Power function determination for sourness and time-intensity measurements of sourness and astrigency for selected acids

Graduation date: 1992Acids contribute important flavor characteristics to\ud many foods and beverages. They occur naturally in these\ud products, arise from fermentation processes, or can be\ud added. Most acids taste sour. However, little is known\ud about their time-intensity characteristics of sourness.\ud This project was set forth to see if selected acids could be\ud characterized, then differentiated according to their time-intensity\ud parameters of sourness. Astringency was also\ud evaluated since it seemed to be another common\ud characteristic of the acids. Power functions were\ud determined for the sourness to investigate the slopes of the\ud individual acids and also to calculate equi-sour\ud concentrations for the time-intensity study. It was found\ud that the slopes of the acids: acetic, lactic, fumaric,\ud fumaric-QD, citric, tartaric, and malic were not\ud significantly different. However, hydrochloric acid with a\ud slope value of 2.02 was significantly different than all of\ud the other acids that had slope values of about 1.25. This\ud study also showed that some panelists consistently responded\ud differently to the sourness of the acids. The time-intensity\ud studies showed that fumaric-QD and lactic acid\ud differed from each other in maximum intensity, area under\ud the curve, perimeter, and duration. Although hydrochloric\ud acid was strong in its overall impact parameters, it\ud elicited a short duration of sourness. The fruit acids -\ud tartaric, malic, and citric - were not very different from\ud one another in their sourness characteristics. For\ud astringency, hydrochloric acid was the most different from\ud all of the other acids mostly in the overall impact\ud parameters. For the time-intensity studies, the acids were\ud never significantly different in time to initial response\ud and time to maximum intensity. However, these two\ud parameters tended to be longer for the astringency response\ud as compared to the sourness response which suggests that\ud astringency occurs after sourness in the taste of acids.\ud Astringency/sourness ratios were calculated based on area\ud under the curve measurements and showed that hydrochloric\ud and lactic acid has significantly higher ratios than all of\ud the other acids indicating that lactic acid may also be an\ud astringent acid. Correlation among the time-intensity\ud parameters showed that the overall impact parameters correlated frequently with one another and occasionally with\ud duration. Peak area and peak time also correlated often.\ud Correlation between the sensory responses and the chemical\ud indices showed that the maximum intensity, area under the\ud curve, and perimeter correlated well with normality and PK[subscript a]\ud for sourness. For astringency, high correlations were found\ud between maximum intensity, area under the curve, and\ud perimeter with pK[subscript a], number of carboxyl groups, and molarity.\ud At level two, a strong relationship between pH and all other\ud time-intensity parameters except time to maximum intensity\ud and peak time is apparent. The principal component analysis\ud for sourness showed significant separation of lactic and\ud fumaric-QD in principal component one, and for astringency,\ud hydrochloric acid was significantly separated from the other\ud acids. Principal components two and three were not able to\ud significantly differentiate the acids