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Transcript
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 – 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 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 Glucose Lactic acid Pyruvate via glycolytic pathway OO HO-C-C-CH3 Pyruvate NADH2 NAD+ O OH HO-C-CH-CH3 Lactate 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. Acetylphosphate 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 ADP Acetate ATP NADH NAD+ Acetaldehyde NADH Glyceraldehyde 3- phosphate (glycolysis) ATP Pyruate NAD+ Ethanol ADP Lactate Lactic Acid Bacteria: Genera • • • • Oenococcus Pediococcus Lactobacillus Leuconostoc Lactobacillus Homolactic on hexoses Heterolactic on hexoses • • • • • • • • • • • L. bavaricus L. casei L. homohoichii L. curvatus L. saki L. plantarum 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 protonmotive 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.
