Impacto do tratamento por alta pressão na qualidade microbiológica e tecnológica do leite para o fabrico do queijo

  • Catarina Alexandra Cruz Marques Simões (Student)

Student thesis: Master's Thesis


High pressure is recognized as one of the most promising low temperature processingtechnologies and can be applied across a wide range of pressure/time/temperature conditionstrinomials. The processing of raw milk by high pressure technology can cause changes in itsmicrobiological, physicochemical and technological properties. Thus, the objective of thisresearch was to evaluate the impact of non-thermal processing by high-pressure technology onmilk, as an alternative to conventional thermal processing, in order to produce microbiologicalsafe milk, but with greater technological aptitude for the manufacture of cheese, expressed inthe form of higher yield. Thus, different pressure/processing time (p/t) of milk were tested inorder to establish the best p/t combination, to allow a better microbiological quality, andconsequently a longer shelf life, as well as curd yield. In a first phase, 3 pressures (300, 450 and600 MPa) were tested for 6 minutes. In a second phase the pressure was set at 600 MPa andtested different processing times (6, 13 and 20 minutes). In all trials the milk, before and aftertreatment, and during storage under refrigeration up to 15 days, was analyzed in terms ofmicrobiological parameters (aerobic mesophiles, aerobic psychrophils, lactic bacteria,enterococci, staphylococci, enterobacteria and molds and yeasts), physical-chemical (color,pH and titratable acidity) and technological aptitude (coagulation yield).From the first phase it was observed that pressures higher than 300 MPa allowed a greaterinhibition of microbial growth. The most sensitive microbial groups at 300 MPa wereenterobacteria and enterococci, but the application of pressures at 450 and 600 MPa resulted ininhibition of all target microbial groups. Regarding physical-chemical parameters, these werepositively affected by the increase of pressure. On the other hand, high pressure application inmilk processing had a variable impact throughout the storage time; after 7 days, 24 to 46% ofcoagulation yield losses were observed. Regardless of the order of magnitude of the High Pressure, only slight changes in luminosity were observed, and the values of a * and b * were observed.From the second phase, it was found that the increasing of the processing time from 6 to 20 minutes at 600 MPa allowed maintaining a viable number of lactic acid bacteria, enterococci,staphylococci and enterobacteria less than detection limits over 7 days and staphylococci andentero bacteria up to 15 days of storage at 4 ° C. Slight decrease in pH values accompanied bya titratable acidity increase was observed over 15 days of storage. Milk samples processed by high pressure at 600 MPa and for 13 and 20 minutes allowed higher and stable coagulationyield values over the entire storage time, again without significant impact on color.
Date of Award10 May 2018
Original languagePortuguese
Awarding Institution
  • Universidade Católica Portuguesa
SupervisorSuzana Tavares da Silva (Supervisor), Ana Maria Gomes (Co-Supervisor) & Ana Cristina Freitas (Co-Supervisor)


  • Milk
  • High pressure processing
  • Microbiological quality
  • Technological adequacy


  • Mestrado em Engenharia Alimentar

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