High Pressure Processing of New Zealand Mussels (Perna canaliculus)

Abstract

This thesis investigates the use of an emerging food preservation technique known as ‘High Pressure Processing (HPP)’ for treating ‘New Zealand mussels (Perna canaliculus) to replace the existing thermal processing procedure which has negative impacts on quality. Mussels can become high risk food if contaminated with food-borne pathogen Listeria monocytogenes, the causative agent of listeriosis. The two major objectives undertaken in the study were Safety and Quality. Food safety has been addressed by measuring and modelling the effects of HPP parameters (as a function of pressure, temperature and time) on a pressure resistant strain of food-borne pathogen (L. monocytogenes FSA 2655). An effective treatment temperature of the system was used to determine the activation energies for inactivation of L. monocytogenes in mussel meat using HPP taking into account the temperature changes caused by adiabatic heating. Quality study involved determining the effect of HPP parameters on autolytic enzymes associated with enzymatic spoilage in mussels viz. alanine aminopeptidase and lipase enzymes. Based on the desired enzyme activity and Listeria inactivation, a potential selected treatment combination of 500 MPa, 30°C and 3 min was identified. Using this chosen combination quality assessment of end-product was carried out by measuring its colour, texture, yield and sensory attributes during a shelf-life study of one week of chilled storage. The results reveal HPP can be successfully used for shucking as well as listericidal step in mussel processing. The kinetic modelling for inactivation of L. monocytogenes in mussels using HPP shows energy efficiency of HPP. Increasing pressure, HPP processing times and temperatures resulted in decreasing levels of Listeria and alanine amino peptidase activity but increasing lipase activity. Significant differences in texture between treatments were detected using the rupture but not using the cutting method. HPP had a similar beneficial effect on microbiological quality to heat processing during subsequent storage. However, careful selection of HPP conditions are required as factors for eg. gut burst or pasty gut textures and/or algal flavours have been identified as conditions which will affect product quality. Chilled storage was unsuitable for storage of HPP mussels due to negative sensory attributes of the product.