2.3. Pretreatment Processes of H. erinaceus by the Design of Experiment

The experimental design was set as a full factorial in a completely randomized design (CRD). Factorial experimentations with triplicate replication (3³), leading a total of 81 runs, were carried out for 3 independent variables, including the sample size (X₁), heating process (X₂), and drying method (X₃). The code level of the variable at −1, 0, and 1 is shown in Table 1. The experimental design results were determined by an analysis of variance (ANOVA) based on the p-value at the 95% confidence level.

The codes of an independent variable on the factorial experimentations for the biogenic amine contents.

H. erinaceus was operated by 3 factors, including the sample size (whole, ripping, and chopping); heating process (non-heating, blanching, and boiling); and drying method (nondrying, hot air drying, and freeze drying). In the case of a sample size of fresh H. erinaceus, the mushroom was ripped up by hand to obtain a sample about the dimensions of 0.1 × 5 cm (width × length) or chopped to small pieces by a blender (Blend-Xtract 3-in-1 Blende, BL237WG, Irving, TX, USA) for 2 min. Samples were blanched at 100 °C for 1 min or boiled at 100 °C for 5 min and measured at the start of boiling [30]. After blanching and boiling, the sample was quickly cooled in cold water (4 °C) [31]. For the drying method, the mushroom samples were subjected to either hot air drying or freeze-drying. In the case of hot air drying, a sample was dried in a laboratory-scale hot air dryer (Drawell, DGT-G135, Shanghai, China). Five hundred grams of the sample was spread on a tray with the dimensions of 25 × 40 cm, and then, the samples were dried at 60 °C until a final moisture content of less than 10% dry weight was reached. In the case of freeze-drying, 200 g of a sample was spread on a tray with the dimensions of 25 × 40 cm, which was located in the freezing dryer (Drawell, DW-F30N, Shanghai, China). The dried sample was packed in an aluminum packet and kept in a desiccator at room temperature until further use.