Effect of addition of Syrian thyme (Thymus syriacus) on physiochemical and sensory quality of Sudanese Mudaffara cheese during storage

Abstract

This study was designed to introduce Syrian thyme (Thymus syriacus) as a new additive flavor for Mudaffara cheese. Mudaffara cheese was prepared from cow’s milk using the commonly used black cumin as control and Syrian thyme (0.3 and 0.5%) as treatment. The physiochemical properties and the sensory attributes were evaluated. The results indicated that Mudaffara cheese samples flavored with 0.3% Syrian thyme were significantly (P < 0.05) higher in protein and acidity content compared to the other cheeses. During the storage period, significant (P < 0.05) differences were obtained for all the studied physicochemical parameters except the ash content. Also the interaction of additives and storage period showed significant (P < 0.05) effect on the protein and fat content of Mudaffara cheese samples. However the additives had no significant effect on all sensory characteristics except the general acceptability. According to the panelist test, the overall acceptability of Mudaffara cheese sample flavored with 0.5% Syrian thyme showed the highest numerical score compared to the others Mudaffara cheese samples. During the storage period, Mudaffara cheese samples revealed significant (P < 0.05) variations in texture, acidity, flavor, taste and general acceptability scores. This study concluded that Mudaffara cheese can be flavored with Syrian thyme at a rate of 0.3 and 0.5%.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-022-05634-7.

Introduction

Cheese is a concentrated form of milk with the benefit of prolonged shelf life and an important health contribution to human. It is primarily a rich source of essential nutrients such as proteins, bioactive peptides, amino acids, fat, fatty acids, vitamins and minerals (Walther et al. 2008).

Cheese is a dairy product that has played a key role in human nutrition for centuries and it is the most popular dairy product in Sudan. The braided; semi hard cheese (Mudaffara) is among the most popular types of cheese in Sudan (Mohammed Salih et al. 2011; Harun et al. 2015; Farah and El Zubeir 2020). Mudaffara cheese is a braided, unmatured semi hard cheese, which originated in the Mediterranean area and now is widely produced and consumed in Sudan (Mohammed Salih et al. 2011; Abdalla and Gamer Eldin 2018; Farah and El Zubeir 2020). Mudaffara cheese is a pickled semi-hard cheese braided into a characteristic shape, to which spices such as black cumin (Nigella sativa) are added (Abdalla et al. 2019). Mudaffara cheese production in Sudan is a small business that each producer develops and adopted his own procedure for its production (Abdel-Razig et al. 2014).

Harun et al. (2015) reported 17.2 ± 2.13% for fat, 21.49 ± 2.53% for protein, 51.89 ± 12.25% for total solids, 10.96 ± 9.32% for ash and 0.48 ± 0.06% for acidity content of Mudaffara cheese. Sudanese braided cheese (Mudaffara) samples had a fat content of 26–37%, while 51% had low protein content (7–10%), moreover 83% of the samples had a total solids content of 55–70%, 70% of samples had an ash content of 3–5.99%, and 39% of the samples revealed highly acidic of 1.0–1.5% (Abdalla et al. 2019). The means reported for Mudaffara cheese by Farah and El Zubeir (2020) were 61.69 ± 0.12% total solids, 30.47 ± 0.31% protein, 22.00 ± 0.28% fat and 4.17 ± 0.06% ash and 0.46 ± 0.29% acidity.

Spices and herbs have been used as flavor, colour, aroma, enhancing agents and for the preservation of foods and the addition of herbs and spices or their extracts to different dairy products make these products act as a carrier for nutraceuticals (El-Sayed and Youssef 2019).

Thyme is an aromatic plant and is widely distributed over the Mediterranean area. The generic name comes from the Greek verb Thym, which translates to perfume, in allusion to the intense and pleasant aroma of the plant (Nieto, 2020). Thyme (Thymus vulgaris) is among the aromatic plants commonly used in Turkish traditional yoghurt drink, yoghurt and various cheese types. In addition to their taste and aromatizing uses in dairy products, bioactive molecules extracted from medicinal plants can be used as natural preservative additives due to their antimicrobial and antioxidant activity (Kaptan and Sivri 2018).

T. syriacus is used as herbal tea and condiment, fresh leaves are used for the aromatization of home-made jams, candies and similar confections, it is also known to have positive results for coughs and other respiratory complaints, as well as some cases of gastrointestinal disorders (Al Mariri et al. 2013).

Mudaffara cheese is commonly flavored with black cumin (N. sativa) seed. Due to some common flavored of Syrian thyme to black cumin, this study was designed to introduce it as a new additive for flavoring Mudaffara cheese. It is also meant to evaluate the effect of addition of Syrian thyme on the physiochemical and sensory quality of Sudanese braided (Mudaffara) cheese during storage.

Materials and methods

This experiment was conducted at the laboratory of Diary Technology, Faculty of Animal Production, University of Khartoum from 9/2/2020 to 24/3/2020.

In this study two different favoring additives (0.5% black cumin and Syrian thyme with two levels: 0.3 and 0.5% were added to the Mudaffara cheese. chemical compositions of cheese were determined weekly for 4 weeks, while the sensory evaluations were carried out for 2 weeks.

The fresh raw cow’s milk used in the processing of Mudaffara cheese in this experiment was obtained from the University of Khartoum farm on 9/2/2020.

Syrian thyme (T. syriacus), black cumin (N. sativa L.) and starter culture were obtained from the local market. Rennet sticks (Christen Hansen’s laboratories—Copenhagen, Denmark was used; 1 stick coagulate 50 kg milk).

Both Syrian thyme and black cumin were cleaned from impurities using hot water and dried before use. Thyme was crushed into powder form, while the whole seed of black cumin before added to the cheese paste.

Manufacture of mudaffara cheese

The steps for cheese processing were described previously by Farah and El Zubeir (2020).

After the milk was filtered and heated to 40 °C, 1% of the starter culture (Lactobacillus bulgaricus and Lactobacillus thermophilus) and 1% of dissolved rennet powder were added and stirred for 2–3 min to ensure uniform distribution of the rennet. The milk mixture was left undisturbed to coagulate into a curd. After about 40 min, coagulation was complete and the whey was drained from the curd that was cut into slices for more whey drainage. The curd was then incubated at 40 °C for 1.5 h to reach the required elasticity and acidity (0.54–0.60%). Every half an hour during this incubation, the inflatable of the curd was measured by dipping a small piece of curd (about 20 g) into hot water (85 °C), then holding it in hands, kneading and pulling it to form a cord of 2 m long. If the curd breaks before reaching this length, ripening is considered incomplete. When the curd became a smooth paste that showed satisfactory stretching to a rope of more than 4 m long and elastic, the curd was cut into strips. Then 4–5 pieces were taken at a time and put in the hot water (65–75 °C) for 3–5 min using wooden paddles until the curd became smooth. The curd was divided into three parts; 700 g each; for the two different flavoring additives (0.5% black cumin and Syrian thyme with the two levels: 0.3 and 0.5%. After that the additives were added to the hot paste before braiding. The curd was then hand worked and drawn to form a long rope which was then braided and washed by immersing it in cold water. The three types of cheese were taken after the cooking process and put in steel buckets. All the braided cheeses were immersed in sterilized salted whey (3% NaCl) for 12 h. Then all samples of Mudaffara cheese were stored in the refrigerator at 4 °C for 4 weeks.

Analysis of Mudaffara cheese

The chemical composition of Mudaffara cheeses was conducted at a week interval for 4 weeks. The fat content (Gerber method), the protein content (Kjeldahl method), total solids content, ash content and the titratable acidity were determined according to the AOAC (2000).

The scores of sensory attributes of Mudaffara cheese samples that were stored in the refrigerator were evaluated by 10 semi-trained panelists; who are familiar with Mudaffara cheese. The judgment was done for the appearance, color, flavor, texture, taste, acidity and overall acceptability. The evaluation was based on on the five-point scale according to the method described by Lim (2011) using sensory evaluation sheet (excellent = 5, very good = 4, good = 3, fair = 2 and poor = 1).

Statistical analysis

The data of the present study were analyzed using the SPSS (Statistical Package for Social Sciences) (version. 16). General Linear Model was used to determine the effect of treatment and storage period on the physicochemical and sensory properties of Mudaffara cheese. The Least Significant Difference test was used for the mean separation between the treatments. The level of significance (P ≤ 0.05) was used to consider the variations among the different treatments to get 95% countenance os accuracy. The graphs were plotted using Microsoft Office Excel 2007.

Results and discussion

Effect of additives on physicochemical characteristics of Mudaffara cheese

Total solids content

The total solids content of Mudaffara cheese was not affected significantly (P > 0.05) by the addition of 0.3 or 0.5% Syrian thyme (48.5 ± 4.5 and 46.0 ± 5.6%, respectively) and black cumin (47.7 ± 4.8%) as shown in Table 1. However Slman et al. (2020) found significantly higher total solids content of Syrian white cheese to which thyme powder was added at the beginning of the storage period and up to 45 days of the storage. Nonetheless, Slman et al. (2020) used higher inclusion levels (1 and 2%), whereas in this study lower levels were used (0.3 and 0.5%), which may explain the differences in findings.

Table 1.

Effect of flavored additives on physicochemical characteristics of Mudaffara cheese (M ± SD)

Treatment	Physicochemical composition (%)
	Total solids	Fat	Protein	Ash	Acidity
Black cumin (0.5%)	47.7 ± 4.8	20.6 ± 4.1	20.9 ± 1.6 c	3.2 ± 0.43	0.60 ± 0.12 b
Syrian thyme (0.3%)	48.5 ± 4.5	21.0 ± 3.9	24.1 ± 7.7 a	3.1 ± 0.30	0.74 ± 0.11a
Syrian thyme (0.5%)	46.0 ± 5.6	22.7 ± 3.5	22.6 ± 6.3 b	3.2 ± 0.51	0.71 ± 0.90 a
LS	NS	NS	***	NS	**

^a,b,cMeans bearing the same superscripts letters in the same column are not significantly different (P > 0.05)

M mean value, SD standard deviation, LS level of significant, NS not significant

***P < 0.001, **P < 0.01

Harun et al. (2015) and Abdalla et al. (2019) reported a higher total solids content (51.89 ± 12.25 and 58.19 ± 4.21%, respectively) for Mudaffara cheese than the one reported in this study (48.5 ± 4.5%).

The differences reported in total solids content could be due to differences in moisture content as a result of the method of manufacture and packaging used in each study. However the total solids content of Mudaffara cheese was significantly (P < 0.05) affected by the storage period (Table 2). It increased gradually at week 2 (51.0% ± 3.4) and then decreased at the end of the storage period. This might be because the cheese was immersed in its brine during the first 2 weeks and the decrease was the result of ripening. After week 2, the cheeses were kept in the refrigerator; this situation might have influence on ripening process. Similarly fluctuation of the total solids content of Mudaffara cheese during the storage was reported previously by Harun et al. (2015) and Abdalla and Gamer Eldin (2018). However slight decrease in the total solids of Mudaffara cheese during the storage was found by Farah and El Zubeir (2020). The difference in the total solids content of Mudaffara cheese may be due to several factors, including the close correlation between moisture content and the total solids, the preservation methods applied and the storage temperature (Abdalla and Gamer Eldin 2018 and Farah and El Zubeir, 2020). Also the expulsion of moisture from cheese curd is the reason for the increase in the total solids content of Mudaffara cheese (Harun et al. 2015). The increase in the total solids contents could be also attributed to a decrease in the moisture content as a result of lactic acid developments, which caused curd contraction (Abdalla et al. 2019). However the decrease in total solids content was due to the degradation of protein and lipolytic activity on the fat content. The refrigerator storage of Mudaffara cheeses after the second week might also be a reason for suppressing the microflora o the cheese and hence reducing the rate of protein and fat degradation.

Table 2.

Effect of storage period on physicochemical characteristics of Mudaffara cheese (M ± SD)

Storage periods	Physicochemical composition (%)
	Total solids	Protein	Fat	Acidity	Ash
Week 1	42.5 ± 3.1b	19.4 ± 2.3c	17.0 ± 2.5c	0.58 ± 0.09b	3.5 ± 0.37
Week 2	51.0 ± 3.4a	28.9 ± 7.3a	22.0 ± 3.2b	0.79 ± 0.05a	2.9 ± 0.42
Week 3	49.4 ± 4.2a	24.0 ± 1.6b	22.7 ± 0.8ab	0.73 ± 0.08a	3.3 ± 0.37
Week 4	46.7 ± 4.8ab	17.9 ± 1.2d	25.0 ± 2.7a	0.62 ± 0.12b	3.1 ± 0.31
LS	*	***	***	***	NS

^a,b,cMeans bearing the same superscripts letters in the same column are not significantly different (P > 0.05)

M mean value, SD standard deviation, LS level of significant, NS not significant

***P < 0.001, *P < 0.05

The interaction of the used additives and the storage period showed no significant (P > 0.05) effect on the total solids content of Mudaffara cheese (Fig. 1a). However, the cheese samples flavored with 0.3% Syrian thyme generally had higher total solids content during the storage period in comparison with cheese samples flavored with 0.5% Syrian thyme and black cumin. The reason could be due to the photolytic effect of Syrian thyme and that the Syrian thyme should be used at a rate of up to 0.3% and not more than 0.5%. This supported the findings drawn by Slman et al. (2020) who found that adding 2% of the thyme powder compared to that using 1% increases the percentage of the total solids in the cheese mass as well as the high concentration of the brine. This is mainly because Mudaffara cheese flavored with 0.3% Syrian thyme revealed higher protein content compared to other cheeses (Table 1). All types of Mudaffara cheese obtained during the present study comply with SSMO for the total solids content (SSMO 2007).

Fig. 1.

a Comparison of the total solids content of Mudaffara cheese flavored by black cumin and Syrian thyme during the storage. b Comparison of the protein content of Mudaffara cheese flavored by black cumin and Syrian thyme during the storage. c Comparison of the fat content of Mudaffara cheese flavored by black cumin and Syrian thyme during the storage. d Comparison of the ash content of Mudaffara cheese flavored by black cumin and Syrian thyme during the storage. e Comparison of the acidity content of Mudaffara cheese flavored by black cumin and Syrian thyme during the storage

Fat content

Data in Table 1 revealed that the fat content of Mudaffara cheese flavored with black cumin (20.6 ± 4.1%) was slightly lower compared to that flavored with Syrian thyme at 0.3% (21.0 ± 3.9%) and 0.5% (22.7 ± 3.5%). This suggested that the fat content is high in Syrian thyme compared to the black cumin. Also Jemaa et al. (2017) reported that for treated milk, in addition to casein antioxidant activity, T. capitatus essential oils also had contributed to the protection of milk fat from oxidation. This is because the antioxidants molecules from T. capitatus essential oils work against oxidation by donating their hydrogen atom to the lipid free radicals to stop the chain reaction from proceeding further.

Lower values were obtained by Harun et al. (2015) who obtained 17.2 ± 2.13% fat content for Mudaffara cheese. Also Abdalla and Gamer Eldin (2018) found that the fat content for Mudaffara cheese brined using 15% salt (19.38%). However Abdalla et al. (2019) reported a higher mean of fat in Mudaffara cheese (26.46 ± 4.94%). The fat content of the cheese was not affected significantly (P > 0.05) by the addition of Syrian thyme and black cumin. This is because both of the flavored additives used are aromatic plants. Moreover various spices, herbs and their volatile oils are included and often identified as being among the most effective natural antioxidants (Bhat et al. 2014). Also Nieto (2020) stated that the development of functional foods could be enhanced by the inclusion of thyme because of its value-added properties, which could be of great interest to both the scientific community and the food industry. In particular, the T. syriacus plant extracts are found to contain various phytochemicals with biological activity that is attributed to the medicinal characteristics of this plant, which can be of valuable therapeutic uses (Tamim and Akrama 2020). Moreover the chemical composition and high-level of antimicrobial activity of its essential oil and major constituents of T. syriacus are efficient against some Gram-negative human pathogenic bacteria (Al Mariri et al. 2013).

The fat content of Mudaffara cheese was affected significantly (P < 0.001) during the storage period, it increased significantly with the advancement of the storage period (Table 2). The fat content of Mudaffara cheese was significantly (P < 0.05) affected by the interactions of the used additives and storage period. The highest value of fat content was found in cheese samples flavored with 0.3% Syrian thyme at week 4 (26.5% ± 2.1), however the lowest value of fat content was found in cheese samples flavored with black cumin (Fig. 1b). The increase in fat content of Mudaffara might be due to high moisture loss during the storage (Harun et al. 2015 and Farah and El Zubeir 2020). The increase in fat content till day 21 might be due to the high moisture loss during the storage, while the decrease in the fat content at end of the storage period may be attributed to breakdown of fat by microorganisms and their loss from cheese (Harun et al. 2015).

Protein content

As shown in Table 1, the protein content of Mudaffara cheese was significantly (P < 0.001) affected by the addition of Syrian thyme. The cheese samples flavored with 0.3% Syrian thyme (24.1 ± 7.7%) showed the highest value of protein content in comparison with the cheese samples flavored with 0.5% Syrian thyme (22.6 ± 6.3%) and black cumin (20.9 ± 1.6%). Abdalla et al. (2019) reported a lower mean for protein (14.72 ± 8.14%) content of Mudaffara cheese in comparison to the current findings. Also Harun et al. (2015) reported 21.49 ± 2.53% for the protein content of Mudaffara cheese. The present findings agree with El-Sayed (2017) who reported that the higher ratios of thyme powder in the blend of Ras processed cheese could lead to the loss in protein network, which is due to the decrease that occurred in the intact casein of the blend with increasing the thyme powder. More explanation was also stated by Tarakçı and Deveci (2019) who found that the cheese incorporated with black cumin possessed higher ripening rates than others added spices and the highest decrease in the amount of β-casein was observed in the thyme-added cheese, followed by the black cumin-added cheeses. They added that thyme was also more effective on αs1-casein fraction. On the other hand, when considering the starters’ contribution to the proteolysis of aS1-casein it would be possible to suggest that the antimicrobial activities of tested spices inhibited the microbial protease activities (Tarakçı and Deveci 2019).

As shown in Table 2, the protein content of Mudaffara cheese was significantly (P < 0.001) affected by the storage period. It increased gradually at week 2 (28.9 ± 7.3) and then decreased at the end of the storage period. The reason for the increase could be due to the loss of the moisture content from the cheese, while the reduction that occurred after week 2 might because of refrigerating storage of the cheese. However Altahir et al. (2014) and Farah and El Zubeir (2020) found that the protein content of Mudaffara cheese was found to decrease significantly during storage. The reduction in protein content was possibly due to the activity of proteolytic microorganisms leading to protein degradation. However the expulsion of moisture from cheese curd could be another reason for the increase in protein content of Mudaffara cheese (Harun et al. 2015).

The interactions of the additives used and the storage period showed a significant (P < 0.001) effect on the protein content of Mudaffara cheese (Fig. 1c). The highest value of protein content was found in the cheese samples flavored with 0.3% Syrian thyme at week 2 (35.2% ± 0.00), while the lowest value of protein content was found in the cheese samples flavored with 0.5% Syrian thyme at week 4 (16.9% ± 0.39). Storing of Mudaffara cheese in the refrigerator after week 2 might be the reason of these contradictory findings. Hence further futures research should be conducted in order to verify and explain the various reasons that might involved during the storage of the cheeses to which some aromatic plants are added. The decrease in the protein content during pickling was a direct result of protein degradation leading to the formation of water-soluble compounds, some of which were lost in the pickling (Farah and El Zubeir 2020). Tarakçı and Deveci (2019) reported that more decrease in the amount of β-casein was found in the thyme-added cheese compared to the cheese incorporated with the black cumin and the increase in parameters of proteolysis leading to protein degradation during cheese ripening is closely related to the increase in bacterial activity and enzyme activity over time.

Ash content

More or less similar values of ash content of Mudaffara cheese flavored with black cumin, 0.3 and 0.5% Syrian thyme were obtained (3.2 ± 0.43, 3.1 ± 0.30 and 3.2 ± 0.51%, respectively). Moreover the results in Table 1 showed that the Syrian thyme and black cumin did not show a significant (P > 0.05) effect on the ash content of Mudaffara cheese. The small variations in the obtained values might be due to the mineral content of the used concentration of the spice added. Thyme has a high level of iron, manganese and copper (Ozkan et al. 2007). The rate of salting the cheese during this study was 3% for all types of Mudaffara cheeses. Similarly the ash content of Mudaffara cheese reported by Abdalla et al. (2019) was 3.52 ± 1.07%. However Harun et al. (2015) reported a higher value (10.96 ± 9.32%) for the ash content of Mudaffara cheese. The variation is an indication of the different level of sodium chloride used for salting the cheese.

The storage period had no significant effect (P > 0.05) on the ash content of Mudaffara cheese. However this study showed a decrease in the ash content of Mudaffara cheese during the storage (Table 2). The results are in disagreement with those who reported that the ash content of cheese increased as the storage period progressed (Altahir et al. 2014).

The results in Fig. 1d showed that the interactions and the used additives and storage period had no significant (P > 0.05) effect on the ash content of Mudaffara cheese. The highest value of the ash content was found in the cheese samples flavored with black cumin at week 1 (3.8 ± 0.05%), whereas the lowest value of the ash content was found in the cheese samples flavored with 0.5% Syrian thyme. This might be because the minerals content of Syrian thyme was low compared to those in black cumin seeds. Similarly Farah and El Zubeir (2020) found that the ash content of Mudaffara cheese was significantly (P < 0.001) higher on day 0 and 7 (4.17 ± 0.06 and 4.08 ± 0.06%, respectively and significantly (P < 0.01) lower value was obtained at day 35 (2.93 ± 0.06%). The ash content in curd and whey was very much affected by the diffusion of salt from curd into the whey.

Acidity content

Table 1 illustrated that highest value of acidity content was found in Mudaffara cheese samples flavored with Syrian thyme at 0.3% (0.74 ± 0.11%) and 0.5% (0.71 ± 0.9%), while the lowest value was found in Mudaffara cheese samples flavored with black cumin (0.6 ± 0.12%). However lower value was reported by Harun et al. (2015) for acidity content (0.48 ± 0.06%) of Mudaffara cheese. The acidity of Mudaffara cheese revealed 0.978 ± 0.294% (Abdalla et al. 2019). The variations could be due to the antimicrobial properties of Syrian thyme and black cumin.

The acidity content of Mudaffara cheese was significantly (P < 0.01) affected by the addition of Syrian thyme (Table 1). Generally higher acidity content was found for Mudaffara cheese flavored with Syrian thyme compared to that flavored with black cumin. The higher level of the acidity in Mudaffara cheese flavored with 3% Syrian thyme compared to that using 5% Syrian thyme is indicative of the antimicrobial activity of the thyme (Al Mariri et al. 2013; Kaptan and Sivri 2018; Tamim and Akrama 2020) as well as black cumin (El Zubeir et al. 2005; Abdel-Gadir et al. 2013). El-Sayed (2017) found that increasing the thyme powder (0.1, 0.2, 0.3, 0.4 and 0.5%) in the base blend of Ras cheese samples decreased the pH values. Moreover they concluded that thyme powder concentrations especially 0.50% thyme; showed the highest effect on the total bacterial count, which suggested its antimicrobial effect on cheese microflora. Similarly Slman et al. (2020) observed higher acidity in the white cheese using 2% thyme powder compared to that using 1%, they attributed this to the presence of some components in thyme that caused the acidity of the product to rise when the added quantities are increased. This could also be due to the high pH value of thyme powder used in all treatments compared to the pH of the control Ras cheeses (El-Sayed, 2017).

The titratable acidity was significantly (P < 0.001) affected by the storage period (Table 2). It increased gradually until week 2 (0.79% ± 0.05), then it decreased at the end of the storage period (0.62% ± 0.12). This might be because Mudaffara cheese was kept in its whey for 2 weeks and was removed from it during the rest of the storage that was done in the refrigerator.

These results are in line with those reported that the acidity content of Mudaffara cheese increased gradually until day 21, then it decreased at the end of the storage period (Harun et al. 2015; Farah and El Zubeir 2020). The increase in the titratable acidity may be due to the growth of lactic acid bacteria that leading to the increase of lactic acid content (Abdalla et al. 2019).

Data in Fig. 1e revealed that the acidity content of Mudaffara cheese did not affected significantly (P > 0.05) by the interaction of the additives used and the storage period. Generally, the cheese samples flavored with black cumin showed lower acidity content during the storage in comparison to the cheese samples flavored with 0.03 and 0.5% Syrian thyme. The antimicrobial and preservative properties of the black cumin were the reasons (El Zubeir et al. 2005; Abdel-Gadir et al. 2013). Also the efficiency of thyme in preventing the growth of some bacteria was proved (El-Sayed, 2017; Kaptan and Sivri 2018; Al-Obaidi and Hussein 2019; Tamim and Akrama 2020).

Effect of additives on the sensory characteristics of Mudaffara cheese

Data in Table 3 revealed that the sensory characteristics of Mudaffara cheese did not affected significantly (P > 0.05) by the additives used except for the overall acceptability. Bhat et al. (2014) reported that spices and herbs are commonly used for seasoning and increasing the shelf life of food and restoring health.

Table 3.

Effect of additives on sensory characteristics of Mudaffara cheese (M ± SD)

Treatment	Sensory characteristics
	Appearance	Color	Texture	Acidity	Flavor	Taste	Overall acceptability
Black cumin (0.5%)	3.6 ± 1.20	3.9 ± 1.30	4.4 ± 1.01	4.1 ± 0.92	4.1 ± 1.02	4.4 ± 0.48	4.4 ± 0.49a
Syrian thyme (0.3%)	3.7 ± 1.40	3.7 ± 1.40	4.0 ± 0.96	4.0 ± 0.96	4.0 ± 1.20	3.9 ± 1.30	3.9 ± 0.95b
Syrian thyme (0.5%)	4.4 ± 0.93	4.6 ± 0.76	4.3 ± 0.99	4.4 ± 0.36	4.4 ± 1.01	4.4 ± 1.01	4.6 ± 0.63a
LS	NS						**

^a,b,cMeans bearing the same superscripts letters in the same column are not significantly different (P > 0.05)

M mean value, SD standard deviation, LS level of significant, NS not significant

**P < 0.01

The appearance (4.4 ± 0.93) and color (4.6 ± 0.76) of Mudaffara cheese samples flavored with 0.5% Syrian thyme showed the highest numerical scores compared to those flavored with 0.3% Syrian thyme and 0.5% black cumin (Table 3). However El-Sayed (2017) reported that there were no changes in the appearance of processed cheese after adding thyme powder up to 0.2%. Increasing the ratio of Syrian thyme up to 0.3% was found to affect slightly the appearance, while with 0.5% the block of the processed cheese showed a slightly off color. Similar to the present study, non significant differences were obtained in the color of the plain soft cheese and those to which 1 or 2 ml of thyme oil/1000 ml milk were added, while a significant difference was found when adding 3 ml of thyme oil/1000 ml milk (Al-Obaidi and Hussein 2019).

The appearance and color of Mudaffara cheese samples showed non significant (P > 0.05) effect during the 2 weeks of the storage (Table 4 and Fig. 2a and 2b, respectively). Also non significant variation was reported in the color of the surface of the cheese slices after 30 days of storage at a temperature of 4 °C when adding Thymus algeriensis (Bukvicki et al. 2018).

Table 4.

Effect of storage period on sensory characteristics of Mudaffara cheese (M ± SD)

Storage periods	Sensory characteristics
	Appearance	Color	Texture	Acidity	Flavor	Taste	Acceptability
Week 1	4.1 ± 1.30	4.4 ± 1.30	4.7 ± 0.46a	4.5 ± 0.75a	4.6 ± 0.67a	4.6 ± 0.59a	4.6 ± 0.51a
Week 2	3.7 ± 1.10	3.8 ± 1.04	3.8 ± 1.10b	3.8 ± 0.94b	3.7 ± 1.20b	3.8 ± 1.20b	4.0 ± 0.89b
LS	NS	NS	***	*	**	**	**

^a,b,cMeans bearing the same superscripts letters in the same column are not significantly different (P > 0.05)

M mean value, SD standard deviation, LS level of significant, NS not significant

***P < 0.001, **P < 0.01, *P < 0.05

Fig. 2.

a Comparison of the appearance scores of Mudaffara cheese flavored by black cumin and Syrian thyme during the storage. b Comparison of the color scores of Mudaffara cheese flavored by black cumin and Syrian thyme during the storage. c Comparison of the texture scores of Mudaffara cheese flavored by black cumin and Syrian thyme during the storage. d Comparison of the acidity scores of Mudaffara cheese flavored by black cumin and Syrian thyme during the storage. e Comparison of the flavor scores of Mudaffara cheese flavored by black cumin and Syrian thyme during the storage. f Comparison of the taste scores of Mudaffara cheese flavored by black cumin and Syrian thyme during the storage. g Comparison of the overall acceptability scores of Mudaffara cheese flavored by black cumin and Syrian thyme during the storage

The highest scores for texture was obtained in Mudaffara cheese samples flavored with black cumin (4.4 ± 1.01) followed by that flavored with 0.5% Syrian thyme (4.3 ± 0.99) compared to the cheese flavored with 0.3% Syrian thyme (4.0 ± 0.96). Similarly El-Sayed (2017) found that with increasing the percentage of thyme powder (0.1, 0.2, 0.3, 0.4 and 0.5%) in the base blend of Ras cheese samples, the oil separation and the firmness were found to increase. However Al-Obaidi and Hussein (2019) reported that the texture score showed non significant differences between the control cheese and those to which different concentrations of thyme oil were added.

The texture of Mudaffara cheese was affected significantly (P < 0.001) during the second week of storage compared to that examined in week 1 (Table 4). The texture score was reported to decrease from 4.7 ± 0.46 in week 1 to 3.7 ± 1.1 in week 2 (Fig. 2c). This result was in line with those reported by Farah and El Zubier (2019) who found that the texture scores changed during the storage period with a decreasing trend. Similar to the present study, El-Sayed (2017) reported that the addition of thyme powder in the blend of 0.1 up to 0.3% improved the body and texture of the block cheese samples during the storage period. However Abdel-Razig et al. (2014) reported a lower value (3.32) for the texture score of the braided cheese at the beginning of the storage compared to the highest score (4.48), which was recorded at the end of the storage period. According to Bukvicki et al. (2018), the result of the sensory evaluation of cheese sprayed with essential oils of T. algeriensis revealed no changes in the texture of the surface of cheese slices after 30 days of storage at a temperature of 4 °C. These differences might be due to the fact that the sensory evaluation of Mudaffara cheese in the present study was evaluated only during week 1 and 2 because we missed the postgraduate students who act as panelist because the University was closed due to the announcement of the prevalence of some cases of covid 19 in Sudan.

The highest value of acid score was found in Mudaffara cheese flavored with Syrian thyme at 0.5% (4.4 ± 0.36) compared to that flavored with 0.3% Syrian thyme (4.0 ± 0.96) or black cumin (4.1 ± 0.92). This indicated that the concentration of the added spices has a role in the acid taste of Mudaffara cheese. The obtained data was not significantly (P > 0.05) different. This matches with the achieved result shown in Fig. 1d that the lactic acid content of Mudaffara cheese did not affected significantly (P > 0.05) by the use of the different additives flavors used in this study. However the acid scores of Mudaffara cheese were significantly (P < 0.05) affected by the storage period (Table 4). The score was decreased from 4.5 ± 0.75 in week 1 to 3.8 ± 0.94 in week 2.

The best flavor score (4.4 ± 1.01) was obtained for Mudaffara cheese flavored with 0.5% Syrian thyme followed by that flavored with black cumin (4.1 ± 1.02) compared to that using 0.3% Syrian thyme (Table 3). The flavor of the processed cheese was enhanced and became more preferable to panelists by incorporating thyme powder in the blend up to 0.2–0.3% compared to the control (El-Sayed, 2017). A significant difference was only found in the flavor score of the soft cheese when increasing the level of essential oil of thyme to 3 ml oil/1000 ml milk, while with the addition of 1 or 2 ml of thyme oil/1000 ml milk non significant variation was found for the flavor score of the soft cheese (Al-Obaidi and Hussein 2019). Moreover the aromatic plants that are used in imparting flavor and aroma in dairy products are also effective in increasing the nutritional value of the product and in extending its shelf life (Kaptan and Sivri 2018).

As shown in Table 4 and Fig. 2e, the score flavor of Mudaffara cheese was significantly (P < 0.01) affected by the storage period. The score was found to decrease from 4.6 ± 0.67 in week 1 to 3.7 ± 1.2 in week 2. However Farah and El Zubier (2019) reported increasing trend for the flavor score during ripening and attributed the variations to differences in the cheese types and their processing conditions. Similarly El-Sayed (2017) reported that the addition of thyme powder in the blend using 0.1 up to 0.3% enhanced the flavor of the block cheese samples during the storage period. The improvement in the flavor was mainly due to the development of lactic acid bacteria, which controls the growth of undesirable microorganisms (Papetti and Carelli 2013). Shuang et al. (2014) also reported that it is important to perfect the flavor by blending and seasoning to improve the market acceptance of the cheese. Moreover the cheese was widely popular worldwide due to its good taste and the nice diverse flavor (Walther et al. (2008). According to Nieto (2020), the main objective of the use of thyme in food is to extend its shelf life; however the main limiting aspect for the use of the essential oil and plant extract of thyme is the development of negative organoleptic characteristics in foods that contributing to an unpleasant odor and taste.

Data in Table 4 and Fig. 2f revealed that the taste scores of Mudaffara cheese were significantly (P < 0.01) affected during the storage period. The taste score was found to decrease from 4.6 ± 0.59 in week 1 to 3.8 ± 1.2 in week 2. The taste scores of Mudaffara cheese made by Farah and El Zubier (2019) also showed high significant (P < 0.01) differences during day 0, 28 and 35 of the storage, with a slight decrease during the rest of the storage period. The variation shown in Table 4 and Fig. 2f might be because of the rich content of vitamin A and C, iron, manganese and copper of thyme in addition to its characteristic sharp aroma that results from the essential oils, which give it the characteristic taste and medical properties as thyme had potent antioxidant effects originating from the thymol, carvacrol and p-cymene content of the plant (Ozkan et al. 2007). Moreover Thymus species are well-known culinary spices widely used all around the world, with pleasant taste and flavor. This in addition to its high antifungal and antiradical abilities, their essential oils could be recommended as natural antimicrobial additives for the shelf-life prolongation of the soft cheese (Nieto, 2020).

According to the panelist, the cheese samples flavored with 0.5% Syrian thyme (4.6 ± 0.63) and black cumin (4.40.49) showed significantly (P < 0.01) higher numerical scores in the overall acceptability compared to cheese samples flavored with 0.3% Syrian thyme (3.9 ± 0.95). Incorporation of 0.5% Syrian thyme showed the best overall acceptability score which supported Al-Obaidi and Hussein (2019) who reported that the high concentration of thyme oil revealed positive effect on the general acceptance of the cheese. Similarly El-Sayed (2017) reported that total scores of the processed cheeses were acceptable and the addition of thyme powder in the blend up to 0.1–0.4% gave a better organoleptic quality compared to the control cheese and that the treatments with 0.6% thyme exhibited significantly lower quality attributes compared to other treatments. Also the higher score reported for the overall acceptability of Mudaffara cheese flavored with black cumin might be because the panelists are used to the flavor of black cumin in Mudaffara cheese. Mudaffara cheese is characterized by a close texture, yellow colour and slightly acidic taste (Abdel-Razig et al. 2014). It could also be attributed to the essential oil of black cumin, which increased sensorial attributes (Mishra et al. 2020). Also black cumin showed a lot of functional properties (Butt and Sultan 2010) and has significant preservative effect in improving the keeping quality of the cheese (El Zubeir et al. 2005; Abdel-Gadir et al. 2013).

Results in Table 4 and Fig. 2g showed that the overall acceptability of Mudaffara cheese was significantly (P < 0.01) affected by the storage period. The score was decreased from 4.6 ± 0.51 in week 1 to 4.0 ± 0.89 in week 2. Similarly Abdel-Razig et al. (2014) reported that the storage period affected significantly the acceptability of Mudaffara cheese as the best acceptability score was obtained at day 30 compared to that obtained after 60 days of storage. However El-Sayed (2017) added that the storage of cheese products for up to 3 months slightly lowered the total quality attributes and this effect was more marked in the cheese samples stored at room temperature.

Results in Fig. 2a–g showed that the interactions of the used additives and the storage period showed non significant (P > 0.05) effect on the sensory characteristics of Mudaffara cheese. Generally, Mudaffara cheese samples flavored with 0.5% Syrian thyme showed the highest numerical scores in all sensory parameters during the storage period except for texture and taste scores. Similarly the meltability and the sensory quality of Ras cheese samples were found to decrease with increasing of the thyme powder (0.1, 0.2, 0.3, 0.4 and 0.5%) in the base blend (El-Sayed, 2017). This suggested that a concentration of less than 5% should be used. Moreover it is better to consume Mudaffara cheese when fresh because all the sensory characteristics scores of Mudaffara cheese decreased from week 1 to week 2. Similarly Farah and El Zubeir (2019) found that the sensory evaluation scores for Mudaffara cheese showed decreasing values during the storage period. Ripening of cheese during the storage has a great influence on its compositional and acceptability as shown in Figs. 1 and 2.

Conclusion

From the results attained in this study, it can be concluded that there is a possibility of using Syrian thyme in addition to the commonly used black cumin in flavoring Mudaffara cheese. Syrian thyme improved physicochemical content at a rate of 0.3% and sensory characteristics at a rate of 0.5% when used as flavoring additives for Mudaffara cheese. The storage period revealed non significant variations for Mudaffara cheese. Consequently, the braided (Mudaffara) cheese industry is an applied method to save the milk and to give a product with high nutritional value with a long shelf life if there are a proper storage conditions. Hence it was recommended that the processing and consumption of braided (Mudaffara) cheese flavored with Syrian thyme should be processed and practiced at a large scale.

Supplementary Information

Below is the link to the electronic supplementary material.

Abbreviations

AOAC

Association of official analytical chemists

SPSS

Statistical package for social sciences

SSMO

Sudanese standard and metrology organization

Author contributions

TMMAE: conceptualization, investigation, data curation, methodology, writing the original draft. OAMJ: data curation, validation, writing–review and editing. IEME: supervision, validation, writing–review and editing.

Funding

Not applicable.

Data availability

All the generated data obtained during this study are included with the submission of the paper.

Declarations

Conflict of interest

The authors declare that they have no competing financial interests for this work.

Consent to participate

Not applicable.

Ethical approval

Not applicable in this study.