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Yoon-Hee Lee Dep. of Food Science & Technology

Y easts and M olds - Using selective media; examining fungi morphology. Yoon-Hee Lee Dep. of Food Science & Technology. FUNGI VS. BACTERIA. Fungi ۰ Larger ۰ Eukaryotic ۰ Aerobic ۰ Slow growth ۰ Grow in both acidic and basic condition ۰ Filamentous - Mycelia. Bacteria ۰ Smaller

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Yoon-Hee Lee Dep. of Food Science & Technology

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  1. YeastsandMolds - Using selective media; examining fungi morphology Yoon-Hee Lee Dep. of Food Science & Technology TheOhioStateUniversity

  2. FUNGI VS. BACTERIA Fungi ۰ Larger ۰ Eukaryotic ۰ Aerobic ۰ Slow growth ۰ Grow in both acidic and basic condition ۰ Filamentous - Mycelia Bacteria ۰ Smaller ۰ Prokaryotic ۰ Aerobic and Anaerobic ۰ Fast growth ۰ Prefer neutral media TheOhioStateUniversity

  3. CLASSIFICATION OF FUNGI ☞ Fungi kingdom (yeasts and molds) • Subkingdom: based on septation of mycelia • Phylum: based on ability to produce and type of sexual spores TheOhioStateUniversity

  4. UBIQUITOUS IN FOOD - Spoilage • Toxicity • Fermented foods • Food additives & processing aids TheOhioStateUniversity

  5. FUNGI OF INTEREST ☞ Yeasts: • Saccharomyces spp. • Zygosaccaromyces spp. • Candida spp. ☞ Molds: • Rhizopus spp. • Asperigillus spp. • Penicillum spp. TheOhioStateUniversity

  6. BUDDING YEAST (Saccharomyces spp.) - The Bakers’ and Brewer’s yeast • Most yeasts, including Saccharomyces reproduce by budding • does not ferment lactose • White or cream colonies • Typical yeasty odor TheOhioStateUniversity

  7. Rhizopus spp. - Nonseptate, root-like structure • Umbrella-shaped columellae • Large sporangiospore with striated wall • Dark sporangia containing dark to pale spore TheOhioStateUniversity

  8. Penicillium spp. - P. digitarum: yellow green conidia • P. italicum and P. expansum: blue-green conidia • P. camemberti: grey conidia TheOhioStateUniversity

  9. Aspergillus spp. - Black, brownish black, purple brown conidiophore • Yellow to green conidia • Dark sclerotia • A. niger: black rot on fruits and vegetables TheOhioStateUniversity

  10. OBJECTIVES ☞ Enumeration of yeasts and molds (difference between processed and fresh grapefruit juices) ☞ Importance of selective and differential media ☞ Compare and contrast fungi morphology macroscopically and microscopically TheOhioStateUniversity

  11. DEFINITION • ☞ Selective media • Allow microorganisms of interest to grow and have a selective advantage over otherwise competing organisms • Contain selective agents • ☞ Deferential media • Distinguish between two microorganisms based on a single or multiple biochemical properties • Contain differential agents TheOhioStateUniversity

  12. SELECTIVE MEDIA • ☞Acidified Potato Dextrose Agar (PDA) • Tartaric acid lowers pH to inhibit bacterial growth • Note: Some acid-tolerant bacteria can still grow leading to an over-estimate of fungi count ☞Antibiotic TSA (Not PCA) - Chloramphenicol and chlortetracycline inhibit bacteria TheOhioStateUniversity

  13. MEDIA CONT’D • ☞Petrifilms • Selective and differential for yeasts and molds • Contain chlortetracycline and chloramphenicol • Indicator: bromo-chloro-indolylphosphate gives yeast a blue-green color • Yeasts: small and defined • Molds: larger and diffuse TheOhioStateUniversity

  14. LAB PERIOD 1 ☞ Cut grapefruit in half and extract juice • Refrigerate (4 °C) it until used ☞ Reconstitute frozen concentrated grapefruit juice • Mix water (about three can) and one can of frozen concentrated grapefruit juice • - Refrigerate (4 °C) it until used. TheOhioStateUniversity

  15. LAB PERIOD 1 ☞ Prepare media: • Add tartaric acid to the PDA • Add antibiotic solution to the TSA • Allow plates to dry 24-48 hours TheOhioStateUniversity

  16. LAB PERIOD 2 ☞ Take 10 ml sample and Prepare 10-1 and 10-2 dilution of the sample using the 9 ml peptone blanks • ☞Spread plate dilutions in duplicate onto Acidified PDA (6) and antibiotic TSA (6) • ☞Transfer 1 ml of the dilutions 10-1 and 10-2 onto Petrifilms • Do not use undiluted sample because this produces artifacts • ☞Incubate at 25 °C for 5 days TheOhioStateUniversity

  17. LAB PERIOD 3 ☞ Enumerate plates • ☞Pick 3 yeast colonies and examine different colony morphologies (macroscopically) and microscopically • ☞Place a drop of lactophenol cotton blue dye on a slide and place tape with mold onto surface – examine micro/macroscopically • Lactic acid: preserve fungal structures • Phenol: killing agent • ☞View demo microscope slides • ☞ Draw and record morphologies TheOhioStateUniversity

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