Abstract
The thinned young apple is a by-product and is generally discarded in the orchard during fruit thinning. The polyphenol content of thinned young apples is about 10 times more than that of ripe apples. In our study, the antibacterial effect of thinned young apple polyphenols (YAP) on the halitosis-related bacteria including Porphyromonas gingivalis, Prevotella intermedius, and Fusobacterium nucleatum was investigated. The minimum inhibitory concentrations of YAP against P. gingivalis, P. intermedia, and F. nucleatum were 8.0, 8.0, and 12.0 mg/ml, while the minimum bactericidal concentrations were 10.0, 10.0, and 14.0 mg/ml, respectively. The scanning electron microscopy and transmission electron microscopy analyses showed that after YAP treatment, the membrane surface of halitosis-related bacterial cells was coarse and the cell wall and membrane were separated and eventually ruptured. The integrity of the cell membrane was determined by flow cytometry, indicating that the cells with the integrity membrane significantly reduced as the YAP concentration treatment increased. The release of proteins and nucleic acids into the cell suspension significantly increased, and the membrane potential reduced after the YAP treatment. This research illustrated the antibacterial mechanism of YAP against halitosis-related bacteria and provided a scientific basis of utilizing the polyphenols from the discarded thinned young apples.
Highlights
Apples are rich in lots of nutrients, such as vitamin, fiber, pectin, and polyphenol which are good for the health
P. gingivalis and F. nucleatum were susceptible to the young apple polyphenols (YAP), with the lower minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC)
The results indicated that YAP could inhibit P. gingivalis, P. intermedius, and F. nucleatum and alter the morphology of bacterial cells and the integrity of cell membranes
Summary
Apples are rich in lots of nutrients, such as vitamin, fiber, pectin, and polyphenol which are good for the health. The major apple producers around the world are China, Italy, France, and United States (Nicolas et al, 1994). The total apple yield all over the world in 2014 was 84.56 × 106 and 40.92 × 106 tons in China, accounting for 48.39% of the total yield (Li et al, 2018). In China, about 1.9 million tons of thinned young apples are abandoned every year (Dou et al, 2015). These thinned young apples are usually directly discarded on the orchard grounds and may become a good energy source for the growth of microorganisms, which could increase the risk of fruit diseases and result in a significant reduction in the quality and yield of fruits (Hou et al, 2019). Nisar et al (2019) reported that pectin films incorporated with young apple polyphenols could efficiently inhibit the growth of Staphylococcus aureus, Escherichia coli, and Listeria monocytogenes
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