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Changes in Quality and Freshness Control of Tilapia during Distribution at Different Channels
本研究係以省產養殖吳郭魚為材料，探討在運輸流通過程中，魚的鮮度及衛生品質變化的情形，並尋求魚的鮮度及衛生品質對其加工適用性的影響和彼此之間的相互關係。以 0℃ 的溫度為流通過程之對照組，檢測吳郭魚之肌肉特性包括凝膠形成能力、肌動凝蛋白之 Ca-ATPase 活性，並以微生物數作為衛生品質的指標。所得結果如下：
1. 吳郭魚在各流通過程中以活魚運輸到達各銷售點的活魚，其 K 值都維持在 10% 以下。且魚肉發生腐敗的現象是開始於死亡後。故只需以活魚為依據，比較死亡後的品質變化情形。
2. 魚在死後會發生僵直的現象，pH 呈現下降趨勢，進入解僵時期則會上升。在 0 天的取樣中以活魚即殺所得 6.92 為高，其他流通方式可能因魚死後一段時間，所以 pH 較低；隨時間的增加 pH 都有上升的趨勢。
3. 魚肉之總生菌數以即殺活魚為最低，在 0℃ 下流通時，生菌數會隨時間增加而上升；生鮮超市進貨時，總菌數值雖高，但隨時間增加，其變化不大，可能為經過前處理之緣故。
4. 吳郭魚肌肉中VBN（volatile basic nitrogen）隨時間的延長而增加，其值都不超過 20 %；隨流通時間的增加，只有少量生物胺產生。
5. K 值方面，以即殺之魚肉 7% 最低，隨時間增加，K 值會增加。一般生鮮超市以開放式冷藏櫃流通，溫差較大，所以 K 值的上升速率較大。
6. 在各種流通過程中，魚肉的色澤中 L 、 a 、 b 值，隨貯藏時間之增加， L 值的變化不大，a、 b 值呈不規則變化；白色度（whiteness）及彩度（chroma）的變化分別與 L 值及 b 值相似。
7. 吳郭魚在不同的流通過程中，魚肉的凝膠特性隨 K 值增加而下降。可能是自溶酵素（autolytic enzyme）作用而造成蛋白質變性，降低鹽溶性蛋白之抽出。
8. 在不同流通過程中，吳郭魚肌動凝蛋白的抽出率及 Ca-ATPase 活性隨時間增加而下降。
9. 由蛋白質溶解度、DSC（differential scanning calorimetry）測定、SEM（scanning electron microscope）觀察等得知吳郭魚肌肉的蛋白質會因流通過程而變性。
10. 吳郭魚以活魚方式流通品質最佳，但其設備費高。以調理狀態流通，雖適合消費者方便性之要求，但流通溫度的控制十分重要，冷藏條件下其貯藏期僅為 4 日。
Tilapia (Orechromis niloticus) was used as raw materials to investigate the changes in freshness and sanitary quality during transportation. The applicability of the fish in different quality was also investigated. Tilapia stored at 0℃ was regarded as control to detect the sanitary quality index for muscle properties including gel forming ability, color, activity of actomyosin Ca-ATPase, and the number of microorganisms. The results obtained were as follows:
1. K value of living tilapia during transportation was lower than 10%. Only the postmortem fish was necessary to be detected the change in quality due to the spoilage of fish began after they died.
2. pH of tilapia decreased during rigor mortis, but increased during post-rigor. The highest pH of 6.92 was found at the stage immediately after being killed.
3. Tilapia immediately killed showed the lowest number of microorganisms, but the number increased for that of stored at 0℃during transportation with extending storage time. Although a lot of total plate counts for the fish initially bought from supermarkets were shown, but almost no change was observed during storage probably due to the pre-treatment.
4. VBN of tilapia muscle stored at normal condition increased during storage. However, it was not over 20% and only very low biogenic amines were detected.
5. Tilapia immediately killed showed the lowest K value 7%. The K value increased with extending the storage time. Open showcases usually used in supermarkets might result in the increase of K value due to temperature fluctuation.
6. Hunter's L value and whiteness of tilapia meat from different transportation channels increased with the increase of storage time. Meanwhile, Hunter's a, b and chroma values changed irregularly.
7. Gel forming property of tilapia meat from different channels decreased with the increase of K value. Autolytic enzymes might act and cause salt-soluble protein to denature.
8. The extraction of actomyosin and the activity of actomyosin Ca-ATPase decreased with the increase of storage time.
9. According to the analysis of protein solubility, DSC, and SEM, the protein of tilapia muscle denatured during distribution at different channels.
10. Transportation by living fish obtains the best quality of tilapia as the source of supply. Though pre-treatment of fish offers the convenience for customers, but temperature has to be well controlled during distribution.
|Appears in Collections:||食品暨應用生物科技學系|
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