Rheological and Microstructural Characteristics of Canola Protein Isolate−Chitosan Complex Coacervates

Wastage of byproducts such as canola meal is a pressing environmental concern, and canola protein isolate (CPI)?chitosan (Ch) coacervates have a good potential to utilize and convert the wastes into a high value added product. Yet so far, there is very limited rheological and microstructural information to assist in proper utilization of CPI ‐Ch complex coacervates. The rheological and microstructural properties of the complex coacervates formed from CPI and chitosan Ch at various CPI‐to‐Ch mixing ratios (1:1, 16:1, 20:1, and 30:1) and pH values (5.0, 6.0, and 7.0) were therefore investigated. These CPI?Ch complex coacervate phases were found to exhibit elastic behavior as evidenced by significantly higher elastic modulus (G?) compared to viscous modulus (G″) in all the tested ratios and pH ranges. They also exhibited shear‐thinning behavior during viscous flow. The complex coacervates formed at the optimum CPI‐to‐Ch ratio of 16:1 and pH of 6.0 demonstrated the highest G?, G″, and shear viscosity, which correlated well with the high strength of electrostatic interaction and thick‐walled, sponge‐like, less‐porous microstructure at this condition. The higher shear viscosity of the coacervate at pH 6.0 was most likely induced by stronger attractive electrostatic interactions between CPI and Ch molecules, due to the formation of a rather densely packed complex coacervate structure. Hence, it can be concluded that the microstructural observations of denser structure correlated well with the rheological findings of stronger intermolecular bonds at the optimum CPI‐to‐Ch ratio of 16:1 and pH of 6.0. The complex coacervate phase formed at a CPI‐to‐Ch ratio of 16:1 and pH of 6.0 also showed glassy consistency at low temperatures and rubbery consistency above its glass‐transition temperature. This study identified the potential for the newly developed CPI–Ch complex coacervate to be used as an encapsulating material due to its favorable strength. This would drastically reduce the wastage of byproducts, provide a solution to tackle the pressing global issue of wastage of byproducts, and bring about a more environmentally friendly paradigm.     

Film forming solutions based on gelatin and poly(vinyl alcohol) blends: Thermal and rheological characterizations

The objective of this work was to study the rheological and thermal properties of film forming solutions (FFS) based on blends of gelatin and poly(vinyl alcohol) (PVA). The effect of the PVA concentration and plasticizer presence on the flow behavior, and viscoelastic and thermal properties of FFS was studied by steady-shear flow and oscillatory experiments, and also, by microcalorimetry. The FFS presented Newtonian behavior at 30 °C, and the viscosity was not affected neither by the PVA concentration nor by the plasticizer. All FFS presented a phase transition during tests applying temperature scanning. It was verified that the PVA affected the viscoelastic properties of FFS by dilution of gelatin. This behavior was confirmed by microcalorimetric analysis. The behaviors of the storage (G′) and loss (G″) moduli as a function of frequency of FFS obtained at 5 °C were typical of physical gels; with the G′ higher than the G″. The strength of the gels was affected by the PVA concentration.     

刺槐豆胶与黄原胶复配体系的流变性

研究刺槐豆胶/黄原胶复配体系的流变性,并采用流变学的Cross模型进行拟合分析。结果表明:刺槐豆胶与黄原胶复配可以产生协同作用,当刺槐豆胶与黄原胶的复配体积比为4∶6时,复配体系的黏度最大,触变测试中形成的滞后环面积最大,并且在黏弹性测试中储能模量G’表现出最大值。因此,刺槐豆胶与黄原胶的最佳复配比例为体积比4∶6。对最佳比例复配体系进行不同温度处理后测试可知,最佳复配体系的最适处理温度为80℃,得到的复配体系黏度最大;复配体系的p H值在6.0~10.0之间时,其黏度变化较小,保持相对稳定。     

Effect of sucrose fatty acid esters with different hydrophilic-lipophilic balance values on pasting and rheological properties of waxy rice flour

Effects of sucrose fatty acid esters (SEs) with hydrophilic-lipophilic balance (HLB) values of 5 (S-570), 9 (S-970), and 15 (S-1570) on the pasting and rheological properties of waxy rice flour (WRF) were investigated. Rapid Visco Analyzer (RVA) showed that addition of SEs affected the pasting properties of WRF. Rheological experiment includes the steady shear flow characteristics, and dynamic viscoelastic properties were also determined using a controlled-stress rheometer. The steady shear tests demonstrated that the viscosity data fitted well with the power law model (R ²≥0.976) and all WRF pastes exhibited typical pseudoplastic and shear-thinning properties. Dynamic rheological measurements revealed that the addition of S-970 and S-1570 significantly increased the values of G′ and G″ of samples, whereas the addition of S-570 decreased these values. The addition of S-1570 reduced the value of tanδ, whereas S-570 and S-970 increased it.     

Rheological properties of myosin-gelatin mixtures

ABSTRACT:  This study was designed to investigate changes of dynamic rheological properties of myosin and gelatin mixtures during heating and cooling. The rheological and calorimetric attributes (G', G", tan δ, and heat flow) of myosin and gelatin mixtures were measured during heating and cooling. The results indicated that gelatin could increase the G' and G" values and decrease the denaturation temperature of myosin. The G' and G" values of myosin and gelatin mixtures decreased with pH over 5.5 to 7.5 and ionic strength over 0.3 to 0.6. Therefore, it is advisable to add gelatin into chicken meat comminuted products in that it could improve the rheological attributes of myosin.     

Effect of salt content on the rheological properties of salad dressing-type emulsions stabilized by emulsifier blends

The effects that salt content and composition of emulsifier blends exert on the rheological properties of salad dressing-type emulsions were studied. Binary blends of egg yolk and different types of amphiphilic molecules (Tween 20, sucrose laurate and pea protein), in several proportions, were used to stabilize emulsions. Salt concentration was ranged from 0 to 2.3% w/w. Steady-state flow tests and small-amplitude oscillatory shear measurements within the linear viscoelastic region were carried out. Rheological tests were complemented with droplet size distribution measurements. Rheological properties and physical stability of the emulsions studied were significantly influenced by salt content and the nature of binary emulsifier blends. In general, the values of rheological parameters studied increased with salt content. However, salt affects in much higher extent the properties of emulsions stabilized by high proportions of egg yolk or pea protein in the emulsifier blend, rather than those mainly stabilized by non-ionic low-molecular-weight surfactants, which are less sensitive to changes in the ionic strength. In this sense, the increase observed in the values of viscosity and linear viscoelastic functions of emulsions is more important when a protein is predominant in the emulsifier blend. This effect was explained on the basis of a more apparent increasing interdroplet interactions and viscosity of the continuous medium, both of them induced by salt addition, which lead to the consecution of an extensively flocculated state and improved creaming stability. On the contrary, different blends of pea protein and egg yolk showed a quite similar evolution of the rheological parameters with salt concentration.     

In vitro mixed ruminal microorganism fermentation of whole cottonseed coated with gelatinized corn starch and urea

We conducted an in vitro mixed ruminal microorganism fermentation study to determine the effect of coating whole cottonseed with gelatinized corn starch and feed grade urea. Treatments were arranged as a 3 x 4 factorial to provide three concentrations of starch (0.0, 2.5, and 5.0%) and four concentrations of urea (0.0, 0.25, 0.5, and 1.0%). All treatments were prepared from one lot of whole cottonseed. Batch culture fermentations were conducted using anaerobic medium that contained 20% (vol/vol) ruminal fluid in 160-ml serum bottles. Whole cottonseed was ground to pass through a 6-mm screen and weighed amounts (0, 0.4, 0.8, and 1.2 g) were added to the serum bottles. As starch increased, H2, CH4, total volatile fatty acids, and molar proportions of propionate increased linearly, whereas pH, molar proportions of acetate, and the acetate to propionate ratio decreased linearly. L-Lactate concentrations were highest with 2.5% starch compared with 0 or 5.0%. As the amount of urea in the coating increased, pH and CH4 increased linearly, whereas H2 concentrations decreased linearly. Ammonia concentrations exhibited a quadratic response due to moderate increases with the addition of 0.25 and 0.5% urea, and a greater increase was observed with 1.0% urea. Interactions between starch and urea were observed for H2, CH4, NH3, and L-lactate. Concentrations of H2 decreased and CH4 was relatively constant as urea increased in the presence of 0 and 2.5% starch, but increased with 5% starch. L-Lactate concentrations were unchanged (0% starch), higher (2.5% starch), or lower (5.0% starch) as urea increased. Ammonia concentrations increased after urea exceeded 10% of the starch concentration. The addition of urea did not prevent the decline in pH, but did reduce H2 and CH4 accumulation with 2.5% starch.     

Apparent viscosity of chicken muscle homogenates. Influence of pH and muscle type

The effect of pH and type of muscle on apparent viscosity of chicken breast, thigh and combined B/T muscles was investigated. The apparent viscosity of thigh muscle homogenate at pH from 5.8 to 6.6, and combined B/T muscle homogenate at pH from 5.8 to 6.3 was increasing. The apparent viscosity of breast muscle homogenate increased with pH increase, reaching a maximum at pH 6.3 and then decreased. When pH raised from 5.8 to 6.3, breast muscle homogenate apparent viscosity increased 3.5-6.0 times more than apparent viscosity of thigh muscle homogenate. An increase of combined B/T muscle homogenate apparent viscosity under shear rate 0.3333-48.6 (s-1) was approximately an average of increases for its individual muscles. At pH 5.8 and 6.0, apparent viscosity of thigh muscle homogenate was approximately two times higher than that of breast muscle homogenate, and reversibly, at pH 6.3, breast muscle homogenate apparent viscosity was about 20% higher than that of thigh muscle homogenate. The apparent viscosity of combined B/T muscle homogenate at pH 5.8 and 6.0, was greater than apparent viscosity of breast muscle homogenate, and at pH 6.3, was greater than apparent viscosity of thigh muscle homogenate. The present data extend the results reported by other researches that there are remarkable differences not only in functional and rheological properties of myofibrillar proteins (SSP, myosin) but also in those of homogenates from chicken white and red muscles.     

Rheological and thermal properties of blend systems of rice flour and potato starch

The rheological and thermal properties of blends of rice flour (RF) with potato starch (PS) at different RF/PS ratios (9/1, 8/2, 7/3, 6/4, and 5/5) were examined. Steady and dynamic shear rheological tests indicated that the consistency index, yield stress, and dynamic moduli (G′ and G″) values of the RF-PS blends increased with an increase in the mixing ratio of PS. All blend samples exhibited high shear-thinning fluid characteristics. Tan δ values of all the blends were lower than those of RF and PS, showing that the presence of PS increased the elastic property of RF. DSC studies showed that the transition temperatures and enthalpies of gelatinization of the blends appeared to be greatly influenced by the addition of PS. In general, these results suggest that the presence of PS in RF modified the rheological and thermal properties, and that these modifications were dependent on the mixing ratio of PS.     

Mixed gels of gelatin and whey proteins, formed by combining temperature and high pressure

Mixed and pure gels of gelatin and whey protein concentrate (WPC) were formed by using temperature and high pressure simultaneously. Combining these gel formation methods enables the two polymer networks to set at the same time. The microstructure of the gels was studied by means of light microscopy and transmission electron microscopy, and the rheological properties by means of dynamic oscillatory measurements and tensile tests. The pH values investigated were 5.4, 6.8 and 7.5. The isoelectric point of the WPC is around pH 5.2 and that of gelatin between pH 7.5 and 9. At pH 5.4, the mixed gel formed a phase-separated system, with a gelatin continuous network and spherical inclusions of the WPC. The storage modulus (G) of the mixed gel was similar to that of a pure gelatin gel. At pH6.8, the mixed gel formed a phase-separated system, composed of an aggregated network and a phase with fine strands. The aggregated network proved to be made up of both gelatin and WPC, and the fine strands were formed of gelatin. The mixed gel at pH 6.8 showed a high G compared with the pure gels, which decreased significantly when the gelatin phase melted. At pH 7.5 the mixed gel was composed of one single aggregated network, in which gelatin and WPC were homogeneously distributed. It was impossible to distinguish the gelatin from the WPC in the mixed network. The mixed gel at pH 7.5 showed a significantly higher G than the pure gels. As the gelatin phase was melted out for the mixed gel, a large decrease in G was observed. The pure gelatin gels, formed by a temperature decrease under high pressure, proved to be pH-dependent, showing an increase in aggregation as the pH increased from 5.4 to 7.5. A fine-stranded, transparent gelatin gel was formed at pH 5.4, while an aggregated, opaque gel was formed at pH 7.5. The stress at fracture for the gelatin gels decreased as the aggregation, and consequently the pore size, increased.     

Microwave heating effect on rheology and microstructure of white sauces

The microstructure and rheological properties of white sauces formulated with different starches were analyzed after being microwave-heated for different times. Significant differences (P < 0.05) in rheological parameters analyzed-storage modulus (G'), loss modulus (G″), and loss tangent (tanδ)-were obtained for sauces made with different starches. Microwave reheating did not affect G' and G″ values until water evaporation became significant. In addition, tanδ values did not change significantly (P < 0.05) even during long reheating times showing that sauce viscoelastic properties did not change after microwave irradiation. However, microstructure assessed by confocal laser scanning microscopy showed changes in fat globule and protein. These microstructural changes did not seem to have a significant effect on rheological measurements since starch and ι-carrageenan are mainly responsible for the viscoelastic behavior of the sauces. Practical Application: The development of products appropriate to microwave heating is constantly rising in food industry. It is necessary to understand the behavior of the ingredients and the final product to microwave heating in order to choose those ingredients which will develop the best performance. Starches are common ingredients in industrial sauces, and rheological and microstructural techniques have shown their usefulness in characterization of starch-based systems.     

香豆胶流变性的研究

研究了香豆胶的流变特性。胶中甘露糖：半乳糖大约为1：1,分子量约为3．12×105。较低浓度时剪切速率范围内剪切速率与粘度无相关性。较高浓度时香豆胶表现剪切变稀现象。由于聚合物水解,粘度随pH的降低而下降。在较高的pH范围,中性聚合物转变为聚电解质,使粘度增加。温度下降,粘度也降低。香豆胶的粘弹性较其它半乳甘露聚糖低,可能是由于较高的半乳糖含量使得内部交联降低,粘度下降。     

明胶与海藻酸钠的相互作用及其应用

研究了不同浓度明胶、海藻酸钠混合溶胶粘度变化 ,以及不同 pH值和不同离子浓度对体系粘度变化的影响 ,结果表明 ,明胶与海藻酸钠主要的交互作用力为二成分间静电引力。在此基础上 ,对仿生鱼翅的生产工艺和配方进行了初步研究。综合粗蛋白含量、硬度、拉伸强度和透明度等结果得出 :8%明胶、2 %海藻酸钠在纺丝原液 pH为 6 0时 ,制备的仿生鱼翅效果最佳。     

Validation of food-grade salts of organic acids as ingredients to control Listeria monocytogenes on pork scrapple during extended refrigerated storage

This study was conducted to investigate control of Listeria monocytogenes on pork scrapple during storage at 4°C. In phase I, scrapple was formulated, with or without citrate-diacetate (0.64%), by a commercial processor to contain various solutions or blends of the following antimicrobials: (i) lactate-diacetate (3.0 or 4.0%), (ii) lactate-diacetate-propionate (2.0 or 2.5%), and (iii) levulinate (2.0 or 2.5%). Regardless of whether citrate-diacetate was included in the formulation, without the subsequent addition of the targeted antimicrobials pathogen levels increased ca. 6.4 log CFU/g within the 50-day storage period. In the absence of citrate-diacetate but when the targeted antimicrobials were included in the formulation, pathogen numbers increased by ca. 1.3 to 5.2 log CFU/g, whereas when citrate-diacetate was included with these antimicrobials, pathogen numbers increased only by ca. 0.7 to 2.3 log CFU/g. In phase II, in the absence of citrate-diacetate, when the pH of the lactate-diacetate-propionate blend (2.5%) was adjusted to pH 5.0 or 5.5 pathogen numbers remained unchanged (≤0.5 log CFU/g increase) over 50 days, whereas when citrate-diacetate was included with the lactate-diacetate-propionate blend adjusted to pH 5.0 or 5.5, pathogen numbers decreased by 0.3 to 0.8 log CFU/g. In phase III, when lower concentrations of the lactate-diacetate-propionate blend (1.5 or 1.94%) were adjusted to pH 5.5, pathogen numbers increased by ca. 6.0 and 4.7 log CFU/g, respectively, whereas when the mixture was adjusted to pH 5.0, pathogen numbers increased by ≤0.62 log CFU/g. Thus, scrapple formulated with lactate-diacetate-propionate (1.5 and 1.94% at pH 5.0) is an unfavorable environment for outgrowth of L. monocytogenes.     

Enhancement of Functional Properties of Wami Tilapia (Oreochromis urolepis hornorum) Skin Gelatin at Different pH Values

The effects of several agents in two different concentrations and pH values (5.0 and 8.0) on the functional properties of tilapia (Oreochromis urolepis hornorum) skin gelatin were evaluated and compared using a control tilapia skin gelatin and a commercial mammalian gelatin. The addition of the agents (sucrose 4 % and 8 % (w/v), glycerol 5 % and 10 % (v/v), NaCl 0.3 and 0.8 mol/L, MgCl₂ 0.3 and 0.8 mol/L, MgSO₄ 0.3 and 0.8 mol/L, KCl 0.3 and 0.8 mol/L, and transglutaminase 10 and 15 mg/mL) slightly increased the turbidity. There were different ratios of rheological properties depending on the agent, concentration, and pH. The addition of all agents increased the viscosity of the gelatin solution, mainly at pH 5.0. The addition of glycerol (10 % (v/v)) raised viscosity up to 7.45 cP. The setting time was prolonged by incorporating the agents. The gelatin samples with the addition of MgSO4 0.8 mol/L showed higher gel strength than the mammalian gelatin, exhibiting values of 298 and 295g_f at pH 5.0 and 8.0, respectively.     

Rheological properties of selected gum solutions

Gums are integral ingredients in fluid foods used for controlling viscosity and mouthfeel. Advances in rheological instrumentations permits enhanced evaluations of the viscoelastic properties of fluids. Rheological properties of twelve gum solutions were investigated at concentrations of 0.05%, 0.1%, and 0.5%. The viscous (η″) and elastic (η″) components of the complex viscosity η1, elastic yield stress, and tan δ were measured as functions of oscillatory shear. Konjac exhibited the highest η′ and η″ components among all gums at 0.5% and 50 s⁻¹. Gum Arabic, methylcellulose and pectin, exhibited the least η′ and no η″ component under the same conditions. Konjac exhibited greatest elastic yield stress, whereas microcrystallinecellulose had the least. Modeling results showed that rheological properties of CMC were characterized by an exponential relationship, whereas riota-carrageenan and xanthan were described by a power type relationship. A substantial increase in tan δ was observed for most 0.5% gums solutions at shear rates beyond 10 s⁻¹, indicating a shift from a visco-elastic regime to a purely viscous one. For gums that showed substantial visco-elasticity, peak tan δ values ranged from 5.7 to 68.3.     

Effect of Goat and Cow Milk Ratios on the Physicochemical,Rheological, and Sensory Properties of a Fresh Panela Cheese

Fresh cheeses, Panela type, were manufactured from cow milk and with goat milk incorporation, constituting 4 blends of milks (G10:C90, G20:C80, G30:C70, G40:C60, v/v). The cheeses were analyzed to determine the effect of the different goat milk ratios on the physicochemical, textural, rheological, and sensory properties over 15 d of storage. Significant differences in protein (14.6% to 18.5%), fat (13.0% to 19.4%), and moisture contents (51.7% to 61.3%), pH (6.38 to 6.67), color (L_h > 64.4, a_h > 1.06, b_h > 5.14), textural (σ_f > 14.8 kPa, ε_C: 0.77 to 0.79, elasticity modulus > 13.5 kPa), and rheological parameters (G′ > G′′, G′: 10.6 to 31.9 kPa, G′′: 2.39 to 7.31 kPa, tan δ: 0.21 to 0.24) were detected as a function of the milks ratio, as well as a function of the storage time. The incorporation of goat milk improved the overall quality in the formulation of Panela cheese, enhancing the texture, flavor and aroma, commonly associated with hand‐crafted cheeses when they are used in the proper ratio. Furthermore, the nutritional value of the cheese is increased with the incorporation of goat milk, which can contribute to a better consumer health.     

Influence of interfacial mechanisms on the rheology of creaming emulsions

A set of protein-stabilised emulsions at pH 7.0, pH 6.0, and pH 5.0, and their counterpart surfactant emulsions, was designed with near-identical droplet size distribution and phase volume to study the specific contribution of hydrodynamic and pair potential interactions to the interfacial mechanisms of these emulsions systems. In this way, further the interfacial layer of these creaming emulsions to enhance perceived fat content could be manipulated. Creaming behaviour, surface shear, and bulk rheological measurements were performed. This work reflects the great importance of local pair potential in the formation of a highly viscoelastic interfacial film, which could be manipulated changing the surface charge of the protein to develop a well-packed cream layer in the protein-stabilised emulsions.     

Water Vapor Permeability of Mammalian and Fish Gelatin Films

ABSTRACT:  Water vapor permeability of cold- and warm-water fish skin gelatins films was evaluated and compared with different types of mammalian gelatins. Alaskan pollock and salmon gelatins were extracted from frozen skins, others were obtained from commercial sources. Water vapor permeability of gelatin films was determined considering differences on percent relative humidity (%RH) at the film underside. Molecular weight distribution, amino acid composition, gel strength, viscoelastic properties, pH, and clarity were also determined for each gelatin. Water vapor permeability of cold-water fish gelatin films (0.93 gmm/m²hkPa) was significantly lower than warm-water fish and mammalian gelatin films (1.31 and 1.88 gmm/m²hkPa, respectively) at 25 °C, 0/80 %RH through 0.05-mm thickness films. This was related to increased hydrophobicity due to reduced amounts of proline and hydroxyproline in cold-water fish gelatins. As expected, gel strength and gel setting temperatures were lower for cold-water fish gelatin than either warm-water fish gelatins or mammalian gelatins. This study demonstrated significant differences in physical, chemical, and rheological properties between mammalian and fish gelatins. Lower water vapor permeability of fish gelatin films can be useful particularly for applications related to reducing water loss from encapsulated drugs and refrigerated or frozen food systems.     

Properties of Alaska Pollock Skin Gelatin: A Comparison with Tilapia and Pork Skin Gelatins

ABSTRACT:  The objective of this work was to compare the physiochemical and rheological properties of Alaska pollock skin gelatin (AG) to those obtained for tilapia and pork skin gelatins. Results were also obtained for some mixed gels containing AG and pork skin gelatin, or AG and tilapia gelatin. AG contained about 7% hydroxyproline (Hyp), which was lower than that of tilapia (∼11%) or pork skin gelatin (∼13%). Most of the protein fractions in AG were α chain, β chain, and other oligomers. The gel strength of AG was 98 gram-force at 10 °C, and increased at a greater rate than other gelatins with decreasing temperature. The gel melting point of AG was the lowest with the oil-drop method, while the viscosity of AG was the highest of the samples studied. The rheological properties of gelatins were determined using small amplitude oscillatory shear testing. G' was nearly independent of frequency for most of the gelatin gels, but AG gels showed a slight dependence on G' and a minimum in G". G' was found to be a power law function of concentration for all gelatins used: G'= k × Cⁿ. In rheological measurements, AG also showed the lowest gel melting temperature and sharpest melting region. Increasing gelatin concentration resulted in a higher melting temperature and a broader melting region for all gelatin gels. For both the AG-pork and AG-tilapia mixed gels, the gel melting temperatures decreased and melting regions narrowed as the AG fraction was increased.