Exercise 8 - Alcoholic and lactic acid fermentation

Fermentation

• anaerobic metabolism that does not require electron acceptors

Advantages of consuming fermented food

• sources of several vitamins essential amino acids, and antioxidants

• probiotics fight against infection caused by pathogenic microbes

• balance gut microflora after taking antibiotics

• sources of antimicrobial compounds

Alcohol fermentation

• Fermentative activity of yeast and bacteria

• Hexose → 2 ethanol + 2CO2

• Young coconut water as a source of fermentation substrate (can be fermented by natural microflora, e.g. coconut wine or tuba)

• Microorganisms can be observed using crystal violet

Lactic acid fermentation

• production of lactic acid from sugar fermentation

• mediated by lactic acid bacteria

Homofermentative pattern

• yields a single fermentation product (lactic acid)

• produces 2 molecules of lactate from glucose using glycolytic pathway

• lactic acid bacteria interaction with aldolase

• e.g. strep

Heterofermentative

• yields other products aside from lactic acid like ethanol and carbon dioxide

• lactic acid bacteria WITHOUT ALDOLASE

• e.g. Leuconostoc

Lactic acid bacteria

• nutritionally fastidious or specific with nutrients

• require complex media for optimal growth

• gram positive rods or cocci

• non-sporeforming bacteria

• aerotolerant, microaerophilic, or facultatively anaerobic

• predominant spoilage organisms in vacuum or modified atmosphere-packaged chill-stored meats

• important in cheese, yogurt, and sauerkraut industries

• aids in aroma and flavor production

• cause spoilage and deterioration of food

MRS agar or broth

• semi-selective cultivation of lactobacilli

• enzymatic digest of animal tissue, beef extract, and yeast extract for carbon, nitrogen, and vitamin sources

• glucose is fermentable carbohydrate

• sodium acetate and ammonium citrate act as selective agents against molds and gram negative

• dipotassaium phosphate is buffering agent

• Magnesium Sulfate provide cations used in metabolism

• Tween 80 is a surfactant that engages uptake of nutrients by lactobacilli

• Agar is solidifying agent

• low pH suppresses accompanying bacterial flora

• durham tubes for gas production

Yogurt Production

• popular fermented dairy product produced by lactic acid bacteria includin streptococcus na dlactobacillus

• bacteria produce lactic acid, decreasing pH and causing milk to coagulate

• bacterial metabolites strongly affect quality of yogurt (nonvolatile acids, carbonyl compounds)

Streptococcus thermophilus

• gram positive

• homofermentative

• termophilic

• facultative anaerobe or microaerophilic

Lacto delbrueckii

• gram positive

• homofermentative

• thermotolerant

• facultative anaerobe or microaerobilic