Other Food Preservation Techniques

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Other Food Preservation Techniques
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Food preservation through fermentation

• Fermentation is breakdown of carbohydrates under
  limited supply of oxygen or under anaerobic
  conditions.
  (Yeasts Sugar ? Alcohol CO2)
• Some aerobic, specific conversions may also
  be referred as fermentation ( Acetobacter
  Ethylalcohol O2 ? acetic acid).
• In nature, natural fermentations occur
  continuously.
• In technically advanced societies, fermented
  foods are produced to add special tastes to
  human diet, in less developed areas fermentation
  is still one of the major preservation methods.
• In contrast to most preservation methods,
  fermentation encourages growth and multiplication
  of selected microorganisms in foods.

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Benefits of fermentation

• Preservation,
• Providing variety to the diet,
• Production of important compounds like organic
  acids and alcohols,
• Fermented foods are often more nutritious than
  their unfermented counterparts because of mainly
  three reasons
• a) while growing in the medium the
  microorganisms also synthesize several complex
  vitamins and other growth factors like riboflavin
  and vitamin B12.
• b) nutrients locked into plant structures
  and cells by indigestible materials can be
  liberated
  c) enzymatic
  splitting of plant materials like
  cellulose,hemicellulose and related polymers
  normally not digestable by human beings.

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Changes caused in foods by fermentation

• Fermentative changes Changes that involve
  carbohydrates
• Proteolytic or putrefactive changes
  Changes that
  involve proteins,
• Lipolytic changes Changes that involve fats.
• In fermentation, fermentative changes
  are encouraged, whereas other changes are
  suppressed. Production of acid helps in
  controlling proteolytic and lipolytic
  microorganisms.
• The end products of fermentation depend
  upon
• The nature of the food,
• The types of microorganisms present,
• The environmental factors affecting microbial
  activity

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Examples of some important fermentations

• Fermentation of sugar by yeasts (basis for wine
  and beer production and leavening of bread)
• C6H12O6 yeast ? 2C2H5OH 2CO2
• Fermentation of alcohol by bacteria (basis for
  vinegar, acetic acid, production)
• C2H5OH O2 bacteria ? CH3COOH H2O
• Fermentation of milk sugar, lactose, by bacteria
  produces lactic acid which causes precipitation
  of the curd in the milk (basis for cheese
  production).

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Controlling fermentation

• The factors that affect fermentation are
• Acidity. Fermentative microorganisms are more
  resistant than proteolytic and lipolytic.
• Level of alcohol. Yeasts cannot tolerate high
  (12-15) alcohol levels. (utilized in the
  production of fermented alcoholic drinks, regular
  alcohol content of wine 9-13, fortified up to
  20)
• Starter cultures. Competition for survival, large
  concentrations dominate the others. In old times
  inoculation with parts of previous batch at high
  concentration. Novadays pure starter cultures
  (concentrates, dehydrated, frozen) available
  commercially.
• Temperature. Growth rate, optimum growth
  temperature of specific microorganisms. Optimum
  temperature regimes are established for various
  fermentations.

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• Level of oxygen. Aerobic, anaerobic
  microorganisms. Extent of fermentative changes
  depend on 02 concentration. In yeasts growth
  favored by aerobic, fermentation favored by
  anaerobic conditions.
• Level of salt.
• (i) 10-18 selectively inhibits activity of
  proteolytic and lipolytic and other spoilage
  organisms and favors growth of fermentative
  organisms.
• (ii) draws juice out of fruits and
  vegetables through osmosis.

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Preservation of foods as sugar concentrates

• Based on reducing the water activity of foods to
  levels low enough to stop microbial activity.
• Increase in solids concentration reduces aW,
  increased acidity helps in preservation.
• 65 or more solids plus acidity enough for
  preservation in the absence of O2. Above 70w
  solids no need for acidity.
• Fruit jellies, jams, marmelades, sweetened
  condensed milk are products. Syrups of different
  strengths are used as preserving media and
  filling liquids for preserving fruits in cans and
  jars. Contact with air should be avoided to stop
  mould growth on the surface.

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• Gelling is an important property of fruits and
  their extracts in the jam and confectionary
  industries. Four substances are needed for
  forming a fruit gel pectin, acid, sugar and
  water. In gelling, the pectin conglomerates and
  forms a network of fibers. This network is able
  to support liquids.
• The concentration of pectin determines the
  continuity of the network and the denseness of
  the formed fibers. The concentration of sugar and
  level of acidity determine the rigidity of the
  network. The higher the concentration of sugar,
  the less water will be supported by the
  structure. The higher the acidity the tougher are
  the fibers.
• Optimum conditions for gel formation
  pH 3.2-3.5,
  solids content (fruit sugar) ? 65w, pectin
  concentration ? 1
• Separation of liquids from gel structures is
  called synerisis. This effect is undesirable and
  should be avoided.

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Preservation of foods with chemical additives

• Critical issue between food scientists, food
  manufacturers, government agencies and consumers.
• A food additive is defined as a substance or a
  mixture of substances, other than a basic
  foodstuff, which is present in food as a
  result of any aspect of production, processing,
  storage or packaging excluding contaminants.
• Chemical additives can contribute substantially
  in the preservation and in quality improvement of
  foods. Legitimate vs. illegitamate uses must be
  well understood and defined.

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• legitimate uses
• The maintenance of the nutritional quality of a
  food,
• The enhancement of keeping quality or stability
  with resulting reduction in food losses,
• Making foods attractive to the consumer in a
  manner which does not lead to deception,
• Providing essential aids in food processing

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• illegitimate uses
• To hide the use of faulty processing and handling
  techniques,
• To deceive the consumer,
• When the result is a substantial reduction of the
  nutritive value of the food,
• When the desired effect can be obtained by good
  manufacturing practices which are economically
  feasible
• Safety of a food additive is very important.
  Thorough examination of its physiological,
  pharmacological and biochemical effects is
  required before allowing use.

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Uses of chemical additives in foods

• Preservatives ( microbial spoilage, chemical
  deterioration, control of insects and rodents )
• Nutritional supplements (vitamins, amino acids,
  minerals, calories)
• Color modifiers (natural colors, certified food
  dyes, derived colors)
• Flavoring agents (synthetic, natural, flavor
  enhancers or extenders)

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• Chemicals which improve functional properties.
• a) Control of colloidal properties (gel,
  emulsion,
• foam, suspensions),
• b) Firming agents,
• c) Maturing agents
• Chemicals used in processing.
• a) For sanitation, public health or
  aesthetic
• purposes
• b) To facilitate removal of unwanted
  coverings
• (skins, feathers, hair etc.)
• c) Antifoaming agents,
• d) Chelating agents
• e) Yeast nutrients

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• Chemicals to control moisture (waxes, anticaking
  agents)
• Chemicals to control pH (acids, bases, salts)
• Chemicals used to control physiological functions
  (ripening agents)
• Others (gases for pressure dispensing)

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Important chemical preservatives

• Natural preservatives. Table salt, sugars,
  vinegars, spices
• Inorganic chemicals
• a) SO2 preservation of fruit
  concentrates, controlling enzymatic browning,
  protecting from attacks by microorganisms and
  insects and avoiding discoloration in dried
  fruits.
• b) H2O2 sterilization of milk, surface
  sterilization of many commodities by spraying,
  disinfecting packaging materials in aseptic
  processing.

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• c) Cl2 disinfectant for water
• d) CO2 preserving effects at high
  pressures for carbonated drinks, controlling
  maturation, improving storage quality of fresh
  fruits (slowing down respiration).
• Organic chemicals
• a) Benzoic acid (benzoates) Protecting
  acid foods from yeasts and molds. Mostly fruits
  and their products.
• b) Fatty acids Effective mold inhibitors.
  Used in bread, pickles.
• c) Sorbic acid Used in controlling mould
  growth in packaged cheese, margarine. Effective
  against many moulds found on meats.

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Emerging Food Preservation Techniques
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• Biotechnology and reduced spoilage rate
• Membrane filtration techniques
• High intensity light
• Ultrasound
• Modified atmosphere packaging
• Pulsed electric fields
• High hydrostatic pressure

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Biotechnology and reduced spoilage rate

• Genetic engineering applied to slow down natural
  senescence process.
• Plant resistance to diseases and pests increased.

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Membrane filtration techniques

• Separating bacterial cells from process streams.
• Concentration.

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High intensity light

• Pulsed (1-20 flashes per second) broad-spectrum
  white light, non-ionizing.
• Rapid inactivation of microorganisms on food
  surfaces, equipment and food packaging materials
  (decontamination).
• Destroying insects, pests, parasites, viruses.

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Ultrasound

• Power ultrasound higher intensity and frequency.
• Surface cleaning by dislodging dirt and bacteria
  from surfaces, especially useful for non-smooth
  surfaces.
• Inactivation of microorganisms (cell damage) and
  enzymes (structural change)

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Modified atmosphere packaging

• Extend shelf life of food products by slowing
  down their rates of spoilage.
• Absence of oxygen retards aerobic MO.
• Carbon dioxide has a strong bacteriostatic effect
  on aerobic MO and inhibitory effects on some
  enzymes.
• Nitrogen used to replace oxygen in the headspace
  or as a filler gas in packages.
• Experimental success with CO, SO2, N2O, NO, He,
  H2, Ar,Cl2, ethylene oxide, propylene oxide on
  specific applications.

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Pulsed electric fields

• Operation at low and moderate temperatures below
  50 deg.C
• Applying short electric pulses (1-20µs) with a
  high field strength(15-80kV per cm) to samples
  placed between two electrodes.
• Microbial cell undergoes reversible membrane
  permeabilization. MP is correlated to microbial
  inactivation caused by breakdown of cell membrane
  locally. Sudden local ohmic heating of the cell
  membranes also contributes to the breakdown

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High hydrostatic pressure

• Enzymes and microorganisms inactivated by
  temperature (60-70 deg.C) / pressure (400-200MPa)
  combination.
• Destruction results from structural changes
  caused in enzymes and physical damage on
  microbial cells.