Sweetness enhancement using naturally occurring aromas is a promising way of reducing the sugar content of flavoured beverages while maintaining taste. Research at NIZO suggests that the ability of consumers to differentiate between taste and aroma is limited, and that aromas can be used to produce long-lasting sweetness-enhancing effects.
An interest in healthier foods is growing on the part of both consumers and the food industry. The demand for products containing less sugar poses a challenge for the producers of flavoured drinks, which by tradition have high sugar content. While many drinks producers have solved this by replacing some or all of the sugar content with artificial or processed sweeteners, consumer organisations are starting to resist the wide application of such sweeteners. The additional dilemma for producers is that while consumers prefer not to compromise on taste, they are also increasingly on the lookout for products that contain natural ingredients, free of E numbers and artificial additives.
This has led to a search for alternative strategies to keep these label-conscious consumers happy while avoiding high sugar content. One such strategy currently being explored at NIZO is to make use of so-called cross-modal effects: by being exposed to many different foods, we learn to associate food aromas with the taste they usually accompany. Therefore adding an aroma to mimic the smell of sugar-rich versions of the food increases the perceived sweetness by mere suggestion. In other words, the brain tells us the sweetness is there, even when the sweet ingredient is not. However, until now it was unclear whether the sweetness-enhancing effect of an aroma is strong enough to enhance taste perception in the longer term.
Using aroma-induced sweetness enhancement in real foods is also a relatively new concept, and studying how taste experience can be improved with aromas requires specialised equipment. NIZO has at its disposal both an olfactometer – that can deliver precise amounts of aromas into a subject’s nose while they are consuming food for example – and a gustometer, used to deliver precise amounts of taste stimuli onto a subject’s tongue.
Such devices have allowed us to demonstrate that a drink is perceived as much sweeter if a sweet-smelling aroma is delivered to the nose at the same time. One of the aromas being tested at NIZO is ethyl hexanoate (HEX), a natural aroma component that is synthesised in apples during ripening. Interestingly, we see the same effect if we add HEX in liquid form to apple juice. While it is fairly easy to persuade people that the apple juice they are tasting contains a higher amount of sugar than it actually does – just by adding HEX to the apple juice – this cross-modal effect is the strongest in untrained test subjects who are exposed to HEX for the first time. This suggests that giving it to the same subjects repeatedly might reduce the effect, and that people can learn to tell the difference between taste and aroma.
To determine whether or not HEX’s sweetness-enhancing effect is stable enough to support long-term application in food products, researchers at NIZO conducted a series of tasting sessions using a panel of 21 test subjects. They monitored the effect of adding HEX to apple juice, whereby the test subjects underwent two types of tasting sessions that alternated in a fixed schedule over a 6-month period. In all tasting sessions, subjects were given apple juice with or without added sugar that varied in HEX content. In the ‘evaluation’ sessions, subjects were asked to taste an unlabelled sample and rate its sweetness. In the ‘feedback’ sessions, a computer screen simply told them whether or not the apple juice they were tasting contained added sugar. This allowed them to learn whether the sweetness they experienced was due to added sugar or added aroma.
As expected, the effect was strongest during the initial session, i.e. before subjects had been given the opportunity to learn the difference between taste and aroma. During this ‘untrained’ session, subjects gave unsweetened apple juice with a higher HEX content a consistently higher sweetness rating. While this effect disappeared just after the feedback sessions, it recovered significantly during the final evaluation at 6 months for all but the highest HEX concentration. This suggests that the subjects in this test panel did not learn to distinguish between sugar and aroma-induced sweetness.
The result is encouraging since the experimental setup was – intentionally – a worst-case scenario: during the feedback sessions subjects were explicitly told whether or not the samples contained added sugar, whereas in real-life situations people are not always fully informed of a product’s content. After all, it is up to consumers themselves to read the label. It is therefore likely that if explicit sugar content provided on a computer screen during tasting does not negatively impact aroma-induced sweetness enhancement in the long term, the effect will also stand the test of time in real life. While a conclusive answer will require a longitudinal consumer study, these results clearly indicate that aromas have potential for enhancing sweetness in flavoured beverages. NIZO is looking forward to helping the food industry make use of such developments to help reduce the levels of sugar in their products while maintaining taste.
The experiments and findings described above were published in a paper presented at the 15th Weurman Flavour Research Symposium in Austria in September 2017 (Brattinga et al, 2017).