FT-IR spectroscopic determination of the degree of esterification of cell wall pectins from stored peaches and correlation to textural changes

The FT-IR spectroscopic study of peach cell walls revealed the existence of two peaks absorbing at 1749 and 1630 cm(-1) assigned, respectively, to the absorption of the esterified and non-esterified carboxyl groups of the pec tin molecules. A linear relationship between the degree of esterification [ (number of esterified carboxylic groups/number of total carboxylic groups) x 100] and the ratio of the area underneath the peak at 1749 cm(-1) over th e sum of the areas underneath the two peaks, at 1749 and 1630 cm(-1), was e stablished using the FT-IR spectra of standard compounds. The use of the 2n d derivative and curve-fitting techniques allowed the elimination of spectr al interferences from other cell wall components. The degree of esterificat ion (D.E.) of pectins from Redhaven peaches immediately after harvest and d uring storage was evaluated from FT-IR data. During storage at 0 degrees C, the D.E. remained practically constant up to 35 days. During storage at hi gher temperatures it decreased approaching a final value - the same for all temperatures. This value was reached after 22 days of storage at 5 degrees C, 15 days at 15 degrees C and after only 6 days at 20 degrees C. The chan ges in the degree of esterification during storage correlated well to fruit firmness. (C) 1998 Elsevier Science Ltd. All rights reserved.