Thirty percent of the samples of fresh or frozen shrimp received for processing into breaded shrimp had bacterial counts in excess of 106/g. The bacterial counts of 56% of plant processed samples of frozen breaded raw shrimp exceeded 106/g. Counts with plate incubation at 7 or 25 C were significantly higher than at 35 C. Little relationship existed between aerobic plate counts and coliform or enterococcal counts. Neither Salmonella nor Vibrio parahaemolyticus was isolated from plant processed samples. Frozen storage of breaded shrimp for 3 to 12 months caused minor reductions in aerobic plate count and coliform count and only minor changes in trimethylamine nitrogen (TMN), total volatile nitrogen (TVN), and odor scores. When frozen breaded raw shrimp were exposed to elevated temperatures (0–10 C) increases in count occurred at 0 C after 3–5 days, at 5.5 C after 2–3 days, and at 10 C after 1–2 days. Coliform bacteria increased at 5.5 C, Escherichia coli and enterococci at 10 C. In samples held at 0–10 C, marked increases in TMN and TVN and decreases in pH value occurred when bacterial counts had increased sharply and when off-odors became noticeable. Gram-positive forms, Bacillus, Microbacterium, Micrococcus, and coryneform bacteria were predominant in retail samples. Many of these samples showed evidence of repeated thawing and freezing. Of the retail samples, 52% had aerobic plate counts of 106/g or higher.
1Published with the approval of the Director of the Texas Agricultural Experiment Station, College Station, Texas.
2A preliminary account of this work was presented at the 59th Annual Meeting of the International Association of Milk, Food, and Environmental Sanitarians, Milwaukee, Wisconsin, August 21–24, 1972.