Ranzell Nickelson

Microbiological and Chemical Changes During Storage of Swordfish (Xiphias gladius) Steaks in Retail Packages Containing CO2-Enriched Atmospheres

Swordfish ( Xiphias gladius ) steaks were held in retail packages containing 100% CO2 and in mixtures of 40% and 70% CO2 in combination with either oxygen or nitrogen. Controls were stored in air. Samples were removed for chemical and microbiological analyses after 2-22 d of storage at 3.5°C. The inhibitory effect of CO2 on psychrotrophic, aerobic gram-negative spoilage bacteria was proportional to the CO2 tension in the packages. Maximum inhibition of growth was achieved with 100% CO2. Except for steaks stored in 40% CO2:60% O2 heterofermentative Lactobacillus spp. became a dominant part of the microflora of steaks stored in CO2-enriched atmospheres. Pseudomonas spp. continued to be a major part of the microflora of steaks stored in 40% CO2:60% O2. During the first 2 d of storage, there was a decrease in the surface pH of the swordfish steaks proportional to the CO2 tension in the packages. Swordfish steaks stored in CO2-enriched atmospheres had lower total volatile nitrogen (TVN), trimethylamine (TMA) and total volatile acid (TVA) values than steaks stored in air. Oxidative rancidity was not a flavor problem of fish in any of the atmospheres after 20 d of refrigerated storage.

Storage Characteristics of Finfish Fillets (Archosargus probatocephalus) Packaged in Modified Gas Atmospheres Containing Carbon Dioxide

Sheepshead ( Archosargus probatocephalus ) fillets were stored in air and in modified gas atmospheres consisting of: 100% CO2, 80% CO2:20% O2, 60% CO2:40% O2, 30% C02:60% O2, 20% CO2:80% O2, 40% CO2:60% N2 and 44% CO2:36% O2:20% N2 At regular intervals during refrigerated storage, numbers and types of microorganisms and total volatile nitrogen (TVN) were determined. Increases in aerobic plate counts of fish fillets held in air and in 20% C02:80% O2 were greater than those for fillets stored in the other gas atmospheres. The most effective combinations of gas for limiting bacterial growth were 100% CO2 and 40% CO2:60% N2. Total volatile nitrogen values of samples stored in air and in 20% CO2:80% O2 increased similarly to those of fish held on ice. At higher CO2 concentrations, however, increases in TVN were slow and the rate of TVN production appeared inversely proportional to CO2 tension.

Bacteriology of Indole Production in Shrimp Homogenates Held at Different Temperatures

Homogenized, head-on, white shrimp ( Penaeus setiferus ) were held at 4, 12 and 22°C until putrefactive spoilage occurred. Repetitive bacterial sampling was performed and 1647 bacterial isolations were made from the shrimp homogenates. Of these, 42 isolates (2.6%) produced indole. Isolates that produced indole belonged to the genera Flavobacterium (52.4%), Aeromonas (23.8%), Proteus (21.4%) and Yersinia (2.5%). No Escherichia coli were isolated. Aeromonas and Proteus exhibited proteolysis and were able to produce indole in shrimp extracts without added L-tryptophan. These organisms favored higher growth temperatures. The majority of the Flavobacterium isolates were psychrotrophic, non-proteolytic and could not produce indole in shrimp extracts without added L-tryptophan. Suppression of bacterial reproduction with antibacterial compounds inhibited indole production. Two paths of indole production are suggested based on temperature of decomposition.

A Direct Microscopic Count Procedure for the Rapid Estimation of Bacterial Numbers on Green-Headless Shrimp1,2

A Direct Microscopic Count (DMC) procedure, utilizing the Gram-stain, was used to estimate bacterial numbers on 149 samples of green-headless (shell-on) shrimp. A correlation of 0.876 (significant at P < 0.01) existed between the log DMC and log agar plate counts done at 25 C for 2 days. Samples judged questionable or unacceptable organoleptically had DMCs of 108 or more.

Effects of Sampling Procedures on Salmonella Recovery from Fresh Water Catfish

To determine the effectiveness of different sampling procedures, 200 frozen catfish known to be contaminated with Salmonella were divided into 350 samples. Variables in sampling included anterior and posterior portions of fish, blending, immersion, swabbing, rinsing and incubation at elevated temperatures. The composite of blended anterior and posterior samples incubated at 43 C and immersion of whole fish incubated at 35 C showed the highest number of positive samples, 50% and 42%, respectively. The contact method of swabbing (14%) and rinsing (14%) were the least effective of the methods examined. The anterior (visceral cavity area) portions of the fish seemed to be more highly contaminated (38% positive) than the posterior portion (26% positive). These data show that the sampling procedure can greatly affect recovery of Salmonella from fresh water catfish. Overall levels of Salmonella were low and the hazards of cross-contamination with other foods seem remote.