The addition of heavy protein to aquafeed causes low digestibility, high cost and significant nitrogen pollution in the water. The addition of protease is an effective way of improving protein absorption, but few proteases have been developed specifically for aquafeeds. The hydrolysis efficiency of protease additives for plant protein in the neutral gut environment and their synergy with endogenous proteases has not been sufficiently investigated. In this study, the performance of the recombinant neutral protease rNpI as an aquafeed additive to reduce the raw protein materials in the diet of Carassius carassius during 56 days of growth was evaluated. rNpI effectively hydrolysed soya bean protein isolates (SPI) with a high degree of hydrolysation and a high small‐peptide yield. The rNpI‐treated SPI exhibited a notable antioxidant activity, which benefited fish health. In vitro digestibility indicated that rNpI complemented trypsin in SPI digestion better than papain or Alcalase. The growth trial showed that the addition of rNpI could warrant a reduction in the crude protein and gross energy of feed while producing a lower feed‐conversion rate (FCR) and better growth performance. Crucian that were fed an RM‐wheat‐E diet (5.5% rapeseed meal and 5% wheat reduction) showed the best performance, with the lowest FCR and highest weight gain. These results indicate that rNpI could be an effective additive for the aquafeed industry and could provide economic benefits by reducing aquafeed protein requirements and nitrogen emissions. This study provides novel information and strategies for additive protease use and development in aquafeed.

中文翻译：

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重组中性蛋白酶rNpI作为鱼饲料添加剂，可改善蛋白质的消化和生长

向水产饲料中添加重蛋白会导致消化率低，成本高以及水中氮污染严重。蛋白酶的添加是提高蛋白质吸收的有效方法，但是很少有蛋白酶专门用于水产饲料。在中性肠道环境中蛋白酶对植物蛋白的水解效率及其与内源蛋白酶的协同作用尚未得到充分研究。在这项研究中，重组中性蛋白酶rNpI作为水产饲料添加剂的性能，以减少粗蛋白质材料的饮食鲫鱼鲫鱼在生长56天期间进行评估。rNpI有效水解大豆蛋白分离物（SPI），具有高度的水解度和较高的小肽产量。经rNpI处理的SPI表现出显着的抗氧化活性，有益于鱼类健康。体外消化率表明，rNpI在SPI消化中比胰蛋白酶或Alcalase更好地补充了胰蛋白酶。生长试验表明，添加rNpI可以保证减少粗蛋白和饲料总能量，同时降低饲料转化率（FCR）和提高生长性能。饲以RM-小麦-E饮食（5.5％的菜籽粕和5％的小麦减少量）的鱼表现最佳，FCR最低，体重增加最高。这些结果表明，rNpI可能是水产饲料行业的有效添加剂，并可以通过降低水产饲料蛋白的需求量和氮排放量而提供经济利益。这项研究为水产饲料中添加剂蛋白酶的使用和开发提供了新的信息和策略。