Application of a microbial sensor to the quality control of meat freshness

Samples of fresh meat stored at 5°C were periodically removed from storage and washed with water for periods of up to 2 weeks. The amount of amino acids, polyamines and viable counts (number of bacteria) in the washed water were measured by using an HPLC system and a colony counting method. At the same time, the washed water was charged into a flow injection analysis (FIA) system combined a microbial sensor using yeast (Trichosporon cutaneum), which was developed in this work for monitoring the freshness of meat. A relationship between the sensor signals obtained by the FIA system and the amounts of polyamines and amino acids produced from the meat and the number of bacteria which had multiplied in the meat during the aging process was investigated. The sensor signal was found to correspond to increases in amino acid levels and viable counts in the meat with the storage time in the course of the first stage of aging. This is due to the fact that amino acids produced initially by enzymes in the meat serve as a source of nutrition for septic bacteria during the aging process, and as a result, the level of bacterial cells increases with increasing amounts of amino acids with the passage of days. A good correlation, with a correlation factor of 0.908, was obtained between the sensor signal and viable counts obtained by the colony counting method. The present sensor method was more sensitive than the colony counting method at the early stage of the aging process, where viable counts were in the vicinity of 104 g−1.