1. Introduction
The colostrum is the secretion produced by the mammary gland immediately after birth [
1]. It represents a rich source of vitamin A with relatively high concentrations of caseins and albumin, containing many essential nutrients in higher concentrations than those usually found in mature milk [
1,
2]. For instance, Jersey cows’ colostrum 24 h after birth presents 4% fat, 15% proteins (12% caseins), 1,5% lactose and 489 IU/dL vitamin A [
3]. Compared to milk, colostrum generally contains less lactose and has a higher content of other components such as fat, protein, ash, vitamins, hormones, and immunoglobulins. After three days, the lactose content increases, while the percentage of other components gradually decreases [
1,
4]. In addition, bovine colostrum (BC) contains bioactive components in relevant amounts, including growth factors, immunoglobulins, lactoperoxidase, lysozyme, lactoferrin, nucleosides, vitamins, peptides, and oligosaccharides, which are extremely relevant to health [
5]. Immunoglobulins can account for more than 80% of total proteins in BC; therefore, its commercial value is currently quoted by the protein concentration and immunoglobulin levels, especially IgG [
6,
7]. Recent research has shown that immune defense proteins in bovine colostrum may be related to protective effects against respiratory diseases such as those caused by SARS-CoV-2 infection (COVID-19) [
8]. Bioactive molecules are allegedly responsible for the effect of passive immunity when BC is consumed by humans [
9]. Despite considerable differences between BC and human colostrum compositions, BC has good tolerability in the human organism [
6] and it is well accepted by most consumers [
7].
The demand for innovative foods grows every day as consumers consider nutrition to address a wide range of health conditions. In this way, industries and research centers promote initiatives to support the production of nutraceuticals and functional foods. Food companies are developing their product lines with a primary focus on promoting people’s health [
10]. In this sense, some products based on bovine colostrum have been developed and are already commercialized as food supplements in countries such as New Zealand, United States, Europe, and China [
11]. Nevertheless, a wide variation in the bioactivity was detected in commercially available colostrum products such as powders and capsules [
7]. A crescent number of patents has been registered across the globe claiming health benefits to colostrum products, with emerging processing technologies being developed to preserve the therapeutic properties of BC bioactive compounds [
12].
Regarding food products, yogurts [
13,
14], mixtures for beverages [
15], cheeses [
16,
17,
18], ice cream [
19], nutritional bars, jellies, and ready-to-drink beverages have used or might use BC as a functional ingredient [
20]. Dairy products, such as cheeses, are a valuable source of proteins, lipids, vitamins, and minerals, and their global consumption is expected to increase by around 13.8% between 2019 and 2029 [
21]. Thus, the production of mixed cheese with milk and colostrum has emerged as an alternative way of utilizing surplus colostrum and an innovation in the dairy industry for providing possible benefits because of the presence of immunoglobulins, which adhere to the intestinal mucosa, functioning as a protective layer and preventing pathogenic microorganisms from colonizing [
22].
Considering the worldwide consumption of cheese, developing this type of product with the inclusion of colostrum could be an innovative alternative to utilizing the surplus production of this raw material. Furthermore, once the health benefits of colostrum and its potential for new products are understood, there is an opportunity for industries to cater to different consumer profiles [
18].
In this sense, this study aimed at (i) developing fresh and mature cheeses added with different bovine colostrum levels and (ii) characterizing the physical-chemical and sensory properties of these cheeses.
3. Results and Discussion
The characteristics of the milk and colostrum used to manufacture the cheeses can be seen in
Table 1. The milk composition is within the legal standards of Regulation No. 76 (IN 76) of the Ministry of Agriculture, Livestock and Supply [
28].
The average colostrum composition values are higher when compared with milk, except for lactose and fat, which had a lower concentration. Conte and Scarantino [
36] report that a gradual increase in lactose values during lactation is expected, particularly in the first days after calving. Sobczuk-Szul et al. [
37] show 23.34 g 100 g
−1 for solids-not-fat in colostrum from Jersey cows, which is higher than the value found in this study (17.46 g 100 g
−1). The 23 g 100 g
−1 total solids value colostrum from Jersey dairy cows is reported by Morrill et al. [
38], being slightly higher than that found in the present study (21.52 g 100 g
−1).
Oliveira et al. [
39] report that the high protein concentration in colostrum is related to the greater amount of casein and immunoglobulins. These immunoglobulins have the function of protecting the calf from various diseases until its body is able to develop its own defense cells. Clinical trials have proven that bovine colostrum immunoglobulins may also benefit human health. Among them, Potiroglu and Kondolot [
40] conducted a study on using bovine colostrum in treating children with upper respiratory tract infections due to IgA deficiency. They observed a reduction in the severity of the infections. Those researchers emphasize that no adverse effects are followed by the patients’ mothers. The use of colostrum for producing immunoglobulins on an industrial scale is interesting because it has high bioavailability and safety compared to blood products [
23]. This makes bovine colostrum a source of bioactive compounds of interest for developing functional foods.
Colostrum shows a pH of 6.4 and acidity of 0.25 g lactic acid/100 mL (
Table 1). The colostrum pH is higher than that reported by Saalfeld et al. [
41] with a pH of 6.29, while the acidity value is similar to colostrum within 24 h from calving (0.25 g of lactic acid/100 mL; [
41]). The acidity value is probably related to the presence of solids-not-fat, such as albumin, caseins, and phosphates; thus, when colostrum is characterized by high protein content, high acidity is expected [
41]. Nardone et al. [
42] also observe higher titratable acidity for colostrum when compared to milk and report a positive correlation with its protein content.
Regarding the composition of cheeses made by processing milk with colostrum (
Table 2), moisture results ranged from 44.77 to 63.22 g 100 g
−1. Differences in moisture between the samples according to the colostrum level and the maturation time (
p < 0.05) are observed. All the fresh cheese formulations with added colostrum (1F, 2F, and 3F) can be classified as very high moisture cheeses, as their moisture content is greater than 55.0 g 100 g
−1. The 0B and 1C cheeses are within the standards for medium-moisture cheeses, with percentages within 44.77 to 45.9 g 100 g
−1 [
23]. The remaining aged cheeses presented moisture ranging from 46.59 to 63.22 g 100 g
−1; therefore, they were classified as high-moisture (46–54.9 g 100 g
−1) to very high-moisture cheeses (above 55 g 100 g
−1) according to the Brazilian regulation [
26]. As expected, the moisture content of the cheese samples is directly linked to the maturation time applied. Cheeses with a short maturation time tend to be moister than cheeses with a lengthier maturation time [
43]. Evaluating the characteristics of rennet-type cheese produced using cow’s milk, Roig et al. [
44] and Santos et al. [
45] observed that the high moisture of the cheeses was due to the greater presence of denatured whey proteins because of the use of pasteurized milk. When analyzing the variability of cheese moisture content in this study, the pasteurization effect seems to affect cheese obtained from milk added with colostrum. According to Souza and Saad [
46] and Santos et al. [
45], another explanation for the difference in cheese moisture would be related to milk and colostrum pH, as the concentration of hydrogen ions leads to a reduction in repulsive forces and a consequent increase in the aggregation of casein micelles, which may explain the lower moisture retention in cheese obtained from only milk.
The treatments with the addition of 15 and 25 mL of colostrum per 100 mL of milk in cheeses matured for 20 and 40 days (3B and 1C, respectively) yielded the highest ash values. The simultaneous effect of colostrum addition and maturation promotes a higher concentration of this component in cheese. Indeed, significant differences (
p < 0.05) are found between different concentrations of colostrum additions, as well as between maturation times (
p < 0.05). Our cheeses added with colostrum reached a higher ash content than those reported by Assunção et al. (3.02 to 3.24 g 100 g
−1) for similar types of artisanal spicy cheeses without colostrum [
47].
Among the treatments, type 0B cheese is classified as fatty cheese, as it has fat in the dry matter within the limits of 45.0 to 59.9 g 100 g
−1 [
26]. Cheeses 0B and 0F showed the highest percentages of FDM with significant differences (
p < 0.05) compared to the other formulations. The 2A cheese sample has the lowest lipid content which is consequently reflected in the FDM (21.21 g 100 g
−1), constituting the lowest value among all treatments. Thus, according to Brazilian standards, cheese 2A is classified as reduced fat (fat content between 10.0 and 24.9 g 100 g
−1) [
26]. All the other cheeses are classified as within the semi-fat criteria, including those with fat content in the dry matter between 25.0 and 44.9 g 100 g
−1 [
26]. The reduction in the lipid index observed in the cheeses with added colostrum can be explained by the differences between the high lipid content found in the fresh milk used for making the cheeses (5.4 g 100 g
−1) and the percentage of this component in the 24-h colostrum (4.05 g 100 g
−1). It may also be due to the formation of more fragile curds, which, according to Sousa et al. [
48], affect the ability to retain fat, influencing the centesimal composition.
Cheeses produced from a different proportion of milk and colostrum are also significantly different regarding SNF (
p < 0.05). This trait is important because it allows the assessment of fat expressed in relation to total dry matter (TDM), correcting for the variation that may occur because of moisture losses [
49]. The control cheese (0B) shows the highest FDM, with this being justified by the higher fat content (5.40 g 100 g
−1) of milk compared to that in the colostrum (4.05 g 100 g
−1). According to Foley and Otterby [
2], bovine colostrum fat decreases with the time interval from calving (fat equal to 6.7 g 100 g
−1 postpartum, 5.4 g 100 g
−1 at 24 h, and 3.9 g 100 g
−1 at 72 h). Raimondo et al. [
50] reported a high quantity of fat colostrum in Jersey cows, from 1.35 ± 1.17 g/dL on the first day from calving to 3.09 ± 2.19 g/dL on the third day of lactation.
The protein content of cheese is similar among treatments, although the percentage was slightly lower in samples without colostrum addition. This can be justified by the higher whey protein content in colostrum and the low proportion of milk’s total protein content [
51].
The titratable acidity of cheese (
Table 2) is expressed as a percentage of lactic acid and varied between 0.02 to 0.08 among treatments, presenting a lower variability compared to that reported by Sousa et al. [
48] for traditional rennet cheese (0.12 to 1.01). Those authors stated that the acidity resulting from lactic acid production has a direct influence on the expulsion of whey, especially during syneresis. In addition, acidity can influence the texture [
52], microbial activity, and maturation index of cheese [
48]. Thus, the low titratable acidity observed in this study reflects the pH values found in the cheese formulations.
Cheese pH mean values (
Table 2) range from 5.02 (3C) to 6.23 (3F). The pH of the fresh cheeses among treatments gradually increased as the colostrum proportion in the formulation increased. A similar pH was found by Simon and coworkers for a cheese made with 100% colostrum (6, 15) [
18]. The presence of immunoglobulins, considered the main antimicrobial factor of colostrum [
50], possibly affected the fermentation process by the lactic acid bacteria added to the cheeses, even if the proteins that remain soluble (including immunoglobulins) are drained in the whey during curd formation. Further studies are needed to analyze the lactic acid bacteria action in cheese fermentation using milk added with colostrum.
Water activity values of cheese samples vary between 0.94 and 0.99 (
p < 0.05;
Table 2). It is known that cheeses with high water activity levels are more susceptible to high microbial development [
53]. Thus, the activity is inversely proportional to the shelf life of cheeses. In general, the longer the ripening period, the lower the water activity; however, in our experiments, no significant differences were observed between ripe and fresh cheeses, meaning the maturation time was not long enough to produce changes in a
w.
Regarding the measurement of color, we report that the variation in the colostrum added to milk produces differences among cheese samples (
Table 3). The cheeses of the present study generally show medium luminosity (L*), with a predominance of yellow (b*) and green (a*). Thus, the cheeses analyzed herein were characterized as yellowish-white, resembling the characteristics of rennet cheese. The L* brightness values ranged from 55.43 to 83.44. The negative a* value represents the intensity of the green color, while the positive value refers to the red one. The b* values ranged from 14.07 to 34.04, representing the intensity of the yellow color.
Generally, increased yellowing is directly related to the amount of fat due to the saturation of adipocytes with beta-carotene from animal metabolism [
54,
55]. During ripening, the concentration of non-aqueous components usually leads to color changes. Although slight differences in the yellowing index (YI) between fresh and matured cheeses can be observed in this study (40-day ripe cheeses achieved YI higher than the fresh formulations), there was no statistical relevance of maturation time on this parameter, except for the cheese produced from milk with the addition of 20 mL 100 mL
−1 colostrum.
Table 4 presents the characteristics of the cheese texture profile among treatments. According to Fontan [
56], cheese texture is affected by composition and maturation. The F0 and A0 samples showed greater firmness (
p < 0.05). There is a tendency to lower firmness in cheeses with increasing colostrum levels in the formulation. These data are consistent with cheese moisture since they present a greater solids dispersion and, therefore, a lower firmness.
Pereira et al. [
57] studied the correlation between the instrumental and sensory texture of several similar commercial types of cheeses. They found that cheeses with low moisture content were generally the firmest. Such findings confirm the results of this work since the control cheese with the lowest moisture percentage (47.52 g 100 g
−1) was the firmest, while the cheeses with the colostrum addition had the highest moisture content and the lowest firmness.
Cohesiveness is instrumentally assessed as the amount of energy necessary to break the internal structure of the cheese, and in sensory analysis, it is defined as the degree to which cheese is compressed between the teeth before breaking [
58]. In the present study, this parameter ranged from 0.34 to 0.57, with fresh control cheese having the lowest value (
p < 0.05). Some of the values found in this study are close to the work of Andrade et al. [
59] in evaluating industrial and artisanal cheeses, finding results ranging from 0.59 to 0.67 and 0.49 to 0.65, respectively.
Among all the treatments, 0F and 0A showed greater chewability (
p < 0.05). According to the results obtained for this parameter, it is possible to observe that cheeses produced from formulations with higher amounts of colostrum were characterized by lower firmness. This phenomenon may possibly be associated with higher moisture content, as water in cheese acts together with fat as a lubricant between casein aggregates [
58]. Thus, the reduction in moisture content results in an increase in cheese hardness and chewability.
Cheese yield is primarily due to the milk quantity and the recovery in the curd of the protein and fat from the milk to the cheese [
53].
Figure 1 shows the cheese yield calculated in liters of milk per kilogram of cheese (L/kg), with the best performance for the formulation with the higher percentage of colostrum (6.08 L needed to produce one kg of cheese). There is also a significant difference (
p < 0.05) between the formulations without colostrum and with the lowest percentage of colostrum (15 mL).
All the cheeses in this experiment were produced with similar production technology to rennet cheese processing and showed a ratio of the amount of milk and colostrum below 10 L of the total volume for each kilogram of cheese produced, which indicates a good yield when compared to cheeses with the same moisture content [
60,
61]. According to Dutra [
62], the average yield for rennet cheese manufacturing by the traditional process is between 10.5 and 12.5 L of milk per kilogram of cheese.
The microbiological profile of milk, colostrum, and cheese samples met the Brazilian criteria determined by the national regulatory agency [
26,
33,
34], which establishes the absence of
Salmonella spp. and
Listeria monocytogenes in a 25 g sample, and a tolerance limit of 1 × 10
3 MPN/g for coagulase-positive staphylococci, 1 × 10
4 MPN/g for total coliforms, 5 × 10
3 MPN/g for thermotolerant coliforms, and 5.0 × 10
3 UFC/g for molds and yeasts.
Table 5 presents the descriptive statistics of sensory attributes obtained for the fresh cheese among different treatments. The appearance and color parameters scores ranged from 7.67 to 8.10 and 7.54 to 7.81, respectively, with no statistical differences (
p < 0.05) in these attributes between the samples.
The control cheese had the highest average for aroma (7.52), texture (7.83), and flavor (7.90) compared to the other treatments (p < 0.05). The control cheese also obtained a significantly higher overall evaluation (7.72). It is worth noting that despite the statistical differences, cheese from milk added with 25 mL 100 mL−1 of colostrum is the treatment showing the closest scores to the control one in terms of overall evaluation and purchase intent.
Moreover, the control cheese obtained the highest AI for all evaluated attributes (
Table 6). However, the 3F treatment scored the highest AI among cheeses produced from milk added with colostrum, except for the appearance and color attributes for which the 2F obtained the highest value.
It was further observed that all the evaluated cheese formulations obtained a satisfactory AI. Dutcosky [
35] suggested that a food product with good acceptability presents average AI values above 70. Good acceptance of colostrum-added dairy products has previously been reported; Saalfeld et al. [
41] observed sensory approval of dairy beverages enriched with colostrum silage. Mouton and Aryana [
19] analyzed the influence of colostrum on the characteristics of ice cream and recommended such an industrial application based on a sensory analysis by trained panelists.