Low Risk Status of Mushrooms: Epidemiological Approach to Risk Assessment

1. Mushrooms: An Inherently Low Risk Food

2. Two Approaches to Risk Assessment • Epidemiological Approach to Risk Assessment • FDA Fresh Produce Risk Assessment 2009 Used Epidemiological Approach • Semi-Quantitative result for pathogen/substrate pairings • Agricultural Risk Factor Assessment • Soil and irrigation water quality • Surrounding land use • Domestic and wild animal incursions Both approaches validate the low risk status of mushrooms.

3. FDA Fresh Produce Risk Ranking (2009) • Mushrooms were compared to: • Leafy Greens (spinach, lettuce, mesclun) • Berries (blackberries, strawberries, raspberries) • Melons (watermelon, honeydew, cantaloupe) • Green onions • Peppers (capsicums) • Herbs (cilantro, basil, parsley) • Tomatoes (Roma, globe) • Cruciferous vegetables (broccoli, cabbage) • Non-citrus fruits (pineapple, mango)

4. Mushrooms were ranked among the lowest risk of all produce items considered by the FDA study. Lowest pathogen prevalence Weakest epidemiological link Fewest illness cases Fewest outbreaks (no documented outbreaks ever) FDA Fresh Produce Risk Ranking U.S. Food & Drug Administration, CFSAN, College Park, MD. 2009. Fresh Produce Risk Ranking Tool Summary: Identification of Priority Pathogen-Commodity Combinations for Quantitative Microbial Risk Assessment.

5. Field Crops Water source & quality are highly variable. Frequent contact with deer, birds, pigs, rodents (and droppings) possible. Flooding contaminates plants and soil. Concentrated animal feed-lots (or runoff) may be in close proximity to field. Highly variable use of manure in farming, composting often not well-controlled. Risk Factor Irrigation Water Quality Wildlife Incursion Flooding of Fields Domestic Animal Contact Use of Soil Amendments Agricultural Risk Factors Mushrooms Irrigation water meets EPA drinking water standard. Mushroom houses protect the product from contact with wildlife. Mushroom houses well-protected from floods. Mushroom house prevents contact with domestic animals. Mushroom compost is steam-pasteurized before it is inoculated with mushroom spawn (process highly lethal to vegetative pathogens).

6. Irrigation Water Quality: Field Crops • Surface water is commonly used – overhead irrigation • Tremendous variability in microbiological and chemical quality • Open ponds and ditches are exposed • Overhead irrigation most common method • Mushroom irrigation water meets EPA drinking water standards for coliforms and E. coli.

7. Wild, Feral & Domestic Animal Incursion • List of animals that can impact field crops is almost endless: e.g. deer, pigs, birds, raccoons, dogs, lizards, insects • Mushroom houses are block wall construction, and are not susceptible to animal incursion. • Pest management programs are required for MGAP certification. • No threat of runoff or seepage from adjacent feedlots.

8. Flooding of Fields • Floodwater can carry raw sewage • Toxic chemicals • Debris of all types Domestic Animals • Used intentionally to graze in orchards • Frequent unintentional presence of dogs, cows, goats, pigs

9. Mushroom Houses In figure above, note concrete floors with drainage, impervious walls and floors. In figure at right, door to growing room is surrounded by filter material. Note wires leading to data-logger – thermocouples are used to monitor air and substrate temperature during and after Phase II pasteurization.

10. Mushroom Bed Composition Casing soil (peat moss) has distinct anti-microbial properties. Mushrooms form within this layer. Casing Soil Substrate Substrate is fermented to an avg. temp of 170oF during Phase1 of compost preparation, and is steam treated and held many hours at ≥ 150oF during Phase 2 In Phase 3, the steam-pasteurized substrate is inoculated with aseptically produced mushroom spores that are carried on sterile grain. The mycelium develops within the substrate and then sends reproductive bodies (mushrooms) up through the casing soil.

11. Mushroom Growth Cycle Phase I – Substrate Preparation Phase I – Substrate Preparation Compost filled into mushroom beds or transferred to tunnels for Phase II treatment. Exothermic fermentation during Phase I raises compost temperature to 170oF. Phase II – Substrate Pasteurization Phase II – Substrate Pasteurization Compost Temp gradually increased to 140oF +with live steam treatment. Compost Temp held at 140 – 142oF for at least 2 hrs. for pasteurizing effect, then cooled. Compost Temp. Equalization: O2, Compost & AirTemp Monitored Phase III – Spawn Run Phase III – Spawn Run Mushroom spores germinate and mycelium runs through substrate. Air temp, substrate temp, % R.H., air circulation are controlled in growing rooms. Mushroom spawn on sterile grain introduced onto the pasteurized substrate. Casing and Cropping Growing Room emptied, cleaned, sanitized and beds treated with steam to prepare for new crop. Top Dressing of casing soil (peat moss) applied to beds to support growth of primordial fruiting bodies Mushroom Buttons appear 16 days after casing. Hand harvesting begins and continues over 21 days.

12. Raw Materials • Raw materials: Hay, Straw, Soybean and Cottonseed Meal, Gypsum, Water (Some Farms Still Use Stable Bedding)

13. Phase 1: 17 Days • Raw materials are blended and watered. • Formed into ricks to create optimal aerobic conditions • Exothermic fermentation process is mediated by fermentative organisms. • Core temperature of ricks can reach 170°-175°F during this process

14. Phase 2: 5 Days • Fill compost into tunnels trays, or beds • Heated to 120° - 165°F for about 4-9 hours (on average) to pasteurize • Different techniques used to convert ammonia to useable nitrogen • Slowly reduce temperatures over next 4 days to promote growth of thermophiles

15. Phase II Pasteurization of Substrate • At a treatment temperature of 65oC (150oF), it takes about 3.2 minutes of exposure to produce a 1 log reduction against Salmonella spp. and Listeria spp. • In a typical pasteurization cycle – 12 hours at a compost temp. of 150oF, more than 200 log reductions would be expected. • Even with variations grower to grower, the safety factor is extremely high. • Growers are obsessive over temperature monitoring since it is directly related to productivity and yield.

16. Casing - 18 Days • Trays are covered with a 13/4” inch layer of peat moss • This provides support structure for mushrooms to grow • Peat helps maintain moisture in the compost • Humic acid and other compounds in peat have a biostatic effect (documented in recent Penn State study)

17. Harvesting Mushrooms - 25 Days • Mushroom grow in flushes, or breaks • We harvest 1st, 2nd and 3rd breaks • Near harvest, mushrooms double in size every 24 hours • Cypress wood is traditional – used for its resistance to decay • Many growing rooms are now using metal trays instead of wooden beds.