LACTIC ACID BACTERIA
LACTIC ACID BACTERIA
NAME : T.L.V.PEIRIS NAME : T.L.V.PEIRIS
DEPARTMENT:FOOD SCIENCE DEPARTMENT:FOOD SCIENCE
UNIVERSITY: UNIVERSITY OF SRI JAYAWARDENAPURA UNIVERSITY: UNIVERSITY OF SRI JAYAWARDENAPURA YEAR : AUGUST 2009
YEAR : AUGUST 2009
STUDENT NUMBER: GS/MSc/Food/3630/08 STUDENT NUMBER: GS/MSc/Food/3630/08
Summery Summery
Lactic acid bacteria in food
Lactic acid bacteria in food are considered as GRAS. This report contents various aspects of are considered as GRAS. This report contents various aspects of lactic acid bacteria. This report gives where
lactic acid bacteria. This report gives where these microorganisms thrive and their physiologicalthese microorganisms thrive and their physiological characteristics. It further explains in very descriptive manner the major metabolic pathways characteristics. It further explains in very descriptive manner the major metabolic pathways which they use to metabolize sugar.
which they use to metabolize sugar. Homofermentive metabolic pathway, HeterofermentativeHomofermentive metabolic pathway, Heterofermentative metabolic pathway (pentose phosphate pathway) and
metabolic pathway (pentose phosphate pathway) and EMP pathways are given in detail.EMP pathways are given in detail. Furthermore this report gives the usage of Lactic acid
Furthermore this report gives the usage of Lactic acid bacteria in food and furthermorebacteria in food and furthermore importance of Lactic acid bacteria as
importance of Lactic acid bacteria as probiotics also briefly explained.probiotics also briefly explained.
Key words: Lactic acid
Key words: Lactic acid , , Heterofermentative pathway, HomofermHeterofermentative pathway, Homofermetative Pathway, EMPetative Pathway, EMP pathway, probiotics
Contents
Contents Page Page numbernumber
Introduction 04
Introduction 04
Characteristics 04-05
Characteristics 04-05
Bio
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iii.i. HeHeteterorofefermrmenentatatitive ve memetatabobolilism sm of of hehexoxosesess iivv.. MMeettaabboolliissm m oof f mmaalliic c aacciidd
v.
v. EmEmbdbdenen-M-Meyeyererhohoffff-P-Pararnanas s papatthwhway ay ((EMEMPP)) i. Activation of Glucose
i. Activation of Glucose ii. Hexose Splitting ii. Hexose Splitting iii Energy Extraction iii Energy Extraction
iv. End Product Formation iv. End Product Formation Lactic
Lactic acid acid bacteria bacteria - - their their uses uses in in food food 1515 Probiotics
Probiotics and and LAB LAB 1616
Reference Reference
Introduction Introduction The
The Lactic Acid Bacteria (LAB)Lactic Acid Bacteria (LAB) comprise acomprise a cladecladeof of Gram-positiveGram-positive, low-, low-GGCC,, acid-tolerant,acid-tolerant, generally non-sporulating, non-respiring rod or cocci that are associated
generally non-sporulating, non-respiring rod or cocci that are associated by their commonby their common metabolic
metabolic andand physiological physiologicalcharacteristics. These bacteriacharacteristics. These bacteria, usually found in decomposing plants, usually found in decomposing plants and lactic products, produce
and lactic products, produce lactic acidlactic acidas the major metabolic end-product of as the major metabolic end-product of carbohydratecarbohydrate
fermentation. This trait has, throughout history, linked LAB with
fermentation. This trait has, throughout history, linked LAB with food fermentationsfood fermentations,, asas acidification inhibits the growth of spoilage agents. Proteinaceous
acidification inhibits the growth of spoilage agents. Proteinaceous bacteriocins bacteriocinsare produced byare produced by several LAB strains and provide an additional
several LAB strains and provide an additional hurdle for spoilage andhurdle for spoilage and pathogenic pathogenic
microorganisms. Furthermore, lactic acid and other metabolic products contribute to the microorganisms. Furthermore, lactic acid and other metabolic products contribute to the organoleptic and textural profile of a food
organoleptic and textural profile of a food item. The industrial importance of the LAB is further item. The industrial importance of the LAB is further evidenced by their reputed safe (
evidenced by their reputed safe (GRASGRAS) status, due to their ubiquitous appearance in food and) status, due to their ubiquitous appearance in food and their contribution to the healthy microflora of human
their contribution to the healthy microflora of human mucosalmucosalsurfaces. Thesurfaces. The generagenera that comprisethat comprise the LAB are at its core
the LAB are at its core Lactobacillus Lactobacillus,, Leuconostoc Leuconostoc,, Pediococcus Pediococcus,, Lactococcus Lactococcus, and, and Streptococcus
Streptococcus as well as the more peripheralas well as the more peripheral Aerococcus Aerococcus,, CarnobacteriumCarnobacterium,, Enterococcus Enterococcus,, Oenococcus
Oenococcus,, SporolactobacillusSporolactobacillus,, TeragenococcusTeragenococcus,, VagococcusVagococcus, and, and WeisellaWeisella; these belong to; these belong to the order
the order LactobacillalesLactobacillales.. Characteristics
Characteristics
The Lactic Acid Bacteria (LAB) are rod-shaped
The Lactic Acid Bacteria (LAB) are rod-shaped bacilli bacillior or coccuscoccus. LAB are characterized by an. LAB are characterized by an increased tolerance to a lower
increased tolerance to a lower pH pHrange. This aspect partially enables LAB to outcompete other range. This aspect partially enables LAB to outcompete other bacteria in a natural
bacteria in a natural fermentationfermentation,, as they can withstand the increased acidity from organic as they can withstand the increased acidity from organic acidacid production (e.g.,
production (e.g., lactic acidlactic acid). Laboratory media used for LAB typically includes a). Laboratory media used for LAB typically includes a carbohydratecarbohydrate
source as most species are incapable of
source as most species are incapable of respiration. LAB arerespiration. LAB are catalasecatalasenegative.negative. There are two main
There are two main hexosehexosefermentationfermentation pathways pathwaysthat are used to classify LAB genera. Under that are used to classify LAB genera. Under conditions of excess
conditions of excess glucoseglucoseand limited oxygen, homolactic LAB catabolize one mole of and limited oxygen, homolactic LAB catabolize one mole of glucose in the
glucose in the Embden-Meyerhof-ParnasEmbden-Meyerhof-Parnas(EMP) pathway to yield two(EMP) pathway to yield two molesmolesof of pyruvate pyruvate.. Intracellular
Intracellular redoxredox balance is maintained through the oxidation of balance is maintained through the oxidation of NADH NADH, concomitant with, concomitant with pyruvate reduction to lactic acid. This process yields two moles
pyruvate reduction to lactic acid. This process yields two moles ATPATPper glucose consumed.per glucose consumed. Representative homolactic LAB genera include
Representative homolactic LAB genera include Lactococcus Lactococcus,, Enterococcus Enterococcus,, StreptococcusStreptococcus,, Pediococcus
Pediococcus, and, andgroup I lactobacilli.group I lactobacilli. Heterofermentative LAB use the
Heterofermentative LAB use the pentose phosphate pathway pentose phosphate pathway, alternatively referred to as the, alternatively referred to as the pentose phosphoketolase pathway. One mole
pentose phosphoketolase pathway. One mole Glucose-6-phosphateGlucose-6-phosphateis initially dehydrogenated tois initially dehydrogenated to 6-phosphogluconate and subsequently decarboxylated to yield one mole of CO
6-phosphogluconate and subsequently decarboxylated to yield one mole of CO22. The resulting. The resulting
pentose-5-phosphate is cleaved into one mole glyceraldehyde phosphate (GAP) and one mole pentose-5-phosphate is cleaved into one mole glyceraldehyde phosphate (GAP) and one mole
acetyl phosphate. GAP is further metabolized to lactate as in
acetyl phosphate. GAP is further metabolized to lactate as in homofermentation, with the acetylhomofermentation, with the acetyl phosphate reduced to
phosphate reduced to ethanolethanolviavia acetyl-CoAacetyl-CoAandand acetaldehydeacetaldehydeintermediates. In theory, end-intermediates. In theory, end- products (including ATP) are produced in equimolar quantities from the
products (including ATP) are produced in equimolar quantities from the catabolismcatabolismof one moleof one mole of glucose. Obligate heterofermentative LAB include
of glucose. Obligate heterofermentative LAB include Leuconostoc Leuconostoc,, OenococcusOenococcus,, WeissellaWeissella, and, and group III lactobacilli.
Lactic acid bacteria Lactic acid bacteria
Metabolism of lactic acid bacteria Metabolism of lactic acid bacteria Metabolism of Sugars
Metabolism of Sugars
Lactic acid bacteria are chemotrophic,
Lactic acid bacteria are chemotrophic, they find the energy required for their entire metabolismthey find the energy required for their entire metabolism from the oxidation of chemical compounds. The oxidation of sugars constitutes the principle from the oxidation of chemical compounds. The oxidation of sugars constitutes the principle energy producing pathway.
energy producing pathway.
Lactic acid bacteria of the genera
Lactic acid bacteria of the genera Lactobacillus, Leuconostoc Lactobacillus, Leuconostoc andand Pediococcus Pediococcus, the important, the important bacteria to winemaking, assimilate sugars by either a homofermentative or heterofermentative bacteria to winemaking, assimilate sugars by either a homofermentative or heterofermentative pathway.
pathway.
Homofermentative Metabolism of Hexoses Homofermentative Metabolism of Hexoses
Homofermentative bacteria transform nearly all of the sugars they use, especially glucose into Homofermentative bacteria transform nearly all of the sugars they use, especially glucose into lactic acid. The homofermentative pathway includes a
lactic acid. The homofermentative pathway includes a first phase of all the reactions of first phase of all the reactions of glycolysis that lead from hexose to pyruvate. The terminal electron acc
glycolysis that lead from hexose to pyruvate. The terminal electron acc eptor in this pathway iseptor in this pathway is pyruvate which is reduced to lactic acid.
pyruvate which is reduced to lactic acid. See Figure 1. In fermentation, pyruvate isSee Figure 1. In fermentation, pyruvate is
decarboxylated to ethanal, which is the terminal electron acceptor, being reduced to ethanol. decarboxylated to ethanal, which is the terminal electron acceptor, being reduced to ethanol. Heterofermentative Metabolism of Hexoses
Heterofermentative Metabolism of Hexoses
Bacteria using the heterofermentative pathway, which includes
Bacteria using the heterofermentative pathway, which includes Leuconostoc Leuconostoc (the most important(the most important bacterium in enology) use the pentose
bacterium in enology) use the pentose phosphate pathway. In this pathway, NADPH is generatedphosphate pathway. In this pathway, NADPH is generated as glucose is oxidized to ribose 5-phosphate.
as glucose is oxidized to ribose 5-phosphate. This five-carbon sugar and its derivatives areThis five-carbon sugar and its derivatives are components of important biomolecules such as ATP, CoA,
components of important biomolecules such as ATP, CoA, NAD+, FAD, RNA andNAD+, FAD, RNA and DNA. NADPH is the currency of readily available reducing p
DNA. NADPH is the currency of readily available reducing p ower in cells (NADH is used in theower in cells (NADH is used in the respiratory chain). This pathway occurs in the cytosol.
respiratory chain). This pathway occurs in the cytosol. After being transported into the cell, a
After being transported into the cell, a glucokinase phosphorylates the glucose into glucose 6-Pglucokinase phosphorylates the glucose into glucose 6-P (glucose 6-phosphate). Its destination is completely different from the glucose 6-P in the
(glucose 6-phosphate). Its destination is completely different from the glucose 6-P in the homofermentative pathway. Two oxidation reactions occur: the
homofermentative pathway. Two oxidation reactions occur: the first leads to gluconate 6-P andfirst leads to gluconate 6-P and the second, accompanied by a decarboxylation, forms ribulose 5-P. See Figure 2. In each
the second, accompanied by a decarboxylation, forms ribulose 5-P. See Figure 2. In each of these reactions a molecule of NADP+ is reduced.
of these reactions a molecule of NADP+ is reduced. Ribulose 5-P can then be Ribulose 5-P can then be epimerized either epimerized either to ribose 5-P or to xylulose5-P.
to ribose 5-P or to xylulose5-P.
Xylulose 5-P is then cleaved into acetyl-phosphate and
Xylulose 5-P is then cleaved into acetyl-phosphate and glyceraldehydes 3-phosphate. See Figureglyceraldehydes 3-phosphate. See Figure 3. The glyceraldehyde 3-phosphate is metabolized
3. The glyceraldehyde 3-phosphate is metabolized into lactic acid by following the sameinto lactic acid by following the same pathway as in the homofermentative pathway. The acetylphosphate has two possible pathway as in the homofermentative pathway. The acetylphosphate has two possible
destinations, depending on environmental conditions. destinations, depending on environmental conditions.
This molecule can be successively reduced into ethanal and ethanol, in which case the molecules This molecule can be successively reduced into ethanal and ethanol, in which case the molecules of the coenzyme NADPH formed during the
of the coenzyme NADPH formed during the two oxidation reactions of glucose at the two oxidation reactions of glucose at the beginningbeginning of the heterofermentative pathway, are reoxidized.
of the heterofermentative pathway, are reoxidized.
This reoxidation is essential for regenerating the coenzymes necessary for this pathway. The This reoxidation is essential for regenerating the coenzymes necessary for this pathway. The final products are then lactate and ethanol.
final products are then lactate and ethanol.
Or the acetyl-phosphate can produce acetate (acetic acid) through the enzyme acetate kinase. Or the acetyl-phosphate can produce acetate (acetic acid) through the enzyme acetate kinase. This reaction also yields a molecule of ATP. The
This reaction also yields a molecule of ATP. The final products of this pathway are then lactatefinal products of this pathway are then lactate and acetate.
and acetate.
Bacteria of the genus
Bacteria of the genus Leuconostoc Leuconostoc preferentially produce lactate and ethanol in a preferentially produce lactate and ethanol in a slightly aeratedslightly aerated environment and lactate and acetate in an aerated environment.
Metabolism of Malic Acid Metabolism of Malic Acid
The majority of bacterial species preponderant in wine
The majority of bacterial species preponderant in wine after alcoholic fermentation break downafter alcoholic fermentation break down malic acid.
malic acid.
The most important bacterium in enology is the
The most important bacterium in enology is the heterofermentative bacteria,heterofermentative bacteria, Leuconostoc oenos Leuconostoc oenos.. This bacterium forms Dlactic acid from glucose and
This bacterium forms Dlactic acid from glucose and L-lactic acid from L-malic acid.L-lactic acid from L-malic acid.
The major distinction between wine and vinegar is the amount of acetic acid. The amount of The major distinction between wine and vinegar is the amount of acetic acid. The amount of acetic acid is estimated from the volatile acidity or VA
acetic acid is estimated from the volatile acidity or VA (the wine is steam distilled and the(the wine is steam distilled and the distillate titrated with sodium hydroxide using phenolphalein). A small amount of acetic acid is distillate titrated with sodium hydroxide using phenolphalein). A small amount of acetic acid is produced by yeasts, in particular
produced by yeasts, in particular Saccharomyces cerevisiaeSaccharomyces cerevisiae to the extent of 100-300 mg.L-1to the extent of 100-300 mg.L-1 (see Figure 5, Yeast
(see Figure 5, Yeast Biochemistry, Sugars).Biochemistry, Sugars). Bacteria degrade must and wine
Bacteria degrade must and wine sugars with a different affinity depending on the species. Insugars with a different affinity depending on the species. In general, bacterial development occurs after yeast dev
general, bacterial development occurs after yeast development. Since the yeast has consumed theelopment. Since the yeast has consumed the sugars, the lactic acid formed from them is small compared to the amount produced from malic sugars, the lactic acid formed from them is small compared to the amount produced from malic acid.
acid. L. oenos
L. oenos can and does produce can and does produce acetic acid from glucose (see figures 3 acetic acid from glucose (see figures 3 & 4), but since the lactic& 4), but since the lactic acid formed from them is low, so is the
acid formed from them is low, so is the acetic acid.acetic acid.
An increase in the VA (acetic acid) of a wine coupled with an abnormal amount of lactic acid An increase in the VA (acetic acid) of a wine coupled with an abnormal amount of lactic acid (>300 mg.L-1) indicates lactic disease and suggests the
(>300 mg.L-1) indicates lactic disease and suggests the L. oenos L. oenos fermented a significant quantityfermented a significant quantity of sugars.
of sugars.
Glycolysis - Embden-Meyerhoff-Parnas pathway (EMP) Glycolysis - Embden-Meyerhoff-Parnas pathway (EMP)
EMP is the most commonly used series of reactions for oxidizing glucose
EMP is the most commonly used series of reactions for oxidizing glucose to pyruvate and manyto pyruvate and many bacteria, animals and plants employ this pathway in their
bacteria, animals and plants employ this pathway in their catabolism. EMP is so ubiquitous thatcatabolism. EMP is so ubiquitous that is worthwhile to use it as an example
is worthwhile to use it as an example of a typical fermentation. It is an essential part of manyof a typical fermentation. It is an essential part of many organisms catabolism, even yours! However, it is not the only method for the fermentation of organisms catabolism, even yours! However, it is not the only method for the fermentation of glucose. Remember that bacteria are remarkably creative
glucose. Remember that bacteria are remarkably creative and other pathways are present inand other pathways are present in different species.
different species.
EMP can be divided into 3
EMP can be divided into 3 stages,stages,activation of glucoseactivation of glucose,,hexose splittinghexose splitting andandenergyenergy extraction
Activation of Glucose Activation of Glucose
Glucose is a relatively stable molecule and in order to degrade it, it must first be destabilized by Glucose is a relatively stable molecule and in order to degrade it, it must first be destabilized by adding high energy phosphates. In
adding high energy phosphates. In the first step a phosphate is donated the first step a phosphate is donated from ATP (or from ATP (or
phosphoenolpyruvate - the source of the phosphate depends on the species of microbe you look phosphoenolpyruvate - the source of the phosphate depends on the species of microbe you look
at) to glucose to form glucose-6-phosphate. The
at) to glucose to form glucose-6-phosphate. The molecule is isomerized to fructose-6-phosphatemolecule is isomerized to fructose-6-phosphate (another sugar) and a second
(another sugar) and a second phosphate is added. Fructose-1,6-bisphosphate is easier to attack phosphate is added. Fructose-1,6-bisphosphate is easier to attack than glucose and is ready to be split.
than glucose and is ready to be split.
Figure 3 - Activation of glucose by ph
Figure 3 - Activation of glucose by phosphorylation with ATP.osphorylation with ATP. Hexose Splitting
Hexose Splitting
Fructose bisphosphate aldolase then breaks the phosphate
Fructose bisphosphate aldolase then breaks the phosphate loaded fructose into two 3 carbonloaded fructose into two 3 carbon compounds, glyceraldehyde-3-phosphate (GAP) and dihydroxyacetonephosphate (DAP). This is compounds, glyceraldehyde-3-phosphate (GAP) and dihydroxyacetonephosphate (DAP). This is the crucial step in the EMP pathway, converting the 6 carbon glucose molecule to two 3 carbon the crucial step in the EMP pathway, converting the 6 carbon glucose molecule to two 3 carbon molecules that will eventually become pyruvate.
molecules that will eventually become pyruvate.
Figure 4 - Splitting of Fructose by aldolase. Figure 4 - Splitting of Fructose by aldolase. Energy Extraction
Energy Extraction
In the next reaction, DAP is converted
In the next reaction, DAP is converted into GAP, which can be into GAP, which can be acted on by the rest of the acted on by the rest of the EMP.EMP. The next step is a very important one. Inorganic phosphate is added to GAP to make
The next step is a very important one. Inorganic phosphate is added to GAP to make 1,3- bisphosphoglycerate (BPG). No energy is required and in fact electrons
bisphosphoglycerate (BPG). No energy is required and in fact electrons are transferred fromare transferred from GAP to NAD
GAP to NAD++. This reaction is the payback for running the pathway and the phosphates added. This reaction is the payback for running the pathway and the phosphates added
here are later transferred to ADP to make ATP.
here are later transferred to ADP to make ATP. After several enzymatic rearrangements, the finalAfter several enzymatic rearrangements, the final product of the EMP pathway is pyruvate.
Figure 5 - Extraction of Energy. Note the
Figure 5 - Extraction of Energy. Note the two reactions highlighted in blue that yield energy.two reactions highlighted in blue that yield energy. Remember that each glucose molecule
Remember that each glucose molecule that comes into glycolysis generates two GAP moleculesthat comes into glycolysis generates two GAP molecules that can then proceed down the latter half of the pathway.
that can then proceed down the latter half of the pathway. The total reaction can be summarized as follows
The total reaction can be summarized as follows 2 ATP + glucose + 4 ADP + 2 P
2 ATP + glucose + 4 ADP + 2 Pii+ 2 NAD+ 2 NAD++ 2 ADP + 2 pyruvate + 4 2 ADP + 2 pyruvate + 4 ATP + 2ATP + 2
NADH NADH
The blue highlight denotes energy
The blue highlight denotes energy put into the reaction. Subtracting this from the energyput into the reaction. Subtracting this from the energy extracted, the net energy gain
extracted, the net energy gain is 2 ATP per glucose. That is a is 2 ATP per glucose. That is a lot of work for just 2 ATP.lot of work for just 2 ATP. Fermentations do not yield large amounts of energy and
Fermentations do not yield large amounts of energy and this explains why fermenting microbesthis explains why fermenting microbes go through so much substrate without much growth.
go through so much substrate without much growth. Some of the NADH that is generated
Some of the NADH that is generated can be used for cell bcan be used for cell biosynthesis, but there is a large excessiosynthesis, but there is a large excess or reducing power. Fermenting bacteria must find a
or reducing power. Fermenting bacteria must find a way to get rid of these extra electrons away to get rid of these extra electrons andnd they do it by adding them to pyruvate to form end products.
they do it by adding them to pyruvate to form end products. End Product Formation
End Product Formation
One of the more familiar fermentations is conversion of glucose
One of the more familiar fermentations is conversion of glucose to ethanol to form alcoholicto ethanol to form alcoholic beverages. After the formation of pyruvate, ethanol is formed
beverages. After the formation of pyruvate, ethanol is formed by two simple reactions. First, COby two simple reactions. First, CO22
is removed from pyruvate to form acetaldehyde. Then
is removed from pyruvate to form acetaldehyde. Then acetaldehyde is reduced by, you guess it,acetaldehyde is reduced by, you guess it, NADH
Figure 6 - Oxidation of NADH. Acetaldehyde
Figure 6 - Oxidation of NADH. Acetaldehyde is reduced to ethanol (the active is reduced to ethanol (the active ingredient iningredient in alcoholic beverages). This is the final step in
alcoholic beverages). This is the final step in yeast fermentation of glucose to ethanol.yeast fermentation of glucose to ethanol. Another favorite microbial fermentation is the formation of lactic acid. This is performed
Another favorite microbial fermentation is the formation of lactic acid. This is performed by theby the lactic acid bacteria. Homofermentative lactic acid bacteria
lactic acid bacteria. Homofermentative lactic acid bacteria use the EMP pathway to makeuse the EMP pathway to make pyruvate and then reduce
pyruvate and then reduce it to lactate using up their excess NADH in it to lactate using up their excess NADH in the process. Other bacteriathe process. Other bacteria use alternative pathways to generate lactate from glucose. Close examination of the
use alternative pathways to generate lactate from glucose. Close examination of the heterofermentative pathway reveals that it does not use EMP at
heterofermentative pathway reveals that it does not use EMP at all. The take home all. The take home message is,message is, EMP is common, but there are many other
EMP is common, but there are many other ways of doing business.ways of doing business. figure 7 - Formation of lactate by homofermentative bacteria. The
figure 7 - Formation of lactate by homofermentative bacteria. The pathway used is identical topathway used is identical to glycolysis. The final end product is lactate which is excreted
glycolysis. The final end product is lactate which is excreted by the cells into their environment.by the cells into their environment.
Figure 8 - Fermentation of glucose by heterofermentative bacteria. In
Figure 8 - Fermentation of glucose by heterofermentative bacteria. In this pathway the top part of this pathway the top part of the glycolytic pathway is not used. Note the recycling
the glycolytic pathway is not used. Note the recycling of NADH and the low yield. Only oneof NADH and the low yield. Only one ATP is generated per glucose fermented.
Lactic acid bacteria - their uses in food Lactic acid bacteria - their uses in food
Lactic acid bacteria have been used to ferment or culture foods for at least 4000 years. They are Lactic acid bacteria have been used to ferment or culture foods for at least 4000 years. They are used in particular in fermented milk products from all over the world, including yoghurt, cheese, used in particular in fermented milk products from all over the world, including yoghurt, cheese, butter, buttermilk, kefir and koumiss.
butter, buttermilk, kefir and koumiss.
Although they are best known for their role in the preparation of fermented dairy products, they Although they are best known for their role in the preparation of fermented dairy products, they are also used for pickling of vegetables,
are also used for pickling of vegetables, baking, winemaking, curing fish, meats and baking, winemaking, curing fish, meats and sausages.sausages. Wi
Withothout ut undeundersrstantandinding g the the scisciententifific ic basbasis, is, peopeople ple thothousausands nds of of yeayears rs ago ago useused d laclactitic c aciacidd bacteria to produce cultured foods with improved preservation properties and with characteristic bacteria to produce cultured foods with improved preservation properties and with characteristic
flavours and textures different from the original food. flavours and textures different from the original food.
Similarly today, a wide variety of fermented milk products including liquid drinks such as kefir Similarly today, a wide variety of fermented milk products including liquid drinks such as kefir and semi-solid or firm products like yoghurt and cheese respectively, make good use of these and semi-solid or firm products like yoghurt and cheese respectively, make good use of these illustrious microbial allies.
illustrious microbial allies.
The manufacture involves a microbial process by which the milk sugar, lactose is converted to The manufacture involves a microbial process by which the milk sugar, lactose is converted to lactic acid. As the acid accumulates, the structure of the milk protein changes (curdling) and thus lactic acid. As the acid accumulates, the structure of the milk protein changes (curdling) and thus the texture of the product. Other variables such as temperature and the composition of the milk, the texture of the product. Other variables such as temperature and the composition of the milk, also contribute to the particular features of different products.
also contribute to the particular features of different products.
Lactic acid also gives fermented milks their slightly tart taste. Additional characteristic flavours Lactic acid also gives fermented milks their slightly tart taste. Additional characteristic flavours an
and d araromomas as arare e ofofteten n ththe e reresusult lt of of ototheher r prprododucucts ts of of lalactctic ic aciacid d bacbacteteriria. a. FoFor r exaexampmplele acetaldehyde, provides the characteristic aroma of yoghurt, while diacetyl imparts a buttery taste acetaldehyde, provides the characteristic aroma of yoghurt, while diacetyl imparts a buttery taste to other fermented milks. Additional micro-organisms such as yeasts can also be included in the to other fermented milks. Additional micro-organisms such as yeasts can also be included in the culture to provide unique tastes. For example, alcohol and carbon dioxide produced by yeasts culture to provide unique tastes. For example, alcohol and carbon dioxide produced by yeasts con
contritributbute e to to the the refrefresreshinhing, g, frofrothy thy tastaste te of of kefkefirir, , koumkoumiss iss and and lebleben. en. OthOther er manmanufaufactucturinringg techniques such as removing the whey or adding flavours, also contribute to the large variety of techniques such as removing the whey or adding flavours, also contribute to the large variety of available products.
available products. For
For yogyoghurhurt, t, the the manmanufaufactucture re depedepends nds on on a a sysymbimbiotiotic c relrelatiationsonship hip betbetween ween two two bacbacterteria,ia, Strept
Streptococcus ococcus thermopthermophilushilus andand Lacto Lactobacilbacillus lus bulgaribulgaricus,cus, whewhere re eaceach h spespeciecies s of of bactbacterieriumum stimulates the growth of the other. This interaction results in a shortened fermentation time and a stimulates the growth of the other. This interaction results in a shortened fermentation time and a product with different characteristics than one fermented with a single species.
product with different characteristics than one fermented with a single species.
With yoghurt and other fermented milks there are considerable opportunities for exploiting lactic With yoghurt and other fermented milks there are considerable opportunities for exploiting lactic aci
acid d bacbacterteria ia as as proprobiobiotitic c culculturtures. es. TheThese se supsuppleplemenment t and and helhelp p our our nornormal mal gut gut bacbacterteria ia toto function more efficiently. The world-wide market for these products continues to increase in function more efficiently. The world-wide market for these products continues to increase in response to the demands of an
response to the demands of an increasingly health-conscious public.increasingly health-conscious public.
Lactic acid bacteria are therefore excellent ambassadors for an often maligned microbial world. Lactic acid bacteria are therefore excellent ambassadors for an often maligned microbial world. They are not only of major economic significance, but are also of value in maintaining and They are not only of major economic significance, but are also of value in maintaining and promoting human health.
Probiotics and LAB Probiotics and LAB Probiotics
Probioticsare products aimed at delivering living, potentially beneficial, bacterial are products aimed at delivering living, potentially beneficial, bacterial cells to the gutcells to the gut ecosystem
ecosystem of humans and other animals, whereasof humans and other animals, whereas prebiotics prebioticsare non-digestibleare non-digestible carbohydratescarbohydrates
delivered in food to the large
delivered in food to the large bowel to provide fermentable substrates for selected bacteria.bowel to provide fermentable substrates for selected bacteria. Strains of LAB are the most common microbes employed a
Strains of LAB are the most common microbes employed a s probiotics. Two principal kinds of s probiotics. Two principal kinds of probiotic bacteria, members of the genera
probiotic bacteria, members of the genera Lactobacillus Lactobacillusandand Bifidobacterium Bifidobacterium, have been studied, have been studied in detail.
in detail.
Most probiotic strains belong to the genus
Most probiotic strains belong to the genus Lactobacillus Lactobacillus.. Probiotics have been evaluated inProbiotics have been evaluated in
research studies in animals and humans with respect to antibiotic-associated diarrhoea, travellers' research studies in animals and humans with respect to antibiotic-associated diarrhoea, travellers' diarrhoea, pediatric diarrhoea,
diarrhoea, pediatric diarrhoea, inflammatory bowel diseaseinflammatory bowel disease, and irritable bowel syndrome, andirritable bowel syndrome. It is. It is possible that, in the future, probiotics will be used
possible that, in the future, probiotics will be used for different gastrointestinal diseases,for different gastrointestinal diseases, vaginosis
vaginosis, or as delivery systems for vaccines, immunoglobulins, and other , or as delivery systems for vaccines, immunoglobulins, and other therapies.therapies. References
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