Kinetic approach of the thermal degradation of b-cryptoxanthin in an aqueous model system of cashew apple juice

L. Q. ZEPKA; C. D. BORSARELLI; R. JORGE; A. Z. MERCADANTE

UNICAMP, Campinas, Brasil

Simposio; 7o SIMPOSIO LATINO AMERICANO DE CIENCIAS DE ALIMENTOS; 2007

FEA-UNICAMP

The kinetic of the thermal degradation at 90 oC of the xanthophyll all-trans--cryptoxanthin (C40H56O) was studied by high performance liquid chromatography (HPLC) connected to a diode array and a mass spectrometer detectors in 20% ethanol aqueous solution acidified at pH 3.8 with 0.5 M of citric acid (CA). The HPLC analysis showed that ca. 92% of all-trans--cryptoxanthin was consumed after 120 min of heating. The major degradation products (ca. 76%) were not detected in this system and are most probably volatile compounds. The minor product fraction of non-volatile compounds (ca. 16%) were distributed mainly in several cis-isomers of -cryptoxanthin (C40H56O), e.g. 9-cis, 13-cis, 15-cis, and traces of oxidation products, such as 5,6-epoxy--cryptoxanthin (C25H56O2) and 12’-apo-3-hydroxy--caroten-12’-al (C25H34O2). The decay of -cryptoxanthin and the growth of the products showed bi-exponential behaviour kinetics with observed first-order rate constants,g1 = 4.1x10-2 min-1 and g2 = 6.3x10-3 min-1, respectively. Considering a global kinetic model where all-trans-b-cryptoxanthin is reversible transformed to all cis-isomers (k1 and k-1) and irreversible degraded to oxidation and unknown volatile products (k3), the solution of the differential equations set showed that the forward and reverse trans-cis isomerization rate were k1 = 9.0x10-3 min-1 and k-1 = 5.4x10-3 min-1, respectively. The formation of degradation products (non- and volatile) was larger, k3 = 4.6x10-2 min-1. These values indicate that the formation of degradation compounds is the major route of thermal transformation of b-cryptoxanthin. On the other hand, a very high stability of b-cryptoxanthin at room temperature was observed by UV-vis spectrophotometer analysis, indicating that high activation energy (Ea > 20 kcal/mol) is required for thermal degradation of b-cryptoxanthin. In addition, the presence of citric acid (0.5 M, pH 3.8) does not affect the degradation of b-cryptoxanthin at room temperature. Keywords: thermal degradation; model system, kinetic model Acknowledgement: The authors thank FAPESP for financial support.