Making better-for-you foods and beverages taste less bitter is possible with a short list of plant-based bitterness blockers, all of them labeled as natural flavor, including naringenin, sugar cane distillate, mushroom mycelia extract, and 1,3- 1,3-propanediol. Alex Woo, Ph.D., CEO of W2O Food Innovation, discussed the neuroscience behind the perception of bitterness and how this knowledge is being used to specifically target and reduce bitterness in foods and beverages. He gave this talk in his 2023 Clean Label Conference presentation, “Clean Label Bitterness Blockers: Neuroscience, Ingredient Technologies, Applications.”
Most of the roughly 100 substances that are bitterants to humans are small, hydrophobic molecules. Detection of bitterness starts in the mouth, where bitterants interact with taste receptors on the tongue. Of the about 40 known human taste receptors, about 25 are bitterness receptors, known as TAS2Rs. The binding of a bitterant to these receptors generates a signal to the brain that results in the perception of bitterness. Two approaches are used to modulate bitterness in foods: masking or blocking, said Woo.
Masking & Blocking Bitterness
First, masking changes the perception of bitterness in the brain but not the binding of the bitterant to its receptor(s). For example, cola itself is bitter, but sweeteners and vanilla added to cola beverages mask cola’s bitterness.
Sweetness at medium and high levels masks bitterness, while saltiness at any concentration suppresses bitterness. Blocking is a more powerful approach to reducing bitterness, utilizing knowledge of the specific taste receptors where bitterants bind. Most bitterness blockers are receptor antagonists or negative allosteric modulators (NAMs).
Receptor antagonists actively block taste receptors. Bitterants bind tightly to their receptors. Antagonists (often similar in structure to bitterants) bind receptors loosely. Not enough to activate the receptor, but enough to block a bitter compound from binding and reduce the signal that generates the perception of bitterness, explained Woo. In contrast, NAMs work indirectly by binding near (but not at) the receptor in a way that alters the receptor’s ability to bind the bitterant.
Many bitterants can activate each TAS2R. Conversely, one bitterant can trigger multiple receptors. Knowledge of the specific relationships between bitterness receptors, bitterants and antagonists can be found in the literature or the BitterDP database. Putative interactions between specific receptors and antagonists can also be inferred from sensory testing. This information can identify strategies to block specific bitterants. Bitterness blockers, categorized as mature (commoditized, patents expired, commonly used); pacing (newer, currently popular blockers); and emerging (not yet in wide use), were discussed.
Mature bitterness blockers include the following:
- Phloretin is extracted from apple bark/roots and may function by enhancing sweetness via positive allosteric modulation.
- Adenosine monophosphate is a natural, highly soluble compound found in milk that may explain why adding milk to coffee makes it less bitter.
- Sodium gluconate, made by fungal fermentation, may be a direct blocker or could interact with a salt ion channel.
Examples of “pacing” blockers were also described:
- Sugar cane distillate (SCD), produced from sugar cane waste, is one of the best universal bitter blockers, as it contains five distinct bitterness blockers.
- Naringenin, extracted from grapefruit, is structurally similar to naringin, the bitter compound in grapefruit, and works across all families of bitterness.
- 1,3-propanediol, a natural product from corn fermentation, blocks multiple TAS2Rs and is highly soluble.
Finally, emerging blockers were discussed:
- Citronellal, a well-known compound found in lemon and lemongrass, was recently shown to block caffeine bitterness receptors and may be responsible for lemon’s reputation for reducing tea’s bitterness.
- Polymethoxyflavones (PMF), derived from citrus fruits, is a patented extract containing multiple blockers that may also act as bitterants at higher concentrations.
- The tryptophan-tryptophan dipeptide blocks multiple receptors, including those associated with caffeine, quinine, and stevia, but is not yet commercialized.
Choosing Bitterness Blockers
Woo recommended several strategies when choosing bitterness blockers. (See chart “Bitterness Blockers: Applications in Foods and Beverages.”)
Start with blockers that work on many receptors (e.g., SCD, naringenin, 1,3-propanediol). Then select blockers that are most water-soluble, especially for beverages. Adopt a mature blocker or validate a pacing blocker in your food product. Going forward, monitor emerging technologies for future competitive advantage.
Woo’s final words of advice were that because blockers may also have some bitterness, remember that more may not be better.
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