Effects of seasonal variations on the quality of set yogurt,stirred yogurt,and Greek-style yogurt

We studied the effects of seasonal variations on the quality of stirred yogurt, set yogurt, and Greek-style yogurt over 2 milking seasons in New Zealand. Correlations between the properties of the yogurts, the characteristics of the milk, and the acid gelation properties induced by glucono-δ-lactone, reported in our previous works, were also explored. Set yogurt and Greek-style yogurt from the early season had the highest firmness over the seasons. The yogurt firmness correlated with the gel strength of glucono-δ-lactone-induced acid gels, indicating that the latter could, to some extent, predict the seasonal variations in the firmness of set yogurt. The correlation studies highlighted the potentially important role of the glycosylation of κ-casein in the seasonal variations in the yogurt structures. Yogurt made from mid-season milk had the lowest water-holding capacity, which may have played a part in lowering its firmness and viscosity. Late-season stirred yogurt displayed the strongest resistance to shear-induced thinning, which might arise from the unique viscoelastic properties of late-season yogurt gels.     

酸乳凝胶特性影响机理的探讨

探讨了不同发酵温度下酸乳的表观黏度与剪切速率及时间之间的关系,并对酸乳持水力、胶体脱水收缩作用敏感性等流变学特性进行了研究。结果表明,不同发酵温度酸乳的黏度随剪切时间的延长而变小,并最终趋于平缓,都形成了触变环。表明是触变体系,酸乳触变环面积(37℃>40℃>43℃)与黏度具有很好的相关性。酸乳的表观黏度随剪切时间的变化曲线符合幂函数y=kx-n的变化规律。37℃发酵酸乳的持水力达到最高值,分别较40℃和43℃发酵酸乳的高出18%和8%,而胶体脱水收缩作用敏感性值最小,比40℃和43℃发酵酸乳的分别低13%和5%。表明低温发酵酸乳的黏度大,乳清析出少,稳定性好。     

Effect of probiotic Lactobacillus casei Zhang on fermentation characteristics of set yogurt

The effect of four inoculation levels of Lactobacillus casei Zhang (0.001, 0.01, 0.1 and 1.0 g/100 g) on the fermentation characteristics of set-style yogurt, and the changes in viable counts of lactic acid bacteria, pH value, syneresis, apparent viscosity, sugar and organic acid contents were determined during fermentation and storage over 21 days. The presence of 0.001 to 0.01 g/100 g L. casei Zhang did not affect the growth of the yogurt strains, and the yogurt inoculated with 0.00 1 g/100 g of L. casei Zhang had the highest apparent viscosity among the samples. However, a high inoculated level of L. casei Zhang (1.0 g/100 g) resulted in yogurts with inferior quality.     

Effect of 'ropy' strains of Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus on rheology of stirred yogurt

The TA-TX2 Texture Analyser and the Brookfield RVT Viscometer have been used to investigate the contribution of ropiness to the texture of stirred yogurts made using ropy strains of bacteria. Back extrusion and texture profile analysis, not commonly used to quantify rheological properties of semi-solid foods, have been found useful in distinguishing the contribution of exopolysaccharides to different texture attributes (Toba et al ., 1990). Thus ropiness, a characteristic which is imparted to the product as a result of fermentation with particular polysaccharide-producing strains, contributes to 'adhesiveness', while 'firmness' and 'elasticity' are likely to be influenced more by the protein matrix of the yogurt than by secretion of the polysaccharide by the ropy strains. Effects on viscosity and ability to recover viscosity after disruption were apparent, although the contribution of ropiness was not always positive. Ropy strains increased viscosity of stirred yogurts when compared to yogurt made with non-ropy cultures. But, whilst a ropy Lactobacillus delbrueckii ssp. bulgaricus (Lb r⁺) combined with a non-ropy Streptococcus thermophilus (St r⁻) produced a viscous product which recovered its viscosity well, a yogurt made by combining both ropy strains did not recover its viscosity as well as yogurt made by combining two non-ropy cultures and lost its structure more rapidly during the destructive testing. These results show therefore that inclusion of a ropy strain will not always lead to improved texture attributes, that while ropy strains may increase viscosity they may not influence 'firmness' and lend support to the view that this latter attribute is more influenced by protein–protein interactions.     

温度对酸乳中乳酸菌胞外多糖作用机制的研究

重点探讨了不同发酵温度下酸乳发酵产生的胞外多糖含量变化以及添加不同来源的胞外多糖对酸乳流变学特性的作用,结果表明:37℃条件下发酵所得酸乳多糖含量最高,达到461.4mg/mL,43℃条件下酸乳多糖含量最低,仅为247.6mg/mL。酸乳产生的内源性胞外多糖表现在产品特性上,其表观黏度及剪切应力随时间的变化都明显(P<0.05)高于外源添加胞外多糖的酸乳。表观黏度随剪切时间的变化曲线符合对数函数y=kLn(x)+b(内、外源R2分别为0.9527、0.9015)的变化规律。此外,酸乳经过发酵产生内源性胞外多糖后,其持水力(WHC)较添加外源性胞外多糖的酸乳高出26%,胶体脱水收缩作用敏感性(STS)较添加外源性胞外多糖的酸乳低46%。这说明低温有利于乳酸菌胞外多糖形成,且内源性胞外多糖酸乳的表观黏度大、持水力高。     

Effect of heat treatment of skim milk and final fermentation pH on graininess and roughness of stirred yogurt

The effects of heat treatment of skim milk (95°C/80 s, 95°C/256 s, 110°C/40 s, 110°C/180 s, 130°C/20 s and 130°C/80 s) and final fermentation pH of yogurt (4.8 and 4.4) on physical characteristics of stirred yogurt were investigated. Physical properties, including graininess and roughness, of stirred yogurt were determined during storage at 4°C for 15 days. Number of grains, perimeter of grains, visual roughness, storage modulus and yield stress decreased, when heating temperature or final fermentation pH increased. For practical applications, processing parameters such as heat treatment and fermentation pH can be optimized to improve quality or modified to create fermented milk products with different physical properties.     

刺梨凝固型酸奶的发酵工艺研究

研究了刺梨及蜂蜜制备的凝固型酸奶的发酵工艺,考察刺梨汁添加量、发酵温度、蜂蜜添加量、乳酸菌接种量及发酵时间对刺梨酸奶感官品质的影响。在单因素试验的基础上采用正交试验优化刺梨凝固型酸奶的发酵工艺。结果表明,刺梨凝固型酸奶最佳发酵条件为：刺梨汁添加量30%、蜂蜜添加量10%、乳酸菌接种量0.15%、发酵温度42 ℃和发酵时间9 h。在此条件下,所得刺梨凝固型酸奶感官评分为92.5分,质地均匀、凝结状态良好、口感细腻,且有浓郁的乳香味和刺梨风味。     

Effect of calcium on the physical properties of stirred probiotic yogurt

The effect of calcium on the viscosity, firmness, and smoothness, as determined by extent of nodulation, of stirred probiotic yogurt produced by bacterial fermentation was investigated. Standardized milk for yogurt manufacture was prepared, and calcium was added or removed from the system. Calcium was added as Ca²⁺ in the form of CaCl₂ (up to 13.6 mM) or nonionic calcium as Gadocal-K (calcium potassium citrate; up to 49.8 mM). Calcium was removed by chelating with sodium citrate (up to 16 mM) or by cation exchange with Amberlite IR-120 plus (sodium form) resin (up to 10 g/L). Calcium chloride and sodium citrate were added either before or after heat treatment of milk, and nonionic calcium was added before heat treatment. Calcium removal by ion exchange was performed before heat treatment. Neither Ca²⁺ addition nor removal by chelation with citrate resulted in stirred yogurt with viscosity, firmness, and smoothness superior to those of the control yogurt, whereas addition of 49.8 mM nonionic calcium and removal of calcium (5.6 mM or ∼10% of total calcium) by cation exchange improved the firmness and viscosity without affecting yogurt smoothness. The study identified Gadocal-K as a possible source of calcium fortification of stirred yogurt without loss of texture.     

用于搅拌型酸奶的稳定剂

<正> 酸奶产品在许多亚洲国家和地区都十分流行,尤以搅拌型酸奶和酸奶饮品最受消费者的青睐。不同国家的人,对酸奶的粘稠度和硬度都有不同的喜好,然而大部分消费者都偏爱具有平滑奶油状和组织丰满的酸奶。     

脂肪替代品对脱脂搅拌型酸奶流变性的影响

研究不同脂肪替代品对脱脂搅拌型酸奶流变性的影响。实验表明:适当浓度的海藻酸丙二醇酯(PGA)、琼脂、高酯果胶、明胶、变性淀粉,都可以使酸奶达到一定的表观黏度,具有增稠的作用,从而解决酸奶组织砂状和口感粗糙、乳清分离等问题。其中添加0.50%变性淀粉及0.10%果胶的抗剪切能力最好。     

脂肪替代品对脱脂搅拌型酸奶流变性的影响

研究了不同脂肪替代品对脱脂搅拌型酸奶流变性的影响。结果表明,适当浓度的海藻酸丙二醇酯(PGA)、琼脂、高酯果胶、明胶、变性淀粉,都可以使酸奶达到一定的表观黏度,具有增稠的作用,解决酸奶组织砂状和口感粗糙、乳清分离等问题。其中添加质量浓度为5g/L变性淀粉及质量浓度为1g/L果胶的抗剪切能力最好。     

稳定剂添加对发酵型酸奶发酵效果的影响

针对凝固型酸奶中常用的明胶、琼脂、果胶、卡拉胶等稳定剂的应用,研究了发酵前添加稳定剂对酸奶发酵效果的影响。结果表明在适宜添加量的情况下,明胶、琼脂、果胶、卡拉胶对发酵剂的产酸规律影响较弱,添加四种胶体后产酸曲线趋势类似,明胶产酸效果较好,优于果胶、琼脂、卡拉胶和不添加对照组。稳定剂添加对产酸量影响效果因稳定剂种类而略有差异,明胶添加量为0.09%(w/v),果胶添加量控制在0.07%~0.1%(w/v)范围内,卡拉胶添加量控制在<0.05%(w/v),琼脂应控制低添加量或者协同其他添加剂使用产酸效果良好。稳定剂添加均能很好的改善酸奶的感官品质,在一定添加量下,不影响其酸度、活菌数,保持了酸奶原有的功能性。     

向日葵低酯果胶对搅拌型酸奶品质特性的影响

以未添加向日葵低酯果胶的酸奶为对照,研究了不同酯化度(DE)范围的低酯果胶对搅拌型酸奶性质的影响。结果表明,低酯果胶能够有效改善酸奶的持水性、黏度、质构和感官评分;加入0.08%(m/v)的酯化度范围为30%左右的低酯果胶较空白对照样品,持水性提高了9.38%;而添加等量酯化度范围为35%左右的低酯果胶后,能够有效提高酸奶的黏度至2824cP,且相比其他低酯果胶,其对应酸奶的感官评分最高。实际生产中可根据产品需求,选择30%～35%酯化度的向日葵低酯果胶对酸奶进行结构状态和感官风味的改善。     

搅拌型燕麦酸奶的研制

以鲜牛奶扔和燕麦为主要原料,研究搅拌型燕麦酸奶的加工工艺条件.通过单因素试验和正交试验确定燕麦最佳糖渍条件和制作燕麦酸奶的最佳工艺参数.结果表明,燕麦最佳糖渍条件:糖渍时间为36 h,糖渍温度为70℃,蔗糖质童分数为50%;当蔗糖添加量为6%,接种量为4%,燕麦添加量为6%(均为质量分数)和在40℃下发酵时间为4h时即可得到优质的燕麦酸奶制品.     

发酵温度及超声波处理对凝固型酸奶质地等的影响

利用质构仪和扫描电子显微镜,研究了发酵温度和超声波处理对凝固型酸奶质地及微观结构的影响。研究发现,降低发酵温度导致酸奶的硬度、黏度及内聚性下降,在酸奶的微观结构中呈现较多的游离酪蛋白胶束末端,凝胶体结构松散、无序。在接种前或接种后使用超声波处理牛乳,发现接种前的超声波处理对酸奶发酵中pH值变化无显著性影响,而接种后的较高功率超声波处理,使酸奶发酵时间比对照样减少0.5h;并且中高功率超声波处理会显著改善酸奶的流变学特性和微观结构,形成连续、致密的空间网状结构。     

搅拌型树莓酸奶的工艺研究

以奶粉、树莓、白糖为主要原料,采用单因素试验和感官评价打分,制出搅拌型树莓酸奶并确定其最佳生产工艺:奶粉添加量为13%,树莓果汁的最适添加量为3.5%,白砂糖的最适添加量为8%,接种量为4%,发酵温度为43℃,发酵时间为3~4h。所得产品口感柔和爽快,风味独特,营养丰富。     

谷氨酰胺转氨酶浓度对搅拌型酸羊乳贮存期品质的影响

为改善搅拌型酸羊乳的品质,采用谷氨酰胺转氨酶(transglutaminase,TG)(浓度为1、2、3 u/g蛋白)处理山羊乳,发酵制备搅拌型酸羊乳,研究其贮存期pH、黏度、持水性、风味物质、乳酸菌的变化,并采用SDS-PAGE电泳分析TG处理羊乳后乳中蛋白质的交联程度。结果表明,TG处理制备的搅拌型酸羊乳在贮存期的pH明显高于对照组;搅拌型酸羊乳在贮存期间的黏度和持水性明显增大,且随着TG浓度增大,效果越明显;搅拌型酸羊乳贮存期间的乙醛和丁二酮的含量逐渐降低,随着TG浓度越大,降低越明显;TG处理对搅拌型酸羊乳贮存期间嗜热链球菌有显著性的抑制作用,且随着TG浓度的增加,嗜热链球菌的含量越低,然而TG处理对保加利亚乳杆菌无明显影响;SDS-PAGE电泳显示,TG处理羊乳后,κ-酪蛋白和α-乳白蛋白发生明显交联,这有利于酸乳凝胶的稳定性。     

抗性糊精对凝固型酸奶品质的影响

以奶粉为主要原料,蔗糖,乳糖,乳清蛋白为辅料,自制抗性糊精添加量为6%,10%,15%,20%,25%,30%的凝固型酸奶。以酸度、持水力、活菌总数、品质质构参数为评价指标,考察抗性糊精添加量对凝固型酸奶品质的影响,抗性糊精的添加量在6%~20%时,可获得优良的感官评定且酸奶的酸度达到标准的要求,持水力达到100%,乳酸菌活菌总数最高也达到5.0×107CFU/m L,硬度为0.230~0.415 N,最大黏附力0.072~0.115N,黏附性为0.261~0.414 m J,内聚性为0.38~0.45,弹性为5.048~6.633 mm,胶黏性为0.102~0.145 N。添加了抗性糊精的酸奶比常规酸奶的变性温度低,变性峰展宽,反应总焓降低。综合各项指标确定抗性糊精添加量为6%~20%,为开发高膳食纤维凝固型酸奶提供理论依据。     

变温发酵法生产双歧杆菌大豆酸奶的研究

根据乳酸菌和双歧杆菌的最适发酵温度存在差异的特点,进行变温发酵试验,生产双歧杆菌大豆酸奶.采用正交试验优化配方及发酵工艺条件,并测定其双歧杆菌活菌数.试验结果表明,在40℃下发酵4 h,然后降温到37℃发酵2.5 h,主发酵完成后在4℃条件下后发酵24 h.最终产品双歧杆菌活菌数达107个/mL,较同一配方恒温发酵产品增加了100倍.     

酸奶的储存温度对产品品质的影响

以酸奶作为研究对象,研究不同储存温度对酸奶粘度指标的影响,并分析酸奶pH及乳酸菌活菌数的变化趋势。实验结果表明,低温环境对于酸奶保证其粘度、pH及较高的乳酸菌活菌有利。