Soft rot is a destructive disease that inflicts significant losses on agricultural production and the economy post-harvest. Biocontrol strategies based on antagonistic microorganisms have a broad application prospect to fight against plant pathogens. This study utilized fluorescence-activated droplet sorting (FADS) technology as an alternative to traditional plate culture methods to isolate microorganisms with antagonistic activity against the soft rot pathogen Erwinia carotovora Ecc15. Initially, the culture performance of the FADS platform was evaluated by analyzing bacterial diversity in droplet culture samples and agar plate culture samples, our data showed that droplet culture exhibited higher species richness and diversity than plate culture, and more than 95% of the operational taxonomic units (OTUs) in the droplet samples belonged to the rare biosphere. Additionally, we developed a green fluorescent protein (GFP)-Ecc15-based FADS screening system, which achieved an enrichment ratio of up to 148. Using this system, we successfully screened 32 antagonistic bacteria from rhizosphere soil sample of healthy konjac plants, and some may be novel microbial resources, including the genera Lelliottia, Buttiauxella and Leclercia. Notably, strain D-62 exhibited the strongest antibacterial ability against Ecc15, with an inhibition zone diameter of (20.86 ± 1.56) mm. In vivo experiments conducted on the corms of Amorphophallus konjac demonstrated that strain D-62 could effectively reduce the infection ability of Ecc15 to the corms, indicating that strain D-62 has the potential to be developed as a biocontrol agent. Our findings suggested that the FADS screening system showed a screening efficiency approximately 3 × 10³ times higher than plate screening system, while significantly reducing costs of infrastructure, labor and consumables, it provides theoretical guidance for the screening of other plant pathogen biocontrol bacteria.

Solid-phase extraction ultrahigh-performance liquid chromatography-tandem mass spectrometry (SPE-UHPLC-MS/MS) was used to evaluate the contamination of ochratoxin A (OTA) and assessed the human exposure risk of OTA in Rasa roxburghii. A more suitable method for OTA extraction and purification of R. roxburghii was obtained. Treated 25 mL of R. roxburghii juice with enzymatic hydrolysis at a concentration of 0.06 mg/mL, filtered the resulting mixture and concentrated the filtrate to dry, then redissolved with 0.2 mL of methanol and diluted with 0.4 mL of ultra-pure water. Added sample solution to the activated hydrophilic-lipophilic balance (HLB) column, washed with 6 mL of ultra-pure water and purified by eluting with 6 mL of methanol. The eluent was collected and dried using nitrogen at 40 ℃, then redissolved in 1 mL of methanol and filtered for detection. The hazard quotient (HQ) values of all R. roxburghii fruit and juice, which were storage at room temperature, 4 and −20 ℃ from 0 day to 63 days, ranged from 0.077% to 35.792%, which were within the allowable limits for human consumption. From the perspective of OTA contamination, the results indicated that the maximal storage time of R. roxburghii fruit were 14 days at room temperature, 35 days at 4 ℃ and 63 days at −20 ℃. And the maximal storage time of R. roxburghii juice were 7 days for sealed storage and the same-day for open storage at room temperature, 14 days for sealed storage and 7 days for open storage at 4 ℃, and 63 days for sealed storage and 56 days for open storage at −20 ℃ during the experiment period. And all thirty samples randomly sampled from the market were OTA negative. The results of this study can lay a foundation for the formulation of OTA limit standards in fruits and juice in the future, and provide a reference for consumers to consume R. roxburghii more healthily.

The objective of this study was to improve the flavor of Rosa sterilis S D Shi juice without reducing its antioxidant activity. Lactobacillus plantarum BJ-1 and Lactobacillus brevis BJ-31, previously isolated and preserved from naturally fermented kimchi, were used to ferment R. sterilis S D Shi juice, and the antioxidant activity and organoleptic properties were measured and analyzed to produce R. sterilis S D Shi juice with no reduction in antioxidant activity but with improved flavor. The experimental results showed that L. plantarum BJ-1 and L. brevis BJ-31 significantly increased the content of total phenolics and flavonoids, the scavenging capacity of 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radicals by 43.11% and 40.70%, and the scavenging capacity of 2, 2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) free radicals by 40% and 40%, respectively. From the organoleptic point of view, the taste and aroma of the R. sterilis S D Shi juice fermented by different lactobacilli gradually improved, and the aromatic amino acids of the fermented BJ-1 juice exceeded those of the non-fermented juice, while the aromatic amino acids and bitter amino acids of the fermented BJ-3 juice exceeded those of the non-fermented juice. R. sterilis S D Shi juice was both higher than those of unfermented juice, indicating that fermentation is a good way to improve the taste and flavor of R. sterilis S D Shi juice. This indicates that there was a significant improvement in the taste and flavor of the R. sterilis S D Shi juice. In this research, adding BJ-1 and BJ-31 respectively to R. sterilis S D Shi juice for fermentation, which significantly improved the taste and flavor of the juice, and this research provides a theoretical basis for probiotic fermentation of R. sterilis S D Shi juice and development.