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

The presence of PUPA (polyunsaturated fatty acids) in cow milk, including conjugated linoleic acids (CIA) 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.