| Global warming is a global issue, and the methods to reduce the amounts of greenhouse gases(GHGs) emissions are carried out by many countries. Since the food system produces large amounts of GHGs, its carbon footprint(CF) arouses widespread concern. Therefore, it is meaningful to develop CF measurement and classification methods for food processes. Because of a wide range of items and diverse production processes, it is a step forward to establish this standard on the basis of the unit operations. In this research, the effects of different freezing methods such as refrigerator freezing, air blast freezing, immersion freezing, cryogenic using liquid nitrogen, and ultrasonic assisted freezing on the CF and food quality of products were investigated. In addition, the effects of different frozen storage methods on the CF and food quality of frozen products were investigated. Finally, a system cluster analysis method was used to evaluate the effects of different freezing methods on the CF and food quality of frozen food for long-term preservation. The results of this research are shown in the following.Firstly, the carbon emissions produced in China was 13,850 million tones CO2 eq in 2010. In addition, per unit CF produced by the food processing enterprices was 24 kgCO2 eq /thousand RMB, and that from Chinese general and special equipment manufacturing sector was 23 kgCO2 eq /thousand RMB.Secondly, this research demonstrated that ultrasonic-assisted freezing could significantly reduce the CF of a product compared to conventional immersion freezing method(p<0.05). The final CFs of freezing process for 1 m L of frozen water were about 16.9±0.8, 13.0±0.3, 12.7±0.3, 13.3±0.3, and 13.7±0.4 E-5 kgCO2 eq for the control, 28 kHz, 40 kHz, 50 kHz, and 80 kHz, respectively. For the conventional immersion freezing method and the ultrasonic-assisted freezing, most of the final product CF was related to electricity and galss bottle used.Thirdly, in this study, the CF of the L. dorsi muscle cut into 4×5×10 cm meat piece frozen from 4 oC to-18 oC was calculated. The CF of samples frozen by refrigerator was 64.43±1.76 gCO2 eq. The CF of samples frozen by air balst freezing at-20,-40, and-60 oC were 1103.38±46.42, 462.35±15.91, 271.80±13.02 gCO2 eq, respectively. The CF of samples frozen by immersion freezing at-20,-30, and-40 oC were 723.92±44.21, 369.66±38.84, 162.45±31.97 gCO2 eq, respectively. The CF of samples frozen by cryogenic using liquid nitrogen at-40,-60, and-80 oC were 164.18±9.66, 182.15±11.68, and 185.16±15.15 gCO2 eq, respectively. Most of the final CF of product frozen by refrigerator, air balst freezing, and immersion freezing was related to electricity used, while the final CF of product frozen by cryogenic using liquid nitrogen was mostly related to nitrogen consumed.Fourthly, the effects of different freezing methods on the quality of frozen samples were investigated. The results showed that the thaw loss of samples frozen by refrigerator was increased significantly(p<0.05) compared to that of samples frozen by other three freezing methods. In addition, the cook loss of frozen samples was increased compared to the fresh samples. The results also showed that the pH of frozen samples was reduced significantly compared to fresh samples(p<0.05). Moreover, the shear force of samples frozen by refrigerator, air balst freezing, and immersion freezing was larger than that of fresh samples while the shear force of product frozen by cryogenic using liquid nitrogen was lower than that of the fresh sample. For the color of samples, the L*and b* of samples frozen by the same freezing method were not significantly different(p>0.05). However, the a* of samples frozen by refrigerator, air balst freezing, and immersion freezing was decreased than that of fresh samples while the a* of product frozen by cryogenic using liquid nitrogen was increased than that of the fresh samples.Fifthly, the effects of different frozen storage methods including refrigerator at-18 oC, refrigerator at-10 oC, and cold storage building on the CF of frozen products were investigated. Varied storage period including 30, 60, 150, and 240 days on the CF of frozen products were also investigated. The results showed that the CF of frozen samples were increased with the increasing of storage period. For the same storage period, the CF of samples from cold storage building was the smallest compared to other two frozen storage methods. On the other hand, the CF of samples from three frozen storage methods were mostly related to the electricity used.Sixthly, the effects of different frozen storage methods by refrigerator at-18 oC, refrigerator at-10 oC, and cold storage building on the quality of samples were investigated. Varied storage period including 30, 60, 150, and 240 days on the quality of frozen products were also investigated. The results showed that quality of frozen products were reduced with the increased storage period. In a word, quality of samples from refrigerator at-18 oC were the best compared to other two frozen storage methods. Take into account the CF and food quality of samples, cold storage building was the best frozen storage method, followed by the refrigerator at-10 oC, and then the refrigerator at-18 oC when the storage period was less than 60 days. On the other hand, the refrigerator at-18 oC should be used when the storage period was more than 150 days.Finally, a system cluster analysis method was used to evaluate the effects of different freezing methods on the CF and food quality of frozen food for long-term preservation. The results showed that for the frozen samples stored for 30 days, air balst freezing at-20 oC was a bad freezing methods based on the evaluate criteria including the CF, thaw loss, TBA, and Ca2+-ATPase. In addition, for the frozen samples stored for 240 days, air balst freezing at-20 oC was also a bad freezing methods based on the evaluate criteria including the CF, thaw loss, TBA, and TVB-N. Take into account the CF and food quality of samples, other freezing methods have similar influence. |
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