Oxidative stability evaluation of milk from cows fed dried distillers grains with solubles, by sensory and chemical analysis

摘要

The feeding of distillers dried grains with solubles (DDGS) to dairy cows has been loosely implicated in formation of oxidized off-flavors in milk. The purpose of this study was to examine the impact of feeding DDGS to dairy cows on the oxidative quality of milk by sensory and chemical analysis. Twenty-four cows were divided into two groups, fed a total mixed ration, with three incorporation levels of DDGS (0% (control), 10%, 25%) in a two-group three-period crossover design. Each group received each of the diets, such that each cow served as her own control. Milk was collected on days 14, 21, 28 during each of the experimental periods. For each diet treatment, pooled fresh milk was HTST pasteurized then divided into three fortification groups (no vitamin addition (control), 0.06% Vitamin E, 0.06% Vitamin C). Milk fat (%), SNF (%), protein (%) were measured using LactiCheck(TM). A 10-member descriptive analysis panel evaluated the milk samples on seven specific descriptors on days 1, 3, 7 of storage. Chemical analyses (peroxides, free fatty acids (FFA)) were conducted on the same milk with SafTest(TM) kits. Milk fat% were similar in 0% and 10% DDGS groups, while it was significantly (p < 0.0001) lower in the 25% DDGS group (2.6%), while SNF% and protein% increased with the inclusion of DDGS (p<0.05). Sensory analysis revealed diet treatment, storage day, and fortification effects (p < 0.05) on oxidized off-flavors. Milk from 25% DDGS, Vitamin C fortification, or collection day 14 had higher off-flavor scores (p<0.05). Though statistically significant, the milks did not exhibit definite oxidized flavor; the scores were lower than 1.5 on a 15-cm line scale. All peroxide and most of the FFA measurements were below detection level, with the exception of few samples that had slightly elevated FFA; the elevated results were not observed in their replicates. With no apparent oxidation in any milk from any treatment, the sensory and chemical analyses support the conclusion that feeding of DDGS at 10% and 25% levels did not decrease the oxidation stability of milk. Spontaneous oxidation is a complex process that cannot be blamed on DDGS alone.