G. Jeyasekaran

Changes in histamine and volatile amines in six commercially important species of fish of the Thoothukkudi coast of Tamil Nadu, India stored at ambient temperature

Abstract Six commercially important species of fish, i.e. mackerel (Rastrelliger kanagurta), sardine (Sardinella fimbriata), emperor bream (Lethrinus miniatus), threadfin bream (Nemipterus japonicus), trevally (Carangoides armatus) and barracuda (Sphyraena barracuda) of the Thoothukkudi coast of Tamil Nadu, India, were examined for changes in histamine and volatile amines (TVB-N and TMA-N) under ambient temperature storage (32±2xa0°C). Fish were organoleptically acceptable up to 15 h of storage, except emperor bream that spoiled after 12 h of storage. Histamine and volatile amines increased progressively on storage, but the rate of change varied with the species of fish. The TVB-N content of barracuda and emperor bream exceeded the acceptable limit of 35 mg/100 g after 15 h of storage while, in other fishes, their formation was slow. However, the TMA-N contents of all the fishes were above 10 mg/100 g after 15 h of storage. The TMA-N content of fish was found to correlate more closely with the sensory changes than the TVB-N content. With regard to the histamine toxicity, the histamine content was above the USFDA maximum allowable limit of 50 ppm in mackerel after 12 h, and, in sardine and trevally, after 15 h of storage. The histamine content did not show any correlation with the sensory changes or with the content of volatile amines. In trevally, it was noted that the histamine formation was very high and similar to that of mackerel. It is therefore concluded that the mackerel, sardine and trevally could cause histamine toxicity problems before they become organoleptically unacceptable.

Skin, bone and muscle collagen extraction from the trash fish, leather jacket (Odonus niger) and their characterization

Acid soluble (ASC) and pepsin soluble (PSC) collagens were extracted from the skin, bone and muscle of a trash fish, leather jacket (Odonus niger) by three different extraction methods. Method I gave 46–50% yield for ASC, Method II gave 49–58% yield for both ASC and PSC and Method III gave 64–71% yield for PSC. The addition of pepsin had increased the yield by 30–45%. The yields of collagen from skin and bone were higher than muscle. SDS-PAGE pattern revealed that skin and bone collagen as Type I collagen with a typical (α1)2α2 chains and muscle collagen as Type V collagen with a typical α1α3α2 chains. Td values of bone and muscle collagen were high (30–32xa0°C) compared to skin collagen (27–28xa0°C). The higher imino acids (190 residues/1,000 residues) were found responsible for the higher Td values. The trash fish, leather jacket can therefore be exploited effectively for collagen as it has got good thermal properties for pharmaceutical and biomedical applications.

Multiplex polymerase chain reaction-based assay for the specific detection of toxin-producing Vibrio cholerae in fish and fishery products

A multiplex polymerase chain reaction (MPCR)-based assay was developed for the simultaneous detection of Vibrios using the genus-specific RNA polymerase subunit A (rpoA) gene and specific detection of toxin-producing Vibrio cholerae strains using two sets of primer based on cholera toxin subunit A (ctxA) and repeat in toxin subunit A (RtxA)-producing genes. The MPCR method developed is applicable to both the simultaneous and the two-step detection of genus Vibrio total and toxigenic V. cholerae species. This assay was specific as no amplification occurred with the other bacterial pathogens tested. The sensitivity of the assay was tested by artificially spiking the shrimp homogenate with the toxigenic strain of V. cholerae (NICED 16582) in different dilutions. The developed MPCR assay could detect three cells of V. cholerae in 12xa0h pre-enrichment in APW. The proposed method is rapid, sensitive, and specific for the detection of Vibrio genus as well as toxin-producing V. cholerae strains in environmental samples.

Morphogenesis, Pathogenesis, Detection and Transmission Risks of White Spot Syndrome Virus in Shrimps

Among the important challenges to shrimp aquaculture worldwide are diseases caused by viruses, in particular by White Spot Syndrome Virus (WSSV) whose genome of 305 kb has been recently sequenced. WSSV, also dubbed White Spot Bacilliform Virus (WSBV), is a major shrimp pathogen with a high mortality rate and a wide host range. The sequencing and characterization of different strains of WSSV has begun to reveal aspects of its biology, virulence and pathogenesis. Knowledge on these aspects is critical for developing effective control methods. The socioeconomic impacts of the diseases caused by the WSSV have been catastrophic in some shrimp producing countries of Asia and the Americas. Thus, these diseases were listed by the World Animal Health Organization (or Office International des Epizootics, OIE) as posing a significant threat to cultured and wild crustaceans as a consequence of international trade or movement of infected organisms. The aim of this review is to present a state-of-the-art knowledge in different aspects of WSSV like morphogenesis, pathogenesis, transmission risks, detection, bio-inoculation studies, and international rules and standards.

Quality Evaluation in Chilled Cuttlefish (Sepia pharaonis) Fillets

ABSTRACT The bacteriological, biochemical and sensory quality of cuttlefish (Sepia pharaonis) fillets chilled in ice was investigated. One lot was immediately iced (II) with flake ice at the ratio of 1:1 (wt/wt) and the other lot was left at room temperature of 32°C for 6 h and then iced and designated as delayed iced (DI). Total bacterial count in both II and DI samples ranged from 103 to 107 cfu/g. Total lactic acid bacteria varied from at 0 to 102 cfu/g. Total coliforms became zero on the 3rd d in II sample. TMA-N and TVB-N did not exceed the limit of acceptability. Hx was in between 0.054 and 4.969 mg/100 g in II sample. Delayed icing of cuttlefish fillets reduced the shelf life by 5 days.

Detection of Salmonella enterica serovars in shrimps in eight hours by multiplex PCR assay

A rapid and sensitive multiplex PCR (MPCR)-based assay was developed for the detection of Salmonella serovars in shrimps within 8xa0h of pre-enrichment. Five sets of primers from different genomic sequences such as fimA, himA, hns, invA and hto genes were selected for the detection of serovars of Salmonella enterica such as S. Typhi, S. Paratyphi A, S. Typhimurium, S. Enteritidis and S. Weltevreden. The selected primers amplified products with sizes of 85xa0bp, 123xa0bp, 152xa0bp, 275xa0bp and 496xa0bp, respectively, for the genus Salmonella. The specificity and sensitivity of the assay were tested by contaminating shrimp homogenate artificially with viable cells of Salmonella. The MPCR assay could detect up to five Salmonella cells within 8xa0h. Amplification of DNA extracted from other genera, viz. Vibrio cholerae and Escherichia coli, yielded negative results. This assay allows for the cost effective and reliable detection of serovars of Salmonella enterica in one reaction tube from mixed bacterial communities occurring in products like shrimp.

Effect of processing treatments on the white spot syndrome virus DNA in farmed shrimps (Penaeus monodon)

Aims:u2002 To investigate the effect of processing treatments on the destruction of white spot syndrome virus (WSSV) DNA in WSSV‐infected farmed shrimps (Penaeus monodon).

Simultaneous detection of Staphylococcus aureus enterotoxin C-producing strains from clinical and environmental samples by multiplex PCR assay

A multiplex PCR (MPCR) assay was developed for the detection of Staphylococcus aureus using selected primers designated on the genus-specific gap gene, species-specific nuc gene and enterotoxin-producing EntC1 gene. The internal regions amplified had a product size of 933xa0bp, 273xa0bp and 531xa0bp, respectively. This MPCR assay had a sensitivity to detect 10 cells of S. aureus and 100xa0pg of genomic DNA of S. aureus. The MPCR assay was found to be specific for S. aureus, as it yielded negative results with other tested bacterial pathogens such as Salmonella typhimurium, Vibrio cholerae and Escherichia coli. Therefore, this developed MPCR assay could be used for the simultaneous detection of S. aureus enterotoxin C-producing strains from clinical and environmental samples.

Changes in Amine Forming Bacteria and Histamine in Yellowfin Tuna (Thunnus albacares) Through the Smoking Process

Abstract The presence of amine forming bacteria and histamine formation in yellowfin tuna (Thunnus albacares) through the hot smoking process was investigated at five different stages of processing. The amine forming bacteria in the raw tuna were very low and were detected in higher proportion (48%) in hot blanched tuna. They survived to a certain extent during the smoking process (7-18%) and were totally absent in the final product because of low moisture (14%) and aw (0.86). The predominant amine forming bacteria identified were Micrococcus, Alcaligenes and Corynebacterium. The histamine level in the raw tuna was very low, which increased gradually through the process and reached a maximum of 12 ppm, which is well below the hazardous limit of 50 ppm prescribed by the USFDA. The result implies that a delay in hot blanching and smoking stage of processing could definitely contribute to the amine formation because of the presence of potential amine forming bacteria even if the initial bacteriological quality of tuna is good.