Preservatives in Food PDF

9 - Preservatives NUT312 - Food Chemistry 1 Introduction  Microorganisms have nutritional requirements remarkably similar to ours 1. Energy is obtained by photosynthesis or by oxidation/fermentation of organic compounds 2. MO exist at mo...

9 - Preservatives NUT312 - Food Chemistry 1 Introduction  Microorganisms have nutritional requirements remarkably similar to ours 1. Energy is obtained by photosynthesis or by oxidation/fermentation of organic compounds 2. MO exist at moderate pH and temperatures, which are conditions found in many food products 2 Introduction  One major aspect of food science to which microbiologists contribute is “Food Safety” ◦ Foodstuffs are ideal carriers of pathogenic and toxin producing bacteria  Using chemicals to deter unwanted microbial activity is of greatest interest ◦ Heat-processing methods required to obtain sterility results in partial destruction of nutrients 3 Introduction  It is unusual for a single antimicrobial procedure to be used alone to protect a food ◦ Many mild procedures are combined to maximize the inhibition of microbial activity while minimizing adverse effects on nutritional/organoleptic quality ◦ Cooked ham: 1. Salt: to maintain low water activity 2. Nitrite: to prevent spore and bacterial growth 3. Cooking: to destroy vegetative bacterial cells 4 Sodium Chloride  Common salt, sodium chloride, was the first antimicrobial substance to be used ◦ Used as a preservative and flavoring agent ◦ With the introduction of canning and refrigeration, the importance of salting has diminished 5 Nitrites  Nowadays, meat is not preserved by common salt alone ◦ Nitrates and/or nitrites are an essential component of the salt mixtures used for curing/preserving bacon and ham ◦ Nitrate results in the attractive red/pink color in preserved meat  In recent years, the use of nitrates in food has been regarded with increasing suspicion owing to the risk of carcinogenic nitrosamine formation ◦ Reduce nitrosamine formation by adding ascorbic acid in curing-salt 6 Nitrites 1. Some of the nitrate is reduced to nitrite by the enzymes of the muscle tissue NO3- + 2[H] → N02- + H20 2. Nitrite oxidizes the iron of the muscle myoglobin (Mb) to the iron(III) state → metmyoglobin (MMb) and nitrogen oxide are formed Fe2+ + N02- + H+ → Fe3+ + NO + OH- 3. The resulting nitrogen oxide reacts with the iron MMb to form nitrosyl metmyoglobin (MMbNO) 4. MMbNO is immediately reduced by the muscle tissue to nitrosyl myoglobin, MbNO, the red/pink pigment of uncooked bacon and ham 7  Smoke  Smoke is the other preservative traditionally associated with meat and fish ◦ The flavoring action of wood smoke was regarded as the only valuable side effect ◦ The preservative action of smoke went unnoticed ◦ The gas phase of wood smoke has the antimicrobial formaldehyde (methanal, HCHO) ◦ Nowadays, meat and fish are rarely preserved by smoking, and refrigeration has made the smoke important for its flavour only ◦ The detection of carcinogens in wood smoke → concern over the safety of smoked foods → Liquid smoke preparations are being used 8 Sulfur Dioxide  SO2 is used in wine-making to control the growth of unwanted microorganisms ◦ Total SO2 levels of around 100 p.p.m. are added  The desirable yeast Saccharomyces cerevisiae is able to grow/ferment sucrose to ethanol at this level, but undesirable yeast and lactic acid bacteria are suppressed 9  Sulfur Dioxide  Recently, high SO2 levels have shown allergic response symptoms in some asthmatics  There is a different nutritional problem with the use of SO2 ◦ The bisulfite ion (HSO3-)reacts with thiamin, Vit B1 ◦ Vegetables that are stored in sulfite solutions before processing lose considerable Vit B1 ◦ Many countries prohibit the use of SO2 in vit B1-rich foodstuffs 10 Benzoates  Benzoic acid occurs naturally in small amounts in some edible plants, notably the cloudberry  The sodium benzoate, being more soluble than benzoic acid, is the form that is usually added to food as a preservative ◦ At the levels used (0.05-0.1%), no deleterious effects on humans have been detected  Benzoic acid is added to low pH (up to 6.5) foods, such as fruit juices 11  Sorbic Acid  Effective inhibitor of mold Acetic Acid  Effective inhibitor of many types of spoilage bacteria and fungi at too low concentrations  Aside from its inevitable presence in vinegar- based food products, acetic acid is becoming increasingly popular as an inhibitor of molds in bread Propionic Acid  Like acetic acid, it is naturally found in many foodstuffs. It has a similar spectrum of antimicrobial activity to that of acetic acid 12  Nisin  Nisin is a polypeptide consisting of 34 amino acids ◦ Produced by Streptococcus lactis bacterium, which commonly occurs in milk ◦ Mainly used in processed cheeses ◦ Defined as an antibiotic, but this term is not usually applied to nisin as it is not used in the treatment of disease 13 Natamycin  Natamycin is an antifungal antibiotic produced by the Streptomyces natalensis, commonly found in soil ◦ It has a limited clinical application in ophthalmics besides its application in food preservation ◦ It is permitted for use as a surface treatment for cheese to deter unwanted mold growth 14