| Recently, more and more consumers are in favor of the fresh walnuts because of their various nutrients, such as unsaturated fatty acid, protein, vitamins and minerals as well as their special flavor. However, fresh walnuts are vulnerable to mold, germinate and become rancid during storage, significantly shortening their shelf life. In this work, “liaohe 2" fresh walnuts were packed by selected modified atmosphere(MA) package after treated by low-dose gamma irradiation, aiming to study the effects of different low-dose rays on the quality related indexes of fresh walnuts during cold storage and shelf life.The results indicated that:To explore the proper MA package for the preservation of fresh walnuts, the changes of nutritional and lipid quality of “Liaohe 2” fresh walnuts were regularly monitored after storing at(0±0.5)℃ and a further 7 days(at 7 ℃). Result showed that all MA packages reduced the O2 concentration and increased that of CO2. Acid value, peroxide value and carbonyl value were lower in walnuts packed by MA packages than that of the control significantly(P<0.01), especially obvious in PE30 and PE50 packages, in which relatively high contents of crude protein and fat were detected. Considered the changes of all indicators and the cost, PE30 can be selected as the suitable MA package of fresh walnuts for better shelf quality after cold storage.The fresh walnuts were treated by 0(control), 75, 100, and 300 Gy, aiming at study the effects of different low-dose rays on physiological indexes of fresh walnuts during cold storage at(0±0.5)℃. in order to explore the reasons why different doses affect the quality of fresh walnuts during cold storage. Through the storage period, ethylene releasing peak did not appear; During 30 to 60 d, H2O2 content rose rapidly, as well as POD and CAT activity, which reached their peaks at 60 d. At 30 and 60 d, the control held a lower POD activity than treatments; the CAT activity, which of treatment groups were lower than the control at 0d, had no difference between the control and treatments during the storage period. Thus, to a certain extent, low-dose rays strengthened the activity of POD. The average of POD activity in 300 Gy-treated was the highest.The fresh walnuts were treated by 0(control), 75, 100, and 300 Gy, aiming at study the effects of different low doses irradiation on quality related indexes of fresh walnuts during cold storage at(0±0.5)℃.Results showed that low-dose irradiation reduced the loss of soluble protein, fat and other nutrients in walnuts, inhibiting the increase of the peroxide value; Among the doses, the contents of nutrients in 300 Gy-treated walnuts were higher than the control and other treatments, including crude protein, crude fat, soluble protein and the content of unsaturated fatty acids, and the peroxide values of walnuts in this treatment were always lower than that of other treatments.To explore the proper irradiation dose for the shelf life of fresh walnuts, the changes of nutritional and lipid quality of “Liaohe 2” fresh walnuts were regularly monitored after storing at(0±0.5)℃ and a further 10 days(at 4℃) after treated by 0(control), 75, 100, and 300 Gy gamma rays. All of the doses maintained good quality of the fresh walnuts during shelf life after cold storage— keeping their high content of moisture, crude fat and crude protein, inhibiting fat oxidative rancidity, and also maintaining high unsaturated fatty acids contents and preservation rate. The most effective dose was 300 Gy, which suppressed the increase of acid value, peroxide value, and the loss of nutrients of the fresh walnuts in shelf life after refrigeration, thus 300 Gy was evaluated as the the appropriate irradiation dose for the fresh walnuts in this study.Taking the change of all the indicators during cold storage and shelf life after refrigeration into consideration, PE30 was identified suitable for packing of fresh walnuts; Among 0, 75, 100, and 300 Gy, 300 Gy was determined as the optimal irradiation dose to keep the quality of fresh walnuts in cold storage and shelf life period. |
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