A Survey on Selected Chemical, Biochemical and Sensory Properties of Kes Cheese, A Traditional Turkish Cheese

Abstract

Kes, a traditional Turkish dairy product, is commonly produced in the northern Anatolian region of Turkey. Kes samples were obtained from local markets in Ordu vicinity and were investigated for some chemical, biochemical, and sensorial analyses. The mean values of dry matter (DM), fat, fat in DM, salt, salt in DM, ash, and pH were found to be 56.17 ± 6.07, 8.79 ± 2.84, 15.78 ± 5.39, 3.22 ± 1.35, 5.68 ± 2.19, 4.31 ± 1.29 g/100 g cheese, and 4.75 ± 0.59, respectively. The WSN/TN, TCA-SN/TN and PTA-SN/TN values were between 1.79–28.53, 1.67–23.24, and 0.44–17.56%, respectively. SDS-PAGE showed that both α_s–CN and β–CN fractions were not completely hydrolyzed in all Kes cheese samples. α_s–CN, β–CN, and γ-casein and other peptides fractions determined as 34.57 ± 5.21, 33.74 ± 4.21, and 31.37 ± 6.82%, respectively. Panelists gave high scores (above 7 out of 10) to all samples for all the attributes considered.

Keywords:

• Kes cheese
• Proteolysis
• Casein fractions

INTRODUCTION

Kurut, dried bricks of yogurt, is made of low-fat milk or of Kes cheese made from buttermilk. In some regions, Kurut is known as Kes cheese. Since it has lower fat and moisture contents, its shelf life is longer. Some of the best-known regional varieties are Kurut of Kars and Bitlis, the Surk cheese of Hatay, the Kes of Mengen, Giresun, Ordu and the dried Cokelek, acid-precipitated curd, of Aydin.[1] Kes, a traditional Turkish dairy product, is commonly produced in the northern Anatolian region of Turkey, especially in Ordu. Traditional producing method has been modified, but generally cow's milk has been used in the production, with or without sheep and buffalo's milk. Production is carried out during summer season.

Cokelek cheese is called as Eksimik in Thrace, Kes in Mediterranean, and Akcakatik, Kesmik or Urda in several regions of Anatolia. In these regions, some wild plants are added into Cokelek in order to give a flavor; ‘boyotu’ (Trigonella foenum - graecum L .) is used in the west and garlic mustard is used in the east. Kes cheese is produced by drying of kneaded Cokelek with several aromatic plants and therefore has a special odor and flavor. It can be classified as hard cheese and its taste is little sour like a puckery taste. It is generally eaten with thin dough bread.[2]

For production of Kes cheese, milk is first filtered through a cheesecloth prior to heat treatment to remove unwanted materials. After clarification, it is cooled to 40–45°C and inoculated with yoghurt culture (2–3%). The inoculated milk is filled into big containers and incubated. The yoghurt is then churned into the butter and Ayran (buttermilk). Ayran is heated to 90–100°C for about 10 min until a white coagulum floats on the surface; the curd is transferred into a cheese cloth and some weight is placed on it to drain water off until the desired solids level is reached. The curd is salted 2–3% with dry salt and filled into cotton bags. The bags are hung up in a warm room for 2–3 days. The bags are occasionally turned over for homogeneous dryness. The cheeses reached up to 60–70% total solids content after storing in a cool place for 4–5 months can be marketed. Kes cheese is commonly produced in small family businesses for their needs and by small dairy processing plants for commercial purposes. In recent years, 20–30% white cheese curd has been added to the curd of Kes cheese in order to make the product more attractive, resulting in a mosaic-like structure in the final product.[3]

Since the production method of Kes cheese is not standardized, the quality of products available in the market varies considerably. There is no enough date in the literature to characterize chemical, biochemical, and sensory properties of Kes cheese. Kes cheese contains 60.69–78.40% dry matter, 21.60–39.31% moisture, 4.5–23.5% fat, 31.22–50.68% protein, 4.36–14.23% ash, 2.84–13.19% salt, and 3.37–4.24 pH.[4] Kes cheese named as Surk in Hatay province had a biochemical composition of 4.32 pH, 1.36% titratable acidity, 52.63% total solids, 7.75% fats, 14.73% fats in total solids, 2.36% NaCl, 1.78% total N, 0.13% water soluble N, and 7.30 % ripening index.[5] Akyüz & Gülümser[6] found Kurut cheeses contained 79.69% total solids, 10.58% fats, 52.89% protein, 11.06%ash, 9.66% salt. In another study, Akyüz et al.[7] determined titratable acidity 1.18%, total solids 85.51%, fat 8.52%, protein 54.64%, ash 14.89%, and salt 12.18%. A survey study about full fat Kes cheeses by Kırdar[2] showed that titratable acidity, pH, protein, fat, and fat in total solids, and salt contents were as follows 1.85%, 4.314.69%, 36.50%, 50.31%, and 4.68%. The chemical and biochemical properties of Kes-similar products have been studied by several researchers.[8 ^- 9 ^- 10 ^- 11] Although some physicochemical, microbiological, and sensory properties of Kes cheeses have already been partially studied but there is no single study including all chemical, biochemical, especially casein fractions, sensory aspects, and the correlations among the variables. Therefore, the aim of this study was to determine chemical, biochemical, and sensory characteristics of Kes cheese.

MATERIALS AND METHODS

Thirty-five Kes cheese samples were purchased from local markets in Ordu. The samples were immediately transported to the laboratory and kept at around 4°C until analyzed.

Chemical Analyses

Total solids content was determined by the oven-drying method. Fat content was measured by the Gerber method.[12] pH was measured using a pH meter (Hanna Instruments, Italy). The samples were analyzed for ash content by the muffle furnace method at 550°C for 24 h. Salt content was determined according to the Mohr method described by Case et al.[13]

Nitrogen Fractionation

The total nitrogen (TN) and nitrogen fractions were determined by Kjeldahl method.[12] The procedure by Polychroniadou et al.[14], with modifications, was followed for water-soluble cheese extract (WSE): 20 g grated cheese was homogenized for 5 min with 100 ml distilled H₂O using a warring blender. The homogenate was held 40°C for 1 h and then centrifuged at 3000 g for 30 min at 4°C. The fatty layer was removed and the supernatant filtered through Whatman 42 filter paper (Whatman Int. Ltd., England). Soluble nitrogen in 12% trichloroacetic acid (TCA-SN) was determined as described by Katsiari et al.[15]. Soluble nitrogen in 5% phosphotungstic acid (PTA-SN) was determined using Kjeldahl method as described by Topçu and Saldamli.[16]. All WSN, 12% TCA and 5% PTA values are expressed as the percentage of the total nitrogen content of the cheese.

Preparation of Cheese Proteins and Electrophoresis

The method used by Yazici and Dervisoglu[17] was followed for preparing the cheese samples and SDS-PAGE gels as well as for the electrophoresis running conditions, and for evaluating the electrophoretograms.

Sensorial Analyses

Kes cheese samples were organoleptically examined by a trained panelist group (6 judges) selected from Ordu University Agricultural Faculty staff members who consumed Kes cheeses heavily in their diets and had previous taste panel experience. Initially, panelists were trained in two-hour sessions prior to evaluation to be familiar with attributes and scaling procedures of cheese samples under study. For panelist training, no standard was used. Cheese samples were examined according to the method modified from Larmond.[18] Category scales for flavor, body and texture, and appearance and color (slight 9, moderate 7, moderate–strong 3, and strong 1) were used with maximum scores of 10. Panelists evaluated seven samples for each of the five sessions. All samples were coded with three-digit random numbers and presented to panelists on a tray in individual boots. Order of serving was completely randomized.

Statistical Analysis

ANOVA were used to analyze data relating various physicochemical, nitrogen and casein fractions and sensory properties of Kes cheese samples using SPSS packet program. Some statistical parameters including mean, standard error, range, standard deviation, correlation, and coefficient of variation were carried out to estimate variability in the data of Kes cheese samples.

RESULTS AND DISCUSSION

Chemical Characteristics

Some chemical characteristics of Kes cheese are presented in Table 1. The DM content ranged from 44.42 and 71.92, averaging 56.17 ± 6.07 g/100 g cheese. These values are similar to those reported by Tarakci et al.[4] for Kes cheeses, higher than the results reported by Keven et al.[11] for Tulum Cokelek cheese and by Durmaz et al.[8] for Surk cheese, and lower than the results reported by Akyuz and Gulumser[6] for Kurut Cokelek. The highest fat content was 16.5, the lowest 5 g/100 g cheese. Fat in DM changed between 9.18 and 31.16 g/100 g cheese. This implies that Kes cheese has been produced from both full fat and non-fat milk. Similar deviations were reported by Tarakci et al.[4] for 20 Kes cheese samples (4.5–23.5 g/100 g cheese) and by Durmaz et al.[8] for Surk cheese (3–25.5 g/100 g cheese). The salt ratio was between 1.17 and 5.85 g/100 g cheese and salt in DM between 2.17 and 9.87 g/100 g cheese. The ash content was in the range of 2.51–6.58 g/100 g cheese. It was obvious that the production method used and the type of salt contributed to the high variation in NaCl and ash values. Salt and ash contents in similar products (Dumas, Cokelek, and Kurut) were higher than our values.[7] The pH values of the samples changed ranged from 3.43–5.81. In general, physicochemical results showed that there was no standard product in the market. Therefore, the milk used for the cheese production, manufacturing process, packaging, and ripening conditions should be standardized to improve quality of the products marketed.

Table 1 Physicochemical characteristics of Kes cheeses

Statistical parameters	pH	g/100g cheese
		Dry matter	Fat	Fat in DM	Salt	Salt in DM	Ash
x ^a	4.75	56.17	8.79	15.78	3.22	5.68	4.31
Min-Max	3.43–5.81	44.42–71.92	5–16.5	9.18–31.16	1.17–5.85	2.17–9.87	2.51–6.58
Sd	0.59	6.07	2.84	5.39	1.35	2.19	1.29
CV ^c	12.42	10.81	32.31	34.16	41.93	38.56	29.93
^a Mean; ^b Standard deviation; ^c Coefficient of variation; n = 35.

Nitrogen and Casein Fractions

The purpose of aging in cheese is to develop specific flavor, body, and texture qualities. These characteristics result from the activity of microorganisms and enzymes.[19] It is necessary to analyze the nitrogen fractions formed during ripening in order to understand the development of proteolysis in cheese.[20] The WSN fraction contains whey proteins, proteose-peptone (soluble proteins, peptides, amino acids, amines, urea, ammonia) and low molecular weight peptides (<15000 Dalton molecular mass) derived from casein hydrolysis.[21] The soluble nitrogen compounds are mainly produced by the action of the coagulant.[22] Protein degradation is clearly demonstrated by the definitive increase in water soluble nitrogen.[23] Table 2 shows nitrogen and casein fractions of Kes cheese samples. The WSN/TN ratio of Kes samples ranged from 1.79–28.53, averaging 9.36 ± 6.69%. This value is similar to those reported by Patir and Ates[9] in Kurut cheese and by Sagdic et al.[5] in fresh Surk cheeses, higher than the results reported by Kucukoner et al.[24] in Cacik, and lower than the results reported by Durmaz et al.[8] in Surk cheese. This difference may be related to the rennet retention and, hence, in the level of residual rennet activity in casein matrix.[25]

Table 2 Nitrogen and casein fractions of Kes cheeses

Statistical parameters	Nitrogen fractions (%)			Casein fractions (% of total scanning density)
	WSN/TN	TCA-SN/TN	PTA-SN/TN	αs–CN	β–CN	γ–CN and peptides
x ^a	9.36	7.17	3.43	34.57	33.74	31.37
Min-Max	1.79–28.53	1.67–23.24	0.44–17.56	20.65–42.7	22.95–41.85	21–56.4
Sd ^b	6.69	4.88	3.91	5.21	4.21	6.82
CV ^c	71.57	68.06	113.99	15.07	12.48	21.74
^a Mean; ^b Standard deviation; ^c Coefficient of variation; n = 35.

The TCA-SN is known to be an indication of the amount of small peptides (<20 amino acid residues) and amino acids present in cheese and its level is regarded as the ripening depth index.[26] The TCA-SN/TN ratios of samples were between 1.67–23.24%. The average TCA-SN/TN ratio was found to be 7.08 ± 1.69% in Herby cheese by Tarakci et al.[27] and 19.35 ± 8.34% in Surk cheese by Durmaz et al.[8] The values obtained in our study are similar to those in Herby cheese, but lower than the majority of the literature values.

PTA-SN is known as the free amino acids index of proteolysis and is obtained by extracting the water-soluble fractions of cheeses with 5% PTA, which only extracts low molecular weight peptides (<600 Da) and amino acids.[28] The PTA-SN/TN values found in this research determined between 0.44 and 17.56% and an average of 3.43 ± 3.91%. These values are similar to those (2.28–5.37%) and mean 3.85% reported by Tarakci et al.[27] in Van herby cheese but higher than the results (1.5–2.5%) reported by Chen et al.[28] in Ovine milk cheese and the mean values of 2.32% found by Dervisoglu et al.[29] in Kulek cheeses. The possible reason for a high variation between samples indicate a lack of standardization of most parameters (milk quality and composition) and manufacturing steps (ripening conditions and packaging).

The results of casein fractions of Kes cheeses are presented in Table 2. SDS-PAGE profile of Kes cheeses is also given as an example of the separation of casein fractions (Fig. 1).The α_s–CN, β–CN and, γ–casein and other peptides fractions of Kes cheeses changed between 20.65–42.7, 22.95–41.85, and 21–56.4 %, respectively. The α_s–CN ratio was reported to be 46.65% in Civil cheese[30], 49.40% in Kulek cheese ripened for 90 days[31] and 41.58–56.49% in Feta cheese ripened for 120 days.[32] SDS-PAGE profile showed that neither α_s–CN and β–CN were completely hydrolyzed in all Kes cheese samples (Fig. 1). The β–CN hydrolysis was found between 38.51–66.24% and an average of 52.24% in ripened Herby cheeses,[33] between 18.3–22.4% Kulek cheeses ripened for 90 days,[31] between 12.2–26% in Golot cheeses,[34] and between 18.2–24.3% in Civil cheeses ripened for 180 days.[17] The γ-casein and other peptides fractions were found to be 0.66–47.87% and an average of 14.49% in Herby cheese, [33] 11.20–35.10% and an average of 19.38% in Civil cheese, [30] 44.9–60.2% in Civil cheeses ripened for 180 days.[17] The ratio of α_s–CN in our cheeses is significantly lower (β–CN ratio is higher) than that found in the Herby cheese by Sagdic et al.[33] The values in our study do not indicate any level of casein degradation because the initial concentration of the fractions is not known.

Figure 1 SDS PAGE profiles of Kes cheeses.

Table 3 shows the correlation coefficients among the casein fractions and the other chemical and biochemical properties of Kes cheese. There was a significant correlation between pH and the nitrogen fractions (positive) and α_s– and β–CN fractions (negative). The significant negative correlation between α_s–, β–CN fractions and the ratio of WSN/ TN, TCA-SN/ TN, and PTA-SN/ TN was found (p < 0.05). This indicates that the nitrogen fractions increased as the α_s– and β–CN fractions decreased.

Table 3 Correlation coefficients between casein fractions and some chemical and biochemical properties of Kes cheese (n = 35)

	pH	Dry matter (g/100 g cheese)	Fat in DM (g/100 g cheese)	Salt in DM (g/100 g cheese)	Ash(g/100 g cheese)	WSN/TN(%)	TCA-SN/ TN (%)	PTA-SN/ TN (%)	αs–CN(%)	β –CN(%)	γ –CN and peptides (%)	Flavor	Body and texture
DM	.087
Fat in DM	−.028	−.242
Salt in DM	.174	.217	−.125
Ash	.094	.512∗∗	−.113	.890∗
WSN/TN	.498∗∗	.329	−.312	.326	.372∗
TCA/TN	.514∗∗	.346∗	−.309	.269	.319	.932∗∗
PTA/TN	.464∗∗	.221	−.338∗	.317	.320	.865∗∗	.854∗∗
αs–CN	−.344∗	−.135	.224	.002	−.094	−.614∗∗	−.578∗∗	−.624∗∗
β–CN	−.286	−.290	.312	−.283	−.266	−.678∗∗	−.660∗∗	−.595∗∗	.075
γ–CN and peptides	.432∗∗	.257	−.355∗	.167	.221	.869∗∗	.831∗∗	.832∗∗	−.801∗∗	−.654∗∗
Flavor	−.226	.018	.465∗∗	−.063	−.020	−.068	−.132	−.211	.039	.231	−.171
Body and texture	−.020	−.122	.873∗∗	−.074	−.097	−.278	−.259	−.311	.162	.318	−.305	.450∗∗
Appearance and color	−.119	−.237	.397∗	−.025	−.108	−.084	−.070	−.088	−.072	.265	−.092	.697∗∗	.537∗∗
Correlation is significant at the 0.05 level.∗∗ Correlation is significant at the 0.01 level.

Sensorial Properties

The results of the assessment of Kes cheeses by sensory panelists are given in Table 4. The average scores for appearance and color, body and texture, and flavor were 7.16, 7.38, and 7.13, respectively. All sensory scores were between 4.5–10. However, standard deviations for the mean scores were high, indicating lack of product uniformity. Since different ingredients (Ayran and non-fat skim milk powder) and manufacturing procedures were used to produce Kes cheese, these variations are normal for the samples. It is clear from Table 2 that all sensory properties were significantly affected from the fat content of the samples. Therefore, compositional (especially fat in dry matter) and biochemical variations (proportions of casein fractions) should be minimized to help to characterize sensory properties of Kes cheeses. Based on chemical and sensory results, Kes cheeses should be classified into different classes in term of fat and moisture, and evaluations and comparisons should be made within these specified groups for better results.

Table 4 The sensory characteristics of Kes cheeses

Properties	Appearance and color	Body and texture	Flavor	Acceptability
x ^a	7.16	7.38	7.13	7.21
Min-Max	5.5–10	5–10	4.5–9.5	4.5–10
Sd ^b	1.13	1.39	1.51	1.29
CV ^c	15.78	18.83	21.18	17.89
^a Mean; ^b Standard deviation; ^c Coefficient of variation; n = 35.

CONCLUSION

The present study has reported the complete chemical, biochemical and sensory properties of traditional Kes cheese. A broad range of values from chemical and biochemical analysis indicate that Kes cheeses collected from retail markets lack of standardization. These variations could probably be due to the type and composition of ayran, skim milk, and cheese used for the production of Kes cheese, and manufacturing techniques, drying and storage conditions.