*2.3. Determination of CAT Activity*

CAT activity value could reflect the activity strength of mold. Therefore, CAT activity value of the maize samples at four moldy levels was determined using the potassium permanganate titration method [29] after hyperspectral image collection. The specific steps of CAT activity determination were as follows:

Step 1: Weigh the sample and place it in a conical flask;

Step 2: Add 40 mL distilled water and 5 mL 0.3% hydrogen peroxide, and set another control group (40 mL distilled water and 5 mL 0.3% hydrogen peroxide in an empty conical bottle), and shake them in a shaker for 20 min;

Step 3: Add 5 mL 3 mol/L sulfuric acid, shake for 5 min, take it out, filter with filter paper, take out 10 mL filtrate, titrate with 0.005 mol/L potassium permanganate solution until light pink, and do not change color for 30 s.

The value of CAT activity (Equation (1)) is expressed as the volume (*mL*) of 0.005 mol/L potassium permanganate consumed in unit weight (*g*) and time (*h*). Where *V*<sup>1</sup> and *V*<sup>2</sup> were the titrated potassium permanganate volume (*mL*) of the control group and sample group, *M* was the mass (*g*) of the sample, and *T* was the unit time (*h*).

$$Value(\frac{mL}{g \times h}) = \frac{(V\_1 - V\_2)}{M \times T} \tag{1}$$
