Enzymatic processing of fish by-products for recovery of peptides (hydrolysates) is a promising technology to reach food grade ingredients of high nutritional quality. Despite this, their bitter taste and “fish” odor block implementation in food products and limit their economic potential. Trimethylamine (TMA) is a known contributor to malodor in fish. Current strategies to mask or remove the odor either are not effective or give rise to undesirable side effects. As an alternative approach to remediate TMA, we propose a novel enzymatic strategy to convert TMA into the odorless trimethylamine N-oxide (TMAO) using TMA monooxygenases (Tmms). We identified a diverse set of bacterial Tmms using a sequence similarity network. Purified, recombinant enzymes were assessed for their biocatalytic capacity by monitoring NADPH consumption and TMAO generation. Selected Tmms were subjected to biochemical characterization and investigated for their ability to oxidize TMA in an industry-relevant substrate. From the 45 bacterial Tmm candidates investigated, eight enzymes from four different taxa were selected for their high activity toward TMA. The three most active enzymes were shown to vary in temperature optimum, with the highest being 45°C. Enzymatic activity dropped at high temperatures, likely due to structural unfolding. The enzymes were all active from pH 6.0 to 8.5, with functional stability being lowest around the optimal pH. All three Tmms, given sufficient NADPH cofactor, were found to generate TMAO in the TMA-rich salmon protein hydrolysate. The Tmms serve as unique starting points for engineering and should be useful for guiding process development for marine biorefineries.

中文翻译：

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含有黄素的单加氧酶，可在鲑鱼蛋白水解物中转化三甲胺。

鱼副产品的酶处理以回收肽（水解产物）是一种有前途的技术，可达到具有高营养品质的食品级成分。尽管如此，它们的苦味和“鱼”味阻碍了食品中的应用，并限制了其经济潜力。三甲胺（TMA）是导致鱼类恶臭的已知原因。当前掩盖或去除异味的策略要么无效，要么产生不良副作用。作为补救TMA的替代方法，我们提出了一种新颖的酶促策略，将TMA转化为无味的三甲胺N-使用TMA单加氧酶（Tmms）进行氧化（TMAO）。我们使用序列相似性网络鉴定了多种细菌Tmms。通过监测NADPH的消耗和TMAO的产生，评估了纯化的重组酶的生物催化能力。对选定的Tmm进行生化表征，并研究其在与行业相关的底物中氧化TMA的能力。从研究的45种细菌性Tmm候选物中，选择了来自四个不同类群的八种酶，因为它们对TMA具有高活性。三种活性最高的酶显示出最佳温度变化，最高为45°C。酶活性在高温下下降，可能是由于结构展开所致。这些酶在pH 6.0至8.5之间均具有活性，在最佳pH附近功能稳定性最低。这三个Tmm 如果给定足够的NADPH辅因子，则会在富含TMA的鲑鱼蛋白水解物中产生TMAO。Tmms是工程学的独特起点，应该对指导海洋生物精炼厂的工艺开发有用。