Kinetics of Thermal Degradation of Chlorophyll in Spinach Puree^a

Abstract

SUMMARY The kinetics of chlorophyll degradation in spinach purée were studied over the temperature range 260—300°F, using thermal‐death‐time tubes heated in a constant‐temperature oil bath. Pigments were separated by column chromatography, and their concentrations determined spectrophotometrically. A semilogarithmic (first‐order) plot of the residual pigment vs. time was used to illustrate the thermal degradation rate (TDR). Although the major portions of the TDR curves were apparently linear, several abnormalities were observed during the initial test intervals. Regression coefficients were computed for the linear portions and used to compute the various thermo‐dynamic functions characteristic of the degradation reactions. The following values respectively represent the average determinations for chlorophylls a and b. The TDR constant k, (2.3/D, D, D being decimal reduction time in sec), 1.1 × 10−2 and 0.52 × 10−2 sec−1; the temperature coefficient Q10 (log−1 18/z, z being °F affecting 10‐fold change in k, or D), 1.58 and 1.26; the activation energy E, 143 and 35 Kcal mole−1; the enthalpy H, 142 and 34 Kcal mole−1; the free energy & Delta;F, 29 and 32 Kcal mole−1; and the entropy & Delta;S, 268 and 5 cal deg−1 mole−1.

Thermal Degradation Kinetics of Chlorophyll in Pureed Coriander Leaves

“…This was also found to be in incongruity with the generally perceived notion that higher the alkalinity more is the chlorophyll stability. This contradiction may be attributed to the fact that in earlier works, the alkaline pH was attained with the addition of organic or inorganic salts of alkaline earth metals (mainly MgCO 3 ) to aid in replenishment of Mg 2+ ions of chlorophyll removed during thermal degradation (Gupte and Francis 1964). However, in the present study, we intended to study the effect of only alkalinity without the compensatory effect of any additional magnesium salt to replenish the degraded chlorophylls, therefore pH was adjusted with 1 N NaOH solution.…”

“…Addition of MgCO 3 to increase the pH of spinach puree when combined with HTST process improved chlorophyll retention only initially; the effect was, however, unstable during storage (Gupte and Francis 1964). Magnesium compounds also resulted in the formation of hard white crystals of magnesium-ammonium-phosphate (Eheart and Odubi 1973).…”

“…Others have attempted to retard the formation of pheophytin and preserve the color by pH control (Clydesdale and Francis 1968) by minimizing heat exposure by applying HTST (Tan and Francis 1962), or by combining HTST with pH adjustments (Gupte and Francis 1964;Clydesdale et al 1970). The major finding of these studies is that both pigment and visual color degradation during thermal processing follows the first-order reaction kinetics.…”

“…A number of researchers (Gupte and Francis 1964;Gunawan and Barringer 2000) have demonstrated the higher stability of chlorophylls at alkaline pH levels. Addition of MgCO 3 to increase the pH of spinach puree when combined with HTST process improved chlorophyll retention only initially; the effect was, however, unstable during storage (Gupte and Francis 1964).…”

Quality of Cucumbers Commercially Fermented in Calcium Chloride Brine without Sodium Salts

“…Color changes in cucumbers exposed to acidic brines have been shown to occur by the production of a combination of pheophorbide and pheophytin pigments [40]. This degradation of brightly colored green chlorophyll to pheophorbide and pheophytin produces a dull olivegreen or olive-yellow color in food products [41]. Fermenting cucumbers have very small concentrations of chlorophyllide, but pheophytin accumulates in large concentrations, so it has been modeled that the accumulation of pheophorbide occurs predominantly using chlorophyllide as an intermediate, while the pathway from pheophytin to pheophorbide is rarely used [39,42].…”