To explore the effects of relative humidity (RH) on the quality of walnut kernels and establish a rapid, effective method/model for identifying their deterioration degree, walnut kernels were stored at 45 ℃ for 90 days under different RH conditions (35%, 50%, 65% and 80%) in this study. Every 15 days, changes in the kernels' color, acid values (AV), peroxide values (POV), fatty acid composition, contents of total phenols and soluble quinones, synchronous fluorescence spectra, and the compositions/contents of volatile organic compounds (VOCs) were analyzed. Partial least squares discriminant analysis (PLS-DA) and variable importance in projection (VIP) were used to conduct differential analysis of VOCs. The deterioration degree of walnut kernels was predicted using Pearson correlation analysis and a Back Propagation Neural Network (BPNN) model. The results showed that RH had a significant effect on the quality of walnut kernels, with 65% RH being the suitable storage condition for them. According to gas chromatography-mass spectrometry (GC-MS) analysis, a total of 40, 34, 23 and 17 characteristic VOCs were identified in the walnut kernels stored at RH of 35%, 50%, 65% and 80%, respectively. Among these VOCs, hexanal, 1-octen-3-ol, 4,5-dimethyltetrahydrofuran-2-one and DL-pantolactone were identified as potential volatile deterioration markers (PVDMs). Based on the POV limit standard of 1.0 mmol/kg for walnut oil, the threshold concentrations of these four PVDMs were 500-1000, 50-100, 10-15, and 30-60 μg/100g, respectively. This research provides a reference for the quality monitoring and evaluation of walnut kernels during storage.

After infrared (IR) pretreatment for 22, 41, 68, 104 and 148 s, the internal temperature of pecan kernels reached 70, 90, 110, 130 and 150 ℃, respectively. To investigate the effect of IR pretreatment on the quality and storage stability of cold-pressed pecan oil, oil yield, fatty acid composition, lipid concomitants, physicochemical indicators, microstructure, and antioxidant capacity and storage stability were analyzed. The results showed that IR pretreatment increased the oil yield of pecan kernels by 11.10%–58.42% compared with the control group, but had no significant effect on the fatty acid composition of cold-pressed pecan oil. Moreover, IR pretreatment significantly the activities of lipase and polyphenol oxidase in pecan oil (P < 0.05). Non-enzymatic browning index, the release of carotenoids and the content of total phenolics were positively correlated with IR pretreatment time, and the color of cold-pressed pecan oil turned darker with increasing time of IR pretreatment. Compared with the control group, IR pretreatment for 148 s resulted in a slight but not significant reduction in γ-tocopherol content (P > 0.05), and a 23.52% and 13.16% increase in 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging capacity and ferric reducing antioxidant power (FRAP), respectively, thereby significantly enhancing the storage stability. To summarize, IR pretreatment for 148 s is the best pretreatment method to obtain cold-pressed pecan oil. The results of this study provide a theoretical basis for the application of IR pretreatment in the preparation of cold-pressed pecan oil.