Smell is the strongest sense we have and its often very sensitive. One sniff of a flower, for example, can transport you to a 20-year-old memory. It’s the same thing for food. Chocolate, the beloved treat that fuels a $140 billion industry, has an extremely distinctive smell.
The sweet, floral notes that waft toward you when you open a chocolate bar or walk into a candy store can be mesmerizing. However, occasionally, chocolate can have an off-putting scent. This occurs when fermentation of cocoas beans goes awry and it is not detected throughout the manufacturing and final packaging processes.
Even with sensory professionals at-line, food manufacturers have called for a more quantitative way to assess off-flavor at the level of incoming goods inspection. In previous studies, researchers used molecular techniques to identify the compounds that contribute to undesirable smoky flavors, but a similar method has not clarified other volatile scent compounds.
In a new study published in ACS’ Journal of Agricultural and Food Chemistry, Martin Steinhaus and colleagues demonstrated a new method that can be used to identify the principal compounds that cause musty and moldy odors in tainted cocoa beans.
Using nine tainted cocoa samples and one normal sample used as a reference, the researchers employed gas chromatography combined with olfactometry (GC-O) and the more traditional mass spectrometry (GC-MS). The method identified 57 molecules that make up the scent profiles of both normal and musty/moldy-smelling cocoa beans.
Of the 57 compounds, four had higher concentrations in the off-smelling samples than the reference: geosmin, MDMF, 1H-indole and 3-methyl-1H-indole.
Geosmin, a well-known product of microbial metabolism, recorded the highest flavor dilution factor, and is the compound responsible for the moldy, beetroot-like smell. Although geosmin-associated off-favors have been previously reported in cereals, drinking water, fish and wine, this is the first study to link the compound to cocoa.
“Moldy-musty off-flavors in cocoa are often associated with mold growth,” the researchers explain. “Mold growth is favored by insufficient mixing of cocoa batches during fermentation, overfermentation, slow or insufficient drying, and by storage in a humid environment. However, it is yet unclear whether molds or rather bacteria, such as the Streptomyces species, account for geosmin formation in cocoa.”
MDMF, an odor-active compound widely found in different kinds of fruit, was responsible for the musty smell in the tainted chocolate samples. Common in guava, kiwi, mango and strawberry, MDMF smells pleasant in lower concentrations, but the team found it turns from sweet and caramel-like to musty when it is present at high concentrations.
Finally, fecal and mothball-like-smelling compounds 1H-indole and 3-methyl-1H-indole were also identified but not directly linked to the moldy, musty off-flavor. Unlike the other compounds, these were detected in the reference sample, but their flavor dilution factors were much fighter in the tainted samples. According to the researchers, 1H-Indole and 3-methyl-1H-indole have been reported as products of the bacterial decomposition of the amino acid L-tryptophan.
Upon further inspection, the research team found geosmin mostly in the cocoa beans’ shells, which are removed during processing, while 3-methyl-1H-indole was detected primarily in the bean nib—which is manufactured into chocolate.
The researchers say measuring the amount of these compounds within cocoa beans could be an objective way to detect off-putting scents and flavors, keeping future batches of chocolate smelling sweet, edible and delicious.
Photo: David Kebu Jnr holding cocoa beans drying in the sun. Credit: Irene Scott/AusAID
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April 30, 2021 at 02:11AM
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Researchers ID the Four Compounds that Make Chocolate Smell Bad - Laboratory Equipment
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