Study Of Some Plant Extracts And Food Additives On Protection Of Salted Dried Fish From Chrysomya Megacephala Infestation

Salted dried fish, a main kind of traditional processing seafood products in Zhejiang province, is processed very popularly in the coastal area. But it is prone to be infested by blowfly, which is a major cause of post-harvest losses of salted dried fish during traditional processing. Besides, blowfly infestation will make the fish present a bad appearance so as to lower its value. At present, many processors use inappropriate insecticides to protect the fish from blowfly infestation, which adversely affect the safety production of salted dried fish, and also threaten the consumers' health.Laboratory studies on the effects of azadirachtin, stabilized chlorine dioxide, natural pyrethrin, teasaponia and capsaicin on repellence, oviposition, larval growth and mortality of blowfly, chrysomya megacephala, during the salted dried fish processing were carried out. The result on the repellence and oviposition indicated that azadirachtin, natural pyrethrin and capsaicin could repel chrysomya megacephala and inhibit its oviposition on fish during the drying days. The inhibition concentration (IC) of them were 21.54 mg/L, 3.31 mg/L and 218.57 mg/L respectively for IC₅₀, 167.75 mg/L, 17.56 mg/L, and 2690.69 mg/L for IC₉₅ during the first drying day, and 31.52 mg/L, 5.05 mg/L, 102.24 mg/L for IC₅₀, 286.67 mg/L, 28.01 mg/L and 903.24 mg/L for IC₉₅ during the second drying day. Stabilized chlorine dioxide could also repel chrysomya megacephala and inhibit its oviposition, but it is effective only for one day. The IC₅₀ and IC₉₅ were 37.14 mg/L and 608.26 mg/L respectively. The result on larval growth and mortality showed that azadirachtin could strongly inhibit larval growth and kill the larvae on the fish. A concentration of 54 mg/L gave a reduction of larval growth by 2/3 and a correction mortality of larvae by 78.76% as compared with the control group. Natural pyrethrin had no influence on larval growth, but it was largely lethiferous to larvae. Concentration of 8 mg/L and 16 mg/L achieved 85% and 100% correction mortality of larvae. While stabilized chlorine dioxide, teasaponia and capsaicin had no effects on larval growth and mortality.The effects of stabilized chlorine dioxide on the acid value and peroxide value of the salted dried fish during storage were also investigated. The result showed that, stabilized chlorine dioxide could increase peroxide value on fish, but had no effect on acid value. During the experiment, the acid value and peroxide value on fish of all treatments were significantly below the standard hygiene requirements.The research on the residues of natural pyrethrin on salted dried fish showed that, the residues on the fish treated by natural pyrethrin at the concentration of 32 mg/L were more than 3 mg/kg, the maximum residue limits (MRL) fixed by FAO/WHO, at the first drying day. But all the other treatments were less than 3 mg/kg at the first drying day, and the residues were less than 0.01 mg/kg after 14 days of storage for all samples.