| More and more cases of excessive formaldehyde (FA) in dried fishery products such as shredded squid were reported in recent years, since formaldehyde is a protoplasmic poison and classified as A1 carcinogenic substance by International Cancer Research Agency (ICRA), food safety of shredded squid has become a social concern. It was found that a great amount of FA was produced during the shredded squid processing and the following storage, but little was reported about the production mechanism. Control technology can be achieved by studying the FA production mechanism and therefore ensure the food safety of shredded squid. The production mechanism, residue and control technology of FA in squid and dried fishery products were studied in this paper with Dosidicus gigas and its shredded products as materials. In order to explore the mechanism, FA and dimethylamine in fresh squid and shredded squid were determined during the storage, meanwhile an in vitro model system of TMAO-Fe(II) was established for a further confirmation. Possible chemical mechanism of formaldehyde production in shredded squids was explored; finally, suitable conditions for the storage of shredded squids were studied. The results were listed as below:1. Background content of FA in shredded squids. Among the 102 squid samples and 257 shredded squid samples, average value of FA in squid was 14.93 mg/kg, and 47.54mg/kg was for shredded squid, these experimental results confirmed the FA production during the processing. Different parts of squid was divided and their FA content were determined, the FA of squid viscera, muscle and head were ranged with order of amount, the FA content were 27.18mg/kg,7.59mg/kg and 5.36mg/kg, respectively. Significant differences of nonparametric test were found among those data. FA content in different layers of edible muscle were found to be inner layer the highest, middle layer the moderate and the outer layer the lowest, the FA content were 8.19mg/kg,7.93mg/kg and 7.21mg/kg, respectively, no significant differences of nonparametric test observed.2.4 species of squid samples were stored at -20℃for 8 months. Rapid increase of FA and DMA content were found in the first 2 months, the increasing rate declined in the following months, the FA and DMA content were stable during the last 3 months.3. Residual changes of FA during processing of shredded squid. Content changes of FA, DMA, TMA and TMAO were monitored during the overall processing of shredded squid made of Dosidicus gigas. It was found that the content of TMAO decreased during the overall processing, the content of DMA and TMA increased gradually. The increase of FA content was the most obvious, especially during the boiling and baking stages.4. Residual changes of squids soaked with FA solution. Squids and dried squids were soaked in FA solutions at different concentration. The FA absorption of squids and dried squids was confirmed, the residual content of FA increased as the raise of soaking time and concentration and accompanied with a pungent odor, at the same time, the content of FA of the FA solution was in a downward trend. Any fishery products soaked with FA solution could only remove the FA on the surface of the products and the smell, while the FA in the products would be harmful for human health.5. Thermal decomposition of TMAO model systems of shreded squid. The effect of heating temperature, heating time and pH on thermal decomposition TMAO was studied and compared with thermal decomposition of TMAO of water extraction from shredded squid; TMAO-Fe(II) model systems of shredded squid were employed to study the thermal decomposition of TMAO. The results showed that:with the temperature increases, the reaction of thermal decomposition of TMAO is severe; after heating for 30min, the content of FA and DMA remained stable; when pH value is 5.0, Fe2+ could promote the thermal decomposition of TMAO most significantly. This study further showed that the effect of 8 additives on thermal decomposition of TMAO. With EDTA, Vc, Cys, Fe3+ added, they served as basis for controlling FA in shreded squid afterwards. The study showed that there was a little impact on formation of FA by those additives. Sucrose played a weak role in promoting the formation of FA; Fe2++Vc,Fe3++Vc,Fe2++Cys,Fe3++Cys,Fe2+could significantly increase the formation of FA. At the same time, citric acid and tea polyphenols could decrease the content of FA, which can be used as an ideal inhibitor in squid.6. Effects of different storage conditions and packaging on the FA content of shreded squid. The effects of different storage conditions (temperature, humidity and light) and packaging methods (vacuum, common and bulk packaging) on the changes of FA content of shreded squid were investigated. The results showed that the shredded squid could produce FA during storage time, and the storage conditions affecting the content of FA of shreded squid mainly include temperature, humidity, light and packaging methods, meanwhile, low-temperture, high humidity, darkness and common packaging could delay the changes of FA content, providing some reference for the storage conditions and packaging methods of the shreded squid.The study determined the background content of FA in squids and shreded squid, and monitored FA content in shreded squid during processing and storage, which proved that the squid could produce FA during the processing and storage. At present, FA formation mechanism of shreded squid has not been reported, and this study combined with TMAO-Fe (Ⅱ) model system to reveal the factors affecting the reaction, and studied the suitable materials and conditions for the packaging of shredded squid to control endogenous formaldehyde, providing technical reserves to ensure the safety of shreded squid.
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