Optimization of low temperature storage and preservation technology of fresh walnut by response surface method

Abstract:【Objective】In order to prevent the loss of nutrients and prolong the shelf life of fresh wal- nut during storage, the best preservation conditions of low temperature storage for fresh walnut were op- timized.【Methods】In this experiment, the fresh fruits of Qingxiang were selected as the test materias. Under the conditions of cold storage [temperature: (-1±0.5) °C, relative humidity: 70%-80%], the wal- nut kernel moisture content, seed coat color difference, peel color conversion index, peel browning in- dex, fruit cracking rate and decay rate were evaluated, and the comprehensive indexes were calculated according to Hassan method. Then, single factor experiments were conducted on the number of 1-meth- ylcyclopropene (1-MCP) preservative bags, the thickness of polyethylene (PE) bags, and the number of holes on the bags. 1-MCP was directly put into the PE bag. The response surface design was used to op- timize the best preservation process parameters with the comprehensive scores as the response value. Fi- nally, according to the best preservation process parameters, the fresh walnut fruits of Qingxiang were kept fresh for 90 days, and the comprehensive quality evaluation and sensory quality level were deter- mined according to the consulting survey results of consumers (18-45 years old). The changes of fresh walnut flavor during the preservation period were analyzed by principal component analysis.【Results】The best technology of low-temperature storage for 5 kg fresh walnut fruits was 1 bag (0.625 g) of 1-MCP , 40 μm PE and 1 holes on the bag (hole diameter 5 mm; fresh keeping bag 400 mm × 600 mm. The theoretical comprehensive score was 94.48. From the perspectives of sensory and flavor evaluation, the sensory quality level and comprehensive quality evaluation of fresh walnut stored at low temperature for 90 days under the best technology were less than grade 2, the color difference of seed coat could not be distinguished by naked eyes, and the flavor basically did not change, which indicated that the best technology of this experiment had a good preservation effect on fresh walnut.【Conclusion】The results showed that the best low-temperature storage technology for 5 kg the Qingxiang fresh wal- nut is 1 bag of 1-MCP, 40 μm PE and 1 hole on the bag. The results of this study would provide a basis for low temperature storage of fresh walnut.