Strawberry aroma is one of the most predominantly used flavors in the food industry. Food manufacturers are able to make synthetic versions of the strawberries consumers are used to, but wild strawberries are a different story. The wild strawberry is highly prized for its intense aroma and uniquely sweet taste—much more so than its store-bought cousin. But, wild strawberry plants are rare and expensive.
In an attempt to better replicate the flavor of wild strawberry, researchers at the Institute of Food Chemistry and Food Biotechnology in Germany turned to Wolfiporia cocos—an edible brown-rot fungus that can break down a variety of foods and release fruity and floral aromas in the process. Fungi have long been an alluring option for biotechnological upcycling. In fact, some species of fungi are already used to convert side streams of waste products and plant material into odor compounds like vanillin, raspberry ketone and benzaldehyde, an almond-like odor.
Holger Zorn and his colleagues found their ideal waste product in the black currant juice industry, which produces pomace—a combination of pulp, seed and fruit skins that is usually thrown away. Using the black currant juice pomace, the researchers grew W. cocos on the waste, tweaking conditions as they went to see if they could get the fungus to naturally produce the unique aroma associated with wild strawberries.
At first, with black currant pomace as the fungus’ sole source of nutrition, W. cocos produced non-distinct fruity and floral aromas. When the team added ammonium nitrate, monohydrate, monopotassium phosphate and a few other substances to the medium, the culture released an aroma similar to wild strawberries. Interestingly, the scientists noted that while sodium L-aspartate had a negative impact on the growth of W. cocos, it positively affected its ability to produce the wild strawberry-like odor.
To further pinpoint the exact compounds that contribute to the unique scent, Zorn and his team employed gas chromatography-mass spectrometry-olfactometry (GC-MS-O). Overall, GC-MS-O found 16 odorants, of which 14 compounds could be identified. Four specific compounds—linalool, geraniol, methyl anthranilate and 2-aminobenzaldehyde—boasted the highest flavor dilution factors, meaning they are most important to odor impressions.
Previous literature has described methyl anthranilate as the key aroma compound in wild strawberries, and it is not found in cultivated strawberries. And while linalool is a known compound in strawberries, the authors showed, for the first time, in their study that the citrus-like and flowery odor of linalool strongly influenced the overall aroma of the cultures. 2-Aminobenzaldehyde has a characteristic wild strawberry and peach-like odor that, according to the study published in ACS’ Journal of Agricultural and Food Chemistry, served to intensify the wild strawberry-like odor of the cultures. The compound, however, has rarely been described as an aroma compound, occurring mostly in flowers, fruits and/or fungi.
“Due to their characteristic wild strawberry-like odor, methyl anthranilate and 2-aminobenzaldehyde are especially important for the odor,” the researchers write in their study. “[But,] further investigations will be necessary to gain knowledge about the genes and enzymes involved in fungal biosynthesis of 2-aminobenzaldehyde and other anthranilic acid derivatives.”
Having a better idea of the odor and flavor profile of wild strawberry, the researchers then combined artificial versions of the four main compounds into a model wild strawberry smell. A trained panel of 10 sensory experts rated the smell as being very similar to the wild strawberry-like odor from the cultivated fungus.
“The cultivation of W. cocos on black currant pomace thus represents a unique fungus–substrate combination for the sustainable and cost-efficient production of the wild strawberry-like flavor,” the researchers conclude.