Evaluation of physicochemical characteristics of microwave vacuum dried mackerel and inhibition of oxidation by essential oils

In the present study, Indian mackerel was dried by microwave vacuum drying (MVD) method and compared its physico chemical quality to mackerel dried by hot air drying (HAD) method. Antioxidant effects of thyme oil (TMO) and clove leaf oils (CLO) during storage were also evaluated. Brine salted mackerel was dried in hot air oven (50-55 °C) and microwave vacuum dryer (600 W and 600 Hg mm). For essential oil treatment, mackerel was dipped in 0.75% TMO and CLO for 5 min. Moisture content of MVD and HAD samples was reduced to 30-32% in 1.2 h and 12 h, respectively. Rehydration ability and water absorption index of MVD samples were significantly higher to that of HAD samples. Mackerel dried by HAD showed significantly higher salt soluble and water soluble protein nitrogen fractions than that of MVD samples. Significantly higher hardness and chewiness values were observed for HAD samples. Color and appearance of uncooked MVD sample was superior to that of HAD samples. As per the results of PV and TBARS, TMO exhibited better antioxidant effect compared to CLO. The study demonstrated that fast drying can be achieved by microwave vacuum dryer and it can produce dried fish having better sensory and textural attributes.

Effect of serine protease inhibitor from squid ovary on gel properties of surimi from Indian mackerel

Effects of serine protease inhibitor from squid ovary (SOSPI) and egg white powder (EWP) on gel properties of surimi from Indian mackerel (Rastrelliger kanagurta) were investigated. Breaking force of gel increased when SOSPI levels increased up to 2%. However, EWP showed higher efficiency in increasing breaking force of resulting surimi gel. Nevertheless, SOSPI (0.5-3%) had no effect on deformation. Trichloroacetic acid-soluble peptide content in surimi gel decreased when the levels of SOSPI and EWP increased (p < .05). This was coincidental with more retained myosin heavy chain. Water holding capacity was increased with the addition of these protein additives, but resulted in lower whiteness. Microstructure study revealed that surimi gel added with 2% EWP was denser and had higher connectivity as compared to that containing 2% SOSPI. The SOSPI had no negative effect on sensory attributes and could serve as the alternative protein additive to improve gel strength of surimi.

PRACTICAL APPLICATIONS

Surimi from dark-fleshed fish is prone to degradation of myofibrillar proteins caused by the endogenous proteases, thereby lowering textural property. To tackle the problem, protease inhibitors (egg white, porcine plasma protein, and bovine plasma protein) have been used by the surimi industries. Due to drawbacks of some particular inhibitors (religious constraints, off-white color, off odor, etc.), the novel additives are still in demand. Ovary from squid processing industry, commonly discarded as the waste, can be an alternative natural protease inhibitor, which can improve the gel properties of surimi, especially produced from dark-fleshed fish.

Combined effects of vacuum packaging and mint extract treatment on the biochemical, sensory and microbial changes of chill stored Indian mackerel

The present study was aimed to investigate the combined effects of vacuum packaging and mint extract treatment on the quality changes of gutted Indian mackerel (Rastrelliger kanagurta) during storage at 0-2 °C for 22 days. Biochemical, total viable count and sensory quality of chill stored mackerel were analysed at periodic intervals. Mint extract treated [dipping in 0.5% (w/v) solution of mint extract for 30 min] and vacuum packed fishes (MEVP) had significantly lower total volatile base nitrogen and trimethyl amine nitrogen compared to those packed under vacuum (CVP) and air (CAP) without mint extract treatment. Nucleotide degradation rate was lower in MEVP followed by CVP and CAP. Vacuum packaging in combination with ME treatment significantly inhibited lipid hydrolysis and lipid oxidation in mackerel as observed from its lower free fatty acid, peroxide value and thiobarbituric acid reactive substances values. Synergistic use of mint extract and vacuum packaging has markedly controlled microbial proliferation in the samples. Based on sensory evaluation, shelf life of Indian mackerel stored at 0-2 °C was determined as 13 days for CAP group, 16 days for CVP group and 21 days for MEVP group, respectively. The present study revealed that combination of vacuum packaging and mint extract treatment can be a promising technology to improve the storage quality of chill stored gutted mackerel.

Trypsin from unicorn leatherjacket (Aluterus monoceros) pyloric caeca: purification and its use for preparation of fish protein hydrolysate with antioxidative activity

BACKGROUND

Fish proteases, especially trypsin, could be used to prepare fish protein hydrolysates with antioxidative activities. In this study, trypsin from the pyloric caeca of unicorn leatherjacket was purified by ammonium sulfate precipitation and soybean trypsin inhibitor (SBTI)-Sepharose 4B affinity chromatography. Hydrolysate from Indian mackerel protein isolate with different degrees of hydrolysis (20, 30 and 40% DH) was prepared using the purified trypsin, and antioxidative activities (1,1-diphenyl-2-picrylhydrazyl and 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) radical-scavenging activities, ferric-reducing antioxidant power and ferrous-chelating activity) of the hydrolysate were determined.

RESULTS

Trypsin was purified 26.43-fold with a yield of 13.43%. The purified trypsin had a molecular weight (MW) of 23.5 kDa and optimal activity at pH 8.0 and 55 °C. It displayed high stability in the pH range of 6.0-11.0 and was thermally stable up to 50 °C. Both SBTI (0.05 mmol L(-1)) and N-p-tosyl-L-lysine-chloromethylketone (5 mmol L(-1)) completely inhibited trypsin activity. Antioxidative activities of the hydrolysate from Indian mackerel protein isolate increased with increasing DH up to 40% (P < 0.05). Based on sodium dodecyl sulfate polyacrylamide gel electrophoresis, the hydrolysate with 40% DH had a MW lower than 6.5 kDa.

CONCLUSION

The purified protease from unicorn leatherjacket pyloric caeca was identified as trypsin based on its ability to hydrolyze a specific synthetic substrate and the response to specific trypsin inhibitors. The purified trypsin could hydrolyze Indian mackerel protein isolate, and the resulting hydrolysate exhibited antioxidative activity depending on its DH.

Antioxidant and antimicrobial properties of grape and papaya seed extracts and their application on the preservation of Indian mackerel (Rastrelliger kanagurta) during ice storage

Antioxidant properties of grape (GSE) and papaya seed extracts (PSE) were tested in vitro at varied concentrations and growth inhibition were seen against gram positive and gram negative bacteria by disc diffusion method. The results revealed that GSE contain four times higher phenolic and six folds higher flavonoid content than PSE. The antioxidant properties of GSE and PSE showed dose dependent activities and were comparatively much higher in GSE. Linoleic acid model of GSE and PSE displayed 67.67 and 46.43 % of inhibition respectively at 500 mg/L. The effect of dip treatment by GSE and PSE at a concentration of 500 and 1000 mg/L respectively on the quality changes of Indian mackerel (Rastrelliger kanagurta) in iced condition were assessed using chemical, microbiological and sensory parameters along with chilled whole control (CWC). The inhibition of primary and secondary lipid oxidation products by GSE at 500 mg/L was comparable to BHT at 200 mg/L. GSE exhibited higher antimicrobial activity on gram-positive strains compared to PSE and reduced the formation of volatile bases significantly. On the day of sensory rejection for CWC, the formation of trimethylamine and total volatile base nitrogen were reduced by 32.27 and 31.85 % in GSE samples and 19.01 and 24.70 % in PSE samples respectively. The dip treatment of GSE increased the shelflife of mackerel up to 15 days, PSE by 12 and 9 days for CWC during ice storage. Therefore, it can be concluded that, GSE can be used as a promising natural preservative and a substitute to the synthetic counterparts.

Comparative evaluation of gum arabic coating and vacuum packaging on chilled storage characteristics of Indian mackerel (Rastrelliger kanagurta)

The effect of edible coating using gum arabic on biochemical, microbiological, textural and sensory characteristics of fresh gutted mackerel stored at 4 °C was investigated. The results were further compared against the samples packed under vacuum (VP) and conventional polyethylene pouches (CP). Coating with gum arabic (GC) markedly retarded lipid oxidation process in gutted mackerel compared to VP and CP samples. Moreover, VP and CP samples showed higher degree of textural deterioration compared to GC samples. Microbiologically, the shelf life of chilled gutted Indian mackerel was estimated to be 7-8, 17 and 19-20 days for CP, GC and VP samples, respectively. The sensory analysis scores confirmed the efficacy of gum coating in retarding the spoilage process during chilled storage. The current study identifies the potential of edible coating with gum arabic to improve the overall quality of Indian mackerel and extend its storage life during chilled storage.

Efficacy of mint (Mentha arvensis) leaf and citrus (Citrus aurantium) peel extracts as natural preservatives for shelf life extension of chill stored Indian mackerel

Efficacy of mint (Mentha arvensis) leaf and citrus (Citrus aurantium) peel extracts in retarding the quality changes in Indian mackerel during chilled storage was investigated. Mint leaf extract showed higher quantity of phenolics and superior in-vitro antioxidant activities than citrus peel extract. Gutted mackerel were given a dip treatment in mint extract (0.5 %, w/v) and citrus extract (1 % w/v), packed in LDPE pouches and stored at 0-2 °C. The biochemical quality indices viz. total volatile base nitrogen (TVB-N), trimethylamine nitrogen (TMA-N), free fattyacids (FFA) were significantly (p < 0.05) lower in mint extract (ME) treated fishes compared to citrus extract (CE) treated and control fishes (C) without any treatment. Plant extract treatment significantly inhibited lipid oxidation in mackerel as indicated by peroxide value (PV) and thiobarbituric acid reactive substances (TBARS). Aerobic plate count (APC) was markedly higher in C group followed by CE group throughout the storage period. As per sensory evaluation, shelf life of Indian mackerel was determined to be 11-13 days for C group, 13-15 days for CE group and 16-17 days for ME group, during storage at 0-2 °C.

Biogenic amines, amino acids and microflora changes in Indian mackerel (Rastrellinger kanagurta) stored at ambient (25-29 °C) and ice temperature (0 °C)

Biogenic amines formation in Indian mackerel of tropical region was investigated during storage at ambient (25-29 °C) and ice temperature (0 °C) in relation with changes of amino acids content and amines forming bacteria. All amines increased significantly during storage at two temperatures except for spermidine and spermine. Histamine concentration of 363.5 ppm was detected after 16 h stored at ambient temperature. Aerobic plate count of fish stored at ambient temperature reached 6.98 log CFU g(-1) after 16 h, close to the upper limit (7 log CFU g(-1)) suggested by International Commission on the Microbiological Specifications for Foods (ICMSF). However, proper icing procedure retarded the formation of histamine effectively, resulting only 8.31 ppm after 16 days of ice storage. Aerobic plate count of 5.99 and 7.72 log CFU g(-1) were recorded for fish stored in ice after 16 days and ambient temperature after 20 h, respectively. Histamine exhibited high correlation with histidine (r(2) = -0.963, P < 0.01) as well as cadaverine with lysine (r(2) = -0.750, P < 0.05). However, tyramine-tyrosine demonstrated a weaker relationship (r(2) = -0.138, P > 0.05). As storage time progressed, the amines forming bacteria grew significantly except for that stored in ice.

Metazoan parasites of the Indian mackerel, Rastrelliger kanagurta (Scombridae) of Visakhapatnam coast, Bay of Bengal

The metazoan parasite fauna of the Indian mackerel Rastrelliger kanagurta of Visakhapatnam coast, Bay of Bengal comprised 15 species including three species of Monogenea, seven species of Digenea and five species of Crustacea. Digeneans were the dominant members in the parasite spectrum while infections with ectoparasitic monogeneans and crustaceans were rare. The digeneans Opechona bacillaris and Lecithocladium angustiovum which occurred with high prevalence and mean intensity are the typical parasites of the mackerel. The parasitic fauna in general is found to be a reflection of the planktonivorous diet of the host. Except for two species of digeneans, Lecithocladium angustiovum and Aponurus laguncula, all the remaining species of metazoans showed narrow specificity to R. kanagurta, indicating a high degree of host specialization. The parasitological data may prove useful for differentiating stocks of R. kanagurta.

Community ecology of the metazoan parasites of the Indian mackerel Rastrelliger kanagurta (Scombridae) from the coast of Visakhapatnam, Bay of Bengal

One hundred and eighty four specimens of the mackerel Rastrelliger kanagurta collected from fish landings at Visakhapatnam coast, Bay of Bengal, between January 2006 and 2007, were examined for analysis of their metazoan parasite community structure at infra and component community levels and study the effects of season and host body length on these communities. Fifteen species of metazoan parasites were collected including 3 spp. Monogenea, 7 spp. Digenea and 5 spp. Copepoda. All the fish were parasitized by one or more metazoan parasite species. A total of 2,004 parasites were collected with a mean of 10.9. The majority were digeneans accounting for 42.4% of total number of parasites collected and the hemiurid Lecithocladium angustiovum is found to be the most dominant species. Mean values of species richness (3.0 ± 1.5), abundance (12.4 ± 9.3) and diversity (H' = 0.92) were within ranges observed for most of the metazoan parasite communities of marine fish from temperate and tropical countries. Seasonally, the mean diversity and parasite species richness of infracommunities were high during December and January and low during September-October. No correlation was found between host total length and any of the community descriptors. Most of the parasites i.e., 12 out of 15 species of parasites collected were host specialists. Only one species Aponurus laguncula was a host generalist. All taxa of metazoan parasites showed a typical over-dispersed pattern of distribution. The dominance of the core species in all the infracommunities and the high degree of host specialization of the parasite species resulted in the predictable component in the infracommunities to be high, each infra community comprising a core species accompanied by a few secondary species.