Let s Talk Yeasts and Molds Mark E. Johnson Wisconsin Center for Dairy Research Center for Dairy Research Solution Based Research Backed by Experience, Passion and Tradition What are Yeasts and Molds? Bacteria (binary fission) Yeasts (multiply by budding) Molds (produce spores) 1
Yeasts on cheese (not crystals) 2
3
Moldy cheese: Notice free serum 4
Washed Rind Cheeses: Yeasts 5
What do you do about yeasts and molds? Reactive approach: We see molds/taste yeasty products Now its time for action Find the source Major cleaning/ sanitation effort Proactive approach: We know that yeasts and molds are in our facility We do all the right things to make sure that their numbers are controlled/eliminated Monitor their numbers in the places that they might call home Requirements for Growth: yeasts and molds Water (but very much less than bacteria) Temperature (can grow under refrigeration) Oxygen for molds (~1-2 %) Oxygen +/ for yeasts Acid, salt and low ph tolerant Nutrition : not much for molds Yeasts require organic matter courtesy of Copyright Dennis Kunkel Microscopy 6
Water activity of various cheeses (1) Cheese aw Brie 0.980 Camembert 0.982 Cheddar 0.950 Cottage cheese 0.988 Gouda 0.950 Gorgonzola 0.970 Parmesan 0.917 (1) Ruegg, M. and Blanc, B, 1981. In Water Activity: Influences on Food Quality, ed. Rockland and Stewart, Academic Press, 799. a w Growth Limits (water = 1.0) E. coli 0.96 C. botulinum 0.93 L. monocytogenes 0.91 S. aureus 0.86 Yeasts and molds 0.65-0.7 7
Sources of Yeasts and Molds Mold: major source is air-borne spores From packaging material (damp boxes) Moldy cheese Anticaking agent (potato starch) Moldy vegetables Condensate water on air-conditioning units, pipes, walls, floors, underneath equipment Yeasts: major source is organic material Vegetables, spices Brine tank (people, contaminated cheese) Residual product on equipment (biofilms) 8
9
Yeast & Mold Monitoring Program Air exposure plates weekly Surface swabs Brines sampled weekly 10
Air and Brine Specification: Call for action Air: Yeast and mold > 10 cfu on exposed plate Plate is exposed for 15 minutes Brine: Yeast and mold >50 cfu/ml Typical Cheese Specification Pathogens negative Coliform <10/g- <100/g (some 10,000/g) E. coli negative Yeast and Mold <100/g (some plants <10/g) 11
Channel Brine System Impact of Brine Nanofiltration Conventional Filtration System Nanofiltration System Salinity 90-100% 90-100% Molds 50-500/ml <10/ml Yeast 100-1000/ml <10/ml Std. Plate Count 25,000- <100/ml 100,000/ml Psychrotrophs 1000-2000/ml <100/ml Susp. Solids 5,000-20,000 mg/l <500mg/l 12
Microorganisms that do not survive Pasteurization Coliforms Pseudomonas Pathogens Vegetative cells of spore formers Lactococcus Yeasts Molds Elimination of Spores Air filtration MERV 13 filters: Holds back particles 1-0.3 um -Minimum Efficiency Reporting Value - established by the American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) Removes ~ 75 % of particles 1-0.3 um -This is not a true HEPA filter which is too impractical for dairy plants - High-Efficiency Particulate Arrestance (99.97 % removal of particles 0.3 um) 13
Traditional cleaning agents used by the food industry (chlorine, hydrogen peroxide, iodine) are ineffective in destroying mold spores. Cleaning with ozone is probably the best method of eliminating food spores in food processing plants. Ozone is more than 3000 times more powerful a disinfectant than chlorine and it is particularly helpful in destroying mold spores by virtue of its high redox potential. Ozone is used in Japan, Europe and Australia, but has been used with limitation in the US. Ozone can be used to clean air or to be incorporated in water (known as ozone charged water and used to clean pipes, tanks, floors, equipment, surfaces, walls, etc. What action do we take? Positive air flow Air treatment with ozone Elimination of moist-humid areas Removal of visible mold and all contaminated materials In product use of mold inhibitors : sorbates, propionates, natamycin Modified atmosphere packaging 14
Checking for gas composition For shreds, soft cheeses: 30-40 % CO2/60-70 % N When mold occurs Bad sealing bars Poor package seals Poor gas blends (more than 0.5-1 % O2) Leakers Checking for Leakers 15
Final Recommendations Food Plants who deep clean equipment as opposed to clean have less micro issues In general, facilities where the ceilings in most areas are of a cleanable material and appear to be maintained and in good repair have less issues Food Plants where the walls and floors have cracks, seams and holes, and when the equipment, contains rust and nothing gets done for a prolonged period have issues. Food Plants where the cooling units are broken down regularly and cleaned have less problems. Facilities where the overhead structures (such as lights) are made accessible for cleaning and sanitation have less issues Bob Hendershot 16
Summary Take a Proactive Approach Sanitation and GMPs are key Must be ever vigilant 17
Enumeration of Yeasts and Molds Dichloran-Rose Bengal-Chloramphenicol (DRBC) Agar Suitable for all dairy products especially to inhibit spreading of mold colonies such as Rhizopus and Mucor May give lower count on yeasts than yeast-extract-glucosechloramphenicol agar (IDF recommended medium for yeasts) 3M Petrifilm Yeast and Mold Count (dry rehydratable film) Yeast appear as blue-green, off-white, small and more defined, sharp edges colonies Molds are more diffuse and take on color of natural pigmentation DO not invert plates-count plates with 15-150 colonies (25 C aerobic conditions for 5 days) 18
19