A ferrous oxidation‐xylenol orange (FOX) method was modified to measure the levels of hydroperoxides in highly pigmented sea cucumber (Cucumaria frondosa) viscera lipid. With the FOX method, oil hydroperoxides oxidize Fe(II) to Fe(III) ions, which in turn bind to xylenol orange (XO) to form a complex that has a maximum absorbance at 560 nm. When applied to lipid extracts containing high levels of carotenoid pigments, the carotenoids interfere in the absorbance measurement because the XO‐complex and carotenoids absorb at the same wavelength. To avoid this, an approach was developed where carotenoids were removed from the solution containing the XO‐complex before absorbance measurements were made. This was accomplished by aqueous extraction of the reaction solution, leaving an organic layer containing the carotenoid pigment. The absorbance of the aqueous layer was subsequently measured at 560 nm allowing for determination of the lipid hydroperoxide content (mmol kg⁻¹) using a cumene hydroperoxide calibration curve. The method was validated using oxidized, unpigmented fish oils. The modified FOX method described herein was linear, accurate, and precise, and was validated over a hydroperoxide concentration range of 5–35 meq kg⁻¹ lipid. This modified FOX method for hydroperoxide determination of highly pigmented lipids is a valuable alternative to the methods presently available for determination of peroxide values.

中文翻译：

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亚铁氧化-二甲酚橙法测定高色素海参内脏脂质中过氧化物的测定

修改了亚铁氧化二甲苯酚橙（FOX）方法以测量高色素海参（Cucumaria frondosa）中的氢过氧化物水平）内脏脂质。利用FOX方法，氢过氧化油将Fe（II）氧化为Fe（III）离子，然后与二甲酚橙（XO）结合形成络合物，该络合物在560 nm处具有最大吸收率。当用于含有大量类胡萝卜素色素的脂质提取物时，类胡萝卜素会干扰吸光度的测量，因为XO-络合物和类胡萝卜素在相同波长下吸收。为避免这种情况，开发了一种方法，在进行吸光度测量之前，先从含有XO复合物的溶液中除去类胡萝卜素。这是通过对反应溶液进行水萃取而完成的，留下了含有类胡萝卜素颜料的有机层。随后在560nm处测量水层的吸光度，从而确定脂质氢过氧化物含量（mmol kg ^-1）使用氢过氧化枯烯校正曲线。使用氧化的，无色素的鱼油验证了该方法。本文所述的改良FOX方法是线性，准确和精确的，并且在5–35 meq kg ^-1脂质的氢过氧化物浓度范围内得到验证。这种改进的FOX方法用于高色素脂质的氢过氧化物测定，是目前可用于测定过氧化物值的方法的一种有价值的替代方法。