Chemical Determinants of Sourness and Related Attributes
Restricted (Penn State Only)
- Author:
- D'Andrea, Astrid
- Graduate Program:
- Food Science
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- March 07, 2025
- Committee Members:
- Helene Hopfer, Thesis Advisor/Co-Advisor
Ryan John Elias, Committee Member
Robert Roberts, Program Head/Chair
John Hayes, Thesis Advisor/Co-Advisor - Keywords:
- citrate
citric acid
counterion
liking
pH
titratable acidity
organic acids
lactic acid
malic acid
fumaric acid
tartaric acid
perception - Abstract:
- Sourness is one of the five basic tastes and its role in perception is initiated by the presence of organic and inorganic acids. In addition to sourness, acids can induce other attributes such as puckering and drying. The following two experiments demonstrate the effect of varying organic acid and/or organic salt chemical properties on perception and liking. For both experiments, participants who were frequent consumers of sour foods and/or beverages (i.e., at least once a month) were recruited to taste a series of sour stimuli. Participants rated the intensity of six attributes (sour, puckering, drying, salty, bitter, sweet) on general Labeled Magnitude Scales (gLMS). For Experiment 2 only, participants also rated solution liking on a visual analogue scale. Dose-response functions were then generated for each experiment, and these functions were used to determine the effect of the different stimuli on sourness and related attributes, namely puckering and drying. In Experiment 1 (Chapter 2), the stimuli were equimolar mixtures of citric acid and citrate salts (monosodium citrate, disodium citrate, trisodium citrate, tripotassium citrate) at three sequential log-step concentrations. Total solution concentration had a significant effect on all six attributes. Dose-response functions revealed a general increase in sourness, puckering, and drying as total concentration increased. The effect of the counterion (defined as the cation in the citrate molecule) was also established. Specifically, the number of counterions (i.e., 1, 2, 3 sodium ions) significantly affected sourness [F(2, 1386) = 15.03, p < 0.01], puckering [F(2, 1386) = 14.37, p < 0.01], and drying [F(2, 1386) = 151.02, p < 0.01], but not saltiness, bitterness, or sweetness (all p > 0.05). The effect of the counterion type (i.e., sodium and potassium) significantly affected sourness [F(1, 918) = 3.89, p = 0.05] and saltiness [F(1, 918) = 8.15, p = 0.01], but not the other attributes. In Experiment 2 (Chapter 3), the stimuli were equimolar single organic acid solutions of lactic acid, malic acid, fumaric acid, tartaric acid, and citric acid at four sequential log-step concentrations. Total concentration had a significant positive effect on sourness, puckering, and drying intensity. Dose-response functions revealed key differences in the attribute intensities based on the organic acid type. Citric acid, a triprotic acid, was more sour and puckering than the other diprotic and monoprotic acids. On the other hand, lactic acid, a monoprotic acid, was less sour and puckering. According to a linear mixed effects model, the effect of the change from lactic acid to the other acids on sourness was strongest for fumaric acid (10.9 ± 2.14; p < 0.01), followed by malic acid (10.8 ± 2.15; p < 0.01), tartaric acid (7.83 ± 2.14; p < 0.01), and citric acid (6.06 ± 2.65; p = 0.02). The collection of affective data allowed for the segmentation of consumers into three sour phenotypes: (1) a strong negative group that showed a strong decrease in liking with increasing concentration, (2) a weak positive or negative group where liking decreased more gradually, and (3) a strong positive group where liking increased with increasing concentration. Within the phenotypes, liking differed based on organic acid type, which may be a result of the influence of sour related attributes, such as puckering, drying, and bitterness, on liking.