To analyze the mechanism by which mustard essential oil nanoemulsion containing citrus pectin and Tween-80(MEO-NE-PT) inhibits the growth of citrus sour rot pathogen, transcriptome sequencing was performed on the mycelia of Geotrichum candidum not treated (control) and treated with 64 μL/L MEO-NE-PT for 4 hours. A total of 2788 differentially expressed genes (DEGs) were identified, including 1364 significantly upregulated and 1424 significantly downregulated genes. These DEGs were significantly enriched in pathways including amino sugar and nucleotide sugar metabolism, steroid biosynthesis, glyoxylate and dicarboxylate metabolism, starch and sucrose metabolism, and ABC transporters. They could synergistically disrupt cellular structure and function and the energy supply, and weaken the pathogen's ability to expel exogenous toxic substances outside the cell. This study provides a scientific basis for the development of eco-friendly preservatives for citrus fruits.

Litsea cubeba essential oil (LCEO) has attracted wide attention as a natural antibacterial material due to its advantages of high safety, no drug resistance and broad-spectrum antibacterial activity. The purpose of this study was to investigate the antibacterial activity of LCEO against Penicillium italicum in citrus fruits and its mechanism. The minimum inhibitory concentration (MIC) of LCEO, and its influence on the mycelial growth, spore germination, release of cell components, extracellular pH and electrical conductivity of Penicillium italicum were determined after LCEO treatment. The changes of the surface morphology of Penicillium italiana mycelia caused by LCEO were observed by scanning electron microscopy (SEM), and the integrity of the spore membrane was detected by propidium iodide (PI) staining. The disease incidence and lesion diameter in citrus fruits infected with Penicillium italicum were determined. The MIC of LCEO against Penicillium italicum was 1.17 mg/mL. LCEO could significantly inhibit the mycelial growth and spore germination of Penicillium italicum, and the inhibition rates of mycelial growth and spore germination were (88.17 ± 0.30)% and (97.78 ± 0.30)% after 1000 mg/L LCEO treatment, respectively. With an increase in LCEO concentration, the extracellular conductivity and extracellular pH of Penicillium italicum increased gradually, and the leakage of nucleic acid became more serious. SEM observation showed the mycelial linearity was lost, and irreversible morphological changes such as distortion, shrinkage and shriveling appeared on the mycelial surface after LCEO treatment. The higher the concentration of LCEO, the more serious the damage to the integrity and permeability of Penicillium italicum mycelia. The results of PI staining showed that the integrity of the cell membrane of the spores was damaged. In addition, the in vivo experiments showed that the disease incidence and lesion diameter of LCEO-treated citrus fruits decreased significantly compared to the untreated control group (P < 0.05), and the best effect was observed at 4800 mg/L concentration. LCEO could effectively inhibit the spread of Penicillium italicum in citrus fruits, and it had a good control effect on citrus blue mold.

Gas chromatography-mass spectrometry (GC-MS) and electronic nose combined with chemometrics were used to analyze the volatile components and overall odor of Osmanthus fragrans extracts from four different varieties. The results showed that a total of 65 volatile components from eight chemical classes were identified, including 28 alcohols, 6 ketones, 4 aldehydes, 4 phenols, 4 acids, 5 alkanes, 8 esters and 6 other substances. Alcohols, ketones and esters were the main volatile components in O. fragrans extracts. Venn diagram and cluster heatmap showed that the types and contents of volatile components in the four O. fragrans extracts were significantly different. By partial least squares discriminant analysis (PLS-DA), nine differential volatile components between these O. fragrans extracts were identified, namely, tetracontane, propanoic acid, 1-cyclohexene-1-propanol, 1-octacosanol, palmitic acid, 9,12-tetradecadien-1-ol, cyclohexanol, 2-butanone, and stigmasterol. The results of electronic nose showed that W2W, W2S, W1W, W1S and W5S were the main sensors to distinguish the odors of different O. fragrans extracts. The overall odors of the four O. fragrans extracts were discriminated well. The volatile components of Liuyang Luteus Group and Liuyang Albus Group extracts were more similar, while those of Xianning Luteus Group and Liuyang Aurantiacus Group extracts were significantly different, which was consistent with the results from GC-MS and cluster analysis. The research findings showed that it was feasible to distinguish O. fragrans extracts from different varieties based on volatile substances.

The aim of this study was to investigate and evaluate the processing adaptability of Osmanthus fragrans pomace, a by-product of O. fragrans extract, in order to provide a reference for its rational utilization. We examined the physical properties, nutrient composition, antioxidant capacity and tyrosinase inhibitory activity of O. fragrans pomace prepared by vacuum microwave drying (VMD), vacuum freeze drying (VFD), or heat pump drying (HPD). The results showed that the VFD sample had good color with the lowest ΔE and browning index of 14.26 ± 0.53 and 12.43 ± 0.65, respectively, and possessed the highest contents of total phenols and total flavonoids, and exhibited the highest water-holding capacity and antioxidant capacity. The VMD sample possessed the highest contents of soluble dietary fiber, total phenylethanol glycosides, actecoside, and salidroside, and exhibited the strongest oil-holding capacity and tyrosinase inhibitory activity. Pearson correlation analysis showed that the antioxidant capacity was significantly and positively correlated with the contents of total phenols and total flavonoids, and the tyrosinase inhibitory activity was significantly and positively correlated with the contents of total phenylethanol glycosides, total sugars, and total tannins. Partial least squares-discriminant analysis (PLS-DA) could distinguish differently dried O. fragrans pomace and the proposed model was stable with good predictability. According to Topsis analysis, the VFD sample had the best quality, and the VMD sample was superior to the HPD sample. In conclusion, O. fragrans pomace has good physical properties, nutrient composition, antioxidant capacity, and tyrosinase inhibitory activity, thereby holding potential as a raw material for functional food and whitening cosmetics. This study provides a reference for the application of differently dried O. fragrans pomace.

In order to investigate the difference in aroma quality among Osmanthus fragrans absolute oil and the permeate and retenate obtained from its membrane separation, a total of 66 volatile organic compounds (VOCs) were detected in the samples by gas chromatography-mass spectrometry (GC-MS). Statistical analysis revealed significant difference in both the types and concentrations of VOCs among different samples (P < 0.05). The application of orthogonal partial least squares-discriminant analysis (OPLS-DA) successfully discriminated the three samples, with a predictive accuracy of 93.6%. In addition, 10 differential compounds were selected using variable important in the projection (VIP) value > 1 as the cutoff, and clustering heatmap analysis identified 9, 3 and 1 major VOCs in the oil, retenate and permeate, respectively. The permeate exhibited good anti-flocculation properties and a stable rheological tend, containing the lowest contents of palmitic acid and its derivatives. The absolute oil exhibited the most prominent floral, fruity, greasy and cologne-like aromas with odor activity value (OAV) of 1371871.65, 41885.15, 37199.21 and 3050.71, respectively, whereas the permeate showed the most intense herbaceous aroma with OAV of 3241379.60. The results from the present study will provide a theoretical basis for the application of membrane separation to the purification of O. fragrans absolute oil and for the evaluation of the characteristic aroma of the oil and its fractions.

This study analyzed and compared the effects of different drying methods on the volatile composition and aroma characteristics of Osmanthus fragrans extract and absolute oil. The volatile composition was determined by gas chromatography-mass spectrometry (GC-MS) and partial least squares-discriminant analysis (PLS-DA), relative odor activity value (ROAV), aroma profile radar and principal component analysis (PCA) were employed to determine the effect of different drying methods on the volatile aroma components of O. fragrans extract and absolute oil. The results showed that a total of 113 volatile components were identified. The types and concentrations of volatile components were significantly different among samples (P < 0.05). Through PLS-DA analysis, 36 volatile marker substances were selected using the cutoff of variable importance in the projection (VIP) score greater than 1, and the accuracy of predictive discrimination of O. fragrans extract and absolute oil prepared by different drying methods was 99.6%. The ROAV and aroma radar plots showed that dihydro-β-ionone, linalool, nonanal, β-ionone, and dihydro-β-iononeone contributed significantly to the aroma of O. fragrans extract and absolute oil, being responsible for the floral, woody, and fruity aromas. Notably, the extract from freeze-dried O. fragrans exhibited a more intense aroma. PCA analysis indicated that freeze-drying contributed to improving the aroma quality of O. fragrans extract and absolute oil. The results of this study provide theoretical support for process optimization and quality improvement of O. fragrans extract products.

Mustard essential oil (MEO) nanoemulsions fortified with citrus pectin and tween-80 (MEO-NE-PT) or tween-80 (MEO-NE-T) were prepared by high-pressure homogenization followed by ultrasonication, and comparative analysis was performed on the microstructure, storage stability, pH, ionic strength and thermal tolerance between MEO-NE-PT and MEO-NE-T. The application of MEO-NE-PT to the postharvest preservation of ‘Shatangju’ mandarin was evaluated. It was found that MEO-NE-PT exhibited superior stability with smaller fluctuations in particle size and polydispersity index (PDI). The minimum inhibitory concentration (MIC) of MEO-NE-PT was 64 μL/L, much lower than those of MEO (256 μL/L) and MEO-NE-T (128 μL/L). Furthermore, after MEO-NE-PT treatment at 64 μL/L for 6 h, the germination rate of Geotrichum candidum spores was only 6.67%, and the length of the germ tube was only 8.57 μm, both significantly lower than 100% and 165.02 μm for the control group (MEO), respectively. The results of scanning electron microscopy (SEM) revealed that treatment with MEO-NE-PT caused the mycelium of Geotrichum candidum to wrinkle and break apart. Compared with the control group, MEO-NE-PT treatment could significantly reduce the decay rate and quality loss of ‘Shatangju’ mandarin, while delaying the decline in hardness and total soluble solids. As a safe and effective antimicrobial agent, MEO-NE-PT could control the growth of Geotrichum candidum and maintain the post-harvest quality of ‘Shatangju’ mandarin.