Food Microbiology Exam 3

field fungi

capable of attacking living plants; invade grain in the field when moisture content is above 20%

genera: Alternaria, Cladosporium, Fusarium

storage fungi

do not cause plant disease; occur during harvest or storage when moisture levels are at 16-20%

genera: Aspergillus, Penicillium

advanced decay fungi

occur after extensive spoilage by field or storage fungi has occurred, and the moisture content has risen as the result of the respiration of these organisms.

include yeasts, some molds

fusarium toxins

zearalenone, deoxynivalenol, T-2 toxin, fumosins

aspergillus toxins

aflatoxins (sp. flavus), ochratoxins (sp. ochraceus)

penicillium toxins

penitrem A (sp. crustosum), patulin (sp. expansum), ochratoxins (sp. verrucosum), citrinin (sp. citrinum)

baked cereal products

practically free of viable microbes, become recontaminated by airborne spores during cooling and slicing before packaging.

lowering moisture content (13 or lower)

how is grain preserved?

xerophilic molds

molds that can grow at low moisture contents i.e. 14-16%

bread preservatives

sodium or calcium propionates (mold inhibitors)

low temperatures

low water activity

preservative action of spices

potassium sorbate spray

sources of produce microbes

soil (large contributor), dust, water, insects, contact with equipment surfaces

low pH and high sugar content, organic acids

features of many fruits that inhibit bacteria and allow molding to predominate

washing, blanching, chlorine

processing that removes most to all microbes from produce

freezing, dehydration

storage conditions that reduce viable organism levels of produce

market diseases

most common type of spoilage of fresh fruits and veg

decay caused by molds and certain bacteria, can readily invade healthy plant tissue

spp: erwinia (bac), alternaria, botrytis, phytophthora (mold)

penicillium expansum

most common source of mold rot in apples, results from mechanical or other damage to apple skin, allowing access to underlying tissue.

appears as a black or dark soft sport

produces patulin, a carcinogen

howard mold count

direct microscopic technique that uses a special slide and a microscope to detect mold fragments in processed fruit and vegetable products

does not ID type of mold, just presence of hyphal fragments

machinery mold

Geotrichum candidum

grows on the moist surfaces of fruit and vegetable processing equipment and plants, and in bottling works

spore-formers

most common bacteria and molds that contaminate herbs and spices

pepper high level contamination

due to growth and processing under poor sanitation in hot, humid areas

commonly Bacillus spores

spice fumigation

effectively lowers microbe counts with ethylene oxide and propylene oxide, leave residues that are controlled by the FDA

irradiation also used, heat not used

spice examination

aerobic plate count, yeast and mold counts, coliform counts

spice essential oil

common source of antimicrobial activity

high in cinnamon and cloves, onion and garlic, mustard seed

not significant in quantities used for flavoring (except cinnamon and cloves)

mycotoxins

toxins produced by molds in food and feeds

excess conidia

can be a respiratory hazard, serving as irritants or allergens, or germinating in the body and causing disease (farmer's lung, aspergillosis). can be a fire hazard in an enclosed area

saccharomyces cerevisiae

domesticated yeast used to produce carbon dioxide and ethanol

penicillium roqueforti

forms the blue in blue cheese, imparts flavor and texture

not the only species in the genus present

aspergillus oryzae

ferments soybeans to make soy sauce

rhizopus oligosporus

ferments soybeans to make tempeh

aspergillus niger

produces most citric acid used in industry

fusarium venenatum

produces the mycoprotein used in Quorn meat substitute

hemocytometer

tool used for direct microscopic counts of fungi

hyphae

filaments formed when a filamentous fungus grows

mycelium

formed by several hyphae together

mold

a filamentous fungus growing in a somewhat diffuse state where they are not wanted. Not a taxonomic term

basidiomycetes

spore bearing structure found in shelf fungi, puffballs, and most mushrooms

ascomycetes

spore-bearing structures found in morels and cup fungi

conidia

asexually-produced spores

sporangia, sporangiospores

a specialized structure (1) that a common group of molds produce their spores (2) in

criteria for mold media

lower water activity

inhibit bacterial growth without affecting yeasts and molds

restrict growth of rapidly spreading, fast growing molds without preventing growth

chloramphenicol

preferred antibiotic for inhibiting bacterial growth

broad spectrum, heat stable through autoclaing

rose bengal, dicholran

(2) used to slow mold colony growth

Dichloran Rose Bengal Chloramphenicol (DRBC)

used for high water activity fresh foods

light sensitive (some compounds become toxic to molds)

Dichloran 18% Glycerol (DG18)

general purpose medium used to grow molds from low moisture, low water activity foods such as grains, nuts, flour, cornmeal, dried fruits, and dry spices

glycerol

reduces the water activity of media, favors xerophilic molds

potato dextrose agar (PDA)

in the past, was the best general purpose medium. can add chloramphenicol to make PDAC

aspergillus flavus and parasiticus (AFPA)

differential medium used to differentiate aflatoxin producers from other molds, including other aspergillus

produce olive green spores on top and orange-yellow bottom

Czapek's yeast agar (CYA), malt extract agar (MEA)

(2) both general, multipurpose fungal growth media, used to ID a lot of molds

25% glycerol nitrate (G25N)

low water activity medium similar to DG18, used to ID a lot of molds