【作者】 赵强忠；

【导师】 赵谋明；

【作者基本信息】 华南理工大学 ， 食品科学， 2006， 博士

【摘要】 本文系统研究了制备工艺、蛋白质、油脂、乳化剂对搅打稀奶油品质(感官品质、搅打起泡率、质构特性、稳定性)的影响,进一步研究了这些因素对乳浊液粒度分布、搅打过程中脂肪部分聚结、界面蛋白质浓度等亚微观参数的作用及作用机理,在此基础上进一步分析了宏观品质和亚微观参数之间的内在联系,同时探讨了搅打稀奶油的搅打充气机理。采用响应曲面设计优化了搅打稀奶油制备工艺条件,结果表明均质压力是影响搅打起泡率、泡沫硬度和稳定时间极显著(P<0.0001)的因素,同时得到最佳工艺条件为:均质压力39.70MPa、老化时间2.98h和热处理温度60.27℃。在此基础上进一步研究了均质压力对搅打稀奶油品质的作用及作用机理,随均质压力升高,脂肪球粒径减小,界面蛋白质浓度降低,脂肪部分聚结速度加快,均质压力在20~40MPa时,搅打稀奶油品质随均质压力升高而明显改善,均质压力为40~60MPa时,其品质随均质压力升高而下降。蛋白质种类和用量直接影响搅打稀奶油的搅打性能和品质。酪蛋白搅打起泡性能较好,与脂肪球结合相对松散,易于被乳化剂竞争解吸,脂肪部分聚结速度快;乳清蛋白在脂肪球界面形成网络结构,阻碍了脂肪球部分聚结的发生,因此脂肪部分聚结率低。研究表明:酪蛋白用量为0.70%时,搅打稀奶油的搅打性能和品质达到最佳,搅打起泡率达到346%、稳定时间2.4h,硬度为303g,入口即化感好,油腻感轻。单一用乳清蛋白,搅打稀奶油的品质很差,不适合用于搅打稀奶油。油脂种类和用量对搅打稀奶油的脂肪部分聚结率和界面蛋白浓度有重要影响,不同熔点油脂对脂肪部分聚结影响很大,但与熔点高低没有明显的相关性,BL-37的脂肪部分聚结速度最快,其次是BL-35和BL-41,最慢是BL-39;随着油脂用量增加,脂肪球数量增加,脂肪球界面吸附的乳化剂和蛋白质减少,脂肪球的稳定性降低,脂肪部分聚结速度增加。最适合生产搅打稀奶油的油脂是BL-41,油脂BL-41的最佳使用范围是20~23%。油脂BL-41用量为20%时,搅打起泡率达到349%,稳定时间2.5h,硬度达到272g,而且感官品质好。乳化剂的HLB值和使用量也是影响搅打稀奶油品质的重要因素。乳化剂HLB值越高,对脂肪球界面的亲和力越弱,解吸脂肪球界面吸附的蛋白质能力越弱,脂肪部分聚结速度慢;在相同乳化剂HLB值时,乳化剂用量增加,解吸界面吸附蛋白质的能力越强,脂肪部分聚结速度越快。研究表明:乳化剂最适HLB值范围为7~8,乳化剂HLB值为7时,乳化剂最适用量为0.60%~0.65%。当乳化剂HLB值为7,用量为0.60%时,搅打起泡率达到366%,稳定时间2.40h,感官品质达到最佳。通过分析搅打充气机理表明,搅打过程大致分为三个阶段:初始阶段,由于液相中未吸附的蛋白质起泡性能好,使气体以大气泡形式充入乳浊液中,在剪切力作用下,部分大气泡破裂成小气泡,从而形成少量的脂肪球部分聚结体,脂肪部分聚结率较低,气泡的稳定性较差;第二阶段,由于乳化剂快速竞争解吸界面吸附的蛋白质,界面吸附的蛋白质急剧减少,降低了界面吸附层的静电和空间稳定作用,界面稳定性急速下降,大气泡开始快速破裂成小气泡,在大气泡破裂成小气泡和小气泡合并成大气泡的动态过程中伴随着脂肪球的部分聚结,导致脂肪球部分聚结速度快速增加,脂肪球粒径明显增大,在此过程中,以大气泡破裂形成小气泡为主,泡沫稳定性显著提高,泡沫硬度、稠度、内聚性和粘性也明显增加;最后阶段,脂肪部分聚结体已相当大,脂肪球部分聚结体容易刺破气泡界面膜,导致起泡率降低,脂肪球开始形成较大且相互联结的聚结体,搅打稀奶油的硬度、稠度、内聚性和粘性迅速提高,如再继续搅打,会造成搅打过度而使搅打稀奶油品质开始下降。更多还原

【Abstract】 The effects of preparation conditions, protein, oil and emulsifier on quality of whipped cream such as organoleptic properties, overrun, textural properties and stability were investigated systematically in this dissertation. The submicroscopical terms of fat globules size distribution, fat globules partial coalescence rate, protein surface concentration were studied in details, and further related with macroscopical quality. Whipping mechanism of whipped cream was discussed.The results of response surface design for optimization of process conditions of emulsions showed that the homogenization pressure had significant effects on overrun, foam firmness and stability (P<0.0001). The process conditions of homogenization pressure of 39.7 MPa, aging time of 2.98 h, heat treatment temperature of 60.27 oC were best for whipped cream according to the results. Mechanism of effects of homogenization pressure on quality of whipped cream was studied. Big fat globules were broken up into small ones by high homogenization pressure, which resulted in decrease of surface protein concentration, so fat globules coalesced partially more quickly. If homogenization pressure was between 20-40 MPa, quality of cream improved with increase of homogenization pressure. However, quality decreased due to higher pressure that was between 40-60 MPa.Type and concentration of protein had significant influence on quality and whipping properties. Whey protein decreased potential for partial coalescence of fat globules by forming a network on interface of fat globules, which resulted in low stability and overrun of whipped cream. Compared with whey protein, casein was displaced by emulsifier more easily and showed better foamability. The study showed that whipped cream containing 0.70% casein reached their best quality such as overrun of 346%, stability of 2.4h, foam firmness of 303g, good sense of melting in mouth and light greasiness. Whey protein was not suited for whipped cream as a single protein in emulsions due to bad quality.Type and concentration of oil were very important for fat globules partial coalescence rate and surface protein concentration. Melting point of oil had great influence on fat globules partial coalescence, but there was not linear relationship between them. Oil melting point effected partial coalescence rate in the order BL-37> BL-35> BL-41> BL-39. Reducing concentration of protein and emulsifier on interface of fat globules by addition of concentration of oil and fat globules led to lower stability against partial coalescence. Emulsions containing 20-23% BL-41 type oil could be whipped into the best foam. The experiment results showed that foam of 20% BL-41 appeared best quality such as overrun of 349%, stability time of 2.5h, foam firmness of 272g and good organoleptic properties.HLB value and concentration of emulsifier affected greatly quality of whipped cream. High HLB value of emulsifier, which affinity to fat globule interface was strong, displaced less adsorbed protein from the interface. Presence of high concentration with same HLB value led to high partial coalescence rate by displacing more protein. The study indicated that emulsion containing 0.60% emulsifier with HLB value 7 could be whipped into foam of good quality such as overrun of 366%, stability time of 2.4 and the best organoleptic properties.Three stages could be distinguished in process of whipping of whipped cream according to whipping mechanism. During the first stage most of the air incorporated into emulsions existed as big bubbles, which was stabilized by protein with good foamability. Some of big bubbles were broken into smaller ones by further whipping. A few fat globules coalesced partially, but they could not coat bubbles effectively, therefore foam was not stable enough. In the second stage, stability of fat globules against partial coalescence dropped due to rapid substitute of protein by emulsifier. Fat globules coalesced partially and rapidly in the dynamic process of bubble break-up and coalescence, which led to rapid increase in aggregates of fat globules. Bigger bubbles broken into smaller ones were main trend in this stage. Smaller bubbles were coated more coalesced fat globules with comparison to the first stage, hence stability, foam firmness, consistency, cohesiveness and viscosity of the responding foam increased significantly. In the last stage, overrun of foam decreased with too much aggregates of fat globules easily penetrating bubbles, accompanied by rapid increase in foam firmness, and further whipping worsened quality of whipped cream.更多还原