Seasonal differences exist in the polyunsaturated fatty acid, mineral and antioxidant content of U.S. grass-finished beef

There is increased consumer interest in grass-finished beef (GFB) with retail sales reaching $272 million in 2016. GFB contains higher omega-3 fatty acid levels compared to grain-finished beef, but variations in fatty acid (FA), mineral, and antioxidant content by producers and season is poorly documented. Hence, GFB samples from cattle finished in both fall and spring were obtained from four producers representing several US sub-regions. FAs were extracted using microwave-assisted extraction, derivatized to methyl-esters, and quantified using gas chromatography-mass spectrometry. Mineral content was quantified using coupled plasma mass-spectrometry and antioxidants were quantified via UV-absorption. Overall, total omega-3 FA content was greater in beef from cattle finished in the spring (13.4 mg/100g beef) than the fall (10.3; PPP = 0.008). Despite using the same feed in fall and spring, cattle from producer 4 had higher total omega-3, omega-6, and total polyunsaturated fatty acids in spring compared to fall (P

消费者对草饲牛肉（grass-finished beef, GFB）的关注度与日俱增，2016年其零售额已达2.72亿美元。相较于谷饲牛肉，草饲牛肉的Omega-3脂肪酸含量更高，但不同生产商与不同季节下，其脂肪酸（fatty acid, FA）、矿物质与抗氧化成分的含量变化却鲜有文献记载。因此，本研究从代表美国多个次区域的四家生产商处采集了秋季与春季育肥肉牛的草饲牛肉样本。采用微波辅助萃取法提取脂肪酸，将其衍生化为脂肪酸甲酯，随后通过气相色谱-质谱联用法进行定量分析；采用电感耦合等离子体质谱法测定矿物质含量，通过紫外吸收法检测抗氧化成分含量。总体而言，春季育肥肉牛的草饲牛肉总Omega-3脂肪酸含量为13.4 mg/100g，高于秋季育肥牛的10.3 mg/100g（PPP=0.008）。尽管秋季与春季采用相同的饲料饲喂，但生产商4提供的肉牛样本中，春季采集的牛肉总Omega-3、Omega-6与总多不饱和脂肪酸含量仍高于秋季（P