12 January - 20 June 2016

Masking the bitterness of green vegetables may improve palatability

Scientists are reporting in the journal Appetite that adding very small amounts of sugar to green vegetables significantly masks the bitterness of green vegetables, and therefore increases palatability without altering other sensory properties.

Scientists are reporting in the journal Appetite that adding very small amounts of sugar to green vegetables significantly masks the bitterness of green vegetables, and therefore increases palatability without altering other sensory properties.  Hayes et al. report that despite the overall health benefits of vegetables only 7% of US children consume the recommended amount of vegetables per day.  They note that previous research has indicated that vegetables are often undesirable to adults and children due to their bitterness.  Whilst repeated exposure to flavours can increase acceptability, the authors’ state that this practice is often not followed with children as parents may avoid offering foods that were previously unaccepted.

Using three different experiments the team investigated if very low amounts of sugar can be added to vegetable purees of kale, spinach and broccoli to mask bitterness and improve acceptance. The first experiment used a trained panel of 9 screened individuals, with a mean age of 38 years.  The panel assessed purees of each vegetable with the addition of sugar at 0%, 0.6%, 1.2% and 1.8%, and also samples of vegetables with 0.2% salt. Compared to samples of vegetables without sugar, the addition of sugar at 1.2% and 1.8% significantly reduced bitterness for all three vegetables with no difference in bitterness between the 1.2% and 1.8%.  Hayes et al. note that the addition of sugar at 0.6% produced mixed results. Bitterness was significantly reduced for Kale but not for broccoli or spinach.  The addition of higher levels of sugar as expected increased the sweetness of the purees.  The addition of salt at 0.2% reduced that bitterness of the purees, with the scientists noting that “the bitterness from the puree with 0.2% (added salt) didn’t differ from the bitterness of the 1.2% and 1.8% added sugar purees.”

The second experiment used 84 adults, who were given purees with either 0% or 2% sugar. Using pairs of vegetables the panellists were asked to select the sample that was more bitter.  For the third experiment, 99 adults with a mean age of 43 years were instructed to rate their liking, using a 9 point hedonic scale, of vegetable purees containing, 0%, 1% or 2% sugar.  They were also asked to rate their agreement of 5 statements around the subject “Children often dislike bitter foods (e.g., green vegetables).  Sugar can be used to mask bitterness.”

Hayes et al found that the addition of 1% and 2% sugar significantly increased overall liking of broccoli and kale purees compared to the control whilst the addition of 2% sugar increased the liking of spinach.  Whilst these findings indicate that sugar can help to improve the palatability of vegetables, the acceptance of the addition of sugar was not so favourable, with only 64% agreeing to the statement “I would be willing to give a young child (ages 6 months – 3 years) vegetable preparations with sugar added to mask bitter taste in an effort to increase the child’s vegetable consumption.  A third of participates were opposed to using sugar to mask bitterness in foods for young children especially when they viewed the amount used as teaspoons of sugar. 

Hayes et al discuss their findings noting that whilst sugar can mask the bitterness, the use of added sweeteners to enhance vegetable liking and acceptable in both children and adults has “substantial drawbacks”.  They discuss guidelines noting that Americans are recommended to limit their sugar intake, although they state that “the highest sugar concentration we used (2%) is the equivalent of adding 2.0g of sugar per 100g of vegetable puree.  This amount is well within the guidelines for adult consumption of added sugars even if an adult were to consume five vegetable servings.” They also report that they found higher sugar content in infant/toddler vegetable sold commercially in US. The study suggests that additional research need to be carried out to determine “if these minimal additions can improve vegetable intake for adults or children.”

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