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Preservatives - A Possible Solution for Biodeterioration
#1
Bio-deterioration is process that involves undesirable change in the natural or other economically important material due to the activities of living beings, plants, animals or microorganisms. The process of bio-deterioration is associated with the negative role of microorganisms in the economically useful products. To inhibit the growth of the microorganisms in the useful products, preservatives in different forms are added to the product. A substance, which may be naturally occurring or synthetically produced, added to different products such as food, medicines, pharmaceutical products, paints, wood, different biological samples, etc to prevent them from biodegradation or deterioration or any other undesirable change by the microorganisms, is known as a preservative. They generally inhibit the growth of the microorganisms or kill them in rare cases.

Antimicrobial preservatives are chemical agents that are normally static in nature i.e. they inhibit the growth of the microorganisms in food, pharmaceuticals or cosmetic products that may be ingested. In most of the countries, based on the approval issued by FDA (Food and Drug Association), there are three categories of preservatives. In Group 1, the natural organic acids like lactic acid, citric acid, etc are included, while in Group 2, the substances, which have been classified as generally regarded as safe (GRAS), such as a) other organic acids such as benzoic acid, sorbic acid, etc., b) the parabens such as esters of para-hydroxybenzoic acid, and c) SO2 are included. The compounds, which do not belong to either Group 1 or Group 2 are included in Group 3. There are some compounds such as common salt, spices, vinegar, oil, etc, which act like preservative, but cannot be classified as ‘added preservatives’, due to the difference in their properties in comparison to the added preservatives. The main properties of the added preservatives in food are that they should be safe, and should be free from any sort of flavour or aroma. They should be added in very low concentration and must not be used to disguise the food from its poor manufacturing practice.

The action of the preservatives depends on the pH of the product, to which they are added. The undissociated form of the preservatives possesses anti-microbial activity. As the pH increases, it is seen that the anti-microbial activity of the compounds reduces, except sorbic acid and parabens, which possess anti-microbial activity until pH 6.5 and pH7.0-8.0 respectively. Hence, parabens have found wide application as preservative in food, pharmaceuticals, and cosmetics due to their favourable properties such as being colourless, tasteless, and stable, apart from their wide pH range. They also have high lethal dose as studied on rats. Lethal dose or LD50 can be defined as the dose of the substance in grams per kilograms of body weight of test animals at which 50% of the population are killed. The apparent drawbacks of using parabens are the low-grade sensitization as exhibited by some individuals ingesting it, their increased tendency to exhibit partition into oil, particularly vegetable oils and also their inability to show complete efficacy in presence of ethylene glycol, glycerol, etc. Although, the parabens inhibit the growth of many types of bacteria, yeasts, fungi, etc., they have been found to be almost ineffective against Gram-negative bacteria. The main action of the parabens is assumed to be on the microbial membranes, however they also affect the nucleic acid metabolism. They are used in mixtures for their synergistic action.

Apart from the organic acids, very few microbial products have found application as preservatives. The antibiotics are generally not used as preservatives due to the development of possible resistance and also the probable disturbance of the microbial ecology in the gut, toxicity, or different allergic reactions. The development of the antibiotics for use as preservatives is a lengthy, expensive and complex procedure. The long-term safety and toxicological study are also major concerns in their development. Natamycin, an antifungal agent that acts as surface antimycotic agent for cut and sliced foods, e.g. cheese and Nisin, a bacteriocin that is effective in heat processed foods and low pH foods, are the only antibiotic agents to be approved for use as food preservatives. Nisin is effective on the gram-positive bacteria but is very less effective against the gram-negative bacteria and yeast. Other biological preservatives used widely are lactoferrin; avidin, a biotin-chelator; ovoinhibitor, an inhibitor of protease; and lactoperoxidase, an SH group oxidiser. Lysozyme has also been used as a preservative, though it has limited bacteriolytic activity spectrum, for bacterial cell lysis. Chitin, a cell wall component of fungi has also found application as a food preservative.

Apart from food, pharmaceuticals and cosmetics, and other economically useful products such as wood, etc have also been found prone to biodeterioration. Due to biodeterioration, the active ingredient in the pharmaceuticals and cosmetics is lost making it useless and in some cases even toxic for use. Hence, the use of non-toxic preservatives in minute concentration have been recommended such that the products remain sterile for a longer period of time and are also safe for use. However, in-depth study about the conditions necessary, the nature of preservatives and its effect on the formulation of the products is very essential.
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#2
Preservation of valuable microbial cultures is one of the important aspects of various industries including in prevention of biodeterioration and use of microbial cultures in fermentation industries. Microbial cultures which have valuable properties like high yielding genes, high quality bio-molecule producing potential are preserved for long time and are used as and when required. They are removed from preservation conditions and are used as per the production schedules and market pulls. First of all screening of cultures for potential is done in which cultures with high quantity productions capabilities are isolated. This screening is critical process and need high technical skills. This skill includes knowledge of identification of morphology and anatomy of microorganism which has co-relation with required cultures. Once such morphological characteristics are identified, they need to known its anatomy and other metabolic characteristics. Once such good quality cultures are identified using their morphological and anatomical characteristics, they are further screened for their production capabilities.
In an industry which does antibiotic production, antibiotic titers are calculated using various analytical tests. This analysis includes use of various sophisticated instruments like HPLC, GC, UV-Spectrophotometer, IR spectrophotometer. In HPLC that is high performance liquid chromatography, separation of bio-molecules is done such that the one of interest is identified and further its quantitative test is performed to know the potential of yield of end product. The titer between various isolated cultures gives clear idea of their potential and quality.
Few examples of such fermentation industries are antibiotic production, semi-synthetic products, bio fertilizers and many such other by-products. This way once the required high yielding isolated are identified using screening techniques, they are sub-cultured and preserved under liquid nitrogen or by lyophilization and kept in deep freezers.
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Preservatives - A Possible Solution for Biodeterioration00