Chemical Preservatives Essay Example

Chemical Preservatives Essay Example Chemical Preservatives Essay Chemical Preservatives Essay It is applied as a chelating agent. Its function is to control the reaction of metal ions with some organic and inorganic components that will result in deterioration of foods. Apart from that, the preservative also acts as antioxidant antimicrobial agent, especially against gram-negative bacteria. Mechanisms of action Ca disodium EDTA blocks the normal reaction of metal ions by binding to their reactive sites. This increases its efficiency as an antioxidant. Consequently, the oxidation of ascorbic acid and fat-soluble vitamins is hindered and also the rancidity of the product. The resistance of gram-negative bacteria is overcome by the removal of lipopolysaccharide containing membrane. 2. Calcium Propionate (C6H10CaO4) It was found in wholemeal bread rolls. Properties It is the salt of propionic acid. It is only soluble in water but insoluble in alcohol. Utilization The antimicrobial activity is particularly against mycotoxin forming moulds, less so against bacteria. No inhibition effect has been demonstrated against yeast. Therefore, it is mainly used for bread preservation, as it will not interrupt the leavening in bakery goods raised by yeast. The other salt of propionic acid, sodium propionate is employed chiefly in confectionery. Mechanisms of action The antimicrobial activity is related to amino acid uptake inhibition and growth inhibition in the cell membrane. Propionic acid carries out neutralization of the protonmotive force by shuttling undissociated molecules through the membrane. They are then dissociated on the inside of the membrane. Apart from that, it can work within a high pH range, which is the condition in most bakery goods owing to low dissociation constant. Moreover, they can combat against moulds and prevent ropiness caused by the action of Bacillus mesentericus. 3. Nisin It was found in Swiss cheese. Properties It is a polypeptide antibiotic, produced by some Lactococcus lactis strains. The polypeptide consists of 34 amino acids. Although it is defined as an antibiotic, it is not used as human medicine in disease treatment. Utilization The inhibitory effect of nisin is restricted to pathogenic gram-positive microorganisms and all spore forming microorganisms. For example, lactic acid bacteria, Streptococci, Bacilli and Clostridia. However, yeast and moulds are not inhibited by nisin. This heat resistant peptide is applied to suppress anaerobes in cheese and cheeses products, especially in hard cheese and processed cheese to inhibit butyric acid fermentation. Mechanisms of action The action of nisin is directed against the cytoplasmic membrane right after the germination of the spore. Its action is pronounced against spores rather than vegetative cells. 4. PHB-esters It was found in chicken and mushroom pastry. Properties They are the alkyl esters of p-hydroxybenzoic acid and are stable. The solubility in water decreases with increasing alkyl chain length. Utilization The esters are mostly antifungal agents. They are effective against yeasts but less so against bacteria, especially those gram-negative bacteria. The uses of PHB-esters are governed by 3 properties: action dependent on the pH value, very low water solubility and particular organoleptic characteristics. Mechanisms of action Its mode of action is very similar to that of benzoic acid. The parabens dissolve in or through the cell membrane, interfering with the membrane-related processes or structures. In addition to that, paraben has been found to inhibit both growth and isolated uptake systems for amino acids. 5. Sodium Ascorbate (C6H7NaO6) It was found in the smoked reformed ham of Italiano ham and cheese tortellini. Properties It is the salt of ascorbic acid (vitamin C). It is soluble in water. In water, it readily reacts with atmospheric oxygen and other oxidizing agents. Utilization Na ascorbate is used as an antioxidant due to its high affinity for oxygen. Furthermore, it is also functions as a colour preservative. It is used as a reducing agent in curing of meat for a good pink colour. In addition, it helps to retard the browning reactions in fruits and vegetable products. Mechanisms of action In this context, Na ascorbate is included in the curing-salt mixtures to reduce the amount of residue nitrite. As a reducing agent, it influences the rate of key reducing reaction in the formation of nitrosyl myoglobin (MbNO). MbNO is responsible for the read pigment of the uncooked bacon and ham. As a result, lower levels of nitrites or nitrates could be used in pickles. At the mean time, it also hinders the nitrosation reaction. 6. Sodium Benzoate It was found in marmalade. Properties It is the salt of benzoic acid. It occurs in the form of white crystalline powder. Its solubility is 200 times greater than benzoic acid. Utilization The inhibition activity of sodium benzoate is mainly against yeasts and moulds. Bacteria are only partially inhibited. It is used for preservation of sour foods, which has a pH of 4-4. 5 or lowers, as they can tolerate at acidic pHs. The usual quantity applied is 0. 05-0. 1% Mechanisms of action The undissociated part of benzoic acid is the effective agent. Its action is pH dependent because it has to penetrate the cell wall of the microorganisms in order to develop its action. Generally, it has been discovered to influence the enzyme controlling acetic acid metabolism and oxidative phosphorylation. Moreover, the preservative also intervene at various points in the tricarboxylic cycle, especially where the dehydrogenases of ? -ketoglutaric acid and succinic acid are involved. 7. Sodium Nitrite (NaNO2) It was found in the honey roast sandwich ham . Properties It is the salt of nitrous acid. It is a white to pale yellowish granular powder with salty taste. It has a high solubility in water. Utilization It is used primarily to preserve the red colour of meat. Apart from this, sodium nitrite also demonstrates antimicrobial activity. It is particularly effective against outgrowth of Clostridium botulinum, which can produce the deadly toxin, botulin. Mechanisms of action The nitrite oxidises the iron ( ) state of the muscle myoglobin to the iron ( ) state. Fe 2+ + No2- + H+Â   Fe3+ + NO + OH- The myoglobin (Mb) is converted to metamyoglobin (MMb). The resulting nitrogen oxide will react with the iron MMb to form nitrosyl metmyoglobin (MMbNO). The respiratory system of the muscle tissue will reduce MMbNO to nitrosyl myoglobin, MbNO, which is the red pigment of the uncooked bacon and ham. The antimicrobial effect, which is termed as Perigo effect , is related to the residual nitrite in ham. During cooking of the ham, much of the residual nitrite is broken down to nitrogen oxide. NO has an inhibition effect on at least one enzyme (namely pyruvate:ferrodoxin oxidoreductase), which plays an important role in the energy metabolism. Interfering activity of NO includes inhibiting oxygen uptake, oxidative phosphorylation and H+ dependent active transport. Furthermore, the uncoupler also causes collapse of proton gradient. As a result, the growth and toxin production of Clostridium botulinum is severely affected. Apart from NaNO2, Sodium nitrate is used in curing of meat to supply the nitrite. This is due to the reason that nitrite is the effective agent. NO3- + 2[H] NO2- + H2O 8. Sorbic acid (C6H8O2) It was found in cheese. Properties It is a white monocyclic crystal with a specific odour and sour taste. It will melt at 132 to 135 0C. The solubility increases with temperature. It is effective over a broad range of pH but ineffective above pH 7. Utilization It is effective against mould and yeast but only marginally effective against bacteria. This makes it very suitable as a cheese preservative because it permits the fermentation action of lactic acid bacteria. Mechanisms of action The activity of sorbic acid is very pH dependent. The un-dissociated acid constituent, which is antimicrobial, will penetrate the cell wall in order to develop action in the cell. Its action includes inhibition of various enzymes such as enolase and lactate dehydrogenase and others. One of the ways is by forming covalent bonds between its own double bonds and the SH groups of enzymes. 9. Sulphur dioxide (SO2) It was found in ready to eat apricot dried fruits. Properties SO2 is a colourless, non-combustible gas with a pungent odour. It dissolves in water to yield sulphurous acid. The density of SO2 is twice higher than that of air. Usage It is widely used in many foods and beverages as preservatives and antioxidants. Its functions include prevention of oxidation, inhibition of chemical and enzymatic reactions and the inhibition of the growth of yeasts, moulds and bacteria. It is commonly used in the form or sodium hydrogen sulphite, sodium metabisulphite, potassium metabisulphite and calcium hydrogen sulphite. Mechanisms of action In the production of dehydrated fruits, SO2 provides protection against oxidative, enzymatic and non-enzymatic browning reactions. Moreover, it also helps to delay colour changes or acts as bleaching agent. SO2 prevents enzymatic browning by inactivating the phenolases, which are mainly found in fruits and vegetables. These enzymes facilitate the conversion of colourless phenolic compounds to highly coloured quinones. Fig 1 Fig 2 In non-enzymatic browning, SO2 inhibits discoloration by blocking compounds with reactive carbonyl groups, the nonreactive hydroxy sulphonate sugar derivatives. Although SO2 itself is successful in many systems in very low concentration, combinations with other preservatives such as sorbic acid, sorbates and ascorbic acid may be more effective for browning prevention in certain foods and beverages. 10. Vitamin E It was found in vegetable fat spread. Properties It is a group of derivatives of 6-hydroxychroman carrying a phytyl side chain. There are two main groups of compound, which have vitamin E activity, the tocopherols and tocotrienols. The vitamin E content of foods is expressed as mg ? tocopherol. Therefore, vitamin E is sometimes labelled as tocopherols in the product. Utilization It functions as an antioxidant in oily and fatty foods. Rancidity of foods resulted from autoxidation of the unsaturated fatty acid is prevented. Mechanisms of action As an antioxidant, vitamin E blocks the free-radical chain reactions of lipid peroxidation. References 1. Belitz, H. D. and W. Grosch (1999) Food Chemistry, (2nd edition), Springer-Verlag Berlin Heidelberg, Germany. 2. Coultate, T. P. (1996), Food: The Chemistry of Its Components, (3rd edition), Royal Society of Chemistry Paperback, Cambridge, p239-241, 247-257.

Leontyne Price, New York Met Opera Star

Leontyne Price, New York Met Opera Star Known for:  New York Metropolitan Opera soprano 1960 – 1985; one of the most popular opera sopranos of recent history, known as the first black American-born prima donna; she was the first black opera singer on televisionOccupation:  opera singerDates:  February 10, 1927 -Also known as: Mary Violet Leontyne Price Background, Family Mother: Kate Baker Price, a midwife, and singer in the church choirFather: James Price, a carpenter who also sang in the church choirHusband: William C. Warfield (married August 31, 1952, divorced 1973; opera singer) Education Central State College (formerly the College of Education and Industrial Arts), Wilberforce, Ohio.  BA, 1949Juilliard School of Music, 1949 - 1952Voice with Florence Page Kimball Leontyne Price Biography A native of Laurel, Mississippi, Mary Violet Leontyne Price pursued a singing career after graduation from college with a B.A. in 1948, where she had studied to be a music teacher. She had been inspired first to pursue singing  upon hearing a Marian Anderson concert when she was nine years old. Her parents encouraged her to learn piano and to sing in the church choir. So after graduating from college, Leontyne Price went to New York, where she studied at the Juilliard School of Music, with Florence Page Kimball guiding her as she would continue to do. Her full scholarship at Juilliard was supplemented by a generous family friend, Elizabeth Chisholm, who covered most of the living expenses. After Juilliard, she had her 1952 debut on Broadway in Virgil Thomson’s revival of Four Saints in Three Acts. Ira Gershwin, based on that performance, chose Price as Bess in a revival of  Porgy and Bess  that played New York City 1952-54 and then toured both nationally and internationally.  She married her co-star, William Warfield who played Porgy to her Bess on the tour, but they separated and later divorced. In 1955, Leontyne Price was chosen to sing the title role in a television production of  Tosca, becoming the first black singer on a television opera production. NBC invited her back for more telecasts of operas in 1956, 1957 and 1960. In 1957, she debuted in her first stage opera, the American premiere of  Dialogues of the Carmelites  by Poulenc. She performed primarily in San Francisco until 1960, appearing in Vienna in 1958 and Milan in 1960.  It was in San Francisco that she first performed in Aida which was to become a signature role; she also played that role in her second Viennese performance.  She also performed with the Chicago Lyric Opera and the American Opera Theater. Returning from a successful international tour, her debut at the Metropolitan Opera House in New York in January 1961, was as Leonora in  Il Trovatore.  The standing ovation lasted 42 minutes. Quickly becoming a leading soprano there, Leontyne Price made the Met her primary base until her retirement in 1985.  She was the fifth black singer in the Met’s opera company, and the first to really achieve stardom there. Associated especially with Verdi and Barber, Leontyne Price sang the role of  Cleopatra, which Barber created for her, at the opening of the new Lincoln Center home for the Met. Between 1961 and 1969, she appeared in 118 productions at the Metropolitan. After that, she began to say â€Å"no† to many appearances at the Metropolitan and elsewhere, her selectivity earning her a reputation as arrogant, though she said she did it to avoid overexposure. She also performed at recitals, especially in the 1970s, and was prolific in her recordings. Many of her recordings were with RCA, with whom she had an exclusive contract for two decades. After her retirement from the Met, she continued to give recitals. Books About Leontyne Price Aida: Leontyne Price, illustrated by Diane and Leo Dillon. Trade Paperback, 1997. Price retells the story of the Ethiopian princess who is sold into slavery in Egypt.Leontyne Price: Opera Superstar  (Library of Famous Women): Richard Steins, Library Binding, 1993.