Department of Food Science and Technology, University of California, Davis, One Shields Avenue, Davis, California, USA.
ESALQ Food, College of Agriculture "Luiz de Queiroz,", University of São Paulo, Piracicaba, São Paulo, Brazil.
J Food Sci. 2021 May;86(5):1791-1801. doi: 10.1111/1750-3841.15697. Epub 2021 Apr 17.
The oxidation of polyunsaturated fatty acids produces bioactive primary oxidation products known as oxylipins. In many biological matrices, the majority of oxylipins are bound (i.e. esterified), and a relatively small proportion (<10%) exists in the free form. The present study tested whether this extends to bovine milk following method evaluation of various extraction and base hydrolysis protocols for measuring bound oxylipins. Free (unbound) oxylipins were also measured. Folch extraction followed by sodium carbonate hydrolysis in the presence of methanol containing 0.1% of acetic acid and 0.1% of butylated hydroxytoluene resulted in greater oxylipin concentrations and better surrogate standard recoveries compared to other methods that did not involve Folch extraction or the addition of methanol with hydrolysis base. Sodium hydroxide was better than sodium carbonate in hydrolyzing bound oxylipins under the same conditions. Milk analysis of oxylipins with mass-spectrometry following Folch extraction and sodium hydroxide hydrolysis revealed that 95% of oxylipins in bovine milk were esterified. Most of the detected oxylipins were derived from linoleic acid, which accounted for 92 and 88% of oxylipins in the free and esterified pools, respectively. These results demonstrate that the majority of bovine milk oxylipins are bound, and that linoleic-acid derived metabolites are the most abundant oxylipin species in free and bound lipid pools. Additional studies are needed to understand the role of different oxylipin pools in both calf and human nutrition. PRACTICAL APPLICATION: A method involving Folch lipid extraction and sodium hydroxide hydrolysis was validated for esterified oxylipin measurements in bovine milk. Application of the method revealed that the majority (∼95%) of oxylipins in bovine milk were bound. Linoleic-acid derived oxylipins were the most abundant species in both bound and free milk fractions (88-92%). The results highlight the presence of a new pool of oxidized lipids in milk, potentially involved in modifying its sensory and nutritional properties.
多不饱和脂肪酸的氧化会产生生物活性的初级氧化产物，称为氧化脂类。在许多生物基质中，大多数氧化脂类是结合的（即酯化的），只有相对较小的比例（<10%）以游离形式存在。本研究通过评估各种提取和碱水解方法来测量结合型氧化脂类，测试了这是否适用于牛初乳。还测量了游离（未结合）氧化脂类。与不涉及 Folch 提取或添加含水解碱的甲醇的其他方法相比，Folch 提取后，用含 0.1%乙酸和 0.1%丁基化羟基甲苯的甲醇进行碳酸钠水解，可得到更高的氧化脂类浓度和更好的替代标准回收率。在相同条件下，氢氧化钠比碳酸钠更能水解结合型氧化脂类。采用 Folch 提取和氢氧化钠水解后，采用质谱法对牛初乳中的氧化脂类进行分析，结果表明，牛初乳中 95%的氧化脂类是酯化的。大多数检测到的氧化脂类来源于亚油酸，分别占游离和酯化池中亚油酸衍生代谢物的 92%和 88%。这些结果表明，大多数牛初乳氧化脂类是结合的，亚油酸衍生代谢物是游离和结合脂质池中亚油酸衍生代谢物中最丰富的氧化脂类。需要进一步的研究来了解不同氧化脂类在小牛和人类营养中的作用。实际应用：验证了一种涉及 Folch 脂质提取和氢氧化钠水解的方法，用于测量牛初乳中的酯化氧化脂类。该方法的应用表明，牛初乳中约 95%的氧化脂类是结合的。亚油酸衍生的氧化脂类是结合和游离乳脂部分中最丰富的物种（88-92%）。这些结果突出了牛奶中存在一种新的氧化脂质池，可能参与改变其感官和营养特性。
