Question

Typical glue like odour in sweetened condensed milk is caused by __________.

• A. Proteus vulgaris
• B. Aspergillus repens
• C. Torulopsis globosa
• D. Thermobacterium mathiacolle

Hint:

"Buttons" and "glue-like odour" in sweetened condensed milk are classic fungal defects caused by Aspergillus species, specifically Aspergillus repens (and sometimes Penicillium species).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Sweetened condensed milk is preserved by its high sugar concentration (sucrose), which lowers the water activity (\(a_w \approx 0.85\text{--}0.86\)) enough to prevent the growth of normal vegetative bacteria.
However, osmophilic and xerophilic fungi (molds and yeasts) can grow if oxygen is available in the headspace of the can.

Step 2: Detailed Explanation:
The mold {Aspergillus repens (a member of the Aspergillus glaucus group) is highly osmophilic and capable of growing at low water activities.
If cans are poorly sealed or have too much headspace oxygen, spores of A. repens germinate and grow on the surface, forming small, localized coagulated masses known as "buttons."
As the mycelium develops, it secretes active proteolytic and lipolytic enzymes that decompose milk proteins and fats at the product-air interface.
This development releases volatile nitrogenous compounds, free fatty acids, and ketones.
These specific compounds combine with the highly concentrated sugar syrup to produce a distinct, characteristic glue-like or musty chemical odour.
Other options like Torulopsis globosa cause gassy fermentation (blowing), and Proteus vulgaris cannot grow in high-sugar environments.

Step 3: Final Answer:
The typical glue-like odor defect in sweetened condensed milk is caused by the osmophilic mold Aspergillus repens.