Effects of Different Liquid Nitrogen Spray Quick-Freezing Temperatures on the Freezing Characteristics and Quality of Agrocybe praecox

This study investigated the effects of different liquid nitrogen spray quick-freezing (LNF) temperatures on the freezing characteristics and multiple quality indicators of Agrocybe praecox, in order to provide a theoretical basis for optimizing its quick-freezing process.

Fresh A. praecox samples were subjected to LNF at –40, –60, –80, and –100 ℃ or conventional air freezing (RF) at –18 and –40 ℃. The freezing curve, drip loss, color, texture properties (hardness, elasticity, and chewiness), cell membrane integrity (relative electrical conductivity and MDA content), nutritional components (total phenols, total flavonoids, soluble sugars, soluble proteins, and free amino acids) and antioxidant activity (1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging capacity, and ferric reducing antioxidant power (FRAP)) were measured. Correlation analysis was also conducted.

The freezing characteristics of A. praecox varied greatly under different freezing temperatures. LNF treatment significantly increased the freezing rate and shortened the time required to pass through the maximum ice crystal formation zone (only 22 seconds at –100 ℃). Compared with the RF group, the LNF group exhibited significantly lower drip loss, color closer to that of fresh samples (lower ΔE values), better texture maintenance, reduced cell membrane damage, better retention of nutrients, and stronger antioxidant activity (lower half maximal inhibitory concentration (IC₅₀) values against DPPH radicals and higher FRAP values). Among the LNF groups, the treatments at –60 and –80 ℃ showed the best overall performance, with antioxidant activity closest to that of fresh samples, while the –100 ℃ treatment offered slight advantages in certain indicators but with limited improvement.

Liquid nitrogen spray quick-freezing effectively preserves the freezing quality of A. praecox with the optimal temperature being in the range of −60 to −80 ℃. Freezing rate is a key factor influencing the quality of A. praecox, and rapid freezing reduces ice crystal damage, protecting cell structure and nutritional components and preserving antioxidant activity.