FOOD MICROBIOLOGY UNIT 1 PART 1

• Preservatives


  Also known as antimicrobial agents, prevent or delay spoilage caused by microbiological, enzymological, chemical, and physical changes, inhibit growth without killing the microbe
• Preservatives


  • Chilling
  • Freezing
  • Water activity reduction
  • Acidification
  • Fermentation
  • Energy
  • Antimicrobial compounds
• Types of preservatives


  • Anti-browning agents
  • Antioxidants
  • Stabilizers
  • Target foodborne pathogenic and spoilage microorganisms
  • Bacteriostatic rather than bactericidal
• Organic Acid


  Found in nature but often manufactured chemically for use in foods, "generally recognized as safe", most useful below their pKa, rarely used in foods with a pH of 5.5, uncharged or protonated acid easily penetrate the cell membrane of a bacterium
• Parabenzoic acids


  Commonly known as parabens, have pKa values similar to that of organic acids, effective pH range of 3.0 to 8.0, used in baked goods, beverages, fruit products, jams and jellies, fermented foods, syrups, salad dressings, wine, and fillings
• Nitrites


  Used in cured meats such as bacon, hot dogs, ham, and bologna, act as an antimicrobial agent, contribute to cured meat flavor and texture, and an antioxidant, effective at lower pH, reducing agents (i.e., ascorbate and iso-ascorbate) enhance its anti-botulinal action, temperature, salt, and microbial load also influences nitrite's effectiveness
• Phosphates


  Charged particles containing mineral phosphorus, naturally found in meat, fish, dairy, fruits, and vegetables, TSPP, STPP, and SHMP inhibit Bacillus subtilis, Clostridium sporogenes, and Clostridium bofermentans, SAPP inhibits C. botulinum toxin production, 0.2 to 1.0% SHMP prevents outgrowth of Bacillus spores
• Sodium chloride


  Used to preserve raw meats and fish, used in canning, pasteurization, or drying, inhibits foodborne pathogens with a water activity of <0.92, Staphylococcus aureus grows at a water activity of 0.83 to 0.86, Listeria monocytogenes survive in saturated salt solutions at low temperatures, causes plasmolysis in cells
• Sulfites


  Used in fruit and vegetable products to control spoilage yeasts and molds, and bacteria, act as an antioxidant that inhibit enzymatic browning, have an inhibitory concentration of 0.1 to 20.0 ppm against Saccharomyces, Zygosaccharomyces, Pichia, Hansenula, and Candida species, inhibit Byssochlamys nivea at 25 to 100 ppm
• Chlorine


  Used as sanitizer in the form of hypochlorous, added to wash waters and water used to convey fruits and vegetables, used to sanitize food contact surfaces, sodium hypochlorite acts as a strong oxidizer against bacteria, yeasts, molds, and viruses, chlorine dioxide is odorless and degrades undesirable compounds in food
• Quaternary ammonium compounds


  Group of chemicals in which four compounds surround a nitrogen atom, the R groups can be saturated or unsaturated, cyclic or non-cyclic, substitutes or unsubstituted alkyl groups, colorless, relatively odorless, and non-corrosive, effective against bacteria, yeasts, fungi, and viruses
• Peroxides


  Hydrogen peroxide used as sanitizer to kill a wide variety of microorganisms, 3-5% concentration is used to sterilize equipment and food contact surfaces, not used as a food additive, peroxy acids used to reduce microbial loads in poultry and meat, used to sterilize food contact surfaces and containers
• Ozone


  A strong oxidant that targets the nucleic acid of microorganisms, "generally recognized as safe" to use for bottle washes, reduce E. coli O157:H7 in raw fruits and vegetables but not in meats
• Lysozyme


  An antimicrobial enzyme produced in eggs, milk, and tears, commercial lysozyme is made from dried egg white, active against gram-positive bacteria because of the more exposed peptidoglycan, inhibits Clostridium botulinum, Clostridium thermosacchharolyticum, Clostridium tyrobutyricum, Bacillus stearothermophillus, Bacillus cereus, and Listeria monocytogenes
• Lactoferrin


  An iron-binding protein in milk, lactoferrin and transferrin have iron-binding sites: bicarbonate and citrate, citrate inhibits lactoferrin's activity, bicarbonate reverses the inhibition, stimulates Clostridium, Escherichia, Listeria, Pseudomonas, Salmonella, Staphylococcus, Vibrio, and Yersinia
• Ovotransferrin


  An iron-binding molecule of the egg albumen, makes up 10-13% of the total egg protein, inhibits gram-positive and negative bacteria, Bacillus and Micrococcus are sensitive to ovotransferrin
• Avidin


  An egg albumen protein that makes up about 0.05% of the total egg albumen protein, stable to heat and a wide pH range, inhibits bacteria and yeasts that require biotin for growth, transports proteins in the E. coli outer membrane suggesting that avidin may inhibit bacteria by interfering with transport
• Spices and their essential oils


  Added to foods as flavoring agents but have antimicrobial activity, cloves, cinnamon, oregano, thyme, sage, and rosemary, terpenes in oils are the primary antimicrobials, active terpenes: eugenol, thymol, and carvacrol
• Onions and garlic


  Inhibit B. subtilis, Serratia marcescens, Mycobacterium, B. cereus, C. botulinum type A, E. coli, Lactobacillus plantarum, Leuconostoc mesenteroides, Salmonella, Shigella, and S. aureus, inhibit fungi such as Aspergillus flavus, Aspergillus parasiticus, Candida albicans, Cryptococcus, Penicillium, Rhodotorula, Saccharomyces, Torulopsis, and Trichosporon, allicin is the major antimicrobial agent in garlic, protocatechuic acid and catechol are antimicrobial phenolic compounds in onion
• Isothiocyanates


  Potent antimicrobials made from glucosinolates in plant cells from the mustard family, found in cabbage, kohlrabi, Brussels sprouts, cauliflower, broccoli, kale, horseradish, mustard, turnips, and rutabaga, inhibit fungi, yeasts, and bacteria at 0.016 to 0.062 µg/ml in vapor phase or 10 to 600 µg/ml in liquid, may inhibit cells by reacting with disulfide bonds or inactivating sulfhydryl enzymes
• Phenolic compounds


  Have aromatic ring with one or more hydroxyl groups and are classified as simple phenols and phenolic acids, hydroxycinnamic acid derivatives, and the flavonoids, gallic acid occurs in plants as quinic acid esters or hydrolysable tannins, used as preservative in wood smoke giving a desirable flavor and a preservative effect on meat, cheeses, fish, and poultry, smoke preparations at 0.25 and 0.50% reduce Listeria monocytogenes viability in buffer, phenolic glycosides inhibit L. plantarum, L. mesenteroides, Pseudomonas fluorescens, B. subtilis, Rhizopus, and Geotrichum candidum
• Erythorbate


  accelerate curing and inhibit nitrosamine formation
• Nitrosamine


  carsinogens formed by reaction of nitrites and amines when subjected to high temperature