Effect Of Chlorine Dioxide Fumigation Combined With Modified Atmosphere Packaging (MAP) On Fresh Walnuts Preservation

As one of the main varieties of walnuts in Xinjiang,’Wen 185’thin-skinned walnut is deeply loved by consumers because of its thin skin,full of nuts and excellent quality.At present,the consumption demand for green-skinned walnuts,fresh walnuts（i.e.peeled fresh walnuts）and fresh walnut kernels are increasing.Although clean shell and easy to eat,wet walnut has gradually become the mainstream product sold in the market,but the key problems of moldy seed shell,stickiness and deterioration of seed kernel quality in the process of product circulation and shelf sales have not been effectively solved,which seriously restrict the product supply and industrial development.Chlorine dioxide（Cl O₂）as an internationally recognized and widely used green and safe spectrum antibacterial and preservative agent,has also been preliminarily confirmed on the mildew control effect of fresh walnuts,spontaneous modified atmosphere packaging（MAP）technology has also made certain research progress in prolonging the storage quality of fresh walnuts,reducing dry consumption and delaying the mechanism and effect of nucleolar rancidity.Therefore,Using the dual effect control technology of Cl O₂bacteriostasis and MAP preservation,aimingat developing the application technology of storage,transportation and preservation suitable for the main fresh walnut varieties in our area,and taking’Wen 185’fresh walnuts as the experimental material,test and analyze（0±1）℃,relative humidity（RH）75%～85%,the effects of different concentrations of Cl O₂atomization fumigation and PE film modified atmosphere packaging with different gas transmittance,The suitable technical parameters for regulating the bacteriostatic effect of wet fresh walnut seed shell and nucleolar quality were selected.On this basis,the compound preservation effect of Cl O₂fumigation combined with MAP on fresh walnut was evaluated and confirmed,In order to provide theoretical reference and scientific basis for the storage,transportation and preservation of fresh walnut.The main conclusions are as follows:（1）The effect of different concentrations of Cl O₂（0,50,100 and 150 mg/L）fumigation treatment of fresh walnuts were studied.Compared with CK,Cl O₂fumigation treatment could significantly inhibit the occurrence of mold on the surface of walnut nuts,reduce the seed coat browning index,maintain the freshness of walnut and better sensory quality of nucleolus,and maintain the acid value and chlorine dioxide residue content at a low level.Among them,100 mg/L and 150 mg/L Cl O₂treatment could delay the occurrence time of mold on the seed shell of fresh walnut by 7 days,and the mold rate decreased by10.67%and 7.33%respectively compared with the control group.Comprehensive analysis showed that fumigation with 100 mg/L Cl O₂had the best effect.When stored for 49 days,the sensory quality grade was2.3,and the good fruit rate reached 86.67%.（2）The effects of different MAP treatments（CK,PE30,PE40 and PE50）on the preservation of fresh walnut were studied.MAP could significantly inhibit the Postharvest respiration rate and ethylene release of fresh walnut fruit,and delay the decline of nucleolar quality.Among them,PE40 packaging（CO₂concentration in balanced bag was 3.20%～4.00%,O₂concentration was 16.90%～17.80%）had the best fresh-keeping effect,which could significantly delay the deterioration of polyunsaturated fatty acids and oil oxidation rate in nucleolus,and reduce the water loss of nucleolus,mass loss and oxidative browning degree of seed coat,It maintained high sensory quality and good fragrance flavor.（3）The effects of ClO₂ fumigation combined with MAP on the preservation of fresh walnut were studied.Compared with Cl O₂（100 mg/L Cl O₂）single treatment,MAP（PE40）and Cl O₂+MAP combined treatment could more effectively inhibit fruit respiration rate;Compared with single MAP treatment,Cl O₂+MAP treatment significantly delayed the occurrence time of fruit surface mildew;The compound treatment has the best fresh-keeping effect,prolonging the storage period for 7 days,which could significantly improve the POD activity of walnut kernel,inhibit its PPO activity,and maintain a low browning index and total phenol content during storage;Cl O₂+MAP compound treatment can effectively delay the rancidity of nucleolar oil and maintain a highγ-VE content.When stored for 56 days,the good fruit rate reached86.67%,and the characteristic volatile flavor substances such as n-hexanal,3-hydroxy-2-butanone（dimer）,2-hexanone,propionaldehyde and acetic acid（monomer）were still maintained.