苜蓿青贮中长链脂肪酸含量在有氧暴露过程中的变化

Study on the dynamic changes of long-chain fatty acids in alfalfa silage during aerobic exposure

以苜蓿为原料,采用小型袋装青贮法进行青贮试验,研究苜蓿青贮在有氧暴露过程中发酵品质、养分含量以及棕榈酸、棕榈油酸、硬脂酸、油酸、亚油酸和亚麻酸六种长链脂肪酸含量的动态变化过程.结果显示,苜蓿青贮有氧暴露后乳酸含量显著降低(P<0.05),pH值、乙酸、丙酸和丁酸含量以及氨态氮占总氮含量显著提高(P<0.05);与苜蓿原料相比,青贮饲料中干物质、粗蛋白、酸性洗涤纤维和可溶性碳水化合物等营养物质含量显著降低(P<0.05),在有氧暴露过程中干物质和粗蛋白含量持续下降(P<0.05).苜蓿原料和青贮饲料中棕榈酸、亚麻酸和亚油酸含量超过1 mg/g,棕榈油酸、硬脂酸和油酸含量较低,且在青贮发酵以及有氧暴露过程中无明显变化.苜蓿厌氧发酵过程中棕榈酸和亚麻酸含量升高,在青贮饲料有氧暴露后棕榈酸含量没有发生明显变化,但亚麻酸含量明显降低.苜蓿厌氧发酵过程中总长链脂肪酸含量显著增加(P<0.05),但在青贮饲料有氧暴露后随之下降,甚至低于苜蓿原料中总长链脂肪酸含量(P<0.05).结果表明,苜蓿青贮饲料在有氧暴露过程中品质明显变差,厌氧发酵阶段积累的长链脂肪酸在此阶段逐渐被消耗.

The objective of this study was to investigate the dynamic changes of fermentation characteristics,nutrient content and long-chain fatty acids,including palmitic acid,palmitoleic acid,stearic acid,oleic acid,linoleic acid and linolenic acid,in alfalfa silage during aerobic exposure by a small bag silage method.The results showed that lactic acid content of alfalfa silage was sig-nificantly decreased during aerobic exposure(P<0.05),while pH value,acetic acid content,propionic acid content,butyric acid content and ammonia nitrogen content in total nitrogen were significantly increased(P<0.05).Compared with raw alfalfa,the contents of dry matter,crude protein,acid detergent fiber and water soluble carbohydrates in silage were significantly de-creased,and the contents of dry matter and crude protein continued to decrease during aerobic exposure(P<0.05).The con-tents of palmitic acid,linolenic acid and linoleic acid in raw alfalfa and silage was more than 1 mg/g,while the contents of palmitoleic acid,stearic acid,and oleic acid were low,and without obvious change during whole process.Contents of palmitic acid and linolenic acid increased during anaerobic fermentation.The content of palmitic acid did not change but linolenic acid decreased during aerobic exposure.The total long-chain fatty acid content in alfalfa silage was significantly increased during an-aerobic fermentation(P<0.05),but decreased after it exposed to air,and reached even lower than that in raw alfalfa(P<0.05).In conclusion,the quality of alfalfa silage was obviously deteriorated during aerobic exposure,and the long-chain fatty acid accumulated in the anaerobic fermentation were gradually consumed.