Influence of the melt holding time on fat droplet size and the viscoelastic properties of model spreadable processed cheeses with different compositions
Introduction
According to Codex Alimentarius Commission (2000), processed cheese (PC) is manufactured from one or more varieties of natural cheese. Moreover, other optional dairy ingredients (e.g., anhydrous butterfat, butter, cream, milk powder, whey, buttermilk, caseinates, coprecipitates) or non-dairy ingredients (preservatives, stabilisers, flavouring agents) can be added into the processed cheese blend to improve functional properties or modify composition (Codex Alimentarius Commission, 2000; Černíková, Nebesářová, Salek, Řiháčková, & Buňka, 2017). Thereafter, the applied raw materials are shredded, blended, melted and emulsified at elevated temperatures in the presence of appropriate emulsifying salts (ES; e.g., sodium, potassium and/or ammonium salts of the citric, lactic, mono-, di- and/or polyphosphoric acids) (Codex Alimentarius Commission, 2000; El-Bakry, Duggan, O'Riordan, & O'Sullivan, 2010). In addition, the relationship between a minimum level of dry matter (DM) and a minimum level of fat in DM (FDM) in PC is also specified by the Codex Alimentarius Commission (2000). However, Codex standards are not legislation. Therefore, on the markets of the European Union (EU), there exist products with DM content lower than the amount required by the standard, whereas they still appear to be named as “processed cheese” (Černíková, Nebesářová, et al., 2017). In particular, the above-mentioned products must comply with the internal legal regulations of the individual member EU countries. In general, according to Hickey (2011), legislation on PC and related products varies a lot around the world.
One of the most important stages of PC manufacture is the continuous heating and stirring of the ingredients for a period of time allowing the formation of a homogenous and smooth mass (Fu & Nakamura, 2020). In addition, during blending and melting, ES partially solubilise caseins due to the ion-exchange (calcium to sodium or potassium) phenomenon (Fu et al., 2018b). In particular, the fat present is emulsified and the proteins are hydrated. Both the solubilisation and the hydration of casein, resulting in a temporary loosening of the protein network and a decrease in the viscosity of the melt. However, because of the swelling of the protein units, the protein–protein interactions intensify as the degree of peptisation increases.
The solubilised protein molecules may also associate with lipids. The proteins present in the formed gel network could form hydrogen and disulphide bonds, as well as electrostatic and hydrophobic interactions may occur. Furthermore, denatured β-lactoglobulin can interact with other proteins in the network such as κ-casein and other whey proteins by forming disulphide bridges. These interactions can cause an increase in the firmness of PC and decrease its meltability (Bowland & Foegeding, 2001; Nogueira de Oliveira, Ustunol, & Tamime, 2011). Calcium bridges and calcium–phosphate complexes may also be involved during the processing (Buňka et al., 2014). The re-association of the proteins results in an increase in viscosity.
The creation of the final network of the PC matrix is called creaming. The latter phenomenon is realised during heating, cooling and storage (Dimitreli, Thomareis, & Smith, 2005; Kawasaki, 2008; Lee, Buwalda, Euston, Foegeding, & McKenna, 2003; Mozuraityte, Berget, Mahdalova, Grønsberg, Øye, & Greiff, 2019).
Furthermore, consistency is one of the most important properties of PC and many factors can influence this. The latter factors can be categorised into three main groups: (i) composition of the raw materials applied (type and degree of maturity of natural cheeses, their chemical composition, type and quantity of ES, additional ingredients, etc.), (ii) processing parameters during manufacturing (temperature during melting, speed of agitation, holding time under melting temperature, rate of cooling), and (iii) storage conditions (temperature, time and permeability of the packaging material used) (Fu et al., 2018a; Fu & Nakamura, 2018; Černíková, Pachlová, et al., 2018).
The effect of processing parameters, such as holding time of the melt, on the consistency of PC spreads has been studied extensively. Swenson, Wendorff, and Lindsay (2000) investigated fat-free PC (with 40%, w/w, DM content) and stated that, the longer the holding time, the lower the firmness of the product. However, Bowland and Foegeding (2001) examined the effect of processing time (10, 20 and 30 min) on the viscoelastic properties of model PC (49.5–52.5%, w/w, DM; 51.4–54.5%, w/w, FDM) over a decreasing temperature regime from 25 °C to 80 °C (to determine sample solidification). The authors concluded that there was no relationship when the small strain analyses (G′, G'´, G∗ and δ) were performed at temperatures lower than 80 °C. Moreover, Lee et al. (2003) found that the apparent viscosity of spreadable processed cheese (SPC) melt containing 50% (w/w) DM and 50% (w/w) FDM rose until 25 mins of processing at 80 °C and then decreased. Furthermore, Černíková et al., 2017a, Černíková et al., 2017b and Černíková, Salek, Kozáčková, and Buňka (2018) investigated the effect of holding time of the melt in a selected temperature on the viscoelastic properties of PC with 35% (w/w) DM and 40% (w/w) and 50% (w/w) FDM content. These authors concluded that the firmness of PC decreased up to the 3rd minute of holding time but then increased significantly (the maximum holding time applied was 20 min). Přikryl et al. (2018) also examined the consistency of PC spreads (37%, w/w, DM and 50%, w/w, FDM) after holding times of 1, 5 and 10 min, they stated that, the longer the melt is maintained at the melting temperature, the more rigid the product becomes.
Nevertheless, the above-mentioned results are contradictory and the effect of holding time on the consistency of PC spreads with different DM and FDM contents remains unclear. Especially, the effect of holding times below 10 min (in close gaps within the holding time range) on SPC samples (with different DM and FDM contents; produced under identical processing protocol) viscoelastic properties described by the complex modulus and phase shift up to now is missing from the existing scientific literature. In general, it is accepted that the short duration of the holding time is economically advantageous. In the present study, model SPCs, manufactured with identical raw materials and under constant processing parameters (temperature, agitation speed) as well as using the same laboratory equipment, were examined. The aim of the research was to determine the effect of the holding time (0, 1, 2, 3, 4, 5, 6, 8 and 10 min) of the SPC melt (at 90 °C) on the size of milk fat droplets and selected viscoelastic properties (complex modulus and phase shift) of model SPC samples with different DM (30 and 40%, w/w) and FDM (30, 40 and 50%, w/w) contents during storage.
Section snippets
Manufacture of the samples
SPC samples [6 different PC formulations (2 DM × 3 FDM = 6)] × 9 (holding times) = 54 samples in total] were manufactured according to the protocol previously described by Černíková et al. (2017b). The formulation of the PC samples is presented in Table 1. The total weight of the produced SPC samples ranged within the interval of 1105.6–1166.4 g per batch. The composition of the ES used was as in the research of Černíková et al. (2017b). However, their total amount was calculated as a constant
Basic chemical composition of the samples
The chemical composition of the model SPC is presented in Table 2. The values of DM were comparable during the 30-day storage time and ranged from 31.11 to 31.39% (w/w) for 30% DM SPC and from 41.09 to 41.49% (w/w) for 40% DM SPC. The calculated FDM levels were also in agreement with the target values (Table 2; P > 0.05). Therefore, these samples can be used to determine the effect of the holding time on the size of milk fat droplets and the viscoelastic properties.
Regardless of the combination
Conclusions
The study of six different types of model SPCs prepared and stored for 30 days showed that the viscoelastic properties depend on the holding time, time of storage and DM and FDM contents. For most of the produced SPCs, it was demonstrated that, on the 1st, 14th and 30th day of storage, G∗ (a measure of consistency) decreased in the first 2 or 3 min of the holding time and gradually increased afterwards. In the most cases of DM and FDM contents, prolonging the holding time from the 3rd min up to
Acknowledgements
This research was supported by Own Scholarship Fund of the University of Agriculture funded by the Rector of University of Agriculture in Cracow. We acknowledge the core facility HR SEM JEOL7401F, Institution Laboratory of Electron Microscopy, Biology Centre CAS, České Budějovice, supported by the MEYS CR (LM2015062 Czech-BioImaging) and ERDF (No. CZ.02.1.01/0.0/0.0/16_013/0001775).
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