The study, reported in the journal PLoS ONE, suggests that changes in starch consistency in the mouth are directly related to the activity of the oral enzyme salivary amylase. The findings link genetic variation in the AMY1 gene to salivary amylase levels and activity, which, in turn are related to the perceived breakdown of starch viscosity over time.
“Specifically, we observed that individuals with high levels of amylase experienced faster and more significant decreases in perceived starch viscosity than did individuals with low levels of amylase,”
“It is possible that the enzyme activity affects preference and intake of starchy foods through its influence on the oral sensory properties of such foods. For example, salivary amylase levels affect both creaminess and the release of flavour compounds […] these characteristics are likely to affect an individual’s liking of a food,” wrote the researchers, led by Dr Abigail Mandel, from the Monell Center.
Changes in viscosity can play an important role in determining food preference. For example the thinning of chocolate and ice cream in the mouth as they melt is considered central to their very high desirability and perceived creaminess, noted the researchers.
The degree to which the perceived viscosity of starch is thinned by salivary amylase ‘pre-digestion’ is therefore important to food manufacturers.
However, research investigating this action and its relevance to sensory perception has been difficult to observe and interpret.
Amylase in action
Salivary amylase accounts for between 40 and 50 per cent of protein in human saliva and rapidly alters the physical properties of starch by breaking it down into simple sugars like maltose.
Genetically, salivary amylase levels are influenced by individual copy number variation of the AMY1 gene, with salivary amylase concentrations positively correlated with the number of copies of AMY1.
The new studies investigated how individual differences in salivary amylase levels affect starch viscosity breakdown, and how this variation in the enzyme affects the perception of starch viscosity.
The results demonstrated that saliva containing high levels of amylase rapidly hydrolyzes a viscous starch solution.
By tracking the oral break down of starch, researchers found individuals with high amylase levels reported faster and more significant decreases in perceived starch viscosity than people with low salivary amylase levels.
They also observed that AMY1 copy number variations are a predictor of individual’s amount and activity of salivary amylase, and therefore ultimately determine the perceived rate of starch viscosity thinning.
Perception and preference
Dr Mandell explained that differences in starch perception due to variations in amylase are likely to affect consumers’ nutritional status by influencing their liking for, and thus their intake of starchy and starch-thickened foods.
“Foods with different starch levels will be perceived very differently by people as a function of how much salivary amylase they produce. What may seem like a thick and resistant pudding or starchy food to some may seem noticeably thin in the mouths of others,” said senior author Dr. Paul Breslin, also of the Monell Center.
The researchers added that such findings may also extend to wider starch digestion and metabolism, and could ultimately provide insight into why some people develop metabolic diseases while others don’t.
“In today’s state of food excess and refined starch ingestion, it is possible that high levels of salivary amylase contribute to the risk of insulin resistance and non-insulin dependent diabetes,” said Mandel.
Source: PLoS ONE
Volume 5 Issue 10, doi: 10.1371/journal.pone.0013352
“Individual Differences in AMY1 Gene Copy Number, Salivary a-Amylase Levels, and the Perception of Oral Starch”
Authors: A.L Mandel, C. Peyrot des Gachons, K.L. Plank, S. Alarcon, P.A.S Breslin