Influence of proteins on the perception of flavored stirred yogurts

Among yogurt dairy components, protein type is known to modify the texture of the products and the volatility of odorous volatile organic compounds. The aim of this study was to investigate the impact of 3 protein ratios (caseinate to total protein) on the sensory properties of 4% fat, strawberry-flavored stirred yogurts. A sensory methodology study was therefore investigated to choose the most efficient method in terms of sensitivity, quantification, and ease with which the panel could distinguish slight differences in olfactory property between the yogurts. Three kinds of product presentation procedures were compared: a monadic presentation, a comparative presentation, and a comparative presentation with a reference. The results showed that the 3 presentation methods emphasized some important texture differences between the yogurts in the same way. However, the comparative procedure with a reference was the only one to reveal clear olfactory property differences between the yogurts. The main effect of protein ratio variation in yogurt concerned the texture properties, which greatly differed between the 3 yogurts and was confirmed by complex viscosity measurements. Olfactory differences between the yogurts were more subtle. Overall, the flavor intensity and the fruity notes were less intense in the yogurts with the high caseinate ratio than in those with the low ratio. This result was in agreement with the physicochemical measurements, which showed a higher retention of a large majority of aroma compounds of the strawberry flavor in the yogurts with a high caseinate ratio.     

中温发酵酸乳的挥发性风味成分与感官特性的研究

通过正交实验研究了球杆菌比例、全脂乳浓度、发酵终点以及蔗糖添加量对中温发酵酸乳的感官和挥发性风味成分的影响。以九个不同工艺配方为研究对象,采用描述分析感官评价法和固相微萃取结合动态顶空方法对酸乳的感官评价值和风味成分进行测定,并运用主成分分析法和偏最小二乘分析法得到感官结果和仪器测定结果的相关性。结果表明:球杆菌比例和全脂乳浓度是影响酸乳风味和挥发性风味成分的重要因素。偏最小二乘回归分析得到3种气味、3种滋味和2种余味与挥发性成分、乳酸和柠檬酸量的相关性。      

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.     

Chia (Salvia hispanica L.) seed mucilage as a fat replacer in yogurts: Effect on their nutritional,technological, and sensory properties

Growing consumer demand for healthy and nutritious products has motivated scientists and food manufacturers to design novel dairy products with higher fiber levels and lower fat content that are free of chemical additives. Chia seed mucilage (CSM) is a healthy natural gel extensively used as a dietary source of soluble fiber, a bulking agent, and a fat replacer in a large variety of foods. In this study, we evaluated the effect of CSM on the nutritional, technological, and sensory properties of skimmed yogurts. The addition of 7.5% CSM to a yogurt formula lowered the degree of syneresis of the resulting yogurt during storage compared with full-fat yogurts. The nutritive value of the enriched yogurts improved due to higher levels of dietary fiber compared with full-fat and skimmed yogurts. Moreover, rheological measurements revealed greater consistency, firmness, and viscosity, as well as the formation of a highly structured network and better resistance to stress in yogurts containing 7.5% CSM. The sensory acceptance of the yogurts enriched with 7.5% CSM was similar to the reference samples in acidity, creaminess, and viscosity terms. These results confirm the feasibility of using CSM as a fat replacer to design novel skimmed yogurts.     

Evaluation of tilapia skin gelatin as a mammalian gelatin replacer in acid milk gels and low-fat stirred yogurt

Tilapia skin gelatin (TSG) was studied in a 3-stage process (cooling, annealing, and heating) for pure gelatin gels and in a 4-stage process (acidification, cooling, annealing, and heating) for acid milk gels and cultured yogurt. The aim was to evaluate the use of TSG as a replacement for mammalian gelatin in yogurt. In pure TSG gels, stronger gels with higher melting temperatures were formed with increasing TSG concentrations. Compared with bovine gelatin (BG), which gelled at a concentration of 2.5%, TSG gels had lower gelling (14.1°C) and melting (24°C) temperatures but comparable storage moduli during annealing. In acid milk gels, addition of TSG increased the firmness of the gels with increasing concentration. Gelling and melting points of TSG in milk gels were observed at sufficient concentrations during cooling and heating. Strands and sheets were observed in the electron micrographs of milk gels with 1% TSG and a very dense structure was observed with 2.5% TSG. Yogurt with 0.4% TSG had similar viscosity, consistency, pseudoplasticity, and thixotropy as yogurt containing 0.4% BG; no difference was perceived by sensory panelists according to a triangle test. Addition of 0.4% TSG completely prevented whey separation from the acid milk gel and yogurt. The results suggest that TSG could be a suitable replacement for mammalian gelatin in low-fat stirred yogurt.     

Effect of trisodium citrate on rheological and physical properties and microstructure of yogurt

The effect of trisodium citrate (TSC) on the rheological and physical properties and microstructure of yogurt was investigated. Reconstituted skim milk was heated at 85° C for 30 min, and various concentrations (5 to 40 mM) of TSC were added to the milk, which was then readjusted to pH 6.50. Milk was inoculated with 2% yogurt culture and incubated at 42° C until pH was 4.6. Acid-base titration was used to determine changes in the state of colloidal calcium phosphate (CCP) in milk. Total and soluble Ca contents of the milk were determined. The storage modulus (G′) and loss tangent (LT) values of yogurts were measured as a function of pH using dynamic oscillatory rheology. Large deformation rheological properties were also measured. Microstructure of yogurt was observed using confocal scanning laser microscopy, and whey separation was also determined. Addition of TSC reduced casein-bound Ca and increased the solubilization of CCP. The G′ value of gels significantly increased with addition of low levels of TSC, and highest G′ values were observed in samples with 10 to 20 mM TSC; higher ( > 20 mM) TSC concentrations resulted in a large decrease in G′ values. The LT of yogurts increased after gelation to attain a maximum at pH ∼5.1, but no maximum was observed in yogurts made with ≥ 25 mM of TSC because CCP was completely dissolved prior to gelation. Partial removal of CCP resulted in an increase in the LT value at pH 5.1. At low TSC levels, the removal of CCP crosslinks may have facilitated greater rearrangement and molecular mobility of the micelle structure, which may have helped to increase G′ and LT values of gels by increasing the formation of crosslinks between strands. At high TSC concentrations the micelles were completely disrupted and CCP crosslinks were dissolved, both of which resulted in very weak yogurt gels with large pores obvious in confocal micrographs. Gelation pH and yield stress significantly decreased with the use of high TSC levels. Lowest whey separation levels were observed in yogurt made with 20 mM TSC, and whey separation greatly increased at > 25 mM TSC. In conclusion, low concentrations of TSC improved several important yogurt characteristics, whereas the use of levels that disrupted casein micelles resulted in poor gel properties. We also conclude that the LT maximum observed in yogurts made from heated milk is due to the presence of CCP because the modification of the CCP content altered this peak and the removal of CCP eliminates this feature in the LT profiles.     

Individual and sequential effects of stirring,smoothing, and cooling on the rheological properties of nonfat yogurts stirred with a technical scale unit

Few studies have considered the impact of unit operations during stirred yogurt manufacture because their operational sequence is difficult to replicate at the laboratory scale. The aim of this study was to investigate the individual and sequential effects of stirring in the yogurt vat, smoothing, and cooling on the rheological properties of yogurts, using a technical scale unit simulating some industrial conditions. The yogurts were prepared from a milk mixture that was standardized to contain 14% total solids, 0% fat, and 4% protein, and then homogenized, heated (94.5°C, 5 min), and inoculated at 41°C with the same thermophilic lactic starter. The operating parameters under investigation were 2 stirring durations in the yogurt vat (5 or 10 min), 2 cooling systems (plate or tubular heat exchanger), and 2 smoothing temperatures (38°C for smoothing before cooling; 20°C for smoothing after cooling). Sampling valves were installed at critical points on the technical scale unit so that the effect of each operation on the properties of stirred yogurt could be quantified individually. Syneresis, apparent viscosity, firmness, and consistency were analyzed after 1 d of storage at 4°C. In general, as the yogurts moved through the technical scale unit, the properties of the yogurts (evaluated after 1 d) changed: viscosity increased but syneresis, firmness, and consistency decreased. The individual effects of the operations showed that smoothing and cooling, compared with stirring duration, made the greatest contribution in terms of modifying yogurt properties. The stirring parameters (5 or 10 min) had similar effects on the yogurts. The use of a plate heat exchanger promoted a decrease in syneresis, whereas a tubular heat exchanger had a greater effect in terms of increasing firmness and consistency. The type of cooling system had no effect on stirred yogurt viscosity. Smoothing at 38°C had a greater effect on the increase in firmness, whereas smoothing at 20°C contributed more to a decrease in syneresis and increases in viscosity and consistency. This study confirms that each unit operation has a defined effect on the rheological properties of a nonfat stirred yogurt, which also depends on the operation sequence.     

Impact of the acidification process, hydrocolloids and protein fortifiers on the physical and sensory properties of frozen yogurt

In our study, two acidification procedures, three stabilizers (guar gum, xanthan and carboxymethylcellulose) and two protein-fortifying agents (skim milk powder and whey powder) were evaluated based on their impact on the quality characteristics of frozen yogurts. Indirect acidification (blending of plain acidified milk with ice cream mix) was found to favour texture while direct acidification (fermentation of ice cream mix with starter culture), although it improved viscosity of mixes, did not enhance the sensory acceptance of frozen yogurts. The addition of 0.2% xanthan gum and the partial substitution (at the ratio of 3 : 1) of skim milk powder by whey powder increased overall acceptance and creaminess.     

双麦麦精对酸奶益生菌及其感官性质的影响

双麦麦精是以大麦,其他麦类为原料通过酶解提取的一种天然营养物质。在酸奶制作过程中添加不同比例的双麦麦精,采用平板涂布的方法检测不同储存时间下,酸奶中的保加利亚乳杆菌和嗜热链球菌的活菌数。并且通过感官实验评定双麦麦精对酸奶口感、口味、色泽以及香味的影响。结果表明,当双麦麦精添加量为3%,蔗糖4%时,对酸奶中益生菌的促生长作用最好。同时验证了3%双麦麦精对双歧杆菌也有明显的益生作用。而且,3%添加量的双麦麦精在益生作用以及感官性质方面都比同等添加量的低聚果糖效果好。     

Simultaneous effects of gelatin and espina corona gum on rheological,physical and sensory properties of cholesterol‐reduced probiotic yoghurts

The effects of gelatin (G) and espina corona gum (ECG) on rheological, physical and sensory properties of cholesterol‐reduced probiotic yoghurts were studied. The results showed that it was possible to efficiently remove the cholesterol (> 85%) and the probiotic microorganism counts were > 7 log₁₀ CFU.g^?1. The addition of G decreased flow behaviour index (n), while consistency index (K) increased with the addition of both thickeners. Thixotropy, initial shear stress of the clot to be deformed by mechanical action (A) and destruction rate of the structure (B) were enhanced by increasing G. ECG imparted greater creaminess, less grittiness and less astringency, while G gave more consistency. Both hydrocolloids helped to reduce acid taste and increased water retention index (> 95%). The optimum formulations were: 0.49% G – 0.41% ECG to obtain set yoghurts and 0.01% G – 0.43% ECG for stirred yoghurts, with desirable sensory, rheological and stability characteristics.     

发酵温度波动对酸奶感官、质构和风味特性的影响

为研究发酵温度波动对酸奶品质的影响,本实验测定了酸奶凝乳时间、酸度、pH和质构指标,用模糊数学法分析了感官指标,并用气相色谱-质谱联用仪(GC-MS)测定了酸奶风味成分,探讨了4种温度波动对酸奶发酵特性和品质的影响。结果表明,与对照组相比,处理组1(41 ℃-42 ℃-43 ℃)酸奶的凝乳时间、质构和感官指标无显著差异(p>0.05);处理组2(36 ℃-38 ℃-42 ℃)凝乳时间增加(p<0.05),硬度、内聚性及感官无显著差异(p>0.05),胶黏性减小(p<0.05);处理组3(42 ℃-38 ℃-36 ℃)凝乳时间、内聚性无显著差异(p>0.05),硬度和胶黏性降低(p<0.05),感官评分显著增加(p<0.05);处理组4(42 ℃-46 ℃-48 ℃)和处理组5(48 ℃-46 ℃-42 ℃)凝乳时间、内聚性及感官无显著差异(p>0.05),硬度显著增大(p<0.05),胶黏性显著减小(p<0.05)。所有处理间的酸度及pH无显著差异(p>0.05)。不同的温度波动处理组间主要挥发性风味物质种类基本相同,但含量存在差异。在实际生产中,对酸奶发酵温度的控制可以不必非常精确,允许小范围波动。     

Influence of carrot fibre powder addition on rheological,microstructure and sensory characteristics of stirred-type yogurt

The incorporation of 1% (E1) and 2% (E2) of the carrot fibre powder obtained from carrot discards to yogurts was studied. The effect of the fibre addition on the physicochemical parameters, water-holding capacity (WHC), microbial counts, rheological, microstructure and sensory characteristics of yogurts was studied in comparison with control yogurt without fibre addition (C). Titratable acidity, global composition and microbial counts showed a similar trend among yogurts. Fibre particles seemed to change the organisation of protein aggregates of the gel network. An open structure with bigger aggregates was observed in E1 and E2 yogurts, while the microstructure appeared more homogenous and without granules in C. However, carrot fibre increased the WHC of yogurt. All the yogurt samples exhibited shear-thinning behaviour and no differences were found in the rheological parameters, excepting for E2 that presented a decrease in apparent viscosity at 200 s^-1 compared with C and E1 samples. Trained sensory panel (12 members) indicated an increase in brownish colour, strange flavour, grittiness and aftertaste and a decrease in overall appearance, odour, sweetness and creaminess in yogurts enriched in fibre. In order to mask these negative characteristics, E1 formulation was produced in the same way but strawberry flavour and colour were added. A consumer test (101 volunteers), purchase intention and a Check All That Apply (CATA) questionnaires were carried out. Flavoured and coloured E1 yogurt was pleasant for consumers, since 93% of the consumers selected positive degrees of acceptability and 68% of them manifested that they are willing to consume the product. Therefore, the addition of carrot fibre powder in yogurts could be an alternative to incorporate dietary fibres into dairy foods.     

The effects of varying sugar content and fruit concentration on the physical properties of vanilla and fruit ice-cream-type frozen yogurts

In this study, the physical properties of samples of ice cream produced from yogurt with varying levels of sugar (18, 20 or 22%) and fruit (strawberry) concentration (15, 20 or 25%) were investigated. The results of the physical analysis indicate that as the amount of sugar and fruit increases, there is an increase in the first dripping time period, viscosity values and the overrun. However, complete melting times decreased in parallel with the increase in sugar content and fruit concentration. It was observed that an increase in the amount of sugar in vanilla frozen yogurt softened the structure. In strawberry ice-cream-type frozen yogurt, the structure hardened in parallel with the increase in fruit concentration. In addition, the results show that frozen yogurts with high sugar (V3) and fruit (St3) concentrations are the type most preferred by the panellists. The results of the sensory analysis suggest that frozen yogurt can be an alternative to other dairy products such as yogurt and ice cream.     

Structure and physical properties of yogurt gels: effect of inoculation rate and incubation temperature

The effects of inoculation rates and incubation temperatures on the physical properties and microstructure of yogurt gels were investigated. A 2-factor experimental design with 3 replicates was used for data analysis. Yogurt gels were made with 0.5, 1, 2, 3, or 4% (wt/wt) inoculation rates and incubated at 40 or approximately 46 degrees C. Dynamic low amplitude oscillatory rheology was performed to monitor the formation of yogurt gels. Gel permeability and the amount of surface whey were determined. Gel structure was examined by confocal scanning laser microscopy. Higher storage modulus values were observed in yogurt gels made at higher inoculation rates and lower incubation temperatures. Gels made at higher inoculation rates and incubation temperatures exhibited higher yield stress and maximum loss tangent values, respectively. Permeability, pore size, and whey separation of yogurt gels increased with decreased inoculation rate and increased incubation temperature. An increase in the inoculation rate resulted in a decrease in the pH where the maximum in the loss tangent occurs, presumably reflecting less efficient solubilization of colloidal calcium phosphate (which is a slow process) and the need to attain a lower pH to complete the solubilization. Significant positive correlations were observed between whey separation and the value of maximum in loss tangent (r = 0.94) and permeability (r = 0.89). Whey separation was negatively correlated with storage modulus (r = -0.48). It was concluded that rearrangements of casein particles in the gel network and the rate at which the solubilization of colloidal calcium phosphate occurred were important driving forces for whey separation and weak gel.     

Evaluation of the effect of salts on chemical,structural, textural,sensory and heating properties of cheese: Contribution of conventional methods and spectral ones

ABSTRACT

Chemical composition, sensory characteristics, textural and functional properties are among the most important characteristics, which directly relates to the global quality of cheese and to consumer acceptability. A number of factors including milk composition, processing conditions and salt content, influences these properties. The past decades many investigations were performed on the possibilities to reduce salt content of cheese due to its adverse health effects, the current lifestyle and the awareness of the consumers for nutrition quality products. Due to the multiple potential effects of reducing NaCl (simple reduction or substitution) on cheese attributes, it is of utmost importance to identify and understand those effects in order to control the global quality and safety of the final product.

In the present review a collection of the different results and conclusions drawn after studying the effect of salts by conventional (e.g. wet chemistry) and instrumental (e.g. spectral) methods on chemical, structural, textural, sensory and heating properties of cheese are presented.     

Probiotic viability and physico-chemical and sensory properties of plain and stirred fruit yogurts made from goat's milk

Probiotic plain and stirred fruit yogurts were made from goat's milk using bacterial cultures comprising, Lactobacillus acidophilus LA-5, Bifidobacterium animalis subsp. lactis BB-12 and Propionibacterium jensenii 702. The products were stored at 4°C for 4weeks, during which time the viability of the yogurt starter culture and probiotic bacteria was analysed weekly. P. jensenii 702 demonstrated the highest viability (10(8)cfu/g) in all types of yogurt throughout the storage period, while the viability of the bifidobacteria (～10(7)cfu/g) also remained above the minimum therapeutic level. The viability of L. acidophilus LA-5 fell below 10(6)cfu/g in yogurts, however, the addition of fruit juice appeared to support the viability of lactobacilli, with higher microorganism numbers observed in fruit yogurts than in plain yogurt throughout the shelf life. Addition of fruit juice significantly increased the syneresis, and decreased viscosity and water holding capacity of yogurts (p<0.05), and also enhanced their sensory acceptability.