Molds are multicellular, filamentous fungi that appear fuzzy or cottony when they grow on foods. While molds can spoil foods and make them inedible, some molds are used to manufacture foods like cheeses and breads. Molds consist of branching filaments called hyphae that make up the mycelium. Hyphae can be either vegetative for nutrition or fertile for reproduction. Molds require less moisture than bacteria or yeast but still need free oxygen and a pH between 2-8.5 to grow. Different molds have varying temperature and moisture requirements for optimal growth.

1. MICROBIOLOGY QUICK LEARN
FOOD MICROBIOLOGY
MOLDS
Saajida Sultaana Mahusook

2. • Molds are multicellular, filamentous fungi whose growth on foods can be
readily recognized by its fuzzy or cottony appearance.
• Generally molds are concerned in the
• spoilage of foods; moldy or mildewed food is considered unfit to eat.
• some molds are used in the manufacture of different foods such as
• ripening of cheese (e.g. Roquefort, Camembert),
• ripening of many oriental foods,
• production of amylase,
• products used in foods, such as enzymes for bread making or
• citric acid used in soft drinks and
• production of several antibiotics.

3. Morphological Characteristics
• Morphological characters are important to identify and classify the molds.
The appearance of a mold growing on a food is helpful to indicate its genus.
Hyphae and Mycelium
• Macroscopically the mold consists of a mass of branching, intertwined
filaments called hyphae (singular hypha), and a mass of hyphae is known as
mycelium.
• The hyphae may be vegetative or fertile.
• Vegetative hyphae are concerned with the nutrition of the mold and fertile
hyphae with the production of reproductive parts.
• Most molds have the fertile hyphae are aerial and some may be submerged.
• The hyphae of some molds are full and smooth, while others are
characteristically thin and ragged.
• A few kinds of molds produce sclerotia (singular sclerotium) which are
tightly packed masses of hyphae, often thick-walled, within the mycelium.
• Sclerotia are more resistant to heat and other adverse conditions and hence
finds importance in some processed foods.

4. • Microscopically, a group of molds are called septate where the hyphae are divided by
cross-walls and the hyphae without cross walls are called aseptate having the nuclei
scattered throughout the length.
• Septate hyphae increase in length by division of the tip cell or cells within the hypha. In
aseptate hyphae, division of nuclei takes place accompanied by increase in length of the
filaments.
• Special mycelial structures such as holdfasts (in Rhizopus), foot cells (Aspergillus) or
dichotomous ― ‘Y’ shaped branching (Geotrichum) are present.
Rhizopus
Geotrichum Aspergillus

5. Cultural Characteristics
• The appearance of mold growing on food is sufficient to indicate its class or
order.
• Molds are loose, fluffy or compact; velvety on the upper surface, dry and
powdery, and wet or gelatinous.
• Presence of pigments ―red, purple, gray, black, etc. is also characteristic of
the mycelium and colored spores are observed in mature mold imparting its
color to a part or all of the growth.

6. Physiological Characteristics
Moisture requirements:
• Molds require less moisture than bacteria and yeasts. The minimum water
activity for spore germination has been found to be as low as 0.62 for some
molds and as high as 0.93 for others. Each mold has an optimum of water
activity and a range of water activity for growth. The reduction of water
activity below the optimum for a mold delays the germination of the spores
and may reduce the growth rate.
Temperature requirements:
• Most molds grow well at ordinary room temperatures and are classified as
mesophilic. The optimum temperature is between 25 and 30°C for most
molds. Some molds grow can even grow fairly well at freezing temperatures
or can grow slowly at sub-zero temperatures.
Oxygen and pH requirements:
• Molds require free oxygen for growth and hence favoring the growth on the
surface of contaminated food. Most molds grow over a wide range of
hydrogen ion concentration (pH 2-8.5), some favoring acid foods such as
fruits.

7. Food requirements:
Generally molds can utilize simple to complex foods. Most of the
common molds possess a variety of hydrolytic enzymes such as
amylases, pectinases, proteinases and lipases.
Inhibitors:
Initiation of growth of molds is slow compared to bacteria or
yeasts. When conditions are favourable for other organisms,
molds usually lose out in competition. After mold growth is
underway, it grows rapidly. Some molds produce compounds that
are inhibitory to the growth of other organisms such as
penicillium from Penicillium notatum and clavicin from
Aspergillus clavatus. Certain chemical compounds are
mycostatic, that inhibits the growth of molds (sorbic acid,
propionates, acetate)or specifically, fungicidal killing molds.

8. Reference
• Food Microbiology by Martin R. Adams and Maurice O. Moss,
3rd e.
• Food Microbiology by William C. Frazier and Dannis C.
Westhoff, 5th e.