Effect Of Anthocyanins In Okinawan Sweet Potato On Growth And Physicochemical Properties Of Salmonella Typhimurium And Listeria Monocytogenes
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2020
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University of Hawaii at Manoa
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Efectos de las antocianinas en la patata dulce de Okinawa en el crecimiento y las propiedades físico-químicas de Salmonella Typhimurium y Listeria monocytogenes
Abstract
Okinawan Sweet Potato (OSP) is a popular tuber among the Hawaiian Islands and the Japanese archipelago, although it is not native to either of those islands. OSP purple flesh is rich in anthocyanins, which have been proven to have antioxidant activity and a modulatory effect on gut microbiota. Balanced gut microbiota is essential for human health, and its alterations have been linked to an increased likelihood of developing diseases such as schizophrenia, dementia or Alzheimer’s disease. There are several reports on the antioxidant activity of anthocyanins, but their effect on gut microbiome has not been studied in depth yet. This study aimed to determine how anthocyanins present in OSP affect the growth and physicochemical properties of harmful and beneficial bacteria. To do so, OSP powder was extracted with an acidified mix of ethanol and ammonium sulfate. Ethanol was removed using a rotary evaporator at 40ºC. The obtained extract was quantified as cyanidin-3-glucoside equivalents using the pH differential method combined with spectrophotometry at 520 nm and 700 nm. To determine the effect of anthocyanins in OSP on bacteria, inhibition tests were performed using the agar well diffusion assay with Salmonella Typhimurium, Listeria monocytogenes and Lactobacillus rhamnosus GG. After a 24-hour incubation at 37ºC, the plates were observed for the presence of inhibition zones. Minimum inhibitory concentration and minimum bactericidal concentration assays of the anthocyanin extract were also performed in order to determine if the treated cells were dead or only inhibited, by incubating the aforementioned bacteria with the anthocyanin extract and plating them and their negative controls to identify the hypothesized antimicrobial effect. Results showed anthocyanins in OSP could inhibit the growth of pathogenic Salmonella Typhimurium and Listeria monocytogenes. But it did not affect probiotic Lactobacillus rhamnosus GG. Based on the obtained MIC and MBC against Salmonella Typhimurium and Listeria monocytogenes, hydrophobicity, autoaggregation, sedimentation, swimming and swarming, and biofilm assays were performed on the pathogenic bacteria exposed to sublethal concentrations of the anthocyanin extract. With the exception of autoaggregation, the rest of tested bacterial physicochemical properties were significantly affected by anthocyanins in OSP. Our results suggest the obtained extract not only acts as a bactericidal agent on the pathogenic bacteria, but also at lower concentrations reduces their colonization activity. These findings could be applied to the food industry, where anthocyanins may serve as a natural food preservative. Anthocyanins in OSP may also be used to modulate and maintain a healthy gut microbiota.
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