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Research analyzes microbiological quality of edible mushrooms

Student Viny Lanza's dissertation focused on mushrooms sold in the Campinas region, aiming to have data on the quality and safety of products

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Audio description: color photography. Young man in a white coat looks at the photo. He holds tweezers in one hand and a bag of mushrooms in the other, which is on a precision scale. More mushroom samples are in a laboratory fume hood.
Research on the quality of mushrooms was defended in December at the Postgraduate Program in Food Science at Unicamp 

The microbiological quality of edible mushrooms sold in Campinas was the subject of student Viny Lanza's master's degree, which also focused on the identification and behavior of bacteria Listeria monocytogenes during the product storage period. The results of the research, defended on December 5th at Unicamp's Postgraduate Program in Food Science, show that there is a high microbiological count in mushrooms. However, the Listeria monocytogenes, a pathogenic bacteria, was only found in a sample of black shimeji.

In total, 195 samples of five species of mushrooms (white shimeji, black shimeji, porto belo, shitake and champingnon) from nine different brands were used. Firstly, a global microbiological analysis was carried out, that is, the count of microorganisms present in the mushrooms, which can give an indication of the quality of the product. A high count was found in all except shitake. “The shitake showed contamination similar to what is normally found in shitake samples from other locations around the world, which may be related to the substrate, as it is produced in wooden logs, which are autoclaved for decontamination”, points out Viny, referring to the log sterilization process.

Black shimeji was the species with the greatest microbial contamination. The student's hypothesis is that this index is related to the substrate where it is produced, in which 'food' for the fungus is generally inserted, such as cereal bran. “Contamination can come from several points. However, I believe it is due to the substrate, because it must go through a contamination reduction process, but the count is so high that I believe the decontamination is not being efficient”. However, because the samples were obtained in commercial establishments, and not directly from producers, it is not possible to say whether the conditions at the cultivation or storage location are responsible for the count.

Regarding the presence of Listeria monocytogenes, of the 195 samples of five species of mushrooms analyzed, only one, black shimeji, contained it. 100 samples of this mushroom species were analyzed. Although the presence of the bacteria should serve as a warning, the small incidence suggests that there is a good sign of the safety of the products. "A Listeria monocytogenes it was only found in a sample of black shimeji. The incidence is very low, 0,51% in the sample I used. In other countries there are mushrooms that have a 10% incidence of this pathogen. Here in Brazil, even though the count was high, there was no significant incidence of pathogens”, explains the student.

audio description: color photograph shows man wearing glasses gesturing. He wears glasses, a blue striped t-shirt. he is in a laboratory and in the background there are refrigerators.
Anderson S. Sant'Ana, professor who supervised the research, points out that microbiological analysis is important as it provides data to control bodies

The research advisor, Professor Anderson S. Sant'Ana, explains the importance of analyzing the microbiological quality of products. “This assessment is important because it provides data that can be used by control and public health authorities, guiding actions. Therefore, we analyzed different brands, different batches of products, as microbial contamination can vary according to the manufacturing batch and type of product”, he explains.

He also explains that the mushroom may be susceptible to microbial contamination due to cultivation conditions, as it requires high air humidity and mild temperatures to develop, and due to consumption habits. “After the mushroom is harvested, it does not go through any washing process, as happens with some other agricultural products. There is no pre-processing. And the custom of consuming mushrooms is that you don't wash them before consuming, as this alters the sensorial characteristics, especially the texture. Furthermore, there are different ways of consuming mushrooms, including raw and in salads”, he notes.

After analyzing the microbiological quality, the behavior of the bacteria was evaluated Listeria monocytogenes in the product to understand the potential for multiplication in the mushroom during storage. This microorganism was chosen by the student because it is a pathogen, that is, it causes disease, and because it is a psychrotrophic bacteria, that is, it multiplies at refrigeration temperatures, precisely the condition under which mushrooms are sold. Viny verified the behavior of the bacteria during storage, storing the samples at temperatures of 5°C, 12°C, 20°C and 30°C. At this stage, the analysis took place only on white and black shimejis.

“The results I obtained were that, under conditions of 12°C, 20°C and 30°C, both mushrooms offer excellent substrate for the growth of Listeria monocytogenes, however the growth was more significant in black shimeji. At 5°C, there was only growth in black shimeji”, points out Viny.

For those dedicated to cultivation, the guideline is to always pay attention to the quality of the substrate, in addition to being careful with the clothing and utensils used when handling mushrooms. “Evaluate the substrate, carry out quality control, see if decontamination is being effective. In addition, evaluate other process points for potential contamination”, says the student.

audio description: color photograph shows two men, student and teacher, around a table. the youngest, the student, gestures as he speaks. they are in a laboratory.
Student points out that decontaminating the substrate is an important step for those who produce the mushroom

Mushroom consumption

The consumption of fresh mushrooms in Brazil has been growing in recent years, driven by several reasons, such as the greater popularity of Asian cuisine and the increase in vegetarians and vegans. In the last ten years, the Mushroom Producers Association estimates that the consumption of these fungi, which are rich in proteins, minerals and vitamins, has doubled. In the same period, the number of producers increased fivefold.

In the interior of the state of São Paulo, where Japanese immigration began, production is concentrated in the country, which is largely carried out by small and medium-sized farmers.

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Audio description: color photography. Young man with his back, in a white coat, holds a mushroom with tweezers. More mushroom samples are in a laboratory fume hood.

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