动物营养学报    2021, Vol. 33 Issue (11): 6147-6160    PDF    
相同营养条件下不同生长速度黄羽肉鸡肉品质的比较研究
范秋丽 , 李龙 , 苟钟勇 , 王一冰 , 林厦菁 , 蒋守群     
广东省农业科学院动物科学研究所, 畜禽育种国家重点实验室, 农业农村部华南动物营养与饲料重点实验室, 广东省畜禽育种与营养研究重点实验室, 广州 510640
摘要: 本试验旨在在相同营养条件下,比较研究市场上具有代表性的不同生长速度(快速、中速和慢速)黄羽肉鸡胸肌和腿肌感官品质、脂肪酸组成和氨基酸含量的异同。选用1日龄的快速型岭南黄鸡、中速型麻黄鸡和慢速型胡须鸡各60只(均为母鸡),随机分为9栏饲养,每种鸡3栏,每栏20只。在相同营养及饲养环境下饲养至上市日龄(岭南黄鸡63日龄、麻黄鸡77日龄和胡须鸡165日龄),每个品种随机挑选接近各自平均体重的14只鸡进行屠宰,测定肌肉感官品质、脂肪酸组成和氨基酸含量。结果表明:1)在感官品质方面,慢速型肉鸡胸肌和腿肌肌苷酸含量最高,且胸肌肌纤维密度最高、肌纤维直径最小,显著优于快速型或中速型(P < 0.05);慢速型肉鸡胸肌宰后24 h pH和45 min肉色红度(a*)值显著高于快速型和中速型(P < 0.05),胸肌宰后45 min和24 h肉色黄度(b*)值显著低于快速型和中速型(P < 0.05);同时,慢速型肉鸡腿肌宰后24 h pH显著高于快速型和中速型(P < 0.05),腿肌宰后45 min和24 h肉色亮度(L*)值和b*值显著低于快速型或中速型(P < 0.05)。2)在脂肪酸组成方面,慢速型肉鸡胸肌饱和脂肪酸含量显著低于快速型和中速型(P < 0.05),其中棕榈酸含量显著低于快速型和中速型(P < 0.05);快速型肉鸡胸肌单不饱和脂肪含量最高,显著高于慢速型(P < 0.05),其中油酸贡献最大,其含量显著高于中速型和慢速型(P < 0.05);慢速型肉鸡胸肌多不饱和脂肪酸含量显著高于快速型和中速型(P < 0.05),其中含量较为丰富的为亚油酸和α-亚麻酸,同样显著高于快速型和中速型(P < 0.05)。快速型肉鸡腿肌棕榈酸和单不饱和脂肪酸含量显著高于中速型或慢速型(P < 0.05),其中油酸对单不饱和脂肪酸的贡献最大,其含量显著高于中速型和慢速型(P < 0.05);慢速型肉鸡腿肌多不饱和脂肪酸含量显著高于快速型和中速型(P < 0.05),其中含量较为丰富的为亚油酸、α-亚麻酸、二十碳三烯酸和花生四稀酸,显著高于快速型或中速型(P < 0.05)。总体上,中速型肉鸡胸肌和腿肌中n-6多不饱和脂肪酸/n-3多不饱和脂肪酸值分别为11.06和8.46,更为接近世界卫生组织推荐的适合人体健康的数值(6~10)。3)在氨基酸含量方面,中速型肉鸡胸肌总氨基酸、鲜味氨基酸和必需氨基酸含量最高,显著高于快速型和慢速型(P < 0.05),其中对鲜味氨基酸含量贡献最大的为谷氨酸和甘氨酸,其含量显著高于快速型和慢速型(P < 0.05);必需氨基酸中缬氨酸、蛋氨酸、异亮氨酸、亮氨酸、苯丙氨酸和赖氨酸含量均为最高,显著高于快速型或慢速型(P < 0.05)。虽然3种不同生长速度黄羽肉鸡腿肌中鲜味氨基酸含量差异不显著(P>0.05),但慢速型肉鸡腿肌中总氨基酸含量最高,显著高于快速型(P < 0.05);中速型肉鸡腿肌中必需氨基酸含量最高,显著高于快速型和慢速型(P < 0.05)。综合上述结果,不同生长速度黄羽肉鸡在相同营养条件下达到出栏重时,以肌肉感官品质为参考,慢速型优于中速型,中速型优于快速型;以肌肉脂肪酸组成和氨基酸含量为参考,中速型优于慢速型,慢速型优于快速型。
关键词: 生长速度    黄羽肉鸡    感官品质    脂肪酸组成    氨基酸含量    
Comparative Study on Meat Quality of Yellow-Feather Chickens with Different Growth Speed under the Same Nutritional Conditions
FAN Qiuli , LI Long , GOU Zhongyong , WANG Yibing , LIN Xiajing , JIANG Shouqun     
Guangdong Provincial Key Laboratory of Animal Breeding and Nutrition, Key Laboratory of Animal Nutrition and Feed Science in South China, Ministry of Agriculture and Rural Affairs, State Key Laboratory of Livestock and Poultry Breeding, Institute of Animal Science, Guangdong Academy of Agricultural Sciences, Guangzhou 510640, China
Abstract: The purpose of this experiment was to comparatively study the similarities and differences of sensory quality, fatty acid composition and amino acid content in breast muscle and thigh muscle of representative yellow-feather chickens with different growth speed (rapid, medium and slow) in the market under the same nutritional conditions. Each sixty rapid-speed type Lingnan yellow chickens, medium-speed type ephedra chickens and slow-speed type beard chickens (all female) of one-day-old were randomly divided into 9 pens with 3 pens for each breed and 20 chickens in each pen. The chickens were fed under the same nutrition and feeding environment until they reached the listing age (Lingnan yellow chickens to 63 days of age, ephedra chickens to 77 days of age, and beard chickens to 165 days of age), and every 14 chickens closed to their average body weight in each breed were randomly selected for slaughter to determine the sensory quality, fatty acid composition and amino acid content in muscle. The results showed as follows: 1) in terms of sensory quality, the inosinic acid content in breast muscle and thigh muscle of slow-speed type chickens was the highest, and the density and diameter of muscle fiber in breast muscle were the highest and the smallest, which were significantly better than those of rapid- or medium-speed type chickens (P < 0.05). The pH at 24 h and meat color redness (a*) value at 45 min after slaughter in breast muscle of slow-speed type chickens were significantly higher than those of rapid- and medium-speed type chickens (P < 0.05), and the meat color yellowness (b*) value at 45 min and 24 h after slaughter in breast muscle was significantly lower than that of rapid- and medium-speed type chickens (P < 0.05). Meanwhile, the pH at 24 h after slaughter in thigh muscle of slow-speed type chickens was significantly higher than that of rapid- and medium-speed type chickens (P < 0.05), and the meat color brightness (L*) value and b* value at 45 min and 24 h after slaughter in thigh muscle were significantly lower than those of rapid- or medium-speed type chickens (P < 0.05). 2) In terms of fatty acid composition, the saturated fatty acid content in breast muscle of slow-speed type chickens was significantly lower than that of rapid- and medium-speed type chickens (P < 0.05), and in which the palmitic acid content was significantly lower than that of rapid- and medium-speed type chickens (P < 0.05). The monounsaturated fat content in breast muscle of rapid-speed type chickens was the highest and significantly higher than that of slow-speed type chickens (P < 0.05), and in which the oleic acid contributed the most and its content was significantly higher than that of medium- and slow-speed type chickens (P < 0.05). The polyunsaturated fatty acid content in breast muscle of slow-speed type chickens was significantly higher than that of rapid- and medium-speed type chickens (P < 0.05), and in which the contents of linoleic acid and α-linolenic acid were relatively abundant and also significantly higher than those of rapid- and medium-speed type chickens (P < 0.05). The contents of palmitic acid and monounsaturated fatty acid in thigh muscle of rapid-speed type chickens were significantly higher than those of medium- or slow-speed type chickens (P < 0.05), and in which the oleic acid contributed the most to monounsaturated fatty acid and its content was significantly higher than that of medium- and slow-speed type chickens (P < 0.05). The polyunsaturated fatty acid content in thigh muscle of slow-speed type chickens was significantly higher than that of rapid- and medium-speed type chickens (P < 0.05), and in which the contents of linoleic acid, α-linolenic acid, epoxyeicosatrienoic acid and arachidonic acid were relatively rich and significantly higher than those of rapid- or medium-speed type chickens (P < 0.05) (P < 0.05). In general, the ratio of n-6 polyunsaturated fatty acid to n-3 polyunsaturated fatty acid in breast muscle and thigh muscle of medium-speed type chickens was 11.06 and 8.46, respectively, which was close to the value recommended by the World Health Organization for human health (6 to 10). 3) In terms of amino acid content, the contents of total amino acids, flavor amino acids and essential amino acids in breast muscle of medium-speed type chickens were the highest and significantly higher than those of rapid- and slow-speed type chickens (P < 0.05), and in which the glutamic acid and glycine contributed the most to the flavor amino acid content and their contents were significantly higher than those of rapid- and slow-speed type chickens (P < 0.05). Among essential amino acids, the contents of valine, methionine, isoleucine, leucine, phenylalanine and lysine were the highest and significantly higher than those of rapid- or slow-speed type chickens (P < 0.05). Although there was no significant difference in the flavor amino acid content in thigh muscle of yellow-feather chickens with three different growth speed (P>0.05), the highest content of total amino acids was found in thigh muscle of slow-speed type chickens which was significantly higher than that of rapid-speed type chickens (P < 0.05), and the highest content of essential amino acids was found in thigh muscle of medium-speed type chickens which was significantly higher than that of rapid- and slow-speed type chickens (P < 0.05). In conclusion, when yellow-feather chickens with different growth speed reached the market weight under the same nutritional conditions, taking sensory quality in muscle as a reference, the slow-speed type chickens are better than the medium-speed type chickens, and the medium-speed type chickens are better than the rapid-speed type chickens; taking fatty acid composition and amino acid content in muscle as references, the medium-speed type chickens are better than the slow-speed type chickens, and the slow-speed type chickens are better than the rapid-speed type chickens.
Key words: growth speed    yellow-feather chickens    sensory quality    fatty acid composition    amino acid content    

目前,黄羽肉鸡年出栏量约40亿只,约占肉鸡总出栏量的40%;按照生长速度和出栏时间,黄羽肉鸡主要分为快速型、中速型和慢速型,这3类鸡市场占有率分别约为50%、30%和20%[1]。随着人民生活水平的提高和营养膳食结构的改善,消费者对鸡肉的品质也提出了更高的要求[2]。前人研究显示,遗传[3]、营养[4]、饲养方式[5]、环境[6]、屠宰方法[7]以及储藏温度[8]等都可影响鸡的肉品质,且遗传是其中重要的影响因素之一。不同品种肉鸡的生长速度、肌肉感官品质、脂肪酸组成和氨基酸含量之间具有显著的差别[9-11]。我国黄羽肉鸡品种繁多,且不同生长速度肉鸡之间肉品质缺乏系统地比较研究。因此,本试验旨在在相同饲粮营养水平、饲养方式、饲养环境、屠宰方法和储藏温度下,比较研究市场上具有代表性的不同生长速度黄羽肉鸡肌肉感官品质、脂肪酸组成和氨基酸含量之间的差异,为这些鸡种的进一步选育和肉质改良提供理论基础。

1 材料与方法 1.1 试验设计和饲养管理

本试验在广东省农业科学院动物科学研究所试验场进行。试验选用初始体重分别为(35.83±0.02) g、(38.79±0.03) g和(31.35±0.02) g的1日龄快速型岭南黄鸡、中速型麻黄鸡和慢速型胡须鸡各60只(均为母鸡),随机分为9栏饲养,其中快速型肉鸡3栏(20只/栏)、中速型肉鸡3栏(20只/栏)和慢速型肉鸡3栏(20只/栏),每栏长×宽为3.5 m×1.3 m。所有试鸡均在同一栋封闭式鸡舍地面平养,地面铺放木屑,自然光照和通风,自由采食颗粒料及饮水,按照常规饲养和免疫程序进行饲养和免疫。试验过程中每天08:00、14:30和17:00记录鸡舍的温度和相对湿度。

1.2 试验饲粮

试验采用玉米-豆粕型基础饲粮,根据《中国饲料成分及营养价值表》(2017年第28版)、并参考《鸡饲养标准》(NY/T 33—2004)中黄羽肉鸡营养需要水平进行配制,其组成及营养水平见表 1。不同生长速度黄羽肉鸡相同日龄营养水平均保持一致。

表 1 基础饲粮组成及营养水平(风干基础) Table 1 Composition and nutrient levels of basal diets (air-dry basis) 
1.3 样品采集和制备

不同生长速度肉鸡饲养至上市日龄(岭南黄鸡63日龄、麻黄鸡77日龄和胡须鸡165日龄),体重分别为(2 252.64±15.85) g、(2 195.04±12.48) g和(1 832.26±18.12) g,各自充分生长、均匀度好,每个品种选取接近各自平均体重的14只鸡进行屠宰取样,取样和样品保存方法均保持一致。试验结束前1天19:00断料供水,次日08:00颈部放血致死,完整剥离两侧无骨无皮的胸肌和腿肌(剔除表面结缔组织和脂肪)。每个样品右侧胸肌和腿肌取相同部位约1 cm3固定于4%多聚甲醛溶液24 h以上,用于测定肌纤维数量和直径;右侧胸肌和腿肌取相同部位约1 g分装于1.5 mL的灭菌离心管,做好标记,立即置于液氮保存,试验结束转移至-80 ℃冰箱保存,备测游离氨基酸含量。剩余的右侧胸肌和腿肌各自分装于封口袋,做好标记,立即置于液氮保存,试验结束转移至-80 ℃冰箱保存,备测肌苷酸和肌内脂肪含量以及脂肪酸组成。

1.4 测定指标和方法 1.4.1 感官品质

肌苷酸含量采用《畜禽肌肉中肌苷酸含量测定高效液相色谱法》(DB 37/T 3816—2019)方法测定,具体为:称取1 g肌肉样品搅碎,均质的肌肉(精确至0.000 1 g)置于50 mL离心管中,准确向离心管中加入20 mL预冷的5%高氯酸溶液,然后放入高速组织匀浆机8 000 r/min匀浆1 min后转入50 mL容量瓶,5%高氯酸定容。移取定容后的溶液20 mL,4 000 r/min离心3 min后准确吸取上清液10 mL,用0.5 mol/L氢氧化钠溶液调pH至6.5,然后转入50 mL容量瓶用一级水(GB/T 6682—2006)定容,定容后的液体用0.45 μm滤膜过滤后上机(HPLC,Waters2695,美国)检测。

肌内脂肪含量测定参考Cui等[12]的方法,取20 g左右肌肉样品绞碎后平铺于干净的培养皿中划十字,-80 ℃放置24 h后取出,迅速放于冻干机(Christ,ALPHA 2-4,德国)冻干72 h;冻干样品粉碎后取3.0 g采用索氏抽提取法(Foss,Electric 2055,丹麦)测定总脂肪含量,结果以总脂肪含量占冻干粉样重量的百分比来表示。

肌纤维密度和直径测定参考Zhao等[13]的方法,经多聚甲醛固定7 d后的肌肉样品取出进行修块、脱水浸蜡、包埋、切片、脱蜡至水、染色和脱水封片,每张切片样品挑选200倍视野进行拍照(尽量让组织充满整个视野,保证每张照片的背景光一致),统计每个视野(约0.763 5 mm2)中的肌纤维数目(Eclipse E100,Nikon,日本),求平均值后换算成每mm2的纤维数,即为肌纤维密度;应用Image-Pro Plus 6.0软件(Media Cybernetics, Inc., 美国)以图片标尺为标准,选取合适的视野,分别测量每张切片5个肌纤维直径(μm)并求出平均值。

取左侧胸肌和腿肌测定pH、肉色、滴水损失和剪切力,其中pH、肉色和滴水损失具体测定方法参考Chodova等[14],剪切力具体测定方法参考Jiang等[15]

1.4.2 脂肪酸组成

脂肪酸组成测定采用气相色谱法,具体参考Cui等[16]的方法,准确称取冻干胸肌粉2.0 g于水解管中,加入4 mL氯乙酰-甲醇溶液(1 ∶ 10)和1 mL内标的十一碳酸甲酯(C11 ∶ 0,1 mg/mL)溶液,80 ℃水浴反应2 h后取出冷却,再加入5 mL 7%碳酸钾溶液振荡混匀,经1 200 r/min离心5 min后,取上清用0.2 μm滤膜过滤后装入进样小瓶,上机(Agilent Technologies,GC-6890N,美国)检测。

1.4.3 游离氨基酸含量

游离氨基酸含量测定参考Tian等[17]的方法,称取1 g左右肌肉样品,按照肌肉(重量) ∶黄基水杨酸钠(体积)=1 ∶ 3的比例加入10%的黄基水杨酸钠,匀浆后12 000 r/min离心15 min,然后用直径0.22 μm的针筒式滤膜过滤器将上清液过滤至2 mL的氨基酸上样瓶,采用氨基酸自动分析仪(HITACHI,L-8900,日本)上机检测。

1.5 数据统计分析

试验数据采用SPSS 19.0软件中的one-way ANOVA程序进行单因素方差分析,当处理效应差异显著(P < 0.05)时再进行Duncan氏法多重比较,试验结果以平均值和均值标准误(SEM)表示。

2 结果 2.1 不同生长速度黄羽肉鸡肌肉感官品质比较

表 2可知,快速型肉鸡末重和平均日增重显著高于中速型(P < 0.05),且中速型显著高于慢速型(P < 0.05)。在胸肌中,快速型肉鸡肌苷酸含量和肌纤维密度显著低于中速型和慢速型(P < 0.05),慢速型肉鸡肌纤维直径显著小于快速型和中速型(P < 0.05);慢速型肉鸡宰后24 h pH显著高于中速型(P < 0.05),且中速型显著高于快速型(P < 0.05);慢速型肉鸡宰后45 min肉色红度(a*)值显著高于快速型和中速型(P < 0.05);慢速型肉鸡宰后45 min和24 h肉色黄度(b*)值显著低于中速型(P < 0.05),且中速型显著低于快速型(P < 0.05)。在腿肌中,快速型肉鸡肌苷酸含量显著低于中速型(P < 0.05),且中速型显著低于慢速型(P < 0.05);慢速型肉鸡宰后24 h pH显著高于快速型和中速型(P < 0.05);快速型肉鸡宰后45 min肉色亮度(L*)值显著高于中速型和慢速型(P < 0.05);慢速型肉鸡宰后45 min和24 h肉色b*值显著低于中速型(P < 0.05),且中速型显著低于快速型(P < 0.05);慢速型肉鸡宰后24 h肉色L*值显著低于中速型,且中速型显著低于快速型(P < 0.05)。

表 2 不同生长速度黄羽肉鸡肌肉感官品质比较 Table 2 Comparison of sensory quality in muscle of yellow-feather chickens with different growth speed
2.2 不同生长速度黄羽肉鸡胸肌脂肪酸组成比较

表 3可知,慢速型肉鸡胸肌豆蔻酸含量显著低于中速型(P < 0.05),且中速型显著低于快速型(P < 0.05);慢速型肉鸡胸肌棕榈酸含量显著低于快速型和中速型(P < 0.05);慢速型肉鸡胸肌花生酸含量显著高于快速型和中速型(P < 0.05);慢速型肉鸡胸肌饱和脂肪酸含量显著低于快速型和中速型(P < 0.05);慢速型肉鸡胸肌油酸含量显著低于中速型(P < 0.05),且中速型显著低于快速型(P < 0.05);慢速型肉鸡胸肌单不饱和脂肪酸含量显著低于快速型和中速型(P < 0.05);慢速型肉鸡胸肌亚油酸、多不饱和脂肪酸、n-6多不饱和脂肪酸和不饱和脂肪酸含量均显著高于中速型和快速型(P < 0.05);慢速型肉鸡胸肌α-亚麻酸含量显著高于中速型(P < 0.05),且中速型显著高于快速型(P < 0.05);中速型肉鸡胸肌二十碳三烯酸、二十碳五烯酸(EPA)和二十二碳六烯酸(DHA)含量显著高于快速型和慢速型(P < 0.05);中速型肉鸡胸肌n-3多不饱和脂肪酸含量显著高于慢速型(P < 0.05),且慢速型显著高于快速型(P < 0.05);快速型肉鸡n-6多不饱和脂肪酸/n-3多不饱和脂肪酸值显著高于中速型(P < 0.05),且中速型显著高于慢速型(P < 0.05)。

表 3 不同生长速度黄羽肉鸡胸肌脂肪酸组成比较 Table 3 Comparison of fatty acid composition in breast muscle of yellow-feather chickens with different growth speed
2.3 不同生长速度黄羽肉鸡腿肌脂肪酸组成比较

表 4可知,慢速型肉鸡腿肌豆蔻酸含量显著低于中速型(P < 0.05),且中速型显著低于快速型(P < 0.05);慢速型肉鸡腿肌棕榈酸含量显著低于中速型和快速型(P < 0.05);中速型和快速型肉鸡腿肌花生酸和木蜡酸含量显著低于慢速型(P < 0.05);慢速型肉鸡腿肌油酸和单不饱和脂肪酸含量显著低于中速型(P < 0.05),且中速型显著低于快速型(P < 0.05);慢速型肉鸡腿肌亚油酸和花生四烯酸含量显著高于中速型和快速型(P < 0.05);慢速型和中速型肉鸡腿肌α-亚麻酸含量显著高于快速型(P < 0.05);慢速型肉鸡腿肌二十碳三烯酸、多不饱和脂肪酸和n-6多不饱和脂肪酸含量显著高于中速型(P < 0.05),且中速型显著高于快速型(P < 0.05);中速型肉鸡腿肌DHA和n-3多不饱和脂肪酸含量显著高于慢速型(P < 0.05),且慢速型显著高于快速型(P < 0.05);中速型肉鸡腿肌n-6多不饱和脂肪酸/n-3多不饱和脂肪酸值显著低于慢速型(P < 0.05),且慢速型显著低于快速型(P < 0.05)。

表 4 不同生长速度黄羽肉鸡腿肌脂肪酸组成比较 Table 4 Comparison of fatty acid composition in thigh muscle of yellow-feather chickens with different growth speed
2.4 不同生长速度黄羽肉鸡胸肌游离氨基酸含量比较

表 5可知,慢速型肉鸡胸肌天冬氨酸含量显著高于快速型和中速型(P < 0.05);中速型肉鸡胸肌谷氨酸、甘氨酸、蛋氨酸、亮氨酸、苯丙氨酸、酪氨酸、总氨基酸和必需氨基酸含量显著高于快速型和慢速型(P < 0.05);中速型和慢速型肉鸡胸肌丝氨酸和赖氨酸含量显著高于快速型(P < 0.05);快速型肉鸡胸肌精氨酸含量显著低于中速型(P < 0.05),且中速型显著低于慢速型(P < 0.05);快速型和中速型肉鸡胸肌苏氨酸含量和必需氨基酸/总氨基酸值显著高于慢速型(P < 0.05);慢速型肉鸡胸肌脯氨酸含量显著高于快速型(P < 0.05);中速型肉鸡胸肌缬氨酸和异亮氨酸含量显著高于快速型(P < 0.05),且快速型显著高于慢速型(P < 0.05);中速型肉鸡胸肌半胱氨酸含量显著高于快速型(P < 0.05);中速型肉鸡胸肌鲜味氨基酸含量显著高于慢速型(P < 0.05),且慢速型显著高于快速型(P < 0.05)。

表 5 不同生长速度黄羽肉鸡胸肌游离氨基酸含量比较 Table 5 Comparison of free amino acid content in breast muscle of yellow-feather chickens with different growth speed  
2.5 不同生长速度黄羽肉鸡腿肌游离氨基酸含量比较

表 6可知,慢速型肉鸡腿肌丝氨酸、脯氨酸、丙氨酸和组氨酸含量均显著高于快速型和中速型(P < 0.05);快速型肉鸡腿肌精氨酸含量显著低于中速型(P < 0.05),且中速型显著低于慢速型(P < 0.05);中速型肉鸡腿肌缬氨酸和异亮氨酸含量显著高于快速型和慢速型(P < 0.05);慢速型和中速型肉鸡腿肌蛋氨酸、苯丙氨酸、酪氨酸和总氨基酸含量显著高于快速型(P < 0.05);中速型肉鸡腿肌赖氨酸和必需氨基酸含量显著高于慢速型(P < 0.05),且慢速型显著高于快速型(P < 0.05)。

表 6 不同生长速度黄羽肉鸡腿肌游离氨基酸含量比较 Table 6 Comparison of free amino acid content in thigh muscle of yellow-feather chickens with different growth speed 
3 讨论 3.1 不同生长速度黄羽肉鸡肌肉感官品质比较

感官品质主要包括物理性状、化学成分和组织形态等。肌苷酸作为畜禽肌肉风味物质之一,是评价感官品质的重要指标[18],本研究结果显示,中速型和慢速型肉鸡胸肌肌苷酸含量显著高于快速型;慢速型肉鸡腿肌肌苷酸含量显著高于中速型,且中速型显著高于快速型。这说明慢速型肉鸡肉质风味优于中速型,而中速型又优于快速型,且肌苷酸含量随着肉鸡日龄的增长呈增加趋势,此结果与李慧芳等[11]在罗曼鸡、康达尔黄羽肉鸡、石岐杂鸡、白耳鸡和泰和乌骨鸡上的研究报道相似。肌内脂肪含量是影响肉类感官品质的关键指标,其含量影响着肉的剪切力和滴水损失,肌内脂肪含量升高,则剪切力降低,滴水损失减少[19]。李龙等[9]研究报道,与120日龄黄羽肉鸡相比,42日龄爱拔益加肉鸡胸肌肌内脂肪含量显著升高,剪切力显著降低。这与本试验不同生长速度黄羽肉鸡胸肌和腿肌肌内脂肪含量以及胸肌剪切力无显著差异的结果不一致,可能与鸡成年后肌纤维增粗,腹脂率增加,肌内脂肪沉积开始下降有关。肌纤维组织学特性与肉类感官品质尤其是食用品质密切相关,其包括纤维直径和纤维密度,且两者间呈负相关,直径越小、密度越大、剪切力越小,肉质越嫩[20-21]。本研究结果显示,中速型和慢速型肉鸡胸肌肌纤维密度显著高于快速型,且慢速型肉鸡胸肌肌纤维直径显著小于快速型和中速型,这说明在嫩度和口感方面慢速型肉鸡优于中速型,中速型优于快速型,这也与本试验剪切力的结果相呼应。pH和肉色是评价感官品质的客观指标,肉鸡宰后糖原酵解引起肌肉pH迅速下降,乳酸大量累积,产生白肌肉(PSE肉)[4],且肉色L*值越高,肌肉水分渗出越高,也越容易形成PSE肉[9]。本研究结果显示,快速型、中速型和慢速型肉鸡宰后24 h胸肌pH依次显著升高,同时慢速型肉鸡宰后24 h腿肌pH显著高于快速型和中速型;中速型和慢速型肉鸡宰后45 min腿肌肉色L*值显著低于快速型;快速型、中速型和慢速型肉鸡宰后24 h腿肌肉色L*值依次显著降低。以上结果说明慢速型肉鸡宰后产生PSE肉的几率最低,快速型肉鸡则最高。肉色a*值和b*值可在一定程度上反映肌肉中色素和肌红蛋白的含量,通常情况下a*值越高、b*值越低,肉感官品质越好[22-23]。本研究结果显示,慢速型肉鸡宰后45 min胸肌肉色a*值显著高于快速型和中速型;快速型、中速型和慢速型肉鸡宰后45 min和24 h胸肌、腿肌肉色b*值依次显著降低,此结果与王珏等[24]在817肉鸡、铁脚麻鸡、矮脚黄鸡和窑鸡配套系上的研究结果相似。以上结果表明,从客观指标评价方面来看,慢速型黄羽肉鸡肌肉感官品质优于中速型,而中速型优于快速型,这也是我国地方小型鸡种较大型鸡种肉品质优越的原因之一,同时也与本研究不同生长速度肉鸡体重和平均日增重的结果相呼应。

3.2 不同生长速度黄羽肉鸡肌肉脂肪酸组成比较

肌肉脂肪酸组成不仅可反映肉的理化性质和风味,而且对健康食品和风味食品的研发都有一定的价值[25]。研究表明,豆蔻酸和血清高胆固醇含量呈正相关,是造成心血管病的最主要因素,棕榈酸则可降低血清胆固醇含量[26];花生酸、木蜡酸与生理功能相关的研究报道目前还没有;单不饱和脂肪酸(油酸)降低血清胆固醇含量的效果与多不饱和脂肪酸相当[27]。本研究结果显示,快速型、中速型和慢速型肉鸡胸肌和腿肌中豆蔻酸、油酸含量依次显著降低;快速型和中速型肉鸡胸肌和腿肌中棕榈酸含量显著高于慢速型,上述结果说明在对人体健康影响方面,中速型肉鸡优于慢速型,慢速型优于快速型。多不饱和脂肪酸具有调控脂类代谢、降低血糖、调节神经发育和免疫等功能的作用[28-30]。本研究结果显示,慢速型肉鸡胸肌中多不饱和脂肪酸含量显著高于中速型和快速型,快速型、中速型和慢速型肉鸡腿肌中多不饱和脂肪酸含量依次显著升高,以上结果说明慢速型肉鸡在调控脂类代谢、神经发育和免疫功能以及降血糖方面功能最优。亚油酸是n-6多不饱和脂肪酸的母体,可衍生出花生四稀酸,而花生四稀酸可参与调节机体炎症反应[28]。本研究结果显示,慢速型肉鸡胸肌和腿肌中亚油酸含量以及腿肌中花生四稀酸含量均显著高于快速型和中速型。α-亚麻酸是n-3多不饱和脂肪酸的母体,在Δ5、Δ6去饱和酶的作用下可转化成EPA和DHA,EPA和DHA又在健脑明目、抗癌、抗炎和治疗心血管疾病方面发挥着重要的作用[31]。本研究结果显示,中速型肉鸡胸肌中EPA和DHA含量以及腿肌中DHA含量均显著高于快速型和慢速型,这说明中速型黄羽肉鸡营养保健价值更高。n-6和n-3多不饱和脂肪酸在功能上相互协调、相互制约,且世界卫生组织推荐的适合人体健康的n-6多不饱和脂肪酸/n-3多不饱和脂肪酸值为6~10,任何一种过多沉积均会引起维生素E水平下降[25],根据本试验结果判断,中速型肉鸡胸肌和腿肌n-6多不饱和脂肪酸/n-3多不饱和脂肪酸值为健康或者接近健康水平。

3.3 不同生长速度黄羽肉鸡肌肉游离氨基酸含量比较

游离氨基酸是肌肉中重要的滋味物质和香味前体物质,具有酸、甜、苦、咸和鲜等多种味道,是评价肉品质的关键指标之一[32-33]。本研究结果显示,中速型肉鸡胸肌中总游离氨基酸含量最高,同时中速型和慢速型肉鸡腿肌中总游离氨基酸含量显著高于快速型。天冬氨酸、谷氨酸、精氨酸、甘氨酸和丙氨酸为鲜味氨基酸,它们的组成和含量影响着肉的鲜美程度[10]。本研究结果显示,中速型肉鸡胸肌中总鲜味氨基酸含量最高,这与谷氨酸和甘氨酸含量显著升高对其的贡献有关;慢速型肉鸡胸肌中总鲜味氨基酸含量次之,主要与天冬氨酸和精氨酸含量显著升高对其的贡献有关。虽然慢速型肉鸡腿肌中精氨酸和丙氨酸含量显著升高,但不同生长速度黄羽肉鸡腿肌总鲜味氨基酸含量之间差异并不显著,可能与剩余其他3种鲜味氨基酸含量分布差异较大有关。人体不能合成7种必需的氨基酸,必须由食物供给,世界卫生组织和联合国粮食及农业组织规定的理想蛋白质标准中必需氨基酸/总氨基酸值为40%[34]。本研究结果显示,中速型肉鸡胸肌中必需氨基酸含量显著高于快速型和慢速型,必需氨基酸/总氨基酸值最接近40%,且其中每种必需氨基酸含量贡献都很突出;快速型、慢速型和中速型肉鸡腿肌中必需氨基酸含量依次显著升高,其中缬氨酸、异亮氨酸和赖氨酸贡献最为突出。

4 结论

不同生长速度黄羽肉鸡(快速型岭南黄鸡、中速型麻黄鸡和慢速型胡须鸡)在相同饲粮营养水平、饲养方式以及饲养环境条件下达到各自出栏体重时,应用相同的屠宰方法和储藏温度,通过检测胸肌和腿肌感官品质、脂肪酸组成和氨基酸含量等肉品质指标,比较分析后得出慢速型肉鸡肌肉感官品质最优,中速型肉鸡肌肉脂肪酸组成和氨基酸含量最佳。

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