Abstract The increased demand for high-quality feed ingredients for the aquaculture industry has led to an increased focus on microbial ingredients as nutrient sources. Limited information exists, however, on the effect of down-stream processing of yeast on nutrient digestibility and health in Atlantic salmon (Salmo salar). In the present study, three laboratory-scale down-stream processing methods were used: direct inactivation by spray-drying, autolysis, or cell crushing. All yeast was inactivated with sray-drying post treatment. The yeast products were evaluated for their nutritional value and health effects in diets for Atlantic salmon. The experimental diets consisted of a high-quality fishmeal-based reference diet (FM) and six experimental diets were 300 g kg−1 of each of the processed yeast candidates were added to the FM control mixture. Fish were fed the diets for 21 days, and at the end of the experiment, feces were collected, and spleen, head kidney, distal intestine (DI) and plasma were sampled for assessment of immune response. Processing of yeast resulted in increased level of soluble protein in the yeast cream, with the highest level for yeast disrupted by cell crushing (20 K PSI). This was confirmed with scanning electron microscopy, where disrupted and cracked cells could be observed. Significant lower protein digestibility of the directly inactivated yeast coincided with the increased detection of whole yeast cells by flow cytometry in the DI content of fish fed the directly inactivated yeast. Autolysis for 16 h resulted in the highest protein digestibility, which was similar to the FM control. Interestingly, 16 h autolyzed yeast induced the secretion of IL-8, while cell crushed yeast induced the secretion of TNFα in the DI as analyzed by ELISA. To conclude, different down-stream processing of S. cerevisiae led to increased protein and β-glucan solubility that further increased protein digestibility in Atlantic salmon. Furthermore, different processing of the yeast triggered different immune stimulatory effects in Atlantic salmon.

中文翻译：

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面包酵母（Saccharomyces cerevisiae）的下游加工——对大西洋鲑鱼（Salmo salar）营养消化率和免疫反应的影响

摘要 水产养殖业对优质饲料原料的需求不断增加，导致人们越来越关注微生物原料作为营养来源。然而，关于酵母下游加工对大西洋鲑鱼（Salmo salar）营养消化率和健康的影响的信息有限。在本研究中，使用了三种实验室规模的下游处理方法：通过喷雾干燥、自溶或细胞破碎直接灭活。通过喷雾干燥后处理灭活所有酵母。评估了酵母产品在大西洋鲑鱼饮食中的营养价值和健康影响。实验日粮由高质量鱼粉参考日粮 (FM) 和六种实验日粮组成，将 300 g kg-1 的每种加工酵母候选物添加到 FM 对照混合物中。给鱼喂食 21 天的饮食，在实验结束时，收集粪便，并对脾脏、头肾、远端肠 (DI) 和血浆进行采样以评估免疫反应。酵母的加工导致酵母奶油中可溶性蛋白质的水平增加，其中最高水平是被细胞破碎 (20 K PSI) 破坏的酵母。扫描电子显微镜证实了这一点，可以观察到破碎和破裂的细胞。直接灭活酵母的蛋白质消化率显着降低，这与通过流式细胞术在直接灭活酵母喂养的鱼的 DI 含量中检测到全酵母细胞的增加相吻合。自溶 16 小时导致最高的蛋白质消化率，这与 FM 控制相似。有趣的是，16 小时自溶酵母诱导 IL-8 的分泌，而细胞粉碎的酵母诱导 DI 中 TNFα 的分泌，如通过 ELISA 分析。总而言之，酿酒酵母的不同下游加工导致蛋白质和 β-葡聚糖溶解度增加，从而进一步增加了大西洋鲑鱼的蛋白质消化率。此外，酵母的不同加工在大西洋鲑鱼中引发了不同的免疫刺激作用。