Analysis of Three Pre-freezing Treatments for Optimal Freezing Suitability of Tricholoma matsutake

To examine the suitability of different pre-freezing treatments for Tricholoma matsutake frozen storage, three pretreatment methods—refrigerator slow freezing (RSF), immersion quick freezing (ICF), and liquid nitrogen spray freezing (LNF) were applied. Tricholoma matsutake were subsequently stored at −20 ℃ for 180 days, during which the effects of different freezing methods on freezing characteristics, post-thawing sensory quality, enzymatic activities, and other critical parameters were comprehensively assessed. Based on the experimental results, significantly shorter phase transition times and higher freezing rates (P<0.05) were observed in ICF- and LNF-treated Tricholoma matsutake compared with RSF-treated samples, with LNF demonstrating the fastest freezing rate at 0.85 ℃/min. Additionally, superior retention capacity for both moisture and soluble solids content was demonstrated in Tricholoma matsutake treated with LNF during frozen storage. During frozen storage, browning and texture softening were observed in Tricholoma matsutake, with the browning index ranking in descending order as RSF>ICF>LNF. At the same time, hardness values were maintained in the sequence LNF>ICF>RSF. Regarding enzymatic activities, a progressive reduction in superoxide dismutase (SOD) and polyphenol oxidase (PPO) activity levels was observed in frozen-stored Tricholoma matsutake throughout the storage period. Among the three methods, the LNF treatment was found to exhibit the optimal retention of SOD activity and the most potent inhibition of PPO activity. With prolonged frozen storage, the total sugars, soluble protein, and total phenolic content were decreasesd in Tricholoma matsutake. The loss of soluble protein was significantly reduced by RSF treatment (P<0.05), while LNF treatment was more effective in retaining total sugars and total phenolic content. In conclusion, LNF treatment was demonstrated to be the most effective approach for maintaining the frozen storage quality of Tricholoma matsutake. It can be considered a novel pretreatment option for Tricholoma matsutake prior to frozen storage.