, feed conversion ratio (FCR) was similar between treatments (P = 0.169). Overall, increasing C. jadinii inclusion linearly increased (P = 0.047) feed intake but had no effect on weight gain or mortality. FCR increased (P < 0.05) linearly with increasing C. jadinii inclusion but only birds fed CJ30 had a significantly poorer FCR compared to the Control. Ileal digestibility was not affected by C. jadinii inclusion, however, there was a significant linear decrease in crude protein and phosphorus, and a tendency for a decrease in fat digestibility. Apparent metabolizable energy (AME) decreased (P < 0.001) quadratically with increasing C. jadinii and was significantly lower in CJ30 compared to the Control. Ileal concentrations of volatile fatty acids (VFAs) were not affected by C. jadinii inclusion, but butyric acid and total VFAs were linearly and quadratically increased and were significantly higher in cecal digesta of birds fed CJ20 and CJ30. Increasing C. jadinii inclusion was associated with an increase (P < 0.05) in the relative abundance of lactobacillus in the ileum and cecum. In conclusion, C. jadinii yeast can supply up to 20% of the total dietary protein without negatively affecting performance, digestibility, or gut health of broilers. The potential confounding role of feed processing and C. jadinii cell wall components on broiler performance is discussed.
... However, fresh baker´s yeast contains 40.6-58.0 % of proteins (32), which indicates that the yeast grown on media containing both molasses and cGE is of high quality. ...
Full-text available
Wine production, regarded as a major sector in food industry, is often associated with the utilization of large amount of resources. Furthermore, wine making produces high quantity of grape pomace that is generally used for low value applications such as fertilizer and animal feed. The present research aims at exploring the possibility of improving the overall sustainability of traditional winemaking. Experimental approach - A zero waste process was developed. It includes the production of white wine and the substantial valorisation of grape pomace, which is transformed into solid biofuel, tartaric acid and concentrated grape extract as a feedstock for industrial baker's yeast production. Please note that this is an unedited version of the manuscript that has been accepted for publication. This version will undergo copyediting and typesetting before its final form for publication. Results and conclusions. We estimate that a substantial renewable energy surplus of approx. 3 MJ/kg processed grapes could be achieved during this transformation. The suitability of grape extract as a potential substrate for industrial baker's yeast production was assessed and the feasibility of its partial replacement of molasses (up to 30%) was demonstrated. Novelty and scientific contribution. We present a circular economy approach to the conversion of winery biowaste into high-value resources such as feedstock and solid biofuel.
... This type of yeast is made from certain species to tolerate relatively high drying temperatures. Dry yeast moisture is between 3 to 8% [1]. The yeast cell wall has 4 macromolecules, which the location is shown in Fig. 1. ...
Conference Paper
Beta-glucans is a β-D-glucose polysaccharide, which has many applications in the food and pharmaceutical industries. Beta-glucans are mainly derived from various sources of bacteria, fungi, yeast, and Cereal. Studies have shown that the properties of different forms of 1,3 and 1,6 and 1,4 beta-glucans are the same, Therefore, the production cost is the best criterion for selecting the appropriate source of beta-glucan production. Yeast is the most economical source of beta-glucan. Depending on the required purity, β-glucan extraction from yeast is done under different stages and conditions. Generally, Extraction steps include cell wall disruption, cell wall removal, and extraction of β-glucan from isolated cell walls. The performance and efficiency of each stage can affect the efficiency and consequently the cost of production. In this research, the effect of two factors of yeast quality, lysis time, and protein removal methods on the efficiency of the alkaline-acidic extraction process of β-glucan was investigated for the proper extraction of beta-glucan from the baker's yeast. To evaluate the quality of yeast, two types of industrial dry yeast and fresh yeast (without emulsifier) were used and it was found that by using fresh yeast purity of β-glucan increases from 39 to 43% with respect to dry yeast, probably the presence of emulsifier in dry yeast has an inhibitory effect on the lysis of the cell, which was shown in the enduring research. To investigate the effect of the cell lysis time, the times of 2 and 4 hours were examined and it was cleared that by increasing the cell lysis time, the purity of β-glucan increased from 43 to 51%, which was possibly due to better lysis of the cell. Also, Study cell lysis revealed that by increasing the cell lysis time, the cell wall disruption was completely performed. In order to reduce the protein content of the final sample, Proteinase K, Sodium Hydroxide, and increased cell lysis time were used and the highest effect was obtained by increasing the cell lysis time.
... It has also been used in producing other types of fermented products such as cheese, soy sauce production, vinegar, sourdoughs, vegetable products and even fermented meat. The role of yeast cannot be overemphasized as it also serves as a source of high nutritional value proteins, enzymes, and vitamins, with uses in the health food sector as nutritional supplements, food additives, conditioners, and flavoring agents, microbiological media as well as animal feeding as a protein source (Bekatorou et al., 2006;Otero et al., 2011). ...
Full-text available
Yeast is the primary organism responsible for the leavening of doughs. In this study, yeast samples were isolated from palm wine samples collected from Nkpa in Abia State. The samples were cultured on malt extract agar (MEA) medium at room temperature of 28 o C to isolate three ascosporogenous yeast strains (Saccharomyces fragilis, Saccharomyces cerevisiae, Pichia spp) from the culture by using identification techniques such as their morphological, fermentative and microscopic properties. The isolated yeast, the combination of the strains and the commercial baker's yeast as the control were each used to produce eight different bread samples and their physical, sensory properties and correlation were examined. Amongst the bread samples examined for physical properties, sample D (Baker's yeast) had the highest value in bread volume followed by Saccharomyces cerevisiae while Pichia spp had the least performance. Likewise, significant differences (p < 0.05) occurred in specific volumes, which ranged from 1.91-3.94. The loaf weight ranged from 276.5-320.1g. The result of the sensory attributes of the bread samples revealed that the taste value ranged from (4.3-8.5), texture (3.5-8.0), aroma (3.5-8.0), crust colour (4.4-8.0), and general acceptability (4.7-7.9). The general acceptability was significantly (p < 0.01) found to be positively correlated with bread volume (r = 0.96), taste (r = 0.90), crust colour (r = 0.86) and negatively correlated with the loaf weight (r = −0.86). Therefore, the data shows that some of the isolated yeast strains and the combination of strains could be valuable in the leavening of doughs.
... Produksi SCP dari limbah dan keuntungan efektif mikroba dibandingkan dengan sumber protein konvensional sudah diketahui (Argyro et al., 2006). Sejumlah produk limbah pertanian dan agroindustri digunakan untuk produksi SCP dan metabolit lainnya termasuk limbah jeruk, limbah mangga, kapas, jerami barley, polisi jagung, jerami jagung, jerami padi, jus bawang, ampas tebu (Nigam et al., 2000), pati singkong, jerami gandum (Abou Hamed, 1993), ampas pisang, bubuk capsicum (Zhao et al., 2010), dan air kelapa. ...
Full-text available
Mikroba sebagai agen bioteknologi secara khusus diulas pada buku ini berikut beberapa studi kasus terkait pemanfaatan mikroba yang diimplementasikan pada berbagai aspek kehidupan manusia. Pemahaman yang konkrit tentang konsep dasar proses-proses biologis mikroba dalam bioteknologi merupakan harapan terbesar yang diharapkan atas terbitnya buku ini sehingga dapat digunakan sebagai acuan untuk meningkatkan kompetensi diri dalam upaya mengimplementasikan wawasan kebioteknologian. Peran mikroba dalam pengembangan dan atau menghasilkan produk yang bermanfaat bagi kehidupan dalam bidang pertanian, Kesehatan dan pengolahan pangan menjadi fokus pembahasan buku ini.
... Yeast biomass is mainly composed of proteins (35%-60% dry basis) of high biological value, because it contains all the essential amino acids (Bekatorou et al., 2006;Ganeva et al., 2020). Therefore, spent yeast is an excellent source that can be found in a widely available by-product, with excellent potential as an alternative source of high-quality proteins. ...
Full-text available
One strategy to reduce cost and improve feasibility of waste-yeast biomass valorization is to obtain a spectrum of marketable products rather than just a single one. This study explores the potential of Pulsed Electric Fields (PEF) for the development of a cascade process designed to obtain several valuable products from Saccharomyces cerevisiae yeast biomass. Yeast biomass was treated by PEF, which affected the viability of 50%, 90%, and over 99% of S. cerevisiae cells, depending on treatment intensity. Electroporation caused by PEF allowed access to the cytoplasm of the yeast cell without causing total breakdown of the cell structure. This outcome was an essential prerequisite to be able to perform a sequential extraction of several value-added biomolecules from yeast cells located in the cytosol and in the cell wall. After incubating yeast biomass previously subjected to a PEF treatment that affected the viability of 90% of cells for 24 h, an extract with 114.91 ± 2.86, 7.08 ± 0.64, and 187.82 ± 3.75 mg/g dry weight of amino acids, glutathione, and protein, respectively, was obtained. In a second step, the extract rich in cytosol components was removed after 24 h of incubation and the remaining cell biomass was re-suspended with the aim of inducing cell wall autolysis processes triggered by the PEF treatment. After 11 days of incubation, a soluble extract containing mannoproteins and pellets rich in β-glucans were obtained. In conclusion, this study proved that electroporation triggered by PEF permitted the development of a cascade procedure designed to obtain a spectrum of valuable biomolecules from S. cerevisiae yeast biomass while reducing the generation of waste.
... The sugar (brix) level decreased appreciably as the specific gravity decreases throughout the fermentation. The decrease in specific gravity could be attributed to the decrease in the total soluble solids as the sugar present in the broth was fermented to alcohol and other by-products such as glycerol and CO 2 [28]. ...
Full-text available
This study investigated the potentials of pineapple waste (fruit skin) as an alternative and cost-effective lignocellulose for bioethanol production by Zymomonas mobilis and Saccharomyces cerevisiae. The substrate was pretreated using dilute hydrochloric acid (HCL) to alter the complex structure of the carbohydrate polymers to removing lignin and hemicelluloses, reduce cellulose crystallinity and increase the porosity of the materials. Enzymatic hydrolysis was carried out to further depolymerize the cellulose component to simple sugars. Hydrolysis and fermentation lasted for five days. Fermentation parameters such as pH, temperature, reducing sugar (brix level) and specific gravity were monitored for five days. The concentrations of reducing sugar (brix level) were calculated based on the relationship: Brix = 261.3×(1-1/S.G).The specific gravity of the wort was determined before and during fermentation using the specific gravity bottle of known weight. The pH and temperature of the wort was determined using calibrated HANNA multi parameter probe (HI9811-5) while ethanol content was determined spectrophotometrically using acid dichromate solution. The specific gravity, pH, temperature and reducing sugar of each of the substrates decreased as the fermentation time increases. The substrate recorded a total reducing sugar content of 17.5mg/ml. The pH of the broth for the substrate decreased during the five days fermentation period with optimum pH for ethanol production ranging from 4.9 to 5.2 for the yeast and 5.0 to 5.8 for the bacterium at 72hrs incubation. Fermentation using S. cerevisiae was slow and required three days to complete with maximum ethanol yield of 51%. The fermentation with Z. mobilis proceeded very rapidly and was completed in three days with maximum ethanol yield of 78%. Sugar utilization was faster in Z. mobilis than in S. cerevisiae with a corresponding increase in ethanol yield. Conclusively, Z. mobilis could be considered a better microorganism for bioethanol production.
... Generation of food waste or side-streams is unavoidable in the processing of food. Use of waste material as substrate is particularly attractive as it valorizes waste streams and reduces waste treatment costs and associated environmental emissions (Bekatorou et al., 2006). The biorefining of food processing side-streams, such as sugarcane molasses (Yan et al., 2018), apple pomace (Gullón et al., 2008), grape pomace (Botella et al., 2007), banana peels and pulp (Naranjo et al., 2014), orange peel (Boukroufa et al., 2015), date waste (Hashempour-Baltork et al., 2020), and corncob (Samanta et al., 2015) for use as substrate has been explored. ...
Production of fish meal and plant-based feed proteins continues to increase to meet the growing demand for seafood, leading to impacts on marine and terrestrial ecosystems. Microbial proteins such as single-cell proteins (SCPs) have been introduced as feed alternatives since they can replace current fish feed ingredients, e.g., soybean, which are associated with negative environmental impacts. Microbial protein production also enables utilization of grain processing side-streams as feedstock sources. This study assesses the environmental impacts of yeast-based SCP using oat side-stream as feedstock (OS-SCP). Life-cycle assessment with a cradle-to-gate approach was used to quantify global warming, freshwater eutrophication, marine eutrophication, terrestrial acidification, land use, and water consumption of OS-SCP production in Finland. Dried and wet side-streams of oat were compared with each other to identify differences in energy consumption and transportation effects. Sensitivity analysis was performed to examine the difference in impacts at various locations and fermentation times. Benchmarking was used to evaluate the environmental impacts of OS-SCP and other feed products, including both conventional and novel protein products. Results highlight the importance of energy sources in quantifying the environmental performance of OS-SCP production. OS-SCP produced with dried side-streams resulted in higher global warming (16.3 %) and water consumption (7.5 %) than OS-SCP produced from wet side-streams, reflecting the energy and water requirements for the drying process. Compared with conventional products, such as soy protein concentrates, OS-SCP resulted in 61 % less land use, while exacerbating the environmental impacts in all the other categories. OS-SCP had more impact on global warming (205-754 %), water consumption (166-1401 %), freshwater eutrophication (118-333 %), and terrestrial acidification (85-340 %) than other novel products, including yeast protein concentrate, methanotrophic bacterial SCP, and insect meal, while lowering global warming (11 %) and freshwater eutrophication (20 %) compared with dry microalgae biomass.
Full-text available
In this study fungi isolated from the effluent of ethanol factories were identified. Optimal conditions for single cell protein (SCP) production and COD reduction of sugar beet stillage are specified for a species of Hansenula in a continuous culture. Under these conditions 5.7 g dm-3 biomass was produced and 31% of COD was reduced without addition of further nutrients to the beet molasses stillage. Adding nitrogen and phosphorus sources, increased the biomass production and COD reduction to 8.5 g dm-3 and 35.7%, respectively. The crude protein content of SCP in the absence and presence of additives was 39.6% and to 50.6% respectively. The amounts of essential amino acids measured were greater than that of the FAO standards reference and are comparable with some other food proteins, such as soya bean and fish meal.
Full-text available
This work was an approach to waste date products valorization through biomass production with the yeast Saccharomyces cerevisiae. The carbon and nitrogen sources of a semi-synthetic fermentation medium were substituted by date-coat (fleshy part) sugar extract, date-seed hydrolysate, and ammonium nitrate. This modified medium was enriched with date-seed ash and date-seed lipid. Date-coat sugar extract as a carbon source was found to be satisfactory at a concentration of 25 g/l (expressed as its glucose concentration) and date-seed hydrolysate as a nitrogen source was equally suitable at 25 g/l. The addition to the medium of 1·0 g/l ammonium nitrate increased the efficiency of yeast biomass formation, as did phosphorus, which produced a maximum when the medium was supplemented with about 6·0 g/l KH2PO4. The presence of 1 g/l date-seed lipid in the medium also increased the efficiency of biomass formation. Finally, the addition of date-seed ash (0·6 g/l), as a mineral source, to the fermentation medium could substitute for MgSO4 and CaCl2 of the semi-synthetic medium.
The development of the production of torula yeast (Candida utilis) in Cuba at large scale is analyzed since 1964 up to the present with the first plant built in the country. This yeast is obtained from final molasses as energy source. The results of its composition and richness especially in respect to amino acids and B-complex vitamins are presented. The principal values of the productive performance are offered in the different swine categories by substituting soybean meal as protein source and also the production cost of torula yeast has been analyzed and compared to soybean. This was determined mainly by final molasses inverted and the energy expenses to produce a ton of dry yeast. Finally, the latest alternatives for producing torula from stillage sludge generated daily in large amounts are analyzed. The stillage sludge constitutes an environmental pollutant of great importance and demands necessarily of some treatment. The need for reinitiating research on animals is stated, as well as that for measuring the technical, economical and environmental impact of this new form of producing torula yeast.
This paper briefly describes the largest ethanol production plant in the Jilin Province, China opened in November 03. The plant has the capacity to process 2.3 million litres/day fuel ethanol. The process technology supplied by Vogelbusch is described and discussed.
Jerusalem artichoke has one of the highest carbohydrate yields of the known agricultural crops and has many distinct advantages over traditional crops. This brief review presents data on the yield and composition of Jerusalem artichoke, techniques of carbohydrate extraction and its utilization for the production of ethanol, single cell protein (SCP), and high-fructose syrup, along with economic considerations.
Leaf protein was separated by heat coagulation (80°C) from leaf juices of four cruciferous plants: turnip (Brassica campestris L.), mustard (Brassica nigra Koch.), radish (Raphanus sativus L.) and cauliflower (Brassica oleracea L. var. botrytis). Three yeasts, Saccharomyces cerevisiae, Torula utilis and Candida lipolytica, were grown in deproteinized leaf juices (DLJ) of these plants. The yeast cells produced in these wheys were found to be rich in protein and vitamins. The chemical oxygen demand (COD) and biological oxygen demand (BOD) values of DLJ samples were reduced significantly by the growth of yeasts.
Marine yeasts (33 strains) were isolated from the coastal and offshore waters off Cochin. The isolates were identified and then characterized for the utilization of starch, gelatin, lipid, cellulose, urea, pectin, lignin, chitin and prawn-shell waste. Most of the isolates were Candida species. Based on the biochemical characterization, four potential strains were selected and their optimum pH and NaCl concentration for growth were determined. These strains were then inoculated into prawn-shell waste and SCP (single cell protein) generation was noted in terms of the increase in protein content of the final product.
The acceptance of torula yeast grown on ethanol was evaluated by incorporation into familiar foods. Three preparations of torula yeast were used : Spray‐dried torula yeast (primary yeast), water‐washed torula yeast, and torula yeast treated to reduce the nucleic acid content. Control diets contained either soy flour or potato flour. These materials (20 ± 2 g) were incorporated into a midday meal and served to young adults (110 males, 85 females) five days per week for a three‐week period. Effects of the test meals were monitored by analysis of uric acid levels in blood and urine and by questionnaire. Subjectively, there were no major differences in the acceptance of test meals. Severe symptoms previously associated with ingestion of torula yeast were not found. Subjects in all test groups, whether consuming yeast, soy or potato, reported minor symptoms; but the incidence and severity did not change during the test period. Uric acid analysis indicated a slight increase in serum uric acid levels in those subjects consuming the primary or water‐washed yeast. The increase occurred during the first week of the study and the levels stabilized during the remainder of the study. Thus, torula yeast was an acceptable food supplement in this trial.
Thermotolerant yeast Candida rugosa isolated from East Africa was used for the continuous production of yeast protein from sugar beet stillages at 40°C. At a dilution rate of 0·15 h−1, biomass productivity was at a maximum (0·85 dm−3 h−1) and the Chemical Oxygen Demand reduction rate of the stillage was 30·4%. This yeast contained 45·1% crude protein, 36·5% actual protein and 5·6% RNA. The yeast protein had adequate essential amino acids, except for sulphur-containing types.
Distillers' yeasts, strains of Saccharomyces cerevisiae, although capable of sexual reproduction, in distillery practice reproduce asexually, by budding. A cell may bring forth another one in 50 min. With every ounce of whiskey produced, 30 billion new cells come to existence. Within a few days, in 4–8 propagation stages, a test tube full of culture will populate 100,000 gallons beer with 150 million cells per ml. Rate of reproduction, the number of new cells per each original cell varies from 5 to 50 in the various propagation stages. The number of new cells produced in a given nutrient is independent from the number of initial cells; and the utilization of the nutrient increases with the dilution of the substrate. Although distillers' yeasts may reproduce at such extremes as 1–46°C, 2½–10½ pH, presence of 0–15% alcohol by volume, and 0.1–25% sugar content, in distillery practice the factors are so selected to maintain conditions close to the optimum. When placed in the nutrient the initial cells will measure the chemical and physical characteristics of the new living space and the cell population, and will prepare a design of reproduction best suited to the conditions. The design includes a symmetry in the grouping of the cells and a rhythmic timing in starting new buds. Each healthy cells is biologically equal to the others and is capable of performing all functions characteristic of the strain. In spite of the sensitive coordination system between the individual cells that regulates their activity, marked differences exist among the cells to the degree of cell individuality. Distillers yeasts are superbly equipped to live and reproduce.