Ahn D U, Sell J L, Jo C, Chamruspollert M, Jeffrey M
Department of Animal Science, Iowa State University, Ames 50011-3150, USA.
Poult Sci. 1999 Jun;78(6):922-8. doi: 10.1093/ps/78.6.922.
Twenty-four, 79-wk-old White Leghorn hens were assigned randomly to three diets containing 0, 2.5, or 5.0% conjugated linoleic acid (CLA). The diets were fed for 4 wk to determine the effect of dietary CLA on quality characteristics of eggs. Eggs were collected daily and stored at 4 C for 1, 7, 21, or 49 d. At the designated times, the eggs were processed to evaluate water content, fatty acid composition, color, proportions and pH of yolk and albumen. Firmness of yolk after the eggs were hard-cooked was also determined. The proportions of myristic, palmitic, stearic, CLA (9-cis, 11-trans CLA and 10-trans, 12-cis CLA isomers), and unidentified fatty acids in egg yolk lipids were increased as dietary CLA increased, but those of palmitoleic, oleic, linoleic, linolenic, arachidonic, and docosahexaenoic acid were decreased. Duration of refrigeration increased the proportion of egg yolk but decreased the contents of albumen and yolk lipids after 21 d or longer of storage. Egg yolk pH increased as refrigeration time increased, regardless of dietary treatment, but the increase was greater in the eggs produced by hens fed the CLA diets. Albumen pH increased significantly after 7 d of storage but remained unchanged until 21 d and then decreased by 49 d. Dietary CLA had no effect on the pH of albumen until 49 d of storage. After 49 d storage, egg albumen pH from hens fed CLA diets was lower than that of albumen from hens fed the control diet. Yolk color was not influenced by the dietary CLA and storage, but the egg yolk surface from hens fed CLA diets sometimes had relatively dark color with light spots. Dietary CLA and storage of CLA eggs increased the firmness of hard-cooked egg yolk. The texture of yolks from hard-cooked CLA eggs was rubbery and elastic, and the yolks were more difficult to break using an Instron. It was speculated that the quality changes of CLA eggs were related to the increase of yolk water content, the movement of ions between yolk and albumen through yolk membrane, and the changes of egg yolk pH during storage.
24只79周龄的白来航母鸡被随机分配到三种日粮组，日粮中分别含有0%、2.5%或5.0%的共轭亚油酸（CLA）。这些日粮喂养4周，以确定日粮CLA对鸡蛋品质特性的影响。每天收集鸡蛋，并在4℃下储存1天、7天、21天或49天。在指定时间，对鸡蛋进行处理，以评估水分含量、脂肪酸组成、颜色、蛋黄和蛋清的比例及pH值。还测定了鸡蛋煮熟后蛋黄的硬度。随着日粮CLA含量的增加，蛋黄脂质中肉豆蔻酸、棕榈酸、硬脂酸、CLA（9-顺式，11-反式CLA和10-反式，12-顺式CLA异构体）以及未鉴定脂肪酸的比例增加，但棕榈油酸、油酸、亚油酸、亚麻酸、花生四烯酸和二十二碳六烯酸的比例降低。冷藏时间延长会增加蛋黄的比例，但在储存21天或更长时间后会降低蛋清和蛋黄脂质的含量。无论日粮处理如何，蛋黄pH值都会随着冷藏时间的增加而升高，但在饲喂CLA日粮的母鸡所产鸡蛋中升高幅度更大。储存7天后蛋清pH值显著升高，但直到21天保持不变，然后到49天时下降。在储存49天之前，日粮CLA对蛋清pH值没有影响。储存49天后，饲喂CLA日粮的母鸡所产鸡蛋的蛋清pH值低于饲喂对照日粮的母鸡所产鸡蛋的蛋清pH值。蛋黄颜色不受日粮CLA和储存的影响，但饲喂CLA日粮的母鸡所产鸡蛋的蛋黄表面有时颜色较深且有浅色斑点。日粮CLA和CLA鸡蛋的储存增加了煮熟鸡蛋蛋黄的硬度。煮熟的CLA鸡蛋的蛋黄质地坚韧且有弹性，使用英斯特朗仪器更难打破。据推测，CLA鸡蛋的品质变化与蛋黄水分含量的增加、离子通过蛋黄膜在蛋黄和蛋清之间的移动以及储存期间蛋黄pH值的变化有关。
