Food processing and Preservation

Fermentation

History

• Since fruits ferment naturally, fermentation precedes human history. Since ancient times, however, humans have been controlling the fermentation process. The earliest evidence of winemaking dates from eight thousand years ago, in Georgia, in the Caucasus area.

• Seven-thousand-year-old jars containing the remains of wine have been excavated in the Zagros Mountains in Iran, which are now on display at the University of Pennsylvania

• French chemist Louis Pasteur was the first known zymologist, when in 1854 he connected yeast to fermentation. Pasteur originally defined fermentation as "respiration without air". Pasteur performed careful research and concluded;

• "I am of the opinion that alcoholic fermentation never occurs without simultaneous organization, development and multiplication of cells.... If asked, in what consists the chemical act whereby the sugar is decomposed ... I am completely ignorant of it."

• When studying the fermentation of sugar to alcohol by yeast, Louis Pasteur concluded that the fermentation was catalyzed by a vital force, called "ferments," within the yeast cells. The "ferments" were thought to function only within living organisms.

• "Alcoholic fermentation is an act correlated with the life and organization of the yeast cells, not with the death or putrefaction of the cells,” he wrote.

Worldwide production of some fermented foods

Food/beverages Quantity

Cheese 15 million tons

Yogurt 3 million tons

Mushroom 1.5 million tons

Fish sauces 300,000 tons

Dried stockfish 250,000 tons

Beer 1000 million liters

Wine 350 million liters

Fermentation

• Fermentation in food processing typically is the conversion of carbohydrates to alcohol and carbon dioxide or organic acids using yeast, bacteria or combination thereof, under anaerobic conditions.

• A more restricted defination of fermentation is the chemical conversion of sugar into ethanol. The science of fermentation is known as zymology

• Fermentation usually implies that the action of microorganisms is desirable, and the process is used to produce alcoholic beverages such as wine, beer, and cider.

• Fermentation is also employed in preservation techniques to create lactic acid in sour foods such as sauerkraut, dry sausages, Kimchi and yogurt, or vinegar (acetic acid) for use in pickling foods.

Food fermentation

• Definition

• Fermentation is the slow decomposition process of organic substances include by-microorganism or by complex nitrogenous substances (enzymes) of plant or animal origins

• It can be describe as a biological change, which is brought about by the anaerobic or partially anaerobic oxidation of carbohydrates by either microorganisms or enzymes

• Bacteria derive their energy during fermentation

• A relatively incomplete biochemical reaction – final product is still in organic compound

• Conversion of food components in to other components by microorganisms

• Sugar alcohol

• Protein peptide, amino acids,

• Lipid fatty acids

• Typical substrates include sugars (e.g. glucose) & amino acids.

• Typical products depend upon the substrate but include organic acids (lactic acid, acetic acid), alOH (etOH, metOH, butOH), ketones (aceton) and gases (H2 & CO2)

• Also used to describe other microbiological related reactions (digestion in the lower intestine for example)

• Usually involves the production of some compound inhibitory to other microorganisms

• e.g. organic acids, diacetyl, acetoin. Hidrogen peroxide, nicin (bacteriocin produced by Lactococcus lactis)

Benefits of Fermentation Benefit Raw material Fermented food

Preservation

Milk Yoghurt, cheese

Enhancement of safety

Acid production Fruit Vinegar

Acid & alcohol production

Barley, Grapes Beer, Wine

Production of bacteriocin

Meat Salami

Benefit Raw material Fermented food

Removal of toxic components

Cassava, soybean

Gari, soysauce

Enhancement of nutritional value

Improved digestability

Wheat Bread

Retention of micronutrients

Leafy vegs Kimchi

Increased fibre content

Coconut Nata de coco

Benefits of Fermentation

Benefits of Food Fermentation

• Preservation/food safety – due to acid & alcohol: pH < 4.6, no pathogens grow (including C. botulinum)

– Certain lactic acid bacteria (e.g. Lactobacillus acidophilus) and moulds have been found to produce antibiotics and bacteriocins

– Alcohol is germicidal & acetic acid is bactericidal

• Improve nutritive value

– Bacteria breakdown several complex compound

– Synthesis of vit B12, riboflavin, precursor of vit C – increase vit levels – exmp Idli (a lactic acid bacteria fermented product consumed in India) is high in thiamine & riboflavin

– Saccharomyces cerevisiae is able to concentrate large quantities of thiamin, nicotinic acid & biotin & thus form enriched products

• Improve nutritive value cont…

– Release of nutrients by rupturing cellulosic & hemicellulosic str – more availability of entrapped nutrients (e.g. moulds with cellulose-splitting enzymes)

– Removal of anti-nutritional factors; e.g. cyanogenic glucoside in cassava removed upon fermentation; trypsin inhibitors, phytate

• Improve nutritive value cont…

– Improve digestability – Microbial cellulases hydrolyse cellulose into sugars which are then readily digested by humans

– The beneficial health effects of lactic acid bacteria on the intestinal flora are well documented

• Improve the textural & sensory properties of food

– Distinct aroma & flavour compounds: acids, carbonyl compounds, esters, ethanol, ketones, lactones, pyrazines, etc

– Altered texture, e.g. milk – cheese/yogurt, cereals – bread, soybean – soysauce.tempe

• Salvaging food waste

– Tempe-bongrek – a protein rich food made in Indonesia by fermenting peanut and coconut press-cake, remaining after oil extraction

– Ontjom – from waste groundnut press cake, tapioca waste and the solid waste of tahu

Typical organisms involved in fermentation

• Lactic acid bacteria

– Lactobacillus

– Lactococcus

– Leuconostoc

–Acidophilus

–Pediococcus

• Yeast

– Saccharomyces

• Moulds

–Penicillium

–Rhizopus

–Aspergillus

–Botrytis

Common Fermentation Activities

• Alcoholic/Ethanolic fermentation

Generally yeast fermentation (S. cerevisiae, S. ellipsoideus), or yeast-like moulds (Amylomyces rouxii) & mould-like yeasts (Endomycopsis)

C6H12O6 2C2H5OH + CO2

The yeasts multiply & ferment rapidly – other organisms (aerobic) cannot compete

CO2 flushes out residual O2 & maintains the fermentation anaerobic

Examples: Wine & Beer, leavening of bread, tapai, rice wines

Common Fermentation Activities cont..

• Mixed alcoholic and Acid Fermentations

If the products of alcoholoc fermentation are not kept anaerobic, Acetobacter bacteria may oxidize portions of the ethanol to acetic acid/vinegar

C6H12O6 + O2 CH3COOH

Examples: vinegar from cider or wine, palm wines, Keffir beers, Kombucha tea

Acetic acid is bacteriostatic

• Lactic acid fermentations

– Fermentable sugars are converted to lactic acid by lactic acid bacteria: Leuconostoc mesentroides, Lactobacillus brevis, Lactobacillus plantarum, Pediococcus cerevisiae, Streptococcus thermophilus, etc

– Provide a wide variety of flavours, aroma & textures

– Examples: Sour milk, yogurt, Kimchi, sauerkraut, pickled vegs

Classificationof Food Fermentations

• Fermentations producing textured vegetable protein meat substitutes in legume. cereal mixtures; e.g. Indonesian Ontjom and tempe

• High salt/savory meat – flavored/amino acid/peptide sauce & paste fermentations; e.g. Chinese soysauce, Japanese shoyu & miso, Korean kanjang, Indonesia tauco, fish sauces. Malaysian budu & belacan etc..

• Lactic acid fermentations – sauerkraut, cucumber & olive pickles, Korean Kimchi. Malaysian tempoyak, yogurts, Russian kefir, India dahi, cheese etc…

• Alcohol fermentations – grape wines, beers, palm wines, rice beer, Japanese sake, sugar cane wines etc…

• Acetic acid/vinegar fermentation – Apple cider, wine vinegars, palm wine vinegars, coconut water vinegar, tea fungus/kombucha tea, nata de coco, nata de pina

• Alkaline fermentations – Nigerian dawadwa, African iru, ogiri, Thai thua-nao

• Leavened breads – Yeast & sourdough breads

• Flat unleaved breads

Controlling Fermentation Process

• Wild/Uncontrolled Fermentation – Sauerkraut, pickles and olives

– Coffee, tea and cocoa

– Tempoyak

• Controlled Fermentation – Adding specific microorganisms to get the desired

product every time or to support the activity of only desired microbes

– Most common controls are: acid level, alcoh level, use of starter, level O2, amount of salt

1. Control of Acid

• Acid suppresses the growth of non-acid tolerant spoilage organisms

• Contaminated moulds can further ferment the acid in presence of O2, the inhibitory effect of acid is lost and some other proteolytic & lipolytic organisms start to grow at the surface, e.g. defect in Cheddar cheese

• Certain yeasts tolerant to high acid – produce alkaline end products (e.g. ammonia) from the breakdown of protein – acid preservation is lost

• Example: Raw milk fermentation

• Various microbial contaminants

• Acid development by Str. Lactis – inhibit other organisms

• Lactobacillus organism more tolerant to acid – take over the acid fermentation

• Example: Raw milk fermentation cont…

• High acidity itself inhibitory to genus Lactobacillus, they start dying

• Acid- tolerant yeast & moulds start growing – gassy product

• Alkaline end products from proteolysis – neutralization of acid by alkaline products

• Example: Raw milk fermentation cont…

• Proteolytic & lipolytic bacteria find a favourable enviroment

• Proteolysis brings down the milk acidity than the fresh one

• Final product – gassy, putrefied, off-odour

2. Control of Alcohol

• Alcohol can be preservative depending on concentration

• Example: Wine production

• Alcohol level in wine depends on: Sugar content of grapes, types of yeast fermentation temperature, level of oxygen

• Yeast cannot tolerate their own alcohol & other fermentation product

• Example: Wine production cont…

• Natural wine contain 9-13 % alcohol by volume – this concentration not enough for preservation – pasteurization needed

• Fortified wine products (20% alcohol) do not need pasteurization

3. Use of Starter Cultures

• Starter cultures – preparations of one or more strains of one or more species of microorganisms: they are subcultures

• Better control on fermentation

3. Use of Starter Cultures cont..

• Domination of desired organism right from beginning

• Special cultures available for: wine, butter, cheese, yogurt, pickles, vinegar, beer, sausage, bread and other fermented foods

• Examples: Butter (mixed culture containing Lactococcus lactis sub spp, lactis cremoris, Leuconostoc mesenteroides sub spp).

• Yogurt (Lactobacillus casei, L. acidophilus, Bifidobacterium).

• Sausage (Lactic acid bacteria).

3. Use of Starter Cultures cont..

• Beer (Geotricum candidum – inhibit undesirable moulds)

• Normally food heated to inactivate detrimental types of organics prior to starter addition

3. Use of Starter Cultures cont..

4. Control of Temperature

• Each organisms has its own optimum growth temperature

• Control of temperature to encourage the growth of desirable organism

• Example: Sauerkraut production

• Three types of bacteria: – Leuconostoc mesenteroids (opt. temp. 21 °C) –

acetic acid, lactic acid, alkoh, CO2

• Lactobacillus cucumeris (opt temp 21 °C) – produce acetis acid when leuconostoc stop growing

• Lactobacillus pentaceticus – still more acetic acid when L. cucumeris ceases

5. Control of Oxygen

• Mould – require oxygen

• Yeast – for alcohol production better with O2

• Bakers yeast Saccharomyces cerevisiae – better in aerobic condition

• Rapid fermentation of sugar under anaerobic condition

• Commercial production of yeast – air bubbling in molasses solution

• Example: Vinegar Production

• Initial aerobic condition – stimulate growth & increases cell mass

• Anaerobic condition – fermentation sugar to alkoh

• Aerobic condition – alcoh to acetic acid (oxidative fermentation)

6. Control of Salt

• Various organisms - different salt tolerance

• Lactic salt bacteria (used in fermenting olives, sauerkraut, meat sausages) tolerant up to 10-18% salt concentration

• Proteolytic & other spoilage organisms not tolerant above 2.5% salt

• Growth of lactic acid bacteria at higher acid & salt concentration

• Different salt levels: 2-2.5% in sauerkraut production; 7-10% in olive fermentation; 15%-18% in cucumber fermentation

• Salt added in cheese curd – prevention from proteolytic bacteria.