Rheological and sensory properties of stirred yoghurt with inulin‐type fructans

This study concerns physicochemical and sensory analysis of stirred yoghurts, in which skim milk powder was partly replaced by different inulins. The composition of basic solutions contained 12% skim milk powder and 4% inulin, while reference yoghurts contained 16% SMP or whole milk powder. Rheological and sensory analysis showed that one‐quarter of milk powder could be substituted by long‐chain inulin in low‐fat stirred yoghurt. Short‐chain inulin and oligofructose can potentially be applied in the production of drinking yoghurt. Sensory evaluation showed that milk fat cannot be successfully substituted by inulin.     

搅拌型酸奶应力松驰行为的研究

目的以搅拌型酸奶为研究对象,建立一种应力松驰行为评价的测试方法。方法对酸奶施加应变,研究其松驰模量随时间的变化规律,并对方法的实验参数进行优化,并对市面上流行的7类搅拌型酸奶进行应力松驰行为的测试。结果通过应变扫描确定了酸奶的线性粘弹性区域,结合不同应变大小时的应力松驰实验结果,最终选择1%作为酸奶应力松驰实验特性研究时的应变值;进一步研究了不同松驰时间对松驰模量的影响,最终选择60 min作为松驰时间。酸奶在松驰初始阶段及松驰结束时的松驰模量差异明显,可以评判酸奶的弹性大小与松驰时间内松驰模量的损耗情况。酸奶的应力松驰行为可以通过6个Maxwell模型进行表征,不同松驰时间下起主要作用的应力松驰特征模量与特征时间的Maxwell模型数存在明显差异。结论通过应力松驰行为的测试可以评价搅拌型酸奶的粘弹性特性。     

复配稳定剂在搅拌型酸奶加工中的应用研究

研究了海藻酸丙二醇酯(PGA)、果胶和变性淀粉作为复配稳定剂在搅拌型酸奶中的应用。结果表明,海藻酸丙二醇酯、果胶与变性淀粉有较好的协同作用,通过三因素二次正交旋转组合设计实验,建立了粘度与三种稳定剂配比之间的动态模型,得出了三种稳定剂的最佳配比(%)是0·15∶0·08∶1·20。在冷藏(4℃)贮存25d后,搅拌型酸奶的组织状态细腻、均匀滑爽、无乳清析出、风味和口感良好。      

蓝莓果酱型搅拌酸乳的配方优化

选择稳定剂品种、稳定荆添加量、发酵剂品种、蓝莓果酱的添加量以及香精添加量5个因素,其中稳定荆添加量为三水平,其他各因素为两水平:采用L12(31×24)正交设计对蓝莓果酱酸乳的配方进行优化.结果表明,蓝莓果酱型酸乳的配方为质量分数0.4%(质量分数,下同)稳定剂添加量、质量分数为100%蓝莓果酱添加量、W2型稳定剂、MY900型发酵剂、质量分数0.3%00香精添加量,此时能得到感官品质与稳定性最佳效果.     

Improved creaminess in stirred yoghurt through amylomaltase-treated starch domains

Amylomaltase-treated starch (ATS) has been described as an excellent fat-replacer in set yoghurt. Its functionality as a creaminess enhancer relates to the ability to form domains, which have melting and yielding characteristics in the mouth. This study was intended to understand the functionality of ATS in stirred yoghurt. Sensory evaluation of reduced fat stirred yoghurt samples showed that the creaminess perception of stirred yoghurt with 1.5% fat and 0.5% ATS was comparable with the reference full fat yoghurt containing 3% fat. This showed that ATS was even more effective as a creaminess enhancer in stirred yoghurt than in set yoghurt. This was related to the higher effectiveness of domain formation during storage after cooling in a dispersed system, as a result of stirring of the yoghurt gel, compared with a gelled set-yoghurt system.     

Rheological properties of stirred yoghurt as affected by gel pH on stirring,storage temperature and pH changes after stirring

The rheological properties of stirred yoghurt were studied as a function of the delay between milk heat-treatment and inoculation (0, 1 and 2 days), of pH in the acid gel on stirring (4.4, 4.7, and 5.0), of the storage temperature (4, 12, and 20 °C) for 24 h following stirring and of over-acidification (allowed or inhibited). At low pH values, the gels exhibited higher elastic modulus (G′) and fracture strength. They yielded stirred yoghurts with higher G′ and viscosity, and higher increase in G′ and viscosity during storage (“rebodying”). Rebodying was only partially explained by over-acidification and cooling. Changing the storage temperature had no impact on the evolution of G′ after stirring; hydrophobic interactions were therefore probably not involved in rebodying. Electrostatic interactions seemed to play a major role in rebodying, as pH on stirring was the significant factor.     

搅拌型酸奶稳定剂的改良研究

在酸奶制品中使用稳定剂的目的是提高酸奶的粘稠度并改善其质地、状态与口感。本研究是以搅拌型酸奶作为目标产品，首先选择若干单体稳定剂按不同比例进行复配，在复与稳定剂添加量、培养时间和培养条件相同的情况下，取终产品的感官和理化指标筛选出最佳配比；然后以市售稳定剂作为对比样，在培养时间和培养条件相同的情况下，根据黏度和感官指标筛选最添加量。结果表明，在保证产品质量不变的情况下，用单体稳定剂可以替代市售稳定剂。这样能为企业节省大量的生产投入，并带来较大的经济效益。     

谷氨酰胺转胺酶对搅拌型酸奶品质的影响

因为谷氨酰胺转胺酶对乳蛋白有交联作用,所以在酸奶制作中加入谷氨酰胺转胺酶可以提高酸奶的品质,将0.2g/L牛乳的谷氨酰胺转胺酶使用不同的添加方法(对酶灭活和不灭活)应用到酸奶制作中,通过酸奶硬度、持水力、流变特性、乳酸菌等指标的变化及综合感官评价,评定谷氨酰胺转胺酶的最适添加方法。结果表明两种不同的酶添加方法都可以减弱酸奶后酸化,提高酸奶硬度、持水力和剪切应力。TGase酶与发酵剂同时加入显著提高了酸奶的理化特性(p<0.05),硬度在第21d达到最大,与对照组相比提高8.48g,持水力随贮存时间的延长,不断增大,增幅为5.41%。在贮存后期TGase酶活力减弱,对酸奶的质构无不良影响,而且这种方法不需要额外的酶反应时间,热处理工序及设备,符合实际生产的需求。      

The rebodying of stirred yoghurt: interactions between proteins

The aim of the present study was to identify the nature of bonds established between protein particles after stirring that are responsible for the texture improvement of stirred yoghurts, called rebodying. Using a constant model yoghurt at pH 4.4, the effects of changes in the physicochemical conditions at stirring were studied on the subsequent rebodying. Short term rebodying was measured as the changes in viscoelastic properties at 4 degrees C during 20 h after stirring, while long-term rebodying was measured as the viscosity changes during 28 d storage at 4 degrees C. Moreover, stirred gels obtained from either set gels that were allowed time or not for ionic equilibration were compared. Increasing or decreasing ionic strength did not change the properties of stirred gels. Calcium chloride addition significantly decreased G'0 h, G'20 h and tan20 h but did not induce changes in the gel microstructure as observed by confocal scanning microscopy. Yoghurt rebodying could not be explained by fulfilling ionic equilibrium. Moreover, N-ethyl maleimide addition had no effect on the stirred yoghurt. Attractive electrostatic and disulphide interactions were not involved in the gel rebodying and increasing calcium concentration in the set gel limited rebodying.     

Graininess and roughness of stirred yoghurt as influenced by processing

The aim of this work was to study how heat treatment, the type of starter culture, incubation temperature, and storage time can affect the physicochemical characteristics of stirred yoghurt. A four-factor experimental design was used for data analysis. Yoghurt milk was heated at 95 °C for 5 min or 130 °C for 80 s. Yoghurts were produced with three different starter cultures that had been incubated at 37, 42 or 45 °C and stored at 4 °C for 15 days. Visual roughness, number of grains, perimeter of grains, storage modulus, and yield stress all decreased when heating temperature was increased, when an exopolysaccharide-producing starter culture was used, or when incubation temperature was decreased. Storage time did not affect any of the physicochemical properties of yoghurt, except for the pH.     

白梨魔芋搅拌型酸奶的工艺研究

研究了以鲜乳、白梨汁为主要原料,魔芋粉为稳定剂,生产搅拌型酸奶的工艺。通过单因素实验和正交实验确定了白梨魔芋搅拌型酸奶最佳配方和发酵工艺。结果表明,魔芋粉添加量0.08%,白梨汁添加量10%,白砂糖添加量6.5%,发酵剂4%,在42℃条件下发酵4h,制得的酸奶品质最好,感官评分91分,持水率为38.5%。      

乳清浓缩蛋白对搅拌型酸奶品质特性影响的研究

研究了以全脂奶粉和乳清浓缩蛋白（WPC-3503）为原料，按照全脂奶粉：乳清浓缩蛋白为100：0，90：10，80：20，70：30的质量配比生产乳固形物含量为12％的酸奶，对含有不同乳清蛋白比例的酸奶在贮藏过程中理化特性、乳酸菌总数的变化以及感官特性进行了比较分析。结果表明，WPC-3503代替10％-20％全脂奶粉生产酸奶时，在贮藏过程中可减缓pH值及酸度的变化速度，提高酸奶的黏度和保水率，改善感官特性，但对乳酸菌总数无明显的影响。     

Structural properties of stirred yoghurt as influenced by whey proteins

The effect of whey protein addition on structural properties of stirred yoghurt systems at different protein and fat content was studied using laser diffraction spectroscopy, rheology and confocal laser scanning microscopy (CLSM). The composition of heated milk systems affected micro- and macroscopic properties of yoghurt gels. Particle size increased as a function of increasing whey protein content and decreased as a function of increased fat level. Firmness (elastic modulus) and apparent viscosity of manufactured yoghurt samples increased as a function of increased interparticle interactions, mainly caused by self-aggregation of whey proteins or aggregated whey protein-coated fat globules, respectively. The resistance towards shear-induced disruption of yoghurt gels increased with an increasing proportion of casein protein in the protein mixture, whereas products with high whey protein level revealed lower resistance behaviour towards shear-forces. CLSM images illustrated that the presence of large whey protein aggregates and lower number of fat globules lead to the formation of an interrupted and coarse gel microstructure characterised by large interstitial spaces. The higher the casein fraction and/or the fat level, the less interspaced voids in the network were observed. However, it is evident that the addition of whey proteins reinforces firmness properties of low-fat yoghurts comparable to characteristics of full-fat yoghurt.     

Characteristics of stirred low-fat yoghurt as affected by high pressure

The effects of high pressure on the physicochemical, chemical, microbiological and sensory characteristics of stirred low-fat yoghurt were studied. Laboratory-made yoghurts were treated at high pressure (100–400 MPa) for 15 min at 20°C. No significant changes in pH and total organic acids were observed after pressuring the yoghurt. Pressures over 200 MPa prevented post-acidification of the yoghurt during chilled storage. Pressurized yoghurts exhibited higher viscosity and amino acid contents than did the untreated controls, and the differences were maintained after chilled storage. High-pressure treatments at 300 and 400 MPa reduced the number of viable cells of lactobacilli to below the legal minimum permitted in many countries. Significant differences in sensory characteristics between untreated and pressurized yoghurts (200–300 MPa) were detected after chilled storage.     

Flavour release at gas/matrix interfaces of stirred yoghurt models

Release of strawberry flavour compounds at vapour/matrix interfaces was studied in model food systems simulating a yoghurt with a fruit preparation syrup. The effect of different parameters including physicochemical characteristics of the flavour compound, the structure and composition of the matrix and the temperature (4 and 10°C) on the release of the flavour compounds were investigated. There was an effect of the composition and structure of the matrix upon the partition of the flavour compounds. In the dairy gel, retention of flavour compounds was caused by the physicochemical interactions with the proteins and the solubilisation in dispersed fat. The addition of syrup to the low-fat dairy gel slightly increased the retention of the flavour compounds; this was attributed to physicochemical interactions with pectin and sucrose. In the presence of fat (5%), the flavour compounds were solubilised in the fat and their release was not affected by the composition of the dispersing medium. As expected, temperature affected the release; an increase from 4 to 10 °C resulted in an increase in the overall amount of flavour released.     

响应面法优化搅拌型板栗酸奶的加工工艺

在单因素试验的基础上,通过响应面分析法优化搅拌型板栗酸奶的加工工艺,考察板栗与牛奶比例、加糖量、接种量、发酵时间对板栗酸奶感官评分的影响,并通过响应面分析法得出回归方程.结果表明:最佳加工工艺条件为板栗与牛奶比例2.34∶8,加糖量6.28％,接种量3.15％,发酵时间4.95h,在此条件下板栗酸奶感官评分为(93.159±0.650)分,与预测值(94.551±0.420)分相吻合.     

花生酸奶的研制

以花生为原料，对花生蛋白提取、花生乳调配、酸奶发酵剂等工艺进行探讨，研制出营养丰富，口感良好的发酵花生酸奶。结果表明．将花生乳与鲜乳以2：3的比例（质量比）混合，再加9％的白砂糖，菌种选用保加利亚乳杆菌和嗜热链球菌以1：1，4％（质量分数）的接种量，在42cc的条件下发酵3．5h，可制得优质风味型花生酸奶。     

Rheological properties of pullulan fermentation broth in a stirred tank fermentor

Abstract

The rheological properties of the fermentation broth during pullulan production from synthetic medium by Aureobasidium pullulans P56 in a stirred tank fermentor were investigated. The mycelial forms and the production of extracellular polysaccharide were responsible for the non‐newtonian flow behaviour of the fermentation broth. The rheological behaviour can be characterized by a power law type of equation. The relationship shear rate/shear stress and shear rate/apparent viscosity showed a non‐newtonian behaviour of the fermentation broth. The power law index was found to be a sensitive factor for the indication of the pseudoplastic behaviour of the broth.     

搅拌型酸奶生产过程中粘度变化的研究

对搅拌型酸奶生产过程中粘度变化进行了研究。通过采集不同酸奶生产厂的相关数据，就生产中搅拌、冷却、输送泵和管路、灌装、冷藏各个环节的综合分析，找出了影响酸奶粘度的主要工艺过程，并给出了合理的工艺参数。通过改善生产工艺提高酸奶的粘度和品质，指导生产实践。