Study of microbial and physicochemical factors determining the long-term preservation of chilled fresh beef at subzero temperatures

Fresh meat is a highly nutritious but extremely perishable food, and its
preservation is a significant challenge since early civilisations. In the past decades, food
trade has become more globalised, forcing supply chains to become larger and more
complex. As such, meat, which typically has a short shelf life, is required to stay fresh for
longer. Extended shelf life in beef may be achieved through strict control of the product
hygiene associated with vacuum packaging and subzero chilling. The research
presented in this thesis was designed to investigate the effect of microbial and
physicochemical factors, namely the growth of spoilage bacteria and oxidation of
myoglobin and lipids, on the long-term preservation of chilled fresh beef at
temperatures above the freezing point of meat (−2°C) but below 0°C.
This research was divided into the following main topics: (1) the study of the
preservation of chilled fresh meat with extremely long shelf life, (2) the study of the
preservation of chilled fresh meat from the Belgian Blue breed and (3) the study of
Carnobacterium maltaromaticum as a protective culture for meat.
This study provided evidence that the use of sub-zero temperatures during
vacuum storage is essential in meat shelf life extension since it retards meat
deterioration, preventing the oxidation of myoglobin (discolouration) and growth of
spoilage bacteria. Intrinsic factors including the metmyoglobin reducing activity as well
as the activity of antioxidant enzymes, such as catalase, superoxide dismutase and glutathione peroxidase, can be associated, in varying degrees of importance, with the
retardation of oxidation reactions in meat. Carnobacterium maltaromaticum was the
dominant bacteria in meats with extremely long shelf life. Selected C. maltaromaticum
isolates obtained from these meats showed an antilisterial activity in vitro, which was
optimised at low temperatures. When studied directly in raw meat with the natural
indigenous microbiota, C. maltaromaticum showed an antimicrobial effect against
Enterobacteriaceae.
Further research on the antioxidant mechanisms and microbial ecosystems
associated with meats with extremely long shelf life will be a key to understand and
improve the extension of the shelf life of fresh meat.