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Effect of vegetable fat on the texture, colour and sensory properties of Macedonian white brined cheese

This study aimed to investigate the influence of substitution of milk fat with palm fat on the composition, yield and technological quality of White cheese, a Macedonian traditional cheese. In this study, fullfat white brined cheese was used as a control sample (WC), while experimental cheeses were prepared from cow milk with vegetable fat (WV) addition and low-fat cheese (WL), respectively. The cheeses have been analysed for physicochemical (acidity, pH, fat, fat acidity, protein), instrumental texture and colour properties (L, a, b) as well as the sensory properties after 1, 20 and 60 days. WV cheeses showed a significantly (P<0.05) lower degree of pH and higher titratable acidity than the WC and WL cheese samples. Cheese that contained vegetable fat showed lower degrees of lipolysis, as assessed by the acid-degree value and received significantly (P<0.05) better appearance, highest hardness value (5226.98 N) and cheese yield scores compared to other samples.


Introduction
The importance of maintaining adequate nutrition has become increasingly important to consumers during recent years. Foods formulation with ingredients that help in lowering health risks has been developed in cheese production in which vegetable fats and oils replaced saturated milk fat.
The nutritional profile of the cheese is improved by replacing milk fat with quality vegetable fat during which cheese becomes lower in cholesterol and changed the composition of saturated and unsaturated fatty acids (Hjalmarsson, 2015). The applications of vegetable fats give rise to different properties in cheese as a result of the vast variations (Wennermark et al., 2014). Cheese imitations are usually defined as cheese-like products made by including non-dairy fats or proteins to form a cohesive cheese-like mass (Noronha et al., 2008). The functional characteristics such as meltability and textural properties are important attributes that influence the quality and the end use of this analogue product and processed cheese (Floury et al., 2009). The yield (kg cheese/kg milk) in cheese manufacturing is of particular interest since it affects commercial feasibility. Probably the most important factor affecting cheese yield is milk composition, in particular the concentration and composition of fat and protein (Fox et al., 2000).
White brined cheese in North Macedonia ("belo salamureno sirenje") is a brine cheese type with a salty taste and close texture. It is similar to the cheeses of different countries on the Balkan Peninsula, which are included in the group of autochthonous dairy products depending on the region, specificity in production technology, quality and name (Mateva et al., 2019). The production of brined cheeses has been practised for centuries, with differences in cultural habits, technological processes and difficult climatic conditions, however, in the last decade of the century the development of standardized industrial production is intensified (Huppertz et al., 2006;Sulejmani, 2014).
A few studies have been focused on the manufacturing technology, microbiology and compositional characteristics (Mojsova et al. 2013; Dabevska-Kostoska et al. 2015) but the texture profile, colour pattern and sensory evaluation of the Macedonian white brined cheese produced with vegetable fat have not been investigated. The main objective of this investigation was to study the effects of vegetable fat on cheese composition, texture, colour and yield of the white brined cheese. Specific aims of the study were to determine the cheese yield and composition of whey during the process and examine the texture, colour and sensory properties of the final cheese. Therefore, cow's milk fat was totally and partially replaced by vegetable oils, such as palm oil to give the cheese a whiter colour, and also to reduce the production costs. The results are expected to extend the knowledge about the use of vegetable fats in cheese production. Further, the results might indicate promising formulas in the development of vegetable fat cheeses.

Cheese manufacture and sampling
White brined cheese production was carried out in industrial scale in the dairy plant "Mlekara Tetovo" using the standard manufacturing protocol ( Figure 1). The vegetable fat blend based on palm oil (Krispy, Malaysia) was added (3.00-3.50 %) to skim milk. Briefly, cow's raw milk supplied from the Tetova region (April -June 2019, North Macedonia) was standardized and pasteurized at 75 °C for 15 seconds. After the milk has been cooled to 37 °C, it is transferred into cheese vats, inoculated with 5 g/100 g starter culture (YFL-3331, CHR Hansen) followed by addition of CaCl 2 (FUDIX TM) at level 0.1 g/L cheese milk. The inoculated milk was held for 15 minutes, after which liquid rennet (CHY-MAX @ Extra, CHR) was added at a level (7 g/100 kg cheese milk) sufficient to coagulate the milk in 55 min. The milk started to coagulate after 45 minutes and the gel was sufficiently firm after 50-55 min. The gel was cut into cubes (1.5 cm) and allowed to rest in whey for 10 min and mixed afterward for 3 times. After the whey drainage, self-pressing was performed for 30-60 min at room temperature 20 °C, until the acidity of the curd reached pH 5.30. The pressure was applied by 20 kg weight per 100 kg of cheese curd until the acidity reached 35 Thorner degrees (°Th). The weights were then removed, the cheesecloth opened, the curd was cut into blocks of about 11.8 x 11.8 x 11.8 cm 3 which were kept in a 15 % brine for 16 hours (until the cheese reached pH at 4.70). After 16 hours the cheese blocks were packed into 10 kg plastic packaging, filled with 10 % brine and ripened at temperature of 18-20 °C and of 80-90 % humidity till the acidity of the cheese reaches minimum 170 °Th, respectively.

Chemical analyses
Titratable acidity (TA) of cow milk and cheese is determined by titrating with 0.1 N caustic soda solution, using phenolphthalein as the indicator and expressed in Thorner degrees (°Th). The quality of the milk was monitored at the dairy laboratory of the Food Institute (Faculty of Veterinary Medicine in Skopje, Macedonia) using the infrared spectroscopy (IR) method (Foss Milkoscan 4000, Denmark) to determine protein, fat and lactose content.
The pH of milk and cheese samples was measured using a digital pH meter (digital pH meter, model MP120FK Mettler Toledo, Greifensee, Switzerland). Cheese samples were analysed for moisture by the oven-drying method at 102 °C, fat, salt and total protein according to the AOAC (2007). The intensity of changes in the lipids of cheeses was evaluated based on the FFA (free fatty acid values) analysis using titration with KOH (IDF, 1991). All chemical measurements were done in triplicate or more. Cheese samples were chemically analysed at 1, 20 and 60 days of ripening. The cheese yield was calculated by the weight of cheese before brining (after 19 to 20 h ripening at 23 to 25 °C) divided by the weight of the milk used.

Instrumental texture analysis
The Texture analyser TAXT plus (Ametek Lloyd Inst. Ltd, UK) equipped with a cylinder probe (10 mm in diameter) was used to analyse the textural profile of chesses. The cheese samples were taken from at least 2 cm deep in the cheese blocks and their dimensions were 2.5 × 2.5 cm. The samples were compressed by 33 cm from the height of the initial sample, using two successive compression cycles at a speed of 0.5 mm / s (Ong et al., 2012).

Colour assessment
Colour intensity was performed with Ocean Optics USB2000 spectrophotometer. The reference light used was D65 (standard daylight). The colour parameters of L*, a* and b* of the samples were determined. A glass plate was placed over the Ocean Optics USB2000 spectrophotometer light probe and standardized using black and white reference plates. Samples were placed on the Petri dish for analysis and all samples were large enough to cover the entire light probe. The samples were placed on the glass plate over the light probe and covered with black glass to prevent outside light from interfering with the readings. This procedure was repeated three times with each sample.

Sensory analysis
The cheeses were evaluated at 1, 20 and 60 days of ripening by 7 trained panellist's familiar with the cheese according to the described procedure for White cheese (Sulejmani et al., 2016). The samples were evaluated by criteria appearance (scale 0-5), odour (scale 0-5), texture (0-10), and flavour (scale 0-15). Water and bread were provided to panellist to rinse their mouths between samples. Sensory analysis was conducted in 3 replicate trials and cheeses were evaluated in duplicate by each panellist in identical conditions ( Figure 2). Sensory profiling was scored on a scale from 1 to 10 points, where higher score meant more expressed attribute.

Statistical analysis
A randomised complete block design, which incorporated three treatments (WC, WV and WL cheeses), three ripening periods (1, 20 and 60 days) and two blocks (trials), was used to analyse the response variables related to cheese composition, texture, colour and sensory data. Duncan's multiple comparison tests were used as a guide for paired comparisons of treatment means. The significance of differences between treatments was considered at P<0.05 using SPSS version 16.0 for Windows (SPSS Inc., Chicago, IL, USA).

Results and discussion
The chemical composition of cow's milk used for the production of cheeses with different amount of fats is shown in Table 1. The mean chemical composition of the milk used in the manufacture of White cheese was 11.81 % total solids, 3.46 % fat, 3.15 % protein, and 4.45 % lactose. The pH of the milk was 6.62. The differences in dry matter content and fat content were significant (P<0.05) whereas pH, protein and lactose content were not different significantly, respectively. From the obtained analysis, raw cow's milk meets the requirements according to the Book of Rules for milk quality (Official Gazette 96/2011).
The gross chemical compositions of the WC, WV and WL cheeses during ripening are presented in Table 2. The fat, salt, protein contents, and lactic acid value of the cheese samples at first day of . Content of the total dry matter significantly increased at the WC and WL cheese samples during 60 days of ripening. This change is accounted by the exudation of the serum from the cheese blocks to the whey due to salt gradient. As a consequence, this results in a reduction of moisture content and a concomitant increase of salt content in the product (Papademas et al., 2000). At first day of ripening, WC cheeses were characterized by higher colour brightness (L*) than cheese-like products and low fat cheeses ( Table 2) vegetable fat white brined-cheese (WV), as assessed by the acid-degree value (ADV), was shown in Figure 3.
The highest levels of acid degree values (ADVs) are present in WC matured cheese (11.9 mEq. KOH g/100 g cheese fat) compared to WV and WL (9.3 mEq KOH g/100 g cheese fat). Full fat cheese showed free acidity values significantly higher compared to low-fat cheese and cheese-like product with fat replacers' addition. The cheese with vegetable fat (WV) and low-fat cheese (WL) resulted in a lower (ADVs) degree due to the slower lipolysis and the formation of free volatile fatty acids. These results were in accordance with those previously reported in the literature which showed the reduction of free acidity values with fat content decrease (Romeih et al., 2002).

Texture profile
Textural parameter profiles are shown in Table  3. Hardness and chewiness values significantly increased (P<0.05) during ripening, probably due to an increase in the salt concentration of brine that resulted in the loss of moisture throughout cheese maturation (except for WV cheeses). For all cheese variants hardness changed regularly during storage. The highest hardness value was observed on day 60 at WV cheese whereas the lowest at WL cheeses. ties in each type of cheese (Marshall, 1991). The cheese containing fat was significantly firmer than the cheeses with reduced fat (P<0.05). In contrasts to Yu and Hammond (2000), no significant differences were found for cheese produced with vegetable fat except in cohesiveness. These findings are in consistent with the result of Lobato-C alleros et al. (1997) but the opposite situation was conducted from the Dinkçi et al. (2011) who reported significant differences in the texture and colour of Turkish Kashar cheese produced with vegetable fat and milk fat.
Cohesiveness probably decreased via casein network breakage and springiness by the loss of moisture. Our results are in consistent with Guinee, (2016) where at low temperatures (<5 °C), milk fat is predominantly solid and adds to the elasticity/ rigidity of the casein matrix.
Gumminess and chewiness show significant change among the cheese with different fat and also the ripening exhibited differences among the same samples (except WV cheeses). Therefore, the increase in hardness and adhesiveness found during the maturation of Ibores cheese were exclusively  (1982) indicated that high acidity in cheese and high protein and total solid contents generally make the cheese harder and with less capacity of deformation, which is in line with our results. However, proteolysis reactions had no considerable effect on the texture formation in this cheese.

Sensory evaluation
Sensory profile of white brined cheese as affected by fat replacement and reduction are presented in Table 4. Appearance, flavour and total acceptance were significantly affected by fat replacement and reduction, while texture and color were not. Cheese containing vegetable fat had low flavor notes and was inferior to that of cheese made from whole milk which was with best results and flavor notes. The milk fat product perceived higher sensory scores even though the vegetable fat product was sensory and texturally acceptable. The texture of higher-fat cheeses is generally more acceptable than texture of their lower-fat counterparts (Muir et al., 1997).
Low-fat cheeses were characterized by a lower overall score compared to all other cheese samples. This could be due to the significantly lower fat content in the low-fat cheese ( Table 2). In addition, significantly higher scores were attributed to both, cheese-like product and full-fat cheese samples in comparison to low-fat cheese (Table 4).
Low-fat white brined cheese-like products received significantly similar scores for body texture compared to full-fat cheese. These findings are in agreement with data reported and Felfoul et al. (2015Felfoul et al. ( , 2016 for Gouda and Katsiari and Voutsinas (1994) for Feta cheeses. According to the panellists, full-fat cheese (WC) showed a significantly higher overall impression with an overall score 92 compared to white brined cheese-like product (WV) and low-fat (WL) with 90 and 75, respectively (Table 4). Fat substitution had a significant effect on the overall assessment of the cheeses. However, all cheeses were appreciated as acceptable by the panellists. This result was in agreement with findings on lowfat Gouda cheese-like product (Felfoul et al., 2015).