The science behind bread spoilage/How bread gets spoiled

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If the bread is left outside for a long time, one can see green/black hairy spots on it. This is nothing but spoiling of bread by the growth of molds. These molds are a type of microorganisms called Fungi.
Factors responsible for growth of mold
1. Moisture: Even though the breads are made at high temperature, centre of the bread contains little moisture which eventually spreads throughout. This slightly moist environment is perfect for mold growth. Additionally, if moisture/water is accidently added onto the stale bread, it is prone to spoilage
2. Nutrients: Bread is rich in sugars which encourages growth of molds
3. Temperature: Bread provides warm temperature (25-30°C) which is ideal for mold growth

Molds causing spoilage of bread
Mold growing on the bread can be microscopic fungi belonging to different species like Penicillium, Rhizopus, Aspergillus, Monascus and Fusarium. They are of different shapes and colors depending on the species.
Rhizopus stolonifer, commonly known as black mold is the most common and fast-growing bread mold. Hence, it is often the first molds to appear on stale bread.
Growth of mold on bread
Molds are reproduced by means of spores. These spores are present in air and grows rapidly in indoor environments. When a spore comes in contact with a substrate such as bread, it first spreads over the surface and penetrates into it forming root-like structures called rhizoids. Rhizoids helps in anchorage of the mold to the substrate and absorbs nutrients from it by releasing digestive enzymes. Later, it produces aerial hyphae called sporangiophores which contains sporangia at their tip. Sporangia contains numerous spores which are released at maturity into the surrounding atmosphere. These spores then may land on a moist surface and the life cycle repeats. This process continuous and eventually the bread gets spoiled. As a result, black/greenish patches appear on the bread. This may take 5-7 days.

Can we consume the moldy bread?
Though some part of the bread appears unspoiled, it is not good to consume unspoiled part/remaining slices of bread as the established hyphe without spores are undetected by naked eye. They can cause asthma and allergic reactions. They also produce toxic by-products called mycotoxins which are carcinogenic.

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