Received Dec 8; Accepted Dec This article has been cited by other articles in PMC. Abstract The response of bacteria, yeast, and mammalian and insects cells to oxidative stress is a topic that has been studied for many years. However, in most the reported studies, the oxidative stress was caused by challenging the organisms with H2O2 and redox-cycling drugs, but not by subjecting the cells to high concentrations of molecular oxygen.
Describe the conditions favorable to the growth of bacteria in food. Some are beneficial, such as those used to make fermented dairy and meat products.
And, a small percentage are harmful or pathogenic. Unlike animals and plants that are composed of many cells, bacteria are single-celled organisms. Each bacterium cell is self-sufficient and so is able to live independently.
Bacteria come in a variety of shapes and are impossible to see without a microscope. For example, about million bacteria clumped together would be about the size of a grain of sugar.
When bacteria grow, they increase in numbers not in size. This process is called cell division or doubling. Under ideal conditions, the number of bacteria can double every 30 minutes.
Therefore, one becomes two, two become four, four become eight, and so on. If you start with one bacterial cell, after 12 hours there would be as many as 33, The rate at which bacteria grow is different for each type or organism and is affected by many factors. Factors Affecting Microbial Growth Many factors affect bacterial growth but the most important ones are: Water -- Bacteria need water to dissolve the food they use for energy and growth.
Water allows the food to get into the cells, is used for the many chemical reactions necessary for life and growth, and allows waste products to escape. Energy sources such as sugars, starch, protein, fats and other compounds provide the nutrients.
Oxygen -- Some bacteria require oxygen to grow aerobes while others can grow only in the absence of oxygen anaerobes. However, many bacteria grow under either condition and they are facultative anaerobes.
Temperature -- Bacteria in general are capable of growing over a wide range of temperatures and are usually classified according to the temperature at which they grow. They cause spoilage in foods stored under refrigeration. Several pathogenic bacteria are psychotrophic -- Yersinia and Listeria.
Most pathogenic bacteria grow at these temperatures. Temperature is the most widely used method of controlling bacterial growth. It is indicated on a scale from 0 to 14, with seven being neutral.
If the pH value is below 7, the food is classified as acid; if it is above 7, the food is classified as alkaline. Most bacteria grow well at neutral pH, but many can reproduce in a pH range from 4.
Although each of the major factors listed above plays an important role, the interplay between the factors ultimately determines whether a microorganism will grow in a given food.
Often, the results of such interplay are unpredictable, as poorly understood synergism or antagonism may occur. An advantage is taken of this interplay with regard to preventing the outgrowth of C.
Food with a pH of 5. Certain processed cheese spreads take advantage of this fact and are therefore shelf stable at room temperature even though each individual factor would permit the outgrowth of C.
Therefore, predictions about whether or not a particular microorganism will grow in a food can, in general, only be made through experimentation.
Also, many microorganisms do not need to multiply in food to cause disease. Food and Drug Administration. The complete publication is available online at:Start studying ch. 4 ap enviro. Learn vocabulary, terms, and more with flashcards, games, and other study tools. Search. D. better survival or reproduction rates by individuals with a particular characteristic.
C. over time they gradually built up speed as . Bacteria are the most important microorganisms to the food processor. Most are harmless, many are highly beneficial, some indicate the probable presence of filth, disease organisms, spoilage and a few cause disease.
Dec 19, · The response of bacteria, yeast, and mammalian and insects cells to oxidative stress is a topic that has been studied for many years. However, in most the reported studies, the oxidative stress was caused by challenging the organisms with H 2 O 2 and redox-cycling drugs, but not by subjecting the cells to high concentrations of molecular oxygen.
Moisture. Bacteria need water to grow and die without a water source. Moist areas are particularly prone to bacterial growth, such as bathrooms and kitchens.
Water content in food also provides an excellent environment for many types of bacteria to grupobittia.comd: Jun 17, Some species form extraordinarily resilient spores, but for bacteria this is a mechanism for survival, not reproduction. Under optimal conditions bacteria can grow extremely rapidly and their numbers can double as quickly as every 20 minutes.
Some bacteria are autotrophs; they can make their own food. The breakdown of inorganic sulfur, iron, or nitrogen compounds often secretes energy. Few bacteria undergo photosynthesis.
The majority of bacteria are heterotrophs, unable to make their own food. This majority enjoins the fight for survival between human beings and bacteria.