Quinine hydrochloride

As taste stimuli, we used a “sweet solution” consisting of a mixture of 0.125% saccharin and 3% glucose (both Sigma-Aldrich, St Louis, MO) or a “bitter solution” consisting of 0.15% (0.0038 M) quinine hydrochloride (Sigma-Aldrich). The saccharin-glucose mixture is avidly ingested by rats [12] (link); the 0.15% quinine is strongly disliked–tasting it elicits negative hedonic responses (i.e., gapes and chin rubs) and it is almost completely avoided in two-bottle preference tests [7] (link). As an intragastric fat load, 20% intralipid was purchased from Sigma-Aldrich (Cat. No. I-141). Radioactive ¹⁴C-triolein was purchased from American Radiolabeled Chemicals Inc (St Louis, MO) and stored at −20°C until use.
The following enzymatic colorimetric kits or ELISA kits were used for the assay of blood components; triglycerides, ketones, glycerol and glucose from Cayman Chemical Co. (Ann Arbor, MI); non-esterified fatty acid from Wako Diagnostics (Richmond, VA); insulin from Alpco Diagnostics (Windham, NH); total GIP, total GLP-1 and leptin from Millipore (Billerica, MA); peptide YY and cholecystokinin from Phoenix Pharmaceuticals (Belmont, CA).

The chalcones were synthesized at the Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences, Sofia, Bulgaria. Chloroquine phosphate, quinine hydrochloride, glutamine, sodium bicarbonate, and β-haematin were purchased from Sigma Aldrich while artemisinin was from IPCA. The study was approved by Institute Ethics Committee Project No. NK/1265/Ph.D/23991 at Post Graduate Institute of Medical Education and Research, Chandigarh, for maintenance of P. falciparum strains in human erythrocytes and AB^+ve human serum.

Chocolate adulteration provides information concerning flexibility of food intake under aversive conditions. Mice were given a free choice between SC and a pellet of the CM adulterated with quinine hydrochloride (Sigma-Aldrich) 1-g/kg food to give it a bitter taste. According to Heyne et al. (2009) (link), flexible mice will avoid or decrease the intake of CM.

Fifteen subjects were recruited among regular eaters of sausages (defined as consuming the product at least once a week). Ten panelists were selected (four males and six females, between 29 and 61 yr. of age) in accordance with ISO standards [26 ]. For this purpose, the four basic tastes were used [27 (link)]. For this purpose, sucrose (Carlo Erba, Milan, Italy), sodium chloride (Carlo Erba, Milan, Italy), citric acid (Carlo Erba, Milan, Italy) and quinine hydrochloride (Sigma-Aldrich, St Louis, MO, USA) at three levels each were used [27 (link)]. The panelists were informed about the taste of each basic concentration. Then, a 10 mL quantity of high and low concentration for each taste solution was served blind. The panelists rinsed their mouths with filtered, de-ionized water between tests. De-ionized water was also used to prepare two blanks. Totaling ten samples (taste solutions and blanks) were presented in random order. The panelists had to identify the intensity (low and high) of each taste solution. The inability to recognize eight out of the 10 taste solutions was used as cutoff point for selection purposes [27 (link)]. Afterwards, panelists were trained for the scale use [28 ].

_L-Tryptophan, _L-isoleucine, denatonium benzoate, quinine hydrochloride, caffeine, salicin, and sucrose were purchased from Sigma (St. Louis, MO, USA). Epigallocatechin gallate was provided by Taiyo Chemicals (Mie, Japan). All compounds were dissolved in deionized water to obtain the indicated concentrations.
The concentrations of bitter solutions used in this study are listed in Table 1. Pilot studies were conducted to determine the concentrations of each compound used in the two-bottle choice tests so that they spanned the range from indifference to marked avoidance [18 (link), 19 (link)]. The concentrations used for conditioned taste aversion (CTA) were set near the aversion threshold in naive animals (NE group). The concentrations used during prolonged exposure periods were the same as those for CTA except for CAF. Lower concentrations of CAF were used during taste aversion conditioning and prolonged exposures because mice exposed to high concentrations of CAF for a long time exhibited abnormal behaviors such as disruption of the day-night cycle and agitated and highly active states in a pilot study.