**3. Use of coagulant in camel milk cheese**

The difficulties in clotting found in this method should be explained by the different casein proportions between cow and camel milk, particularly the lower concentration of κ-casein: 3−4% of casein, compared to 13−15% in cow milk. Furthermore, camel milk's casein micelles cannot coagulate well with the bovine chymosin utilized in the dairy industry, resulting in a weak curd. Therefore, the first difficulty addressed by researchers studying camels and dairy plants processing camel milk was obtaining a hard coagulum [9]. Animal rennins, such as pepsin and chymosin, plant-based proteases, starter cultures, or organic acids, for acidification are all utilized as coagulants while making cheese. After neutralizing the negative charges of the κ-casein, hydrolysis by enzymes or precipitation by acids lead to the instability and precipitation of the casein micelles, which is how milk coagulation with proteolytic enzymes proceeds [27, 28].

#### **3.1 Animal source rennet enzymes**

The animal source rennet enzymes are aspartic peptidase, and the most used are the combinations of chymosin A, B, C, and pepsin extracted from the stomach of calves and other ruminants [29]. When utilizing bovine chymosin, numerous investigations have consistently indicated that the coagulation of camel milk proceeds at significantly lower rates and results in a more fragile coagulum than that of bovine milk [30]. It was discovered that camel chymosin, which does not effectively coagulate camel milk, had 70% greater clotting activity for bovine milk than bovine chymosin [31]. Due to a lack of coagulation enzymes for camel milk, different researches have been conducted for substitute proteolytic enzymes that worked similarly. This led to the development of many microbial recombinant chymosin products as an alternative to animal rennet in the cheese-making process. Camel chymosin is a desirable alternative for both smalland large-scale cheese productions due to its high clotting activity [32].

Comparatively to the Phe105-Met106 bond in bovine κ-casein, camel and bovine chymosins preferentially cleave the Phe97-Ile98 bond in camel κ-casein. This results in the hydrophilic C terminal of κ-casein dissociating from it, destabilizing the casein micelles, and causing the milk to aggregate and coagulate as a result. Better substrate binding, made possible by camel chymosin's surface charge, is thought to be the cause of its increased milk-clotting activity. By expressing the camel chymosin gene in a strain of Aspergillus niger, recombinant camel chymosin is created [33]. Studies that recently assessed the usage of camel chymosin to produce soft white cheese from camel milk discovered that chymosin when combined with other ingredients improves cheese yield [34, 35].

The effect of camel chymosin on coagulation and preparation of soft unripened cheese made from camel milk has been studied by employing three levels of camel chymosin concentrations (40, 70, and 100 IMCU/L) and two levels of cooking (cooked and uncooked curd) [35]. The shortest gelation time was reported for camel chymosin concentration of 100 IMCU/L and 70 IMCU/L, whereas the highest maximum gel firmness was observed for camel chymosin level of 40 IMCU/L. In this study, it was found that highest cheese yield was observed for uncooked cheese at 100 IMCU/L coagulant level. In this investigation, it was discovered that raw cheese with a coagulant level of 100 IMCU/L produced the largest amount of cheese. Protein, total solids, ash, and hardness were considerably higher in cooked cheese prepared with 100 IMCU/L. Protein, total solids, ash, and hardness were considerably higher in cooked cheese prepared with 100 IMCU/L. On the other hand, 40 IMCU/L cooked cheese received higher ratings for color, texture, and aesthetics. However, the cooked cheese prepared with 70 IMCU/L received the greatest rating for taste, scent, and acceptability. It was determined that heating camel milk curd and employing medium-level chymosin concentration (70 IMCU/L) could be effective methods for producing soft and unripened cheese from camel milk [35].

Another study examined the protein degradation, rheological characteristics, sensory characteristics, and aroma profile of soft brined cheese made from camel milk over a ripening period of 60 days using two levels of brine (2% or 5% NaCl, w/w) and two levels of coagulant (camel chymosin) [55 and 85 International Milk Clotting Units (IMCU)/L] [6]. The finding showed that when cheese ripened and coagulant levels rose, casein degradation in soft brined camel milk cheese increased. With rising levels of salt and moisture in the cheese during ripening, Young's modulus and stress at fracture rose. However, cheese prepared with 85 (IMCU)/L coagulant had a softer texture and absorbed more salt. The experimental cheeses were described as salty,

sour, and hard using descriptive sensory analysis. The amount of coagulant, NaCl content, and ripening duration all have an impact on the volatile fragrance molecules produced in soft-ripened camel milk cheese [6].

#### **3.2 Plant source rennet enzymes**

Recombinant enzymes are unpopular in some countries due to religious matters and diets. Additionally, the decreasing supply and rising cost of calf rennet, along with the rising demand for cheese on a global scale, have prompted researchers to look at alternative clotting enzymes that could take the place of traditional rennet in the cheese-making process. Furthermore, different rennet alternatives have emerged as a result of religious considerations and those connected to the vegetarianism of some consumers [36, 37]. Due to the difficulty in producing cheese of a high enough quantity and quality from camel milk, research on plant-based coagulants has been conducted recently to investigate potential substitutes for rennet enzymes. Several milk-clotting enzymes produced from plants are now used in cheese making. Many attempts have been made to contrast their effects with those brought on by animal rennet in terms of the rheological and sensory characteristics of cheese. However, due to their strong proteolytic activity, which aids in the formation of a bitter flavor, vegetable coagulation enzymes are still only partially suited for cheese making [37].

Plant proteases have been divided into groups based on the hydrolytic process mechanism: aspartate, serine, and cysteine proteases [38]. Studies conducted on plant source coagulants such as *Zingiber officinale* extracts [39], cysteine proteases isolated from *Ficus carica* [40], and aspartic proteases from *Withania coagulans* [41] have been used in camel milk cheese production and the resultant cheeses were found acceptable.

The study carried out on the clotting activity of camel milk using ginger rhizome (*Zingiber officinale*) crude extracts (GCE) reported that GCE would result in strong coagulation of camel milk [39]. According to the finding of this study, the camel milk's clotting activity (MCA) was highest at pH 5.0, 65°C, and 10% crude extract by volume of milk, while pH 4.5, 55°C, and 40% GCE by volume of camel milk produced the lowest value. According to a study on the clotting activity of camel milk using crude extracts of ginger (*Zingiber officinale*), camel milk will strongly coagulate when using GCE [39]. According to the report, the highest camel milk clotting activity (MCA) was noted at pH 5.0, temperature 65°C, and crude extract concentration of 10% by volume of milk, while the lowest value was noted at pH 4.5, temperature 55°C, and GCE concentration of 40% by volume of camel milk.

The experiment conducted by fractions of latex protease from *Ficus carica* on camel milk-clotting properties for use as rennet alternatives revealed that latex fractions, extracted from the fig tree, have a proteolytic activity of 23491.24 IU LG1 (*Ficus carica*), showed proteolytic and milk-clotting activity. *Ficus carica* latex protease, which may coagulate milk after production, can be utilized as an alternative to commercial animal chymosin in the cheese-making process. The amount of cheese produced at various enzyme doses was evaluated, and it was discovered that 1mL of the enzyme extract in 100 mL of camel milk produced 15% of the cheese [40].

The effects of camel chymosin and *Withania coagulans* extract on camel and bovine milk cheeses were performed on cheese's yield and hardness [41]. The result showed that pure Withania extract exhibited the lower coagulating effect resulting in cheeses with low yield, hardness, fat, protein, and total solids compared to camel chymosin. It was concluded that *Withania coagulans* extract protease alone is not

#### *Innovative Approach of Cheese Making from Camel Milk: A Review DOI: http://dx.doi.org/10.5772/intechopen.108700*

sufficient to produce good quality cheese, especially camel milk cheese but a mixture of *W. coagulans* and camel chymosin produced better quality camel and bovine milk cheeses than chymosin alone [41].

In a comparison of the effects of camel chymosin and *Withania coagulans* extracts on the yield and textural quality of camel milk and bovine milk cheeses, it was discovered that camel milk had a longer gelation time and softer cheese than bovine milk [41]. This study demonstrated that higher moisture entrapment, which lowered cheese hardness, consistently resulted in better yields of unripened camel milk cheese generated by chymosin or the Withania extracts than that of bovine milk cheeses. This study also showed that optimal camel milk as well as bovine milk cheese hardness was obtained by clotting the milk with mixtures of Withania extracts and chymosin suggesting some synergistic interactions, an effect that deserves further investigations.

#### **3.3 Effect of acid coagulants on camel milk cheese making**

Acidification is an established process commonly used in combination with heat treatment or rennet addition to prepare fermented milk products (yogurt) and acidfresh cheeses [42]. The foundation for a huge variety of cultured dairy products is the acid coagulation of milk. By lowering their charge, dissolving part of the insoluble calcium phosphate crosslinks, and altering internal protein bonds, acidification has a direct impact on the stability of casein micelles. At some crucial point, when electrostatic repulsion is diminished and is unable to repel attractive forces, such as hydrophobic contacts and aggregates, eventually gels begin to develop. Acid-induced milk gels become more rigid over time as a result of continuing casein particle-to-casein link formation inside the network.

Cheese prepared from camel milk by direct acidification of milk and by adding starter culture of lactic acid bacteria was evaluated. When starter culture was added to milk to coagulate it, a larger cheese yield was obtained than when cheese was made directly by acidification. Additionally, the starting culture-made cheese contained more total solids, protein, and fat. It was suggested that camel milk can be used to make cheese by coagulating it with starting culture [11]. Another study conducted on the effect of starter cultures on camel milk cheese properties revealed that camel milk treated with nonaromatic cultures such as STI-12, RST-743, and R-707 (see **Table 1**) for SWC manufacture showed a rapid acidification rate and formation of appreciable fine curd properties. As a result, camel milk SWC made using nonaromatic cultures gave better curd firmness, cheese compositional quality, and texture [12].
