3.3.1. Physicochemical Properties and Yield of Cheese
Calcium chloride is usually added to milk during cheese making (up to 0.5 g L
−1 CaCl
2) to aid coagulation, improve the cheese-making process, or increase yield. The addition of calcium to the processing milk increases the bridging of calcium between casein micelles, facilitating more cross bonding and fat entrapment in the curd during cheese production [
64]. The cheese matrix is a complex of individual components. Protein, especially casein, hydrated with water, forms networks (within the cheese matrix) in which fat globules, minerals, bacteria and dissolved solutes such as lactic acid, potentially residual lactose, soluble salts and peptides are interwoven [
67,
68]. The way the individual ingredients combine in the cheese matrix and their interactions determine the structure of the cheese [
69].
Similarly to goat’s milk after pasteurization (
Table 2), the addition of increasing doses of calcium carbonate significantly increased the pH value of the cheese (r = 0.9973) (
Table 3). Cheese with carbonate showed a pH value of 0.19 higher than the control cheese. In contrast, adding chloride, gluconate, and lactate to the milk reduced the pH of cheese. The pH value of the cheese was reduced most strongly by the addition of increasing doses of calcium lactate (r = −0.9521). According to Wątróbska-Świetlikowska [
70], calcium chloride has a low molecular weight and high solubility in water; therefore, it dissociates rapidly in water into calcium and chloride ions. Moreover, it provides a higher concentration of calcium ions due to its high solubility and complete dissociation. Calcium chloride is commonly used in cheese production because it provides fast and strong coagulation due to its high calcium ion concentration and immediate availability. Calcium chloride is an inorganic salt that contains a higher amount of calcium available to combine with free phosphate, leading to precipitation due to the higher dissociation constant of calcium chloride compared to calcium gluconate, an organic salt. In addition, organic calcium compounds have a lower degree of dissociation than inorganic calcium chloride. In contrast, calcium carbonate is highly susceptible to pH changes and readily soluble in acidic environments. Due to these properties, it is used as a stabilizer in foods. The solubility of carbonate depends on pH and its precipitation increases with increasing pH. Precipitation of calcium carbonate occurs spontaneously under alkaline conditions, while an acidic environment prevents precipitation and promotes the dissolution of this compound [
71]. Calcium carbonate is an alkaline compound that can neutralize acids in foods. In an acidic environment, calcium carbonate dissociates into ionized calcium (Ca
2+) and carbonate anion (CO
32−). The carbonate anion then binds to free protons (H
+), increasing the pH of the environment by reducing the concentration of hydrogen ions [
72]. Thus, the significantly higher pH value of cheese with added calcium carbonate. Acidity is an essential element that influences the physicochemical characteristics of cheese since it directly impacts the stability of casein micelles and milk minerals [
73]. Lactose in milk is transformed into lactic acid due to lactic acid bacteria fermentation. The accumulation of lactic acid reduces pH, protects against the growth of unwanted microbes, and contributes to syneresis [
74]. Reducing the pH of milk has the most profound implications for micellar calcium phosphate dissolution, casein net charge decrease, and casein dissociation from micelles [
75]. Miloradovic et al. [
76], based on the results of a study of ricotta cheese made from goat’s milk, found that a limited reduction in pH leads to an increase in the milk gel’s firming rate. During fresh cheese production, acid coagulation at 30 °C to a pH of 4.6 causes calcium solubilization. The buffering capacity of the milk controls the rate of pH change during fermentation [
77,
78]. In a study by Sakr et al. [
79], the addition of calcium chloride to milk at a level of 200 mg 100 mL
−1 resulted in Karish cheese with a pH of 4.69, while the addition of 300 mg 100 mL
−1 calcium chloride lowered the pH of the cheese to 4.50. Kajak-Siemaszko et al. [
74] reported the pH value of fresh acid rennet cheese made from goat’s milk from 5.86 to 6.16, depending on the starter culture used. However, Dmytrów et al. [
80] measured the pH of acid goat cheese at 4.7. The authors claim that the acidifying properties of goat milk are influenced by its chemical composition. The high proportion of proteins and minerals promotes the activity of lactic acid bacteria.
Each cheese sample showed increased fat content with the addition of calcium. Adding only 5 mg Ca 100 g
−1 of milk enhanced fat retention in the cheese from 1.42% to 3.66%. The control cheese in the carbonate group showed the highest level of fat, which may explain the highest level of this parameter in the cheese with the addition of 15 and 20 mg Ca 100 g
−1, from 3.51% to 3.56% higher compared to the control. However, when considering the level of fat content between cheese samples with all calcium compounds, no significant differences were found (
p ≤ 0.05). During cheese production, milk fat and protein (mainly the casein fraction) are concentrated, leading to a complex and heterogeneous system. According to Vilela et al. [
81], cheese can be described as a bicontinuous gel structure consisting of a porous protein matrix (casein) interspersed with localized fat domains. According to Ong et al. [
82], enhanced protein hydration at pH 5.0 results in the formation of more protein–fat cheese aggregates. Additionally, at a lower pH (4.3), the protein and fat network exhibited higher continuity, characterized by smaller pores compared to the more porous microstructure observed at a higher pH (5.0). This microstructure comprises clusters of small fat globules coated extensively with protein aggregates, forming a corpuscular structure. The protein network surrounding the fat droplets within the cheese matrix was noted to expand with increasing pH, potentially due to the swelling of the casein network, likely a result of heightened hydration and interactions between protein and water. In our investigation, cheese containing calcium carbonate, especially at concentrations of 15 and 20 mg Ca, exhibited a higher pH compared to the other cheese samples. This higher pH possibly led to a more porous cheese structure, facilitating the formation of larger fat−protein aggregates and, consequently, higher fat retention. The moisture content of the cheese was similar, ranging from 67.72% to 71.49%. Adding 5–20 mg Ca 100 g
−1 to the processed milk in the form of chloride influenced a slight reduction in the water content of the cheese compared to the control sample. It may be hypothesized that the increased calcium content in milk resulted in stronger protein–protein interactions in the cheese matrix and, through syneresis at reduced pH, led to the exclusion of moisture from the cheese matrix during cheese production. Other calcium-enriched cheese samples with gluconate, lactate, and carbonate at each addition level showed a slight increase in the water content. In a research conducted by Tarapata et al. [
4] on cow’s milk acid rennet gels and calcium chloride, high chloride levels (54 mmol L
−1 and 72 mmol L
−1) induced alterations in water-holding capacity. The gel structure exhibited uniformity, featuring a compact protein network and diminutive pore sizes. Gels with this protein network are assumed to enclose a larger portion of the aqueous phase confined within the pores, owing to their heightened capillary strength [
83,
84]. In our study, only adding calcium chloride did not reduce protein retention from goat’s milk to cheese (
Table 3). The addition of calcium gluconate to milk at a dose of 20 mg Ca 100 g
−1 of milk reduced protein retention by 7.66% compared to the control cheese. Adding 15 mg Ca in the form of gluconate and lactate significantly reduced protein retention from milk to cheese from 2.5% to 4.25% (
p ≤ 0.05). Furthermore, negative correlation coefficients confirm the significant effect of calcium addition on protein retention from milk to cheese (
p ≤ 0.05). When milk is heated to temperatures above 70 °C, denaturation of whey proteins, mainly β-lactoglobulin and α-lactalbumin, occurs, forming soluble polymers and protein aggregates that can interact with casein micelles. Heat-induced protein complexes can be separated from milk by coagulation at the isoelectric point of casein. Complex protein interactions involving calcium influence the extent to which milk components are retained in acid cheese [
85]. The addition of calcium chloride notably enhanced the retention of proteins from milk into the cheese. Pre-pasteurization addition of calcium ions to milk resulted in an expanded surface area of casein micelles, heightened polymerization and aggregation of whey proteins, thereby intensifying the interaction between casein and whey protein aggregates. This fact can be related to the good solubility of this compound and its rapid dissociation, resulting in fast acidification of the environment. As a result, the calcium added with the chloride was more accessible during the coagulation process, which may have influenced the good retention of the protein from the milk into the cheese. High heat treatment of milk results in high levels of whey protein denaturation. Caseins are responsible for networking in cheese made from unheated (or minimally heated) milk. In contrast, denatured whey proteins and caseins are responsible for networking in cheese made from highly heated milk. Moreover, denatured whey protein bound to the surface of casein micelles can limit the regrouping or fusion of casein particles in cheese made from highly heat-treated milk [
69]. Sakr et al. [
79] reported that the addition of calcium chloride to milk at a level of 200 mg 100 mL
−1 resulted in Karish acid cheese with a protein content of 14.72%, while the addition of 300 mg 100 mL
−1 calcium chloride increased the level of this component by 1.43%. In contrast, the control cheese had a lower protein content of 10.03%.
In our research, adding 20 mg Ca 100 g
−1 milk in the form of gluconate resulted in the greatest increase in cheese yield (by 4.04% compared to the control). The same dose of chloride addition increased the yield by 2.55% and carbonate by only 0.1%. In contrast, adding 20 mg Ca 100 g
−1 of milk in the form of lactate reduced cheese yield by 2.3%. Cheese from the chloride group was characterized by a relatively high water content and slightly increased protein retention from milk to cheese, which could affect the high yield. However, the yield of the gluconate cheese could be related to the highest fat level. Moreover, the pH value might affect the yield of cheese. Applying calcium carbonate, which impacts the higher pH value of the cheese, resulted in lower cheese yield. This is probably related to the higher amount of lost whey proteins, which despite the high pasteurization temperature of goat milk, did not bind to casein. Increasing the pH value results in weaker protein interactions due to increased calcium solubility. In contrast, a more acidic environment improves these interactions and allows for the formation of a denser protein network structure with a small pore size [
86]. Confirmation of this thesis could be found in the results of our study, where the yield of cheese from milk with calcium gluconate is higher, while the yield of cheese from milk with calcium carbonate is lower. Calcium gluconate was shown to be the most optimal calcium compound participating in the formation of a dense milk gel structure and improving cheese. Cheese manufacturing concentrates milk components, especially fat and protein levels, which are determinants of cheese yield [
87]. According to Siemianowski and Szpendowski [
21], the calcium-thermal method of milk coagulation may be applied to manufacturing acid and acid rennet cheese and provides a potential 10–15% improvement in product yield. Miloradovic et al. [
76] highlighted that subjecting goat’s milk to high temperatures affects its components, particularly proteins, in a manner different from cow’s milk. Therefore, utilizing high heat treatment on goat’s milk is practicable for goat cheese production. The raised temperatures lead to the denaturation of whey proteins and the formation of coaggregates, ensuring these components become part of the cheese curd. This incorporation enhances the yield of goat cheese and increases its nutritional value. The casein fraction is concentrated in the curd during milk coagulation. The proportion of casein proteins to total proteins can vary noticeably due to genetic or physiological factors, but not in proportion to total protein content. However, other milk properties can promote protein solubilization, alter rennet formation (number of somatic cells in milk, pH, mineral content) or affect curdling, and thus more or less affect cheese yield. Also, milk storage parameters (time, temperature) or technological mistakes can cause fat and protein losses during the cheese-making process, affecting cheese yield [
87]. The results of a study by Santos et al. [
66] on Minas cheese produced from cow’s milk with the addition of calcium chloride (0, 150, and 300 mg L
−1) showed that the addition of calcium at different concentrations did not affect wet and dry yields, protein, fat and calcium content, regardless of the pH of the cheese samples produced. In contrast, Sakr et al. [
79] in acid Karish cheese obtained a 6.97% increase in yield using 200 mg 100 mL
−1 of calcium chloride and an 11.5% increase in yield using 300 mg 100 mL
−1 of calcium chloride.
A significant increase in the concentration of calcium in cheese samples with increased calcium dosage (
Table 4) is confirmed by a high positive correlation coefficient (r > 0.8). The highest calcium levels were found in cheese with the addition of 20 mg Ca 100 g
−1 of milk in the form of lactate, which was higher by 20.81 mg compared to the control sample. In contrast, adding 20 mg Ca in the form of carbonate resulted in the lowest increase in calcium content compared to the control cheese (by 15.06 mg). Goat cheese is a rich source of major (Ca, K, Mg, Na) and trace (Co, Cu, Cr, Fe, Mn, Mo, Se, Zn) minerals. However, the mineral content in the cheese can be modified by feeding goats, heat treatment of milk, and the cheese manufacturing process (coagulation, cutting, pressing) [
88]. Calcium and phosphorus are the two most abundant minerals in goat cheese. Calcium is well known for maintaining bone health and muscle function, while phosphorus is crucial for cell structure and energy metabolism. Studies [
89,
90] found that calcium and phosphorus in goat cheese are highly bioavailable, contributing to their potential health benefits. According to Zhao et al. [
57], both soluble ionic salts (calcium chloride) and insoluble nonionic salts (calcium carbonate) addition can increase the calcium concentration in milk. These findings were confirmed by our results, where adding each calcium compound to goat’s milk significantly increased calcium levels in the cheese (
p ≤ 0.05). In our previous study [
91], adding 40 mg Ca 100 g
−1 of milk in the form of bisglycinate increased the calcium content of cheese by 99.24 mg compared to the control. Whereas the use of calcium citrate at a dose of 20 mg Ca 100 g
−1 of milk increased the calcium content of acid rennet cheese by 26.62 mg compared to the control sample [
29]. Baran et al. [
92] determined 128.30 mg 100 g
−1 calcium in acid goat cheese, which was comparable to the results of our study. According to Santos et al. [
66], a decrease in the pH of milk tends to solubilize protein-bound calcium, which is then lost in the whey during cheese making, leading to a lower calcium content in the final cheese. A decrease in pH causes calcium solubilization and can also affect protein–protein interactions due to a reduction in casein loading when pH is lowered toward the isoelectric point. In the authors’ study, this phenomenon did not occur in the case of curds produced with different calcium concentrations at pH 5.8, where no differences were shown between different curds for calcium content and retention.
Control cheese samples contained between 134.95 mg and 148.07 mg 100 g
−1 of phosphorus. The addition of calcium to goat’s milk in the form of all analyzed compounds increased the phosphorus content of the cheese, and the highest level was found in the sample with gluconate (by 31.53 mg compared to the control cheese). Adding 20 mg of Ca to the milk as lactate increased the cheese’s phosphorus content by only 4.5 mg per 100 g. Soft fresh goat cheese analyzed by Park et al. [
93] contained 275 mg 100 g
−1 of phosphorus, which was a higher value than obtained in our study. The authors state that the mineral content of the cheese is affected by the coagulation conditions of the milk. The reduction in calcium and phosphorus levels is due to the loss of calcium phosphate from the whey as it changes from a colloidal state to a soluble state during coagulation, with a curd pH value of around 4.45. High calcium and phosphorus losses may also be related to the size of the curd grain, which significantly affects the retention of these two minerals in cottage cheese. The control cheese in the gluconate group had the highest pH value, and adding 20 mg Ca 100 g
−1 of milk lowered the pH to 4.61. This might be related to the high phosphorus content in cheese.
Increasing the calcium dosage through chloride and lactate reduced the magnesium and potassium content of goat cheese. Conversely, when using calcium gluconate and calcium carbonate, increasing doses of these compounds resulted in notably raised levels of magnesium and potassium in the cheese (
p ≤ 0.05). Stocco et al. [
94] reported that naturally occurring potassium in milk does not appear to be actively involved in coagulation and cheese production. In a study by Chumak et al. [
95], Bryndza goat cheese was characterized by a magnesium content of 45.00 mg 100 g
−1 and a potassium content of 161.00 mg 100 g
−1. Rojo-Gutiérrez et al. [
96] produced Chihuahua cheese with various doses of magnesium chloride. The authors claim that the cheese structure, consisting mainly of calcium paracaseinate, contains large amounts of divalent cations and salt complexes, acting as a natural mineral reservoir. The addition of calcium chloride shows the potential of casein micelles to bind divalent ions in excess of those naturally present. Considering that casein micelles are selectively retained in cheese, some of the added magnesium may also have been incorporated into casein micelles, causing micellar magnesium retention in enriched cheeses as a result of the dynamic mineral balance achieved between micelles and milk whey before curdling [
16,
64,
96]. In our study, the control cheese in the gluconate group had the highest calcium levels. The addition of increasing doses of gluconate significantly increased the calcium levels in the cheese (r = 0.8404). This cheese group, with 5–20 mg Ca 100 g
−1 of milk gluconate addition, also had the highest magnesium levels (from 25.11 to 26.21 mg 100 g
−1).
In all groups of goat cheese, similar contents of manganese, molybdenum, and selenium were determined. The type of calcium compound and its dose did not significantly differentiate the level of trace elements in the cheese (
p ≤ 0.05). Manganese content ranged from 6.03 to 6.20 µg 100 g
−1, molybdenum from 2.57 to 2.93 µg 100 g
−1, and selenium from 6.20 to 7.22 µg 100 g
−1. In a study by Baran et al. [
92], fresh acid goat cheese contained more manganese (53.32 µg 100 g
−1) than acid rennet cheese (44.83 µg 100 g
−1), and these results were much higher than those obtained in our study. In contrast, Martin-Hernandez and Juarez [
97] obtained goat rennet cheese with manganese contents ranging from 12.6 to 13.6 µg 100 g
−1. Herrera Garcia et al. [
98] determined the selenium content in fresh goat cheese at 7.29 µg 100 g
−1 and semi-hard cheese at 15.20 µg 100 g
−1. These were similar to our results, as the goat cheese was characterized by a selenium content from 6.20 to 7.22 µg 100 g
−1.
3.3.2. Texture of Cheese
Table 5 presents the texture of fresh acid rennet cheese from goat’s milk with calcium chloride, gluconate, lactate, and carbonate addition. The results of our study demonstrate that calcium content significantly affects cheese hardness, with higher calcium concentrations leading to increased hardness. The control goat cheese’s hardness ranged from 1.87 N to 2.75 N. Increasing the calcium dosage, mainly gluconate (r = 0.5003) and lactate (r = 0.7444), resulted in increased cheese hardness, as evidenced by positive simple correlation coefficients between hardness and calcium dose. Compared to the other samples with chloride and carbonate, the addition of 15 and 20 mg Ca 100 g
−1 of milk in the form of gluconate and lactate resulted in a significant increase in the cheese’s hardness. Compared to the control sample, adding calcium carbonate at a concentration of 5 to 15 mg Ca 100 g
−1 milk did not significantly improve the hardness of the cheese (
p ≤ 0.05). In contrast, adding 20 mg Ca in the form of carbonate resulted in a significant increase in the hardness of fresh goat cheese compared to the control (
p ≤ 0.05). A similar trend was shown for calcium chloride (
Table 5). Hardness, a crucial texture attribute, is the force required to deform or penetrate the cheese. It is affected by curd formation, whey expulsion, and post-manufacturing treatments [
99].
The cohesiveness of the cheese is influenced by factors such as water content, protein interactions, and fat distribution [
68]. The control cheese samples had similar cohesiveness ranging from 0.23 to 0.30, with a minor increase in cohesiveness with increasing calcium dose in cheese with added calcium gluconate, lactate, and carbonate (
Table 5). In contrast, lower compression work in both test cycles, meaning lower cohesiveness with increasing calcium dosage, was determined in cheese with added calcium chloride. The cheese with the addition of calcium carbonate had the highest cohesiveness (0.30–0.31). Adding 15 mg Ca in the form of gluconate to goat’s milk also resulted in a cheese with a cohesiveness of 0.30. The addition of calcium chloride to caprine milk at doses of 5, 10, and 20 mg Ca 100 g
−1 of milk resulted in a lower cohesiveness compared to the control, but the differences were not significant (
p ≤ 0.05). The cohesiveness of cheese results from the complex interaction of chemical and physical processes. Cheese is a matrix of proteins, fat, water, minerals, and enzymes. Proteins play a crucial role in the coagulation and structure of cheese. Casein proteins bond to form a network held by calcium ions, creating a three-dimensional structure known as a protein gel. Fat globules intertwine within this protein network, contributing to cheese’s creamy, sometimes smeary texture [
68,
100]. Cheese produced from goat’s milk with calcium lactate and calcium carbonate showed the highest increase in fat and water content with increasing calcium dose (
Table 3). This could be the reason for obtaining cheese samples with the highest level of cohesiveness, which also showed an increase with increasing calcium dose.
According to Kumar et al. [
101], springiness is the rate at which the sample returns to its original shape when the deforming force is removed. The maximum springiness (3.94 mm) was found in the cheese samples with the addition of 15 mg Ca 100 g
−1 of milk in the form of gluconate, while the minimum springiness (1.27 mm) was found in cheese with 5 mg Ca in the form of chloride (
Table 5). There was a significant positive correlation between the springiness of the cheese and the dose of calcium added in the form of lactate (r > 0.7;
p ≤ 0.05), demonstrating that the cheese samples became more springy as the amount of calcium added increased. Similarly, the cheese with gluconate and chloride showed increased springiness with increasing calcium dosage. In a study by Chevanan et al. [
102], a low calcium content resulted in a softer and more pliable Cheddar cheese than Cheddar prepared with a high calcium content, with calcium chloride addition. The higher springiness observed in high-calcium cheese may be due to more cross links and lower moisture content in these types of cheese. Kajak-Siemaszko et al. [
74] studied the springiness of fresh acid rennet goat cheese. The value of this parameter ranged from 8.77 mm to 8.87 mm, depending on the starter culture used. The goat cheese was similar to Polish traditional Bundz cheese, which may explain its higher springiness than in our study. Sant’Ana et al. [
103] found that the cohesiveness and springiness of cheese correlate with the protein network structure and the moisture and fat content. As stated by Ong et al. [
82], alterations in the pH of the acid gel can impact the incorporation of whey proteins and the calcium composition within the cheese, consequently influencing its microstructure and texture. Changes in pH may lead to protein swelling, larger corpuscular formations, reduced interactions between whey proteins and casein, and an increased β-sheet protein structure, all of which can contribute to the decreased hardness of acid cheese at higher pH levels. Conversely, a lower pH level results in a denser microstructure, smaller corpuscular formations, and increased aggregated β-sheet protein structure, resulting in a firmer acid cheese. The denser casein structure of reduced-fat cheese is associated with higher springiness. Compared with the lower hardness and springiness of full-fat cheese, fat reduction makes the cheese firmer and springier. Fat acts as a plasticizer of the casein matrix, reducing the mechanical strength and softening cheese. The milk fat globules fill in the porous protein matrix to make cheese soft [
104]. Rogers et al. [
105] explained that lower-fat cheese is characterized by a more homogeneous network than full-fat cheese. The more homogeneous structure, with denser pores, might be the reason for the higher springiness of lower-fat cheese. An increase in fat content results in a cheese matrix with larger pores with fat−protein aggregates. These weaknesses cause greater deformation, resulting in lower hardness, lower springiness, and a higher degree of disintegration during chewing. In our study, cheese with gluconate showed the highest springiness, which might have been related to the more homogeneous network and lower fat content. The opposite observation was made in cheese with calcium carbonate, characterized by higher fat content and reduced springiness.
Adhesiveness refers to the tendency of a food to stick to oral surfaces during chewing [
106]. The ratio of proteins to lipids can affect the adhesiveness of cheese. Higher protein content is related to increased adhesiveness due to the formation of protein networks that contribute to stickiness, while the calcium content of milk plays a role in the formation of protein networks. Moreover, the pH value of cheese affects protein–protein interactions in cheese, affecting its adhesiveness. In addition, excessive moisture content can lead to a higher adhesiveness. Cheese from milk with added calcium chloride had the highest adhesiveness (from 1.67 mJ to 1.82 mJ) (
Table 5). The highest retention of protein from milk was also determined in this type of cheese (
Table 3). The addition of calcium compounds increased the adhesiveness of cheese compared to controls. A significant positive correlation coefficient was calculated between cheese adhesiveness with chloride (r = 0.7896) and gluconate (r = 0.5465) and calcium dose (
p ≤ 0.05). In contrast, the lowest adhesiveness was observed in goat’s milk cheese with calcium lactate. Samples adding 5, 10, and 15 mg Ca 100 g
−1 milk had lower adhesiveness than the calcium lactate control cheese. Only adding the highest dose of calcium lactate resulted in increased adhesiveness of the cheese compared to the control sample. All goat cheese samples showed an increase in adhesiveness, with a correlating increase in fat content. Cheese with the highest fat content (from milk with chloride and with carbonate) also had the highest adhesiveness. According to Zheng et al. [
107], the milk fat, existing as globules within the protein matrix network in cheese curds, was identified as a plasticizer, impeding the creation of cross links between casein chains. In a study by McMahon et al. [
108], mozzarella cheese containing 0.3% calcium was softer and more adhesive than cheese containing 0.6% calcium. According to Lepesioti et al. [
109], fat reduction results in lower adhesiveness of rennet cheese. Low-fat rennet cheese has a more compact structure, which increases hardness and springiness and decreases adhesiveness and cohesiveness. Moreover, the authors claim that the milk treatment at 90 °C for 5 min resulted in the denaturation of whey proteins and caused the cheese to be characterized by high hardness and springiness and was the least cohesive, softest and most adhesive.
The composition of goat cheese, including moisture, fat, protein, and mineral content, significantly impacts its texture. Higher moisture content tends to result in softer cheese, while increased fat and protein content contribute to a firmer texture. The mineral concentration, particularly calcium, has a vital role in curd formation and subsequent cheese structure development [
110,
111]. Moreover, the texture of goat cheese plays a crucial role in its sensory attributes [
112]. The TPA test simulates the human chewing action by subjecting the sample to a compressive deformation (first bite), followed by relaxation and a second deformation (second bite) [
101]. According to Carpino et al. [
113], the cheese-making process, encompassing coagulation, curd cutting, whey drainage, and curd pressing, profoundly affects the final texture of cheese. The type of coagulant used (rennet, acid), curd-cutting size, drainage time, and pressing intensity influence the size and distribution of curd particles, impacting the cheese’s overall texture. Innovative processing techniques, such as the possibility of using of various calcium compounds to enhance the texture of goat cheese, may lead to improved product quality. Calcium is a critical component of cheese, influencing protein interactions and contributing to curd formation and texture development. It affects protein cross linking, thereby affecting the gelation process during coagulation. Calcium is commonly added during cheese production to manipulate curd firmness and texture [
68,
114]. Lefebvre-Cases et al. [
115] studied the interaction forces in the rennet and acid milk gels using different dissociating agents. The authors claim that hydrophobic interactions and calcium bonds are the essential forces stabilizing the structure of rennet gels. In contrast, in acid milk gels, hydrophobic and electrostatic interactions and hydrogen bonds were major forces, while the participation of calcium bonds appeared less critical, probably due to the solubilization of colloidal calcium at reduced pH value [
1].
The concentration of calcium ions has been shown to influence cheese texture, with higher calcium levels leading to firmer curd [
108]. Calcium lactate is a water-soluble compound characterized by its ability to dissociate into calcium and lactate ions in aqueous solutions. This solubility contributes to its potential for interacting with proteins during cheese production, affecting curd formation, whey expulsion, and ultimately, cheese texture [
116,
117]. Calcium lactate’s solubility allows for a gradual release of calcium ions during curd formation, resulting in a more controlled and uniform curd development. This phenomenon can lead to improved texture uniformity and reduced defects in the cheese matrix and might enhance the goat cheese’s hardness and springiness. Moreover, the water solubility of calcium gluconate facilitates its uniform distribution throughout the curd matrix, ensuring the consistent texture of cheese [
117]. The interaction between calcium and casein proteins affects the curd structure and influences the mechanical properties of the cheese matrix [
118]. Calcium ions facilitate the interaction between casein micelles, promoting their aggregation and subsequent curd formation. Calcium compounds aid in modulating the calcium concentration in milk, thereby influencing the kinetics of rennet coagulation and curd firmness. The addition of calcium compounds during cheese production can alter the size and structure of casein micelles, ultimately impacting the rheological properties of the curd [
119,
120].
3.3.3. Organoleptic Evaluation of Cheese
The organoleptic evaluation of goat cheese with the addition of various calcium compounds is shown in
Table 6 and
Figure 1. All samples of the control cheese were characterized by a slightly sour taste, an odor of fermentation and diacetyl, with a slightly perceptible goaty odor, and a homogeneous white color, sometimes with visible drops of whey. The cheese with calcium chloride, despite the dose of calcium used, had the highest overall acceptability compared to the other cheese samples. The addition of 20 mg of calcium in the form of carbonate significantly reduced the overall acceptability of cheese (
p ≤ 0.05). However, it should be noted that the other cheese samples with added calcium and their controls had high overall acceptability. Panelists scored the individual cheese samples high, ranging from 4.36 points to 5.00 points for the appearance of all calcium-enriched goat cheese and their control samples, and the differences shown were not significant either between the calcium doses used or the calcium compounds (
p ≤ 0.05). Cheese with calcium addition had an imperceptible goaty taste and odor at a 5 mg Ca 100 g
−1 dose. The addition of increasing doses of calcium gluconate significantly (
p ≤ 0.05) improved the taste (r = 0.6777) and odor (r = 0.7685) of the cheese compared to the control sample; however, it negatively affected the consistency (r = −0.5646). Cheese samples with calcium chloride, gluconate, and lactate were characterized by a more firm and homogeneous creamy texture compared to their control counterparts. However, the addition of calcium carbonate influenced a slightly perceptible graininess as well as sandiness and stickiness in its consistency and provided a slightly perceptible chalky taste, but these differences were not significant (
p ≤ 0.05). Moreover, the consistency of the cheese with carbonate was less firm and more smeary and soft, which may have lowered its rating. The addition of calcium to caprine milk before pasteurization also resulted in a lower score for the appearance of the cheese with carbonate.
A previous study [
91] also showed that adding calcium could neutralize the goaty taste, as no goaty aftertaste was found in cheese manufactured from milk with the addition of calcium amino acid chelate, which was observed in control cheese. The reason for the characteristic goaty taste and odor not always acceptable to consumers is the presence of 4-methyl-octanoic, 4-ethyl-acetic, hexanoic, octanoic, nonanoic, and decanoic acids in goat milk [
121,
122]. Moreover, the acid profile of goat milk fat affects its organoleptic characteristics, mainly its odor. Goat milk fat contains a significantly higher amount of short- and medium-chain fatty acids than cow’s milk, including C 6:0 caproic acid (about 6%), C 8:0 caprylic acid, and C 10:0 capric acid (about 15%). The human body more easily digests these acids in contrast to long-chain fatty acids, which are more abundant in cow’s milk, especially C 18:1 oleic acid. As much as 46% of lipoprotein lipase is located on the surface of fat globules, 46% in milk serum and 8% on the surface of casein micelles, while in cow’s milk, only 6% of lipase is located on the surface of fat globules. This enzyme improves the milk’s susceptibility to lipolytic processes, activated by cooling the raw material. As a result of spontaneous lipolysis, combined with a high content of short-chain fatty acids, a characteristic goaty odor is produced [
15,
48]. The curd obtained from goat’s milk is also characterized by lower viscosity and compactness, has a finer structure, and is very easily dispersed [
123].
According to Palacios et al. [
124], adding calcium should not induce alterations in the final product’s taste, odor, appearance, or color. It has been known that fortifying with calcium might intensify acidity, produce a chalky texture, and increase bitterness, thereby modifying the food’s taste. The taste impact of calcium ions varies based on the compound type, the food’s composition, and the manufacturing process. While high calcium chloride and calcium lactate concentrations may be unpleasant, most calcium salts taste neutral. Additionally, using large amounts of calcium carbonate can increase a chalky flavor and a gritty mouthfeel. Most calcium compounds are colorless or white, exerting no influence on the product’s color [
125]. However, specific insoluble calcium compounds might lighten the food’s color. Conversely, soluble salts could interact with other food constituents, like tannins or anthocyanins, leading to darkening or a change from red to blue.