Material
Dried walnut (Xinxin No. 2) was supported by Xinjiang Academy of Forestry Sciences (Urumqi, China) and harvested in September of 2022. The shelled walnut kernel formed from a proximate composition of 20.08±1.38% protein, 5.11±0.18% moisture content, 63.22±5.12% oil and 1.71±0.06% ash [15]. The norleucine was bought from Sigma Chemical Co. (St Louis, MO, USA). The pepsin (3000 U mg-1) and pancreatin from porcine pancreas (4000 U mg-1) were purchased from the Novozymes (Bagsværd, Denmark). All other reagents were analytical grade, and bought from Sinopharm Chemical Reagent Co., Ltd (Beijing, China).