Time Courses of Total Volatile Basic Nitrogen (TVB-N) in Seafoods Inoculated Singly or as Mixtures with Spoilage Yeasts or Bacteria

Abstract

Previously, we reported on the amount of T-VBN produced by yeasts or bacteria. Candida lipolytica produced the largest amount of T-VBN among the 5 yeast species tested, while Staphylococcus epidermidis produced the smallest amount, and Pseudomonas fluorescens produced the largest amount among the 4 bacterial species tested. In this paper, the microbiological and chemical changes of these 3 species were compared. C. lipolytica, S. epidermidis and P. fluorescens were inoculated singly or as mixtures into 3 different kinds of sterile seafood homogenate (common mackerel, black tiger shrimp and neon flying squid), and incubated at either 5, 15 or 25°C. The time courses of viable counts, pH values, and TVB-N values determined according to the microdiffusion method of Conway were observed for up to 7 days.(1) Viable counts: The growth curves of C. lipolytica at 15 and 25°C showed gradual slopes, and reached the stationary phase on day 7. The growth curves of P. fluorescens and a mixture containing C. lipolytica, S. epidermidis and P. fluorescens at 15 and 25°C reached the stationary phases on day 2. The growth curves of S. epidermidis at 5 and 15°C were lower than those of C. lipolytica, P. fluorescens and a mixture of all three.(2) pH: The pH values in the seafood homogenate inoculated with C. lipolytica, P. fluorescens and a mixture of all three increased with temperature and duration of incubation.(3) TVB-N: Whereas the viable counts at 25°C of C. lipolytica were less than those of P. fluorescens, S. epidermidis and the mixture, the production of TVB-N by C. lipolytica was at almost the same levels as those of P. fluorescens and the mixture, and considerably more than that of S. epidermidis. The results of the previous and present experiments have thus confirmed that the yeasts produced the same spoilage phenomenon as the bacteria.