Food preservation
v Introduction
Many of variety of ways by that food is unbroken from
spoilage when harvest or slaughter. Such practices date to prehistoric times.
Among the oldest ways of preservation ar drying, refrigeration, and
fermentation.
v Spoilage Mechanisms
Food spoilage is also outlined as any amendment that renders
food unfit for human consumption. These changes is also caused by varied
factors, as well as contamination by microorganisms, infestation by insects, or
degradation by endogenous enzymes (those present naturally in the food). In
addition, physical and chemical changes, like the tearing of plant or animal
tissues or the oxidisation of bound constituents of food, may promote food
spoilage. Foods obtained from plant or animal sources begin to spoil presently
when harvest or slaughter. The enzymes contained within the cells of plant and
animal tissues is also free as a results of any mechanical injury inflicted
throughout postharvest handling. These enzymes begin to interrupt down the
cellular material. The chemical reactions catalyzed by the enzymes lead to the
degradation of food quality, like the event of off-flavours, the deterioration
of texture, and the loss of nutrients.
Bacteria and fungi (yeasts and molds) ar the principal sorts
of microorganisms that cause food spoilage and food-borne diseases. Foods is
also contaminated by microorganisms at any time throughout harvest, storage,
processing, distribution, handling, or preparation. The primary sources of
microorganism contamination ar soil, air, animal feed, animal hides and
intestines, plant surfaces, sewage, and food process machinery or utensils.
v Bacteria
Bacteria ar living thing organisms that have a
straightforward internal structure compared with the cells of different
organisms. The increase within the range of microorganism in an exceedingly
population is usually mentioned as microorganism growth by microbiologists.
This growth is that the results of the division of 1 microorganism cell into 2
identical microorganism cells, a method known as binary fission. Under optimum
growth conditions, a microorganism cell could divide about each twenty minutes.
Thus, one cell will turn out virtually seventy billion cells in twelve hours.
The factors that influence the expansion of microorganism embody nutrient
handiness, moisture, pH, gas levels, and therefore the presence or absence of
inhibiting substances (e.g., antibiotics).
The nutritionary needs of most microorganism ar chemical
parts like carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur, magnesium,
potassium, sodium, calcium, and iron. The microorganism obtain these parts by
utilizing gases within the atmosphere and by metabolizing sure food
constituents like carbohydrates and proteins.
Temperature and pH play a major role in dominant the expansion
rates of bacterium. Bacteria is also classified into 3 teams supported their
temperature demand for best growth: thermophiles (55–75 °C, or 130–170 °F),
mesophiles (20–45 °C, or 70–115 °F), or psychrotrophs (10–20 °C, or 50–70 °F).
In addition, most microorganism grow best in an exceedingly neutral setting (pH
capable 7).
Bacteria conjointly need an exact quantity of accessible
water for his or her growth. The availability of water is expressed as water
activity and is outlined by the quantitative relation of the vapor pressure of
water within the food to the vapor pressure of pure water at a specific
temperature. Therefore, the water activity of any foodstuff is usually a worth
between zero and one, with zero representing Associate in Nursing absence of
water and one representing pure water. Most bacterium don't grow in foods with
a water activity below zero.91, though some halophilic microorganism (those
able to tolerate high salt concentrations) will grow in foods with a water
activity lower than 0.75. Growth is also controlled by lowering the water
activity—either by adding solutes like sugar, glycerol, and salt or by removing
water through dehydration.
The gas needs for best growth vary significantly for various
bacterium. Some microorganism need the presence of free gas for growth and ar
referred to as obligate aerobes, whereas different microorganism ar poisoned by
the presence of gas and ar known as obligate anaerobes. Facultative anaerobes
ar microorganism that may grow in each the presence or absence of gas. In
addition to gas concentration, the gas reduction potential of the expansion
medium influences microorganism growth. The gas reduction potential may be a
relative live of the oxidizing or reducing capability of the expansion medium.
A microorganism
population is expressed either per gram or per sq. metric linear unit of
expanse. Rarely will the whole microorganism population exceed 1010 cells
per gram. A population of but 106 cells per gram doesn't cause any noticeable
spoilage except in milk. Populations of between 106 and 107 cells per gram
cause spoilage in some foods; as an example, they'll generate off-odours in
vacuum-packaged meats. Populations of between 107 and 108 cells per gram
manufacture off-odours in meats and a few vegetables. At levels on top of five
× 107 cells per gram, most foods exhibit some sort of spoilage.
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When the conditions for microorganism cell growth ar
unfavourable (e.g., low or high temperatures or low wet content), many species
of bacterium will manufacture resistant cells known as endospores. Endospores
ar extremely proof against heat, chemicals, desiccation (drying out), and UV.
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