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Article

Physicochemical Characteristics of Commercially Available Greek Yoghurts

by
Eleni C. Pappa
1,
Efthymia Kondyli
1,
Athanasios C. Pappas
2,*,
Panagiota Kyriakaki
2,
Evangelos Zoidis
2,
Lida Papalamprou
3,4,
Agori Karageorgou
5,
Panagiotis Simitzis
5,
Michael Goliomytis
5,
Eleni Tsiplakou
2 and
Constantinos A. Georgiou
3,4
1
Dairy Research Department, Institute of Technology of Agricultural Products, Hellenic Agricultural Organization-DIMITRA, Ethnikis Antistaseos 3, Katsikas, 45221 Ioannina, Greece
2
Laboratory of Nutritional Physiology and Feeding, Faculty of Animal Science, Agricultural University of Athens, 75 Iera Odos, 11855 Athens, Greece
3
Chemistry Laboratory, Department of Food Science and Human Nutrition, Agricultural University of Athens, 75 Iera Odos, 11855 Athens, Greece
4
FoodomicsGR Research Infrastructure, Agricultural University of Athens, 75 Iera Odos, 11855 Athens, Greece
5
Laboratory of Animal Breeding and Husbandry, Department of Animal Science, Agricultural University of Athens, 75 Iera Odos, 11855 Athens, Greece
*
Author to whom correspondence should be addressed.
Dairy 2024, 5(3), 436-450; https://doi.org/10.3390/dairy5030034
Submission received: 29 May 2024 / Revised: 16 July 2024 / Accepted: 24 July 2024 / Published: 30 July 2024
(This article belongs to the Section Metabolomics and Foodomics)
Browse Figures
Versions Notes

Abstract

:
In the present study, the physicochemical characteristics of 108 yoghurts purchased from the Greek market have been assessed. Generally, the range of the mean pH values of samples was 3.58–4.64, of fat 0–10.8%, of protein 3.29–10.05%, of total solids 10.75–25.18%, and of ash 0.5–1.17%. Samples were categorized as strained and non-strained (traditional with a crust or plain without a crust). The milk origin was classified as being from sheep, goats, cows, mixture of sheep–goat–cow milk, or cow–donkey milk combination. A significant effect of species origin was determined for yoghurt physicochemical attributes, whereas geographical origin, mainland or island, affected yoghurt acidity only. Discriminant analysis revealed MDA, pH, acidity, syneresis, fat, and protein content and color lightness and redness as the traits responsible for the discrimination of yoghurts into milk-type classes, whereas fat, protein, and ash content, pH, and syneresis attributes were responsible for the discrimination into fat content classes. Yoghurt samples were sufficiently clustered according to their fat content, whereas protein content and species origin discriminated yoghurts to a lesser extent. This first in-depth descriptive research on a wide range of samples of the renowned Greek yoghurt showed that several physicochemical characteristics can be used for sample discrimination.

1. Introduction

Yoghurt is an important dairy product that is very popular all over the world. Yoghurt has a large portion in the market of dairy products and its consumption provides several health benefits, including but not limited to people who are intolerant to lactose as well as to those who suffer from hypertension, diabetes, and cardiovascular diseases [1,2].
Various types of yoghurts can be found in the Greek market. Strained yoghurt is a high-protein dairy product with low lactose content [3,4] that is manufactured traditionally using cloth bags for whey drainage, but mechanical separators, membrane filtration techniques, or product formulation are widely applied in their industrial production [5]. Other non-strained yoghurts that can be found are the traditional ones with a crust and the plain ones, which are non-strained and without a crust. In the market, low-fat (0.5–3%) or non-fat (less than 0.5% milk fat) yoghurts can also be found, which are preferred by consumers for health reasons [6], and in some countries, the fat content can be used for yoghurt categorization [7]. Internationally, Greek yoghurt (Greek-style yoghurt) is also known as strained yoghurt, and its sales exceed 50% of yoghurt sales in the US, in 2022 exceeding USD 7.2 billion [8].
There is a vast number of studies on yoghurts, detailing the importance of this dairy product for both consumers and the industry. Studies on the characteristics of yoghurt purchased from the market have been conducted in Canada [9], Nigeria [10,11], Bulgaria [12], the United Kingdom [13], Turkey [14,15], Poland [16,17], Slovak Republic [18], Iraq [19], Uganda [7], the US [20,21], Pakistan [22,23], Libya [24], Sudan [25], Cameroon [26], and Lebanon [27].
The present study was part of a bigger project on the physicochemical properties, fatty acid, and elemental profile of Protected Designation of Origin (PDO) and non-PDO Greek cheeses and yoghurts. Previously, the physicochemical properties of PDO [28] and non-PDO [29] Greek cheeses were studied. During the design of the present study, the following issues were taken into consideration: (a) the necessity to survey the Greek market for yoghurts available to consumers, and (b) the necessity to analyze these yoghurts to highlight any compositional differences. Therefore, the aim of the present work was to determine the physicochemical differences of Greek commercial yoghurts by determining their composition, syneresis, color, and lipid peroxidation degree in order to establish their profile and to assess if the samples could be clustered using different factors such as milk type or fat content.

2. Materials and Methods

2.1. Yoghurt Sample Collection

In sum, 108 yoghurt samples were bought from different regions of Greece from January to May 2023. The name “yoghurt” was reported on the label. Products designated “desserts” were excluded from the present study. All samples were produced from natural dairy ingredients (milk, culture, and/or milk cream, and/or milk proteins) according to their labeling. None of the samples studied, contained other ingredients, such as fruits, nuts, etc. All of them were reported to be produced from Greek milk only. The samples collected were from different producers, which were small-, medium-, or large-scale industries. After purchase, they were stored in a refrigerator at 3–5 °C and were immediately analyzed. No analyses were conducted after the expiry date.

2.2. Yoghurt Classification

Yoghurts in the present study were categorized into different groups as strained with a minimum 5.6% protein content for cow or goat milk or 8% for sheep milk samples [30]. Non strained yoghurts were categorized as traditional (i.e., with a crust) or plain (i.e., without a crust). In the plain category, baby yoghurts, according to the label, were also collected. In the present work, 38 strained samples, 48 traditional samples, and 22 plain, of which 3 were baby yoghurt samples, were used.
Of the 108 yoghurts, 81 samples were full fat (>3% fat content), 25 samples were low fat (0.5–3%), and 2 samples were fat-free or non-fat (less than 0.5% milk fat). In the present study, 30 samples were manufactured exclusively from sheep milk, 18 samples from goat milk, 53 samples were from cow milk, 5 were a mixture of sheep, goat, and cow milk, and 2 were from cow–donkey milk. All samples were analyzed in duplicate. A map of collected samples from different regions of Greece is presented in Figure 1.

2.3. Physicochemical Traits

The yoghurts were analyzed for pH with a pH meter (Micro pH 2002; Crison, Barcelona, Spain), fat [31], titratable acidity [32], total solids [33], ash [34] and protein content after total nitrogen determination by the Kjeldahl method [35]. Carbohydrate/lactose content was determined by subtracting from the total solids the sum of proteins, fat, and ash content. The syneresis index was calculated as described by Pappa et al. [36].
Yoghurt color was measured with a Miniscan XE chromameter (HunterLab, Reston, VA, USA) set on the L* (lightness), a* (redness), and b* (yellowness) system [37].
Yoghurt oxidative stability was assessed based on the malondialdehyde (MDA) content that was calculated by third-order derivative (3D) spectrophotometry (Hitachi U3010 Spectrophotometer, Hitachi High-Technologies Corporation, Japan) in the range of 500–550 nm, according to Bostoglou et al. [38].

2.4. Statistical Analysis

Data were subjected to analysis of variance with the type of milk, yoghurt fat content, yoghurt protein content, and the origin, island or mainland Greece, as fixed factors. The Bonferroni adjustment was applied for multiple comparisons. Classification of yoghurt samples according to type of milk, yoghurt fat content, and yoghurt protein content was evaluated by a discriminant analysis of the physicochemical characteristics. A stepwise discriminant analysis was performed in order to reveal characteristics that were mainly responsible for the observed classification. The level of significance, p-value, was set at 0.05. Statistical analysis was performed using SAS software [39]. Physicochemical characteristics of the yoghurts are presented as mean values, while the effect of main factors in the composition and physicochemical characteristics of yoghurts are presented as least square mean values.

3. Results and Discussion

The physicochemical characteristics of a yoghurt are affected by the composition of milk used (which is affected by various factors such as animal genetic differences, stage of lactation, diet of animals, age), the strains of bacteria used and the manufacturing conditions (temperature and time of lactic acid fermentation, storage temperature [16,40]). Also, the technological production scheme of yoghurts may vary among dairy industries, so various commercial products with differences in physicochemical composition may exist in the dairy market [41]. In the present study, the results of the physicochemical analyses of yoghurt samples are presented in Table 1.

3.1. pH Values of Yoghurts

Generally, the mean pH values of samples ranged between 3.58 and 4.64, in line with other previous studies [7,10,22,25]. Specifically, sheep yoghurts had pH values that ranged from 3.69 to 4.64, goat samples had 3.82–4.57, cow had 3.58–4.59, mixture of sheep, goat, and cow had 3.75–4.56, and mixed cow–donkey milk had 3.94–4.04. Strained yoghurts had 3.58–4.59, traditional samples had 3.69–4.64, plain had 3.58–4.56, and baby samples had 4.44–4.54. Full-fat samples had 3.58–4.64, low fat had 3.58–4.59, and fat-free had 4.28–4.50.
It is known that variations between studies in pH values can be due to variations in processing during yoghurt manufacture, such as the time and the temperature of incubation in order to achieve a value around 4.6, which is the isoelectric point of casein [26]. A pH range of 4.1–4.6 is preferable for the aggregation of casein particles, for the formation of a coagulum avoiding syneresis, for the prevention of the growth of undesirable microorganisms, and for developing the desired flavor [20,42].

3.2. Fat Content of Yoghurt

Fat is an important constituent of yoghurt, as the energy that it provides is twice the energy that is produced from the same quantity of protein and of carbohydrate [43]. Nowadays, consumers are aware of the health risks that are associated with food rich in fat; therefore, there is a growing demand for diets that have low fat content, and this has led to an increase in the production of low-fat yoghurts [44].
The fat content of all yoghurt samples ranged between 0 and 10.8%. Specifically, the fat content of sheep yoghurts ranged from 1.30% to 10.30% and the mixed sheep–goat–cow and cow–donkey samples were full fat, with fat content ranges of 3.3–7.5% and 7.5–8.5%, respectively. The fat content of goat samples was 2–9% and of cow were 0–10.8%. Strained yoghurts had 0–10.8%, traditional samples had 1.8–8.5%, and plain had 1.3–8.5%, of which baby samples had 2–2.30% fat content. The Codex Alimentarius [45] for fermented milks defines that yoghurt should contain less than 15% fat, and this agrees with the results of the present study. As indicated in Table 1, the milk type had a significant effect on the percentage of fat, with sheep milk yoghurts exhibiting the highest compared to yoghurts made with other milk types.
Various fat content is reported in the literature, i.e., from 0.1% (fat-free) to 10.9% (full fat) for the strained yoghurt Labneh [27], 0.2% (low fat)–10.1% (full fat) for industrial strained yoghurt [4], 0.52–4.62% for traditional cow samples, 2.3–6.89% for traditional sheep samples, 2.33–3.55% for traditional goat yoghurts [6], and 5.51–11.61% for cow strained yoghurts [14]. The variations in fat content could be attributed to variations in the raw milk or to treatments applied in order to reduce fat [7].

3.3. Lactose Content of Yoghurts

Samples of the Greek market had 2.75–7.14% carbohydrate/lactose content. Similar values (8.47%) were assessed for Nestlé yoghurt samples in Pakistan [23] and in Egypt (3%) by Nasralla et al. [46]. Higher values (10.62–14.57%) were found in Uganda by Mukisa and Kyoshabire [7], and lower values (0.05–0.7%) were determined for commercially strained yoghurt (Labneh) in Lebanon by Abou Jaoude et al. [27]. The differences may be attributed to the starter culture used during the manufacture of yoghurt [27].
In the present study, sheep yoghurts had 2.75–6.79%, goat samples had 3.29–6.20%, cow had 3.02–7.14%, mixed sheep–goat–cow had 3.56–5.65%, and mixed cow–donkey yoghurts had 4.02–4.47%. None of the examined factors affected lactose content (Table 1), and thus all yoghurt types had similar content. In detail, strained yoghurt samples had 3.26–7.14%, traditional had 2.75–6.99%, and plain had 3.56–6.79%, of which baby had 4.12–5.05%. Full-fat, low-fat, and fat-free samples had 2.75–7.14%, 4.12–6.9%, and 4.82–5.29%, respectively.

3.4. Protein Content of Yoghurts

According to the Greek Codex Alimentarius [30], strained yoghurt is derived from full-fat yoghurt after part removal (drainage) of the whey. It should have a minimum of 5.6% protein content when cow or goat milk is used and 8% when sheep milk is used. Non-strained yoghurt from cow or goat milk should have a 3.2% minimum protein content and sheep milk 5.5%. Traditional yoghurt is manufactured either with the traditional method, which leads to the formation of a crust at its surface or is derived from the coagulation of raw or pasteurized milk whose natural composition has not been altered, except the fat content, in order to produce the crust [30]. In Greece, traditional yoghurts are still much appreciated by consumers. During their manufacture, no milk standardization or homogenization takes place and fermentation is conducted using yoghurt manufactured the previous day, as inoculum starter culture [6].
Different types of milk are used for yoghurt manufacture. Cow yoghurt is consumed widely because of its low price and also due to the less characteristic smell compared to that from other animals [47]. Generally, the use of sheep milk in yoghurt manufacture is more suitable, because sheep milk has a high content of total solids (proteins and fat), resulting in a final product with a richer and creamier texture and a pleasant and more mouthfeel taste compared to that made from cow milk [40,48]. In general, sheep milk and its products are produced seasonally, and therefore the production of some of them can be limited. The microstructure of caprine yoghurt is more fragile than that of bovine, though yoghurt starter grows better in goat than in cow milk [49]. The composition of donkey milk makes it similar to human milk. It can be a good alternative for children with allergy problems and it also has other therapeutic effects for infectious diseases, fever, and asthma [50]. However, in order to achieve a firm clot gel during yoghurt manufacture, donkey milk is mixed with the milk of other animal species [51].
Milk and fat were significant factors affecting total yoghurt protein content (Table 1). The protein content of all yoghurt samples in this work ranged from 3.29% to 10.05%. In the Codex Alimentarius [45], a minimum of 2.7% protein is necessary, and this is in line with the results of the present study. Specifically, strained yoghurts from the Greek market contained protein between 5.56% and 10.05%, traditional samples 3.29% and 6.4%, and plain yoghurt 3.33% and 6.74%, with baby 3.78% and 4.07%. Protein content in sheep samples ranged 4.09–9.94%, goat samples 3.29–7.13%, cow samples 3.33–10.05%, mixed sheep–goat–cow samples 3.89–6.74%, and mixed cow–donkey samples 5.04–5.12%. Full-fat yoghurt samples had 3.33–9.94%, low fat had 3.29–9.64%, and fat-free had 9.98–10.05% protein content. Similar protein values were obtained by Serafeimidou et al. [6] for traditional commercial Greek yoghurt samples (i.e., 3.46–5.73%), by Desai et al. [21] for commercial strained yoghurts (i.e., 5.8–10.6%), and by Somer and Kilic [14] for strained cow samples (i.e., 5.73–8.57%). Nowadays, people are aware of the health benefits of diets rich in protein, and this has increased the consumption of strained yoghurt [21].
In Greece in 2021, the production of strained yoghurt was 140.091 tn, of sheep (not strained) yoghurt was 14.094 tn, of cow (not strained) yoghurt was 23.780 tn, of goat (not strained) yoghurt was 3.595 tn, of other types of yoghurt (i.e., using mixtures of different types of milk or of buffalo milk, etc.) was 7.233 tn, and of yoghurt-type desserts was 66.004 tn [52]. The chemical characteristics, fatty acid composition, and conjugated linoleic acid of 24 samples of traditional Greek yoghurts produced from cow, sheep, and goat milk from various districts of the mainland were studied by Serafeimidou et al. [6], and the anti-thrombotic and sensory properties, as well as the fatty acid profiles of cow, goat, and sheep yoghurts from the Greek market were assessed by Megalemou et al. [47], revealing that low-fat cow milk yoghurts were rich in polyunsaturated fatty acids and that ewe yoghurt was the most palatable of Greek yoghurts compared to cow and goat yoghurts. The results of the present work revealed that strained yoghurts are a good source of animal protein in a diet.

3.5. Ash Content of Yoghurts

The assessment of ash content can provide useful information regarding the mineral content of elements that are important for the formation of teeth, growth of bones, and other functions of the body [11]. The ash content of all samples was 0.5–1.17%. Specifically, sheep samples had 0.52–1.12%, goat had 0.65–0.88%, cow 0.56–1.17%, mixed sheep–goat–cow had 0.76–0.90%, and mixed cow–donkey had 0.5–0.6%. The full-fat samples had 0.5–1.12%, the low-fat samples had 0.62–1.17%, and the fat-free samples had 0.63–0.7%. The strained yoghurts had 0.60–1.17%, the traditional samples had 0.52–1%, and the plain samples had 0.5–1.12%, of which the baby samples had 0.62–0.69%. Similar findings have been presented in other researchers’ work [6,11,25,41]. However, higher values (1.48%) were found in strained yoghurts from local Turkish markets by Somer and Kilic [14].

3.6. Total Solid Content of Yoghurts

The mean values of total solid content of all samples ranged from 10.75% to 25.18%. Variations in total solid content of the strained yoghurts could be due to many factors, such as the chemical composition of the milk used in the manufacture of yoghurts, the time and temperature applied during production, etc. [14]. In detail, in the present work, strained yoghurts contained between 15.22% and 25.18%, traditional samples 12% and 18.86%, and plain yoghurts 10.75% and 18.65%, of which baby samples had 10.75% and 11.61% total solids. Milk, fat, and protein content were significant factors affecting total solids (Table 1). Sheep samples had 12.61–25.18%, goat samples had 10.75–20.44%, cow samples had 11.11–25.09%, mixed sheep–goat–cow samples had 14.67–18.65%, and mixed cow–donkey samples had 17.24–18.51%. Full-fat yoghurt samples had 12.70–25.18%, low-fat samples had 10.75–18.3% and fat-free samples had 15.93–16.04%. These values were in line with those reported in other studies [4,7,10,21], although higher values were found by Somer and Kilic [14].

3.7. Titratable Acidity of Yoghurts

The titratable acidity (TA) ranged from 0.79% to 2.07%. According to the Codex Alimentarius [46], a minimum acidity of 0.6% is necessary for yoghurt, since at this percentage, the formation of the coagulum starts. Results of the present study are in agreement with this statement. The characteristics of the starter culture, the level of acidity that is produced from the starter culture, a high temperature of yoghurt incubation, and a long period of incubation can be some reasons for the acidity differences observed [14]. Also, the level of acidity can affect consumers’ preferences [20].
In the present study, sheep yoghurts had 1.01–2.07% TA, goat samples had 0.79–1.46%, cow samples 0.81–1.61%, mixed sheep–goat–cow yoghurts had 0.95–1.69%, and mixed cow–donkey samples had 1.21–1.3%. Strained yoghurts had 0.81–2.07%, traditional samples had 0.79–1.83%, and plain had 0.85–1.71%, of which baby samples had 0.87–0.9% TA. Full-fat yoghurts had 0.81–2.07%, low fat had 0.79–1.73%, and fat-free had 1.30–1.38% TA. Yoghurts made with sheep and sheep milk mixtures had higher acidity compared to yoghurts made with other milk types (Table 1). Like our results, Somer and Kilic [14] found 1.69–2.05% titratable acidity in commercial strained yoghurts made from cow milk, Serafeimidou et al. [6] 0.91–1.57% TA for market traditional yoghurts made from different types of milk and fat content, Haj et al. [25] 0.93–1.12% TA, and Younus et al. [22] 0.87–1.16% TA in yoghurt samples from the market.

3.8. Syneresis Index of Yoghurts

Syneresis is the expulsion of the entrapped serum (whey) from the continuous network of yoghurt. It is a physical defect that is observed after keeping yoghurt for a particular time. It is undesirable, affecting consumers’ acceptance, as it may result in water leakage it. Different factors, such as low levels of protein, fat, acid production, or insufficient heating of the milk can cause yoghurt syneresis [14], and this was true in the present study, as milk, fat, and protein content were significant factors affecting syneresis (Table 1). However, syneresis can be prevented by homogenizing the fat, increasing the protein level to more than 3.5%, sufficient acid development (pH 4.0–4.4), and taking care in the handling of the yoghurt [20].
In the present study, mean syneresis values were between 0.01 and 0.56. Specifically, sheep yoghurts had syneresis values ranging from 0.03 to 0.47, goat samples had 0.09–0.56, cow had 0.01–0.52, mixture of sheep–goat–cow had 0.15–0.40, and mixed cow–donkey milk had 0.06–0.09. Strained yoghurts had 0.01–0.37, traditional samples had 0.09–0.56, and plain had 0.06–0.52, of which baby samples had 0.28–0.40. Full-fat samples had 0.01–0.52, low fat had 0.07–0.56, and fat-free had 0.24–0.37. Kroger [20] reported that protein content lower than 3.4% may be associated with syneresis. The results of the present study are in line with previous studies. Reported syneresis values for commercial yoghurt samples in the literature were 22.8% to 36.8% (0.228–0.368) [22], 29.47–53.63% (0.2947–0.5363) [7], and 1.67–9.22% (0.0167–0.092) [14]. The increased protein content promotes yoghurt’s gel firmness [53]; therefore, strained yoghurt has been reported with reduced levels of syneresis, which was confirmed in the present study.

3.9. Oxidative Stability of Yoghurts

Oxidation has a negative effect on the chemical composition and shelf life of dairy products, especially these with high fat content. Peroxides are generated by the reaction between oxygen and unsaturated fatty acids, leading to the production of carbonyl compounds that induce strong off-flavors and deteriorate nutritional quality [54]. Under the scope of the present study, the MDA of yoghurts was determined to reveal potential effects of exposure to natural and artificial light throughout processing prior to packaging. Thiobarbituric acid (TBA) methods are already used for the determination of secondary oxidation products [55]. In the present study, mean MDA values were between 2.78 and 55.90 ng/g. As shown in Table 1, sheep (17.07) and mixed sheep–goat–cow (21.16) yoghurts had greater MDA values (ng/g) compared to cow (4.53) and goat (9.17) yoghurts. Sheep milk contains a higher PUFA content (~25%) compared with cow milk, leading to a higher risk of lipid peroxidation and consequently to a higher MDA content. Indeed, the MDA content in sheep compared with cow milk was higher (13.40 vs. 8.07%) after 24 h of storage at room temperature, in line with previous studies [56].

3.10. Color Attributes of Yoghurts

The color of the dairy products can reveal undesired physicochemical changes. In this context, color attributes are vital quality indicators, and thus instrumental color analysis has been widely used in identifying color variations in dairy products [57]. In the present study, mean values observed for lightness, redness (greenness), and yellowness were between 86.30 and 95.00, −3.13 and −0.02, and 4.75 and 14.30, respectively. The values observed for lightness, redness (greenness), and yellowness for cow, goat, and sheep yoghurt samples (Table 1) are within the normal range reported by others [37]. In general, sheep samples show inferior values for a* compared to cow samples, with goat samples having intermediate values, as also indicated in our study (−2.61, −1.85, and −2.17 for sheep, cow, and goat yoghurt samples, respectively). In addition, the a* value of sheep is lower compared with that of cow samples [58], since plasma carotenoids are lower in ovine milk than in bovine milk [59]. In general, the higher the protein content of milk, the greener the yoghurt [37], as illustrated in Table 1 for strained, traditional, and plain yoghurt samples (−1.88, −2.26, and −2.09, respectively). On the other hand, yellowness is positively correlated with fat content [60], as also shown in our results, since full-fat yoghurts had greater b* values compared to non-fat and low-fat ones (10.16 vs. 7.19 and 8.90, respectively).

3.11. Discriminant Analysis

Discriminant analysis was applied to the physicochemical attributes determined in yoghurt samples to examine if the 108 samples could be distinguished according to type of milk, yoghurt fat content, and yoghurt protein content. Stepwise discriminant analysis on classification according to milk type showed that 8 out of 12 attributes were responsible for the discrimination of yoghurt samples into milk-type groups. These physicochemical attributes were MDA, pH, acidity, syneresis, fat and protein content, and color attributes L and a. Two discriminant functions were found to be significant (p < 0.01) for classification of samples among the different milk types. The finding that MDA content is an important factor for discrimination of yoghurts and that it was lower in yoghurts made of cow’s milk compared to yoghurts made of other types of milk may be related to the differences in chemical composition of milk originating from cow, sheep, and goat milk and possibly due to manufacturing differences. However, compared to cow milk, sheep milk has been reported to be preferable by several dairy producers (most notably in cheese manufacture) due its higher protein, fat, and total solids [61,62]. Under the scope of oxidation, it is well established that yoghurt contains bioactive peptides, formed by hydrolysis of milk proteins during the fermentation process, and antioxidant activity [63]. The graph of the two discriminant functions is presented in Figure 2, showing that yoghurt samples made of milk from a single species, i.e., cow, goat, or sheep, were clearly distinguished in separate clusters, whereas yoghurt samples made of a mixture of milk types were dispersed among cow, goat, and sheep clusters.
The two samples made of a mixture of donkey and cow milk were reasonably close to the cluster of samples made of cow milk, because most of the milk in the mixture used (>85%) was cow’s milk. The clear distinction of yoghurt samples in classes of milk of a single species is also evident by the high rate of yoghurt samples that were correctly classified in the appropriate milk-type group—81.5% (Table 2).
A higher rate of misclassification was determined for 22.6% of cow samples that were misclassified as yoghurt samples made of goat milk. The composition of goat and cow milk is not so different, and this fact may explain the observed misclassified samples. In a positive view, this misclassification between goat and cow milk may expand the use of goat milk during cheese and yoghurt manufacture, given that there is a growing consumer interest in goat’s milk and its dairy products due to nutritive values and potential positive health benefits [64]. Milk from goats is primarily known for the presence of health-promoting compounds, low allergenic potential, and better digestibility compared to cow’s milk [65]. It should be noted that cow yoghurt is consumed largely due to both low price and less distinctive smell compared to those derived from sheep/ewe and goat [47]. The misclassification rate of cow samples was followed by 10% of sheep samples that were misclassified as yoghurt made of a mixture of sheep, goat, and/or cow milk. In a recent comparative study, the physicochemical, biochemical, textural, and rheological properties of yoghurts made of buffalo, camel, cow, goat, and sheep milk were evaluated [66]. The same authors reported the superiority of yoghurt made of camel’s milk in several parameters. The study of yoghurt made of camel’s milk was out of the scope of the present work, given camel milk’s absence in Greece. However, it reveals the need to examine different milk type sources that seem to have a potential in yoghurt manufacture in depth, and also reveals a tendency to surpass the dominance of cow’s milk in yoghurt manufacture.
Discriminant analysis of the physicochemical yoghurt attributes according to their fat content is presented in Figure 3.
Samples were clearly distinguished in fat content clusters. This finding is also supported by the high percentage of samples correctly classified in the appropriate fat content class—92.5% (Table 3). Stepwise analysis showed that fat, protein, and ash content, pH, and syneresis attributes were found responsible for the discrimination of yoghurt samples into fat content classes.
Discriminant analysis of the physicochemical yoghurt attributes according to their protein content is presented in Figure 4.
Strained yoghurt samples were clearly distinguished from traditional and plain yoghurt samples, which consisted of a separate cluster. This finding was reflected in the percentages of traditional and plain yoghurt samples that were misclassified as plain and traditional: 29.2% and 22.7%, respectively (Table 4).
Overall, the proportion of samples correctly classified into protein content classes was 80.3%. Separation of traditional and plain yoghurt samples in the same cluster may be explained by their processing, which is different from that of strained yoghurt. The straining process eliminates the whey and other liquids from regular yoghurt and therefore increases total solids and protein content in yoghurt. Consequently, plain and traditional yoghurt samples have lower protein content in comparison with strained yoghurt samples, and this is evident in the present study, both in Table 1 and in the graph of discriminant analysis in Figure 4. The attributes responsible for samples’ separation into protein content classes according to stepwise analysis were found to be color attribute a, pH, acidity, syneresis, and total solid, fat, and protein content.

4. Conclusions

Yoghurt is a very popular fermented dairy product all over the world. This study revealed that commercial yoghurt samples from the Greek market varied regarding their physicochemical characteristics; therefore, a wide range of different products exists in the market, meeting consumers’ needs and preferences. In the present work, the characteristics of baby yoghurts as well as of those manufactured with a mixture of cow and donkey milk selected from the Greek market are reported also. In general, the data found in the present study match those written on the label. In addition, in the samples of the present study, the maximum fat content was 10.8%, in line with the Codex Alimentarius, where a maximum fat content of 15% is set for fermented milk. Similarly, in this study, the minimum protein content was 3.29%, in line with the specifications defined in the Codex Alimentarius for fermented milk, setting a minimum protein content of 2.7%. Further studies are necessary to determine other nutritional characteristics of Greek yoghurt samples, such as their fatty acid and mineral content.

Author Contributions

Conceptualization, E.C.P. and E.K.; methodology, E.C.P., E.K., A.C.P., P.K., E.Z., E.T., A.K., L.P., P.S., M.G. and C.A.G.; software, M.G.; validation, M.G.; formal analysis, E.C.P., E.K., A.C.P., P.K., E.Z., L.P., A.K., E.T., P.S., M.G. and C.A.G.; investigation, E.C.P., E.K., A.C.P., P.K., A.K., E.Z., L.P., E.T., P.S., M.G. and C.A.G.; resources, E.C.P., E.K., A.C.P., E.T., P.S., M.G. and C.A.G.; data curation, M.G.; writing—original draft preparation, E.C.P., E.K., A.C.P., P.K., E.Z., E.T., P.S., M.G. and C.A.G.; writing—review and editing, E.C.P., E.K., A.C.P., P.K., E.Z., L.P., E.T., P.S., M.G. and C.A.G.; visualization, M.G.; supervision, E.C.P., E.K. and C.A.G.; project administration, E.C.P., E.K. and C.A.G.; funding acquisition, C.A.G. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the project FoodOmicsGR Comprehensive Characterisation of Foods (MIS 5029057), which is implemented under the action Reinforcement of the Research and Innovation Infrastructure, funded by the operational program Competitiveness, Entrepreneurship, and Innovation (NSRF 2014–2020) and co-financed by Greece and the European Union (European Regional Development Fund). Dairy 05 00034 i001

Data Availability Statement

Data is contained within the article.

Conflicts of Interest

The authors declare no conflicts of interest. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Dairy 05 00034 g001
Figure 1. Map of Greece showing the regions of yoghurt manufacture.
Figure 1. Map of Greece showing the regions of yoghurt manufacture.
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Figure 2. Discriminant analysis for different milk types using two discriminant functions of physicochemical properties of Greek yoghurt samples (+ indicates group centroid).
Figure 2. Discriminant analysis for different milk types using two discriminant functions of physicochemical properties of Greek yoghurt samples (+ indicates group centroid).
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Figure 3. Discriminant analysis for different fat content classes using two discriminant functions of physicochemical properties of Greek yoghurt samples (+ indicates group centroid).
Figure 3. Discriminant analysis for different fat content classes using two discriminant functions of physicochemical properties of Greek yoghurt samples (+ indicates group centroid).
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Figure 4. Discriminant analysis for different protein content classes using two discriminant functions of physicochemical properties of Greek yoghurt samples (+ indicates group centroid).
Figure 4. Discriminant analysis for different protein content classes using two discriminant functions of physicochemical properties of Greek yoghurt samples (+ indicates group centroid).
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Table 1. The effect of location, type of milk, yoghurt fat and protein content category on the composition and physicochemical characteristics of Greek yoghurt samples from the Greek market (least square mean ± pooled standard error).
Table 1. The effect of location, type of milk, yoghurt fat and protein content category on the composition and physicochemical characteristics of Greek yoghurt samples from the Greek market (least square mean ± pooled standard error).
Factor npHFat %Lactose %Protein %Ash %Total Solids %Titratable Acidity %Syneresis Index MDA (ng/g)L*a*b*
LocationMainland984.212.834.83 7.030.7315.411.400.2716.1091.8−2.138.23
Island104.333.675.066.870.6716.271.240.3311.9691.3−2.029.27
Pooled S.E. 0.090.520.320.310.050.510.070.043.050.580.160.73
p-value 0.1350.0770.4270.58530.1220.6770.0220.1070.1370.3680.4100.119
Milk typeCow534.332.37 a5.146.08 a0.71 ab14.30 a1.09 a0.36 a4.53 a91.4−1.85 a8.03
Goat184.292.31 a5.076.23 ab0.70 ab14.28 a1.17 a0.36 a9.17 ab91.7−2.17 a7.79
Sheep304.313.86 b4.657.58 c0.79α16.88 b1.46 b0.31 ab17.07 c90.9−2.61 b9.12
Sheep, goat, and/or cow54.242.45 ab5.077.36 bc0.79 ab15.66 ab1.53 b0.34 ab21.16 c90.3−2.22 ab8.32
Donkey and cow24.155.25 ab4.817.50 abc0.52 b18.07 b1.37 ab0.12 b18.25 abc93.3−1.53 a10.47
Pooled S.E. 0.110.650.400.390.060.640.100.053.790.730.200.91
p-value 0.839<0.0010.326<0.0010.008<0.001<0.0010.012<0.0010.072<0.0010.071
Fat contentNon-fat (<0.5%)24.350.25 a4.798.59 a0.5913.70 a1.390.39 a12.1591.68−2.227.19 a
Low fat (0.5–3%)254.282.73 b5.276.57 b0.7815.36 a1.340.28 a13.4291.25−2.118.90 ab
Full fat (3–10%)814.177.27 c4.775.69 c0.7318.46 b1.260.21 b16.5391.65−1.9010.16 a
Pooled S.E. 0.100.600.370.360.050.600.090.043.540.670.180.84
p-value 0.147<0.0010.065<0.0010.037<0.0010.2280.0040.2640.5750.1010.008
Protein contentStrained384.305.13 a5.139.17 a0.7420.10 a1.44 a0.18 a14.0692.3 a−1.88 a9.21
Traditional 484.245.04 b5.045.96 b0.6913.97 b1.34 ab0.36 b14.3991.2 b−2.26 b8.72
Plain 224.264.66 b4.665.72 b0.6713.45 b1.20 b0.36 b13.6691.0 b−2.09 ab8.31
Pooled S.E. 0.090.520.330.310.050.520.080.043.080.580.160.73
p-value 0.694<0.0010.177<0.0010.198<0.0010.002<0.0010.9480.0130.0050.321
a– Means in a column within a factor sharing no common superscript are significantly different (p < 0.05).
Table 2. Classification table for different milk types based on the composition and physicochemical characteristics of Greek yoghurt samples through discriminant analysis.
Table 2. Classification table for different milk types based on the composition and physicochemical characteristics of Greek yoghurt samples through discriminant analysis.
Predicted Milk Type
Actual Milk TypeGroup SizeCowGoatSheepSheep and Goat and/or CowDonkey and Cow
Cow533812003
(71.7%)(22.6%)(0%)(0%)(8.11%)
Goat18116001
(5.6%)(88.9%)(0%)(0.0%)(5.6%)
Sheep30012630
(0%)(3.3%)(86.7%)(10%)(0%)
Cow, Sheep and/or Goat 501130
(0%)(20%)(20%)(60%)(0%)
Donkey and Cow200002
(0.0%)(0.0%)(0%)(0%)(100%)
Cases correctly classified: 81.5%.
Table 3. Classification table for different fat content classes based on the physicochemical characteristics of Greek yoghurt samples through discriminant analysis.
Table 3. Classification table for different fat content classes based on the physicochemical characteristics of Greek yoghurt samples through discriminant analysis.
Predicted Fat Content Class
Actual Fat Content ClassGroup SizeNon-Fat (<0.5%)Low Fat
(0.5–3%)		Full Fat (3–10%)
Non-fat (<0.5%)2200
(100%)(0%)(0%)
Low fat (0.5–3%)253202
(12%)(80%)(8%)
Full fat (3–10%)810279
(0%)(2.5%)(97.5%)
Cases correctly classified: 92.5%.
Table 4. Classification table for different protein content based on the composition and physicochemical characteristics of Greek yoghurt samples through discriminant analysis.
Table 4. Classification table for different protein content based on the composition and physicochemical characteristics of Greek yoghurt samples through discriminant analysis.
Predicted Protein Content
Actual Protein ContentGroup SizeStrainedTraditionalPlain
Strained 383701
(97.4%)(0%)(2.6%)
Traditional4803414
(0%)(70.8%)(29.2%)
Plain221516
(4.6%)(22.7%)(72.7%)
Cases correctly classified: 80.3%.
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Pappa, E.C.; Kondyli, E.; Pappas, A.C.; Kyriakaki, P.; Zoidis, E.; Papalamprou, L.; Karageorgou, A.; Simitzis, P.; Goliomytis, M.; Tsiplakou, E.; et al. Physicochemical Characteristics of Commercially Available Greek Yoghurts. Dairy 2024, 5, 436-450. https://doi.org/10.3390/dairy5030034

AMA Style

Pappa EC, Kondyli E, Pappas AC, Kyriakaki P, Zoidis E, Papalamprou L, Karageorgou A, Simitzis P, Goliomytis M, Tsiplakou E, et al. Physicochemical Characteristics of Commercially Available Greek Yoghurts. Dairy. 2024; 5(3):436-450. https://doi.org/10.3390/dairy5030034

Chicago/Turabian Style

Pappa, Eleni C., Efthymia Kondyli, Athanasios C. Pappas, Panagiota Kyriakaki, Evangelos Zoidis, Lida Papalamprou, Agori Karageorgou, Panagiotis Simitzis, Michael Goliomytis, Eleni Tsiplakou, and et al. 2024. "Physicochemical Characteristics of Commercially Available Greek Yoghurts" Dairy 5, no. 3: 436-450. https://doi.org/10.3390/dairy5030034

APA Style

Pappa, E. C., Kondyli, E., Pappas, A. C., Kyriakaki, P., Zoidis, E., Papalamprou, L., Karageorgou, A., Simitzis, P., Goliomytis, M., Tsiplakou, E., & Georgiou, C. A. (2024). Physicochemical Characteristics of Commercially Available Greek Yoghurts. Dairy, 5(3), 436-450. https://doi.org/10.3390/dairy5030034

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