Quality changes of tilapia sashimi and water-cooked meat

• Main Authors: Yang, Huey- Chyau, 楊惠喬
• Other Authors: Kong, Ming- Sheng
• Format: Others
• Language: zh-TW
• Published: 1999
• Online Access: http://ndltd.ncl.edu.tw/handle/45810562239033513814

碩士 === 國立海洋大學 === 食品科學系 === 87 === Quality changes of raw tilapia meat (sashimi) resulted from postmortem storing at 4oC and 25oC as well as its cooked meat resulted from not water dip-cooking where the raw meat had pre-aged to different extents were investigated. Rigrometer, DSC and various biochemical analyses were adopted to study muscle protein and its related physiochemical changes. Meat eating quality indices, including muscle shortening, dripping loss, water holding capacity (WHC), shear (penetration) force, umami component IMP content and VBN / K-value were used to evaluate the raw and cooked meat quality changes during storing and cooking. These results are valuable as used to establish proper raw meat storage and cookery conditions and to understand the physiochemical changes in effecting the qualities during the processing. As on the study of storage in effecting the raw meat quality, it is evident that the most freshly meat obtained right after slaughter possesses the most juicy and tender texture reflected by its high WHC and relatively low shear force detected, respectively. Aging at 4oC, it was found that cold shortening effect as well as inhibiting of tenderization effect were accounted by the cooling；only 12 hr aging was sufficient to bring muscle to reach the maximum shortening (on set of full-rigor), on contrary it required as long as 24 hrs to reach its optimal tenderization. Consequently, the rigor dependent development of quality indices, including muscle shortening, dripping loss, loss of WHC, increase meat of shear force were increased significantly in the first 12 hr aging；parley IMP was increased to its maximum at round 9 hr of aging. On contrary, decreasing in shear force was observed in the next 12 hr of aging which should be of tenderization in control. VBN and K- value indicated that high freshness could be maintained for 24 hrs aging at 4oC. These results indicate the chill- storage meat are more chewable and more rich in umami within 24 hr of aging, and these features are most pronounced after around 12 hr of aging at 4oC. Aging at 25oC, slower postmortem shortening and faster tenderization were observed. It required 24hr and 12 hr to reach their optimal rigor and tenderization, respectively. Retarded by the rapid tenderization, shear force would only be increased slightly in a short 6 ~ 8 hr aging period and then fallen rapidly below the original value. Only slightly increasing in IMP content could be detected and high freshness could only be maintained in this same period. Therefore, very short period about 6 ~ 8 hr aging is allowed for sashimi to be storage and consumed at 25oC. While on the study of dipping cookery, hot water of 65oCand 80oC were used to do the cooking. It is evident by DSC thermograms that a lower cooking temperature around 65oC ~ 70oC is sufficient to bring fresh muscle protein to full denaturation, however higher temperature about 80oC is required to bring aged meat to full denaturation. A three phases meat quality changes of cookery were always observed, regardless the differences of meat thickness, pre-aging history, and cookery temperature adopted in the cookery experiments. The first stage is the taking place of heat denaturation of major muscle proteins, which would cause shortening, loss of WHC. In the same period, heat hydrolysis of collagen was also observed and it should be the cause of the muscle softening reflected by the decreasing in meat shear force detected. The second phase is a quality plateau phase, in which no significant change in meat qualities would be observed. This is the sign that the meat has been properly cooked. The onset of third phase was evidenced by the appearance of the meat texture breakdown indicating that meat is over cooked. Furthermore, it was found that improved meat qualities including higher WHC, reduced shortening and improved cooking yield could be achieved obtained upon adopting a thicker fillet or a higher cooking temperature for the dipping cookery. This might be caused by the temperature gradient effect that earlier denaturation of muscle in thee surface layer forms a sealed outer shell to prevent the interior muscle to contract and loss of water in the layer phase of cookery.