Friday, July 16, 2010

Chemical Changes in Food Spoilage

Food waste is any food material whether it is raw or cooked is discarded intentionally or unintentionally. In my opinion, food wastage was an irresponsible human act because food discarding may cause our beautiful earth to suffer air pollution. The food waste has causes the releasing of methane gas through the herbaceous digestion process, this may cause the production of methane gas in the earth increases by time and resulting air pollution. In a year, the Americans waste about 100 billion pound of food and approximately 1.5 pounds of food is waste by each of us in our daily life. Have you ever consider about why food is wasted? And what causes the food spoilage?

The food is said to be blemished when it is unhealthy for human health. For vegetables and some fruits, it changes its colour to brown when it contacts with oxygen. In the presence of oxygen, the polyphenal oxidize enzyme which also referred as phenoloxidase, phenolare, monophenol oxidase, diphenol and tyrosinase in chloroplast of plant cells will oxidize the phenolic chemical to o-quinones. There chemicals work together with amino acids from proteins or the chemicals work on itself to create brown polymers. At this stage, the vegetables and fruits are said to be spoiled.

Meat is spoiled by sort of factors but the ordinary cause of meat spoilage is caused by micro-organisms. The factors affecting the growth of the micro-organisms is temperature, osmotic pressure, PH value and oxidation-reduction potential. As temperature increase, the growth rate of the microbial increase too. The microbial attack the glucose and amino acids in the meat therefore results meat spoilage. Sometimes salt is added to inhibits the deterioration action of the microbial because the sodium ions (Na+) has an effect on inhibits the action on certain micro-organism. However the micro-organism which resistant to high salt concentration have an ability to lower down the nitrate and nitrite concentration through its metabolisms with the production of nitrous oxide. The nitrate which found in the curing brine is reduced to nitrite and further into nitric oxide through the microbial action. The nitric oxide can reacts with the myoglobin in meat resulting colour fixation. As the salt concentration increases, the concentration of nitrite and nitrate decreases through the enzymes activity found in tissue and without the present of micro-organisms. Salt may inactive certain bacteria that cause the discoloration of meat and some particular salt may stimulate proteolytic anaerobes and preventing meat from curing.

Amount of lactic acid which produced from glycogen during the anaerobic glycolysis process is used to determine the port-mortem pH of meat. Most bacteria grow at approximately pH7 and not well at too acidic or too alkali condition. When muscle is death, the pH value of the muscle will increases due to the lack of the glucose level in muscle. At low glucose level condition, the micro-organisms tend to attack amino acids and causing spoilage to the meat, such as bad odor and discolouration. Besides that, pH determines the amount of the nitrite which present as un-dissociated nitrous acid and inhibits the growth of bacterial. Nitrite also plays an important role in stability of cooked and uncooked cured meats. It lowers the salt concentration which required stabilizing the meat. At the pH range 5.5 to 6.8, the raises of concentration of nitrite, salt, isoascorbate or nitrate in the medium and increase in heat may decrease the manufacture of toxin by the organism. Even though polyphosphate in meat may increase the toxin production, but it uplifts the action of isoascorbate in decreasing toxin production at the same time.

Oxidation-reduction potential is one of the meat spoilage factors. The oxidation-reduction potential (Eh) change accordingly to the myoglobin content, enzymatic activity in the muscle of the organisms and time post-mortem. The Eh delay the initial log phase on microbial growth, so that the eventual growth rate is not affected. The Eh in meat is also affected by the oxygen level and the concentration of molecules which have a marked electropositive character. Cured meats apply an indirect antibacterial effect through raising the Eh of the system in the present of nitrate. At low PH anaerobic condition, nitrate protects bacteria against nitrite.

The youtube video about the change of fresh apple to rotted apple.

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1 comment:

  1. This is useful and interesting info! If we know what are the detailed factors that cause food spoilage, then we can find ways to inhibit the chemical reactions that lead to the spoilage.