MCB 180 LEC - Yeasts and Molds

___________ are mostly unicellular.

Yeasts

60% sucrose

Yeasts grow in ___________.

Yeasts grow in ___________.

18% alcohol

Cultural Characteristic of Yeast

pigment formation, colony appearance, film or pellicle formation

Shape of Yeasts

spheroidal to oval, elongated/cylindrical, apiculate

Asexual Reproduction in Yeasts

budding or fission

Sexual Reproduction in Yeasts

ascospores

oxidative metabolism

When oxygen is present, yeasts perform _________________.

End Products of Yeasts in Oxidative Metabolism

cells, carbon dioxide (CO₂), and water (H₂O)

fermentation

In the absence of oxygen, yeasts perform _____________________.

Product of Fermentation

alcohol

Saccharomyces

yeast for food and beverage production

Z. rouxii

Xerophilic Zygosaccharomyces

Z. bailii

Acidophilic Zygosaccharomyces

Zygosaccharomyces bailii

yeast that spoils acidic foods such as salad dressing

Schizosaccharomyces pombe

osmophilic schizosaccharomyces, fission yeast

Candida

yeast for beef and poultry spoilage

Candida sp.

yeast responsible for cacao seeds fermentation

Kluyveromyces

yeast most prevalent in dairy products

lactose

Kluyveromyces uses __________ as CHO source.

lactase

Kluyveromyces produces __________.

Debaryomyces

yeast also prevalent in dairy products (aside from Kluyveromyces)

D. hansenii

Halophilic Debaryomyces

Debaryomyces sp.

responsible for yogurt and juice concentrate spoilage

Pichia

yeast responsible for pickle spoilage

Pichia sp.

hat-shaped ascospores

Hanseniaspora

teleomorph (sexual stage) of Kloeckera, apiculate cells

Rhodotorula

pink, red or orange yeasts

psychrotrophs

Rhodotorula are _________trophs.

Rhodotorula sp.

yeast responsible for spoilage of refrigerated foods (meat, butter, seafoods)

Molds

filamentous fungi

cottony or fuzzy appearance

appearance of molds

Are molds aerobic?

Yes

Enumeration and Isolation of Molds

surface plating, direct microscopic count

Potato Dextrose Agar

example of surface plating for molds

Howard Mold Count Chamber

example of direct microscopic count for molds

Morphology of Mold Hypha and Mycelium based on presence of crosswalls

coenocytic or septated (uni- or multinucleate)

Morphology of Mold Hypha and Mycelium based on presence of function

vegetative or fertile/aerial

Stolons

horizontal hyphae (filamentous structures) present in molds

Rhizoids

root-like structures that anchor the mold to its substrate

Foot cells

specialized cells at the base of reproductive structures (molds)

Conidiophore

specialized hyphal structure that produces asexual spores called conidia

Sporangiophore

specialized hyphal structure that produces spores within a sac-like structure called a sporangium

Arthrospores

formed by the fragmentation of hyphae into individual cells or spores

Chlamydospores

thick-walled, durable spores that form within the hyphae

Ascospores

formed inside an ascus, a sac-like structure that holds the spores

Zygospores

formed by the fusion of specialized structures called zygosporangia, produced by two mating types of hyphae

Asexual reproduction in Molds

sporangiospores, conidia, arthrospores, and chlamydospores

Sexual reproduction in Molds

ascospores and zygospores

Teleomorph

sexual state (both sexual and asexual reproduction)

Anamorph

asexual or conidial state (asexual reproduction only)

Rhizopus

bread mold

Mucor mucedo

whiskers in refrigerated meat (mold)

Penicillium

mold in rotting fruits

Penicillium roqueforti

mold for blue cheese

Talaromyces

mold for juice concentrate spoilage and has heat resistant spores

Trichoderma

mold for fruit spoilage

Alternaria

brown to black rots in fruits, wheat and meats (mold)

Fusarium

spoilage mold in fruits and grains

Geotrichum

dairy mold, machine mold

Byssochlamys

heat-resistant ascospores responsible for spoilage of some high-acid canned foods

Thamnidium

whiskers on refrigerated meats

T. elegans

produce proteases used as meat tenderizer

Wallemia

mold associated with dried and salted fish

W. sebi

species of Wallemia that can grow at very low Aw

Xeromyces

mold responsible for spoilage of prunes, chocolate and syrups

X. bisporus

Xerophilic Xeromyces

Aspergillus

mold responsible for yellow to green to black rot of fruits, meats

A. niger

Aspergillus species that produces many enzymes (B-galactosidase, invertase, and lipase; pectinase)

Eurotium

xerophilic Aspergillus

Neosartorya

heat-resistant ascospores in Aspergillus

Mycotoxins

toxic secondary metabolites produced by fungi

Hepatotoxicity

aflatoxins can damage the liver

Teratogenic

aflatoxins can cause developmental defects in embryos, leading to birth defects

Immunosuppressive

aflatoxins weaken the immune system

B1

most toxic and carcinogenic form of aflatoxins

G1 and G2

aflatoxins with fluorescent properties under UV light

Aflatoxin producers

A. flavus, A. parasiticus, A. nomius

trophophase

active growth phase of the mold (vegetative growth)

Idiophase

stationary phase when secondary metabolites like mycotoxins are produced

methanol, acetonitrile, chloroform

solvents used for aflatoxin extraction

Thin-Layer Chromatography (TLC) and High-Performance Liquid Chromatography (HPLC)

techniques used for resolution of aflatoxins

Name four mycotoxigenic molds.

Aspergillus, Penicillium, Fusarium, Claviceps.

Patulin, citrinin, ochratoxin A

mycotoxins produced by Penicillium

Aflatoxins, ochratoxin A, sterigmatocystin, cyclopiazonic acid

mycotoxins produced by Aspergillus

Trichothecenes (e.g., DON, T-2 toxin), zearalenone, fumonisins

mycotoxins produced by Fusarium

Aflatoxins, ochratoxin, zearalenone, deoxynivalenol (DON), fumonisins

major mycotoxins of greatest concern

Ergot alkaloids - ergotism

toxic compound produced by Claviceps, and condition it causes