Introdução da tecnologia de congelação na produção de queijo de ovelha | Introduction of freezing on the production of ewe's milk cheese

Doutoramento em Engenharia Agro-Industrial - Instituto Superior de Agronomia

The present thesis was performed to study the introduction of freezing on the production of raw ewe’s milk semi-soft cheese, e.g. Serpa cheese. The study has integrated the monitoring of physico-chemical and structural properties during ripening and the optimisation of parameters related to the freezing process: i) the optimum stage of ripening to perform the freezing, 28, 35, and 42 days; ii) type of freezing, slow freezing in a normal -20 ºC freezer and fast freezing in a forced convection -30 ºC ultra-freezing; iii) freezing temperature, -10 ºC and -20 ºC; and iv) frozen storage period, from 2 to 12 months. From the mechanical spectra and the texturogram evolution during ripening, it was possible to observe a predictable softening of the cheese core, concomitant to a pH reduction and an augment of the nitrogen fractions, considered as proteolysis indicators. A model to estimate Serpa cheese ripening time was established, considering rheological, physical and chemical parameters, using multiple linear regression (MLR), with an estimation error of 1,74 days. The results have evidenced that it is possible the frozen storage of this type of cheese at –20 ºC, for periods no longer than 6 months, with the preservation of its specific characteristics. Moreover, it was possible to ascertain that the type of freezing (fast or slow) does not influence the cheese properties, and that the best stage of ripening to introduce the freezing was the longest that was tested (42 days).