Utilização de agentes antimicrobianos naturais como alternativas na conservação e melhoria da qualidade microbiológica de produtos de charcutaria

  • Joana Maria Carvalho Gomes (Student)

Student thesis: Master's Thesis


The microbiological quality of food is of considerable concern to the food industry since the activity ofmicroorganisms can result in food spoilage and, more seriously, affect the health of consumers. Theuse of food additives, the application of a suitable heat treatment and Good Manufacturing Practicesare essential to reducing microbial loads in foods.The present work was developed in the Microbiology laboratory of Centro de Biotecnologia e QuímicaFina (CBQF) and at the food company Primor.In the laboratory, the objectives of the study were to test the antimicrobial activity of 3 naturalcompounds – chitosan, ethanolic extract of propolis, and nisin – against various microorganisms, 21Gram-positive, 15 Gram-negative bacteria and 2 fungi and, also, to compare with the antimicrobialaction of the chemical compound sodium nitrite, alone and in combination with sodium chloride. Theminimal inhibitory concentration was determined through the agar dilution and the drop agar diffusionmethods, to examine any differences between both methods. Antimicrobial activity was also tested atdifferent pH values of the culture medium at 5, 6 and 7 and different temperatures of incubation at 4,12, 20 and 37 °C, with the objectives of determining the influences of pH and temperature on theinhibition of microorganisms and simulating the presence of the pathogens in different food productsand different storage conditions. The natural compounds tested had greater inhibitory effect againstthe various microorganisms compared with sodium nitrite alone and in combination with sodiumchloride, in the different conditions of pH and temperature. With the concentration of 0.65% (w/v) ofchitosan it was possible to inhibit most of the tested microorganisms. With a concentration of 10mg/mL of propolis, fungi, most of the Gram-positive microorganisms and some of the Gram-negativeswere inhibited. With a concentration of 25 μg/mL of nisin it was possible to inhibit most of the Grampositivemicroorganisms.The work developed in Primor had as objectives the development of a new heat treatment for chouriçocorrente and implementation of improvements in Good Practices in its production process to reducethe number of lactic acid bacteria, the major contaminant of the product. To reduce the number ofsuch spoilage microorganisms and also total microorganisms, and to improve the microbiologicalsafety of chouriço, chitosan was added to this charcuterie product. After i) the application of baking at77 °C for 40 minutes on the chouriço corrente, with 100% humidity and with the stove chimney semiopen,and ii) the application of Good Practices monitoring methodologies with greater effectiveness,including greater control of the chouriço production process, the number of lactic acid bacteria in thesamples after packing was lower than in the samples produced by the standard baking process andalso lower than in samples obtained through a non-monitored process. With the addition of 0.15%(w/v) of chitosan to the chouriço, the number of lactic acid bacteria and total microorganisms waslower compared with the chouriço with nitrite, after 14 days of storage. Therefore, the application of analternative heat treatment to the one used in the standard chouriço corrente and the implementation ofimprovements in Good Manufacturing Practices resulted in an improvement in the microbiologicalsafety and shelf-life of the food product after packing. Additionally, chitosan appears to be a naturalalternative with interesting characteristics for application in a food product.
Date of Award8 Mar 2017
Original languagePortuguese
Awarding Institution
  • Universidade Católica Portuguesa
SupervisorPaula Teixeira (Supervisor)


  • Mestrado em Microbiologia Aplicada

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