In this study, the mechanism through which hot air (HA) treatment maintains the volatile components of ‘Benihoppe’ strawberry fruits during postharvest storage was elucidated by analyzing changes in physiological quality, free and bound volatile components and the activity of key enzymes in the lipoxygenase (LOX) metabolic pathway. The results indicated that the optimal HA treatment conditions were 45 ℃ and 4.5 h. In comparison to the control group, HA treated strawberry fruits exhibited higher soluble solid content (SSC) during the mid-to-late storage period (from day 4 to day 7), and maintained its firmness throughout the storage period. After 7 days of storage, fruit firmness increased by 95.3% compared with the untreated group. Despite the 45 ℃/4.5 h treatment showing the highest decay index of 85.1% on the last day (day 7), the decay index increased more slowly during 0–5 days of storage, which decreased by 32.5% compared with the control group on day 5. A total of 41 free volatile compounds and 13 bound volatile compounds were detected during the entire storage period. Furthermore, HA treatment maintained the content of strawberry aroma compounds represented by esters while significantly reducing alcohols associated with spoilage odors. HA treatment increased LOX and alcohol acyltransferase (AAT) activities by 48.12% and 104.71% on day 0 of storage, respectively and decreased alcohol dehydrogenase (ADH) activity by 10.25%. The treatment moderately enhanced LOX and alcohol AAT activities during storage, promoting the generation of volatile alcohols, aldehydes, and esters, which in turn enhanced the fruity aroma. It also delayed premature release of free aroma compounds, and retarded the release of key aroma components through inhibition and regulation of β-glucosidase and ADH activities in the early storage period, achieving a more balanced flavor and prolonging the persistence of the aroma. Finally, HA treatment maintained the volatile content of strawberry fruits, significantly enhancing the stability of strawberry volatile compounds over the storage period.

A non-destructive method for the detection of gray mold in strawberry fruit based on odor information was proposed in order to monitor the decay process of strawberry fruit. A portable electoral nose (E-nose) was utilized to collect the odor information of samples every 24 h. Healthy strawberry fruit were taken as the control group. The volatile compounds of samples were then quantitatively detected by headspace solid phase micro-extraction (HS-SPME) combined with gas chromatography-mass spectrometry (GC-MS). Finally, a regression model for predicting the microbial load in artificially infected strawberry fruit was established based on E-nose datasets by partial least squares regression (PLSR). The results showed that after 120 h storage, the contents of esters, aldehydes and alcohols in infected strawberry fruit were significantly changed, and the content of alcohol (mainly ethanol) increased rapidly from 0.85 to 3.95 μg/g. Principal component analysis (PCA) showed a high correlation between the microbial load and the stable response of E-nose sensors. The optimal PLSR model for the microbial load showed a coefficient of determination for prediction of (R_p²) 0.815, and a relative percent deviation (RPD) of 2.270. Furthermore, the non-destructive detection method based on stable signals of E-nose sensors could identify early diseased strawberry fruit with an accuracy of 92.9%. These results can provide a reference for non-destructive monitoring and early detection of strawberry postharvest diseases.

Cadmium ion (Cd²⁺) detection technology plays a prominent role in food safety and human health. Herein, we designed and constructed an 2-aminoethyl dihydrogen phosphate (AEP)@upconversion nanoparticles (UCNPs) fluorescence sensor for quantitative detection of Cd²⁺ in paddy rice based on inner filter effect (IFE) combined with enzyme inhibition mechanism. The AEP modification UCNPs can offer a stable fluorescence donor at 658 nm and be quenched by the oxidized tetramethylbenzidine (oxTMB) catalyzed by horseradish peroxidase (HRP) enzymes. Without addition of Cd²⁺, the fluorescence of AEP@UCNPs fluorescence sensor was weaken due to the IFE between AEP@UCNPs and oxTMB. With addition of Cd²⁺, HRP enzyme activity was inhibited by Cd²⁺, leading to the decreased oxTMB, resulting in the enhance upconversion fluorescence intensity. As a result, the fluorescence intensity signal at 658 nm of the IFE-based AEP@UCNPs fluorescence sensor increased linearly with the increase in Cd²⁺ in a wide range from 0.5 μmol/L to 6 μmol/L and the limit of detection (LOD) was 24.6 nmol/L. In addition, our proposed IFE-based AEP@UCNPs fluorescence sensor can achieve Cd²⁺ detection in paddy rice in 30 min.