Firmness Of Yoghurt Research Articles

Effects of Preheat on the Flavor and Texture Properties of Yoghurt Made of Reconstituted Milk

Reconstituted milk replaced fresh milk has been applied in the production of yoghurt. The flavor compounds and texture profile analysis of yoghurt produced from reconstituted milk were investigated. Using SPME-GC-MS, 24 and 22 volatiles were found in reconstituted whole milk and reconstituted skim milk, while 32 and 28 volatiles were found in their yoghurt products, respectively. Levels of aldehydes, methyl ketones, alkanes olefinic aldehydes, ketenes in liquid milk and yoghurt increased with increasing the intensity of heat treatments. Two-Pentanone, 2, 3-butanedione, 2, 3-pentanedione, 3-hydroxy-2-butanone, ethyl butyrate and 2-octanone that were metabolized by starter culture organisms showed an opposite tendency. Principle component analysis for flavor impact compounds indicated that the main difference occurred among the treatments. On the other hand, firmness, adhesiveness, chewiness and viscosity of yoghurt increased with increasing the heat intensity, while springiness, cohesiveness and resilience decreased. There was a significant difference in the textural property between the reconstituted whole milk and reconstituted skim milk (p<0.05).

Rheological and physical properties of yogurt enriched with phytosterol during storage.

Phytosterols enriched products are innovative types of functional foods, in which dairy products, like low fat yogurt are ideal vehicles for this functional component. In this study, phytosterol dispersions were prepared using an oil/water (O/W) emulsion. The emulsion was added to yogurt milk. pH, titratable acidity (TA), syneresis, firmness and apparent viscosity of enriched yogurt were determined during storage. Moreover, phytosterols distribution in different parts of enriched yogurt was studied. Results indicated that in enriched yogurt, apparent viscosity and syneresis were lower and firmness was higher compared to the control. Addition of phytosterol to the yogurt had significant effect on acidity. Distribution of phytosterols in different parts of one sample was not uniform. Sensory results showed that there was no significant difference between enriched and control on texture, appearance, flavor and overall acceptance.

Influence of Galactooligosaccharides and Modified Waxy Maize Starch on Some Attributes of Yogurt

This study examined the influence of galactooligosaccharides (GOS) and modified waxy maize starch (MWMS) addition on the growth of starter cultures, and syneresis and firmness of low-fat yogurt during storage for 28 d at 4 °C. The control yogurt (CY) was prepared without any prebiotics. Incorporation of 2.0% (w/v) GOS improved the growth of L. delbrueckii ssp. bulgaricus ATCC 11842 resulting in a shorter fermentation time. There was a significant (P < 0.05) increase in proteolysis in yogurt made with GOS (GOSY) as measured by absorbance value (0.728). Addition of GOS resulted in higher (P < 0.05) concentration of lactic and acetic acids in comparison with that of MWMSY and the CY up to day 14, thereafter, the product showed a decrease in lactic acid content in all 3 batches until the end of storage. The level of syneresis was the lowest (2.14%) in MWMSY as compared with that of GOSY (2.35%) and CY (2.53%). There was no statistically significant (P > 0.05) difference in the firmness among the 3 types of yogurt.

Iogurte probiótico com frutanos tipo inulina de diferentes graus de polimerização: características físico-químicas e microbiológicas e estabilidade ao armazenamento

The effect of the addition of inulin-type fructans of different degrees of polymerization (DP) on the physicochemical and microbiological characteristics and storage stability (4°C for 28 days) of nonfat probiotic yoghurt was investigated. The yoghurts were prepared using traditional lactic culture (Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus) and Lactobacillus paracasei ssp. paracasei as probiotic. The formulations contained inulin- type fructans of DP: low (P95 oligofructose, DP 5), medium (ST inulin, DP 10) or high (HP inulin, DP 23) in a concentration of 2g 100g of milk-1, meeting the current Brazilian legislation and, thus their claim of functional properties could be utilized; and were compared to a Normal formulation (without inulin-type fructans addition). The addition of inulin-type fructans with different DP did not alter the L*, a* and b* color parameters, the syneresis and the viability of the probiotic culture in yoghurts. Yoghurts with inulin-type fructans of low DP were more acidic (lower pH values and higher values of acidity). The high DP inulin caused a reduction in the firmness of yoghurt. The products contained Lactobacillus paracasei ssp. paracasei at concentrations higher than that recommended to consider them as probiotic foods throughout the storage period. The refrigerated storage resulted in decreased pH and viability of the probiotic culture and increased acidity and syneresis of yoghurt, regardless of the use of inulin-type fructans. It can be concluded that the addition of inulin-type fructans of different DP does not adversely affect the physicochemical and microbiological characteristics of yoghurts and their stability to storage, thus, the selection of the type to be used depend on the purpose of the manufacturer and the intended use.

Development of made‐in‐transit set culture yoghurt: effect of increasing the concentration of reconstituted skim milk as the milk base

SummaryThe fermentation time, yoghurt acidity expressed as lactic acid, starter culture growth, viscosity and firmness of made‐in‐transit (MIT) set culture yoghurt produced using different concentrations of reconstituted skim milk powder (SMP) from 12% to 20% (w/v) as the milk base were investigated. All milk base formulations were ultra‐high temperature sterilised at 138 °C for 6 s. The results revealed that increasing the SMP concentration increased the viscosity and firmness of MIT set culture yoghurt. At 20% SMP, viscosity and firmness were 4650.8 cP and 1.266 N, respectively. Fermentation of MIT set culture yoghurt with 20% SMP was observed to be faster than with the other conditions. The fermentation time for a medium containing from 14% to 20% SMP could be extended to 168 h, reaching a final pH of 4.50–4.37 and at the same time improving the texture of the MIT set culture yoghurt. The SMP concentration had no influence on the total viable counts of starter bacteria in the yoghurt. The texture of MIT set culture yoghurt may be improved by increasing the concentration of SMP.

Dietary supplementation with nonconventional feeds from the Middle East: Assessing the effects on physicochemical and organoleptic properties of Awassi sheep milk and yogurt

Increased feed costs affect the livelihoods of dairy sheep farmers in the Middle East. Farmers endure high risks with large fluctuations in the price of grain used as animal feed, which is further affected by drought and declining range productivity. Using agricultural by-products and treated straw or vetch grazing for supplementing sheep diets would provide resource-poor dairy farmers with increased options to reduce feed costs, but the effects of such feeds on the quality of yogurt (the main product) need to be better understood. Two experiments were conducted to evaluate these effects. The first trial evaluated alternative diets using locally available feedstuffs, including agricultural by-products, compared with traditional diets used by dairy sheep farmers, and was conducted on-station at the International Center for Agricultural Research in Dry Areas (ICARDA, Tel Hadya, Aleppo, Syria). Milking Awassi ewes (n=56) were used to test 6 alternative diets against a traditional control diet containing barley, wheat bran, and barley straw. The 6 alternative diets contained 4 or more of the following ingredients: barley, sugar beet pulp, molasses, cotton seed cake, wheat bran, urea-treated wheat straw, and barley straw. Ewes on one of the alternative diets grazed vetch pasture, whereas ewes on the control diet and the 5 alternative diets grazed native range pasture. The milk fat content was higher in diets containing urea-treated straw. Yogurt firmness and adhesiveness were significantly lower in energy-rich diets (e.g., the control diet) and in the diets rich in soluble sugar (molasses). The effects of diet on yogurt color and on citric and succinic acid contents were significant. A yogurt produced from the milk of the group grazing on vetch was the most yellowish in color, which is appealing to Syrian consumers. The content of citric acid tended to be higher in yogurts produced from diets containing molasses. The second trial was conducted on 3 farms in northern Syria to assess an alternative diet (1 of the 6 tested in the first trial) on 15 milking ewes compared with the farmer's traditional diet (control). The alternative diet increased yogurt firmness and adhesiveness by 7 to 9% and 10 to 16%, respectively. The use of nonconventional feeds available in the region enhances yogurt quality, may reduce requirements for expensive grains, and thus, increase farmers’ livelihoods by targeting expanding markets with better quality products.

Physical properties and microstructure of yoghurt enriched with milk fat globule membrane material

Milk fat globule membrane (MFGM) material was isolated from industrial buttermilk powder (BMP) and both were used as a supplement for the production of yoghurt. MFGM isolated from BMP contained a high concentration of skim milk proteins. The pH measurements indicated no retardation effect of MFGM material to yoghurt fermentation. Comparing yoghurts with the same amount of dry solids, an increase in the concentration of MFGM-enriched material resulted in increasing water-holding capacity and adhesiveness. Supplementation of the MFGM material altered the firmness of yoghurt. Based on confocal laser scanning microscopy, the microstructure of MFGM-enriched yoghurts was denser from that of plain skim milk and BMP-enriched yoghurts. These results indicate the high potential of MFGM material to be used as a novel ingredient for the development of new functional products, utilizing both the technological functionalities as well as the nutritional properties of the material.

Whey Protein Concentrate and Gum Tragacanth as Fat Replacers in Nonfat Yogurt: Chemical, Physical, and Microstructural Properties

The effect of whey protein concentrate (WPC) and gum tragacanth (GT) as fat replacers on the chemical, physical, and microstructural properties of nonfat yogurt was investigated. The WPC (7.5, 15, and 20g/L) and GT (0.25, 0.5, 0.75, and 1g/L) were incorporated into the skim milk slowly at 40 to 45°C with agitation. The yogurt mixes were pasteurized at 90°C for 10min, inoculated with 0.1% starter culture, and incubated at 42°C to pH 4.6, then refrigerated overnight at 5°C. A control nonfat yogurt and control full fat yogurt were prepared as described, but without addition of WPC and GT. Increasing amount of WPC led to the increase in total solids, total protein, acidity, and ash content, whereas GT did not affect chemical parameters. Increasing WPC caused a more compact structure consisting of robust casein particles and large aggregates. Firmness was increased and susceptibility to syneresis was decreased as WPC increased. No significant difference was observed for firmness and syneresis of yogurt fortified with GT up to 0.5g/L compared with control nonfat yogurt. Increasing the amount of gum above 0.5g/L produced softer gels with a greater tendency for syneresis than the ones prepared without it. Addition of GT led to the coarser and more open structure compared with control yogurt.

MEASUREMENT OF FIRMNESS OF STIRRED YOGURT IN ROUTINE QUALITY CONTROL

ABSTRACT The objectives of the present work were to evaluate the potential use of the vane method and penetration tests as a tool to measure the variability in firmness of stirred yogurt in routine quality control, and to evaluate the effect of distribution on yogurt firmness. Twelve batches of plain stirred yogurt of a commercial brand were studied, acquired both from a manufacturing plant and three retail stores. Both vane method and penetration tests allowed the detection of changes in the firmness of yogurts, confirming that they could be useful in routine quality control to characterize the firmness of yogurt. The yield stress of samples from the manufacturing plant varied within a range of 250 Pa. This important variation was partially explained by variations in the final acidity during fermentation, showing the importance of a standardized production in order to obtain a uniform texture. The yield stress of yogurts from the manufacturing plant was significantly higher than that of samples from the different retail stores. Averaged values being considered, the yogurts lost 53 Pa of their original yield stress during distribution and handling inside retail stores, probably due to mechanical damage. This mechanical damage also caused the occurrence of syneresis.

Physical characteristics of yoghurts made using exopolysaccharide-producing starter cultures and varying casein to whey protein ratios

This study investigated the physical characteristics of set and stirred yoghurts made at 9% (w/w) total solids with various casein (CN)-to-whey protein (WP) ratios and with exopolysaccharide (EPS)-producing starter cultures (capsular or ropy) during storage. The yoghurt was evaluated for composition, firmness and syneresis of set yoghurt, and for the flow curve and the area of hysteresis loop between the upward and downward curve of stirred yoghurt. Viable counts of starter bacteria and concentrations of lactic acid and EPS in the yoghurt were also determined. EPS concentration did not decrease during storage for 28 d. Firmness and syneresis of set yoghurt decreased when the CN-to-WP ratio was reduced from ratio 4:1 to 1:1 and when EPS starter cultures (especially ropy EPS) were used. Stirred yoghurt with a CN-to-WP ratio of 3:1 and made using ropy EPS-producing starter cultures had a higher shear stress and hysteresis loop area than yoghurt made using capsular EPS- or non-EPS-producing starter cultures. The results suggested that the physical characteristics of set and stirred yoghurts can be improved by varying CN-to-WP ratio and by the use of EPS-producing starter cultures.

Textural Properties of Yogurt Made with Encapsulated Nonropy Lactic Cultures

The effects of encapsulated strains of lactic acid bacteria on the textural properties of yogurt were determined. Yogurt made with encapsulated nonropy single strains of lactobacilli exhibited the lowest firmness and lowest curd tension. Yogurt made with encapsulated cultures of mixed strains was less firm and had lower curd tension than that made with unencapsulated cultures. Although firmness of yogurt at pH 4.6 made with a single ropy strain was similar to that made with unencapsulated cultures, ropy yogurt at pH 4.2 made with a combination of ropy Lactobacillus delbrueckii ssp. bulgaricus and nonropy Streptococcus thermophilus was significantly less firm. Yogurt made with encapsulated nonropy cultures bound more water than did yogurt made with unencapsulated cultures but less water than did the ropy yogurt. Both ropy yogurt and yogurt made with encapsulated nonropy cultures were less susceptible to syneresis than yogurt made with unencapsulated culture.

EFFECTS OF STARTER CULTURES ON LINEAR VISCOELASTIC AND PHYSICAL PROPERTIES OF YOGURT GELS

ABSTRACTSet‐style yogurts were produced from cow's milk under standard conditions by using 11 commercially available starter cultures. Samples were prepared in control beakers and within the Couette device of a dynamic rheometer. Repeatability of rheometer yogurt fermentations proved to be satisfactory. Within the linear viscoelastic region a significant inverse relationship between storage modulus and tan δ of yogurt samples was found. Specific properties of starter cultures clearly affected response in dynamic frequency sweeps and in stress relaxation experiments. Dynamic and relaxation data showed good agreement. Relaxation spectra H(τ) were obtained from dynamic measurements and stress relaxation by approximation methods. Both the shape of H‐τ curves and the magnitude of H was affected by starter cultures. As compared to literature data on model casein gels and microstructural findings on yogurt the results imply that (a) a permanent network exists in yogurt, (b) interactions with long relaxation times contribute less to viscoelasticity in the case of yogurt produced with viscous starter cultures, and (c) attachment of mucogenic bacteria to the protein matrix via exogenic polysaccharides decreases yogurt firmness.

Physical Properties of Yogurt: A Comparison of Vat Versus Continuous Heating Systems of Milk

Milk was processed by vat (85°C for 10 to 40min), high temperature, short time (98°C for .5 to 1.87min), and ultra-high temperature (140°C for 2 to 8s) heating systems and made into yogurt. Yogurt firmness ranged from 90 to 104g force for vat treatments, 74 to 96g for high temperature, short time treatments, and 47 to 65g for ultra-high temperature treatments. Planned contrasts between heating systems indicated significantly higher yogurt firmness and viscosity for vat versus high temperature, short time and ultra-high temperature systems. Yogurt from high temperature, short time milk showed the highest water-holding capacity, followed by ultra-high temperature and vat treatments. Correlation coefficient between yogurt firmness and whey protein denaturation was .83 and between apparent viscosity and whey protein denaturation was .89. Sensory evaluation indicated an overall preference for yogurt made from high temperature, short time (1.87min) milk.

THE EFFECT OF ULTRA-HIGH TEMPERATURE MILK PROCESSING ON YOGURT TEXTURE

Skim milk fortified with 3.0% nonfat dry milk, heated by a conventional process (82C 20 min) and by ultra-high-temperature (UHT) processes (138C for 3 or 6 s), was inoculated with 0.5% each of Streptococcus thermophilus and Lactobacillus bulgaricus and incubated at 40C. The yogurt systems were stored at4C and were evaluated for texture by stirred viscosity (consistency), by Instron penetration (penetration force, flow coefficient) and by sensory evaluation. Trends for penetration force, flow coefficient, and consistency were significantly correlated. Conventional yogurt had higher firmness and viscosity data but also had more syneresis than did UHT yogurt. Increased holding time in UHT processing significantly (p<0.05) increased yogurt firmness and consistency.

A heat-induced change in the ultrastructure of milk and its effect on gel formation in yoghurt

SummaryMicelles of milk heated at 95 °C for 10 min or autoclaved at 121·7 °C for 15 min were observed by electron microscopy to bear filamentous appendages, whereas micelles from raw milk had relatively smooth contours with no appendages. Experiments suggested that the appendages were composed of denatured β-lactoglobulin and showed that their development was sensitive to sulphydryl blocking agents. Firmness and syneresis of yoghurt were associated with the extent to which micelles coalesced during fermentation; the appendages of micelles in heated milk appeared to inhibit coalescence giving rise to a firmer curd with a lower tendency to syneresis.