Rheology, microstructure, and functionality of low-fat Iranian white cheese made with different concentrations of rennet

A batch of full-fat (23% target fat) and 3 batches of low-fat (6% target fat) Iranian white cheese with different rennet concentrations (1-, 2-, and 3-fold the normal usage) were produced to study the effect of fat content reduction and promoted proteolysis on the textural and functional properties of the product. Cheese samples were analyzed with respect to their rheological parameters (uniaxial compression and small amplitude oscillatory shear), meltability, microstructure, and sensory characteristics. Reduction of fat content from 23 to 6% had adverse effects on the texture, functionality, cheese-making yield, and sensory characteristics of Iranian white cheese. Fat reduction increased the instrumental hardness parameters (storage modulus, stress at fracture, and Young's modulus of elasticity), decreased the cheese meltability and yield, and made the microstructure more compact. Doubling the rennet concentration reduced values of instrumental hardness parameters, increased the meltability, and improved the sensory impression of texture. Although increasing the rennet concentration to 2-fold the normal usage resembled somewhat the low-fat cheese to its full-fat counterpart, it appeared to cause more reduction in yield. Increasing the rennet concentration 3-fold the normal usage produced a product slightly more elastic than the low-fat cheese with normal concentration of rennet. Increasing the rennet concentration to 2-fold the normal usage was useful for improving the textural, functional, and sensory properties of low-fat Iranian white cheese.     

Monitoring the chemical and textural changes during ripening of Iranian White cheese made with different concentrations of starter

The effect of the concentration of starter inoculated to milk on the composition, free tyrosine-tryptophan content, microstructure, opacity, and fracture stress of Iranian White cheese (IWC) was studied during 50 d of ripening in brine. Three treatments of cheese were made using 1-fold (IWC1S), 2-fold (IWC2S), and 4-fold (IWC4S) concentrations of a direct-to-vat mesophilic mixed culture containing Lactococcus lactis ssp. cremoris and Lactococcus lactis ssp. lactis as starter. As ripening progressed, moisture and protein contents of the treatments continuously decreased, whereas their total ash, salt, and salt in moisture contents increased. Fat content and pH of cheeses remained stable during ripening. The pH of cheese milk at the time of renneting, which decreased by increasing the concentration of starter (6.57, 6.49, and 6.29 for IWC1S, IWC2S, and IWC4S, respectively), significantly affected most of the chemical characteristics and opacity of cheese. Lower pH values at renneting decreased moisture and ash contents, whereas cheese protein content increased. The concentration of free tyrosine-tryptophan in curd increased at first 29 d but decreased between d 29 and 49 of aging. The changes observed in cheese whiteness followed the changes in moisture content of the treatments. As the concentration of starter inoculated to milk increased, the value of fracture stress at a given ripening time significantly decreased, leading to a less resistant body against applied stress. A similar trend was also observed for fracture strain during cheese ripening. The micrographs taken by scanning electron microscopy provided a meaningful explanation for decrease in the value of fracture stress. As the cheese ripening progressed or the concentration of starter increased, the surface area occupied by the protein fraction in cheese microstructure decreased, leading the way to lower the force-bearing component in cheese texture.     

Microstructure and rheological properties of Iranian white cheese coagulated at various temperatures

The effect of milk coagulation temperature on the composition, microstructure monitored using scanning electron micrographs, opacity measured by a Hunter lab system, and rheological behavior measured by uniaxial compression and small amplitude oscillatory shear were studied. Three treatments of Iranian White cheese were made by applying coagulation temperatures of 34, 37, and 41.5°C during the cheese-making procedure. A higher coagulation temperature resulted in increased fat and protein contents, and decreased the moisture content and ratio of moisture to protein. The highest temperature (41.5°C) had a significant effect on the opacity of Iranian White cheese. Milk coagulation at this temperature decreased the whiteness index (Hunter L value) and increased the yellowness index (Hunter b value) of the aged product compared with cheeses coagulated at lower temperatures. Microstructure of the cheese coagulated at 41.5°C was more compact and undisturbed, reflecting the higher values of stress at fracture and storage modulus measured for this treatment.     

The effect of aging on low-fat, reduced-fat, and full-fat Cheddar cheese texture

This study investigated the effects of aging and fat content on the texture of Cheddar cheese, both mechanical and sensory aspects, over a 9-mo aging period. Cheeses of 6, 16, and 33% fat were tested at 0.5, 3, 6, and 9 mo of aging. Cheeses were evaluated by a trained sensory panel using an established texture lexicon as well as instrumental methods, which were used to probe cheese structure. Sensory analysis showed that low-fat cheeses were differentiated from full-fat cheeses by being more springy and firm and this difference widened as the cheeses aged. In addition, full-fat cheeses broke down more during chewing than the lower fat cheeses and the degree of breakdown increased with aging. Mechanical properties were divided by magnitude of deformation during the test and separated into 3 ranges: the linear viscoelastic region, the nonlinear region, and fracture point. These regions represent a stress/strain response from low to high magnitude, respectively. Strong relationships between sensory terms and rheological properties determined in the linear (maximum compliance) and nonlinear (critical stress and strain and a nonlinear shape factor) regions were revealed. Some correlations were seen with fracture values, but these were not as high as terms related to the nonlinear region of the cheeses. The correlations pointed to strain-weakening behavior being the critical mechanical property. This was associated with higher fat content cheeses breaking down more as strain increased up to fracture. Increased strain weakening associated with an increase in fat content was attributed to fat producing weak points in the protein network, which became initiation sites for fracture within the structure. This suggests that fat replacers need to serve this functional role.     

Effect of gum tragacanth on rheological and physical properties of a flavored milk drink made with date syrup

Date syrup as a nutritional additive and safe alternative to added sugar is one of the best choices for milk flavoring. In this study, a flavored milk beverage was formulated using date syrup for flavoring the product and gum tragacanth to obtain an acceptable mouth feel. Steady shear and dynamic oscillatory rheological properties of the samples contained 3 concentrations (0, 0.1, 0.2, and 0.3%, wt/wt) of 2 types of gum tragacanth (Astragalus gossypinus and Astragalus rahensis) which at 3°C, were studied. Particle size distribution and colorimetric assays were determined by laser diffractometry and using reflection spectrometer, respectively. Sensory analysis was performed with 25 semitrained panelists, using a 5-point hedonic scale. The results showed that viscoelastic properties, flow behavior parameters, particle size, and color parameters (L^*, a^*, and b^*, where L^* represents lightness, a^* represents the redness/greenness quality of the color, and b^* represents the yellowness and blueness quality of the colors) were significantly affected by the concentration of the gum tragacanth and the severity of this effect was influenced by the type of gum. The use of appropriate type and concentration of gum tragacanth in date milk formulation can improve the texture and mouth feel by affecting on particle size and the flow behavior of this product.     

Rheological properties and microstructure of Cheddar cheese made with different fat contents

Reduced- and low-fat cheeses are desired based on composition but often fall short on overall quality. One of the major problems with fat reduction in cheese is the development of a firm texture that does not break down during mastication, unlike that observed in full-fat cheeses. The objective of this investigation was to determine how the amount of fat affects the structure of Cheddar cheese from initial formation (2 wk) through 24 wk of aging. Cheeses were made with target fat contents of 3 to 33% (wt/wt) and moisture to protein ratios of 1.5:1. This allowed for comparisons based on relative amounts of fat and protein gel phases. Cheese microstructure was determined by confocal scanning laser microscopy combined with quantitative image analysis. Rheological analysis was used to determine changes in mechanical properties. Increasing fat content caused an increase in size of fat globules and a higher percentage of nonspherical globules. However, no changes in fat globules were observed with aging. Cheese rigidity (storage modulus) increased with fat content at 10°C, but differences attributable to fat were not apparent at 25°C. This was attributable to the storage modulus of fat approaching that of the protein gel; therefore, the amount of fat or gel phase did not have an effect on the cheese storage modulus. The rigidity of cheese decreased with storage and, because changes in the fat phase were not detected, it appeared to be attributable to changes in the gel network. It appeared that the diminished textural quality in low-fat Cheddar cheese is attributed to changes in the breakdown pattern during chewing, as altered by fat disrupting the cheese network.     

Development of low‐fat sausages using basil seed gum (Ocimum bacilicum L.) and gelatin as a fat replacer

This research was performed to evaluate the rheological properties of myofibrillar protein gels (MPs) with basil seed gum (BSG) alone or in combination with gelatin (0.25%, 0.5%), and to determine the physicochemical properties of low‐fat sausages (LFSs) manufactured with BSG alone (0.5%) or combined with gelatin (0.25%). Viscosity and cooking yields (%) of MPs with BSG alone or in combination with gelatin were higher than those of the control. However, gel strength of MPs with the combination of BSG and gelatin (0.25%) was higher than that with BSG alone. The combination of BSG and gelatin produced a more stable and denser structure than control or BSG alone. In the LFSs, the addition of BSG reduced the percentages of expressible moisture and cooking loss, and the combination of the BSG and gelatin improved gumminess and cohesiveness compared to BSG alone. The use of BSG as a water binding agent and gelatin to improve gel formation will be considered as fat replacer for the manufacture of low‐fat comminuted sausages.     

On the stabilization mechanism of Doogh (Iranian yoghurt drink) by gum tragacanth

Serum separation in Doogh, a favorite acidic dairy drink in the Middle East, is a major problem which happens due to low pH (≤4.00) and aggregation of caseins. Therefore, in the present study the influence of gum tragacanth (GT) and its soluble and insoluble fractions on prevention of serum separation as well as stabilization mechanisms were investigated using rheological, zeta potential and microscopic measurements. According to our findings, the soluble tragacanthin (T) and GT prevented serum separation at concentrations of 0.100 and 0.200%, respectively. Furthermore, the proper rheological model for control was Newtonian whereas for the others it was Power law. Based on viscoelastic experiments, Dooghs containing T and GT exhibited dominant viscose and elastic behaviors, respectively. In addition, the presence of T and GT changed the zeta potential values from positive to negative. It was elucidated that T adsorbs onto casein and induces stabilization via electrostatic and steric repulsions. Moreover, the insoluble bassorin (B) may assist stabilization by increasing the viscosity.     

Accelerated ripening of low fat Ras cheese by attenuated lactobacilli cells

Thirteen Ras cheese were made from 4% fat raw milk; 3% raw and heat treated; 2% raw and heat treated milks in order to study the effect of freeze-shocked or heat-shocked L. casei NIH 334 or L. helveticus CNRZ 53 on the quality of the resultant cheeses. The soluble nitrogen, soluble tyrosine, soluble tryptophan, total volatile fatty acids, titratable acidity and organoleptic evaluation scores increased as ripening period progressed, while moisture decreased. Neither strain nor the heated lactobacilli had significant effects on moisture content of cheeses, while increasing their acidity. Cheeses with freeze-shocked L. casei or L. helveticus had higher titratable acidity than cheeses in which heat-shocked cells were added. However, cheeses added L. helveticus had higher acidity than those with L. casei. Ripening indices (soluble nitrogen, soluble tyrosine, soluble tryptophan and total volatile fatty acids) and organoleptic evaluation scores had similar trends. Cheeses with attenuated lactobacilli had higher ripening indices and cheese scores than cheeses without lactobacilli. Addition of either freeze-shocked L. casei or L. helveticus yielded cheeses having higher ripening indices and organoleptic scores than cheeses made with heat-shocked lactobacilli. The best cheeses were made from 3% fat milk heated to 70 °C, and containing freeze-shocked L. helveticus followed by cheeses made from 2% fat milk heated to 75 °C and containing freeze-shocked L. helveticus.     

Effect of increasing the protein-to-fat ratio and reducing fat content on the chemical and physical properties of processed cheese product

Scientific studies indicate that the intake of dietary fat and saturated fats in the modern Western diet is excessive and contributes adversely to health, lifestyle, and longevity. In response, manufacturers of cheese and processed cheese products (PCP) are pursuing the development of products with reduced fat contents. The present study investigated the effect of altering the fat level (13.8, 18.2, 22.7, 27.9, and 32.5 g/100 g) in PCP on their chemical and physical properties. The PCP were formulated in triplicate to different fat levels using Cheddar cheese, skim milk cheese, anhydrous milk fat, emulsifying salt (ES), NaCl, and water. The formulations were designed to give fixed moisture (~53 g/100 g) and ES:protein ratio (0.105). The resultant PCP, and their water-soluble extracts (WSE), prepared from a macerated blend of PCP and water at a weight ratio of 1:2, were analyzed at 4 d. Reducing the fat content significantly increased the firmness of the unheated PCP and reduced the flowability and maximum loss tangent (fluidity) of the melted PCP. These changes coincided with increases in the levels of total protein, water-soluble protein, water-insoluble protein, and water-soluble Ca, and a decrease in the molar ratio of water-soluble Ca to soluble P. However, both water-soluble Ca and water-soluble protein decreased when expressed as percentages of total protein and total Ca, respectively, in the PCP. The high level of protein was a major factor contributing to the deterioration in physical properties as the fat content of PCP was reduced. Diluting the protein content or reducing the potential of the protein to aggregate, and thereby form structures that contribute to rigidity, may provide a means for improving quality of reduced-fat PCP by using natural cheese with lower intact casein content and lower calcium:casein ratio, for example, or by decreasing the ratio of sodium phosphate to sodium citrate-based ES.     

Free oil and rheology of Cheddar cheese containing fat globules stabilized with different proteins

Cheddar cheese was manufactured from recombined milk containing fat globules coated with alpha(s1)-CN (casein), alpha(s2)-CN, beta-CN, kappa-CN, alpha-lactalbumin, or beta-lactoglobulin. The effect of the coating on fat globule structure, free oil formation, and cheese rheology was investigated to determine if globule coating affected the physical structure of cheese. Fat globule size and shape were determined in cheese using confocal laser scanning microscopy, and the rheological properties measured by uniaxial compression after maturation for 35 and 70 d. Fat globules were elongated and clustered in the control cheese coated with native membrane material and in cheese where the globules were coated with alpha(s2)-CN, but were more circular and distinct than all others. Cheese containing globules coated with alpha(s2)-CN fractured at a lower strain and with a lower stress than other experimental cheeses. Free oil decreased in cheese as the stress at fracture of the cheese protein matrix increased. Strain at fracture increased as pH increased from 4.7 to 5.3. There was no correlation between free oil and fat globule circularity. Cheddar cheese aroma was not evident in experimental cheeses.     

Reduced-fat cheddar cheese manufactured using a novel fat removal process

Normally, reduced-fat Cheddar cheese is made by removal of fat from milk prior to cheese making. Typical aged flavor may not develop when 50% reduced-fat Cheddar cheese is produced by this approach. Moreover, the texture of the reduced-fat cheeses produced by the current method may often be hard and rubbery. Previous researchers have demonstrated that aged Cheddar cheese flavor intensity resides in the water-soluble fraction. Therefore, we investigated the feasibility of fat removal after the aging of Cheddar cheese. We hypothesized the typical aged cheese flavor would remain with the cheese following fat removal. A physical process for the removal of fat from full-fat aged Cheddar cheese was developed. The efficiency of fat removal at various temperatures, gravitational forces, and for various durations of applied forces was determined. Temperature had the greatest effect on the removal of fat. Gravitational force and the duration of applied force were less important at higher temperatures. A positive linear relationship between temperature and fat removal was observed from 20 to 33 degrees C. Conditions of 30 degrees C and 23,500 x g for 5 min removed 50% of the fat. The removed fat had some aroma but little or no taste. The fatty acid composition, triglyceride molecular weight distribution, and melting profile of the fat retained in the reduced-fat cheeses were all consistent with a slight increase in the proportion of saturated fat relative to the full-fat cheeses. The process of fat removal decreased the grams of saturated fat per serving of cheese from 6.30 to 3.11 g. The flavor intensity of the reduced-fat cheeses were at least as intense as the full-fat cheeses.     

Effect of ultrasonic treatment on the rheological properties and particle size of gum tragacanth dispersions from different species

Dispersions of different species of gum tragacanth were sonicated at a frequency of 24 kHz with a total nominal output power of 200 W for different time intervals (0, 7, 15, 45 and 90 s). Various species behave differently under sonication, which is related to structural differences in these species. In the case of Astragaslus compactus and A. rahensus dispersions, as the sonication time increased, the viscosity and particle size of the dispersions decreased, just as in gum Arabic solutions. However, A. gossypinus gum behaved differently compared to the other species. At early stages of sonication (up to 15 s), the viscosity of the dispersions increased sharply and reached its maximum value (106.04 mPa s) as the particle size increased slightly to 275.69 μm. Continuing sonication led to a decrease in the viscosity of the dispersions, though the particle size did not show any changes. This behaviour is thought to be due to the rupture and aggregation of particles.     

凝乳酶对低脂干酪微观结构和功能特性的影响

研究了低脂干酪成熟过程中蛋白质水解程度对干酪本身的微观结构和功能特性的影响.以低脂乳为原料,添加不同剂量的凝乳酶制备低脂干酪,测定干酪不同成熟期的熔度及质量分数为12%的TCA-SN并观察干酪的微观结构.结果表明,在低脂干酪中添加双倍的凝乳酶时可以减少干酪的硬度、增加熔度和改善其感官状态;当添加3倍凝乳酶时将会导致产品比添加正常凝乳酶量时更有胶弹性.因此,添加双倍凝乳酶时能有效改善低脂干酪的质构、功能特性及感官状态.     

Compositional analysis and rheological characterization of gum tragacanth exudates from six species of Iranian Astragalus

The sugar composition and viscoelastic behaviour of Iranian gum tragacanth exuded by six species of Astragalus was investigated at a concentration of 1.3% and varying ionic strength using a controlled shear-rate rheometer. Compositional analysis of the six species of gum tragacanth by high-performance anion-exchange chromatography with pulsed amperometric detection suggested the occurrence of arabinose, xylose, glucose, galactose, fucose, rhamnose and galacturonic acid residues in the gum structure; however, the proportions of each sugar varied significantly among the gums from the different species of Astragalus, and this variation led to interesting differences in functional properties. Rheological measurements performed on dispersions of the six species of gum tragacanth demonstrated viscoelastic properties. The mechanical spectra derived from strain sweep and frequency sweep measurements indicated that the different gum tragacanth dispersions had distinctive viscoelastic behaviours. Investigation of the viscoelastic properties of the different gum dispersions in the presence of NaCl revealed that the addition of NaCl could lead to slight to drastic decreases in the G′, G″ or η^∗ values of the various gums. In general, the results indicated that the six varieties of gum tragacanth studied exhibited significantly different rheological properties; therefore, these different gums may find use in a variety of applications as stabilisers, thickeners, emulsifiers and suspending agents depending on their rheological behaviour.     

Changes in the rheological properties of Iranian UF-Feta cheese during ripening

The frequency sweep test was used to evaluate storage modulus (G′), loss modulus (G′′) and loss tangent [tan (δ)] of Iranian UF-Feta cheese during ripening period (3, 20, 40 and 60 days). With development of ripening, storage and loss moduli increased at varying rates. The rate of increase in G′ was greater than that in G′′ resulting in a reduction in tan (δ). That is, storage modulus was dominant to loss modulus and as a result the elasticity nature was greater than the viscous nature of cheese samples. Due to the disruption of fat globules and proteolysis, protein matrix rearranged and formed a more compact texture containing aggregates of casein. Ripening did not influence the pH level and also the concentrations of dry matter, fat, salt, and total nitrogen in dry matter. However, water soluble nitrogen increased significantly (P < 0.05).     

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。     

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。