WATER ACTIVITY OF SMOKED PASTA FILATA CHEESE DURING STORAGE
DOI:10.30825/5.EJPAU.189.2020.23.2

Jakub Biegalski
Department of Dairy Products Quality, Faculty of Food Science and Nutrition, Poznań University of Life Sciences, Poland

ABSTRACT

Cheeses have been produced for many thousands of years. They were and still are one of the most important dairy products. One of the most popular type are Pasta Filata cheeses. In literature it is noted that in food production water activity is one of the most important, especially when designing production process. Based on the available information, a hypothesis is proposed that conditions and shelf life of Pasta Filata cheeses can have a significant impact on their water activity. To verify this hypothesis, aw was measured in samples of Polish Pasta Filata cheese known as Rolada Ustrzycka. Samples were stored in  conditions of different temperature and time. During the analysis of the numerical data it was found that, among others, storage temperature affects the water activity of this type of  cheeses. Conclusions can be used to improve the quality of cheese during storage.

Key words: Pasta Filata cheese, water activity, durability.

INTRODUCTION

There are thousands of extremely different types of cheese around the world. They can differ in almost every aspect including taste, smell, appearance, texture, color, hardness, chemical composition, maturation time, type of microflora used, and most importantly – production methods and storage conditions [13]. A very popular type of cheeses, especially in recent years, are Pasta Filata [11]. This group includes cheeses such as Mozzarella, Scamorza, Caciocavallo, Kashkaval, as well as Polish Oscypek and Rolada Ustrzycka. It is accepted that the popularity of these products is growing every year. This is due, amongst others, to a significant increase in the consumption of dishes where one of the main ingredients is melted cheese such as pizza and casseroles. The nutritional value is also an advantage [1, 7].

Cheese structure of Pasta Filata cheeses is characterized by elasticity, flexibility and uniformity in its entire volume. There is a possibility of a split in the structure in this type of dairy products [2]. However, slightly brittle, hard structure with occasional fine bubbles or inter-grain fissures is allowed. The taste and smell of fresh Pasta Filata cheese is delicate, slightly sour and salty. The older the cheese, the more essential it becomes, not only in terms of smell, but also in terms of taste. Production technology of these products is particularly unique. Main stages of their production process are: acidification, heating and stretching of the cheese mass [1]. Especially important is the processing of the cheese mass, which has previously been subjected to acidification in water or salted whey, at a temperature of 50 °C to 70 °C. In this case, the mass softens and becomes more elastic, which allows it to submit to various shapes by pressing it into molds typical for each kind [9, 16]. During food production (including dairy products), a very important indicator affecting a wide range of biochemical changes is water activity (aw). Since water is one of the basic ingredients of all food products, monitoring its parameters is a key activity during production and storage. Water in food can come in many different forms and undergo various transformations [4]. The form in which water occurs in food products is also subject of constant transformations and interactions with other ingredients of these products. This is mainly due to the structure of its molecules.

The hypothesis adopted in this paper is: storage time and conditions of Pasta Filata cheese affect their water activity. In order to verify this hypothesis, an instrumental measurement of aw was made, based on dew point. Samples were vacuum stored under various temperature and time conditions.

MATERIALS AND METHODS

1. Preparation of Samples
The research material was Pasta Filata cheese (Rolada Ustrzycka cheese), produced through an  industrial process. It was a commercial product, store-bought in the city of Poznań. The total net weight of tested cheese was about 300 g. The cheese was of cylindrical shape, with length of 12.5 cm and width of 5.5 cm (at its widest point). The cheese (Fig. 1) was divided into 18 pieces. At first, cheese was cut with a knife into two equal halves. For simplicity, they have been marked as left and right part. Left part was first divided into 3 and then into 9 equal fragments (Fig. 2) marked as 11, 21a, 21b, 31, 41a, 41b, 51, 61a, 61b. Right part was also divided into 9 identical fragments marked as 12, 22a, 22b, 32, 42a, 42b, 52, 62a, 62b (Fig. 2). The measurement was made immediately after their preparation (T0) and after storage for 10 days at temperature +3 °C and +6 °C (T1).

2. Water activity
Water activity during storage was measured with an AquaLab Series 4TE instrument (Decagon Devices Inc., Pullman, USA) equipped with a thermostatic chamber controlled by means of measuring elements using the thermoelectric Peltier effect described by Tomaszewska-Gras et. al [19]. The accuracy of the measurement was ± 0.003 aw and the measuring range 0.03 - 1.000 aw. Measurements were carried out under conditions of thermodynamic equilibrium. The following salt solutions were used for reference: 0.5 M KCl about aw = 0.984 (15 °C), 6 M NaCl of aw = 0.760 (20 °C), 8.57 M LiCl of aw = 0.500 (25 °C) and 13.41 M LiCl of aw = 0.250 (25 °C). Samples of v = 15 mL were placed in a DE 501 measurement vessel (Decagon Devices Inc., Pullman, USA) and tested at 15 °C [6].

3. Statistical evaluation
For verification of statistical hypothesis, a level of significance at α = 0.05 was adopted. The statistical calculations were made using StatSoft, Inc. (2011) STATISTICA (data analysis software system), version 10.

RESULTS

It was shown that in samples from cheese taken immediately after unpacking, water activity was lower compared to samples stored for 10 days at temperature +3 °C (for both left and right parts) (Table 1). The higher the storage temperature of the cheese (regardless of the length of storage period), the greater this tendency may be. It was also shown that water activity of some samples was higher after storage at temperature +6 °C. This may indicate that the value of water activity may be significantly affected not by the storage time, but by temperature of this storage (Table 2). Water activity of the central part of cheese was higher than the outer edge layer. This difference was statistically significant. This tendency has been demonstrated for cheeses, regardless of their storage temperature.

DISCUSSIONS

In the literature, values of water activity are very diverse. For example, for Parmesan, the aw  value is on average 0.9160 [4, 14], for Paneer aw  = 0.950, similarly for fresh, white Mexican cheese [2, 18]. Water activity of the commercial cheeses is on average from 0.9550 (in the case of curd cheese) to 0.9240 (in the case of Gouda type cheeses) [5, 8]. This was reflected in the tested material. According to Bonczar et al. [5], differences in water activity also occur when comparing cheeses made from raw and pasteurized milk. Bonczar et al. [4] indicate that Petkova and Kozhev [17] made observations, which showed that in Kashkaval cheeses made from sheep’s milk, after 8 and 12 months of ripening, the aw  significantly decreased [3, 17]. It was also shown by authors during the study on Teleme cheeses, which were made from sheep’s, goat’s, cow’s and mixed milk, did not record changes in aw  that were likely to be significant during maturation [5, 14]. According to Bonczar et al. [4], storage time actually affects changes in the value of various tested parameters. However, changes in increasing water activity, lowering pH, chewiness and cohesiveness of cheese were statistically most significant [4].

Baranowska et al. [4] proved that water activity of soft smoked cheeses is lower than in non-smoked cheeses. The authors indicated that aw for smoked cheese is around 0.9615 (± 0.0004). They confirmed this using methods such as DSC or NMR [3]. This value is similar to the water activity of material tested, especially in case of samples from top layers of cheese, where contact with smoke was higher. Earlier mentioned authors came to the conclusion that non-smoked cheeses contain more water (by volume) than smoked cheeses. This fact suggests that smoking process may itself cause differences in distribution and binding of water to their protein-lipid matrix [4]. Before measurements, the presence of water and fat was observed inside the packaging of tested material.

Pasta Filata cheeses are suitable for consumption within a few weeks from the day of production. However it should be emphasized that the ripening process still occurs during this time. Significant changes in the quality of stored cheese may also occur  [10, 12, 15]. Changes mainly concern the surface of the product, although it may seem that they will be particularly noticeable at the very beginning in taste, smell or structure of cheese.

CONCLUSIONS

Water activity of Pasta Filata cheese ranged from 0.9157 to 0.9661. Significantly higher values were found in the middle layers compared to the top layers. This difference was smaller in cheese stored for 10 days. Significantly higher value was measured in the outer layer of cheese after storage. The higher temperature of storage, the greater the change. Such a large variations in value of aw in individual layers of Pasta Filata cheese (depending on time and temperature) indicates the fact of water dislocation.

Received: 1.062020
Reviewed: 26.06.2020
Accepted: 28.06.2020

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