Zhiqiang Yi,Yusen Yue,Jianquan Kan,Zhirong Wang,Sameh Awad,Amel Ahmed Ibrahim,Muying Du
Gastrodia elata Bl. Is susceptible to infestation by the fungus Fusarium oxysporum , which can cause severe post-harvest diseases. This paper presents the findings of an investigation into the control and bacteriostatic mechanisms of Lactobacillus curvatus 2768-VOCs on F. oxysporum -infected G. elata . The results of both in vitro and in vivo tests demonstrated that L. curvatus 2768-VOCs exhibited inhibitory effects against F. oxysporum , with inhibition rates of 63.37% and 44.4%, respectively. The results of the in vivo test also demonstrated that the pre-fumigation approach exhibited superior efficacy compared to direct fumigation, with the former showing a preventive effect. Furthermore, it was discovered that VOCs disrupted the integrity of F. oxysporum cell membranes and altered their permeability, resulting in the leakage of cell contents. The fumigation caused damage to the mycelial structure, accompanied by a notable decline in the total lipid and ergosterol content, and an appreciable increase in MDA content. Moreover, the fumigation of VOCs markedly diminished the activities of ATPase and mitochondrial dehydrogenase, thereby disrupting the respiration of F. oxysporum and its energy metabolism. The VOCs were subjected to GC-MS analysis, which revealed that the relative content of acids was the highest, particularly formic acid and glyoxalic acid. The study offers a theoretical basis for the biological control of postharvest diseases in G. elata .
Freeze-drying is a common method to prepare dried starter cultures with high stability and a long storage time. However, the bacterial cells suffer varying degrees of damage during the freeze-drying process. This study aimed to provide an effective strategy to improve the survival rate of Lactobacillus curvatus and to explore its potential protective mechanisms. The survival rates of bacterial cells in different cryoprotectants before and after freeze-drying were measured using the plate count method. The protective effects of composite cryoprotectants on bacterial cells were investigated from multiple perspectives, including key enzyme activities, the internal morphology of bacterial cells, and cell membrane integrity. Results showed that the freeze-drying survival rate of bacterial cells in the composite cryoprotectants consisting of trehalose, oleic acid and skimmed milk (85.38%) was significantly improved compared to that in PBS solution (2.04%). The addition of composite cryoprotectants could reduce damage to the cell wall and cell membrane, maintain the normal morphology of bacterial cells and cell membrane integrity, and improve key enzyme activities (lactate dehydrogenase, pyruvate kinase and ATPases) during the freeze-drying process. The viability of freeze-dried cultures was also monitored at different temperatures during storage, and the cell survival of freeze-dried cultures at −20 °C was the highest, reaching 61.13%. The findings obtained in this work offer a new method to improve the viability of Lactobacillus curvatus after freeze-drying, and may promote the wide use of freeze-dried cultures in the food fermentation industry.
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