Evaluation of microbial behavior in selective culture media for the microbiological analysis for fruit preparations

Abstract

In the food industry, when a microbiological analysis is performed, it is generally based on the detection of microorganisms in immunological, visual, or biochemical ways. Nowadays, it is possible to cultivate microorganisms and induce the proliferation of cells by adding sufficient nutrients to the culture media. The study developed had the main objective of developing an optimum culture media for the growth of yeasts, bacteria and moulds. These culture media are intended to mimic the fruit preparations and guarantee that if the samples are contaminated, the microorganism will grow in the media and grow faster and more significantly to identify the microorganism quickly. To achieve this first was made an overview by adding different components to simpler culture media, like NA and PDA, to understand how each component affected the growth of the different microorganisms, being the microorganisms used throughout the study Bacillus cereus, Escherichia coli, Leuconostoc mesenteroides, Pseudomonas aeruginosa, Saccharomyces cerevisiae, Pichia fermentans, Candida intermedia e Neosartorya fischeri. Later, a confirmation was performed to see if, at a statistical and qualitative level, the components negatively or positively affected the growth of the microorganisms. Finally, the components with better results were mixed in the media. The culture media that better enhanced the bacteria growth were 201 and 203, where both sucrose and lysine were added, 201 magnesium and 203 magnesium and iron, once three different bacteria had positive outcomes in their three inoculums for both culture media. For yeasts, of the six media tested, only one stood out, being 601, where fructose, lysine, biotin thiamine, magnesium and irom were incorporated into the medium. This media had a positive result for two yeasts, S. cerevisiae and P. fermentans, and the yeast C. intermedia. The media may not have had a positive outcome but did not have a negative result, which means that it does not negatively compromise the growth of the yeast. The only mould tested was N. fischeri, and it was possible to perceive that it grows better in PDA than in the tested media, so it is possible to assume that simpler culture media, like PDA, are better for growth for this mould. Then was possible to conclude that the combination of certain components, when added to simpler media, made the bacteria and yeasts colonies to grow larger. The opposite was observed in the case of the mould, in which its colonies grew larger in simpler media.

Date of Award	3 Nov 2023
Original language	English
Awarding Institution	Universidade Católica Portuguesa
Supervisor	Paula Teixeira (Supervisor)