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Chemical and sensory characteristics of Galotyri-type cheese made using different procedures
Food Control 19 (2008) 301–307 www.elsevier.com/locate/foodcont
Chemical and sensory characteristics of Galotyri-type cheese made using different procedures E. Kondyli *, M.C. Katsiari, L.P. Voutsinas National Agricultural Research Foundation, Dairy Research Institute, 452 21 Ioannina, Greece Received 22 August 2006; received in revised form 30 March 2007; accepted 6 April 2007
Abstract The objective of this study was to determine the effects of different manufacturing processes of Galotyri-type cheese on its chemical and sensory characteristics, with the aim to help cheesemakers to produce cheese of more consistent and high quality. Three cheesemaking methods were evaluated, namely production of cheese using salted ewes’ milk, starter culture and rennet (SM + R), and starter culture with or without rennet and salting the curd after draining (R + SC or SC, respectively). The SC cheese had significantly (P < 0.05) higher moisture and lower fat and protein contents than the other two cheeses made with rennet. No significant (P > 0.05) differences in fat-in-dry matter, lactose, salt, salt-in-moisture, ash, pH, acidity and yield were observed among the cheeses studied. The cheesemaking method significantly affected cheese proteolysis as shown by the determination of water soluble nitrogen (WSN). Omission of rennet during Galotyri-type cheese preparation resulted in reduced proteolysis during manufacture and storage. The SM + R cheese had higher levels of WSN than the other cheeses throughout storage. No bitterness or off-flavour was noted by any member of the taste panel in SC and R + SC cheeses. On the contrary, the SM + R cheese exhibited slight bitterness and unclean flavour after 15 days from manufacture. The R + SC cheese had the most consistent quality during storage and was the most preferred by the panelists. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Galotyri cheese; Fresh cheese; Acid/rennet-curd cheese
1. Introduction Galotyri is considered as one of the oldest traditional cheeses in Greece (Anifantakis, 1991; Eekhof-Stork, 1976) made from ewe or goat milk or mixtures of both. According to Zygouris (1952) and Davis (1976) Galotyri is produced in many regions of Greece in many ways. Details about six manufacturing methods (i.e., salting the cheese milk or curd, using or not rennet as well as starter, etc.) are given by Zygouris (1952). The existence of different manufacturing methods has as result the production of different types of Galotyri cheese with variations regarding the appearance and sensory properties (Anifantakis,
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1991). There is a National Individual Standard for Galotyri cheese (General Chemical State Laboratories, 1988), which was further completed (Anonymous, 1994) and submitted to European Economic Community (EEC) for approval. In 1996, the EEC with the regulation 1107/96 gave Galotyri cheese the designation of Prodected Denomination of Origin (PDO). According to this, the milk used for Galotyri production should be of good quality, whole raw or pasteurized, derived from the regions of Epirus and Thessaly. The addition of traditional rennet or other enzymes as well as of harmless starter cultures is allowed. The use of milk powder or concentrate, milk proteins, casein salts, colouring substances, preservatives, other than sodium chloride, and antibiotics are prohibited. According to the PDO cheese-making procedure, the raw milk is boiled, and then is placed in a vessel, preferably made of clay, where it is left for about 24 h at room temperature. After that, it is salted with 3.5–4.0% NaCl, mixed thoroughly
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and left for two more days, with periodic stirring, and gradually acidity is developed. Occasionally, rennet and or lactic culture may be added before salting to facilitate milk acidification and coagulation. The curd is then transferred to cloth or leather bags or wooden barrels for draining. The above process is repeated to the milk of the next milkings until the barrels or bags are filled up; these are then sealed and transferred to dry cold storage rooms (68 °C) for up to two months for ripening, in case the cheese is produced from raw milk. Galotyri is a white cheese with spreadable texture, without a rind and holes and is characterized by a sourish and pleasant refreshing taste and aroma (Anonymous, 1994). Due to its high moisture content (675%), the shelf-life of Galotyri is limited to 30 days at 4 °C. Since Galotyri cheese has pleasant organoleptic characteristics much appreciated by the Greek consumers, in recent years there is a great demand for its production. As a result, small and big dairies in many regions of the country produce a cheese, which resembles Galotyri, using processes different from the above-mentioned for the PDO cheese (i.e. curd salting with 62% NaCl and very short or no ripening). Thus, today there are several Galotyri-type fresh cheeses in the market, which differ in chemical composition and sensory characteristics. To date, no study to determine the effects of different manufacturing processes of Galotyri-type cheese currently being used in dairies on its chemical and sensory characteristics has been done. Thus, our objective was to compare different production procedures of Galotyri-type cheese with the main goal to determine the one leading to a consistently high quality product.
cooled to 30 °C, and inoculated with a freeze-dried concentrated mesophilic starter culture, MA011 (Danisco, France), consisting of a mixture of Lactococcus lactis ssp. lactis and Lactococcus lactis ssp. cremoris. The freeze – dried culture was added directly to the cheese milk at the supplier’s recommended level, i.e. at a rate of 2.5 units/100 L cheese milk. At the same time, calf rennet powder (HA-LA, Hansen’s Laboratorium, Denmank), dissolved in cold water, was added at a quantity of 0.25 g/100 L milk, and mixed well. Coagulation at 30 °C was stopped when the pH was dropped to a value of 4.4, after 20 h. The curd was transferred in a cloth bag, using a ladle, which was then hung from a rafter in the store room for curd draining at 15 °C for 6 h. After draining, the curd was taken out from the bag on a clean board, mixed well with dry salt (1.5%, w/w), and packed in plastic containers which were transferred to a cold room (2–3 °C) for storage up to 30 days. The experiment was replicated three times. A flow chart of the Galotyritype cheese manufacture using different procedures is presented in Fig. 1.
Standardization of milk
Heating (85 ˚C for 10 min) Addition of salt 1 (1.5 %, w/v) Cooling (30 ˚C)
Addition of starter culture (2.5U/100 L milk)
2. Materials and methods 2.1. Cheese manufacture Bulk ewes’ milk from the morning milking was obtained from the herd of the Agricultural Research Station of Ioannina. The average composition of standardized cheese milk was fat 6.01%, protein 5.65%, lactose 4.97%, solids-non-fat (SNF) 11.3% and pH 6.62. Three vats of cheese were made on the same day at the pilot plant of the Institute on a 10 kg scale. The treatments tested, and thus the resultant cheeses, were designated as following, depending on whether the milk or the curd was salted and if rennet was used or not: SM + R, cheese made from salted milk with commercial starter culture and rennet; SC, cheese made using starter culture, no rennet and dry salting of curd after draining; R + SC, cheese made with starter culture and rennet and dry salting of curd after draining. The raw milk was poured in a single-wall, stainless-steel vessel, over a gas burner, to simulate the traditional manufacturing method and heated to 85 °C for 10 min. After heating, salt (1.5%, w/v) was added in the milk, if required, and then the milk was
Addition of rennet 2 (0.25 g/100 L milk)
Incubation (30 ˚C, until pH to 4.4, ~ 20h) Curd transferring in cloth bag
Curd draining (15 ˚C for ~ 6h) Curd dry salting 1 (1.5 %, w/w)
Packaging in plastic containers
Storage (2-3 ˚C for 30 days) Fig. 1. Generalized flow chart of Galotyri-type cheese production. 1 Salt is added either in the cheese milk or in the curd. 2 Addition of rennet is optional.
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2.2. Chemical analyses Samples of cheese milk were analysed for fat, protein, lactose and SNF using Milkoscan, model FT 600 (Foss Electric, Denmark). The pH of the milk was determined using a Hanna model HI 98240 pH-meter (Hanna Instruments, USA) and continuously recorded during incubation using a strip chart recorder. Cheese samples were analysed for moisture (IDF, 1958), fat (BSI, 1955), protein (IDF, 1986), salt (Kosikowski, 1978) and ash (IDF, 1964). The lactose content was determined by subtracting the sum of fat, protein and ash contents of each cheese sample from the corresponding total solids content. The cheese pH was measured with the above mentioned pH-meter and the titratable acidity according to Ling (1963). Yield of Galotyri cheese was determined as the ratio of weight of produced cheese to the initial weight of milk used. Cheese proteolysis was followed by determining the water soluble nitrogen (WSN) as described by Katsiari and Voutsinas (1994). The concentration of WSN was expressed as percentage of total nitrogen (TN). 2.3. Sensory evaluation of cheese Samples of Galotyri-type cheese were placed in white plastic cups coded with three-digit random numbers. The samples were tempered by holding at ambient temperature (18 ± 2 °C) and then presented to the panelists in a random order for testing. Water was provided for mouth washing between samples. The cheeses were evaluated organoleptically at 2, 15 and 30 days after manufacture by a five-member panel from the Institute’s staff familiar with Galotyri cheese, following the recommendations of IDF (1997). The panelists had attended a general program (attributes, scale, description of sensory impressions and common cheese defects) on the sensory evaluation of cheese. Moreover, prior to sensory evaluation, the panelists participated in a review session. Panel members evaluated cheese for appearance, body and texture, and flavour (odor and taste) using a 10-point scale, with 1 being the worst and 10 the best quality. Importance was given predominantly to the attributes of flavour and of body and texture over the appearance of the cheese. Thus, the scores obtained for these two attributes were multiplied by 5 and 4, respectively. The total score was obtained by adding the scores for the three sensory attributes. An excellent cheese received a total score of 100. Panel members were also instructed to report any defects in appearance, body and texture or flavor, using the quality terms of the IDF (1997) guide for the sensory evaluation of cheese. 2.4. Statistical analysis The data were subjected to an analysis of variance using Statgraphics (Statistical Graphics Corp., Rockville, MD). When significant (P < 0.05) differences were found among
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treatments, means were compared using Tukey’s test (Steel & Torrie, 1960). 3. Results and discussion 3.1. Chemical characteristics It should be mentioned that in preliminary experiments, we also tested the production of Galotyri-type cheese from salted milk with starter culture but not rennet. However, this production procedure was excluded from further experiments because of the long coagulation time (48 h) required and the fact that the curd could not be drained well, with concomitant result the cheese to have a higher than permitted moisture content and a very watery texture. The mean values for the chemical characteristics of Galotyri-type cheese produced by different methods at the age of 2 days are shown in Table 1. No significant (P > 0.05) differences in the moisture content between the cheeses made using rennet were found. On the other hand, the SC cheeses made without rennet had significantly (P < 0.05) higher moisture content compared to the cheeses made with rennet, which was above the maximum permitted limit of 75% set by the Greek Standard for Galotyri cheese (Anonymous, 1994). This finding may be attributed to the firmer texture of the latter cheeses than that of the SC cheese. Fresh cheeses are usually produced using small amount of rennet in order to improve the draining characteristics of the curd and increase curd firmness (Jelen & Renz-Schauen, 1989). The SC cheese also had significantly Table 1 Chemical characteristicsc at 2 days and proteolysis during storage of Galotyri-type cheese made by different methods Component
Production methodd SM + R
SC
R + SC
Moisture (%) Fat (%) FDM (%) Protein (%) NaCl (%) Lactose (%) S/M (%) Ash (%) pH Acidity (%lactic acid) Yield (%) WSN (%TN) at 1 day WSN (%TN) at 15 days WSN (%TN) at 30 days DWSN (%TN) 30 dayse
74.1 ± 0.74b 10.8 ± 0.29a 40.3 ± 1.08a 9.78 ± 0.06a 1.56 ± 0.02a 3.20 ± 0.13a 2.11 ± 0.02a 2.19 ± 0.01a 4.39 ± 0.03a 0.73 ± 0.01a 52.0 ± 0.59a 6.97 ± 0.38a 7.30 ± 0.30a 8.67 ± 0.22a 1.70 ± 0.37a
76.4 ± 0.13a 9.50 ± 0.29b 40.2 ± 1.37a 9.19 ± 0.06b 1.58 ± 0.10a 2.69 ± 0.23a 2.07 ± 0.13a 2.27 ± 0.04a 4.41 ± 0.02a 0.71 ± 0.01a 52.1 ± 0.77a 5.73 ± 0.11b 6.10 ± 0.26b 6.76 ± 0.17b 1.03 ± 0.17a
73.9 ± 0.39b 10.67 ± 0.51a 40.8 ± 1.70a 10.1 ± 0.24a 1.60 ± 0.04a 3.00 ± 0.27a 2.17 ± 0.06a 2.38 ± 0.10a 4.40 ± 0.03a 0.74 ± 0.01a 51.7 ± 0.29a 6.09 ± 0.13ab 6.49 ± 0.07ab 7.13 ± 0.06b 1.04 ± 0.20a
a,b Means in each row bearing a common superscript did not differ significantly (P > 0.05). c Mean values ± SE of three trials. d SM + R, cheese made from salted milk with starter culture and rennet; SC, cheese made with starter culture, no rennet and dry salting of curd after draining; R + SC, cheese made with starter culture and rennet and dry salting of curd after draining. e Increase in WSN (% TN) between 1 and 30 days.
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(P < 0.05) lower fat content than the other two cheeses. However, the fat-in-dry matter (FDM) contents of all cheeses met the Greek legal specification of a minimum of 40% for Galotyri cheese (Anonymous, 1994). These results are in agreement with those found for commercial and pilot (industrial or artisan) Galotyri cheeses by Rogga et al. (2005) but higher than those reported for moisture (70.8%) and fat (13.8%) by Anifantakis (1991). Moreover, Papageorgiou, Bori, and Mantis (1998) reported a value of 65% for moisture in traditional Galotyri. There were significant (P < 0.05) differences in protein content among the Galotyri-type cheeses. Thus, the cheeses made with rennet contained more protein than the cheese made without rennet (Table 1). This difference was probably due to the significantly (P < 0.05) higher moisture content of the latter cheese. The protein contents of Galotyri-type cheeses found in the present study were close to the value of 9.8% reported for the protein of traditional Galotyri by Anifantakis (1991). As may be seen from Table 1, no significant (P > 0.05) differences in lactose, salt, salt-in-moisture (S/M), ash, pH, acidity and yield were observed among the cheeses. The salt content of cheeses was remarkably lower than that of 2.8% and 3.0% reported for traditional and pilot Galotyri cheeses by Anifantakis (1991) and Rogga et al. (2005), respectively. In recent years, Galotyri-type cheeses are less salted compared to the traditional cheese in order to meet the current consumers’ demands in terms of taste habits and health concerns. Fig. 2 shows the effect of different production methods of Galotyri-type cheese on pH development during milk coagulation. The pH of all cheese milks was slowly decreased during the first 4 h of fermentation, rapidly up to 12 h and then levelled off. The rate of pH decrease between 4 and 12 h of fermentation was higher in the cheeses salted after draining than in the cheese made from salted milk. It should be noted that the pH of all cheeses remained constant during draining and storage, despite their high lactose content. This indicates that the activity of the starter culture used was inhibited by the low pH achieved. It is known that meso-
6.5
pH
6.0 5.5 5.0 4.5 0
2
4
6
8
10
12
14
Time (h) Fig. 2. pH changes during coagulation, for various Galotyri-type cheese production methods: SM + R, cheese made from salted milk with starter culture and rennet (n); SC, cheese made with starter culture, no rennet and salted after draining (s); R + SC, cheese made with starter culture and rennet and salted after draining (j).
philic cocci are not acid tolerant and are rapidly inhibited when the pH falls below 5.5 (Parente & Cogan, 2004). The pH values of cheeses (Table 1) was close to that (4.2) found for Galotyri-type samples bought from the local market, but higher than that (3.8–4.0) found for Galotyri cheese by Anifantakis (1991) and Rogga et al. (2005). The average value (52%) for the cheese yield found in the present study is similar to that reported for the traditional Galotyri cheese by Zygouris (1952). Moreover, the finding that no significant difference in yield was observed among cheeses (Table 1), despite the fact that the moisture content of the SC cheese was significantly higher than that of the other two cheeses, can be attributed to the higher loss of fines through the cloth in the former cheese during draining because of its weaker body. As can be seen from Table 1, the SC cheese had significantly lower fat and protein contents than the other cheeses. Proteolysis in cheese is often measured by means of quantification of WSN fraction of cheese, which consists of whey proteins, medium- and small-sized peptides from the degradation of caseins and free amino acids (Christensen, Bech, & Werner, 1991). Rennet is responsible for the initial hydrolysis of caseins and the production of most of WSN in the cheese; the action of starter bacteria or other enzymes is less important at this level of proteolysis but is primarily responsible for the production of small peptides and free amino acids (Fox, Singh, & McSweeney, 1995). The WSN fraction can be used in interpreting sensory analysis data of cheese (McGugan, Emmons, & Larmond, 1979). Proteolysis in Galotyri-type cheese was found to be significantly affected by the manufacturing process. As shown in Table 1, the level of WSN, as expected, was higher in the cheeses made with rennet than in the SC cheese made without rennet at all sampling ages. This suggests the important role of rennet in proteolysis of Galotyri-type cheese during manufacture and storage, consistent with the findings of Zakrzewski, Stepaniak, Abrahamsen, and Sørhaug (1991) and Mara and Kelly (1998) for Quarg cheese. The cheese produced without rennet (SC) showed some proteolysis, indicating that rennet is not the sole active proteolytic agent. The SM + R cheese had higher WSN values than the R + SC cheese, especially after storage for 30 days (Table 1). The increased early proteolysis in SM + R cheese may be attributed to the increased activity of rennet during cheese manufacture due to the presence of NaCl in the cheese milk. The level of WSN increased in all cheeses during storage (Table 1), but not significantly (P > 0.05), indicating that the low storage temperature inhibited the rennet activity. Mara and Kelly (1998) also found that the level of WSN was increased in all experimental Quarg cheeses during a 4 week storage at 5 °C. Moreover, Xanthopoulos, Polychroniadou, Litopoulou-Tzanetaki, and Tzanetakis (2000) reported that the level of proteolysis (mg of L-glycine equivalent per kg cheese) was continuously increased in Anevato cheese, a traditional fresh spreadable Greek PDO cheese, during storage at 4 °C.
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3.2. Sensory characteristics The results of the sensory panel’s assessment of cheese quality at the age of 2, 15 and 30 days are shown in Table 2. The appearance scores for the cheeses made with rennet were significantly (P < 0.05) higher than those of the SC cheese made without rennet at all sampling ages. The former cheeses had a rough appearance whereas the latter cheese had a more uniform and viscous yoghurt-like appearance. No whey separation from the cheeses was observed during storage. It should be noted that firmer Galotyri is more desirable by the consumers. The body and texture scores of the cheeses made with rennet were significantly (P < 0.05) higher than those of cheese made without rennet at all sampling ages (Table 2). Moreover, no significant (P > 0.05) difference in body and texture score was observed between the cheeses made with rennet but salted at different stage of manufacture. The SC cheeses had a smooth, weak body and texture and exhibited difficulties to remove sufficient whey during draining. Conversely, the cheeses made with rennet had a firmer consistency. As can be seen from Table 2, the cheese made with rennet and salted after draining (R + SC) received higher flavour scores than the other two experimental cheeses, and especially the one made from salted milk (SM + R). Moreover, the flavour score of the latter cheese decreased greatly at 15 days and then remained almost constant by the end of storage. On the contrary, the flavour scores of the other two cheeses remained relatively constant up to 15 days and then slightly decreased at 30 days. The total score (total assessment) of R + SC cheese was significantly (P < 0.05) higher than those of the other two cheeses almost at all sampling ages (Table 2). Moreover, there was no significant (P > 0.05) difference in total score between SM + R and SC cheeses, except at 2 days. In general, the R + SC cheese
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exhibited the most consistent quality and was the most preferred by the panelists, followed by the SC cheese (Table 2). Some of the panelists commented that all cheeses had a less acidic taste than some of the corresponding commercial products available on the market. These products have pH values about 3.8–4.0 (Rogga et al., 2005) and very sour taste which is not desirable by many, especially young, consumers which generally prefer cheeses with mild taste. No off-flavour or bitterness was noted by any member of the taste panel in the SC and R + SC cheeses during storage. On the contrary, the SM + R cheese was criticized by all panelists for slight bitterness and unclean flavours after 15 and 30 days of storage. It should be pointed out, however, that despite these flavour defects the cheese was of acceptable quality, as indicated in Table 2. There are several factors influencing the bitterness development in cheese during storage, such as rennet retention and activity, enzymes from the starter culture used and enzymes from adventitious microflora due to microbial contamination (Jelen & Renz-Schauen, 1989). The fact that off-flavour and bitterness were noted only in the SM + R cheese and not in the SC and the R + SC cheeses indicates that microbial contamination and the starter culture used were not the causes of these flavour defects. Therefore, these defects may be attributed to the increased activity of rennet and the concomitant increased level of primary proteolysis in the former cheese during manufacture and storage (Table 1), probably as a result of the NaCl present in the cheese milk. It is known that the proteolytic activity of rennet on asl-casein is stimulated by NaCl concentrations up to an optimum at 5% (Guinee & Fox, 1987). Similar bitterness development in a 2–4 week old traditional Quarg cheese, a fresh acid – or acid/rennet – coagulated cheese, has been correlated with the amount of rennet used (Sohal, Roehl, & Jelen, 1988) indicating that the prob-
Table 2 Sensory characteristicsc of Galotyri-type cheese made by different methods during storage Sensory characteristic
Age of cheese (days)
Production methodd SM + R
e
SC
R + SC
Appearance (10)
2 15 30
9.36 ± 0.18 9.13 ± 0.13a 9.23 ± 0.03a
8.12 ± 0.11 8.13 ± 0.12b 8.40 ± 0.10b
9.13 ± 0.09a 9.13 ± 0.13a 9.30 ± 0.15a
Body and texture (40)e
2 15 30
36.4 ± 0.23a 36.1 ± 0.81a 35.6 ± 0.61a
31.3 ± 0.48b 31.2 ± 0.92b 32.3 ± 0.27b
35.7 ± 0.33a 36.5 ± 0.53a 36.1 ± 0.93a
Flavour (50)e
2 15 30
44.0 ± 0.50a 35.8 ± 2.10b 36.3 ± 0.83b
41.4 ± 0.30b 42.8 ± 0.60ab 41.3 ± 1.52ab
43.9 ± 0.58a 43.5 ± 2.02a 42.1 ± 1.10a
Total (100)e
2 15 30
89.8 ± 0.75a 81.1 ± 1.14b 81.2 ± 1.42b
80.9 ± 0.33b 82.2 ± 1.48b 81.9 ± 1.83b
88.7 ± 0.65a 89.2 ± 1.49a 87.5 ± 1.03a
a,b
a
b
Means in each row bearing a common superscript did not differ significantly (P > 0.05). Mean values ± SE of three trials. d SM + R, cheese made from salted milk with starter culture and rennet; SC, cheese made with starter culture, no rennet and dry salting of curd after draining; R + SC, cheese made with starter culture and rennet and salting of curd after draining. e Values in parentheses are maximum attainable scores. c
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lem may be the increased proteolytic activity of the residual rennet in the high moisture (75%), low-pH (4.4) environment of Quarg. When the rennet used was lowered, the bitterness was reduced and an acceptable product was obtained. As expected, significantly higher proteolysis during storage was observed in Quarg produced with than without rennet (Mara & Kelly, 1998; Sohal et al., 1988; Zakrzewski et al., 1991). Moreover, it has been reported that starter proteinases contribute little to primary proteolysis and bitterness in Quarg (Mara & Kelly, 1998; Sohal et al., 1988), probably due to the fact that lactic acid bacteria are generally weakly proteolytic (Fox, O’ Connor, McSweeney, Guinee, & O’ Brien, 1996). Galotyri-type cheese is a nutritious food with high content of valuable dairy protein (Table 1). Thus, it is a much richer source of protein than yoghurt. Moreover, its low fat content, compared to other cheese varieties, is undoubtedly an important factor in Galotyri-type cheese acceptance by the nutrition-conscious consumer. Therefore, the market potential for excellent quality Galotyri-type cheese is very good, giving the dairy industry the opportunity to satisfy the current consumer demand for low fat and protein containing dairy foods. 4. Conclusions The results from the comparative study of different manufacturing processes of Galotyri-type cheese currently being used in dairies showed that the cheesemaking technology had a significant impact on cheese quality, by affecting the development of proteolysis in cheese. Addition of rennet improved the draining characteristics of the curd and increased curd firmness. Salting the cheese milk resulted in a significant deterioration of Galotyri-type cheese flavour during storage, due to the development of bitterness and off-flavour. The use of rennet and the salting of curd, rather than the cheese milk, contributed to a more consistent Galotyri-type cheese quality. Thus, the cheese made with starter culture and rennet and dry salting of curd after draining was the most preferred by the panelists among the three cheeses studied. This study has provided a flow chart of the cheesemaking process for the production of a very good quality Galotyri-type cheese. Further work is underway in order to determine the effect of different commercial starter cultures on the quality of Galotyri-type cheese made using the cheesemaking process for the R + SC cheese, with the aim to select the starter giving the best and most consistent during storage cheese quality. Acknowledgements The authors thank the Greek Dairy Organization for the financial support of this study, A. Velivassis for his valuable help in cheesemaking, Vardoulis S.A. (Trikala, Greece) for providing free samples of the starter culture, and S. Koutelida for typing the manuscript.
References Anifantakis, E. M. (1991). Greek cheeses: A tradition of centuries. Athens: National Dairy Committee of Greece, pp. 55–57. Anonymous (1994). Newspaper of the Government of the Hellenic Republic. Issue 2, No. 8 (pp. 60–61). Athens: National Printing Office. BSI (1955). Gerber method for the determination of fat in milk and milk products. British Standard 696. London: British Standards Institution. Christensen, T. M. I. E., Bech, A.-M., & Werner, H. (1991). Methods for crude fractionation (extraction and precipitation) of nitrogen components in cheese. IDF Bulletin 261. Brussels: International Dairy Federation, pp. 4–9. Davis, J. G. (1976). Cheese, Vol. III, Manufacturing methods. London: Churchill Livingstone, p. 879. Eekhof-Stork, N. (1976). The world atlas of cheese. London: Paddington Press Ltd., p. 136. Fox, P. F., O’ Connor, T. P., McSweeney, P. L. H., Guinee, T. P., & O’ Brien, N. M. (1996). Cheese: Physical, biochemical and nutritional aspects. Advances in Food and Nutrition Research, 39, 163– 328. Fox, P. F., Singh, T. K., & McSweeney, P. L. H. (1995). Biogenesis of flavour compounds in cheese. In E. L. Malin & M. H. Tunick (Eds.), Chemistry of structure-function relationships in cheese (pp. 59–98). New York: Plenum Publishing Corporation. General Chemical State Laboratories (1988). Newspaper of the Government of the Helenic Republic, Issue 2, No. 892 (p. 8401). Athens: National Printing Office. Guinee, T. P., & Fox, P. F. (1987). Salt in cheese: Physical, chemical and biological aspects. In P. F. Fox (Ed.), Cheese: Chemistry, physics and microbiology. General aspects (Vol.1, pp. 251–297). London: Elsevier Academic Press. IDF (1958). Determination of dry matter in cheese and processed cheese. IDF Standard 4. Brussels: International Dairy Federation. IDF (1964). Determination of the ash content of processed cheese products. IDF Standard 27. Brussels: International Dairy Federation. IDF (1986). Milk. Determination of nitrogen content (Kjeldahl method) and calculation of crude protein content. IDF Standard 20A. Brussels: International Dairy Federation. IDF (1997). Sensory evaluation of dairy products by scoring. IDF Standard 99C. Brussels: International Dairy Federation. Jelen, P., & Renz-Schauen, A. (1989). Quarg manufacturing innovations and their effects on quality, nutritive value, and consumer acceptance. Food Technology, 43(3), 74–81. Katsiari, M. C., & Voutsinas, L. P. (1994). Manufacture of lowfat Kefalograviera cheese. International Dairy Journal, 4, 533–553. Kosikowski, F. V. (1978). Cheese and fermented milk foods (2nd ed.). New York: FV Kosikowski and Associates. Ling, E. R. (1963). A textbook of dairy chemistry (3rd ed.). London: Chapman & Hall Ltd. Mara, O., & Kelly, A. I. (1998). Contribution of milk enzymes, starter and rennet to proteolysis during storage of Quarg. International Dairy Journal, 8, 973–979. McGugan, W. A., Emmons, D. B., & Larmond, E. (1979). Influence of volatile and nonvolatile fractions on intensity of cheddar cheese flavour. Journal of Dairy Science, 62, 398–403. Papageorgiou, D. K., Bori, M., & Mantis, A. (1998). Survival of Listeria monocytogenes during storage of soft cheeses Galotyri and Touloumotyri at 5 °C and 12 °C. Bulletin of the Hellenic Veterinary Medical Society, 49, 48–53. Parente, E., & Cogan, T. M. (2004). Starter cultures: General aspects. In P. F. Fox, P. L. H. McSweeney, T. M. Cogan, & T. P. Guinee (Eds.), Cheese: Chemistry, physics and microbiology, Vol. 1, General aspects (3rd ed., pp. 123–147). London: Elsevier Academic Press. Rogga, K. J., Samelis, J., Kakouri, A., Katsiari, M. C., Savvaidis, I. N., & Kontominas, M. G. (2005). Survival of Listeria monocytogenes in Galotyri, a traditional Greek soft acid-curd cheese, stored aerobically at 4 °C and 12 °C. International Dairy Journal, 15, 59–67.
E. Kondyli et al. / Food Control 19 (2008) 301–307 Sohal, T. S., Roehl, D., & Jelen, P. (1988). Rennet as a cause of bitterness developments in Quarg. Journal of Dairy Science, 71, 3188–3196. Steel, R. G. D., & Torrie, J. H. (1960). Principles and procedures of statistics with special reference to the biological science. New York: McGraw-Hill. Xanthopoulos, V., Polychroniadou, A., Litopoulou-Tzanetaki, E., & Tzanetakis, N. (2000). Characteristics of Anevato cheese made from
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raw or heat-treated goat milk inoculated with a lactic starter. Lebensmittel- Wissenschaft und- Technologie, 33, 483–488. Zakrzewski, E., Stepaniak, L., Abrahamsen, R. K., & Sørhaug, T. (1991). Effect of thermization on the quality of Quarg. International Dairy Journal, 1, 199–208. Zygouris, N. (1952). The milk industry (2nd ed.). Athens: Ministry of Agriculture, pp. 428–429.
Chemical and sensory characteristics of Galotyri-type cheese made using different procedures E. Kondyli *, M.C. Katsiari, L.P. Voutsinas National Agricultural Research Foundation, Dairy Research Institute, 452 21 Ioannina, Greece Received 22 August 2006; received in revised form 30 March 2007; accepted 6 April 2007
Abstract The objective of this study was to determine the effects of different manufacturing processes of Galotyri-type cheese on its chemical and sensory characteristics, with the aim to help cheesemakers to produce cheese of more consistent and high quality. Three cheesemaking methods were evaluated, namely production of cheese using salted ewes’ milk, starter culture and rennet (SM + R), and starter culture with or without rennet and salting the curd after draining (R + SC or SC, respectively). The SC cheese had significantly (P < 0.05) higher moisture and lower fat and protein contents than the other two cheeses made with rennet. No significant (P > 0.05) differences in fat-in-dry matter, lactose, salt, salt-in-moisture, ash, pH, acidity and yield were observed among the cheeses studied. The cheesemaking method significantly affected cheese proteolysis as shown by the determination of water soluble nitrogen (WSN). Omission of rennet during Galotyri-type cheese preparation resulted in reduced proteolysis during manufacture and storage. The SM + R cheese had higher levels of WSN than the other cheeses throughout storage. No bitterness or off-flavour was noted by any member of the taste panel in SC and R + SC cheeses. On the contrary, the SM + R cheese exhibited slight bitterness and unclean flavour after 15 days from manufacture. The R + SC cheese had the most consistent quality during storage and was the most preferred by the panelists. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Galotyri cheese; Fresh cheese; Acid/rennet-curd cheese
1. Introduction Galotyri is considered as one of the oldest traditional cheeses in Greece (Anifantakis, 1991; Eekhof-Stork, 1976) made from ewe or goat milk or mixtures of both. According to Zygouris (1952) and Davis (1976) Galotyri is produced in many regions of Greece in many ways. Details about six manufacturing methods (i.e., salting the cheese milk or curd, using or not rennet as well as starter, etc.) are given by Zygouris (1952). The existence of different manufacturing methods has as result the production of different types of Galotyri cheese with variations regarding the appearance and sensory properties (Anifantakis,
*
Corresponding author. Tel.: +30 26510 94783; fax: +30 26510 92523. E-mail address: efi[email protected] (E. Kondyli).
0956-7135/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodcont.2007.04.007
1991). There is a National Individual Standard for Galotyri cheese (General Chemical State Laboratories, 1988), which was further completed (Anonymous, 1994) and submitted to European Economic Community (EEC) for approval. In 1996, the EEC with the regulation 1107/96 gave Galotyri cheese the designation of Prodected Denomination of Origin (PDO). According to this, the milk used for Galotyri production should be of good quality, whole raw or pasteurized, derived from the regions of Epirus and Thessaly. The addition of traditional rennet or other enzymes as well as of harmless starter cultures is allowed. The use of milk powder or concentrate, milk proteins, casein salts, colouring substances, preservatives, other than sodium chloride, and antibiotics are prohibited. According to the PDO cheese-making procedure, the raw milk is boiled, and then is placed in a vessel, preferably made of clay, where it is left for about 24 h at room temperature. After that, it is salted with 3.5–4.0% NaCl, mixed thoroughly
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and left for two more days, with periodic stirring, and gradually acidity is developed. Occasionally, rennet and or lactic culture may be added before salting to facilitate milk acidification and coagulation. The curd is then transferred to cloth or leather bags or wooden barrels for draining. The above process is repeated to the milk of the next milkings until the barrels or bags are filled up; these are then sealed and transferred to dry cold storage rooms (68 °C) for up to two months for ripening, in case the cheese is produced from raw milk. Galotyri is a white cheese with spreadable texture, without a rind and holes and is characterized by a sourish and pleasant refreshing taste and aroma (Anonymous, 1994). Due to its high moisture content (675%), the shelf-life of Galotyri is limited to 30 days at 4 °C. Since Galotyri cheese has pleasant organoleptic characteristics much appreciated by the Greek consumers, in recent years there is a great demand for its production. As a result, small and big dairies in many regions of the country produce a cheese, which resembles Galotyri, using processes different from the above-mentioned for the PDO cheese (i.e. curd salting with 62% NaCl and very short or no ripening). Thus, today there are several Galotyri-type fresh cheeses in the market, which differ in chemical composition and sensory characteristics. To date, no study to determine the effects of different manufacturing processes of Galotyri-type cheese currently being used in dairies on its chemical and sensory characteristics has been done. Thus, our objective was to compare different production procedures of Galotyri-type cheese with the main goal to determine the one leading to a consistently high quality product.
cooled to 30 °C, and inoculated with a freeze-dried concentrated mesophilic starter culture, MA011 (Danisco, France), consisting of a mixture of Lactococcus lactis ssp. lactis and Lactococcus lactis ssp. cremoris. The freeze – dried culture was added directly to the cheese milk at the supplier’s recommended level, i.e. at a rate of 2.5 units/100 L cheese milk. At the same time, calf rennet powder (HA-LA, Hansen’s Laboratorium, Denmank), dissolved in cold water, was added at a quantity of 0.25 g/100 L milk, and mixed well. Coagulation at 30 °C was stopped when the pH was dropped to a value of 4.4, after 20 h. The curd was transferred in a cloth bag, using a ladle, which was then hung from a rafter in the store room for curd draining at 15 °C for 6 h. After draining, the curd was taken out from the bag on a clean board, mixed well with dry salt (1.5%, w/w), and packed in plastic containers which were transferred to a cold room (2–3 °C) for storage up to 30 days. The experiment was replicated three times. A flow chart of the Galotyritype cheese manufacture using different procedures is presented in Fig. 1.
Standardization of milk
Heating (85 ˚C for 10 min) Addition of salt 1 (1.5 %, w/v) Cooling (30 ˚C)
Addition of starter culture (2.5U/100 L milk)
2. Materials and methods 2.1. Cheese manufacture Bulk ewes’ milk from the morning milking was obtained from the herd of the Agricultural Research Station of Ioannina. The average composition of standardized cheese milk was fat 6.01%, protein 5.65%, lactose 4.97%, solids-non-fat (SNF) 11.3% and pH 6.62. Three vats of cheese were made on the same day at the pilot plant of the Institute on a 10 kg scale. The treatments tested, and thus the resultant cheeses, were designated as following, depending on whether the milk or the curd was salted and if rennet was used or not: SM + R, cheese made from salted milk with commercial starter culture and rennet; SC, cheese made using starter culture, no rennet and dry salting of curd after draining; R + SC, cheese made with starter culture and rennet and dry salting of curd after draining. The raw milk was poured in a single-wall, stainless-steel vessel, over a gas burner, to simulate the traditional manufacturing method and heated to 85 °C for 10 min. After heating, salt (1.5%, w/v) was added in the milk, if required, and then the milk was
Addition of rennet 2 (0.25 g/100 L milk)
Incubation (30 ˚C, until pH to 4.4, ~ 20h) Curd transferring in cloth bag
Curd draining (15 ˚C for ~ 6h) Curd dry salting 1 (1.5 %, w/w)
Packaging in plastic containers
Storage (2-3 ˚C for 30 days) Fig. 1. Generalized flow chart of Galotyri-type cheese production. 1 Salt is added either in the cheese milk or in the curd. 2 Addition of rennet is optional.
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2.2. Chemical analyses Samples of cheese milk were analysed for fat, protein, lactose and SNF using Milkoscan, model FT 600 (Foss Electric, Denmark). The pH of the milk was determined using a Hanna model HI 98240 pH-meter (Hanna Instruments, USA) and continuously recorded during incubation using a strip chart recorder. Cheese samples were analysed for moisture (IDF, 1958), fat (BSI, 1955), protein (IDF, 1986), salt (Kosikowski, 1978) and ash (IDF, 1964). The lactose content was determined by subtracting the sum of fat, protein and ash contents of each cheese sample from the corresponding total solids content. The cheese pH was measured with the above mentioned pH-meter and the titratable acidity according to Ling (1963). Yield of Galotyri cheese was determined as the ratio of weight of produced cheese to the initial weight of milk used. Cheese proteolysis was followed by determining the water soluble nitrogen (WSN) as described by Katsiari and Voutsinas (1994). The concentration of WSN was expressed as percentage of total nitrogen (TN). 2.3. Sensory evaluation of cheese Samples of Galotyri-type cheese were placed in white plastic cups coded with three-digit random numbers. The samples were tempered by holding at ambient temperature (18 ± 2 °C) and then presented to the panelists in a random order for testing. Water was provided for mouth washing between samples. The cheeses were evaluated organoleptically at 2, 15 and 30 days after manufacture by a five-member panel from the Institute’s staff familiar with Galotyri cheese, following the recommendations of IDF (1997). The panelists had attended a general program (attributes, scale, description of sensory impressions and common cheese defects) on the sensory evaluation of cheese. Moreover, prior to sensory evaluation, the panelists participated in a review session. Panel members evaluated cheese for appearance, body and texture, and flavour (odor and taste) using a 10-point scale, with 1 being the worst and 10 the best quality. Importance was given predominantly to the attributes of flavour and of body and texture over the appearance of the cheese. Thus, the scores obtained for these two attributes were multiplied by 5 and 4, respectively. The total score was obtained by adding the scores for the three sensory attributes. An excellent cheese received a total score of 100. Panel members were also instructed to report any defects in appearance, body and texture or flavor, using the quality terms of the IDF (1997) guide for the sensory evaluation of cheese. 2.4. Statistical analysis The data were subjected to an analysis of variance using Statgraphics (Statistical Graphics Corp., Rockville, MD). When significant (P < 0.05) differences were found among
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treatments, means were compared using Tukey’s test (Steel & Torrie, 1960). 3. Results and discussion 3.1. Chemical characteristics It should be mentioned that in preliminary experiments, we also tested the production of Galotyri-type cheese from salted milk with starter culture but not rennet. However, this production procedure was excluded from further experiments because of the long coagulation time (48 h) required and the fact that the curd could not be drained well, with concomitant result the cheese to have a higher than permitted moisture content and a very watery texture. The mean values for the chemical characteristics of Galotyri-type cheese produced by different methods at the age of 2 days are shown in Table 1. No significant (P > 0.05) differences in the moisture content between the cheeses made using rennet were found. On the other hand, the SC cheeses made without rennet had significantly (P < 0.05) higher moisture content compared to the cheeses made with rennet, which was above the maximum permitted limit of 75% set by the Greek Standard for Galotyri cheese (Anonymous, 1994). This finding may be attributed to the firmer texture of the latter cheeses than that of the SC cheese. Fresh cheeses are usually produced using small amount of rennet in order to improve the draining characteristics of the curd and increase curd firmness (Jelen & Renz-Schauen, 1989). The SC cheese also had significantly Table 1 Chemical characteristicsc at 2 days and proteolysis during storage of Galotyri-type cheese made by different methods Component
Production methodd SM + R
SC
R + SC
Moisture (%) Fat (%) FDM (%) Protein (%) NaCl (%) Lactose (%) S/M (%) Ash (%) pH Acidity (%lactic acid) Yield (%) WSN (%TN) at 1 day WSN (%TN) at 15 days WSN (%TN) at 30 days DWSN (%TN) 30 dayse
74.1 ± 0.74b 10.8 ± 0.29a 40.3 ± 1.08a 9.78 ± 0.06a 1.56 ± 0.02a 3.20 ± 0.13a 2.11 ± 0.02a 2.19 ± 0.01a 4.39 ± 0.03a 0.73 ± 0.01a 52.0 ± 0.59a 6.97 ± 0.38a 7.30 ± 0.30a 8.67 ± 0.22a 1.70 ± 0.37a
76.4 ± 0.13a 9.50 ± 0.29b 40.2 ± 1.37a 9.19 ± 0.06b 1.58 ± 0.10a 2.69 ± 0.23a 2.07 ± 0.13a 2.27 ± 0.04a 4.41 ± 0.02a 0.71 ± 0.01a 52.1 ± 0.77a 5.73 ± 0.11b 6.10 ± 0.26b 6.76 ± 0.17b 1.03 ± 0.17a
73.9 ± 0.39b 10.67 ± 0.51a 40.8 ± 1.70a 10.1 ± 0.24a 1.60 ± 0.04a 3.00 ± 0.27a 2.17 ± 0.06a 2.38 ± 0.10a 4.40 ± 0.03a 0.74 ± 0.01a 51.7 ± 0.29a 6.09 ± 0.13ab 6.49 ± 0.07ab 7.13 ± 0.06b 1.04 ± 0.20a
a,b Means in each row bearing a common superscript did not differ significantly (P > 0.05). c Mean values ± SE of three trials. d SM + R, cheese made from salted milk with starter culture and rennet; SC, cheese made with starter culture, no rennet and dry salting of curd after draining; R + SC, cheese made with starter culture and rennet and dry salting of curd after draining. e Increase in WSN (% TN) between 1 and 30 days.
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(P < 0.05) lower fat content than the other two cheeses. However, the fat-in-dry matter (FDM) contents of all cheeses met the Greek legal specification of a minimum of 40% for Galotyri cheese (Anonymous, 1994). These results are in agreement with those found for commercial and pilot (industrial or artisan) Galotyri cheeses by Rogga et al. (2005) but higher than those reported for moisture (70.8%) and fat (13.8%) by Anifantakis (1991). Moreover, Papageorgiou, Bori, and Mantis (1998) reported a value of 65% for moisture in traditional Galotyri. There were significant (P < 0.05) differences in protein content among the Galotyri-type cheeses. Thus, the cheeses made with rennet contained more protein than the cheese made without rennet (Table 1). This difference was probably due to the significantly (P < 0.05) higher moisture content of the latter cheese. The protein contents of Galotyri-type cheeses found in the present study were close to the value of 9.8% reported for the protein of traditional Galotyri by Anifantakis (1991). As may be seen from Table 1, no significant (P > 0.05) differences in lactose, salt, salt-in-moisture (S/M), ash, pH, acidity and yield were observed among the cheeses. The salt content of cheeses was remarkably lower than that of 2.8% and 3.0% reported for traditional and pilot Galotyri cheeses by Anifantakis (1991) and Rogga et al. (2005), respectively. In recent years, Galotyri-type cheeses are less salted compared to the traditional cheese in order to meet the current consumers’ demands in terms of taste habits and health concerns. Fig. 2 shows the effect of different production methods of Galotyri-type cheese on pH development during milk coagulation. The pH of all cheese milks was slowly decreased during the first 4 h of fermentation, rapidly up to 12 h and then levelled off. The rate of pH decrease between 4 and 12 h of fermentation was higher in the cheeses salted after draining than in the cheese made from salted milk. It should be noted that the pH of all cheeses remained constant during draining and storage, despite their high lactose content. This indicates that the activity of the starter culture used was inhibited by the low pH achieved. It is known that meso-
6.5
pH
6.0 5.5 5.0 4.5 0
2
4
6
8
10
12
14
Time (h) Fig. 2. pH changes during coagulation, for various Galotyri-type cheese production methods: SM + R, cheese made from salted milk with starter culture and rennet (n); SC, cheese made with starter culture, no rennet and salted after draining (s); R + SC, cheese made with starter culture and rennet and salted after draining (j).
philic cocci are not acid tolerant and are rapidly inhibited when the pH falls below 5.5 (Parente & Cogan, 2004). The pH values of cheeses (Table 1) was close to that (4.2) found for Galotyri-type samples bought from the local market, but higher than that (3.8–4.0) found for Galotyri cheese by Anifantakis (1991) and Rogga et al. (2005). The average value (52%) for the cheese yield found in the present study is similar to that reported for the traditional Galotyri cheese by Zygouris (1952). Moreover, the finding that no significant difference in yield was observed among cheeses (Table 1), despite the fact that the moisture content of the SC cheese was significantly higher than that of the other two cheeses, can be attributed to the higher loss of fines through the cloth in the former cheese during draining because of its weaker body. As can be seen from Table 1, the SC cheese had significantly lower fat and protein contents than the other cheeses. Proteolysis in cheese is often measured by means of quantification of WSN fraction of cheese, which consists of whey proteins, medium- and small-sized peptides from the degradation of caseins and free amino acids (Christensen, Bech, & Werner, 1991). Rennet is responsible for the initial hydrolysis of caseins and the production of most of WSN in the cheese; the action of starter bacteria or other enzymes is less important at this level of proteolysis but is primarily responsible for the production of small peptides and free amino acids (Fox, Singh, & McSweeney, 1995). The WSN fraction can be used in interpreting sensory analysis data of cheese (McGugan, Emmons, & Larmond, 1979). Proteolysis in Galotyri-type cheese was found to be significantly affected by the manufacturing process. As shown in Table 1, the level of WSN, as expected, was higher in the cheeses made with rennet than in the SC cheese made without rennet at all sampling ages. This suggests the important role of rennet in proteolysis of Galotyri-type cheese during manufacture and storage, consistent with the findings of Zakrzewski, Stepaniak, Abrahamsen, and Sørhaug (1991) and Mara and Kelly (1998) for Quarg cheese. The cheese produced without rennet (SC) showed some proteolysis, indicating that rennet is not the sole active proteolytic agent. The SM + R cheese had higher WSN values than the R + SC cheese, especially after storage for 30 days (Table 1). The increased early proteolysis in SM + R cheese may be attributed to the increased activity of rennet during cheese manufacture due to the presence of NaCl in the cheese milk. The level of WSN increased in all cheeses during storage (Table 1), but not significantly (P > 0.05), indicating that the low storage temperature inhibited the rennet activity. Mara and Kelly (1998) also found that the level of WSN was increased in all experimental Quarg cheeses during a 4 week storage at 5 °C. Moreover, Xanthopoulos, Polychroniadou, Litopoulou-Tzanetaki, and Tzanetakis (2000) reported that the level of proteolysis (mg of L-glycine equivalent per kg cheese) was continuously increased in Anevato cheese, a traditional fresh spreadable Greek PDO cheese, during storage at 4 °C.
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3.2. Sensory characteristics The results of the sensory panel’s assessment of cheese quality at the age of 2, 15 and 30 days are shown in Table 2. The appearance scores for the cheeses made with rennet were significantly (P < 0.05) higher than those of the SC cheese made without rennet at all sampling ages. The former cheeses had a rough appearance whereas the latter cheese had a more uniform and viscous yoghurt-like appearance. No whey separation from the cheeses was observed during storage. It should be noted that firmer Galotyri is more desirable by the consumers. The body and texture scores of the cheeses made with rennet were significantly (P < 0.05) higher than those of cheese made without rennet at all sampling ages (Table 2). Moreover, no significant (P > 0.05) difference in body and texture score was observed between the cheeses made with rennet but salted at different stage of manufacture. The SC cheeses had a smooth, weak body and texture and exhibited difficulties to remove sufficient whey during draining. Conversely, the cheeses made with rennet had a firmer consistency. As can be seen from Table 2, the cheese made with rennet and salted after draining (R + SC) received higher flavour scores than the other two experimental cheeses, and especially the one made from salted milk (SM + R). Moreover, the flavour score of the latter cheese decreased greatly at 15 days and then remained almost constant by the end of storage. On the contrary, the flavour scores of the other two cheeses remained relatively constant up to 15 days and then slightly decreased at 30 days. The total score (total assessment) of R + SC cheese was significantly (P < 0.05) higher than those of the other two cheeses almost at all sampling ages (Table 2). Moreover, there was no significant (P > 0.05) difference in total score between SM + R and SC cheeses, except at 2 days. In general, the R + SC cheese
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exhibited the most consistent quality and was the most preferred by the panelists, followed by the SC cheese (Table 2). Some of the panelists commented that all cheeses had a less acidic taste than some of the corresponding commercial products available on the market. These products have pH values about 3.8–4.0 (Rogga et al., 2005) and very sour taste which is not desirable by many, especially young, consumers which generally prefer cheeses with mild taste. No off-flavour or bitterness was noted by any member of the taste panel in the SC and R + SC cheeses during storage. On the contrary, the SM + R cheese was criticized by all panelists for slight bitterness and unclean flavours after 15 and 30 days of storage. It should be pointed out, however, that despite these flavour defects the cheese was of acceptable quality, as indicated in Table 2. There are several factors influencing the bitterness development in cheese during storage, such as rennet retention and activity, enzymes from the starter culture used and enzymes from adventitious microflora due to microbial contamination (Jelen & Renz-Schauen, 1989). The fact that off-flavour and bitterness were noted only in the SM + R cheese and not in the SC and the R + SC cheeses indicates that microbial contamination and the starter culture used were not the causes of these flavour defects. Therefore, these defects may be attributed to the increased activity of rennet and the concomitant increased level of primary proteolysis in the former cheese during manufacture and storage (Table 1), probably as a result of the NaCl present in the cheese milk. It is known that the proteolytic activity of rennet on asl-casein is stimulated by NaCl concentrations up to an optimum at 5% (Guinee & Fox, 1987). Similar bitterness development in a 2–4 week old traditional Quarg cheese, a fresh acid – or acid/rennet – coagulated cheese, has been correlated with the amount of rennet used (Sohal, Roehl, & Jelen, 1988) indicating that the prob-
Table 2 Sensory characteristicsc of Galotyri-type cheese made by different methods during storage Sensory characteristic
Age of cheese (days)
Production methodd SM + R
e
SC
R + SC
Appearance (10)
2 15 30
9.36 ± 0.18 9.13 ± 0.13a 9.23 ± 0.03a
8.12 ± 0.11 8.13 ± 0.12b 8.40 ± 0.10b
9.13 ± 0.09a 9.13 ± 0.13a 9.30 ± 0.15a
Body and texture (40)e
2 15 30
36.4 ± 0.23a 36.1 ± 0.81a 35.6 ± 0.61a
31.3 ± 0.48b 31.2 ± 0.92b 32.3 ± 0.27b
35.7 ± 0.33a 36.5 ± 0.53a 36.1 ± 0.93a
Flavour (50)e
2 15 30
44.0 ± 0.50a 35.8 ± 2.10b 36.3 ± 0.83b
41.4 ± 0.30b 42.8 ± 0.60ab 41.3 ± 1.52ab
43.9 ± 0.58a 43.5 ± 2.02a 42.1 ± 1.10a
Total (100)e
2 15 30
89.8 ± 0.75a 81.1 ± 1.14b 81.2 ± 1.42b
80.9 ± 0.33b 82.2 ± 1.48b 81.9 ± 1.83b
88.7 ± 0.65a 89.2 ± 1.49a 87.5 ± 1.03a
a,b
a
b
Means in each row bearing a common superscript did not differ significantly (P > 0.05). Mean values ± SE of three trials. d SM + R, cheese made from salted milk with starter culture and rennet; SC, cheese made with starter culture, no rennet and dry salting of curd after draining; R + SC, cheese made with starter culture and rennet and salting of curd after draining. e Values in parentheses are maximum attainable scores. c
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lem may be the increased proteolytic activity of the residual rennet in the high moisture (75%), low-pH (4.4) environment of Quarg. When the rennet used was lowered, the bitterness was reduced and an acceptable product was obtained. As expected, significantly higher proteolysis during storage was observed in Quarg produced with than without rennet (Mara & Kelly, 1998; Sohal et al., 1988; Zakrzewski et al., 1991). Moreover, it has been reported that starter proteinases contribute little to primary proteolysis and bitterness in Quarg (Mara & Kelly, 1998; Sohal et al., 1988), probably due to the fact that lactic acid bacteria are generally weakly proteolytic (Fox, O’ Connor, McSweeney, Guinee, & O’ Brien, 1996). Galotyri-type cheese is a nutritious food with high content of valuable dairy protein (Table 1). Thus, it is a much richer source of protein than yoghurt. Moreover, its low fat content, compared to other cheese varieties, is undoubtedly an important factor in Galotyri-type cheese acceptance by the nutrition-conscious consumer. Therefore, the market potential for excellent quality Galotyri-type cheese is very good, giving the dairy industry the opportunity to satisfy the current consumer demand for low fat and protein containing dairy foods. 4. Conclusions The results from the comparative study of different manufacturing processes of Galotyri-type cheese currently being used in dairies showed that the cheesemaking technology had a significant impact on cheese quality, by affecting the development of proteolysis in cheese. Addition of rennet improved the draining characteristics of the curd and increased curd firmness. Salting the cheese milk resulted in a significant deterioration of Galotyri-type cheese flavour during storage, due to the development of bitterness and off-flavour. The use of rennet and the salting of curd, rather than the cheese milk, contributed to a more consistent Galotyri-type cheese quality. Thus, the cheese made with starter culture and rennet and dry salting of curd after draining was the most preferred by the panelists among the three cheeses studied. This study has provided a flow chart of the cheesemaking process for the production of a very good quality Galotyri-type cheese. Further work is underway in order to determine the effect of different commercial starter cultures on the quality of Galotyri-type cheese made using the cheesemaking process for the R + SC cheese, with the aim to select the starter giving the best and most consistent during storage cheese quality. Acknowledgements The authors thank the Greek Dairy Organization for the financial support of this study, A. Velivassis for his valuable help in cheesemaking, Vardoulis S.A. (Trikala, Greece) for providing free samples of the starter culture, and S. Koutelida for typing the manuscript.
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