Kinetics of Maneb Degradation during Thermal Treatment of Tomatoes

Abstract

The kinetics of maneb degradation in tomato homogenates at high temperatures and at two pH values (4 and 9) and the rate of formation of the toxic metabolite, ethylenethiourea (ETU), were studied. Maneb was measured as carbon disulfide by headspace gas-chromatography and ETU by high-performance liquid chromatography with photodiode array detection. First-order kinetics adequately described the degradation of maneb in tomato homogenates. The degradation rate constants exhibited an Arrhenius temperature dependence in the range from 50 to 90 degrees C and the apparent activation energy (E(a)) was calculated to be 36 KJ mol(-1) in homogenates with natural pH (4). Raising temperature from 60 to 75 and to 90 degrees C, ETU formation was significantly increased. Interestingly, the selectivity toward ETU showed a downward trend when the total conversion increased at longer heating times. When the pH of the tomato homogenates was adjusted to 9, the degradation of maneb proceeded faster at both 60 and 90 degrees C. The combination of alkaline pH and the highest temperature (90 degrees C) resulted in the maximum ETU conversion rates. The results of the present study on the fate of maneb and ETU residues during tomato processing, may prove valuable in estimating potential risk from dietary exposure.

Preliminary study of the volatile fraction in the raw meat of pork, duck and goose

“…Normally sulphur compounds are created from sulphur-containing amino acids (cysteine and methionine) developed by proteolysis enzymes contained in psychotropic bacteria (such as Enterobatteriacee, usually present in slaughterhouses). Carbon disulphide can also derive from ethylene-bis-dithiocarbamates fungicides used in agriculture (Kontou et al, 2004).…”

Fate of Pesticide Residues on Raw Agricultural Crops after Postharvest Storage and Food Processing to Edible Portions

“…In particular, pesticides such as carbamates, amides, ureas, thiocarbonyl and those containing imino groups may be readily hydrolyzed in the presence of trace amounts of acid and/or base during heating or boiling. On this topic, a substantially amount of work (Chavarri et al, 2005;Kontou et al, 2004a;Kontou et al, 2004b;Knio et al, 2000) has been published on the fate of pesticide residues of dithiocarbamates and the more toxic ETU that during cooking concluding that during cooking dithiocarbamates may be conversed to ETU by a factor of 30-48%. Although, ETU residues during boiling may pass into the boiling water, a significant amount remains in the processed food.…”

Effects of chlorine, hydrogen peroxide, and ozone on the reduction of mancozeb residues on tomatoes

“…Food processing is the major pathway by which exposure to ETU occurs. In particular, thermal treatments are associated with the higher conversion factors of EBDCs to ETU (Knio et al, 2000;Kontou et al, 2004;Kaushik et al, 2009;Certel et al, 2012). Tomato is frequently subjected to thermal treatments such as evaporation, blanching, sterilizing, and canning in order to be consumed as juice, paste, ketchup, or canned products.…”