【作者】 葛武鹏；

【导师】 李元瑞；

【作者基本信息】 西北农林科技大学 ， 食品科学， 2008， 博士

【摘要】 牛羊乳营养价值很高,人们已做了大量基础研究工作,但牛羊乳的营养特性及加工特性存在许多异同处,这方面研究有待于进一步深入,特别是羊乳的营养特性及对嗜酸乳杆菌增菌发酵效能的研究更是空白,羊乳在陕西省资源丰富,奶山羊存栏数、产量居全国首位,已形成特色经济优势,呈现连续平稳增长态势,主要产区包括富平、蓝田、千阳、三原、泾阳、杨凌等,陕西山羊品种主要包括莎能奶山羊和关中奶山羊,羊乳的加工在陕西省多年来始终处于初级加工阶段,每年产能的90%以上加工成乳粉外销国内外,属于典型的优势资源低效益利用。为了开辟羊乳资源利用新途径,新方法,新思路,实现羊乳产业健康及经济效益最大化,有必要对陕西羊乳的营养特性做进一步的分析及其对益生菌增菌发酵效能展开研究。本研究结合陕西羊乳特色乳业资源优势,对羊乳从其营养特点、质构特性、加工特性、风味特性、微生物发酵特性等多方面展开研究,同时与牛乳相关特性进行比较,得到了一些有价值的结论与思路,为陕西羊乳资源科学利用提供了新的参考。主要结论如下:(1)陕西羊乳质量较稳定,全省范围内各项指标波动幅度不大。主要理化指标结果如下:密度D2 401.0282±0.0019×103kg·m-3, pH值6.694±0.018,滴定酸度11.86±0.203°T,蛋白质31.92±1.96 g·L-1脂肪含量38.94±0.97g·L-1,,乳糖含量43.54±6.58 g·L-1,灰分7.655±0.388 g·L-1,总乳固体(TS)123.96±2.16 g·L-1,非脂乳固体(SNF)84.63±2.77%。各营养成分指标除乳糖外全年变化规律遵循:春冬季含量高,夏秋季含量低,7~8月份最低,乳糖含量变化正好与此相反。羊乳物理特性指标:粘度(η)1.37±0.16 mPa?s(20℃);电导率K 4.715±0.25 mS/m(20℃);表面张力P 50.370±4.096 mN/m(20℃);折光系数nD 1.3462±0.0014(20℃),牛羊乳之间主要物理指标无显著性差异(P>0.05)。(2)凝固型羊酸乳物性学指标:硬度(Firmness)羊酸乳108.73±4.15g;稠度(Consistency)羊酸乳2139.31±90.88g·s;粘聚性(Cohesiveness)羊酸乳43.70±8.79g;粘性指数(Index of viscosity)羊酸乳34.89±14.42 g·s。与凝固型牛酸乳比较,硬度和粘性指数差异显著(P<0.05),凝固型牛酸乳的4项物性指标均高于凝固型羊酸乳;搅拌型羊酸乳物性学指标:硬度93.42±9.85g,稠度691.58±110.10 g·s;粘聚性35.15±5.83g;粘性指数20.79±10.10 g·s。搅拌型牛、羊酸乳间比较粘性指数差异显著(P<0.05);羊奶酪(半硬质)质构特性指标:羊奶酪:硬度(hardness)为2269.28±246.97g,粘性(Stickiness)指标为214.95±31.33g。硬度指标与牛奶酪比较存在显著性差异(P<0.05)。(3)自然状态下,牛、羊乳脂肪球颗粒大小不一,羊乳脂肪球波动范围0.183~8.544μm,平均2.6580μm,牛乳脂肪球波动范围0.277~9.552μm,平均3.4573μm,牛、羊乳脂肪球大小服从正态分布。辛酸和癸酸是羊乳的特征风味脂肪酸,含量为11.60%;牛、羊乳加工后,长链饱和脂肪酸含量降低,短链饱和脂肪酸含量增加,加工后的乳制品的营养价值提高,其中短链饱和脂肪酸含量的增加更有利于人体消化和吸收;牛、羊初乳中的不饱和脂肪酸含量分别高达36.91%和33.06%,牛初乳、羊奶酪和羊初乳中SFA:MUFA:PUFA比例最佳,分别为5.58:2.86:1,9.20:3.77:1,9.34:3.93:1,其脂肪酸营养价值高于其它牛羊乳制品;牛初乳、羊初乳是自然界较为理想的保健食物资源。(4)牛、羊乳及其制品水解蛋白质中含有18种氨基酸,其中谷氨酸含量最高,色氨酸含量最低。羊乳中除丙氨酸、蛋氨酸、异亮氨酸、酪氨酸外其余各种氨基酸含量均高于牛乳中相应氨基酸含量,8种必需氨基酸比例合适,接近FAO/WHO推荐的理想模式之比例,羊营养价值高;牛初乳、羊初乳蛋白质质量优于其常乳,均属于优质蛋白质食物资源。通过分析牛、羊乳及其制品氨基酸组成及含量变化,运用TEAA/TAA、AAS、RC、SRC、EAAI等多项氨基酸营养学评价指标综合评判,羊乳制品蛋白质质量优于牛乳制品蛋白质质量,加热处理后牛乳优于羊乳;微生物发酵处理后,羊乳制品优于牛乳制品,羊乳耐加热性能差,更适合于制作发酵乳制品;羊乳及其制品蛋白质营养评价结果依次是:羊奶酪>羊酸乳>纯羊乳>巴杀羊乳>UHT羊乳。牛乳及其制品蛋白质营养评价结果依次是:牛酸乳>牛奶酪>巴杀牛乳>UHT牛乳>牛乳。(5)牛、羊乳及其制品挥发性风味物质构成复杂,含量丰富,包括羧酸类、醇及呋喃类、醛类、酮类、酯类、烃类、其他类等7大类,本研究结果显示牛羊乳及其制品挥发性风味化合物共有:羊乳53种、牛乳52种、巴杀羊乳53种、巴杀牛乳52种、UHT羊乳54种、UHT牛乳53种、UHP羊乳50种、UHP牛乳53种、羊酸乳53种、牛酸乳52种、羊奶酪52种、牛奶酪53种。牛、羊乳及其制品风味物质构成种类基本相同,各风味成分含量存在差异,风味贡献度存在差异,牛、羊乳及其制品风味各具特色。(6)羊乳基质中增菌因子最佳配比:低聚果糖1.0%,乳清粉1.2%,胡萝卜汁5.0%,蜂蜜2.0%,菊粉1.0%,乳糖1.0%,酪蛋白磷酸肽1.0%,主次顺序是:乳清粉>低聚果糖>蜂蜜>酪蛋白磷酸肽>菊粉>乳糖>胡萝卜汁。羊乳基质增菌培养基中嗜酸乳杆菌活菌数最高可达9.955×1011 Cfu·mL-1。牛乳基质培养基中增菌因子最佳配比是:低聚果糖1.5%,乳清粉1.8%,胡萝卜汁7.5%,蜂蜜2.0%,菊粉1.5%,乳糖1.0%,酪蛋白磷酸肽(CPP) 1.0%,主次顺序是:酪蛋白磷酸肽>低聚果糖>菊粉>蜂蜜>乳清粉>胡萝卜汁>乳糖。牛乳基质嗜酸乳杆菌活菌数最高可达9.875×1011 Cfu·mL-1。两种乳基质培养基添加增菌因子浓缩冻干后菌粉活菌数均达到1012 Cfu·g-1级。(7)羊乳基质培养基保护剂最佳配方是:添加甘油4.0%,L-半胱氨酸0.30%,抗坏血酸0.75%,海藻糖1.0%制备菌悬液效果最好,可有效保护菌体细胞,减少冷冻干燥伤害,嗜酸乳杆菌存活率最高,主次顺序是:抗坏血酸>甘油>海藻糖>L-半胱氨酸。验证试验表明,添加保护剂后,菌粉冻干存活率可达85.55%,干菌粉活菌数达到8.877×1012 Cfu·g-1;牛乳基质培养基保护剂最佳配方是:添加甘油4.0%、L-半胱氨酸0.30%、抗坏血酸0.75%、海藻糖3.0%制备菌悬液效果最好,可有效保护菌体细胞,减少冷冻干燥伤害,嗜酸乳杆菌存活率最高。主次顺序是:抗坏血酸>海藻糖>甘油>L-半胱氨酸。验证试验表明,添加保护剂后,菌粉冻干存活率可达85.60%,干菌粉活菌数达到7.283×1012 Cfu·g-1。( 8 )嗜酸乳杆菌在MRS培养基增菌发酵,回归模型是: YMRS(t)= 3.45888/(1+12.92378*exp(-0.35632*t)),相关性数R=0.9967,决定系数DC=0.9934,差异显著性P < 0.01 ;在羊乳基质培养基中增菌发酵,回归模型是:YCAP(t)=33.2056/(1+0.437297* exp(-0.080136*t))决定系数DC=0.9981 ,相关系数R=0.9989,差异显著性P<0.01;在牛乳基质培养基中增菌发酵,回归模型是:YB0V(t) = 33.5013/ (1+0.442989*exp(-0.075401*t)),决定系数DC=0.9919,相关系数R=0.9959,差异显著性P<0.01。更多还原

【Abstract】 The high valuable nutrient of bovine and caprine milk is spoken highly of based on plenty of fundamental researches. Yet the further exploration will be continued due to the discrepancies existing between the properties of the nutrients of the bovine and caprines’milk and the features of the processing, especially the study on the nutritious caprine milk merits and its application in Lactobacillus acidophilus (L.A.) are still vacant. There are a great abundance of caprine milk resources in Shaanxi province. The quantities of heads and the productivities of caprine milk have ranked priority domestically. The formed economic specialties have been ranked steadily and continuously. The main producing areas of caprine milk distribute in places like FuPing, LanTian, QianYang, SanYuan, JingYang and YangLing and so on. And the species of caprines are chiefly ShaNeng and GuanZhong caprines. However, the remaining preliminary level of processing in Shaanxi resulted in typical deficiency utilization by advantageous resources; more than 90% of the processed milk powder is exported to domestic and abroad too. To seek the new methods and advanced spirits taking use of the caprine milk, to realize the perfect combination between the effects of caprine milk nutrients and maximum economic profits, it’s highly necessary to make a comparative analysis of caprine milk and cow milk, coming with the deeper research on fermentation efficiency for Lactobacillus acidophilus. The precious conclusion and inspiration is concluded from the relatively comparisons between caprine milk and cow milk on different characteristics of nourishment, textural properties, processes, flavor and microbiology fermentation. It provides the latest referent for the scientific utilization of the caprine resources in Shaanxi. The primary conclusions are the following:1. The quality of caprine milk is quite stable in Shaanxi; there is a slight wave of nutrient compositions among the provincial yearly standards. The main physiochemical items resulted as follows: density( D2 40,20℃/4℃)1.0282±0.0019×103kg·m-3, pH 6.694±0.018, titratable acidity 11.86±0.203°T, crude protein 31.92±1.96 g·L-1, lipid 38.94±0.97 g·L-1, lactose 43.54±6.58 g·L-1,mineral content 7.655±0.388 g·L-1, total solids(TS)123.96±2.16 g·L-1, non-fat solids(NFS)84.63±2.77 g·L-1.The yearly varies of nutrient compositions, with the exception of lactose; abide by the regulation as follows: The content of nutrition items is higher in spring and winter, it’s lower in summer and autumn, and it remains the lowest in July and August. Yet as for lactose, the regularity is just opposite. The physical items of caprine milk are as follows: viscosity (η)1.37±0.16 mPa?s(20℃),electrode conductivity(K) 4.715±0.25 mS/m(20℃), the surface tension (P)50.370±4.096 mN/m(20℃), the refraction index (nD)1.3462±0.0014(20℃). The physical properties of caprine and cow milk is no significance (P>0.05).2. The textural properties of caprine set yoghurt are as follows: firmness 108.73±4.15g, consistency 2139.31±90.88g·s, cohesiveness 43.70±8.79g, index of viscosity 34.89±14.42 g·s. Compared to the bovine set yoghurt, the firmness and index of viscosity exist significance (P<0.05). The textural properties of caprine stirred yoghurt are as follows: firmness 93.42±9.85g, consistency 691.58±110.10g·s, cohesiveness 35.15±5.83g, index of viscosity 20.79±10.10g·s. Compared to the bovine stirred yoghurt, the index of viscosity exist significance (P<0.05). The textural properties of caprine cheese are as follows: hardness 2269.28±246.97g, Stickiness 214.95±31.33g. Compared to bovine cheese, the hardness and stickness exist significance(P<0.05).3. before homogenizing, the particles of fat globule of bovine and caprine revealed in various sizes. The diameter range of caprine fats globule is within 0.183~8.544μm,the average diameter is 2.6580μm;The diameter range of bovine fats globule is within 0.277~9.552μm, the average diameter is 3.4573μm. The particles of fat globule of caprines and bovines conforms normal distribution. The caprylic acid and the capric acid are the characteristics fatty acids of caprine. The sum of contents is 11.60%. After processing, the contents of the long chain of saturated fatty acids are decreased, but the contents of the short chain of saturated fatty acids are increased. The nutrition valve will be upgraded after it’s processed. And the supplement of the short chain of fat acids is easier for Human body to digest and absorb. The contents of unsaturated fat acids in colostrums of caprines’and cows’reach as high as 36.91% and 33.06% respectively. The ratio of SFA:MUFA:PUFA of bovine colostrums, caprine cheese and caprine colostrums are 5.58:2.86:1 , 9.20:3.77:1 and 9.34:3.93:1 comparatively. Their nutrition values are relatively higher than other analyzed dairy products. The colostrums both bovine and caprine are ideally healthy food resources.4. Under the synthetic analysis of amino acid nutrition evaluation items, proved by the ratio of TEAA/TAA、AAS、RC、SRC、EAAI, the quality of caprine proteins are superior to that of the bovine’s, but it will be inferior to the bovine’s after it’s heated. However after fermented by the microorganism, the quality of caprine proteins will be better than that of the bovine’s. The poor performance of heat-resistance of caprine milk is more adapted to be produced as fermented dairy. The nutrition evaluation results of bovine milk and their products in turns are: bovine yoghurt, bovine cheese, pasteurized milk, UHT milk and pure bovine milk. And that of the caprine milk series are caprine cheese, pure caprine milk, caprine yoghurt, pasteurized caprine milk and UHT caprine milk.5. There is a complexity in flavor substances of bovine and caprine milk and their products. They are rich in carboxylic acids, alcohols and furans, aldehydes, ketones, esters, hydrocarbons and others. The result of the flavor compounds of bovine and caprine and their products shows that there are 52 kinds in bovine milk, 53 in caprine milk, 52 in pasteurized bovine milk, 53 in pasteurized caprine milk, 53 in UHT caprine milk, 54 in UHT bovine milk, 53in UHP bovine milk, 50 in UHP caprine milk, 52 in bovine yoghurt, 53 in caprine yoghurt, 53 in bovine cheese, 52 in caprine cheese. There is a basic similarity between the constituents of flavor substances of bovine and caprine milk and their products. The contents of flavor constituents and their distribution ability have a slight difference. Each of the flavors runs a different feature.6. The optimized ingredients, of enriched incubating of L.A. in caprine substrate, is: 1.0% fructo-oligosaccharides (FOS), 1.2% whey, 5.0% carrot juice, 2.0% honey, 1.0% inulin, 1.0% lactose, 1.0% casein phosphopeptide(CCP), The important order comes by whey, FOS, honey, CPP, inulin, lactose and carrot juice. The highest living counts in caprine milk substrate reaches to 9.955×1011 Cfu·mL-1. The optimized ingredients, of enriched incubating of L.A. in bovine substrate medium, is FOS 1.5%, 1.8% whey, 7.5% carrot juice, 2.0% honey,1.5% inulin, 1.0% lactose, and 1.0% CPP. The important order comes by CCP, FOS, inulin, honey, whey, carrot juice and lactose. The highest living counts in bovine substrate reaches to 9.875×1011 Cfu·mL-1. The living counts of the freeze-dried L.A. powder of these two sorts of dairy substrate media reach to the grade of 1012 Cfu·g-17. The optimum formula of protectants in caprine milk substrate is: with the addition of 4.0% glycerin, 0.30% L-cysteine, 0.75% ascorbic acid, 1.0% trehalose, it affects the same result as in bovine substrate. The important order follows by ascorbic acid, glycerin, trehalose, L-cysteine. The verifying test shows the survival rate of L.A. powder reaches to 85.55% and living counts reach to 8.877×1012 Cfu·g-1 after adding optimized protectants.The optimum formula of protectants in bovine milk substrate are: with the addition of 4.0% glycerin, 0.30% L-cysteine, 0.75% ascorbic acid, 3.0% trehalose, effects best in making bacterial suspension. It protects L.A. cells more efficiently; decrease the hurt from freezing, the survival rate of L. A. is the highest. The important order follows by ascorbic acid, trehalose, glycerin, L-cysteine. The verifying test shows the survival rate of L.A. powder reaches to 85.60% and living counts reach to 7.283×1012 Cfu·g-1 after adding optimized protectants. 8. The regression model of the L.A. augment fermentation in MRS medium is YMRS(t)= 3.45888/(1+12.92378*exp(-0.35632*t)), the determination coefficient is DC=0.9934,the relative index is R=0.9967, there is significance(P<0.01). The regression model of LA in caprine substrate is YCAP(t)=33.2056/(1+0.437297* exp(-0.080136*t)) DC=0.9981, R=0.9989, P<0.01;The regression model of LA in bovine substrate is YB0V(t) = 33.5013/ (1+0.442989*exp(-0.075401*t)), DC=0.9919, R=0.9959, P<0.01.更多还原