Industrial Lecture 3
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Transcript of Industrial Lecture 3
8/4/2019 Industrial Lecture 3
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BIO 425Industrial Microbiology
Seyhun YURDUGÜL
Lecture 3Malolactic fermentation of wines
andother alcoholic beverages
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C
ontent outline� Malolactic fermentation
� Beer making� Microorganisms of beer
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Malolactic fermentation� After alcoholic fermentation
� Starts about 2-3 weeks after the alcoholicfermentation
� lasts about 2-4 weeks
� Lactic acid bacteria: Lactobacillus, Leuconostoc and Pediococcus species areresponsible
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Main rxn of Malolactic Fermentation� L-malic acid L-lactic acid + CO2
ÇDecarboxylation rxn by Malate carboxylase(malolactic enzyme)
Ç
Provides a rise of pH between 0.3-0.5 units
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Importance of acidity� Provides a very softer, good quality
drinkable and very good taste
� Completion of malolactic fermentationleads to greater microbiological stability &wines are less prone to spoilage by other
species of bacteria
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Taste of wines are designed by
µmalolactic fermentation¶
� Malolactic bacteria produce off-flavors likediacetyl & acetoin to give a fruitful blend
� Increase the attitude through taste
perception� If microbial load increase Unwanted wines
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Alternatives to deacidify wines� Yeast addition
� S chizosaccharomyces pombe
� S chizosaccharomyces malidevorans
� Completely metabolize malic acid-anaerobically
� Malic acid Pyruvate Acetaldehyde
Ethanol
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Beer production� Fermented extract of malted cereal grains,
principally barley
� Has an ethanol content of 2-6% and adistinctive flavor
� Flavor arises from the constituents of malt,
extracts of hops and products of yeastmetabolism
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Beer production� S accharomyces cerevisiae -formerly calledS accharomyces carlsbergensis andS accharomyces uvarum
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Outline of processBarley
Malting (Steeping, Germination, Kilning)
Malt
Mashing
Wort
Boiling
Fermentation
Water Adjuncts, Enzymes
Spent grain
Spent hopsHopped wort
Pitching yeast
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Malting & Steeping� Cause enzymatic degradation of raw
material into fermentable sugars
� First stage is steeping, where barley grainsare soaked in water at 10-15° C for 3 days
� Increase moisture to speed up germination
� Synthesis of enzymes e.g. amylases, proteases, peptidases
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Kilning� Terminates germination
� Heat is applied for drying of grains up to85° C
� Browning Gives the color
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Mashing� Extraction of fermentable sugars from the
grain
� Further enzymatic degradation of starch & protein
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Fermentation tanks� Designed as
� Large
� Stainless steel, cylindroconical vessels
� Facilities for temperature control, stirringand cleaning in place(CIP)
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Fermentation style of beer � Primary & secondary
� Primary ferm. consists separation of
sedimented yeast cells� Further clarification for packaging or
transferred to another tank for low T(3-5°C)
& secondary ferm. + maturation� Secondary ferm. is provided by residualsugar & yeast cells
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Important points in fermentation
process where m/o have impact upon beer quality
� Preparation of barley & malt
� Management of the wort� Primary fermentation
� Secondary fermentation & maturation
� Retailing of bulk beer
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M/o¶s of beer � For barley & malt
� Depends on climatic conditions,contamination of barley kernels duringharvesting, post harvest storage conditions,m/o growth on kernels during malting, m/o
survival after kilning of malted barley
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M/o¶s of beer � Some of the important genera
� Bacteria: Bacillus, Brevibacterium,
Corynebacterium, Microbacterium,
S treptomyces, Pseudomonas spp.
� Yeast: Rhodotorula, S porobolomyces,
Hansenula, Candida, Cryptococcus spp.
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M/o¶s of beer � Mold: Alternaria alternata, Cladosporium
spp.
� If moisture of barley (12.5%), A spergillus,Penicillum,Fusarium spp. maysignificantly grow
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M/o¶s of beer � At wort phase
� If hygiene is delayed: Bacillus( B.
stearothermophilus, B. coagulans),Clostridium spp.
� Produce lactic & butyric acid, leads to
acidification & off-flavors
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Fermentation� Dominated by S accharomyces cerevisiae
� Recombinant DNA & classical geneticmethods are applicable
� Leads µacceptable flavor¶
� Range of strains leads to different varietiesof beers (present in quality assurance
programs of breweries)
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Fermentation� Initiated by inoculating(pitching) the wort
with desired S.cerevisiae (start pop. 10-15
X 106 cfu/mL)� Breweries produce own yeast for pitching-
start with a pure slant & propagate cells in
progressively increasing volumes of sterilized wort to give the amount neededfor pitching
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Fermentation� On pitching the wort,
� yeasts commence growth with very little lag phase
� Active fermentation is visible by 12-24 hr.
� In 2-4 days, yeasts multiply up to 6-8 X 107
cfu / mL
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Main factors affecting the rate of
fermentation� Yeast concentration & viability of yeast
cells inoculated
� Temperature of fermentation
� Dissolved oxygen in the wort at pitchingtime
� Fermentable carbohydrates and available N2
concentration in the wort
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If improper hygiene!� Contamination
� Killer yeast strains of S.cerevisiae,
Hanseniaspora, Kluvyeromyces,
Torulaspora, Zygosaccharomyces spp
� Enterobacter spp. , Zymomonas mobilis for
bacterial contaminants.
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LIT
ERAT
UREC
IT
ED� Forsythe, S.J. The Microbiology of Safe
Food, Blackwell Science, Cambridge, 2000.
� Wood, B. J. B., Microbiology of FermentedFoods, Vol.1 and 2, Blackie Academic andProfessional, London, Second edition, 1998.