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The effectiveness of natamycin against carrot mold post-harvest

As stated previously in this section, research on new applications for Natamycin in the food industry is constantly being carried out all over the world.

We have also covered its successful application in the maintenance of the post-harvest quality of plants such as red fruits, and now we discuss a study on one of the most widely consumed succulent root vegetables in the world: carrots.

The study summarised here was carried out by Chinese researchers for the Brazilian Phytopathology Society, and recently published in the journal Tropical Plant Pathology.

The study examined the inhibitory effect of  Natamycin on the fungus Sclerotinia Sclerotiorum, the pathogen causing white mold in carrots post-harvest.

In this case, the fungus does not attack carrots in storage after they have been harvested, but lies dormant in the soil.  It can survive for up to ten years in the ground.

The study demonstrated that Natamycin is an important anti-fungal agent against S. sclerotiorum both in vitro and in vivo.

In order to study the effect of natamycin under conditions as close as possible to real ones (in vivo), fresh carrots in perfect condition were submerged in increasing concentrations of Natamycin (50, 100, 150 and 200 mg of L-1) and then air dried for 2.5 hours. A sample of the pathogen was then placed on top of these carrots.

The severity of the infection was evaluated six days after the carrots had been inoculated, by measuring the length of the lesion created by the fungus on the root.

The image below shows the results of the tests carried out in vitro (a/b and c/d) and in vivo (e/f).

carrot natamycin

Source: Tropical Plant Pathology. 3 June 2020.

Samples b and d are the control sample without any Natamycin, while a and c contain a concentration of Natamycin of 1.5 mg l-1. The a/b pair is the samples after 5 days (there is no linear growth of the fungus in a, while there is in b), and the c/d pair is the same samples after 15 days of culture in vitro (the blackish structures of the fungus do not grow in c as they do in d).

In vivo tests showed that the concentration of inoculated Natamycin should be at least 50 mg l-1 if it is to be effective against white mold in carrots. In the e/f pair, sample e contains natamycin and it appears to be protected after 6 days, while sample f presents a generalised infection from the centre to the ends over the same period of time.

Although previous studies had highlighted substances such as chitosan, silicon and UVC radiation as potential means to reduce infection by white mold, this more recent study suggests that Natamycin is another tool that can be used in countries where its use is authorised in order to prevent the loss of more than 50% of the harvest due to white mold under storage conditions that favour the fungus.