Flavour-tactile cross-modal sensory interactions: The case for astringency

The objective of the present study determined cross-modal sensory interactions between volatile stimuli elicited by 3-isobutyl-2-methoxypyrazine (IBMP) and orange extract, and the astringent stimulus aluminium ammonium sulphate dodecahydrate (alum). Three concentration levels of each volatile stimulus was individually combined with three levels of alum in aqueous solutions, giving a 32 full factorial design per alum-volatile combination. A panel of 12 assessors participated in the study; they were familiarised with the perceptual characters of the stimuli individually, as well as practise on scale usage for rating attribute intensities. Three sensory attributes (flavour, astringency and sourness intensity) were evaluated for each alum-volatile mixture in aqueous solutions, in duplicate. Orange flavour intensities were significantly (p = 0.016) enhanced by the addition of alum, specifically at 700 mg/L alum when compared from the control of no added alum. Astringency of alum was significantly (p = 0.014) enhanced by IBMP, in particular at 4 ng/L but not at 14 ng/L. The mechanisms behind orange flavour enhancement may stem from the sourness of alum as opposed to its astringency, but this requires further confirmatory tests. Astringency enhancement by IBMP on the other hand may have occurred either from previous learning, from an innate biological mechanism, or a combination of both. All cross-modal interaction effects were repeatable and quantified enhancement of astringency by aroma has been demonstrated in the current study for the first time.