This is a nice overview of preservation of food and medical products

1. Antimicrobial Preservation Overview Jim McElroy

2. Composition and Structure of Microorganisms The cell surface differentiates cells from one another The cell envelope is the rate limiting barrier for the partitioning of : Nutrients Waste products Chemicals

3. Cell membranes Main components are phospholipids and proteins Major proteins are hydrophobic The plasma structure is stabilized by hydrogen bonding Mg2+ and Ca2+ cations stabilize the membrane

4. Comparison

5. Yeast and Mold Yeast: Cell wall is composed of two or more protein polysacharide complexes held together by covalent bonds Yeast: Mannan is a cell wall component Mold: Cell wall is composed of two or more protein polysaccharide complexes held together by covalent bonds Mold: Mannan is not a cell wall component

6. Comparison (bacteria, yeast & mold)

7. What is a preservative? A chemical substance that is used to preserve pharmaceuticals, food or other organic material from decomposition or fermentationby preventing the growth of microorganisms.

8. Commonly used preservatives Ingestible & Topical Methyl, ethyl, propyl and butyl Parabens Sorbic acid Na, K & Ca Sorbate Benzoic acid Na, K & Ca Benzoate Sodium metabisulfite Propylene glycol (15-30%) BHT, BHA Flavors w/ benzaldehyde Topical Only Formaldehyde donors Essential Oils Monoglyceride Phenol Mercury compounds

9. Parabens Parabens are among the most commonly used preservatives. They are relatively active against a broad spectrum of microorganisms. The methyl ester is most effective against bacteria and molds while the ethyl, propyl and butyl esters are more active against yeast and molds. Parabens are more effective against gram negative than gram positive organisms.

10. Parabens and pH Parabens disassociate at high pH (8 or more) and are rendered ineffective.

11. Parabens have limited solubility in H2O

12. Partition Coefficients and Emulsions It is important to pay close attention to preservative partitioning in emulsion systems. Parabens prefer the oil phase thus leaving little in the water phase where it is needed. Water phase Oil droplet surfactant

13. Partitioning of Parabens Parabens are lipophilic. Parabens will partition disproportionately into the oil phase of an emulsion. If large amounts of the preservative partition into the oil phase, it is not available for antimicrobial action.

14. Partition Coefficient Measurement Cw is the preservative left in the water phase C is overall % of preservative Kw is the partition coefficient ά is phase volume ratio Cw=C* ά + 1 / Kw + 1

15. Partition Coefficients For Parabens & Other Preservatives

16. Chelating Agents as Preservative Enhancers Alkaline earth metals such as Ca+ and Mg+ are important for the stabilization of the outer membrane of cellular organisms. Chelating agents sequester these ions. This contributes to the partial solubilization of the cell membrane which allow preservatives a pathway into the cell. EDTA is a typical chelating agent used in formulations.

17. Ingredients That Enhance Preservative Efficacy Solutes (salts & high concentration of sugars) Esters Cationic and anionic surfactants Humectants (glycerin, propylene glycol) Phenolic antioxidants (BHT) Chelating agents (EDTA) Fragrances Low water activity

18. Ingredients That Hinder Preservative Efficacy Sugars and alcohol sugars Proteins, peptides, yeast extract Natural gums & cellulose thickeners Plant extracts (aloe vera, starch,…) Vitamins Clay compounds High water activity Surfactants (Tween 80)

19. Manufacturing Steps That Enhance Preservative Efficacy Sanitary condition of equipment Treatment of raw materials Heat treatment of sub-phase or final batch Sub-micron filtration Hot fill Aseptic fill

20. Packaging Components and Preservative Efficacy Design of opening or dispenser Susceptibility to contamination from environment Susceptibility to contamination from human contact

21. Conclusion It is important to take into consideration all aspects of the formula before considering a preservative system. This includes type of formula, bulk handling and packaging.