51B-5

B. MUñOZ¹, P. Mañas, J. Raso, and F. J. Sala. (1) Tecnología de los Alimentos, Facultad de Veterinaria, Universidad de Zaragoza, C/ Miguel Servet, 177, Zaragoza, 50013, Spain

JUSTIFICATION: Lysozyme has been shown to be effective in preserving a variety of foods, such as cheese, meat products, wines or fish products, among others. This enzyme has a variety of important properties for a food preservative, as its high activity at low acid pHs, its stability to freeze-drying and its lack of toxicity. Its thermal stability at temperatures below 100ºC makes it promising for use in pasteurized foods. Lysozyme has a strong bactericidal activity against gram-positive heat-resistant sporulated microorganisms (Bacillus and Clostridium). This property suggests its use also in sterilized foods. However, the thermal stability of this enzyme at higher temperatures (above 100ºC) is not well known.

OBJECTIVE: The objective of this work was to investigate the thermal inactivation of lysozyme at sterilization temperatures.

METHODS: Thermal treatments were carried out from 90 to 130ºC in a specially designed instrument (thermoresistometer) in pH 6.2 phosphate buffer. The residual enzymatic activities after different heating times at each temperature studied, were determined by the initial reduction in turbidity of a suspension of dried Micrococcus lysodeikticus cells, and kinetic parameters (D and z values) were calculated.

RESULTS: The thermal inactivation of lysozyme in pH 6.2 phosphate buffer followed first order kinetics within the whole range of temperatures studied (90-130ºC). This enzyme showed a high thermal stability, with a D120ºC of 0.6 minutes and a z value of 17.3ºC.

SIGNIFICANCE: Lysozyme could be useful for preventing spoilage of sterilized foods by sporulated microorganisms. The addition of lysozyme could also allow reducing the intensity of the thermal treatments, without increased risk of spoilage and with a better preservation of the organoleptic and nutritive characteristics of foods.