Microbiological quality study of Macrobrachium rosenbergii (de Man 1879) during storage at -20°C temperature

The shelf life of fresh water prawn Macrobrachium rosenbergii by applying low temperature was investigated. M. rosenbergii preserved at -20°C was subjected for quality assessment before storage and at 15, 30, 45, and 90 days of storage period. The quality assessments as done microbiological viz. total bacterial count (TBC), total mould count (TMC), total yeast count (TYC), total coliform count (TCC) and salmonella count. All the samples were acceptable during 90 days because the upper limit of all spoilage indicator was not exceeding within the experimental time period.

Effect of gamma radiation in combination with freezing on the microbiological changes in frozen shrimp Penaeus monodon

In this study gamma radiation (3, 6 and 9 kGy) in combination with low temperature (-20°C) were applied to retain the quality and shelf-life of shrimp, Penaeus monodon for a longer period. The quality was assessed by monitoring microbiological changes (TBC, TMC, TYC, TCC and Salmonella count) in irradiated and non-irradiated (control) samples. Among microbiological indicators of spoilage, total bacterial count (TBC) values for irradiated shrimps were found to be 1875, 1625 and 1525 cfugˉ¹ of sample at 3, 6 and 9 kGy respectively after 90 days whereas for non-irradiated samples it was found 2475 cfugˉ¹ of sample. Total moulds count (TMC) value for non-irradiated samples after 90 days were found 425 cfugˉ¹ sample whereas that for irradiated shrimps at 3, 6 and 9 kGy were found to be 275, 250 and 200 cfugˉ¹ sample respectively. Total yeast count (TYC) value for non-irradiated samples after 90 days were found 4125 cfugˉ¹ sample whereas that for irradiated shrimps at 3, 6 and 9 kGy were found to be 2850, 2150 and 1725 cfugˉ¹ sample respectively. Total coliform count and Salmonella count showed that those were absent during 90 days storage period. From this study, it was clear that gamma radiation in combination with low temperature showed shelf-life extension (90 days) in each dose of radiation used but during the use of 9 kGy radiation, Penaeus monodon showed best quality.

Study of physicochemical, microbial and sensory properties of surimi produced from black mouth croaker (Atrobucca nibe) at freezing condition (-18ºC)

Black mouth croaker (Atrobucca nibe) is considered as a new valuable fish stock in the Oman Sea. In this study, surimi was manufactured from nonmarket size of the fish, manually and different cryoprotectant agents were added to the surimi. Finally changes in physiochemical, microbiological and sensory quality, characteristics of the surimi and kamaboko gel samples were assessed during 6 months at freezing storage (-18ºC). Surimi samples with the addition of Iranian tragacanth gum (TG), xanthan gum (XG), chitosan (CS) and whey protein concentrate (WPC) at 1% (w/w) were prepared to evaluate their impacts as a cryoprotectant on the surimi, individually. The results showed that the whiteness and lightness indexes in all surimi samples were gradually decreased during frozen storage. This trend of decreasing was more intensity in the control sample from 61.08±0.131 to 54.21±0.067 was recorded (p<0.05). Water holding capacity (WHC) in all treatments was decreased during 6 months. The lowest WHC (g/g) was obtained in the surimi without cryoprotectants and maximum WHC was measured in Tcs and Twpc samples, respectively (p<0.05). The lowest breaking force was calculated in Txg (166.00±22.627 g) and Tc (271.50±263.16 g) during 6 months at frozen storage, respectively (p<0.05), while Twpc treatment with slight variations showed the highest breaking force (p<0.05). Also, the lowest gel strength was obtained in Txg (68.22±6.740 g.cm) after 6 month of frozen storage (p<0.05). All Kamaboko surimi gels texture profile analysis parameters decreaced with increasing shelf life. This decreasing trend in the control sample was more severe. Floding results were reduced in all samples during storage (p<0.05). The best protective results probably were obtained in WPC, chitosan and commercial cryoprotectant agents, respectively due to protein stabilization of myofibrillar proteins and the protein-protein network structure, leading to the formation of surimi gel with strong textural properties during frozen conditions. The average number of surimi polygonal structures were significantly decreased (number per mm2) and their area were significantly increased (μm2) in all treatments (p<0.05). With increasing storage time, moisture, protein contents and pH were decreaced. Maximun TVB-N index was calculated in Tc (7.93±0.400 mg/100g) and Txg (7.88±0.477), respectively (p<0.05). TBRAs index was increased in all treatments during frozen storage, while this trend was reached in maximum value in Tc (p<0.05). Sensory evaluation of the fish finger quality characteristics (color, odor, texture and overall acceptability) preapare from frozen black mouth croaker surimi was decreaced during 6 month frozen storage. After the period of frozen storage the highest quality scores were measured in Twpc, Tcs and Tcc samples, respectively (p<0.05). In this study, coliform bacteria were not found in all treatments during frozen storage. The surimi sample containing chitosan showed lower mesophilic and psychrotropic bacteria (log cfu/g) than other treatments during frozen storage (p<0.05). Salt-soluble proteins extractions of all treatments were decreased during frozen storage. This decreacing trend was highest in Tcs (45.74±0.176%) and lowest in Tc treatments after 6 month of frozen storage (29.92±0.224%) (p<0.05). Although commercial cryoprotectant agents were successful in limiting the denaturation of proteins but sugar contents were not accepted for diabetics or those who disagree with the sweet taste and high calorie food. Hence, commercial cryoprotectant agents can be replaced with whey protein concentrate and chitosan at 1% level (w/w) consider that they were showed proper protection of the surimi myofibrillar proteins during storage.