THREE TYPES OF FOOD FERMENTATION Alcohol Acetic Acid Lactic Acid - Largest of all Homofermentative Heterofermentative

Bacteria lactic acid bacteria acetic acid bacteria food bioprocessing food biopreservation Probiotic

FOOD FERMENTATIONS Lactic Acid Bacteria SWEET PICKLES 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 thermophilic probiotics 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 microbes Dairy 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 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 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 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 NADH2 NAD+ O OH

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 ATP ADP NADP+ NADPH CO2 Ribulose 5-phosphate NADP+ NADPH Xylulose 5-phosphate Acetyl-phosphate Glyceraldehyde 3- phosphate NADH NAD+ ADP ATP ADP ATP (glycolysis) Acetate Acetaldehyde Pyruate NADH NAD+ Ethanol Lactate

Lactic Acid Bacteria: Genera Oenococcus Pediococcus Lactobacillus Leuconostoc

Lactobacillus L. bavaricus L. casei L. homohoichii L. curvatus L. saki 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.