THREE TYPES OF FOOD FERMENTATION

•Alcohol•Acetic Acid•Lactic Acid - Largest of all

– Homofermentative– Heterofermentative

Bacteria

lactic acid bacteriaacetic acid bacteria

food bioprocessingfood biopreservation

Probiotic

FOOD FERMENTATIONS

Lactic Acid Bacteria– Vegetables and Fruits

SWEET PICKLES

Lactobacillus helveticus Lactobacillus delbrueckii sub. bulgaricus

Lactobacillus lactis

Fermented Milks

• majority of fermented milk products rely on lactic acid bacteria belonging to the genera Lactobacillus, Lactococcus, Leuconostoc, and Streptococcus– gram-positives that tolerate acidic

conditions, are non-spore forming, and are aerotolerant with a strictly fermentative metabolism

Fermented Milks…• mesophilic

– Lactobacillus and Lactococcus– buttermilk and sour cream

• thermophilic – Lactobacillus and Streptococcus– yogurt

• probiotics– Lactobacillus and Bifidobacterium– addition of microbes to the diet to improve

health beyond basic nutritive value

FOOD FERMENTATIONS

Lactic Acid Bacteria– Meats

FOOD FERMENTATIONS

Lactic Acid Bacteria– Dairy Products

FOOD FERMENTATIONS

Lactic acid with other microbesDairy Products

• With other bacteria• With yeasts• With molds

Vegetable Products

Lactic acid bacteria (LAB)

• G+, non-spore forming cocci or rods• Microaerophilic or anaerobic• Metabolize carbohydrates through

fermentative pathways– Acid production as the major end-product

• Common genera– Lactococcus, Lactobacillus, Leuconostoc,

Pediococcus, Streptococcus, Oenococcus

Lactic Acid BacteriaLactic Acid Bacteria

• Gram (+) rods (Lactobacillus) and cocci (Streptococcus, Lactococcus, Leuconostoc)

• Produce large amount of lactic acid• Aerotolerant anaerobes: grow

fermentatively• Require many growth factors (vitamins

and amino acids)• Found in nutrient-rich environments

(decomposition)

Lactic Acid BacteriaLactic Acid Bacteria

• Used to ferment or culture foods for 4000 years• Used in fermenting yogurt, cheese, butter, kefir

and in pickling vegetables• Lactose (milk sugar) converted to lactic acid; low

pH precipitates protein, causing curdling• Low pH also inhibits growth of other bacteria• Give tart taste to fermented milks• Growth is self-limiting (build up of waste products)• Used in probiotics (presence in livestock feed

inhibits E. coli)• Also produce bacteriocins (antimicrobial agents)

Lactic Acid BacteriaLactic Acid Bacteria

• Produce large amount of lactic acid, lowering pH

• Can grow at < pH 5• Predominate in acidic environment if

it:– Is anaerobic– Is rich in nutrients– Contains a fermentable carbohydrate

Lactic Acid Bacteria: Divisions

• Group I: Strict homofermenters

• Group II: Facultative heterofermenters

• Group III: Strict heterofermenters

Homofermentative Metabolism

85% of Glucose Lactic acid

Glucose Pyruvate via glycolytic pathway

HO-C-C-CH3 Pyruvate

HO-C-CH-CH3 Lactate

O O

O OH

NADH2

NAD+

Heterofermentative Metabolism

Organisms metabolize glucose via the pentose phosphate pathway.

End products can vary depending upon level of aeration and presence of other proton and electron acceptors. Acetyl-phosphate can be converted to acetate and ATP or reduced to ethanol without ATP production.

Pentose Phosphate Pathway

Lactic Acid Bacteria can also metabolize pentoses such as ribose, arabinose and xylose, via the pentose phosphate pathway.

Acetyl-phosphate leads to the generation of acetate and ATP exclusively in pentose metabolism.

Pentose Phosphate Pathway

Glucose Phospho-6-gluconate

Ribulose 5-phosphate

Xylulose 5-phosphate

CO2

Glyceraldehyde 3- phosphate

Pyruate

Lactate

Acetyl-phosphate

Acetate Acetaldehyde

Ethanol

(glycolysis)

NADP+

NADPH

NADP+

NADPH

NADH

NAD+

NADH

NAD+ADP

ATP

ADP

ATP

ATP ADP

Lactic Acid Bacteria: Genera

• Oenococcus

• Pediococcus

• Lactobacillus

• Leuconostoc

Lactobacillus

Homolactic on hexoses

• L. bavaricus• L. casei• L. homohoichii• L. curvatus• L. saki• L. plantarum

Heterolactic on hexoses

• L. fermentum• L. brevis• L. buchneri• L. fructovorans• L. hilgardii

Bacteriocins

• Antimicrobial peptides produced by some bacteria that inhibit closely related species

• Membrane-active agents that form pores in cytoplasmic membrane and dissipate proton-motive force

• Significant in food safety to control pathogens– Lactococcus lactis subsp. lactis and NISIN

Nisin

• Class I bacteriocin: lantibiotic, <5 KDa

• Producer: Lactococcus lactis subsp. lactis

• Active against G+ bacteria (Clostridium botulinum, Listeria monocytogenes, LAB)

• Commercially available

• Cheese and dairy products, canned foods, mayonnaise

• Only bacteriocin approved for use in U.S.