Thaumatin, derived from the fruit of a West African tropical plant (Thaumatococcus daniellii), is a sweet-tasting and flavour-modifying protein that consists of a single chain of 207 amino acid residues.
Its sweetness, which can also only be perceived by humans and primates, is around 100,000 times sweeter than sucrose at a molar level, while its ability to mask bitterness means it has been used in combination with stevia which is known for its lingering liquorice aftertaste.
However until now the mechanism that allows us to taste the sweetness of thaumatin has been a mystery, said lead researcher Tetsuya Masuda.
"Now that we've taken steps in the right direction, I'm excited about developing applications for a stronger form of thaumatin," he said, adding that the results could be a huge plus for the food industry and of great use in preventing lifestyle-related diseases.
The researchers from Kyoto University previously studied the composition and structure of thaumatin using X-rays and found that basic amino acids are crucial in eliciting the sweet taste.
Hypothesising that by replacing acidic amino acids with basic ones would increase the sweetness, they replaced aspartic acid with asparagine. The result was a variation of thaumatin that was 1.7 times sweeter.
“In the hope of using more potent sweeteners the biotechnological production of sweet-tasting proteins has been implemented but to design proteins even sweeter than natural ones it is essential to clarify the mechanisms for the elicitation of sweetness,” write the authors in Nature Journal.
“Understanding [this] has been a challenging problem from the start, soon after the discovery of taste receptors, essentially for two reasons: there is a single receptor for all sweet molecules and there are no commonalities among sweet proteins.”
EFSA extends thaumatin applications
In November last year European Food Safety Authority (EFSA) gave the green light to extending the number of categories in which the protein sweetener and flavour modifier could be used to include food flavourings, salt substitutes, soups, sauces and snacks, energy-reduced breakfast cereals, jams and jellies, food supplements and alcoholic beverages.
It also increased the maximum usage level from 0.5 mg per litre to 5 mg per litre in flavoured drinks.
Prior to this it had been approved in the EU for chewing gum, energy-reduced or no-sugar-added sugar confectionery, table-top sweeteners, dairy and non-dairy desserts and syrup and chewable food supplements.
Source: Nature Journal
“A Hypersweet Protein: Removal of the Specific Negative Charge at Asp21 Enhances Thaumatin Sweetness”
First published online: 3 February 2016, doi:10.1038/srep20255
Authors: Tetsuya Masuda, Keisuke Ohta, Naoko Ojiro et al.