microbiology waseeem

1. Education University LMC Lahore
Topic :
Role of Microbes in dairy industry
Introduction:
Since ancienttimes,dairyproductshave beenpartof humandiet.These serve asgoodsource of
calcium,vitaminD,proteinsandotheressential nutrients.Theseproductsalsoprovidephosphorus,

2. potassium,magnesium,andvariousvitaminsviz.vitaminA (retinols),vitaminB12(cyanocobalamin),
and riboflavin.Variousfermenteddairyproductsare preparedusingdifferentmicrobialstrains.
Microbesfermentthe carbohydratespresentinmilk,whichismainlylactose tolacticacidand some
otherproducts.The acid precipitatesthe proteinsinthe milk;therefore fermentedproductsare usually
of thickerconsistencythanmilk.The highacidityandlow pHhindersthe growthof otherbacteria
includingpathogens.The fermentationof milkprovidedasimple wayto increase itsshelf-lifewhile
improvingitssafety.Humanslearnedtocontrol fermentationprocessesfromthe initial accidental
eventsinfermentation.Thislearningof controlledfermentationof milkindomesticpracticesgave rise
to a diverse dairyproductsinfluencedbyhabitsof differentethnicities,geographical environmentsand
type of dairy farming[1].
Now,a huge varietyof fermenteddairyproductsare available forconsumers.Althoughasmall
proportionof these productsare homemade,mostof themare producedindustrially.The productionof
fermentedproductsiseconomicallyimportantinmanycountries.Asthe requirementof fermented
productsis increasingdaybyday,and inmany countriesdairyindustriesare contributingineconomic
growth. The firstexample of fermentedmilkwaspresumablyproducedaccidentallybynomads.This
milkturnedsourand coagulatedunderthe influenceof certainmicroorganisms.Byluckitwas having
harmless,acidifyingtype andnontoxinproducingbacteria.
Varioustypesof fermentedmilksandderivedproductshave beendevelopedinall partsof the world
each withitsowncharacteristichistory.Theirnature dependsverymuchonthe type of milkused,on
the pre-treatmentof the milk,onthe temperature(climate),conditionsof fermentationandonthe
subsequenttechnological treatments.Mostcommonlyuseddairyproductsinclude curd,yogurt,cheese,
kefirandkumis
Curd
Curd ismade by curdlingorcoagulatingthe milk.Thiscan be done bymixingedibleacidicsubstancesin
to the milk,suchas lemonjuice orvinegar.Byaddingthese substancestothe milk,itwill curdle the milk
and separate intotwoparts.The liquidpartisthe wheyandthe solidmilkisthe curd.The wheycontains

3. wheyproteinsof the milk,whereasthe curdsare the milkproteinsorcasein.Sometimesoldmilkmight
getsouredand isseparatedwithoutanyaddedacidicsubstance.Thishappensbecauseraw milk
containsLactobacillus.Lactobacillusisagenusof bacteriathat convertssugarsintolactic acidby means
of fermentation.Milkcontainsasugarcalledaslactose,a disaccharide (compound sugar) havingβ-1,4-
glycosidicbondbetweengalactoseand glucose.Lactobacillusconvertslactoseof the milkintolacticacid
whichimpartsthe sour taste to curd .
Yogurt
Yogurt ismost commonlyuseddairyproduct.Itispreparedbyheatingthe milkupto nearly80°C in
orderto kill anyadditional bacteria thatmaybe presentandto denature milkproteins.The milkisthen
allowedtocool slowlytoaround45°C, and thereafter,itisinoculatedwithabacteria,andis allowedto
fermentatroom temperature.The bacteriausedare Lactobacillusdelbrueckii subsp.bulgaricusand
Streptococcussalivariussubsp.thermophilus.If bacteriaisnotavailable,thenaspoonful of yogurtcan
alsobe usedasit containsbacteria.ProbioticbacterialikeStreptococcusthermophilus,Lactobacillus
acidophilusandbifidobacteriacanalsobe usedforthe productionof yogurtandit iscommonlyreferred
as bioyogurt.Manyevidencesindicatedthatconsumptionof ‘probiotic’microorganismshelpsin
maintainingafavorable microbial profile andisresultedinseveraltherapeuticbenefits
[4].
In industry,large quantityof yogurtisproducedthatisaffectedbynumberof factorsviz.choice of milk,
milkstandardization,milkadditives,de-aeration,homogenizationandheat-treatment,choice of culture
and plantdesign.The milkusedforyogurtproductionmustbe of the highestbacteriological quality.It
musthave a lowcontentof bacteriaand substanceswhichmayimpede the developmentof the yogurt
culture.Itmust notcontainantibiotics,bacteriophagesorsterilizingagents.The fatanddrysolids
contentsof the milkmustbe standardizedandadditiveslike sweetenerorsugarand stabilizercanbe

4. used.The air contentof the milkshouldbe as low as possible sothatviscosityandstabilityof the yogurt
isimproved.Toassure uniformdistributionof milkfatandtopreventcreamingduringincubation
period,milkishomogenized.The milkisheatedbeforeinoculationtoimproveitspropertiesasa
substrate forthe bacterial culture.Manytypesof yogurt culturesare available thatcanbe selected
basedon the type of yogurt production.The plantlayoutisveryimportantasthe selectionand
dimensionsof pipes,valves,pumps,coolersetcaffectsthe production[5].
Cheese:
Cheese isafermentedmilkproductandhistoricallyservingasameanof preservingmilk.Cheese making
occurs inthree mainstages:In the firststage,milkismouldedintosolidcurdandliquidwheybythe
coagulationof the milkprotein,casein.The coagulationof caseinisdone throughtwocomplementary
methods:acidificationandproteolysis.Acidificationoccurswhenlacticacidbacteriafermentthe
disaccharide lactose toproduce lacticacid.Originally,itcanbe done bynaturallyoccurringlacticacid
bacteriainthe milkbuttoday,dairyindustriesusuallystandardize the processbythe additionof
domesticatedbacterialcultures,includingstrainsof Lactococcuslactis,Streptococcusthermophilusand
Lactobacillussp.The productionof acidby these bacteriacausescaseintocoagulate slowly.Thisprocess
isoftenassistedbythe additionof the enzyme,chymosin(active ingredientinrennet).Chymosin
removesnegativelychargedportionof caseinthatresultsinrapidaggregationof caseinproteins.
In the secondstage,curd isseparatedcontainingthe caseinandmilkfatfromthe whey.Dependingon
the type of cheese,the curdcan be heated,salted,pressedandismouldedintovariousshapesand
sizes.Cheesecanbe eatenafreshat thispoint,orcan be lefttoage ina damp, cool place.Duringthe
agingstage,cheese istrulytransformedfromfreshcheeseintothe myriadflavours,aromas,and
texturesof mature cheese.Asanormal part of the agingprocess,culturesandlacticacid bacteria
continue togrow andmetabolize the interiorof the cheese,while the surface of acheese iscolonizedby
bacteriaand fungi thatform a multispeciesbio-filmcalledas‘rind’of the cheese [6].

5. Diversityinthe cheese flavor,smell andtexture isbecause of differentmicrobes.Cheeseflavoris
associatedwiththe aminoacidcatabolism.The abilityof lacticacidbacteriaandothercheese
microorganismstodegrade aminoacidstoaroma compoundsishighlystraindependent.These are
equippedwithenzymesystemsforusingaminoacidsintheirmetabolism.Differentamino acids
catabolismgivesdifferentflavors’asfollows[7,8]:
I. Branched-chainaminoacids(Leu,Ile,Val)are convertedtomalty,fruityandsweatyflavors.
II. Aromaticaminoacids(Phe,Tyr,Trp) produce floral,chemical andfaecal flavors.
III. Asparticacid (Asp) iscatabolisedintobutteryflavors.
IV. Sulphur containing amino acids (Met, Cys) are transferred to boiled cabbage, meaty and garlic
flavors.
Kefir
Kefirisa fermentedmilkbeverage whichhasitsancientorigininEasternEurope.Thislightalcoholic
beverage ispreparedbyinoculationof raw milkwithirregularlyshaped,gelatinouswhite/yellow grain
calledkefirgrains.These Kefirgrainshave varyingandcomplex microbialcompositionthatincludes
speciesof yeasts,lacticacidbacteria,aceticacidbacteriaand mycelial fungi.Lacticacidbacteria
includedinkefirare Lactobacillusfermentum, Lactobacillusacidophilus,Lactobacillushelveticus,
Lactobacilluscasei,Lactobacilluskefiri,Leuconostocmesenteroides,Lactobacillusparakefiri,
LactobacillusbrevisandLactococcuslactis.Aceticacidbacteriainclude Acetobacteraceti and
Acetobacterrasens;yeastsincludeCandidalambica,Kluyveromycesmarxianus,Saccharomyces
exiguousandTorulakefir.The populationcompositionmaydifferbasedonthe originof grainor the
methodandsubstrate bywhichgrainshave been cultured.tured.A symbioticrelanotionshipexists

6. betweenthe microbespresentinthe Kefirgrainsandithas beenshownthatthere are specificspecies
that always occur inthe grains .
Kumis (Koumiss)
Kumisandkefirare similardairyproductsbutkumisisproducedfroma liquidstarterculture as
comparedto solidkefir"grains".Ithasmildalcohol contentascomparedtokefirbecause mare'smilk
containsmore sugarsthan othermilks.Itis verypopularinKirgizstan,Mongolia,Kazakhstanandsome
regionsof RussiaandBulgaria.It isusuallymade from, area’smilkbyspontaneousfermentationof
lactose to lacticacid andalcohol.Dependingonthe lacticacid contents,kumisisof three types- strong,
moderate andlight.
A. Strong kumis: It is generated by lactic acid bacteria like Lactobacillus bulgaricus, Lactobacillus
rhamnosus. There is acidification of milk to pH 3.6–3.3 and conversion ratio of lactose into lactic acid
isabout 80–90%.
B. Moderate kumis: It involves Lactobacillus bacteria viz. L. Acidophilus, L. Plantarum, L. Casei, L.
fermentum with restricted acidification properties that lower the pH to 4.5–3.9 at the end of the
processand the conversionratioaverages50%.

7. C. Light kumis: It is a slightly acidified product (pH 4.5– 5.0) and is produced using Streptococcus
thermophilusandStreptococcuscremoris[11].
Role of mocrobial enzymes in flavour development in foods:
There are four main sources of enzymes in foods—these being the inherent enzymes, enzymes
from microbial contaminants, enzymes elaborated by microorganisms added to foods, and specific
enzymes added to foods. This study primarily deals with the latter two sources of enzymes in food.
Although both plants and animals serve as sources of enzymes, they are not as economical or
versatile sources as are enzymes obtained from microorganisms. In the meat industry, proteases
are used to tenderize muscle and to obtain flavor precursors. In the preparation of cured meat
products such as sausages, lipases, and proteases from bacterial cultures are utilized. Similarly,
proteases and lipases are used in the dairy industry to develop flavor compounds. Proteases and
amylases also have applications in the baking and milling industries where they are used to produce
precursors for the nonenzymatic browning reactions. Carbohydrases such as amylase,
amyloglucosidase, and glucose isomerase have found usage in the starch and syrup industry for the
production of high dextrose and high fructose syrups. Other enzymes such as glucose oxidase,
pectinase, and naringinase are of value to the wine and fruit juice industries. A better understanding
of the mode of action of enzymes as well as the mechanisms of development of flavor compounds
will further enhance the use of microbial enzymes to develop specific and desired flavors in foods.

8. Fermenteddairyproducts:
Fermented dairy products have been prepared and consumed by people for
centuries due to their high nutritional values.
 The fermentation is usually performed by lactic acid bacteria which ferment the lactose
in milk and convert it to lactic acid leading to precipitation of the proteins.
 There is a tremendous variety of fermented dairy products in many regions in the world.
The properties of each product depend on the local strains used for the fermentation.
 Many lactic acid bacteria have also been investigated for medicinal health benefits in the
past few decades but so far the results are inconclusive.
Fermented milk or dairy products have been part of human diet since ancient
times. Various fermented products are made by different strains. Lactic acid
fermentation is performed most often by lactic acid bacteria. Due to their
abundance in nature, including mucosal surfaces of the human body, and their
use in fermented foods they are labeled as GRAS (generally recognized as safe).
The main genera that belong to the lactic acid bacteria group
are: Lactobacillus, Leuconostoc, Lactococcus, Pediococcusand Streptococcus.
These bacteria ferment the carbohydrates in milk, the major one being lactose,
to lactic acid and some other products. The acid precipitates the proteins in the
milk and that is why fermented products are usually of thicker consistency than
milk. The high acidity and low pH hinders the growth of other bacteria, including
pathogens. Some lactic acid bacteria can produce agents with antimicrobial
properties. Since milk is rich in many nutrients such as protein, calcium,
phosphorus, and B vitamins dairy products are an excellent food

9. The single most important development permitting the
formation of civilization was the ability to produce and store
large quantities of food . Hunter-gatherer societies lived
from day to day either starving or gorging themselves based
upon the amount of food they could find in a day. When it
became possible for one person to produce more food then
they needed, time from gathering food could be apportioned
to culture and science. Following this trend, it became
beneficial to be able to store as much food as possible in order
to minimize the amount of time spent gathering that food.
Food storage has always been at odds with food spoilage.
Some of the earliest evidence of food preservation comes from
the post-glacial era, from 15,000 to 10,000 BC. The first use
of biological methods was from 6000 to 1000 BC when
fermentation was used to produce beer, bread, wine, vinegar,
yoghurt, cheese and butter. In 1864, Louis Pasteur proved
that microorganisms in foods were the cause of food
spoilage, that heat treatment of food killed these microbes
and that sealed containers helped to preserve food by
preventing recontamination from atmospheric air. A major
development in the distribution and storage of foods came in
002

10. 1940 with the availability of low cost home refrigerators and
freezers. Other developments included the artificial drying,
vaccum packaging, ionizing radiations and chemical
preservation.
Now-a-days consumers are concerned about the synthetic
chemicals used as preservatives in food , and there is resulting
trend towards less processed food. These untreated foods can
harbour dangerous pathogens which can multiply under
refrigeration and without oxygen . A solution to this dilemma
is the use of antimicrobial metabolites of fermentative
microorganisms . Many antimicrobial chemicals have been in
use for a long time without any known adverse effects. Many
of the organic compounds which have stirred interest are
antimicrobial metabolites of bacteria used to produce , or
associated with fermented foods.
In fermentation, the raw materials are converted by
microorganisms (bacteria , yeast and molds) to products that
have acceptable qualities of food. In common fermented
products such as yogurt, lactic acid is produced by the starter
culture bacteria to prevent the growth of undesirable
microorganisms (Ray and Daeschel 1992). Food fermentationhave a
great economic value and it has been accepted that

11. these products contribute in improving human health. LAB
have contributed in the increased volume of fermented foods
world wide especially in foods containing probiotics or health
promoting bacteria.
Micro-organisms of genera Lactococcus, Lactobacillus,
Leuconostoc, Streptococcus and Pediococcus are involved in
these fermentations. In addition, Lactobacillus spp. and
species of Bifidobacterium which is not LAB in nature are part
of normal human intestinal microflora and they exert a positive
effect on human health. (Daly and Davis, 1998).
This review will focus on some of the properties of LAB that
contribute to their roles in biopreservation and in modulating the
health of their hosts.

12. Bacteriocin
Producer organism
Properties
Nisin
Lactococcus lactis subsp. lactis
Lantibiotic, broad spectrum,chromosome/plasmid mediated,
ATCC 11454
bactericidal, produced late in the growth cycle
Pediocin A
Pediococcus
Broad spectrum, plasmid mediated
pentosaceus FBB61
and L-7230
Pediocin AcH
Pediococcus
Broad spectrum, plasmid mediated
acidilactici H
Leucocin
Leuconostoc gelidum
Broad spectrum, plasmid
UAL 187

13. mediated, bacteriostatic, produced early in the
growth cycle
Helveticin J
L.helveticus 481
Narrow spectrum, chromosomally mediated, bactericidal
Carnobacteriocin
Carnobacterium
Narrow spectrum, plasmid mediated, produced early in the growth
cycle.