Characteristics of digestive processes in Atlantic salmon (Salmo salar). Enzyme pH optima, chyme pH, and enzyme activities
Characteristics of digestive processes in Atlantic salmon (Salmo salar). Enzyme pH optima, chyme pH, and enzyme activities
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DOI：
10.1016/j.aquaculture.2015.02.032
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发表时间：
2015-12-01
期刊：
影响因子：
4.5
通讯作者：
Holm, Halvor
中科院分区：
文献类型：
--
作者：
Krogdahl, Ashild;Sundby, Anne;Holm, Halvor
在过去10-15年中，在养殖鲑鱼中观察到消化功能障碍的症状，至少部分原因是使用了新的饲料成分。目前关于鱼类消化功能的许多方面的知识是有限的，特别是大西洋鲑鱼。需要加强了解胃肠道健康挑战的潜在机制，并找到预防其发展的方法。本文介绍了大西洋鲑鱼消化道消化酶的最佳状态和稳定性、食糜pH值和酶活性。提交的数据包括来自四项大西洋鲑鱼研究的新数据，以及对各种其他鱼类研究的比较文献的回顾。四项试验分别选用不同大小的鲑鱼，分别饲养在咸水或淡水中，饲喂不同蛋白能比（P/E）的高鱼粉饲料。这些研究表明，在饲料和实验中，胃食糜的平均pH值为4.8 (SD = 0.7)，而胃蛋白酶的最佳pH值为3.0。在肠道食糜中，整个肠道的pH值从近端肠道的平均值8.1 （SD = 0.23）增加到中肠（SD = 0.27）和远端肠道（SD = 0.29）的8.4。以酪蛋白为底物的所有蛋白水解酶的功的总和来衡量，近端肠食糜的总蛋白水解活性在pH 8.8时达到最大值，即明显高于现行食糜pH。对于单个蛋白水解酶，pH的最佳值从弹性蛋白酶1的7.10到胰蛋白酶的8.98。食糜pH值似乎不受鱼类大小的影响，但在淡水中饲养的鱼类食糜pH值显著高于在咸水中饲养的鱼类。肠道食糜pH值与饲粮市盈率呈显著负相关。肠道食糜胰酶活性由近端向远端递减，粪便活性较近端低。而亮氨酸氨基肽酶（LAP）的活性分布则从肠中部到远端呈上升趋势。肠道食糜酶活性在各试验间无明显差异，肠道食糜酶活性的P/E与试验间无明显关系。其蛋白水解酶活性具有较好的体外稳定性。(C) 2015 Elsevier B.V.版权所有
Symptoms indicating digestive malfunction have been observed in cultivated salmon over the last 10-15 years, at least partially as a consequence of use of new feed ingredients. The present knowledge on many aspects of digestive functions in fish is limited, in particular for Atlantic salmon. Strengthening is needed to understand the mechanisms underlying challenges to gastrointestinal health and to find means to prevent their development. The present paper supplies information regarding digestive enzyme optima and stability, chyme pH and enzyme activities along the digestive tract of Atlantic salmon. The data presented includes new data from four studies on Atlantic salmon as well as a review of comparative literature from various other fish studies. The four experiments comprised salmon of different sizes, kept in salt or fresh water, and fed high fish meal diets with different protein to energy ratios (P/E). These studies showed an average pH in the stomach chyme, i.e. across diets and experiments, of 4.8 (SD = 0.7), whereas the observed pH optimum for pepsin was 3.0. In the intestinal chyme, pH increased throughout the intestine from a mean of 8.1 (SD = 0.23) in the proximal intestine to 8.4 in the mid intestine (SD = 0.27) and distal intestine (SD = 0.29). Total proteolytic activity of chyme in the proximal intestine, measured as the sum of the work of all proteolytic enzymes on casein as substrate, showed its maximum at pH 8.8, i.e. clearly above prevailing chyme pH. For the individual proteolytic enzymes, pH optimum varied from 7.10 for elastase 1 to 8.98 for trypsin. Chyme pH did not appear to be influenced by fish size, but was significantly higher in the fish raised in fresh water than in those raised in salt water. In the intestinal chyme pH showed a significant negative regression on diet P/E. For the investigated pancreatic enzymes in the intestinal chyme, the activity in the chyme decreased from proximal to distal regions and faecal activities were very low compared to the activities in the proximal intestine. The activity profile for leucine aminopeptidase (LAP), however, trended to increase from mid to distal intestine. Chyme enzyme activities along the intestinal tract did not differ clearly between the experiments and no clear relationship between P/E on enzyme activities along the intestinal tract was observed. Remarkable in vitro stability was observed for the proteolytic enzyme activities. (C) 2015 Elsevier B.V. All rights reserved.