Syllabus •General characteristics of yeasts •Classification and identification of yeasts •Yeasts of industrial importance

1. YEAST & MOLD
BY
MS. ALKA KUMARI
ASSISTANT PROFESSOR
DEPT. OF FOOD
TECHNOLOGY
VIGNAN’S UNIVERSITY

2. YEAST
Syllabus:
•General characteristics of yeasts
•Classification and identification of yeasts
•Yeasts of industrial importance

3. YEAST
Yeasts are-
• Eukaryotic
• Single-celled microorganisms
• Fungus kingdom
Morphology:
Size: 3–4 µm in diameter (up to 40 µm)
Shape:
• spherical to ovoid
• lemon shaped, pear
• shaped, cylindrical, triangular

5. Peroxysome
Function:
• breakdown of very
long chain fatty acids
through oxidation

6. Cytosol
• Liquid phase of the cytoplasm in
an intact cell
• This excludes any part of the
cytoplasm that is contained within
organelles
• It constitutes most of
the intracellular fluid (ICF)

7. Vacuole
• Extremely complex organelle
• involved in a wide variety of
functions
• Carries out degradative processes
• primary storage site for certain
small molecules and biosynthetic
precursors such as basic amino acids
and polyphosphate
• Maintains intracellular pH

8. Vacuole
• Maintains osmoregulation
Osmoregulation:
• It is the active regulation of the osmotic pressure of an organism's
body fluids to maintain the homeostasis of the organism's water
content
• it maintains the fluid balance and the concentration of electrolytes
(salts in solution) to keep the fluids from becoming too diluted or
too concentrated

9. Asexual
Reproduction through
• Budding (Most common
mode)
• Binary fission
Sexual
• formation of the
appropriate spore
structure
• Ascospre
Yeasts- Reproduction

10. Asexual / Vegetative Reproduction in Yeast - Budding

11. Asexual / Vegetative Reproduction in Yeast - Budding
• This method of reproduction takes place in
favourable conditions
when the yeast cells grow in sugar solution
• Form of asexual reproduction in which
a new organism develops from an outgrowth or
bud due to cell division at one particular site

12. Asexual Reproduction in Yeast by Budding
• The new organism remains attached as it grows
• separates from the parent organism only when it is mature
• Bud leaves behind scar tissue
• The newly created organism is a clone
• genetically identical to the parent organism

13. Asexual Reproduction by Chlamydospores
• a thick-walled hyphal cell which functions like a spore.
• for example, Candida, Rhodotorula, and Cryptococcus.
• http://ec.asm.org/content/4/10/1746.full

14. Sexual Reproduction-Ascospore
• An ascus is the sexual spore-bearing cell produced
in ascomycete fungi
• Asci usually contain eight ascospores, produced by
meiosis followed, in most species, by a mitotic cell
division.

15. Sexual Reproduction-Ascospore

16. Sexual Reproduction-Ascospore, Meiosis Cell Division

17. Physiological Characteristics of Yeast
• Grow best with a plentiful moisture
• Many yeasts grow in the presence of greater
concentrations of solutes (such as sugar or salt).
• Require less moisture than most bacteria
• Most yeast requires more moisture than molds

18. Types of Yeast on the basis of water activity
Ordinary Yeast
• Do not grow in high
concentrations of solutes
• Can’t grow in low water
activity food materials
• aw : 0.88 to 0.94
Osmophilic Yeast
• Grow in high concentrations of
solutes
• grow in low water activity food
materials
• May grow slowly in media with
an aw as low as 0.62 to 0.65 in
syrups

19. • Osmophilic yeast aw= 0.6 (<
mold and bacteria)
• Optimum Temp: 25-30 0C
• Optimum pH: 4-4.5
• Lack chlorophyll
• Need Carbon source (eg.
Sugar)
• Source of Nitrogen:
Ammonia
Nitrate
Urea
Protein
Peptide
Amino acid
• Yeasts grow best under aerobic
conditions
• Some are anaerobic
Physiological Characteristics of Yeast

20. Growth factors
Vitamins:
• Some yeast can synthesize all vitamins and some very few
• Riboflavin and folic acid is synthesized by all
• Biotin is the limiting factor in growth medium
Minerals:
• Generally sulfur and phosphorus is needed
Physiological Characteristics of Yeast

21. Cultural characteristics
• http://www.eolss.net/sample-chapters/c10/e5-08-06-03.pdf

22. • Colonies:
moist
slimy
dry
wrinkled
• Colony Colour:
Whitish
cream-colored
pink
Cultural characteristics

23. Oxidative Yeast
• oxidize organic acids and alcohol
CH3CH2COOH CH3CH2CH2OH
• Grow at the surface as pellicle or
scum
Fermentative yeast
• Ferment glucose to ethanol and
carbon dioxide
C6H12O6 CH3CH2OH+ CO2
• grow throughout the liquid
Cultural characteristics

24. Classification and identification of yeasts
1. Reproduction: Sexual or asexual
• If Sexual:
Appearance of ascospores: shape, size, and color
Number of ascospores per ascus: one, two, four, or eight
• If Asexual:
Budding
Chlamydospore
Fission

25. 2. Mycelium
Production of a mycelium,
pseudo mycelium, or no
mycelium
3. Growth:
Film yeast over surface of a
liquid (film yeasts) or
growth throughout medium
Classification and identification of yeasts

26. • 4. Colour of the colony 5. Physiology:
Source of Nitrogen, carbon
Vitamins requirement
Oxidative or fermentative
Classification and identification of yeasts

27. Yeasts of Industrial importance

28. Genus Saccharomyces
Top Yeast
• Top yeasts are very active
fermenters
• grow rapidly at 20 0C
• The clumping of the cells and the
rapid evolution of CO2 sweep the
cells to the surface, hence the
term top yeast
Bottom yeast
• do not clump
• grow more slowly
• best fermenters at lower
temperatures:10 to 15 0C
• The absence of clumping and the
slower growth and evolution of
CO2 permit the yeast to settle to
the bottom, hence the term
bottom yeast

29. Genus Saccharomyces
• S. cerevisiae var. ellipsoideus is a
high-alcohol-yielding variety used
to produce
industrial alcohol
Wines
distilled liquors
• S. uvarum
bottom yeast
used in making beer
• S.fragilis and S. Lactis
ability to ferment lactose
important in milk or milk
products
• S. rouxii and S. mellis are
osmophilic

30. Genus Zygosaccharomyces
• Osmophilic (high concentrations of sugar)
• Involved in the spoilage of
Honey
Sirups
Molasses
soy sauce
wines.
• Zygosaccharomyces nussbaumeri grows in honey
S. rouxii and S. mellis are osmophilic

31. Genus Pichia
• These oval to cylindrical yeasts may form pseudomycelia
• Ascospores are round or hat-shaped
• there are one to four spores per ascus
• A pellicle is formed on liquids
e.g., P. membranaefaciens grows
a pellicle on beers or wines.

32. Genus Debaryomyces
• These round or oval yeasts
• form pellicles on meat brines
• Ascospores have a warty surface.
• D. kloeckeri grows on cheese and sausage.

33. False Yeasts: Fungi Imperfect ??
• Lack Sexual Mode of reproduction
• Example
Genus Torulopsis
Genus Rhodotorula
Genus Candida
Genus Brettanomyces
Genus Kloeckera
Genus Trichosporon
CANDIDA

34. False Yeast- Torulopsis
• Shape: round to oval
• fermentative yeasts
• Asexual Reproduction:
multilateral budding
• cause trouble in
 breweries
T. sphaerica ferments lactose and
may spoil milk products
• Other species can spoil sweetened
condensed milk
fruit-juice concentrates
acid foods

35. False Yeast-Candida
• Asexual Reproduction by-
budding
Chlamydospores
• spoil foods high in acid and salt
Fruit juice
Pickle
• C. utilis is grown for food and feed
• C. krusei has been grown with
dairy starter cultures for
maintaining the LAB activity
increasing the longevity of
the lactic acid bacteria
• Lipolytic C. lipolytica can spoil
 butter
oleomargarine

36. False Yeast- Rhodotorula
• cause discolorations on foods like
Red
Pink- pink areas in sauerkraut
yellow
produce coloured spots on meats

37. MOLD

38. MOLD
Syllabus:
General characteristic of moulds
 Morphological characteristic
 Physiological characteristic
 Cultural characteristic
Reproduction
Classification and identification of moulds

39. Morphological Characteristics
• multicellular filamentous fungi
• fuzzy or cottony appearance
• The thallus/vegetative body lack
true roots
Stems
leaves

40. Morphological Characteristics
• Hyphae: it is a long, branching filamentous structure in fungi

41. • Mycelium: It is the vegetative part of a fungus consisting of a mass
of branching, thread-like hyphae
Morphological Characteristics

42. Cultural Characteristics
Molds may grow as
loose and fluffy
compact
velvety on the upper
surface
dry and powdery and
wet or gelatinous.

43. • Mycelium may grow coloured
Red
Yellow- P. notatum
Brown- A. flavus
Grey- Mucor, Botrytis cinerea
Black- Cladosporium
 blue-green- P. chrysogenum
Purple
Cultural Characteristics

44. Cultural Characteristics

45. Physiological characteristics
1. Moisture Requirements:
require less moisture than do most yeasts and bacteria
Growth inhibited below 14 to 15 %
moisture in flour, dried fruits will greatly delay Mold
growth

46. Physiological characteristics: Temperature requirement
Mesophilic:
• most of the Mold
• The optimal temperature: 25 to 30
0C
• some grow well at 35 to 370C or
above, e.g., Aspergillus spp
Thermophilic:
• Very few molds
• high optimal temperature: 60 to
62 0C
• Eg.Thermomyces lanuginosus
Psychrotrophic:
• grow fairly well at refrigeration
temp
• Only few molds
• Temp: - 5 to - 100C

47. Physiological characteristics
Oxygen Requirement
• Aerobic
• They require oxygen for
growth
pH Requirements
• pH- 2 to 9.5
• the majority are favoured
by an acid pH

48. Physiological characteristics
• Compounds inhibitory to other organisms are produced
by some molds
• Example
Penicillin from Penicillium chrysogenum and
Clavacin from Aspergillus clavatus

49. Reproduction in Mold
1) Asexual
2) Sexual

50. Asexual Reproduction
• Most common mode
• Spores:
produced in large numbers
small and light
resistant to drying
readily spread through the air
Grow as new Mold thallus under favourable condition
Asexual Spores

51. Germination of Spores
• A

52. 1. Conidia:
• Conidia are cut off, or bud, from special fertile
hyphae called conidiophores
• not enclosed in any container
• Formed in Penicillium and Aspergillus
MOLD- Types of Asexual Spores

53. 2. Arthrospores or Oidia
• The hypha breaks up into small
pieces and develop into spores
• cannot survive in unfavourable
conditions.
MOLD- Types of Asexual Spores

54. 3. sporangiospores:
• spores that are produced in a
sporangium (plural: sporangia)
• Sporangium: It is an enclosure in
which spores are formed
• Eg. Rhizopus and Mucor
MOLD- Types of Asexual Spores

55. Sexual Spores
1. Oospores:
• Oospores are termed Oomycetes
• These molds are mostly aquatic
• important plant pathogens
• The oospores are formed by the union of a small male gamete and
a large female gamete

56. 2. Zygospores:
• Zygomycetes form zygospores by the union of the tips of two
hyphae
• Hyphae may come from the same mycelium or from different
mycelia
• Zygospores are covered by a tough wall and can survive drying for
long periods.
MOLD- Sexual Spores

57. Zygospores formation
• Two hyphae of opposite strain come in contact and develop
short outgrowth called protuberance.
• Accumulation of cytoplasm and nuclei takes place at the
protuberance
• swelling occur in each protuberance which forms
progametangium
• A septum is formed in each progametangium which separates
terminal fertile more nucleated part into gametangium and
basal sterile more vacuolated part into suspensor

58. Zygospore formation
• Each gametangium work as gamete
• gametes fuse and form diploid zygote.
• Zygote enlarges in size and get surrounded by the thick-walled
structure and change into a zygospores
• Zygospore is dark black in colour and has two covering
layer
• The outer layer is exosporium and the inner layer is
endosporium
• Zygospore is resting spore, it undergoes resting period.

59. Zygospores formation

60. Sexual Spores- ZYGOSPORE

61. 3. Ascospores:
• The Ascomycetes (septate) form sexual spores known as ascopores,
It is formed after the union of two cells from the same mycelium
or from two separate mycelia
• The ascospores, are in an ascus, or sac, with usual eight spores per
ascus
MOLD- Sexual Spores

62. • Ascospore formation:
Sexual Spores

63. Classification and identification of molds
1. Hyphae
septate or
non-septate
2. Mycelium
clear or
dark
(smoky)
3. Mycelium
coloured or
colourless

64. MOLDS OF INDUSTRIAL IMPORTANCE

65. MUCOR
• Structure:
Mucor is a hyphal fungus body structure consists of a fine thin thread
like tubular branch colony mass of mycelium
• Hyphae:
Unit structure of mycelium
Hypha is coenocytic

66. Mucor
Mucor - Part of hypha showing detailed structure and Mycelium of Mucor with
Sporangiophores

67. TYPES OF HYPHA
• Prostrate Hypha
It horizontally grows on substratum
Absorbs nutrition from the substratum.
• Sub-terranean Hypha
It is more branched and deeply penetrating prostrate hypha
absorb nutrition from the substratum
• Aerial Hypha
It is erect hypha developing from prostrate hypha
called as sporangiophores which bears sporangium at its tip

68. REPRODUCTION IN MUCOR
• Asexual reproduction takes place by fragmentation of hypha
• Fig. Mucor - Different types of vegetative reproduction in fungi.

69. ASEXUAL REPRODUCTION
• Asexual reproduction by formation of asexual spores like
sporangiospores
Chlamydospore
oidia
1. Sporangiospore:
• Most common mode
• Sporangiospores is produced inside sporangium at the tip of
sporangiophore
• formed in favourable condition

70. Growing of Sporangiospores
In favourable condition
prostrate hypha develop erect hypha
accumulation of more nuclei and cytoplasm takes place at
the tip
Swelling of the tip of erect hypha occurs
young sporangium is formed
differentiation of cytoplasm takes place

71. Growing of Sporangiospores
• Peripheral fertile cytoplasm with many nuclei and dense
cytoplasm is called sporeplasm
• central part with few nuclei is called is called columella
which is dome shaped sterile part
• Cleavage occurs in sporeplasm which separates much mass
of cytoplasm with few nuclei

72. Growing of Sporangiospores
• the wall formation takes place around it
• results in the formation of many thin-walled multinucleate
spores called sporangiospores
• Sporangiospores is yellowish brown in colour

73. Dispersal of sporangium

74. Dispersal of sporangium
• the sporangium gets matured
• dome shaped sterile part of columella swells up
• this creates pressure on the wall of sporangium
• bursting of sporangium occurs
• Sporangiospores are released in the air as dark powdery form
• when they obtain suitable substratum they germinate
immediately without resting period.

75. Asexual spore- Chlamydospore
• They are thick-walled resting spore formed in unfavourable
conditions
• In unfavourable condition mature hypha become septate
• Accumulation of nuclei and cytoplasm takes place at the septated part

76. Asexual spore- Chlamydospores
• Thick wall is formed around it and change into the chlamydospore
• They undergo resting period
• In return of favourable condition germination of Chlamydospores start
• Give rise to new mycelium

77. Asexual Reproduction by Oidia
• In aquatic species of Mucor, where their is high acidity and
more sugar-rich substance hypha become sepated
• septated portion become round in shape
• separate from the parent hypha
• These are thin walled asexual spore called oidia.

78. Penicillium
• Fd

79. Penicillium
• Ascomycetous fungi
• The mycelia consists of a highly branched network of
multinucleate, septate hyphae
• Many-branched conidiophores, bearing conidiophore
• Spore: Green colour

80. Penicillium

81. Penicillium
• P. expansum:
the blue-green-spored mold
causes soft rots of fruits
• P. digitatum:
with olive, or yellowish-green conidia
causing a soft rot of citrus fruits
• P. italicum
called the “blue contact mold” with blue green conidia
rot citrus fruit

82. Penicillium
P. italiticum growing on AppleP. Digitatum growing on orange

83. Penicillium
• P. camemberti:
with grayish conidia
useful in the ripening of Camembert cheese
• P. roqueforti
with bluish-green conidia
aiding in the ripening of blue cheeses
• e.g., Roquefort Cheese

84. Penicillium
• P. chrysogenum- Penicillin (antibiotic)
• (previously known as P. notatum)

85. Geotrichum
• Species may be white, yellowish, orange, or red, with the
• growth appearing first as a firm, felt like mass that later
becomes soft and creamy.
• Geotrichum candidum called the "dairy mold,” gives
white to cream-colored growth

86. Rhizopus

87. Rhizopus

88. Rhizopus
• Rhizoid: root like part of the hyphae that anchors the
fungus
• Stolon: horizontal hyphae that connects the group of
hyphae to each other

89. Growth of Rhizopus on bread
• Dgh