【作者】 韩卫杰；

【导师】 陈玉林；

【作者基本信息】 西北农林科技大学 ， 动物遗传育种与繁殖， 2010， 博士

【摘要】 羊肉具有特殊的风味,俗称“膻味”,这种风味在一定程度上影响了人们对羊肉的消费,而我国又是世界上养羊第一大国,因此对羊肉膻味形成的物质基础及其形成机制展开深入研究,做到对羊肉膻味进行人为调控必定有助于扩大羊肉消费市场,促进肉羊业的快速发展。本试验首先借鉴国外对挥发性物质的研究方法,建立了绵羊脂肪组织中致膻物质的测定方法,并对致膻物质的种类及其影响因素进行了研究,最后对羊脂肪组织中致膻物质的形成机理进行了初步探索,取得如下研究结果:1.应用研究结果表明,采用脂肪组织样品用量100 g、同时蒸馏时间60 min、应用极性较强的色谱柱、4℃/min的升温速率等参数条件基本上满足了对脂肪组织中挥发性脂肪酸的研究要求。2.通过对猪、牛和绵羊脂肪组织中挥发性脂肪的研究,结果表明在猪脂肪组织中没有检测到支链脂肪酸;在牛脂肪组织中检测到了4-甲基辛酸,含量为7.508 mg/kg,但这浓度远小于绵羊脂肪组织中4-甲基辛酸的浓度;在绵羊脂肪组织中检测到了丰富的4-甲基辛酸和4甲基壬酸,其含量分别为36.169 mg/kg和6.174 mg/kg;同时,绵羊脂肪组织中癸酸的含量也显著高于猪和牛的含量,表明丰富的4-甲基辛酸是绵羊脂肪组织中挥发性脂肪酸的特有特征。3.通过对强、中和弱三个级别膻味脂肪组织进行研究,结果表明在强级别中,丁酸、己酸、辛酸、4-甲基辛酸和癸酸,均显著高于中级别和弱级别(P<0.05);在4-甲基辛酸方面,三个级别的脂肪酸样品明显的呈现出梯度差异,经统计检验,差异显著(P<0.05);而4-甲基壬酸的变化规律与膻味强弱的变化趋势的一致性较低,因此,推定对于羊肉膻味的行成4-甲基辛酸起主要作用,而4-甲基壬酸起辅助作用。对于癸酸的含量,也表现强烈的与膻味变化程度一致,但由于自身产生的不是羊肉膻味的气味特征而是较为难闻气味特征,因此大量癸酸存在也在一定程度可降低人们对羊肉的接受意愿。4.通过对小尾寒羊、滩羊和同羊脂肪组织中挥发性脂肪酸组成的研究,结果表明对羊肉膻味贡献较大的4-甲基辛酸和4-甲基壬酸在小尾寒羊、滩羊、同羊3个绵羊品种脂肪组织中分别为20.317 mg/kg,3.546 mg/kg和14.150 mg/kg,5.597 mg/kg及12.835 mg/kg,6.403 mg/kg。4-甲基辛酸被认为是对羊肉膻味起主要作用,其在三个品种之间的排序为:小尾寒羊>滩羊>同羊;小尾寒羊4-甲基辛酸浓度分别是滩羊和同羊的1.43和1.57倍,而滩羊和同羊大致相同。同时说明在这三个品种之间,遗传因素对羊肉膻味的形成具有一定作用。5.通过对河南和宁夏两地区小尾寒羊脂肪组织中挥发性脂肪酸组成分析,结果表明河南地区小尾寒羊脂肪组织中辛酸、4-甲基辛酸和癸酸的含量分别为52.823 mg/kg、35.745 mg/kg和118.217 mg/kg,大于宁夏地区43.942 mg/kg、20.317 mg/kg和51.949 mg/kg,差异显著(P<0.05)。对羊肉膻味起骨架作用得4-甲基辛酸,河南地区是宁夏地区的1.75倍;对羊肉膻味的形成起辅助作用4-甲基壬酸,在两地区之间差异不明显;同时在癸酸含量方面,河南地区是宁夏地区2.27倍。这些数据表明地域对羊肉膻味有一定影响。6.通过对绵羊脂肪酸合成酶AT/MT基因的研究,结果表明绵羊和山羊脂肪酸合成酶的AT/MT基因同源性最高为98.3%;其次是牛,为94.8%;再其次是猪、人和鼠,分别为86.5%、85.4%和81.5%。在核酸序列方面,绵羊和山羊的AT/MT基因核苷酸序与其他物种有10处存在明显的差异;在氨基酸序列方面,绵羊和山羊的AT-MT氨基酸序列与其他物种在六处存在明显差异,其中在92处AA的缺失和在224处AA的性质的改变,最为重要。在二级结构分布方面,山羊和绵羊在133-140氨基酸形成螺旋结构;绵羊和山羊脂肪酸合成酶AT/MT与其他物种相比较的的特殊结构,可能是造成其较为容易运转带有支链的底物参与脂肪酸的合成,使得羊类脂肪组织中支链脂肪酸较为丰富的原因。更多还原

【Abstract】 Mutton can release a special odor in cooking, commonly known as“goaty flavour”. The odor affected people’s mutton consumption in a certain extent. Our country was biggest country of feeding goat and sheep in the world, can produce millions of tons of mutton every year. So, that the material and mechanism of forming mutton smell was deeply studied is very important to the rapid development of sheep industry. Under foreign research methods of volatile substance, the study firstly established determination method of causing mutton smell material, and studied material of causing mutton smell and its influencing factors. At last, the forming mechanism of causing mutton of smell in sheep adipose tissue was preliminary explored. The results were showed in following.1. Research results showed that taking into account the extract concentration in the extract, the feasibility of sample collection and separation of volatile fatty acids operability. The parameters of 100 g adipose tissue sample and 60 min extraction time can meet the research needs of volatile fatty acids of adipose tissue. In GC separation, Polarity GC column and heating rate of 4℃/min can separated volatile fatty acids. Volatile fatty acids including have important role mutton smell were detected. After testing, the repeatability and recovery of the method meet the needs of studying mutton smell.2. By analyzed volatile fatty acids of adipose tissue from pig, cattle and sheep, the results showed that the adipose tissue of pig hasn’t contain volatile branched chain fatty acids. The adipose tissue of cattle contained a lot of 3-methylbutyric acid, it’s concentration 186.513 mg/kg. At the same time, 4-methyloctanoic acid was detected, it’s concentration 7.508 mg/kg, which was lower than sheep adipose tissue. Adipose tissue of sheep has detected pentanoic acid, heptanoic acid, 4-methyloctanoic acid and 4-methylnonanoic acid, their concentration was 12.928 mg/kg, 16.276 mg/kg, 36.169 mg/kg, and 6.174 mg/kg, respectively. Decanoic acid of sheep adipose tissue was more than pig and cattle. 4-methyloctanoic acid and 4-methylnonanoic acid have mutton odor trait. which less than detecting value of this study. Decanoic acid can release very unpleasant odor. So, forming mutton odor, inducing low acceptability of mutton has close relationship of 4-methyloctanoic acid, 4-methylnonanoic acid and decanoic acid.3. By analyzed volatile fatty acids of adipose tissue from strong, middle and low mutton odor. The results showed that the butanoic acid, hexanoic acid, octanoic acid, 4-methyloctanoic acid and decanoic acid of strong mutton odor sample were significantly higher than middle and low mutton odor sample(P<0.05). The change of hexanoic acid, octanoic acid, 4-methyloctanoic acid and decanoic acid among of volatile fatty acids was consistent with mutton odor. The change 4-methylnonanoic acid was not consistent with mutton odor. So, we speculated 4-methyloctanoic acid has important role to forming mutton odor, 4-methylnonanoic acid was helping role. The higher concentration decanoic acid can reduce acceptability of mutton.4. The effects of breed on volatile fatty acids in sheep adipose tissue were researched in this test. The results showed that the concentration of 4-methyloctanoic acid and 4-methylnonanoic acid, which have important role to mutton odor, from small tail Han sheep, Tan sheep and Tong sheep were 20.317 mg/kg,3.546 mg/kg ;14.150 mg/kg,5.597 mg/kg and 12.835 mg/kg , 6.403 mg/kg, respectively. The sort of 4-methyloctanoic acid concentration among three sheep breed is small tail Han sheep > Tan sheep > Tong sheep. The 4-methyloctanoic acid concentration of small tail Han sheep is 1.43 and 1.57 fold of Tan sheep and Tong sheep. Tan sheep was same with Tong sheep. The change date was same with experience of life people. Among sheep breeds, genetic factor can affected mutton odor forming.5. The effects of area on volatile fatty acids in sheep adipose tissue were researched in this test. The results showed that the concentration of octanoic acid, 4-methyloctanoic acid, decanoic acid of Small Tail Han sheep from Henan were 52.823 mg/kg、35.745 mg/kg and 118.217 mg/kg, which more than 43.942mg/kg、20.317 mg/kg and 51.949 mg/kg from Ningxia. The concentration of 4-methyloctanoic acid of Henan was 1.75 fold of Ningxia. On 4-methylnonanoic acid, two area were same. The concentration of decanoic acid of Henan was 2.27 fold of Ningxia. The date indicated mutton odor of Henan was stronger than Ningxia, which was same with experience of people life. The phenomenon showed region has significantly effects to mutton odor.6. The AT-MT gene sequence of fatty acid synthase from sheep was cloned and analyzed. The results showed that the gene homology between sheep and goat was 98.3%, followed by cattle, 94.8%, then followed by pigs, and rats, respectively, 85.0%, 83.7% and 80.4%. In the nucleic acids, the AT-MT gene of sheep and goat has eight significant differences comparing with other animal. In the amino acid sequence, the AT-MT gene of sheep and goat has six significant differences, in which the difference of 244 was caused by changed of amino acid nature. In the secondary structure distribution, the spiral and folded structure of sheep and goats AT-MT gene amino acid sequence formed have specific structure comparing with other species.更多还原