9.               Byssochlamys/ Heat Resistant Molds

Reference B-17

9.1.          Background/Description

Byssochlamys is a heat-resistant mold which is present in many foods, particularly fruits.  Its ascospores can survive temperatures (e.g., 100^oC) incorporated in the processing of acidic foods and, if allowed to grow, this mold can cause serious spoilage problems.  For example, Byssochlamys can destroy the texture of canned fruits resulting from its pectinolytic enzymes, and can produce off-flavors and objectionable mycelial masses when growing in juices or drinks.  Furthermore, byssochlamic acid (a metabolite of the mold) has shown to possess low-level animal toxicity.
          

Two type species are normally encountered in foods.  They arespan style="mso-spacerun: yes;">  Byssochlamys         
fulva and B.                 nivea, which produce dull yellow and white colonies, respectively,
when growing on acidified agar media. 

The method described here employs a pour plate procedure for the enumeration
of Byssochlamys. 

9.1.1.       Materials and Equipment

Incubator at 30^oC 250 mL Erlenmeyer flasksWater bath at 80^oCPetri DishesBlender or StomacherParafilm

9.1.2.     Culture Media and reagents

Potato Dextrose Agar (PDA)Malt Extract Agar (MEA)

9.2.          Standard Procedure

1.       Add 100 grams of sample and 100 mL sterile water to a sterile blender or  
large stomacher bag and thoroughly blend the sample.

2.       Transfer two 50 mL samples to sterile 250 mL Erlenmeyer flasks and cover
with sterile sponge stoppers or sterile foil.

3.       Place the flasks in an 80^oC (176ºF) water bath for 30 minutes.

4.       After heating, evenly distribute the 50 mL of each sample between 4 petri
dishes.

5.       To each dish, add 10 mL of 1.5 strength PDA or MEA agar, swirl, then allow
to solidify.  Wrap the petri dishes in parafilm to prevent drying, then incubate
at 30^oC (86ºF)for 7 - 10 days.

9.2.1.     Interpretation

Count the colonies on all 4 plates and determine original count per 100 grams of   
sample.  If no colonies are present, allow the plates to incubate for up to 30 days.

9.3.        Capri Sun Procedure

1.       Prepare a 1:10 sample dilution using 0.1% peptone diluent. 

2.       Place the sample dilution in an 80°C water bath for 30 minutes.

3.       Plate 10 mL onto a 150 x 15 mm petri dish using acidified PDA.

4.       Incubate for 5 days at 25°C.

Notespan style="mso-spacerun: yes;">  Juice concentrates can be composited by mixing 10 g of each sample (up to 10 samples) in a sterile cup.

9.3.1.     Interpretation

Count the colonies on the plate and report cfu per g.