Mushrooms: An Mushrooms: An Inherently Low Inherently Low

Risk FoodRisk Food

Two Approaches to Risk Assessment

1. Epidemiological Approach to Risk Assessment– FDA Fresh Produce Risk Assessment 2009 Used

Epidemiological Approach– Semi-Quantitative result for pathogen/substrate pairings

2. 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.

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)

FDA Fresh Produce Risk Ranking

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)

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.

Agricultural Risk Factors

Field CropsWater 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 Factor1. Irrigation Water Quality

2. Wildlife Incursion

3. Flooding of Fields

4. Domestic Animal Contact

5. Use of Soil Amendments

MushroomsIrrigation 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).

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.

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.

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

Mushroom Houses

In figure above, note concrete floors with drainage, impervious walls and floors.

In figure at right, door to growing room is surroundedby filter material. Note wires leading to data-logger – thermocouples are used to monitor air and substrate temperature during and after Phase II pasteurization.

Mushroom Bed Composition

Substrate

Casing Soil

Casing soil (peat moss) has distinct anti-microbial properties. Mushrooms form within this layer.

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.

Phase I – Substrate Preparation

Phase II – Substrate Pasteurization

 

Phase III – Spawn Run

Mushroom Growth Cycle

Growing Room emptied, cleaned, sanitized and beds

treated with steam to prepare for new crop.

Compost filled into mushroom beds or transferred to tunnels

for Phase II treatment. 

Compost Temp. Equalization: O2, Compost & Air

Temp Monitored

 

 

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.

 

 

Mushroom spawn on sterile grain introduced onto the pasteurized

substrate.

Air temp, substrate temp, %

R.H., air circulation are controlled

in growing rooms.

Mushroom spores germinate and mycelium runs through

substrate.

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.

 

Exothermic fermentation during Phase I raises compost temperature to 170oF.

Phase I – Substrate Preparation

Phase II – Substrate Pasteurization

 

Phase III – Spawn Run

Casing and Cropping

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

Raw Materials

• Raw materials are blended and watered.

• Formed into ricks to create optimal aerobic conditions

• Exothermic fermentation process is mediated by fermentative organisms.

Phase 1: 17 Days

• Core temperature of ricks can reach 170°-175°F during this process

• 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

Phase 2: 5 Days

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.

• 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)

Casing - 18 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.

Harvesting Mushrooms - 25 Days