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Control of Microorganisms by Lowering pH (by Adding Organic Acids)

Control of Microorganisms by Lowering pH (by Adding Organic Acids)

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Control of Microorganisms by Lowering pH (by Adding Organic Acids)

  1. 1. 1 | P a g e CONTROL OF MICROORGANISMS by lowering ph (by adding organic acids)
  2. 2. 2 | P a g e Contents  Introduction  Type of CONTROL OF MICROORGANISMS  Methods of controlling Microbes  Conditions Influencing Antimicrobial Activity  CONTROL OF MICROORGANISMS by lowering ph (addition of organic acids)  pH  PRINCIPLES FOR USING Disinfectants  Influence of pH on the preservation of foods  Lower pH  Acidification  Measuring pH  Organic Acids  SORBIC ACID  BENZOIC AC1D  Acetic Acid  PROPIONIC ACID
  3. 3. 3 | P a g e CONTROL OF MICROORGANISMS Sterilization Sterilization is a treatment that kills or removes all living cells, including viruses and spores, from a substance or object. Disinfection Disinfection is a treatment that reduces the total number of microbes on an object or surface, but does not necessarily remove or kill all of the microbes. Sanitation Sanitation is the reduction of the microbial population to levels considered safe by public health standards. Antiseptic Antiseptic is a mild disinfectant agent suitable for use on skin surfaces. -cidal A suffix meaning that “the agent kills.” For example, a bacteriocidal agent kills bacteria. -static A suffix that means, “The agent inhibits growth.” For example, a fungistatic agent inhibits the growth of fungi, but doesn’t necessarily kill it. Type of CONTROL OF MICROORGANISMS Controlling microorganisms can either be positive or negative: POSITIVE control - we want to make microbes grow: Industrial Fermentations; beer, wine and bread making NEGATIVE control - we want to destroy them by (1) physical or chemical means or (2) antibiotics Usually we mean negative control.
  4. 4. 4 | P a g e Methods of controlling Microbes Two methods are used in this contex: 1. Physical methods 2. Chemical methods Conditions Influencing Antimicrobial Activity Several critical factors play key roles in determining the effectiveness of an antimicrobial agent, including:  Population size  Types of organisms  Concentration of the antimicrobial agent  Duration of exposure  Temperature  pH  Organic matter  Biofilm formation CONTROL OF MICROORGANISMS by lowering ph (addition of organic acids) Factor pH is generally related to the chemical way of controlling microbes because pH is generally reduced by adding the organic acids, which are a type of disinfectant. pH The pH scale was introduced by the Danish chemist Søren Sørensen in 1909, when he controlled the quality of beer brewing. This scale is now widely used in chemistry, geology, ecology, medicine, industry and agriculture. In aqueous solution, the pH is defined as: pH = - log [H+ ] Acids can be used to control microbes, sometimes they work by destruction of microbial cells, or they work because they create extremes of pH in which microbes
  5. 5. 5 | P a g e cannot grow - as with the use of vinegar in canning of vegetables to prevent bacterial growth. PRINCIPLES FOR USING Disinfectants  Most agents are weak acids.  Most work when in the un-ionized form.  Most are not effective above their pKa's.  Most affect flavor.  Most are affected by processing, order of addition. Influence of pH on the preservation of foods Weathering reactions, whether chemical, enzymatic or microbiological, are largely influenced by the pH of the medium. Effect of pH on the reactions of impaired food Weathering reactions Minimum pH Optimum pH Maximum pH Growth of mold 1.5 to 3.5 4.5 to 6.8 8 to 11 Growth of bacteria 4.5 6.5 to 7.5 9.0 Growth of yeasts 1.5 to 3.5 4.0 to 6.5 8.0 to 8.5 Enzymatic browning 5 6 to 6.5 7 The above table shows that most microorganisms grow best at a pH close to 7 (4 to 7.5). Some bacteria, including lactic and acetic bacteria, are able to grow at pH lower than 4. Lower pH The reduction of pH of food products can be achieved by two methods. 1. The first is a direct method is to acidification of the product by adding one or more acids, organic acids are most commonly used acetic acid (vinegar) and citric acid. 2. The second is an indirect method based on the use of microorganisms in fermentation.
  6. 6. 6 | P a g e Acidification The acidification is the addition of an organic acid (as acetic acid) or an acidic ingredient (such as lemon) to a food that is initially slightly acidic. The acid or acidic ingredient must be added to the proportions determined for the pH of the finished product is below 4.5. The foods preserved by acidity have a pH of 4.6 or less. At these levels, production of deadly toxins by the organism that causes botulism is inhibited. To prevent this spoilage, processors usually heat acid acidified foods to 180°F and package them hot. This process kills yeast and mold spores on the products and in the container and cap. Foods that have a pH greater than 4.6 are called low-acid foods. Most fruits and fruit products are acid foods, and most vegetables and meats are low-acid foods. pH Values of Common Foods Measuring pH The pH of a food is usually determined using a pH meter. Electrodes from the meter are inserted into solution to measure the pH electronically. Organic Acids Various organic acids and their salts are common antimicrobials in foods.  Food preservatives  Safe in foods  Mold control in foods and drinks Agent pH Range Benzoic acid 2.5-4.0 Sorbic acid 3.0-6.5
  7. 7. 7 | P a g e Proplonic acid 2.5-5.0 Acetic acid 3.0-5.0 EFFECTIVE PH RANGE OF COMMON ORGANIC ACIDS SORBIC ACID  pKa = 4.8  Usage level limited to 0.1%.  Broad spectrum against yeast and molds. Lactic acid bacteria at low pH.  Major usage in salad dressings, fruit juices, cottage cheese.  Potassium salt is the most widely used form. o Potassium sorbate o Sodium sorbate o Sorbic acid BENZOIC AC1D  pKa = 4.2  Usage level limited to less than 0.1% by regulation.  Most active against yeast and molds.  Major uses in beverages, juices, non-standard "Jellies". margarine.  Acid form relatively insoluble and not used much. o Benzoic acid o Sodium benzoate Acetic Acid  pKa = 4.76  Usage level limited by taste.  More effective against yeast and bacteria.  Major usage in "Pickled" foods. Also In "natural" breads.  Sodium diacetate used in some breads. o Sodium diacetate. PROPIONIC ACID  pKa = 4.87  Usage limited to 0.1%.  Effective against molds, but no effect an yeast.  Major usage in broad and baked goods.  Calcium salt most used form. o Propionic acid. o Calcium propionate. o Sodium propionate.
  8. 8. 8 | P a g e References 1. Montville T.J. and Matthews K. R., 2005. Food Microbiology: an Introduction. ASM Press. New York. 2. Nakai S. A. and Siebert K. J., 2003. Validation of bacterial growth inhibition models based on molecular properties of organic acids. International Journal of Food Microbiology. 86: 249-255. 3. Russell J. B. and Diez-Gonzalez F., 1998. The effects of fermentation acids on bacterial growth. Advances in Microbial Physiology. 39: 205-234.

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