Antioxidant activity and lipid oxidation in milk from cows with soybean oil and propolis extract added to their feed

Abstract The presence of PUFA (polyunsaturated fatty acids) in cow milk, including conjugated linoleic acids (CLA) isomers, makes milk susceptible to lipid oxidation, and may lead to the formation of volatile products responsible for a rancid smell. Consequently, including natural antioxidants in the diet of dairy cattle can assist in preventing lipid oxidation. In this study, soybean oil (a source of PUFA) and different ethanolic extracts of Brazilian propolis were included in the cows' feed, and the antioxidant activity and lipid oxidation of the animals' milk was assessed. Antioxidant activity was analyzed using the DPPH method, potassium ferricyanide reduction and chelating ability. Total phenolic compounds and flavonoids were also determined. Lipid oxidation was assessed by determining conjugated dienes and the production of aldehydes (propanal, pentanal, hexanal and octanal). Increased antioxidant activity was seen in the samples of milk from cows receiving propolis. Similarly, the addition of ethanolic extract of propolis to the diet of dairy cattle increased milk protection for two treatments with propolis against lipid oxidation in terms of production of propanal and hexanal. These results confirm the positive effect of applying this natural additive to the diet of lactating cows, improving the nutritional quality of the milk produced.

摘要：牛乳中含有多不饱和脂肪酸（polyunsaturated fatty acids，PUFA），包括共轭亚油酸（conjugated linoleic acids，CLA）异构体，这使得牛乳易发生脂质氧化，并可能产生挥发性产物，进而引发哈喇味。因此，在奶牛日粮中添加天然抗氧化剂，有助于预防脂质氧化反应。

本研究在奶牛饲料中添加大豆油（多不饱和脂肪酸来源）以及不同的巴西蜂胶乙醇提取物，对牛乳的抗氧化活性与脂质氧化水平进行了评估。抗氧化活性采用DPPH法、铁氰化钾还原法与螯合能力进行分析，同时测定了样品中的总酚类化合物与总黄酮含量。脂质氧化水平则通过测定共轭二烯值以及醛类物质（丙醛、戊醛、己醛、辛醛）的生成量进行评估。

结果显示，投喂蜂胶的泌乳奶牛所产牛乳样品的抗氧化活性显著提升。同样地，在奶牛日粮中添加蜂胶乙醇提取物，可使两个蜂胶处理组的牛乳针对脂质氧化的防护能力得到提升，具体体现为丙醛与己醛的生成量得到有效抑制。上述结果证实，在泌乳奶牛日粮中添加该天然添加剂具有积极作用，可有效改善所产牛乳的营养品质。