Physicochemical quality of milk
Figure 1 expresses the density of pasteurized milk, pH, fat content, and dornic acidity of pasteurized milk used for making cheese. The results show that the density of milk varies between 1.028 and 1.031 with an average of 1.030 and a standard deviation of 0.0015.These values are within the range mentioned in the AFNOR standards., 1985. but the density of the skimmed milk used for test 4 is approximately 1.035, i.e. slightly higher than the value of the density of whole milk. According to Bonnefoye et al. (2002), for values between 1.028 to 1.032, the density of milk is classified as normal. As for the density of skimmed milk, it is greater than 1.035 (Vierling, 2008) since milk skimming leads to an increase in its density (Luquet, 1985).In our tests, the pH value of the milk varied between 6.5 to 6.8 with an average of 6.60 and a standard deviation of 0.11, so it is within the normal values for cow milk. According to (Hebboul et al., 2005; Dillon, 2008), pH is slightly acidic between (6.5 and 6.8). Bovine milk pH is between 6.6 and 6.8 (Antonio.c et al 2020). Fat values are between 28 g / l and 46 g / l with an average of 29.2 and a standard deviation of 9.12 for whole milk. The observation of the experimental values shows that the titratable acidity of milk is between 15.5 ° D and 18 ° D with an average of 16.83 and a standard deviation of 0.70, a value comparable to the NM 08.4.005 standard. These values are situated within the ranges of the AFNOR standard, 1985. The curve obtained (Figure 1) is characterized by an almost stable acidity value based on the studied samples, and the small variation in acidity is within the [15 -17 ° D] interval defined by AFNOR., 1985. So the obtained values of dornic acidity ensure the milk’s conformity for this parameter. The experimental data from the physicochemical characterization show a certain regularity in the milk’s quality. This is quite normal as all the supplies have been provided by a single supplier in order to allow consistency of the raw material in the cheese making tests.
Physicochemical quality during cheese manufacturing
pH: (Figure 2) shows that the pH values after the maturation step characterized by the presence of ferments vary between 6.2 to 6.6. The pH value after the coagulation step characterized by the addition of rennet is between 6.0 to 6.4. The ability of milk to coagulate depends on its initial pH (C. HURTAUD et al 2008). pH values drop from one step to another during processing, this drop is caused by the role and activity of starter cultures indicating lactic acid production. The production of this acid by lactic bacteria leads to a decrease in the pH of the medium (Guiraud et al, 2003). Lactic fermentation decreases around pH values of 4.6 and 4.8 (Antonio.c et al 2020). P. candidum consumes lactic acid for growth, deacidifying the surface of cheese and promoting lactate migration from the inside to the outside of the cheese (Antonio.c et al 2020) ABRAHAM et al., 2007).
Dornic acidity: The titratable acidity, expressed in Dornic degrees (° D) is from 15 to 18 ° D (figure 3). We distinguish natural acidity, which characterizes fresh milk, from a developed acidity resulting from the transformation of lactose into lactic acid by various microorganisms (CIPC lait, 2011). The value of titratable acidity after maturation is between 14.5 ° D and 20 ° D, and between 10 ° D and 71 ° D after the coagulation step. The value of titratable acidity is variable during milk processing as is observed in figure 3. It was found that the value of the titratable acidity for tests can increase then decrease until the renneting step as can be seen in the case of test 1, it can decrease consecutively like the case of tests 2 and 3, and can also increase consecutively as is the case for test 4, but for test 15 the value decreased to 10 ° D because of the diluted rennet added to milk.
Physicochemical quality of cheese
pH: During the production of Camembert cheese, its pH was measured after drainage and the values obtained are between 4.5 and 5. The changes in pH are shown in figure 4. On the cheese surface, pH increases rapidly to reach values between 5.9 to 6.3. In the cheese core, pH slightly changes to values between 4.2 and 5.9 but it was observed that pH values of cheese are similar to mean pH values between the rind of the cheese and its core (roughly from 5.8 to 5.99), similar to the ones reported by (Kikuchi, 1966) as well as the one reported by (Lenoir et al., 1985; Leclercq-Perlat et al., 2004a) indicating that for Camembert-type cheeses, pH rises quickly and reaches a value close to 7 on the cheese surface well before the end of the ripening, while the increase in pH inside the cheese is much slower.
Danton Batty et al 2018 reported that cheese pH during salting was 4.31, rind pH increased rapidly to reach a pH value of 6.98 and a maximum pH value of 7.92 at 35 days. Increases in core pH were slow, as expected, reaching 6.15 in 21 days. On day 50, rind pH and core pH were harmonized from 7.65 to 7.70. (Denise Felix da Silva et al 2020, Leclercq-Perlat et al., 2015; Spinnler & Gripon, 2004) reported that pH varied between 4.85 ± 0.1 and 7.2 0.1 in camembert cheeses, which is related to the development of microbial flora and, therefore, to the degree of maturation. Thus, the following authors (Antonio.c et al 2020 and SPINNLER, 2017) reported that external (rind) pH is around 7.0 and internal pH is around 6.0 at the end of the ripening period (5-6 weeks). The faster pH increase at the surface of the cheese in comparison to the core is due to the higher concentration of ripening bacteria at the surface. Surface microflora have two main functions in ripening: they produce enzymes; lipases and proteinases which hydrolyze fat and proteins. Peptidases hydrolyze small peptides and amino acids and they deacidize cheese surface. It is mainly yeasts and molds that have this function. By oxidizing lactate, CO2 is emitted, which contributes to the increase in pH from 4.8 to 5.8 (TORMO, 2010).
Dornic acidity: The Dornic acidity of the cheese increases during ripening to values between 43 ° D and 80 ° D for all test cheeses obtained during the research period (Figure 5). There is a strong increase in the titratable acidity of Camembert cheese compared to that of pasteurized milk, which indicates a significant lactic fermentation in this product. The acidity of milk increases over time as the lactose turns into lactic acid. This acidity constitutes an indicator of the degree of preservation for which Dornic degree (° D) is used (Hebboul et al., 2005; Dillon, 2008).
Microbiological quality
Microbiological quality of milk: Table 2 shows a total absence of pathogenic bacteria which means that the milk’s microbiological quality is satisfactory, the pasteurization was done well.
Microbiological quality of cheese (Camembert): Table 3 shows the results of the microbiological analyses of cheese, the germs counted are considered as indicators of the quality of cheese as well as hygiene practices during production. A total of four tests have either less than 9 bacterial colonies or no colonies at all in the case of staphylococcus. Enumeration is performed if the number of colonies is between 30 and 300 colonies, but in our case we found that the number of colonies is less than 30 so our cheese complies with Moroccan standards from a hygienic standpoint.
Viability rate of ferments
The objective of the microbiological analysis of ferments is to characterize lactic flora, which makes it possible to learn if this flora is alive as is required by standards. The results of the microbiological analyses of the ferments expressed in CFU/g are presented in Table 4. For the ferments used during this work the composition was not mentioned on the ferment packaging so we used the commercial names of ferments, e.g. mesophile (Flora Danica). The results of the microbiological analyses of the 4 samples of ferments were determined on the same day the work was carried out. Each ferment conveys the concentration of living cells used for each test, it was observed that the viability rate decreases successively over time, for example, in the case of mesophilic ferment, cell concentration used in the first test is approximately 3.9 x 103, it decreases to 2.4 x 102 CFU/g in test 7. The same was observed for other ferments such as thermophile, yeast and mold. This means that the viability rate is increasingly affected depending on storage temperature and duration, these two parameters influence the quality of the ferments. For tests from 8 to 15, we tried to use new ferments similar to the ferments used in the first tests, with the only difference being the survival rate of the bacterial cells contained in the ferments. The change in ferments led to a higher result of surviving strains than the previous ferments, this causes a change in the transformation criteria observed during the first tests for coagulation, gel type, and cheese yield. The viability rate differs from one ferment to another and from one test to another, for example, the concentration of new ferments is about 8.5 x 103 for mesophile, 6 x 103 for thermophile, 104 for yeast, and 9.5 x 103 for mold. But these values decrease more and more over time. So if the survival rate of the strains is low, then the cohesion between curd grains is minimal which means that the small curd grains are passed into the serum thus a low yield of cheese is obtained. According to Leclercq-Perlat MN et al, yeasts are added to milk at a concentration varying between 104 and 106 cells (or spores) / ml of milk. Ferments inoculated simultaneously should be found alive in cheese at a higher rate than that of surviving lyophilized ferments. This is because the ferments during coagulation, drainage and ripening were multiplying, leading to a rapid increase of colonies. The concentration of the ferments used in tests 4 to 7 ranges from low to very low, which is why coagulation time was increased. For tests from 8 to 15 the ferments were used at a higher concentration which coagulates the milk in an hour and 15 minutes and produces high quality cheeses. In France, the 1963 decree specifies that these lactic acid bacteria must remain alive until the cheese is delivered to the consumer at a rate of at least 10 million bacteria per gram. In fact, in France, on Camembert cheeses produced on a pilot-scale, the active growth phase of G. candidum is observed in the first 12 days of ripening and its population can reach 107CFU / g [Leclercq Perlat MN et al (2004)].
Gel type and ferments quality
In this work, fifteen samples of cheese were produced in the laboratory. Each test is characterized by a fat content and a specific microbiological quality of the ferments. Table 5 shows that the quality of the ferments used for tests 1-2-3 is high and that the fat content varies between 28 and 36 g / l, which produces a firm gel for 1h15min. The milk used is skimmed and contains only 3g / l in fat content, and the quality of the ferments used is low, which produces during 1h 15min a crumbly gel, in this test it was observed during the molding that most of the small curd grains are passed into the serum which produces a small amount of curd. For test 5, it was observed that during 1h15min of coagulation a very crumbly gel is obtained and due to this the coagulation time was increased to obtain a firm gel, but during 3h a slightly crumbly gel is obtained due to the poor quality of ferment even if the fat content is important 29g / l. So in this case it can be deduced that the quality of the ferments plays a more important role on gel type. For test 6, gel type was monitored alongside coagulation time, and after 1h15 min a very crumbly gel was obtained and after 3h the gel obtained is crumbly, fortunately, after 7h 30min a firm gel is obtained, so coagulation time must be increased if the quality of the ferments is low in order to give lactic acid bacteria the chance to multiply. For test 7, even if the coagulation time is increased to 6 hours, the quality of the ferment impacts gel type negatively, resulting in a soft gel. For tests from 8 to 14, a firm gel is obtained for 1 hour 15 minutes thanks to the high quality of the ferments used. For test 15, it was observed that the fat content of 46% and the quality of the ferments influence gel quality by contributing to the production of a very firm gel. It was observed that the growth rate of the strains and the fat content play a very important role on curd cohesion, which determines gel type and coagulation time. So it can be deduced that if the growth activity of the strains is high, coagulation time is short, and the gels range from very firm to firm, and if the growth activity of the strains used is low, the coagulation time is long, and the gels obtained are either soft or crumbly. It was also observed that the gel is in the form of small grains which pass with the serum. pH influences setting time, drainage and coagulum firmness (C HURTAUD et al 2001; Mietton et al, 1994; Martin er Coulon, 1995), thus cheese stabilization is mainly achieved by controlling the rate and level of lactic acid development during drainage for a final pH value greater than or equal to 5.2 after drainage (Gripon, 1997; Danton Batty et al 2018).
Ferments quantity
It was observed in this work that the cheeses from tests 11 to 15 are of higher quality than the cheeses from other tests. It was also observed that the tests made with a higher quantity of yeast than mold produce slightly harder cheeses than the ones made using two doses of mold for one dose of yeast. It was found that the quantity of the ferments used to make Camembert-type cheese during this work is acceptable and is between the values mentioned in Table 6, if the quantity of rennet is between 0.25ml / l and 0.4ml / l, and if the viability rate of the bacterial strains is between the values mentioned in Table 6, the latter values make it possible to reduce milk pH to 6.2 for 40 min to allow rennet to perform its activity when its activity drops rapidly above pH 6.3. So rennet must be added if milk pH is less than 6.3. The values of these parameters (viability rate, amount of ferment and amount of rennet) give the gel a good (firm) quality for 1h15 min at a temperature of 35°C. It was also observed that if the bacterial viability rate is low, the quantity of ferments must increase. The best dose formula of ferment used in this work is two doses of mesophiles for one dose of thermophile and two doses of Penicillum C mold for two doses of Geotrichum C yeast.
Yield
Yield assessment during the cheese making process
During the manufacturing of Camembert, the quantity of serum is measured, weighings and samplings were carried out for anlyses, in order to monitor the evolution of the weight of cheese before and after ripening, Dornic acidity, pH of the top layer and underlayers as well as the appearance of cheeses.At the beginning of ripening, it was found that the cheese produced by the ferment has a low concentration disturbing a large amount of water (figure 6),even if the ripening conditions conform to standards, a temperature of 12°C and a humidity of 90%. Cheese yield is the mathematical expression of the quantity of cheese obtained from a given quantity of milk (often 100 L or 100 kg) (VANDEWEGH, 1997). Cheese yield is expressed according to the following formula (HANNO et al. 1991; LIBOUGA et al. 2006).
Yield = (FQ / IQ) x 100
Yield: Yield of final product in%. / FQ: final quantity in g. / IQ: initial quantity of milk ml.
At the beginning of ripening, a cheese weighed on average 219.315g and approximately 160.85g after 15 days, i.e. an average loss of 58.465g; 26.6% and an average daily loss of 3.9g. The percentage of cheese produced in general during of this study is 6% to 13% (figure 8) . During this work, attempts to prepare Camembert using skimmed milk produced cheeses in smaller quantities than cheeses made using milk with high fat content, which shows that the higher the fat content, the greater the quantity of cheese. Cheese yields correspond to the amount of cheese that can be obtained with a fixed amount of milk. They mainly vary according to the quantity of water retained in the cheese, defined by the technological parameters and the protein and fat content of milk, with the latter being helpful with predicting cheese yields (C. HURTAUD et al. ).
Description of obtained cheeses
The evaluation of the sensory quality of Camembert cheeses is carried out by a jury of trained tasters who give for each sample to be compared with samples of Camembert purchased at large retail outlets, a score for sensory descriptors.
Visual appearance: All the cheeses obtained have thin top layers thanks to penicillium candidum. However, a defect was observed in the cheese obtained on test 7, such defect can appear when the milk used is skimmed or the ripening is insufficient or when the quantity of Geotrichum candidum is higher than penicilum condidum. This defect is classified among the texture defects of cheese due to which the resulting cheeses are too dry or plastery. The rind obtained from the cheese is very thin and flowery with a fluffy white coating. P. Candidaum is covered with a thin layer of mycelium on the Camembert surface. The cheese obtains its white and fluffy rind that characterizes it (Bockelmann, 2010). The acceptability of the sensory characteristics of cheese largely depends on the taste and shape during maturation. Two classes of important compounds contribute to flavor : volatile sulfur compounds and fatty acids. Free fatty acids contribute to the development of taste and aroma to a large extent. Lipolysis is one of the main biochemical processes that contribute to the development of taste during cheese ripening (Tatiana Voblikova et al 2020).
Texture: The cheese made during this work has a similar texture to the desired cheese, and was well appreciated by the tasting panel. It is characterized by a smooth and homogeneous paste, this can be explained according to NUNEZ et al. (1991), only test 7 cheese is dry and plastery. In this work, it was observed that the cheese produced using a higher quantity of Geotrichum C than Penicillium C has a hard rind, and due to that, we tried to make the cheese by the application of the following dose : two doses of PC for a dose of GC, which produced a flexible white to light yellow product with a better texture that isn’t runny, and without softness. The cheese is firm from the edges to the center. Fat decrease proved to be a challenge, as fat is important for the texture and taste of dairy products, especially for cheese. Fat decrease in cheese leads to an unwanted texture, a lack of taste or presence of extraneous flavors. The profile of fatty acids in the process of cheese maturation has changed significantly (Tatiana Voblikova et al 2020).
Taste: The tasting panel assessed the taste of the manufactured cheese, they judged it to be very acceptable: a slightly acidic and moderately salty taste with a mild mushroom taste, and a pronounced fruity flavor.
Color and odor: All the manufactured cheeses are characterized by a white rind which is formed by Penicillium C., a ripening ferment. Ripened cheeses have a hazelnut odor. The color, texture, odor and taste of all the samples meet the requirements for Camembert-type cheeses. In addition, the organoleptic qualities of the cheeses were assessed and compared to one another by the tasting panel.