24-3

K. R. CONCA, Combat Feeding Program, Natick Soldier Center, US Army SBCCOM, Kansas Street, Natick, MA 01760-5018 and W. L. Porter.

(1) JUSTIFICATION : Severe thermal abuse inflicted by retort processing often results in a poor texture quality of fruits and vegetables. There is a need for a higher quality or crunchy firm texture of canned fruits and vegetables. An alternative process without the need for significant equipment changeover would be preferable for industry. Phenolic acids have been implicated and may be effective in creating structural cross-linkages within plant cell walls which strongly influence the texture of plant foods.

(2) OBJECTIVE : Investigations of crosslinking cell wall components either through intrinsic or added compounds such as ferulic acid, a phenolic acid were conducted using the enzymes peroxidase and laccase.

(3) METHODS : Cross linking experiments were conducted with the enzymes peroxidase and laccase, both with free ferulic acid solutions and on homogenized beet tissue, with and without added free ferulic acid. Beets were homogenized and washed to remove the betanin beet color, to prevent fluorescence and absorbance interference. An enzyme was added to test solutions and ferulic acid polymerization was monitored over time by solution fluorescence. Front face fluorescence was used to analyze homogenized beet tissue.

(4) RESULTS : Esterified ferulic acid within homogenized beet tissue and spectral shifts upon adding NH₄OH can be detected by front face fluorescence. A red shift in the excitation fluorescence spectrum ranging from 20-30nm was observed after incubation of the laccase enzyme with a ferulic acid solution at pH 7. A red shift was also seen in the emission fluorescence spectrum of about 16nm. The shifts seen in both the excitation and emission fluorescence spectra were time dependent.

(5) SIGNIFICANCE The fluorescence shifts were indicative of an extension of the ferulic acid conjugation suggesting a polymerization and possible cross-linking. Front face methods thus permit monitoring of oxidative cross-linking of esterified ferulic acid in cell walls.