MICROBIOLOGY OF FERMENTED FOODS AND BEVERAGES

BY: MOMINA MASUD

CONTENTS

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 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. Preservation.2. Nutrition.3. Functionality.4. Organoleptic.5. Uniqueness.6. 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

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

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 Hetero fermentative

Pathway: almost 90% pathway: 50% conversion of sugar conversion to lactic acidsubstrate just to rest is converted to Lactic acid. 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.

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

thermophilus-important 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:

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

ROLE OF MOLDS AND YEASTS IN THE PRODUCTION OF FERMENTED FOODS AND BEVERAGES

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 Lagers: requires yeastS.cerevisiae. Referred S.pastorianus. referred as top fermenting bottom fermenting yeastsyeasts as they flocculate as they settle at the at the top of the bottom of the vessel.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 sojaeUsed in the manufacture of soy

pastes, soya sauces and rice wines.

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 subspbulgaricusThese also act as probiotics. Lactobacillus acidophilus and bifidobacterium are

indirectly involved in yogurt fermentation.

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.

CHEESE 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

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