In this study, the method of maintaining the controlled freezing point and the effect of controlled freezing‐point vacuum drying (CFVD) on the quality of Muraenesox cinereus fillets were investigated. The quality assessment was based on color, 5‐inosine monophosphate (IMP), free amino acids (FAAs) and volatile compounds. Furthermore, comparisons were made among CFVD samples, those dried by hot air drying (HAD) and vacuum freeze drying (VFD). The results showed that the fillet temperature can be controlled within the scope of controlled freezing point by setting the vacuum pressure at 10–12 mbar, turning on the cold trap 40 min after CFVD (at −1 ± 1C) and regulating the heating plate temperature during the drying period. The highest increase in IMP (22.17%) and FAA content (34.54%) compared with the fresh fillets as well as the best color were observed in CFVD fillets. As to the carbonyl compounds, the major contributors to the odor and flavor of fresh fillets, the amount and types were the largest in HAD fillets, while the HAD fillets showed the significant browning. Therefore, CFVD is an effective method to control browning and increase the taste of fillets compared with HAD and VFD. Practical Applications Fish is a greatly perishable product because of its high protein content. Drying has been shown to be an efficient method of conservation. Controlled freezing‐point vacuum drying (CFVD) has been developed. In this study, the key technology challenge of CFVD and its effect on color and flavor of fillet, as well as the differences among the hot air drying and vacuum freeze drying, have been studied. The result shows that CFVD enables best quality in appearance and taste, which is quite helpful to establish an optimal drying condition for a more nutritious and high‐quality dried products.

This paper introduced a kind of fluid supply system on ejector throttling. Comparing with the fluid supply system of thermodynamic expansion valve this paper studied two kinds of fluid supply system on the freezing time overall energy consumption and uniformity temperature distribute. The results showed that, in this working condition, the fluid supply system of ejector is 14% shorter than the thermodynamic expansion valve in freezing time, which reducing the power consumption by shortening the working time of compressor, condenser and other equipment. Meanwhile, Ejector can act like isentropy and recycle some expansion work, which could increase the refrigerant capacity of evaporator to save about 6.3% power consumption compared with the isoenthalpy throttling of thermodynamic expansion valve. The system can reducing 10°C temperature difference by avoiding two-phase flow fluid supply of the evaporator and reduce the flow resistance of refrigerant in evaporator. Thus, the quality of the product is improved.

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Taken Pseudosciaena Crocea fillets as experimental material, effects of three drying methods on the quality of fish fillet were compared, including hot air drying, controlled freezing-point vacuum drying and vacuum freeze drying. The result showed: when the final moisture content was set to 20%, hot air drying rate was the fastest after 8h, followed by ice temperature vacuum drying, while vacuum freeze was the slowest at 24h; K value of hot air drying was significantly higher than those of controlled freezing-point vacuum drying and vacuum freeze drying, reaching 40.24%, while the latter both remained the excellent grade (less than 10%); On the contrary, controlled freezing-point vacuum drying increased by 38mg/100g instead. From microorganisms and TVB-N, values of three drying ways were far below the fresh and controlled freezing-point vacuum drying showed the lowest. It inferred that: the quality of fillet dealt by controlled freezing-point drying was the best.

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