Recent Trends on Camel Milk Cheese Processing: Nutritional and Health Value

Abstract

The capacity of dairy components to prevent chronic diseases has piqued researchers’ interest in the role they play in the creation of functional meals. In this regard, the demand for camel milk has increased dramatically due to its outstanding therapeutic properties and health-promoting effects. Ever since ancient times, camel milk has only ever used unprocessed for the consumption of the nomads and their own families. The limited use of camel milk is due to its manufacturing difficulties. For a long time, cheese-making from camel milk was considered a challenge, due to its unique composition. However, due to the development of processes, and enzymatic and microbial technologies, the dairy sector is now able to offer consumers camel cheese with improved functionality and nutritional advantages. The current chapter highlights the recent processing opportunities regarding the cheese-making from camel milk and summarizes existing knowledge on the nutritional value of camel milk cheese.

1. Introduction

Currently, great importance is given to nutrition as a vector of health. Milk is one of the food substances considered very nourishing and necessary for the growth of young children. Over the years, a particular attention has been paid to milk from non-bovine species such as goat, ewe, mare, and camel. The camel milk sector is gaining importance due to the particular composition of this milk and its potential value in improving the consumer health. Indeed, some people start consuming camel’s milk because they think that camel’s milk can cure various diseases, such as jaundice, diabetes, ulcers, autism, asthma, allergies, and cancer [1]. Several studies have provided an opportunity to understand the potential benefits of camel milk through the production of bioactive peptides. Thus, numerous such peptides are identified such as angiotensin-converting enzyme inhibitors, antimicrobial, anti-inflammatory, anti-obesity, antioxidant as well as antidiabetic and anti-proliferative peptides [2, 3, 4, 5]. In recent years, the research on camel milk transformation has gradually increased. Much of the work in this field has focused on making yogurt, butter, ice cream, and cheese from camel milk. However, one of the major issues confronting the camel milk cheese-making is the low yield, the long coagulation time, the watery consistency, and the fragile and poor structure, affecting both product performance and customer sensory perception [6]. This behavior is probably due to the large size of casein micelles [7], the low amount of κ-casein to β-casein ratio and its specific enzyme cleavage site, and the lack of β-lactoglobulin in camel milk [8]. The small size of camel milk fat globule could be another cause of poor gel structuring in camel milk [9].

Many attempts have been made to solve this problem including the use of enzymes as coagulants and/or the addition of acidification of the milk with different starter cultures or acids [10, 11, 12, 13, 14, 15]. Some researchers mixed camel milk with other milk in order to enhance the yield and organoleptic properties of camel cheese [16, 17, 18], whereas others used plant protease [19, 20, 21, 22] or microbial transglutaminase [22, 23, 24]. Additionally, it could be possible to overcome the associated difficulty regarding camel milk cheese-making through the application of new technologies [8, 25] or optimization of processing conditions [7, 26, 27, 28].

In the current chapter are highlighted advanced approaches used in camel cheese-making process steps. In addition, selected camel cheese varieties’ specific characteristics and their typical nutritional value and functionalities are also described.

2. Constraints associated with camel’s milk cheese-manufacturing

Cheese is one of the most consumed dairy products worldwide due to its tremendous nutritional benefits such as richness of proteins, fatty acids, calcium, vitamins A and B₁₂, and bioactive peptides coming from milk fermentation with lactic acid bacteria [29]. Cheese is usually produced from casein coagulation and precipitation following acidifying or/and fermentation.

The main factors responsible for crud formation are listed as follows:

• Whey proteins (β-lactoglobulin (β-LG) and α-lactalbumin (α- LA)) and their thermal stability,

• Characteristic of casein micelle (size and mineralization),

• Ratio κ-casein/β-casein content,

• Total solids content and

• Size of the fat globules.

Moreover, these different components have particularities in camel milk. It is found that whey proteins in camel milk account for 20–25% [30]. As in human milk, the major and most allergenic protein of bovine milk, β-lactoglobulin (β-LG), is not detected in camel milk, but it is the α-lactalbumin (α-LA) which is the most abundant protein [31, 32]. The absence of β-LG in camel milk presents itself as an obstacle in the camel cheese-making. In fact, the implication of β-LG on milk transformation is important mainly through its heat-induced association with κ-CN.

Since heat treatment is necessary for eliminating harmful bacteria, extending the shelf life of milk, and guaranteeing its safety for human consumption, it is a crucial component of the dairy processing sector [33]. It is known that the manufacture of cheese is always preceded by a step of milk heat treatment (pasteurization). Differing from cow milk, camel milk is less stable and more sensitive to various heat treatments and this instability provides a crud with a weak structure [34]. It is important to note that casein distribution and micelle size are limiting factors in cheese coagulation. The primary structure of the four caseins was elucidated by Kappeller et al. [35] deducing that camel caseins are less phosphorylated and less rich in micellar calcium phosphate than their bovine counterparts. The camel casein micelles are also larger in diameter than bovine milk casein, this character associated with reduced surface area provided a long coagulation time and weak cheese coagulum [36]. Camel’s milk caseins, on the other hand, are richer in proline residues (particularly β-casein), residues known by their stereo-chemical rigidity, thus explaining the destabilization of the secondary structures of these proteins in a more pronounced way than occurs in bovine caseins. Camel κ-casein represents 3.5% of total camel caseins and it contains two phosphate residues present in two positions: Ser¹⁴¹ and Ser¹⁵⁹. Only κ-casein is a glycoprotein with amphiphilic properties. Camel and bovine κ-casein do not have the same affinity for camel and bovine rennet calf [35].

The cleavage site of camel κ-casein by chymosin is different from that of bovine κ-casein, the hydrolysis taking place at the Phe⁹⁷-Ile⁹⁸ bond splitting a macro-peptide of 65 amino acids. A classification into two groups of κ-caseins of different species has been proposed by Nakhasi et al. [37]. These two groups differ in the site of cleavage by chymosin: Phe-Met bond for group I (ewe, buffalo, goat, and cow) and Phe-Ile or Phe-Leu for group II (Camel, woman, rat, mouse, and sow). This difference probably reflects differences in the ability of ruminant and non-ruminant milk to coagulate.

The protein κ-casein is considered the constituent limiting the growth of submicelles as well as the size of the micelles [35]. It is also the stabilizing factor of the micelle thanks to the hydrophilic C-terminal groups of this protein which are responsible for the steric repulsive forces, which oppose the flocculation of the micelles [38]. For these reasons, κ-casein is most likely localized to the periphery of the casein micelle.

On the other hand, the high amount of β-casein seems to have an important implication in the softer aspect of camel cheese compared to bovine one. It is the major protein in camel milk and represents more than 65% of total caseins. As compared to the other milk proteins, CN-β is more hydrophobic and exhibits more chaperone-like behaviors, which prevents protein aggregation [35]. Moreover, CN-β with its amphiphilic nature rises for non-polar residues to adsorb at hydrophobic surfaces, resulting in good emulsifying properties that are responsible for the smoothness of cheese [39]. Apart from this, milk fat also plays an important role in cheese quality and yield. Camel milk fat globules, surrounded by thick membranes, are small in size ranging from 1 to 9 μm in diameter according to Mehaïa et al. [40]. Camel milk fat is also distinguished by high levels of phospholipids [41], which are good emulsifiers, that give camel milk cheese its soft texture and great water retention.

3. Camel milk cheese historical background and recent insights into cheese-making

In the past, people used the process of creating cheese to preserve milk. The first cheese was made in the United States. There were more than 45 million kg of cheese manufactured in the United States in 1849. Raw milk was used to make the majority of the cheese. Despite being a novel technology, pasteurizing milk for making cheese was not widely practiced in 1914. The most popular cheeses today are Parmesan and Gorgonzola from Italy, Emmental from Switzerland, Roquefort and Camembert from France, and Edam from Holland. Since then, cheese has gained enormous popularity throughout the world. Research on cheese from minor milk species has increased in the last 30 years, especially for camel milk. This interest was initially influenced by the difficulties of camel’s milk coagulation. Furthermore, its technologies that are currently being applied for the cow’s cheese-making are not successfully applicable to turn camel milk into cheese. Earlier attempts at creating camel cheese involved combining camel milk with goat and sheep milk and the use of bovine rennet, but the obtained coagulum was extremely soft and crumbly [42, 43]. After that, the difficulty of camel milk coagulation and the low cheese’s yield has been confirmed by the author’s observations [44, 45] who are into the idea of overdosing the rennet concentrations about four times more than that used for cow milk. The used rennet was that of the calf combined with a coagulant preparation derived from a mold conventionally used in the dairy industry named Rhizomucor miehei. Additionally, they demonstrated how the camel milk may be supplemented with calcium chloride or calcium phosphate to somewhat sidestep this challenge. In fact, salts modify the ionic environment of the casein micelle and bring about a lowering of the pH value of the milk, which promotes the activity of the rennet and the process of aggregation of the casein leading to the coagulation. Unlike, the obtained cheese turned out to be fragile and crumbly, the cheese’s yield was low with high loss in fat-which led to not creamy product.

More recently, many researchers used Camifloc—a specific rennet used to coagulate camel milk—as a coagulant [28, 46]. Later, some authors used Camifloc to coagulate camel milk either by adding sheep’s milk at 50 and 75% levels [47] or by varying the levels of added salts [28]. In concert, these results demonstrate a reduction in coagulation time and an improvement of the texture of cheese as well as sensory appreciation. Other alternative has been considered such as introducing the camel chymosin synthesis gene into Aspergillus niger to obtain a specific recombinant enzyme for camel milk coagulation named Chymax-M1000® produced by Ch. Hansen©. Hence, the camel cheese qualities were enhanced [10, 26]. Then, several studies have demonstrated that the association of camel chymosin with starter cultures improves the camel cheese yields. Different starters were added like thermophilc, mesophilic or blended strains, and yogurt starters [10, 19, 21, 48, 49]. Walle et al. [50] reported that cooking camel milk coagulated with camel chymosin combined with starter cultures improved the hardness of cheese.

The production issues related to camel cheese were resolved by mixing the milk of other bovines such as cow, buffalo, sheep, and goat milk in order to boost the casein concentration in camel milk. According to the research of Shahein et al. [17], the 30% (w/w) addition of buffalo milk to camel milk improved the rennet’s ability to coagulate, increased curd yield, improved curd hardness, reduced weight loss, and improved the sensory and microbiological quality of the finished product [17]. However, Saadi et al. [18] produced soft cheese by adding sheep’s milk to camel milk, and discovered a significant improvement in the yield and cheese quality.

Moreover, processing conditions could affect greatly the quality and the nutritional value of produced cheese. For instance, raising the total solid content in camel milk using the ultrafiltration process was found to increase the cheese yield, firmness, and nutritional value due to the end product’s higher protein and fat, in comparison with conventional processing [8, 51]. Furthermore, the addition of Allium roseum powder to UF camel milk produces a camel cheese with higher anti-oxidant activities [8]. Likewise, it has been documented that cheese hardness is significantly influenced by the milk pasteurization temperature, high-pressure treatment, and pre-acidification. Mbye et al. [25] showed that camel milk pasteurization at temperatures not exceeding 65°C for 30 min or high-pressure processing at 350 MHz for 5 min at 4°C are more effective in providing cheeses from camel milk with a semi-hard texture.

In fact, the most notable modifications during cheese-making are observed after high-pressure processing or homogenization resulting in the reduction of the size of the native milk fat globule. In addition to that, high-pressure processing alters the conformational shape of casein micelles by reducing electrostatic and hydrophobic interactions, which causes micellar fragments to disaggregate and improves milk’s physico-chemical and technological applications. Casein micelles are broken apart, increasing the surface area and hastening the rennet coagulation process. Consequently, this treatment can lead to the formation of new clusters of fat and protein, providing the opportunity for many different cheese textures. Some research has come out and has been studied the effect of pre-acidification technology on camel cheese aspect. The pre-acidification of the milk before adding the enzyme can be done by adding directly acids or by using bacteria that can metabolite lactic acid. In both cases, the presence of acid in the milk attributes to the decrease of its pH value and decreases the coagulation time of camel milk [10, 11, 12, 13, 14, 15].

Other trials have been tested by various authors in order to improve camel milk cheese’s textural and sensorial qualities. These include the use of rennet substitutes of animal origin such as bovine pepsins and pepsins extracted from poultry proventriculi such as chicken and duck [18, 52]. Recently, a great deal of research has been undertaken in order to find effective and competitive coagulants using plant extracts such as ginger (Zingiber officinale) [53], Moringa oleifera L. [20], Withania (Withania coagulans) [21], and nettle (Urtica dioica) leaves [19]. The results of these studies showed that the ability of partially purified plant extracts to coagulate camel milk and form a firm curd. It has also been demonstrated that camel milk cheese produced using a combination of withania extract and camel chymosin exhibited a higher quality when compared to chymosin alone [21]. At the same time, other studies have been devoted to improving camel milk coagulation using microbial transglutaminase (MTGase). Abou-Soliman et al. [23] reported that adding MTGase to camel milk at a concentration of 80 U after 20 min of renneting is recommended to improve the yield, textural, and some sensory properties of soft cheese made from camel milk. Alia et al. [22] found that MTGase and the Cynara cardunculus L. flower extracts showed excellent coagulating properties and immense potential as coagulants for cheese production using camel milk.

4. Camel cheese nutritional value and bioactive components

4.1 Substances composition of camel cheese

The variation of composition observed in the camel cheese may be due to the original milk composition and cheese-making processing circumstances. The total solids components, including protein and fat, progressively concentrate into the cheese curd depending on how the cheese is prepared and how the whey is drained. Additionally, the kind, amount of ash, and salt addition can all affect the minerals in the cheese during the cheese-making process. In addition to its impact on milk clotting, the acidification process is essential for the removal of colloidal minerals from casein micelles, coagulant retention in the curd, coagulum strength, and cheese yield. The chemical composition of the different camel cheeses is detailed in Table 1.

Cheese variety	Total solids	Protein	Fat	Yield	Reference
	Soft unripened Cheese
		With whole camel milk
		Enzymes used as coagulant
Without any addition	28.38–39.90	15.62–22.32	0.88–20.21	11.4–13.07	[11, 13, 49, 51, 53, 54, 55]
With different level of salts	31.10–42.92	15.29–21.59	15.69–18.51	13.45–13.95	[18, 26, 28, 55]
With processed milk	29.54–40.9	13.2–21.90	0.15–22.2	11.7–17.0	[8, 16, 25]
With pre-acidification
Direct acidification	34.0–41.28	8.56–35.55	3.85–16.50	9.86–25.56	[11, 13, 14, 56]
Starter cultures	30.90–44.36	11.12–21.30	13.14–20.91	13.22–18.10	[13, 15, 23, 49]
		Plant protease as coagulant
	35.40–40.76	10.16–16.40	10.71–19.7	8.70–11.73	[14, 25]
With other milks
Cow milk	32.51–38.58	25.70–31.55	3.73–3.97	—	[56]
With buffalo milk	41.24–45.33	13.10–14.03	17.50–20.50	14.7–20.1	[17]
With sheep milk	42.92–53.26	21.59–25.27	18.51–24.9	—	[18, 57]
		Domiati-Type cheese
	29.4–46.5	13.51–20.61	1.0–26.2	—	[12]
		Mozzarella cheese
	46.3 ± 0.42	29.0 ± 0.59	13.9 ± 0.44	—	[58]
		Akawi-cheese
	37.6–38.1	23.3–23.7	9.8–9.8	—	[58]
		Brined cheese
		Soft brined cheese
Day of ripening
0–60	45.02–36.46	20.37–14.39	26.0–22.75	9.43–13.44	[48, 59]
0–30	35.39–36.68	14.44–12.67	13.20–14.25	13.22	[60]
0–7	48.17–49.07	29.25–40.48	1.30–1.17	65.57	[61]
		Dry brined cheese (Feta-type)
	48.68 ± 5.65	30.64 ± 3.90	57.4 ± 2.70		[62]

Table 1.

Composition and yield of different types of camel milk cheese (%).

4.2 Proteins

Protein is one of the main nutritional substances in camel milk cheese. The protein content in camel milk directly affects the nutritional value of camel dairy products. The protein content in camel milk cheese is affected by several factors, such as the type of starter culture used for cheese-making, meaning that a camel cheese made with thermophilic (STI-12) and blended (RST-743 and XPL-2) cultures had a significantly higher protein value [15]. The variation of protein content into the categories of camel cheese obtained might be attributed to the processing condition of cheese manufacture. The ultrafiltration process and cheese fortification enhanced significantly the protein content of soft camel cheese [8]. Moreover, the protein content into the cheese curd depends on how the whey is drained. Besides mixing camel milk with other dairy animal milk has a substantial effect on the protein amount in camel cheese [58].

4.3 Fat

Fat is an important factor that may be responsible for cheese quality. Fat contents are progressively concentrated into the cheese curd according to cheese processing and the method used to drain the whey. Castillo [63] reported that the rheological and micro-structural properties of gels’ strength and the higher curd loss from the cheese vat resulted in excess whey fat loss. A huge variation of fat content in camel mozzarella cheese blends of bovine milk and 30% of camel milk [58]. A significant difference in fat cheese was observed in soft white cheese with different starter cultures [15], whereas the variation of percentages of salt to make Domiati-type camel cheese has no effect on fat content [12]. El-Hatmi et al. [8] reported a low content in soft camel cheese due to a loss of fat in permeate during the ultrafiltration process.

4.4 Total solids

According to the studies focused on camel cheese characterization, there is a variation in total solids observed, and this variation might be attributed to the original milk composition on protein and fat, the processing condition of cheese manufacturing and the method used in why draining. In fact, total solids are concentrated into the cheese curd. The acidifying process of milk during cheese-making, is a determining factor in the dry matter content of cheese, and this is due to its important role in the removal of colloidal minerals from casein micelles, the retention of coagulant in the curd, syneresis of the gel, coagulum strength, and cheese yield [64, 65].

4.5 Biological properties

The bioactive peptides derived from camel milk proteins and products, particularly fermented milk, have received much attention during the last decade. However, limited studies have been done with camel cheese as a source of bioactive peptides. There are mainly two approaches used to produce bioactive peptides from camel milk, that is, bacterial fermentation and enzymatic hydrolysis. Identified camel peptides of single and/or multiple functions have been reported as follows:

• Anti-oxidant peptides:

  Several anti-oxidant peptides have been obtained from the action of digestive enzymes or lactic acid bacteria proteinase on camel milk casein. These peptides have been identified as fragments of a camel β-CN, α-CN, GlyCAM-1, and PGRP-1 [2, 66, 67]. To our knowledge, antioxidant peptides of camel cheese have never been identified, but the anti-oxidant activity of camel milk cheese was well documented. El-Hatmi et al. [8] reported that UF camel milk cheese exhibited antioxidant activity and this power was improved after cheese fortification with Allium roseum powder [8] or quinoa flour [68]. Whereas Abou Soliman et al. [23] showed that the cross-linking between camel-milk proteins caused by MTGase negatively influenced the antioxidant activity of cheese.

• Antimicrobial peptides:

  The presence of antimicrobial activity in the camel whey protein digests has also been reported [2]. Jrad et al. [69] identified cationic peptides from the peptic digests of camel lactoferrin (LF). They found these peptides to have antimicrobial activities against Listeria innocua. Digestion of camel LF with pepsin resulted in an antimicrobial peptide homologous to cow lactoferrampin B. The camel lactoferrampin represents LF fragment f 271–284 with the sequence LVKAQEKFGRGKPS [69]. In addition, other antibacterial peptide derived from a camel β-CN was identified and presented high homology with casesidin bovine peptide [70]. Low molecular-identified antimicrobial peptides were generated from fermented camel milk with Lactobacillus plantarum [71].

• ACE-inhibitory peptides:

  The ACE-inhibitory peptides found in hydrolyzed camel proteins and in products of camel milk have received much attention. The ACE-inhibitory peptides isolated from the digests of camel milk casein with potential activity are dipeptides (“AI,” “IY,” “VY,” “LY,” “TF”) and tri-peptides (“IPP,” “LHP”) [72]. The angiotensin-converting enzyme inhibition of camel cheese was also investigated, but there is no information about derived peptides [73].

• Anti-diabetic peptides:

  Camel milk constitutes a center of interest for scientists due to its known beneficial impact on diabetes. Identification of camel milk-derived peptides and their structure-activity relationship study and characterization in the context of molecular markers related to diabetes are studied. The main targeted enzymes for their inhibition by camel milk proteins/peptides are carbohydrate digestive enzymes, specifically intestinal α-glucosidase and pancreatic α-amylase, and the dipeptidyl peptidase IV (DPP-IV), an enzyme that breaks down major incretin hormones that stimulate the release of insulin in response to glucose [3, 74]. It is now obvious that identified antidiabetic peptides that target the key molecular pathways involved in overall glucose homeostasis liberated from both camel milk whey and casein [75]. Moreover, camel cheese exhibited α-amylase and α-glucosidase inhibition activity [73].

Extensive other in vitro studies have found that camel milk and its derived products possess anti-obesity, anti-biofilm, anti-cancer, anti-inflammatory, anti-hemolytic, and anti-hyperpigmentation activities. This provides potential for the development of functional products using camel milk.

5. Conclusions

Worldwide, camel milk and its derivative products production and consumption have increased due to its medicinal and health-promoting potential, which makes it the best choice as a substitute of cow’s milk. However, the processing methodology of camel milk into dairy products is facing several difficulties. In fact, making cheese from camel milk using the same conventional methods used for cheese manufacture from cow’s milk is challenging and occasionally impossible because of a number of issues, such as prolonged coagulation times, weak curd formation, and ultimately lower cheese yield. Therefore, with current advancements in dairy technology, the processing of camel milk into cheese become now possible. Camel milk cheeses made with camel chymosin, with starting cultures and through technological processing, have significantly improved in some cheese-making qualities. Moreover, it was discovered that clotting camel milk with plant protease and chymosin is a successful method to make cheese from camel milk. Additionally, camel milk has significant enhancement in various features of cheeses when combined with other milk species. Some studies have focused on the functional characteristics and nutritional quality of camel milk cheeses, but additional clinical studies are required to confirm the therapeutic effects of these functionalities in the human body.

Conflict of interest

The authors declare that they have no conflict of interest.