2.2. Products

Four food models were developed using commercially available base ingredients. In the early stages of the Italian Taste project, we developed recipes and preparation procedures to obtain semisolid products that were easy to prepare, preserve, and serve. Pear juice (PJ), chocolate pudding (CP), bean purée (BP), and tomato juice (TJ) were selected as the most appropriate food models to test the responses towards a series of TSs. For each food model, four different concentration levels varying in TS were developed. Each level was expected to increase the perceived TS intensity and, in parallel, increase or decrease the responsiveness to other oral sensations characterizing that specific food model. The ingredient composition and tastant concentration levels within each food model and the oral sensations measured are listed in Table 1.

Food models: food product (PJ = Pear Juice, BP = Bean Purée, CP = Chocolate Pudding, and TJ = Tomato Juice), ingredients, ingredient brand, tastant concentration at each level, target, and other measured sensations are reported (tastants responsible for the target sensation are written in bold).

The four concentration levels of PJ were prepared to obtain different amounts of citric acid in each sample. The addition of citric acid was expected to increase sourness (TS) while decreasing sweetness. For CP, four concentration levels varying in the amount of sucrose were developed. The addition of sucrose was expected to increase sweetness (TS) while decreasing bitterness and astringency. The four concentration levels of BP were prepared by adding different amounts of sodium chloride. This addition was expected to increase saltiness (TS) and enhance the umami taste. A last series of samples for TJ was prepared to obtain four different capsaicin concentrations. The addition of capsaicin was expected to increase pungency (TS) but also to impact sourness and sweetness. The TS stimuli concentrations were chosen based on published psychophysical data reported by Monteleone and colleagues [2], and verified by preliminary tests with trained panels (unpublished data).

To assess individual responsiveness to chemosensory stimulation, seven aqueous solutions containing only one stimulus at a time were included in the study. The stimuli corresponded to the basic tastes (i.e., bitterness, sourness, sweetness, saltiness, and umami), the chemesthetic sensation of pungency, and the tactile sensation of astringency. The aqueous solutions were prepared to elicit an expected moderate/strong sensation on a general Labeled Magnitude Scale (gLMS) presented in vertical position [51]. The concentrations of the chemical reagents (European Pharmacopoeia Reference Standard Sigma-Aldrich, Milano, Italy) were as follows: citric acid, 4 g/kg (sourness); caffeine, 3 g/kg (bitterness); sucrose, 200 g/kg (sweetness); sodium chloride, 15 g/kg (saltiness); monosodium glutamate, 10 g/kg (umami); capsaicin, 1.5 mg/kg (pungent); and aluminium sulphate, 0.8 g/kg (astringency).

To assess participants’ PROP taster status, supra-threshold 3.2 mM PROP solution was prepared by dissolving 0.5447 g/L of 6-n-propyl-2-thiouracil (European Pharmacopoeia Reference Standard, Sigma-Aldrich, Milano, Italy) in deionized water in accordance with the PROP status assessment procedure described in [52].