Comparative Analysis of the Impact of Three Drying Methods on the Properties of Citrus reticulata Blanco cv. Dahongpao Powder and Solid Drinks.

Citrus reticulata Blanco cv. Dahongpao is a traditional Chinese citrus variety. Due to the high investment in storage and transport of Citrus reticulata Blanco cv. Dahongpao and the lack of market demand, the fresh fruit is wasted. The processing of fresh fruit into fruit drinks can solve the problem of storage and transport difficulties and open up new markets. Investigating the effects of different drying processes (hot air, freeze, and spray drying) on fruit powders is a crucial step in identifying a suitable production process. The experiment measured the effects of different drying methods (hot air drying, freeze drying, and spray drying) on the nutrient, bioactive substance, and physical characteristics of fruit powder. This study measured the influence of three different drying methods (hot air, freeze, and spray drying) on the nutritional, bioactive substance, and physical characteristics of fruit powder. The results showed that compared to vacuum freeze-drying at low temperature (-60 °C) and spray-drying at high temperatures (150 °C), hot air drying at 50 °C produced fruit powder with superior nutritional quality, higher levels of active substances, and better physical properties. Hot air drying produced fruit powder that had the highest content of amino acids (11.48 ± 0.08 mg/g DW), vitamin C (112.09 ± 2.86 µg/g DW), total phenols (14.78 ± 0.30 mg/g GAE DW), total flavonoids (6.45 ± 0.11 mg/g RE DW), organic acids, and antioxidant activity capacity. Additionally, this method yielded the highest amounts of zinc (8.88 ± 0.03 mg/Kg DW) and soluble sugars, low water content, high solubility, and brown coloration of the fruit powder and juice. Therefore, hot air drying is one of the best production methods for producing high-quality fruit powder in factory production.

Polymethoxylated flavonoids (PMFs)-loaded citral nanoemulsion controls green mold in citrus by damaging the cell membrane of Penicillium digitatum.

Citrus is susceptible to Penicillium digitatum (P. digitatum) infection in post-harvest storage, resulting in enormous economic losses. This study aimed to investigate the antifungal activity and potential mechanism of the combination of Polymethoxylated flavones (PMFs) and citral (two natural antifungal components derived from citrus) against P. digitatum in vitro and citrus fruit. The results show that PMFs can enhance the antifungal activity of citral nanoemulsion, and PMFs-loaded citral nanoemulsion (PCT) has significant antifungal activity in a concentration-dependent manner. PCT can evidently inhibit spore germination and mycelial growth in vitro, and effectively control the growth of green mold on postharvest citrus fruit. Furthermore, PCT treatment resulted in the alteration of mycelia morphology, accumulation of reactive oxygen species, and membrane lipid peroxidation. These changes can disrupt the normal structure and function of the cell membrane, as evidenced by the reduction of total lipid and ergosterol content in the mycelia and the stronger red fluorescence of the cells emitted after PI staining. Based on the above results, we infer that PCT has a strong inhibitory effect on P. digitatum, and its potential mechanism is related to the destruction of the cell membrane. Therefore, PCT can be considered as a botanical fungicide for citrus preservation.

Antifungal Activity of Polymethoxylated Flavonoids (PMFs)-Loaded Citral Nanoemulsion against Penicillium italicum by Causing Cell Membrane Damage.

A major citrus postharvest pathogen, Penicillium italicum (P. italicum), causes substantial economic losses in citrus. In this study, a citral nanoemulsion containing polymethoxylated flavonoids (PMFs), the antimicrobial compounds from citrus, was prepared. The antifungal activity and potential antifungal mechanisms of the nanoemulsion against P. italicum were evaluated. The results showed that the growth of P. italicum was effectively inhibited by the nanoemulsion, with a minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) of 62.5 and 250 mg L−1, respectively. The nanoemulsion significantly inhibited spore germination and mycelial growth, and it altered the morphology of P. italicum. In addition, the permeability of the cell membrane increased with increasing nanoemulsion concentrations, as evidenced by a rapid rise in extracellular electric conductivity and stronger red fluorescence from mycelia (propidium iodide staining). Compared with the control, the nanoemulsion treatment induced a decrease in total lipid and ergosterol contents in P. italicum cells by 64.61% and 60.58%, respectively, demonstrating that membrane integrity had been disrupted. The results indicated that the PMFs-loaded nanoemulsion exerted antifungal activity against P. italicum by disrupting cell membrane integrity and permeability; such a nanoemulsion may be used as a potential fungicide substitute for preservation in citrus fruits.