Fundamental Food Microbiology, Third Edition - Fuad Fathir

94 FUNDAMENTAL FOOD MICROBIOLOGY
II. MOLD SPORES
Molds form spores by both asexual and sexual reproduction and on this basis are
classified as perfect or imperfect molds, respectively. Molds form large numbers of
asexual spores and, depending on the type, can form conidia, sporangiaspores, and
arthrospores. Conidia are produced on special fertile hyphae called conidiophores
(Figure 8.1). Among the important molds in food, Aspergillus and Penicillium species
form conidia. Sporangiospores are formed in a sack (sporangium) at the tip of a
fertile hypha (sporangiophores). Mucor and Rhizopus species are examples of molds
that form sporangiospores. Arthrospores, formed by the segmentation of a hypha,
are produced by Geotrichum. An asexual spore in a suitable environment germinates
to form a hypha and resumes growth to produce the thallus. Sexual spores form
from the union of the tips of two hyphae, two gametes, or two cells. However, among
the molds important in food, sexual reproduction is rarely observed. Some examples
include Mucor and Neurospora.
III. YEAST SPORES
On the basis of sporeforming ability, yeasts important in food are divided into two
groups: those that can produce sexual ascospores are designated as Ascomycetes (true
yeasts), and those that do not form spores are called false yeasts. Examples of some
yeasts important in food that form ascospores are Saccharomyces, Kluyveromyces,
a b c
d e f
(ii)
Figure 8.1 Schematic diagrams of spores of molds and yeasts. Conidiophore with condial
head and condia (one magnified in each) of (a) Aspergillus spp., (b) Penicillum
spp., and (c) Fusarium spp.; (d) arthrospore in Geotrichum spp.; (e) sporangiophore
with sporangium containing sporangispores (one magnified) of Rhizopus
spp.; (f) ascopore formation in yeasts by conjugation of (i) mother–daughter and
(ii) two separate cells.
(i)