39B-7

S. T. TALCOTT, Institute of Food Science and Engineering, University of Arkansas, 272 Young Ave, Fayetteville, AR 72704 and L. R. Howard.

A temperature dependant decline in pH occurs in strained carrots during thermal processing and long-term storage that increases the sensory perception of bitter and sour flavors, leading to loss of quality. Identification of the mechanism(s) responsible for the pH decline would allow for development of control strategies.

Our objective was to investigate possible chemical mechanisms responsible for the decline in pH of strained carrots after thermal processing and storage at elevated temperatures.

Based on preliminary studies, changes in pectic substances were implicated as potential mechanism(s) responsible for the pH decline. Therefore, a 2% aqueous slurry of alcohol insoluble solids (AIS) isolated from fresh and ethylene treated carrots, was vacuum hydrated, and treated with alkali (pH 10), acid (pH 4), and sulfite (1mM) as compared to a control. Slurries were retorted for 30 min. at 250°C and stored at elevated temperatures (40 and 60°C) for six days. Chemical analysis included changes in water, chelator, and dilute alkali soluble pectic substances. Free galacturonic acid and phenolic acids liberated after thermal processing and storage were separated and quantified by HPLC.

Free galacturonic acid liberated during processing decreased the slurry pH during processing. Release of cell wall bound phenolic acids caused a pH decline of 0.37 units during storage between samples stored at 40°C versus 60°C, demonstrating a temperature dependent reaction. The initial pH of each pretreatment affected the declines in pH during thermal processing and storage due to altered buffering capacity of the model system. Thermal processing and storage caused hydrolysis of 25% of the wall-bound phenolic compounds with p-hydroxybenzoic acid being the predominant compound released.

Identification of mechanisms responsible for declines in pH will assist food processors in developing strategies to control flavor changes during processing and storage.