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

by Straub, Angela Marie

Abstract (Summary)
Acids contribute important flavor characteristics to

many foods and beverages. They occur naturally in these

products, arise from fermentation processes, or can be

added. Most acids taste sour. However, little is known

about their time-intensity characteristics of sourness.

This project was set forth to see if selected acids could be

characterized, then differentiated according to their time-intensity

parameters of sourness. Astringency was also

evaluated since it seemed to be another common

characteristic of the acids. Power functions were

determined for the sourness to investigate the slopes of the

individual acids and also to calculate equi-sour

concentrations for the time-intensity study. It was found

that the slopes of the acids: acetic, lactic, fumaric,

fumaric-QD, citric, tartaric, and malic were not

significantly different. However, hydrochloric acid with a

slope value of 2.02 was significantly different than all of

the other acids that had slope values of about 1.25. This

study also showed that some panelists consistently responded

differently to the sourness of the acids. The time-intensity

studies showed that fumaric-QD and lactic acid

differed from each other in maximum intensity, area under

the curve, perimeter, and duration. Although hydrochloric

acid was strong in its overall impact parameters, it

elicited a short duration of sourness. The fruit acids -

tartaric, malic, and citric - were not very different from

one another in their sourness characteristics. For

astringency, hydrochloric acid was the most different from

all of the other acids mostly in the overall impact

parameters. For the time-intensity studies, the acids were

never significantly different in time to initial response

and time to maximum intensity. However, these two

parameters tended to be longer for the astringency response

as compared to the sourness response which suggests that

astringency occurs after sourness in the taste of acids.

Astringency/sourness ratios were calculated based on area

under the curve measurements and showed that hydrochloric

and lactic acid has significantly higher ratios than all of

the other acids indicating that lactic acid may also be an

astringent acid. Correlation among the time-intensity

parameters showed that the overall impact parameters correlated frequently with one another and occasionally with

duration. Peak area and peak time also correlated often.

Correlation between the sensory responses and the chemical

indices showed that the maximum intensity, area under the

curve, and perimeter correlated well with normality and PK[subscript a]

for sourness. For astringency, high correlations were found

between maximum intensity, area under the curve, and

perimeter with pK[subscript a], number of carboxyl groups, and molarity.

At level two, a strong relationship between pH and all other

time-intensity parameters except time to maximum intensity

and peak time is apparent. The principal component analysis

for sourness showed significant separation of lactic and

fumaric-QD in principal component one, and for astringency,

hydrochloric acid was significantly separated from the other

acids. Principal components two and three were not able to

significantly differentiate the acids.

Bibliographical Information:

Advisor:McDaniel, Mina R.; Wrolstad, Ron

School:Oregon State University

School Location:USA - Oregon

Source Type:Master's Thesis

Keywords:organic acids analysis food sensory evaluation flavor


Date of Publication:10/06/1989

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