1. Antimicrobial factors and water activity August 29, 2016

2. Inhibition of microorganisms Bacteriocide – a compound that will kill pathogens and nonpathogens but may not kill spores. Bacteriostatic – the action of a compound that will inhibit microorganisms but not necessarily kill them.

3. http://nayfahsai.blogspot.com/feeds/posts/default Mechanism of action of antimicrobials Permeablize cell membrane Destabilize membrane (EDTA) Acidify cytoplasm Digest cell wall Chelate essential nutrients or minerals

4. Antimicrobial barriers Types: – Biological structure – Natural inhibitors – Developed inhibitors – Added inhibitors (discussed later)

5. Biological structure Dry Barrier Importance of care during mechanical harvesting, shipping, etc www.elephantjournal.com Wikipedia

6. Natural inhibitors (phytoalexins) Allium family (onions, leeks, garlic) Inhibitory to broad range of bacteria/fungi Chemical reaction slide from Wikipedia http://www.sciencedirect.com/science/article/pii/S0005273699001741

7. Natural inhibitors: Isothiocyanates 4-methylphenol White mustard 3-methylindole (skatole) Cabbage R = Cruciferae (mustard) family: Brussel sprouts, cauliflower, kale, broccoli Inhibit fungi and bacteria

8. Natural inhibitors in eggs Lysozyme – mainly Gram positive bacteria Ethylenediaminetetraacetic acid (EDTA) Ovotransferrin (10% total protein in white); iron chelator Lactoferrin, transferrin Avidin combines with biotin http://www.hennypennyhatching.com.au/hph/Page-TakingChicksHome.asp

9. Natural inhibitors: essential oils Oleuropein (green olives): must be removed by alkali extraction. Inhibits lactic acid bacteria

10. Cinnamomum cassia oil Food Control 2014. 46:374-381

11. Developed inhibitors Acids in fermented products – Propionate (Swiss cheese) – Lactic acid (dairy products) Alcohols (beers, wines) Bacteriocins – L. lactis Nisin – Propionibacterium shermanii Pediocin (MicroGard) – GRAS http://commons.wikimedia.org/wiki/File:NCI_swiss_cheese.jpg

12. Spores vs. vegetative cells Spores are more resistant to preservatives than vegetative cells Growth phase impacts susceptibility to antimicrobials…how…

13. Water activity “available water”; a w = P/P o ; R.H. = a w x 100 Reduce by: – Dehydration, evaporation, freeze drying – Water-binding polymers (pectin, gelatin, gums, agar) – Solutes such as salts and sugars Water: 92% Water activity: 0.97-0.99 pectin Water activity: 0.75-0.8 Water: 92%

14. a w and concentration of salt solutions From BC Center for Disease Control, Jan 2013

15. Sucrose and a w From BC Center for Disease Control, Jan 2013

16. Measuring water activity https://www.youtube.com/watch?v=g4xa3e3T5 s8

17. S. aureus: only makes toxins a w >0.93 Above Figure from Adams and Moss Food Microbiology, 3 rd Ed

18. Microorganisms Minimum a w Most spoilage bacteria0.90 - 0.91 Most spoilage yeasts0.87 - 0.94 Most spoilage molds0.70 - 0.80 Halophilic bacteria0.75 Xerophilic molds0.60 - 0.70 Osmophilic yeasts0.60 - 0.78 Pseudomonas0.96 - 0.98 E. coli0.94 - 0.97 C. botulinum, types A and B0.93 - 0.96 S. aureus0.83 - 0.92 Aspergillus0.70 Penicillium0.81 Minimum Water Activity for Growth

19. Other bits about water activity Spore germination: – Bacillus cereus: 0.93-0.97 – Clostridium perfringens: 0.97-0.98 Gram positives generally lower a w than gram negatives – E. coli, Pseudomonas sp. require 0.94-0.96, Staphylococcus and Micrococcus require ~0.86 and 0.90, respectively Water activityDefinitionRefrigeration? >0.85Moist foodYes 0.60-0.85Intermediate moisture food (IMF) Not to control pathogens; needed for spoilage yeasts and molds Below 0.60Low moisture foodNo

20. Time/Temperature control for food safety (TCS) Once called “potentially hazardous foods” Page 22 of FDA Food Code

21. TCS foods do not include: Air cooled egg with shell intact; Unopened sealed container that was treated to maintain commercial sterility; A PA food where lab tests show intrinsic/extrinsic factors are sufficient to prevent pathogen growth or toxin production.

22. http://www.fda.gov/Food/FoodScienceResearch/SafePracticesforFoodProcesses/ucm094159.htm

23. Hurdle effect Nutrients, pH, Eh, antimicrobials, water activity,