| Macrobrachium rosenbergii,also known as giant freshwater prawn,has been popular with consumers because of its larger individual size,fresh meat,and good nutrient composition.Besides fresh sales of Macrobrachium rosenbergii,frozen whole prawn and frozen peeled prawn are main types of current processing.However,many processing companies have discovered that there are some questions when using the traditional freezing and frozen storage conditions.With the extension of frozen time,the quality of prawn meat will become soft and inelastic,and the color of prawn head will turn black,which seriously affect the quality of the product.Therefore,there is an urgent need to solve the problems of poor frozen quality.In this paper,the effects of different freezing methods and frozen storage conditions(frozen temperatures and ice-glazing)on the quality of Macrobrachium rosenbergii during the frozen storage were studied.The best frozen process parameters were selected to improve the quality of Macrobrachium rosenbergii.The purpose of above research is to finally provide the theoretical support for industrial production of high quality frozen Macrobrachium rosenbergii.Firstly,the effects of different freezing methods on the quality of Macrobrachium rosenbergii during frozen storage were studied.The qualities of frozen products treated with liquid nitrogen immersing freezing,air-blast quick freezing and refrigerator direct freezing were evaluated using water holding capacity(WHC),texture properties,freshness index,lipid oxidation,microstructure and sensory characteristics.The results showed that the time required for liquid nitrogen immersing freezing to reach the-18? center temperature of prawn was only 20 s,while air-blast quick freezing and refrigerator direct freezing needed 11 and 110 min,respectively.In terms of texture properties,compared with fresh prawn,the prawns' hardness of liquid nitrogen immersing freezing,air-blast quick freezing and refrigerator direct freezing had fallen by 44.86%,62.90% and 70.45%,respectively after frozen 8 weeks.The texture deterioration of Macrobrachium rosenbergii was the most serious in the early 8 weeks,and then slowly changed.Besides in the aspect of freshness,according to Chinese total volatile basic nitrogen(TVB-N)hygienic standard for aquatic product(GB 2733-2015),the limit level of TVB-N content for freshwater prawn product is 20.00 mg/100 g.The TVB-N content of the freshwater prawn treated with refrigerator direct freezing in 12 th week was 22.74 mg/100 g,which had exceeded the limit level,and the TVB-N content of the freshwater prawn treated with air-blast quick freezing had exceeded the limit level in 16 th week(21.70 mg/100 g).While the TVB-N content of the freshwater prawn treated with liquid nitrogen immersing freezing was still below the limit level in 20 th week(19.75 mg/100 g).According to the results of hardness and freshness indexes,the shelf life of Macrobrachium rosenbergii treated with liquid nitrogen immersing freezing was about 4 weeks and 8 weeks longer than that of air-blast quick freezing and refrigerator direct freezing.Liquid nitrogen immersing freezing treatment had the ice crystals with smaller size and uniform distribution,and less protein denaturation and degradation and total number of colony,resulting in better quality of Macrobrachium rosenbergii.Secondly,the effects of different frozen temperature on the quality of Macrobrachium rosenbergii during frozen storage were studied.The WHC,texture properties,freshness index,the electronic nose smell response value and sensory characteristics of Macrobrachium rosenbergii frozen at-50 and-18? were investigated.The results showed that the similar decline of WHC,freshness index and texture were observed in two treatments with a trend of rapid growth in the early stage and then slow change.The shear force of Macrobrachium rosenbergii decreased significantly in the early frozen stage.The shear force of prawn had fallen by 55.62%(-50?)and 63.88%(-18?)after frozen 4 weeks and 76.35%(-50?)and 81.47%(-18?)after frozen 20 weeks.At the same time,the TVB-N content of Macrobrachium rosenbergii frozen in the two temperatures were still below the limit level during the frozen storage,but the TVB-N content of prawn frozen at-50? was always below that of prawn frozen at-18?.In addition,the electronic nose smell response values of Macrobrachium rosenbergii frozen at-50? were closer to fresh samples compared to prawn frozen at-18?.Therefore,lower storage temperature improved the quality of frozen Macrobrachium rosenbergii during the frozen process.Finally,the effects of ice-glazing on the quality of Macrobrachium rosenbergii during frozen storage were studied.The effects of different ice-glazing clothes on the qualities of Macrobrachium rosenbergii were evaluated using WHC,hardness,TVB-N content,TBARS value and redness(a*).The results showed that the TVB-N content of ice-glazing with chitosan exceeded the limit level in 20 th week(21.02 mg/100 g),while the TVB-N content of ice-glazing with tea polyphenols(21.00 mg/100 g),water(20.73 mg/100 g)and control group(21.70 mg/100 g)exceeded the limit level in 16 th week.It showed that ice-glazing with chitosan played a role in keeping freshness of Macrobrachium rosenbergii during the frozen process.And a* value of ice-glazing with tea polyphenols(1.22)was significantly lower than chitosan group(1.76),water group(2.20)and control group(3.04)in 20 th week,which showed that ice-glazing with tea polyphenols could effectively inhibit browning reaction.Therefore,ice-glazing treatment,especially containing antibacterial substances and anti-oxidants,was beneficial to maintain the quality of Macrobrachium rosenbergii during the frozen storage. |
PDF Full Text Request