Fermented Foods n Foods that have been subjected

Fermented Foods n Foods that have been subjected to the action of microorganisms or enzymes, in order to bring about a desirable change. n Numerous food products owe their production and characteristics to the fermentative activities of microorganisms. n Fermented foods originated many thousands of years ago when presumably micro-organism contaminated local foods.

Fermented Foods n Micro-organisms cause changes in the foods which: ¨ Help to preserve the food, ¨ Extend shelf-life considerably over that of the raw materials from which they are made, ¨ Improve aroma and flavour characteristics, ¨ Increase its vitamin content or its digestibility compared to the raw materials.

Table 1 Benefits of fermentation Benefit Preservation Enhancement of safety Acid production Acid and alcohol production Production of bacteriocins Removal of toxic components Enhancement of nutritional value Improved digestibility Retention of micronutrients Increased fibre content Synthesis of probiotic compounds Improvement of flavour Raw material Fermented food Milk Yoghurt, cheese (Most materials) Fruit Barley Grapes Meat Cassava Soybean Wheat Leafy veges. Coconut Milk Coffee beans Grapes Vinegar Beer Wine Salami Gari, polviho azedo Soy sauce Bread Kimchi, sauerkraut Nata de coco Bifidus milk, Yakult, Acidophilus yoghurt Coffee Wine

Lactic Acid Bacteria n Major group of Fermentative organisms. n This group is comprised of 11 genera of gram-positive bacteria: n Carnobacterium, Oenococcus, Enterococcus, Pediococcus, Lactococcus, Streptococcus, Lactobacillus, Vagococcus, Lactosphaera, Weissells and Lecconostoc n Related to this group are genera such as Aerococcus, Microbacterium, and Propionbacterium.

Lactic Acid Bacteria n While this is a loosely defined group with no precise boundaries all members share the property of producing lactic acid from hexoses. n As fermenting organisms, they lack functional heme-linked electron transport systems or cytochromes, they do not have a functional Krebs cycle. n Energy is obtained by substrate-level phosphorylation while oxidising carbohydrates.

Lactic Acid Bacteria n The lactic acid bacteria can be divided into two groups based on the end products of glucose metabolism. n Those that produce lactic acid as the major or sole product of glucose fermentation are designated homofermentative. n Those that produce equal amounts of lactic acid, ethanol and CO 2 are termed heterofermentative. n The homolactics are able to extract about twice as much energy from a given quantity of glucose as the heterolactics.

Fermentation – Definition n Fermentation is the metabolic process in which carbohydrates and related compounds are partially oxidised, with the release of energy, in the absence of any external electron acceptors. n The final electron acceptors are organic compounds produced directly from the breakdown of the carbohydrates. n With fermentation, incomplete breakdown of the parent compound occurs and only a small amount of energy is released during the process. n The products of fermentation consist of some organic compounds that are more reduced than others

Glycolysis and Fermentation n Glycolysis, also called the Embden-Meyerhof pathway, is the metabolic pathway used to, begin to, break down glucose. Used by: most autotrophic and heterotrophic organisms, ¨ aerobes and anaerobes. ¨ n The name glycolysis literally means splitting (lysis) of sugar (glyco-). n It does not require oxygen and can occur in its presence or absence.

Glycolysis ATP Required at steps 1 and 3, Released at steps 7 and 10. Each glucose yields 2, three carbon sugars. There is a net yield of 2 ATP per glucose.

Sugar Catabolism n The metabolism of glucose, or another sugar by glycolysis is a process carried out by nearly all cells. The end result of glcolysis is pyruvic acid. n How pyruvic acid is subsequently catabolised depends on whether it is broken down by: ¨ Aerobic Metabolism (Respiration) or ¨ Anaerobic Metabolism (Fermentation)

Aerobic Metabolism Formation of Acetyl-Co. A and the Krebs cycle n. Energetically far more efficient than fermentation n. In conjunction with the electron transport chain where oxygen is the terminal electron acceptor n n. Produces 34 ATP (plus 4 from glcolysis) from each molecule of glucose

Fermentation n Process by which pyruvic acid is metabolised in the absence of oxygen n Result of the need to recycle the limited amount of NAD by passing the electrons off to other molecules n Two of the most important and commonly occurring pathways are: ¨ homolactic acid fermentation and ¨ alcoholic fermentation.

Homolactic Acid Fermentation n Reduced NAD H + H+ O O H 3 C - C - OH Pyruvic acid Oxidised NAD n OH O H 3 C - C - OH n H Lactic Acid n Does not capture energy in ATP from the metabolism of pyruvic acid, but removes electrons from reduced NAD so that it can continue to act as an electron acceptor. Alcoholic fermentation is a similar process Thus, they indirectly foster energy capture by keeping glycolysis going. Fermenation can occur via many other pathways