2.1. Sample preparation

Samples of He13 soybean kernels ( Figure S1 in Supplementary Material ) were obtained from Shu County Agricultural Management Company. Soybeans with smooth surface were selected and considered as healthy ones. Healthy soybeans were soaked in warm water for 10 min and dried using a drying oven at 100 °C for 2 h to obtain broken soybeans. Moldy soybeans were prepared as follows. 1) Healthy soybeans were soaked in warm water for 10 min and placed in a glass Petri dish. 2) The dish was placed in an incubator with constant temperature of 34°C and humidity of 80% to obtain different degrees of moldy soybeans. 3) Moldy soybeans were collected daily. Mildly moldy soybeans have few spots on the epidermis, whereas severely moldy soybeans have mycelia on the epidermis.

Aflatoxin B1 test strip was used to determine the toxin of moldy soybeans. The lower limit of AFB1 toxin detection was 10 ppb, mildly moldy was in the range of 10–20 ppb, and severely moldy was greater than 20 ppb. For HSI and RGB image acquisition, 2,160 samples were collected, including 560 healthy kernels, 560 broken kernels, 560 mildly moldy kernels, and 480 severely moldy kernels.