Thakor R. Patel

Listeria in seafoods: a review

Listeria is an environmental contaminant which has been isolated from marine and fresh waters, as well as various seafoods. Furthermore, Listeria , including Listeria monocytogenes , has been isolated from processed seafood products such as smoked fish, cooked and frozen seafoods, marinated fish, surimi products, etc. The pathogen, L. monocytogenes , does have a certain degree of heat resistance. It was found to survive in internally infected shrimp after boiled for up to 5 min. However, the commercial pasteurization process for crab meat was found to be sufficient to inactivate Listeria . The current recovery methodology for L. monocytogenes from seafoods is the Food and Drug Administration Listeria protocol.

Occurrence of Listeria in hot and cold smoked seafood products

Over a one-year period, 258 samples of smoked fish products were obtained from retail outlets in Newfoundland and processed for Listeria. Of these, 142 were hot smoked and 116 cold smoked, and the samples comprised of nine species of fish. The Canadian FDA listeria isolation protocol consisted of a two-stage enrichment followed by plating on selective isolation media, Oxford, and LPM. An additional selective medium, PALCAM, was also used. Listeria spp. were isolated from 43 of 258 (16.7%) samples processed in all, with hot smoked products yielding 25.4% (36/142) of the isolates, and cold smoked products yielding 6% of the isolates (7/116). Among the nine species tested, cod had the highest rate of Listeria contamination at 46.7%. Of the 43 Listeria spp. isolated, 18 (41.9%) were L. innocua, 13 (30.2%) were L. welshimeri and 12 (27.9%) were L. monocytogenes.

Cometabolic Degradation of Polychlorinated Biphenyls at Low Temperature by Psychrotolerant Bacterium Hydrogenophaga sp. IA3-A

A biphenyl-utilizing bacterium isolated from polychlorinated biphenyls (PCBs)-contaminated soils grew on tryptic soy at temperatures between 4 and 40°C. The Gram-negative rod bacterium formed yellow colonies on nutrient agar and it denitrified nitrate to nitrogen. Analysis of cellular fatty acids showed that it was most closely related to Hydrogenophaga taeniospiralis. At 5°C, biphenyl-grown cells cometabolically degraded di- and trichlorinated isomers of PCBs in 10 ppm of Aroclor 1248. At 30°C, PCBs that were removed included a congener with four chlorine substituents. At 5°C, cells transformed 2,4′-dichlorobiphenyl (2,4′-DCB) and accumulated ortho-chlorinated meta-cleavage product as a stable metabolite. Analysis of extracts of culture supernatant by gas chromatography–mass spectrometry indicated that products of transformation of 2,4′-DCB included 2- and 4-chlorobenzoic acid (2- and 4-CBA), suggesting that (chloro)biphenyl-degrading upper-pathway enzymes of the bacterium are active at low temperature. The bacterium Hydrogenophaga sp. IA3-A is a PCB-degrading psychrotolerant strain.

Growth parameters for the yeast Rhodotorula rubra grown in peat extracts

Abstract A newly-isolated strain of Rhodotorula rubra, which has been reported to have the ability to synthesize high concentrations of carotenoids, has been adapted and grown in liquid phase using acid extracts of peat as the main substrate source. The growth of the yeast was studied as a function of the medium carbohydrate concentration, pH, time, temperature, and agitation rate. The optimal growth conditions were found to be an initial total carbohydrate concentration of 15 g·l−1, a pH of 5.5, an incubation time of 3.5 d, a temperature of 22°C, and an agitation rate of 200 rpm. Under those conditions, the growth parameters were: approximately 4.8 g· l−1 dry biomass, 70% yield and 32% efficiency. Also, a total β-carotene concentration of 1,256 μg·g−1 dry biomass was produced by the yeast.

An overview of pigment production in biological systems: Functions, biosynthesis, and applications in food industry

Abstract Since times immemorial, colors in the living world have always fascinated and amazed humans and left them wonderstruck; the present study has also been inspired by their provocative and conspicuous nature. The structural colors, wherein a variety of optical properties emerge as a result of the physical nature of the surface of the tissue, are, however, excluded from the present review. To give a brief account, two predominant structural colors encountered in the biological systems are Tyndall blue colors and iridescent colors. The former are produced as a result of light scattering by very small particles, examples being the color of human eyes and feathers of many birds. The iridescent colors result from interference with light by thin films or laminations, and examples of such colors are abundant in the animal kingdom, in birds, insects, and fishes. It should be noted that no pigment per se is extractable in either of the structural colors discussed. For a detailed account, the readers may refe...

Prevalence of Listeria in Smoked Fish

Smoked fish samples (71) were surveyed from Newfoundland retail markets and tested for the prevalence of Listeria . Staphylococcus aureus and fecal coliforms were also detected in the samples. Listeria was present in 11.3% of the smoked seafood products; 4 smoked cod, 3 smoked mackerel, and 1 smoked caplin were found to harbor the bacterium. The Food and Drug Administration protocol was also analyzed with regards to testing smoked seafoods. The secondary enrichment broth showed a 68% false-positive rate, whereas all positive samples were detected after 24 h of primary enrichment.

Study of Growth Parameters for Phaffia rhodozyma Cultivated in Peat Hydrolysates

The yeastPhaffia rhodozyma, known for its ability to synthesize carotenoids, was adapted and cultivated in liquid-phase media using peat hydrolysates as the main substrate source. The hydrolysates were prepared using high-pressure treatment at 185°C, without the addition of acid. The growth of the yeast was studied as a function of the pH, temperature, culture time, and agitation speed. The best conditions for the growth of the yeast were: a pH of 7, a temperature of 18°C, 5-d culture time, and 200-rpm agitation. Under those conditions, P.rhodozyma produced a concentration of 1279.82 μg carotenoids g-1 dry yeast, which compares well with other previously reported results.

Bacteriological quality of ice used in mucuripe market, Fortaleza, Brazil

Abstract A close examination of the microbiological quality of the ice made and used in the local markets in Fortaleza, Brazil, revealed it to be of poor quality. Besides the common food spoilage organisms often encountered in sea foods, foodbourne pathogens (streptococcus, listeria and fecal coliforms) were also detected. Gramnegative bacilli/cococacilli outnumbered all other groups by representing 78% of the total 90 isolates. The remaining 12% included gram-positive non-spore forming rods and gram-positive cocci.

Sorbates in fish and fish products—a review

Abstract A large number of studies have been carried out to determine the efficacy of sorbates in extending the shelf‐life of fish and fish products. The results of these studies indicate that sorbates in combination with other compounds or techniques inhibit the growth of microorganisms including some potential pathogens in these products, thereby extending their shelf‐life. Sorbates retarded the chemical changes occurring in fish during storage and inhibited the formation of trimethylamine and other chemicals responsible for fish spoilage. Sorbates prevented the development of off‐odors in fish and fish products by preventing oxidation in them. The acceptability scores of sorbate‐treated products were higher as compared to untreated control samples. In short, studies conducted on the use of sorbates in fish and fish products suggest that sorbates in combination with other compounds or techniques can be used as an effective preservative for extending the shelf‐life of fish products.

Effect of cold smoking and storage temperatures on Listeria monocytogenes in inoculated cod fillets (Gadus morhus)

Abstract Experiments were conducted to study the effects of the cold smoking process and storage on Listeria monocytogenes inoculated onto cod fillets. In three trials, cod fillets were surface inoculated with L. monocytogenes , cold smoked, vacuum-packaged, and stored at 4°C for 3 weeks or at −20°C for 3 months. Samples were removed at each stage of the smoking process and during storage, and Listeria were enumerated using the three-tube most probable number MPN method. The initial inoculation concentrations were 10 5 MPN/g in trial 1, 10 6 MPN/g in trial 2, and 10 1 in trial 3. Numbers of the organism remained relatively stable during the smoking process, increased with storage at 4°C, but decreased in cell number with storage at −20°C. Substantial growth occurred in trials 1 and 2, but was very slow in trial 3 where the inoculum level was low. Hence, L. monocytogenes contamination in smoked seafoods which are not cooked prior to consumption, may pose a health risk to the consumer.