Rheological and physical properties of camel and cow milk gels enriched with phosphate and calcium during acid-induced gelation

Invited review: Camel milk and gut health-Understanding digestibility and the effect on gut microbiota

Camel milk (CM), known for its immune-regulatory, anti-inflammatory, antiapoptotic, and antidiabetic properties, is a natural healthy food. It is easily digestible due to the high levels of β-casein and diverse secreted antibodies, exhibiting superior antibacterial and antiviral activities compared with bovine milk. β-casein is less allergic and more digestible because it is more susceptible to digestive hydrolysis in the gut; therefore, higher levels of β-casein make CM advantageous for human health. Furthermore, antibodies help the digestive system by destroying the antigens, which are then overwhelmed and digested by macrophages. The connection between the gut microbiota and human health has gained substantial research attention, as it offers potential benefits and supports disease treatment. The gut microbiota has a vital role in regulating the host's health because it helps in several biological functions, such as protection against pathogens, immune function regulation, energy harvesting from digested foods, and reinforcement of digestive tract biochemical barriers. These functions could be affected by the changes in the gut microbiota profile, and gut microbiota differences are associated with several diseases, such as inflammatory bowel disease, colon cancer, irritable bowel disorder, mental illness, allergy, and obesity. This review focuses on the digestibility of CM components, particularly protein and fat, and their influence on gut microbiota modulation. Notably, the hypoallergenic properties and small fat globules of CM contribute to its enhanced digestibility. Considering the rapid digestion of its proteins under conditions simulating infant gastrointestinal digestion, CM exhibits promise as a potential alternative for infant formula preparation due to the high β-/αs-casein ratio and protective proteins, in addition to the absence of β-lactoglobulin.

Digestive properties and peptide profiles exhibited significant differences between skim camel milk and bovine milk powder after static in vitro simulated infant gastrointestinal digestion

This study aims to analyze the differences in digestion properties and peptide profiles between the skim camel and bovine milk powder after static in vitro simulated infant gastrointestinal digestion. The hydrolysis degree of camel milk proteins exceeded by 13.18% that of bovine milk. The concentration and release rate of free amino groups in the camel milk digesta was higher than that of bovine milk powder, which was likely due to the higher β-/αs-casein ratio and larger casein micelle size in camel milk. Camel milk powder presented higher β-CN coverage and comparatively shorter bioactive peptides compared to bovine milk powder. The anti-inflammatory peptide KVLPVPQ displayed the highest abundance in camel milk powder. Outcomes of this study showed that camel milk proteins possessed superior digestibility and unique peptides, which outlined the potential nutritional implications of camel milk for infants.

Effect of whey protein isolate addition on set-type camel milk yogurt: Rheological properties and biological activities of the bioaccessible fraction

The manufacture of camel milk (CM) yogurt has been associated with several challenges, such as the weak structure and watery texture, thereby decreasing its acceptability. Therefore, this study aimed to investigate the effect of whey protein isolate (WPI) addition on the health-promoting benefits, texture profile, and rheological properties of CM yogurt after 1 and 15 d of storage. Yogurt was prepared from CM supplemented with 0, 3, and 5% of WPI and compared with bovine milk yogurt. The results show that the water holding capacity was affected by WPI addition representing 31.3%, 56.8%, 64.7%, and 45.1% for yogurt from CM containing 0, 3 or 5% WPI, and bovine milk yogurt, respectively, after 15 d. The addition of WPI increased yogurt hardness, adhesiveness, and decreased the resilience. CM yogurt without WPI showed lower apparent viscosity, storage modulus, and loss modulus values compared with other samples. The supplementation of CM with WPI improved the rheological properties of the obtained yogurt. Furthermore, the antioxidant activities of yogurt before and after in vitro digestion varied among yogurt treatments, which significantly increased after digestion except the superoxide anion scavenging and lipid oxidation inhibition. After in vitro digestion at d 1, the superoxide anion scavenging of the 4 yogurt treatments respectively decreased from 83.7%, 83.0%, 79.1%, and 87.4% to 36.7%, 38.3%, 44.6%, and 41.3%. The inhibition of α-amylase and α-glucosidase, angiotensin-converting enzyme inhibition, cholesterol removal, and degree of hydrolysis exhibited different values before and after in vitro digestion.

Fermented camel milk influenced by soy extract: Apparent viscosity, viscoelastic properties, thixotropic behavior, and biological activities

During fermentation, camel milk forms a fragile, acid-induced gel, which is less stable compared with the gel formed by bovine milk. In this study, camel milk was supplemented with different levels of soy extract, and the obtained blends were fermented with 2 different starter culture strains (a high acidic culture and a low acidic culture). The camel milk-soy extract yogurt treatments were evaluated for pH value, acidity, total phenolic compounds, antioxidant capacities, degree of hydrolysis, α-amylase and α-glucosidase inhibition, angiotensin-converting enzyme inhibition, antiproliferative activities, and rheological properties after 1 and 21 d of storage at 4°C. The results revealed that some of the investigated parameters were significantly affected by the starter culture strain and storage period. For instance, the effect of starter cultures was evident for the degree of hydrolysis, antioxidant capacities, proliferation inhibition, and rheological properties because these treatments led to different responses. Furthermore, the characteristics of camel milk-soy extract yogurt were also influenced by the supplementation level of soy extract, particularly after 21 d of storage. This study could provide valuable knowledge to the dairy industry because it highlighted the characteristics of camel milk-soy yogurt prepared with 2 different starter culture strains.

Caseins: Versatility of Their Micellar Organization in Relation to the Functional and Nutritional Properties of Milk

The milk of mammals is a complex fluid mixture of various proteins, minerals, lipids, and other micronutrients that play a critical role in providing nutrition and immunity to newborns. Casein proteins together with calcium phosphate form large colloidal particles, called casein micelles. Caseins and their micelles have received great scientific interest, but their versatility and role in the functional and nutritional properties of milk from different animal species are not fully understood. Caseins belong to a class of proteins that exhibit open and flexible conformations. Here, we discuss the key features that maintain the structures of the protein sequences in four selected animal species: cow, camel, human, and African elephant. The primary sequences of these proteins and their posttranslational modifications (phosphorylation and glycosylation) that determine their secondary structures have distinctively evolved in these different animal species, leading to differences in their structural, functional, and nutritional properties. The variability in the structures of milk caseins influence the properties of their dairy products, such as cheese and yogurt, as well as their digestibility and allergic properties. Such differences are beneficial to the development of different functionally improved casein molecules with variable biological and industrial utilities.

Acid Gelation Properties of Camel Milk—Effect of Gelatin and Processing Conditions

This study investigated the effects of glucono-delta-lactone (GDL) concentrations (0.8–1.2%, w/w), gelatin content (0.6–1.0%, w/w) and processing conditions on the properties of camel milk acid gels. Although the pH of camel milk reduced to 4.3 within 4 h of acidification at 1.0% GDL, it was unable to form a suitable gel for a yoghurt-like product unless gelatin was added. At 0.8% gelatin, camel milk gels had similar hardness, lower viscosity and rheological strength, and higher water holding capacity as compared to cow milk gels. Heating of camel milk (85 °C/15–20 min), 2-stage homogenization (150/50 bar) or their combination did not significantly affect the water holding capacity, hardness, viscosity, rheological strength and microstructure of camel milk gels. These processing conditions did not affect protein integrity as confirmed by sodium dodecyl-sulphate polyacrylamide gel electrophoresis (SDS-PAGE) analysis.

High-Moisture Extrusion of Mixed Proteins from Soy and Surimi: Effect of Protein Gelling Properties on the Product Quality

The high-moisture extrusion of proteins from plant and animal sources should be a new way for developing alternative protein products with meat-like texture. The protein gelling properties are considered an important factor for the meat-like texture formation during the high-moisture extrusion processing. In this study, the mixed protein gelling properties from soy protein isolate (SPI) and surimi at different ratios (90:10, 80:20, 70:30, 60:40 and 50:50) were investigated to relate to the high-moisture (70%) extruding product textural properties, correspondingly. Results showed that at SPI–surimi ratio 60:40, the heat-induced gelation time was clearly extended and the gel strength became much weaker. During the high-moisture extrusion processing, at SPI–surimi ratio 80:20, the extrudate showed the higher hardness, chewiness, gel strength and fibrous degree, while excessive surimi (more than 40%) in the blends would hinder the fibrous-oriented structure formation. It suggested that SPI may act as the continuous phase that is dispersed by surimi during the high-moisture extrusion processing. Interestingly, it was found that the gel strength of SPI–surimi blends was nonlinearly correlated with the specific mechanical energy (SME) and product textural properties. The study would be helpful for improving the textural properties of alternative protein products from soy and surimi.

Digestibility of proteins in camel milk in comparison to bovine and human milk using an in vitro infant gastrointestinal digestion system

The absence of β-lactoglobulin, high β-/α_s-casein ratio and protective proteins make camel milk a promising alternative protein base for making human infant formulae. In this study, protein digestibility of camel milk was compared with that of bovine and human milk using an in vitro infant gastrointestinal digestion system. A low degree of gastric proteolysis was observed in all three kinds of milk, and a single clot was formed in camel milk. The soluble milk proteins remaining in the gastric digesta were digested rapidly and extensively in the intestinal phase, while the proteins in the camel milk clot were hydrolysed gradually. Despite several similarities, bioactive peptides unique to individual milk were identified in the three intestinal milk digesta. The results suggest that camel milk proteins are equally digestible as bovine and human milk proteins under infant gastrointestinal digestion conditions, and it may be a prospective substitute for infant formula base.

The effects of camel chymosin and Withania coagulans extract on camel and bovine milk cheeses

Withania coagulans (W. coagulans) extract and camel chymosin have aspartic protease capable of coagulating milk for cheese production. This study investigated the quality of camel and bovine milk cheeses coagulated using Withania extracts, came chymosin, and their mixture in two experiments. In Experiment (1), a factorial design with four factors (W. coagulans, camel chymosin, incubation time, and incubation temperature) was performed. The effect of these factors on cheese's yield and hardness were assessed. An enzyme concentration corresponding to a 36 µg/L of milk of W. coagulans, 50 IMCU/L of camel chymosin, holding time of 4 h, and incubation temperature of 60 °C provided the optimal textural hardness for both camel and bovine milk cheeses. Seven treatments were analyzed in experiment (2) were analyzed for physicochemical properties, yield, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGEitation). The results showed that pure Withania extract exhibited the lower coagulating effect resulting in cheeses with low yield, hardness, fat, protein, and total solids. The SDS-PAGE electropherograms of camel cheese showed several low molecular weight bands as compared to bovine cheese. This phenomenon is due to excessive proteolysis in camel cheese, which we believed is caused by the presence of endogenous enzymes.

Effect of Camel Milk on the Physicochemical, Rheological, and Sensory Qualities of Bread

An increase in bread production has been achieved to meet the increasing demand of the growing population. During the manufacturing process, refined wheat flour, the main ingredient for bread making, loses its nutritional qualities. Hence, it is necessary to use additional nutritional sources to maintain nutritional value. In this study, the rheological, physicochemical, and sensory qualities of bread, prepared using camel milk and water, were evaluated. The increase in the camel milk content resulted in the significant increase in the protein, oil, and ash contents of bread and a decrease in the carbohydrate content. The protein content was increased from 11.95% (100% water) to 14.01% (100% camel milk). The use of camel milk resulted in the progressive increase in the content of two essential fatty acids, α-linolenic acid and linoleic acid ( $P<0.05$ ; maximum increase: 1.65% and 20.9%, resp.). The rheological properties of bread (peak viscosity, gelatinisation temperature, and water absorption capacity) could be improved using camel milk. However, reduced dough stability and peak viscosity–temperature were also observed. The increase in the water absorption capacity from 61% to 67% indicated that the supplemented dough was more suitable than the original dough for preparing bread. The physical properties of bread prepared using camel milk (30%) and water (70%) were better than the properties of the control bread sample. Improved sensory attributes were observed under these formulation conditions. Bread containing ≥70% camel milk received lower sensory scores. The results indicated that the use of the formulation consisting of camel milk (30%) and water (70%) could enhance the nutritional value of bread without significantly affecting the acceptability. The results can provide a platform for extending the application of camel milk, primarily used to produce fermented milk, in the food industry. It could be potentially used to address the global problem of acute malnutrition.

Compositional and functional properties of milk and dairy products derived from cows fed pasture or concentrate-based diets

Worldwide milk production is predominantly founded on indoor, high-concentrate feeding systems, whereas pasture-based feeding systems are most common in New Zealand and Ireland but have received greater attention recently in countries utilizing conventional systems. Consumer interest in 'pasture-fed' dairy products has also increased, arising from environmental, ethical, and nutritional concerns. A substantial body of research exists describing the effect of different feeding strategies on the composition of milk, with several recent studies focusing on the comparison of pasture- and concentrate-based feeding regimes. Significant variation is typically observed in the gross composition of milk produced from different supplemental feeds, but various changes in the discrete composition of macromolecular components in milk have also been associated with dietary influence, particularly in relation to the fatty acid profile. Changes in milk composition have also been shown to have implications for milk and dairy product processability, functionality and sensory properties. Methods to determine the traceability of dairy products or verify marketing claims such as 'pasture-fed' have also been established, based on compositional variation due to diet. This review explores the effects of feed types on milk composition and quality, along with the ultimate effect of diet-induced changes on milk and dairy product functionality, with particular emphasis placed on pasture- and concentrate-based feeding systems.

Composition, Structure, and Digestive Dynamics of Milk From Different Species-A Review

Background: The traditional dairy-cattle-based industry is becoming increasingly diversified with milk and milk products from non-cattle dairy species. The interest in non-cattle milks has increased because there have been several anecdotal reports about the nutritional benefits of these milks and reports both of individuals tolerating and digesting some non-cattle milks better than cattle milk and of certain characteristics that non-cattle milks are thought to share in common with human milk. Thus, non-cattle milks are considered to have potential applications in infant, children, and elderly nutrition for the development of specialized products with better nutritional profiles. However, there is very little scientific information and understanding about the digestion behavior of non-cattle milks. Scope and Approach: The general properties of some non-cattle milks, in comparison with human and cattle milks, particularly focusing on their protein profile, fat composition, hypoallergenic potential, and digestibility, are reviewed. The coagulation behaviors of different milks in the stomach and their impact on the rates of protein and fat digestion are reviewed in detail. Key findings and Conclusions: Milk from different species vary in composition, structure, and physicochemical properties. This may be a key factor in their different digestion behaviors. The curds formed in the stomach during the gastric digestion of some non-cattle milks are considered to be relatively softer than those formed from cattle milk, which is thought to contribute to the degree to which non-cattle milks can be easily digested or tolerated. The rates of protein and fat delivery to the small intestine are likely to be a function of the macro- and micro-structure of the curd formed in the stomach, which in turn is affected by factors such as casein composition, fat globule and casein micelle size distribution, and protein-to-fat ratio. However, as no information on the coagulation behavior of non-cattle milks in the human stomach is available, in-depth scientific studies are needed in order to understand the impact of compositional and structural differences on the digestive dynamics of milk from different species.

Comparison of the viscosity of camel milk with model milk systems in relation to their atomization properties

To correlate the viscosity of camel milk with its atomization properties, first, the viscosity profiles of camel milk are compared with model milk systems (reconstituted skimmed cow milk powder). Then, atomization experiment was conducted using model milk systems and finally, the findings of the atomization experiments were coincided with the viscosity profiles. The effect of total solids of whole (10% to 40%) and skimmed (7.5% to 30%) camel milks on its viscosity was investigated. At 30% total solids level and a temperature of 20 °C, skimmed camel milk exhibited a viscosity of 7.68 mPa.s whereas whole camel milk 8.96 mPa.s. This value is small compared to suspension of reconstituted skimmed cow milk powder, which reached up to 18.55 mPa.s and to that of suspension of whey protein concentrate (28.15 mPa.s). By raising the total solid from 20% to 30%, it was shown that, the average spray droplet size would be changed from 18.77 to 29.40 µm and the span from 1.76 to 1.55. Based on their viscosity profiles, these values would be obtained for camel milk at total solid values of 35% for whole and 38% for skimmed milks. This would allow camel milk to be concentrated to higher total solid levels than bovine milk. PRACTICAL APPLICATION: Converting camel milk into powder by spray drying will have a great role in its commercialization. To do so, establishing knowledge on the viscosity of camel milk at different total solids levels in relation to its atomization properties would be of paramount importance. Because, this would enable us to fine tune the viscosity of the milk to arrive at a quality powder with all the desired techno-functional properties. Moreover, it will also contribute by furnishing engineering data pertinent to the development, design, or choice of appropriate nozzles for atomization of the milk during spray drying at different drying set ups.

Gelation of milks of different species (dairy cattle, goat, sheep, red deer, and water buffalo) using glucono-δ-lactone and pepsin

Dynamic low-amplitude oscillatory rheology was used to study the gelation properties of skim milk gels made at 37°C, using glucono-δ-lactone alone (acid gels) or a combination of glucono-δ-lactone and porcine pepsin ("combination gels"). The protein contents of the skim milks increased in the order goat milk < cattle milk < buffalo milk < sheep milk < deer milk, whereas the average casein micelle diameters increased in the order cattle milk < buffalo milk < goat milk < sheep milk ≃ deer milk. The gelation pH (4.55-4.73) of all milks were close to the isoelectric pH (4.6) of casein, except for buffalo milk, which had a significantly higher gelation pH (5.72). The storage moduli (G') of the acid gels increased with time in the milks of all species except for buffalo milk, for which a double peak in G' was observed. The final storage moduli after 6 h (G'_final) increased in the order goat milk < cattle milk < sheep milk < deer milk < buffalo milk. In general, for the combination gels, the G'_final values and the gelation pH increased to variable extents, except for goat milk. Confocal scanning laser microscopy showed that goat milk and cattle milk formed gels with more open protein networks compared with the dense clustered protein networks of the milks with high protein content (buffalo, sheep, and deer milks). This study indicates that milks from different species respond differently under the action of an acid precursor and pepsin. These results can be used to provide a better understanding of curd making and the digestion properties of noncattle milks.

Rheological and Structural Properties of Camel Milk/Sweet Potato Starch Gel

The unique composition of camel milk limited its use for fermented products preparation. In this research, camel milk (CAM) or cow milk (COM) was blended with sweet potato starch (SPS). Blends were precooked and the rheological properties of the gel were determined. Since the elastic modulus (G′) was much greater than the viscous modulus (G″), milk + SPS gels are considered viscoelastic. The tan δ of all blends was <1.0, signifying solid-like behavior; however, variations between CAM gels or COM were identified. Unlike COM, CAM was more frequency-dependent at low frequencies (0.1 to 1.0 rad/sec). Gels exhibited shear thinning according to the nonlinear rheological tests. Camel milk exhibited gel hardness much higher than cow milk. Because of the domination of G′ and the low power law exponent, camel milk is expected to present processing complications such as in extrusion cooking.

Physicochemical and rheological changes of acidified camel milk added with commercial low methoxyl-pectin

The influence of the addition of low methoxyl amidated pectin (LMA) on acid milk gels from whole camel milk (WCM) on physicochemical and rheological proprieties were studied. The zeta potential, particle size, viscosity, dynamic oscillatory rheology and isothermal titration calorimetry were monitored. The presence of LM-pectin in milk had an impact on the average size of the casein micelles and a large and dominant influence on rheological behavior during acidification. Zeta potential and viscosity of gels with 0.5% pectin were not affected. However, milk gels containing 1%, 1.5% and 2% of LM-pectin showed highest values of particle size at pH4. This modification of the structure of the casein micelles induces a significant improvement (p<0.05) on its acid gelation behavior. Therefore, the addition of pectin enhanced the rheological proprieties. Higher pectin concentration led to a strong gel with higher G' values. This result could be attributed to the formation of complexes and the mechanical spectra prove the hypothesis that pectin forms strands with caseins micelles. Isothermal titration calorimetry results showed that pectin concentration had a marked influence on the gels structure and that this polysaccharide stabilizes caseins micelles in acidified camel milk gel due to electrostatic interaction and steric repulsion.

Physico-chemical, microstructural and rheological properties of camel-milk yogurt as enhanced by microbial transglutaminase

Camel milk produces watery texture when it is processed to yogurt. Despite the extensive studies on microbial transglutaminase (MTGase) in dairy research, the effect of this enzyme on the properties of yogurt made from camel milk has not been studied. This study aims to investigate the impact of MTGase with and without bovine skimmed milk powder (SMP), whey protein concentrate (WPC),or β-lactoglobulin (β-lg) on physico-chemical, rheological, microstructural, and sensory properties of camel-milk yogurt during 15 days of storage period. MTGase treatment markedly reduced the fermentation time of unfortified and SMP-fortified camel milk. The fortification of camel milk without MTGase failed to give set-type yogurt. The treatment of unfortified milk with MTGase enormously improved the viscosity and the body of yogurt samples. Fortification of MTGase-treated milk impacted positively on the viscosity, the water holding capacity, and the density of the protein matrix in the gel microstructure, which were influenced by the type of dairy ingredients. All MTGase-treated yogurts differed from each other in hardness and adhesiveness values. Electrophoresis results showed that the susceptibility of the individual milk proteins to MTGase varied, and there were differences among the treatments toward the enzyme. SMP-fortified yogurt was the most accepted product. Generally, the addition of MTGase preparation at a concentration of 0.4%, simultaneously with starter culture, to fortified camel milk was considered an effective tool to solve the challenges of producing set-type yogurt from this milk.