Antimicrobial Agents

Food preservation has long been practiced since the olden times with processes such as heating , drying, fermentation and refrigeration. In spite of this, physical methods are not enough to eliminate all microorganisms found in foods. Therefore, antimicrobial agents are needed to destroy these foodborne pathogens, so that the food will have a longer shelf-life. As technology progresses, improvements in the processing procedure and packaging systems considerably contribute to the preservation of food. Even so, antimicrobial agents still play an important role in protecting the food supply. Antimicrobial agents are chemical compounds biosynthetically or synthetically produced which either destroy or usefully suppress the growth or metabolism of a variety of microscopic or submicroscopic forms of life. 2. Factors Affecting the Selection of Antimicrobial agents 2. 1 Antimicrobial activity against different organisms It is desirable to use an antimicrobial agent that can inhibit a wide range of spoilagecausing microorganism. A good understanding of the chemicals mode of action is also useful in selecting a preservative. 2. 2 Microbial load of the food product . The food must be of the highest microbiological quality initially. Food should always be processed under the most meticulous sanitary conditions to minimize contamination. A high microbial population would require higher doses of antimicrobial agents. Use of antimicrobial agents should not be viewed as a substitute for good sanitation. 2. 3. Chemical and physical properties In choosing an antimicrobial agent, properties such as solubility, boiling point, and dissociation are mportant. Water solubility is important since microbial growth requires water. 1 Volatile preservatives are easily lost if the food is heated during processing. Dissociation of sorbic acid has an important bearing on its effectiveness in inhibiting harmful microbes. Most compounds are effective in their undissociated form. Stability Constituents in food such as protein and fiber can react with the preservative and reduce its effectiveness. For this reason, the stability of antimicrobial agents during storage is very important. 2. Processing and storage conditions The conditions of storage and interactions with other processes must be evaluated to ensure that the antimicrobial will remain functional over time. 2. 6 Flavor The addition of the antimicrobial agent should not interfere with the flavour of the food product, or rather enhance it. 2. 7 Cost The choice of antimicrobial should be cost-effective and suited to the food product. 2. 8 Safety and legality Antimicrobials agents must not be toxic to humans. The use of antimicrobial agents is often strictly regulated. As a processor, it is essential to use chemicals as prescribed by the regulations. 3. Types of Antimicrobial agents and their Functions 3. 1 Benzoic Acid and Sodium Benzoate ? Structure: Fig 1. Structures of Benzoic Acid and Sodium Benzoat e (Image from Wibbertman, Mangelsdorf Melber, 2000) ? Sources: o Benzoic acid occurs naturally in many plants and resins such as cranberries, plums, prunes, cinnamon. However, benzoic acid can be produced commercially by the reaction of toluene with oxygen at temperature around 200C in the liquid phase. The process is catalyzed by cobalt or manganese salts. Fig. 2 Production of Benzoic Acid (Image from Wikipedia. rg) o Sodium benzoate Sodium benzoate is produced by the neutralization of benzoic acid with sodium hydroxide. ? Properties: Benzoic acid is a white solid that starts to sublime at 100Â °C, with a melting point of 122Â °C and a boiling point of 249Â °C. Its solubility iin water is low (2. 9 g/litre at 20Â °C). 3 The undissociated form of benzoic acid (pKa=4. 2) is the most effective antimicrobial agent. It was reported that the compound was 100x as effective in acid solutions as in neutral solutions. Sodium benzoate is a white crystalline powder with a sweet astringent taste. It has a melting point above 300Â °C. It is very soluble in water (550-630 g/litre at 20Â °. Benzoates are most effective at pH 2. 5-4. 0and least effective at pH 4. 5. ? Primary use: Benzoic acid and its salts are used as antimycotic agents against yeast and molds, such as Saccharomyces cerevisae and Aspergillus parasiticus. ? Mechanism/s of action: o Formation of benzoic acid-oxidase complex Benzoic acid inhibits amino acid uptake in molds and bacteria. Benzoates also inhibit enzymes in the bacterial cell such as those controlling acetic acid metabolism and oxidative phosphorylation. Klein and Kamin (1940) reported that the activity of the d-amino acid oxidase was decreased by benzoic aci ( e. g. , the rate of oxidation of 1 mg. of d(-)-alanine by preparations of the oxidase was decreased about 60 per cent by benzoic acid). They suggested that the inhibitory effect of benzoic acid is due to the formation of a benzoic acid- oxidase complex. o Inhibition via depression of internal pH of the cell ? Applications: Sodium benzoate is used in carbonated and still beverages, margarine, soy sauce, jams and jellies, storage of vegetables, fish preserves, fruit salads, and other high acid foods. ? Regulatory Status: GRAS, up to a maximum of 0. 1%. Toxicology: Low order of toxicity for animals and humans. The reason is because humans and animals have an effective detoxification mechanism for benzoates. 4 3. 2 Sorbic Acid and Sorbates ? Structure: Fig. 3 Sorbic Acid (Image from John Wiley Sons, 2000) ? Sources: Sorbic acid, which is also known as 2,4-hexadienoic acid, was fi rst isolated from rowanberry (berries of the mountain ash tree) decades ago by A. W. van Hoffman, a German chemist. It is now prepared for industrial use via condensation of malonic acid and crotonaldehyde: Fig. 4 Synthesis of Sorbic acid (Image taken from Lookchem. com/Chempedia) ? Primary use: Sorbic acid and its salts targets yeasts, molds, and bacteria. Some of these include species Candida, Oospora, Fusarium, Mucor and Trichoderma. ? Properties: Sorbic acid is a white crystalline powder and is slightly soluble in water (0. 16g/100mL).