ch 5 food fermentation

7/24/2019 Ch 5 Food Fermentation

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Food Fermentation Microbiology

[email protected]


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INTRODUCTION

Industrial microbiology uses microorganisms,typically grown on a large scale, to produce

valuable commercial products or to carry out

important chemical transformations.

This process is commonly referred to as

Fermentation


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FERMENTATION

PROS

Extended shelf life of

food (ex. Cheese)

Eases Digestion (ex.

Wild rice)

New [better] flavours

(ex. Chocolate)

CONS

Can be unpredictable

(i.e. bad bacteria win

the battle)

New [worse] flavours

(ex. Mouldy breadtastes terrible)


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Foods or food ingredients that rely on

microbial growth as part of their processingor production

WHAT ARE FERMENTED FOODS?


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METABOLIC ACTIVITIES OCCUR DURING

FERMENTATION

Extend shelf life by producing acids

Change flavor and texture by producing

certain compounds such as alcohol

Improve the nutritive value of the

product by:

Microorganisms can synthesizevitamins

Breakdown indigestible materials to

release nutrients, i.e., bound

nutrients


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FERMENTED FOODS

Foods fermented by

yeast

MaltBeer

Fruit (grapes) Wine

Rice Saki Bread dough Bread

Foods fermented by

mold Soybeans Soy sauce

Cheese Swiss

cheese

Foods fermented bybacteria

Cucumbers Dill

pickles

CabbageSauerkraut

Cream Sour cream

Milk Yogurt


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In food fermentations, we exploitmicroorganisms metabolism for food

production and preservation.

Where do the microorganisms come from to

initiate the food fermentation?

Two ways to initiate a food fermentation.

...traditional & controlled fermentations

FOOD FERMENTATIONS


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CONTROLLED VS. NATURAL FERMENTATION

Natural fermentation Create conditions to inhibit undesirable

fermentation yet allow desirable

fermentation

Examples:

Vegetable fermentationsVegetables + salt


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CONTROLLED VS. NATURAL FERMENTATION

Controlled fermentation Deliberately add microorganisms to

ensure desired fermentation

Example: fermented dairy products

Lactose Lactic acid

Starter culture

Lactics or Lactic starter or Lactic acid bacteria

(LAB)


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Raw material with

indigenous microflora

Incubation

under specific

conditions

Final product

Disadvantage: Process and product are unpredictable depending on source of

raw material, season, cleanliness of facility, etc.

Advantage: Some flavors unique to a region or product may only be attained this

way.

= desirable m/os= undesirable (pathogen or spoilage) m/os

TRADITIONAL / NATURAL FERMENTATION


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Two main starter culture types are used toinoculate the raw material:

1. Pure microbial cultures prepared specifically

for a particular food fermentation.

2. Backslop method = Using some of the

product from a previous successful

fermentation to inoculate the next batch of raw

material.

CONTROLLED FERMENTATION: STARTER CULTURE


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Add pure microbial

culture

Final product

Incubation

under specific

conditions

Raw material

Pure culture

CONTROLLED FERMENTATION: PURE CULTURES


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Final product

Incubation

under specific

conditions

Add product (or byproduct)

from a recent successful

fermentation

Raw material

Final product from a previous

fermentation (traditional or

controlled)

CONTROLLED FERMENTATION: BACKSLOP METHOD


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ANAEROBIC VS. AEROBIC FERMENTATION

Aerobic

Fermentation

Release of energy

from glucose or

another organic

substrate in the

presence of oxygen

CO2, H2O, an energyproduced

Anaerobic

Fermentation

Release of energy

from glucose or

another organicsubstrate in the

absence of oxygen

Products: CO2, energy,and alcohol or various

organic acids


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EXAMPLES OF ANAEROBIC FERMENTATION PATHWAYS

Lactic acid fermentation

Found in many bacteria;

e.g. Streptococcus cremoris,

Lactobacillus acidophilus

Mixed acid fermentation e.g. Escherichia coli

Basis of the methyl red test

2,3-Butanediol fermentation e.g. Enterobacter aerogenes

Basis of the Voges-Proskauer

reaction


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LACTIC ACID FERMENTATION PATHWAYS


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MIXED ACID FERMENTATION PATHWAYS


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2, 3- BUTANEDIOL FERMENTATION PATHWAYS


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TYPES OF FERMENTATION

Bacterial fermentation

Yeast fermentation

Mold and Enzyme fermentation


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BACTERIAL FERMENTATION (4 TYPES)

Lactic Acid Bacteria (pickles, sauerkraut) Acetic Acid Bacteria (vinegar)

Carbon Dioxide Bacteria (Edam, Gouda,

Swiss) Proteolytic Bacteria (cocoa, chocolate)


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LACTIC ACID BACTERIA

Major group of Fermentative organisms.

This group is comprised of 11 genera of gram-positive bacteria:

Carnobacterium, Oenococcus, Enterococcus, Pediococcus,Lactococcus, Streptococcus, Lactobacillus, Vagococcus,

Lactosphaera, Weissells and Lecconostoc

Related to this group are genera such as

Aerococcus, Microbacterium, andPropionbacterium.


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Lack functional heme-linked electrontransport systems or cytochromes,

They do not have a functional krebs cycle.

Energy is obtained by substrate-levelphosphorylation while oxidising

carbohydrates.

CHARACTERISTICS LACTIC ACID BACTERIA


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Groups of Lactic Acid Bacteria

The lactic acid bacteria can be divided into twogroups based on the end products of glucosemetabolism.

Homofermentative:

Those that produce lactic acid as themajor or sole product of glucosefermentation are designated

Heterofermentative: Those that produce equal amounts of

lactic acid, ethanol and CO2 aretermed.

O O CO O S O


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FAVOURABLE ENVIRONMENTAL CONDITIONS FOR

LACTIC ACID BACTERIAL GROWTH

The lactic acid bacteria are mesophiles:

They generally grow over a temperaturerange of about 10 to 40oc,

An optimum between 25 and 35oc.

Some can grow below 5 and as high as 45oc.

Most can grow in the pH range from 4 to 8.Though some as low as 3.2 and as high as9.6.


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Benefits of Fermented Foods

Increase in variety of foods available:

Example: 1000 different types of cheeses

Use as ingredients for a variety of dishes:

Example: pepperoni in pizza and cheeses in

many dishes

Health Benefits:

Examples: yoghurt can reduce serum cholesterol

levels and helps avoid cancer


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Improve Digestibility: Example: People who cannot digest lactose

properly can often consume fermented dairy

products like yoghurts

Detoxification of raw materials:

May remove toxic chemicals found in the

raw material

Benefits of Fermented Foods


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THANK YOU

ch 5 food fermentation

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