Fermented Foods • Foods that have been subjected to the action of microorganisms or enzymes, in order to bring about a desirable change. • Numerous food products owe their production and characteristics to the fermentative activities of microorganisms. • Fermented foods originated many thousands of years ago when presumably micro-organism contaminated local foods.
Fermented Foods • 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 History and origins of some fermented foods Food Mushrooms Soy sauce Wine Fermented milk Cheese Beer Bread Fermented Meats Sourdough bread Fish sauce Pickled vegetables Tea Approximate year of introduction 4000 BC 3000 BC 2000 BC 1500 BC 1000 BC 200 BC Region China, Korea, Japan North Africa, Europe Middle East North Africa, China Egypt, Europe Middle East Europe Southeast Asia, North Africa China, Europe China
Fermented Foods • The term “biological ennoblement” has been used to describe the nutritional benefits of fermented foods. • Fermented foods comprise about onethird of the world wide consumption of food and 20 - 40 % (by weight) of individual diets.
Table 2 Worldwide production of some fermented foods Food Quantity (t) Beverage Quantity (hl) Cheese 15 million Beer 1000 million Yoghurt 3 million Wine 350 million Mushrooms 1. 5 million Fish sauce 300 000 Dried stockfish 250 000
Table 3 Individual consumption of some fermented foods: average person per year Annual Food Country consumption Beer (I) Wine (I) Yoghurt (I) Kimchi (kg) Tempeh (kg) Soy sauce (I) Cheese (kg) Miso (kg) Germany Italy, Portugal Argentina Finland Netherlands Korea Indonesia Japan UK Japan 130 90 70 40 25 22 18 10 10 7
Table 4 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 Vinegar Beer Wine Salami Gari, polviho azedo Soy sauce Wheat Leafy veges. Coconut Milk Bread Kimchi, sauerkraut Nata de coco Bifidus milk, Yakult, Acidophilus yoghurt Coffee Wine Coffee beans Grapes
Cassava • • • Fresh cassava contains cyanhydric acid (HCN) that should be eliminated from any product originating from cassava to render it for human consumption. Depending on the production method (particularly traditional methods) gari could contains up to 20 mg / kg of HCN - against 43 mg / kg for fresh peeled cassava. Gari is a fermented, gelled and dehydrated food produced from fresh cassava. It is a popular diet in Nigeria, Benin, Togo, Ghana and in other West Africa's countries. The consumption area even expands to Central Africa: Gabon, Cameroon, Congo Brazzaville and Angola. Polvilho is a fine tapioca/manioc/cassava flour. it can be found at latino markets in california as "sour starch" (polvilho azedo) or "sweet starch" (polvilho doce)
Nata de Coco • • • A high fiber, zero fat Philippino dessert. A chewy, translucent, jelly-like food product produced by the bacterial fermentation of coconut milk. Commonly sweetened as a candy or dessert, and can accompany many things including pickles, drinks, ice cream, and fruit mixes. Highly regarded for its high dietary fiber, and its zero fat and cholesterol content. It is produced through a series of steps ranging from milk extraction, mixing, fermentation, separating, cleaning, cutting to packaging.
Lactic Acid Bacteria • Major group of Fermentative organisms. • This group is comprised of 11 genera of gram-positive bacteria: • Carnobacterium, Oenococcus, Enterococcus, Pediococcus, Lactococcus, Streptococcus, Lactobacillus, Vagococcus, Lactosphaera, Weissells and Lecconostoc • Related to this group are genera such as Aerococcus, Microbacterium, and Propionbacterium.
Lactic Acid Bacteria • While this is a loosely defined group with no precise boundaries all members share the property of producing lactic acid from hexoses. • As fermenting organisms, they lack functional heme-linked electron transport systems or cytochromes, they do not have a functional Krebs cycle. • Energy is obtained by substrate-level phosphorylation while oxidising carbohydrates.
Lactic Acid Bacteria • The lactic acid bacteria can be divided into two groups based on the end products of glucose metabolism. • Those that produce lactic acid as the major or sole product of glucose fermentation are designated homofermentative. • Those that produce equal amounts of lactic acid, ethanol and CO 2 are termed heterofermentative. • The homolactics are able to extract about twice as much energy from a given quantity of glucose as the heterolactics.
Lactic Acid Bacteria • All members of Pediococcus, Lactococcus, Streptococcus, Vagococcus, along with some lactobacilli are homofermenters. • Carnobacterium, Oenococcus, Enterococcus, Lactosphaera, Weissells and Lecconostoc and some Lactobacilli are heterofermenters • The heterolactics are more important than the homolactics in producing flavour and aroma components such as acetylaldehyde and diacetyl.
Lactic Acid Bacteria - Growth • The lactic acid bacteria are mesophiles: – they generally grow over a temperature range of about 10 to 40 o. C, – an optimum between 25 and 35 o. C. – Some can grow below 5 and as high as 45 o. C. • Most can grow in the p. H range from 4 to 8. Though some as low as 3. 2 and as high as 9. 6.
Starter Cultures • Traditionally the fermenting organisms came from the natural microflora or a portion of the previous fermentation. • In many cases the natural microflora is either inefficient, uncontrollable, and unpredictable, or is destroyed during preparation of the sample prior to fermentation (eg pasteurisation). • A starter culture can provide particular characteristics in a more controlled and predictable fermentation.
Starter Cultures • Lactic starters always include bacteria that convert sugars to lactic acid, usually: – Lactococcus lactis subsp. lactis, – Lactococcus lactis subsp. cremoris or – Lactococccus lactis subsp. lactis biovar diacetylactis. • Where flavour and aroma compounds such as diacetyl are desired the lactic acid starter will include heterofermentative organisms such as: – Leuconostoc citrovorum or – Leuconostoc dextranicum.
Starter Cultures • The primary function of lactic starters is the production of lactic acid from sugars • Other functions of starter cultures may include the following: • flavour, aroma, and alcohol production • proteolytic and lipolytic activities • inhibition of undesirable organisms
A good starter CULTURE will: • Convert most of the sugars to lactic acid • Increase the lactic acid concentration to 0. 8 to 1. 2 % (Titratable acidity) • Drop the p. H to between 4. 3 to 4. 5
• Food scientists frequently use the ability of bacterial cells to grow and form colonies on solid media to: – isolate bacteria from foods, – to determine what types and – how many bacteria are present. • Streak plates A single bacterial colony
The streak plate technique • Bacteria are “streaked”over the surface of an agar plate so as to obtain single colonies. • Obtaining single colonies is important as it enables; – the size, – shape and – colour of the individual colonies to be examined. – It can also highlight the presence of contaminating micro-organisms
The Streak Plate Technique
When conditions are right bacteria can double in number every 20 minutes
Microscopic examination • Can provide information on the size and shape of the bacteria – Rods (1) – Cocci (2) – Spiral (3) • It cannot provide enough information to enable bacteria to be identified
Microscopic views of stained bacteria Lactobacillus spp. Lactococcus spp.
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