Ultraviolet light induced degradation of patulin and ascorbic acid in apple juice.

摘要

The overall goal of this research was to study the effect of UV processing on patulin (a mycotoxin commonly found in apple cider and juice) and ascorbic acid (vitamin C) in model apple juice system and in apple juice.;The first objective was to study the kinetics of patulin degradation during exposure to UV light in 0.5% malic acid buffer (model apple juice system). A collimated-beam batch UV (254 nm) apparatus was used. The effects of added ascorbic acid (AA), tannic acid, and suspended solids on patulin degradation in 0.5% malic acid buffer were studied using Box-Behnken design. Results showed a first order degradation kinetics for patulin. The degradation rate constant (cm2/J) was not significantly affected by incident intensity (0.8--1.8 mJ/cm2) (p>0.05), buffer pH (3.0--3.6) (p>0.05) and initial concentration of patulin (0--1000 ppb) (p>0.05). Presence of tannic acid, (0--1 g/L) and suspended particles (0--100 NTU) significantly reduced the patulin degradation rate constant (p0.05), while AA (0--100 mg/L) did not affect the reaction rate constant (p>0.05).;The second objective was to study the UV induced degradation of AA in 0.5% malic acid buffer (apple juice model system) and in apple juice. AA degradation occurred more rapidly in juice compared to 0.5% malic acid. Further studies demonstrated that UV degradation of AA in 0.5% malic acid was more rapid at higher UV dose levels and that reaction deviated from zero order. AA degradation did not change significantly (p>0.05) between pH 2.4 and 3.3, but increased as the pH of the buffer was raised from 3.3 to 5.5 (p0.05). Increasing malic acid concentration between 0.1 and 1%, at a constant pH of 3.3, increased AA degradation (p0.05) although there was no difference between 0.5 and 1.0% (p>0.05). With increasing concentration of tannic acid in buffer, AA degradation rate decreased significantly (p0.05), possibly due to competitive absorption of UV light. Addition of 10% sucrose to buffer showed no significant effects (p>0.05), but addition of 10% glucose decreased AA degradation (p0.05). However, addition of 10% fructose increased AA degradation significantly (p0.05), perhaps due to breakdown products of this sugars reacting with AA. AA degradation in malic acid and in apple juice continued during storage in the absence of light. Post UV treatment degradation was more rapid at higher initial UV dose levels and at higher storage temperature.;The third objective was to understand the mechanism of UV induced AA degradation. Electron paramagnetic resonance (EPR) spectroscopy studies demonstrated that ascorbate radicals formed in AA solutions in phosphate buffer at pH 7.0 and in malic acid buffer between pH 3.3 and 6.0. Lesser amounts of ascorbate radicals formed at lower pH levels and only trace amounts were detected at pH 3.3. Ascorbate radicals in UV treated AA solutions continued to form at higher rates than that for identically stored untreated AA solution. High pressure liquid chromatography-mass spectroscopy (HPLC-MS) analysis of UV treated samples demonstrated that as AA levels decreased, dehydroascorbic acid (DHA) and 2, 3-diketogulonic acid (DKGA) levels increased. We propose that UV processing of AA leads to formation of ascorbate radical that leads to the formation of DHA, which further degrades into DKGA.