Transcript Microbiology Of Fermented Foods and Beverages

MICROBIOLOGY OF FERMENTED
FOODS AND BEVERAGES
BY: MOMINA MASUD
CONTENTS
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Introduction.
Properties of fermented foods and beverages.
Microorganisms and metabolisms.
Role of bacteria in the production.
Lactic acid bacteria.
The main genera of lactic acid bacteria.
Role of molds and yeast in the production.
Cultured dairy products.
Cheese
Beer fermentation
INTRODUCTION
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Fermented foods and beverages are one of the
first foods used by human beings.
Tastes better and well conserved.
It is important to regulate the growth and
activity of microorganisms.
Microorganisms need to be standardized.
Activity constantly fluctuates due to encounter
with different inhibitory chemicals.
Fermented food and beverages industry must
meet demands of:
1. Steadiness
2. Superiority and
3. Protection
PROPERTIES OF FERMENTED FOODS AND
BEVERAGES
1.
2.
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6.
Preservation.
Nutrition.
Functionality.
Organoleptic.
Uniqueness.
Economic value.
MICROORGANISMS AND METABOLISMS
Ethanol producing yeasts and bacteria producing
lactic acid are the most frequently used.
 Some organisms play involuntary role.
 For example the production of tempeh,
 Manufactured after the inoculation of soybeans
with rhizopus oligosporus
 Contamination may occur due to presence of
vitamin B12 synthesizing bacteria.
 Makes tempeh a fine source of vitamin B12
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ROLE OF BACTERIA IN THE PRODUCTION OF
FERMENTED FOOD AND BEVERAGES
The bacteria are divided into three main phyla:
1. Firmicutes.
a) gram positive bacteria-lactic acid bacteria
b) bacillus and brevibacterium-less common
2. Proteobacteria.
a) gram negative bacteria-vinegar fermentation and
wine spoilage.
3. Actinobacteria.
a) staphylococcus-used in meats for flavoring.
b) bifidobacterium-added to enhance nutritional
worth.
c) micrococcus.
THE LACTIC ACID BACTERIA
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Gram positive rods and cocci, non spore forming.
Aero tolerant, acid tolerant and facultative anaerobes.
Heterotrophic chemoorganotrophs, due to their carbon and
energy needs.
Consist of species which are adaptable to less nutrient rich
environments.
Inhabit habitats like: meat, low pH foods, ethanolic
environments, milk etc.
Capable of breaking down sugars to produce lactic acid and
other products.
Make them very important in fermentations.
Two Fermentative pathways
Homo fermentative
Pathway: almost 90%
conversion of sugar
substrate just to
Lactic acid.
Hetero fermentative
pathway: 50%
conversion to lactic acid
rest is converted to
CO2, acetic acid and
ethanol.
RESPIRATION IN LACTIC ACID BACTERIA
Lactococcus lactis contains an integral respiratory
pathway consisting of:
1. cytochromes
2. dehydrogenases
3. menoquinones
4. Gene cydAB-encodes for cytochrome oxidase,
supplies the terminal oxidase.
note: heme is missing in this pathway and needs to
be added, as it is essential for the activity of
catalase enzyme and cytochrome proteins.
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After a fermentative period, respiratory growth period
follows.
Lactococci were provided respiring conditions (aerobic
and presence of heme)-cell growth was much better.
Growth of cells extended over longer period of time.
Cell densities higher as compared to cells not undergoing
respiration.
Viability of respiring cells extended over a longer period
since pH around 6.0, fermentation produced little lactic
acid.
Aim is maximum cell biomass while maintaining cell
viability.
Lactococci lack citric acid cycle, therefore NADH should
be generated through other pathways.
MAIN GENERA OF LACTIC ACID BACTERIA AND
THEIR ROLE IN FERMENTATION
1. Lactococcus:
 Non motile, home fermentative and facultative anaerobes.
 Optimum growth temperature 30o C
 L.lactis plays an important role in the dairy industry.
 Two different species:
a) L.lactis subsp lactis-most strains of this grow at 40o C, greater
tolerance to salt up to 4%.
b) L.lactis subsp cremoris-most strains of this grow at a temperature of
above 38o C, lesser tolerance to salt.
 The latter sub specie is measured to be less tolerant during dairy
fermentation due to its encounter with environmental pressures
 Despite of this it is known to make better quality cheese, conditions
need to be optimized.
2. Streptococcus:
 Varied species, extensive range of locales.
 Non motile, homo fermentative and facultative
anaerobe.
 Most important specie, Streptococcus thermophilusimportant role in fermentation.
 It is well adapted to milk environments.
 Produces lactic acid after the fermentation of
lactose.
 High optimum temperature of 40o C to 42o C.
 Needs amino acids as it is fairly proteolytic.
 Salt tolerant, limited metabolic diversity
and bile sensitive.
3. Lactobacillus:
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Comprises of 80 or more species.
Live in diverse habitats-plant and vegetable material, juice, dairy
and meat environments, fermented beverages.
Presence in gastrointestinal tracts, act as probiotics.
Play a role in spoilage of fermented as well as non-fermented
foods.
Optimum temperature for growth varies from 30oC to 45oC.
High tolerance to salt, low water activity and osmotic pressure.
Many strains grow in acidic environments.
Some show tolerance against ethanol and bile.
Require nutrient rich environment-fatty acids, peptides and
amino acids. Some require nucleotides and vitamins.
Lactobacilli can ferment a wide range of sugars provided
they have a fermentable source of carbohydrates.
 Ferment common sugars like: lactose, glucose, fructose.
 Ferment plant derived carbohydrates: trehalose,
cellobiose, amygdalin.
 May act directly or indirectly.
 Act directly by being added in starter cultures.
 Act indirectly by their presence in equipment and raw
materials.
 Two main species used in dairy starter cultures:
a) lactobacillus helveticus
b) lactobacillus delbrueckii
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ROLE OF MOLDS AND YEASTS IN THE
PRODUCTION OF FERMENTED FOODS AND
BEVERAGES
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Molds: filamentous and multi cellular, produce sexual
and asexual spores. Most commonly used mold in
fermentation are: penicillin and aspergillus.
Yeast: non filamentous and uni cellular, non sporulating
and produce only sexual spores. Most important are
sacchromyces.
Sacchromyces are needed in the production of fermented
products like wine, beer, bread products.
Wine fermentations may be natural or spontaneous and
different yeasts might be involved.
Two common styles of beer production through
fermentation include:
Ales: requires yeast
S.cerevisiae. Referred
as top fermenting
yeasts as they flocculate
at the top of the
vessel.
Lagers: requires yeast
S.pastorianus. referred
bottom fermenting yeasts
as they settle at the
bottom of the vessel.
Penicillium:
a) Penicillium roquefort: famous
species n fermentation. Gives
blue-veined cheese its typical
color. Vital for characteristics of
cheeses like flavor and aroma.
b) Penicillium camemberti: white
mold species. Vital because it
takes part in the fermentation of
Brie and camembert cheeses.
 Aspergillus:
a) Aspergillus oryzae
b) Aspergillus sojae
Used in the manufacture of soy
pastes, soya sauces and rice
wines.
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CULTURED DAIRY PRODUCTS
Milk has a carbohydrate rich, nutrient dense composition,
suitable as a fermentation substrate.
 Fresh milk has characteristics in which microorganism can grow
easily.
 Lactic acid bacteria can take part in fermentation and
conveniently grow in milk
 Make a hostile environment for pathogenic bacteria by producing
lactic acid from lactose.
 Common dairy products include yogurt, buttermilk, cream.
 These products have increased nutritional worth.
 Yogurt starter culture includes:
a) Streptococcus thermophilus.
b) Lactobacillus delbrueckii subspbulgaricus
These also act as probiotics.
 Lactobacillus acidophilus and bifidobacterium are indirectly
involved in yogurt fermentation.
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Lactic acid fermentation should cause the pH to decrease
and isoelectric point of casein should be reached.
At the isoelectric point, the pH of the protein is such that
the net electrical charge is zero and protein is at a point
where it has lowest solubility.
There are acidic and basic amino acids present which become
protonated by the decrease in pH.
The amino acids become more positive and at a point positive
and negative charges are equal.
Isoelectric point of casein is 4.6
After isoelectric point is reached, a
coagulum forms.
 Ethanol, acetaldehyde and acetic acid are
also produced by cultures.
 Contribute to flavor and texture.
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CHEESE
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Also a product of fermentation. Raw materials simple,
end product unbelievable.
Solid part is concentrated, water eliminated.
Concentration processes decrease microbial and
enzymatic activity-longer shelf life.
Concentration process comprises of concentration of
protein and fat, elimination of water.
High temperature and low pH improves elimination of
water.
A very high temperature not useful, inactivates
microbes, poor quality cheese.
Coagulation is the process by which liquid milk
converted to solid cheese.
Coagulum not left attached, cut into curds.
Cooking and washing steps.
BEER FERMENTATION
Fermented beverage. Well
preserved.
 Processes are not easy to control
and optimize.
 Filtering of beer to enhance
clearness might have adverse
affects, might eliminate the
pleasing taste.
 Two main phases of beer making:
a) First phase-mashing
b) Second phase-fermentation phase
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First phase-mashing (enzymatic nature)
Starch
Sugars
fermented by yeast
Alteration of barley, the cereal grain
Malt
Mash
Wort, growth medium which is nutrient rich
Second phase-fermentation
(microbiological nature)
Growth of yeasts in wort
Yeast grows in anaerobic conditions-fermentation
Sugars converted to ethanol and CO2
Beer in misty form-unstable.
Steps to eliminate extra microbes and yeast
Carbonation