Effects of dissolved carbon dioxide in fat phase of cream on manufacturing and physical properties of butter
Graphical abstract
Introduction
Butter is manufactured by transforming dairy cream, an oil-in-water emulsion, to a water-in-oil emulsion by a mechanical phase-inversion process, known as churning. In the butter making, milk fat in the cream is partially crystallised during cooling and/or holding, in the “ripening” or “ageing” step, prior to churning. Upon churning the fat globules are subjected to mechanical destabilisation. The milk fat globule membrane (MFGM) is disrupted allowing non-crystalline oil phase leakage and coalescence of fat. Subsequently, phase inversion occurs, to form butter grains and butter milk. After separating out the butter milk, butter grains are worked into a mass of plastic fat by mechanical agitation and stirring (Kessler, 2002). The microstructure of the final butter consists of a continuous oil phase containing aggregates of crystalline fat, intact and damaged fat globules in which aqueous droplets and air cells are dispersed (Juriaanse and Heertje, 1988). In well-worked butter, intensive working is used to incorporate the aqueous phase as fine droplets (2.3–10.6 μm) (Van Dalen, 2002, Van Lent et al., 2008). Current international standards require that butter shall contain a maximum of 16% (w/w) of water (Codex Alimentarius, 2011).
The physical properties and complex microstructure on butter are governed by many different factors, including chemical composition of milk fat, thermal treatment of cream, processing conditions (shearing rate, churning temperature, working temperature etc.), water content and storage conditions (Buldo et al., 2013b, Hurtaud and Peyraud, 2007, Kulkarni and Murthy, 1985, Ronholt et al., 2012, Ronholt et al., 2014c, Rønholt et al., 2014, Schaffer et al., 2000, Shukla and Rizvi, 1996). Among them, for unfractionated, pure butter, the thermal treatment and “ageing” of cream has been regarded as the best economical approach to achieve desirable physical functionalities, through manipulation of parameters such as fat crystal size, shape and the presence of specific polymorphs (Precht, 1988). A range of manufacturing interventions have been investigated to manipulate the physical functionality of butter, particularly in relation to cold spreadability. These include modifying the composition of milk fat (Banks and Christie, 1990, Gerson and Escher, 1966, Hurtaud and Peyraud, 2007, Pabst et al., 1992, Precht et al., 2001), thermal treatment of cream prior to churning and varying time-temperature treatments during the ripening phase (Deman and Wood, 1958, Dixon, 1970, Dolby, 1954, Precht et al., 1990). Manipulation of gas content of the product is another approach that has been investigated for modification of spreadability. It was reported that the butter having reduced air content tended to possess glossy and smooth texture but firmer consistency (Swartling et al., 1956). Use of nitrogen to whip butter has been reported to enhance spreadability but the resulting texture was crumbly (Kleyn, 1992). Besides these reports, no information can be found on using gases to alter crystallisation conditions of cream prior to churning whereby crystal size, shape and fat polymorphs might be modified.
In previous research on pure, anhydrous milk fat (AMF) it was shown that dissolved CO2 up to 2000 ppm in the AMF can modify the crystallisation kinetics of the triglycerides (Truong et al., 2017a). For instance, dissolved CO2 concentration of 1379 ppm was found to induce higher onset crystallisation temperature of fat (25.3 ± 1.6 °C) than that of non-carbonated AMF (19.2 ± 0.4 °C) during cooling from 35 to 5 °C at 0.5 °C min−1. In the presence of dissolved CO2 AMF crystallised in mixed crystals of α, β′ and β polymorphs whereas non-treated AMF exhibited only β′ and β fat polymorphs. When 2000 ppm CO2-treated AMF was isothermally crystallised at 28 °C for 20 min, the solid fraction (4% versus 1.5%) and crystal number (800 versus 300) were 2–3-fold greater than those of 1000 ppm and 0 ppm-carbonated AMF as quantifying by microscopic image analysis. The bulk properties of the fat appeared to mirror the microstructural differences, in that the texture of CO2-treated AMF was harder (0.26–0.29 N versus 0.22 N) when being crystallised at 25 °C for 48 h. Hardness of the CO2-treated AMF tended to have lower value (39–42 N versus 46 N) when allowing to cool from 35 to 5 °C and store at 5 °C for 48 h (Truong et al., 2017a). Based on these findings it was hypothesized, but not demonstrated, that modulation of milk fat crystallisation in cream by using dissolved CO2 might provide a means to control crystallisation of milk fat and subsequently physical functionality of butter and other fat-based dairy products. Carbonation of cream and butter has been investigated previously in relation to its effect on CO2 dissolution behaviour (Ma and Barbano, 2003), microbial growth, flavour and keeping quality (Hunziker, 1924, Prucha et al., 1925). Prucha et al. (1925) studied various effects of the injection of CO2 during the entire churning process. In the first set of experiment CO2 flow was supplied for 3 min through a glass tube inserted into sweet cream, which was kept at 4.5 and 21.1 °C and aged up to 4 days. In the second set of experiment CO2 was introduced to the system at the time of churning process. According to their report, this injection method produced no measurable benefits on bacterial count and sensory attributes of the butter. Since this early work, there appear to be no more reports in the literature of any studies of cream carbonation in relation to butter quality.
The present study aimed to investigate the effects of dissolved CO2 in cream on milk fat crystallisation and whether carbonation of cream prior to churning influences the processing and physical properties of butter. Carbonation was applied to warm dairy cream at 35 °C (when the fat phase was still in liquid state) and the carbonated cream was subjected to butter making at laboratory scale with batch churning method. Churning time of the cream and changes in physical properties of resulting butter were examined. The effects of ageing time (0, 3 and 17 h) alone and coupled with carbonation treatment were also investigated. Reference samples of commercial butter were also included in this study. We also investigate whether carbonation of cream prior to churning induces any sensory defects of produced butter as perceived by consumer panellists using a triangle test.
Section snippets
Materials
Commercial cream (40% w/w fat, 2.1% protein) from Pauls® (Australia) and two commercial butter samples from Western Star and Devondale (Australia; referred as commercial butters 1 & 2, respectively) were purchased from a local grocery store. According to the manufacturers, fat contents of commercial butter 1 and 2 were 82.7% and 81.0% (w/w), respectively. Fat contents of the commercial cream and butters were verified by Roeder's weighing method as described by Dhungana et al. (2017). In brief,
pH and residual CO2 content of butter and butter milk
Previous studies on AMF showed that dissolution of CO2 increased with increasing carbonation level up to 2000 ppm (Truong et al., 2017a). Similar results were obtained in the dairy cream. CO2 is highly dissolved in warm cream at 35 °C with 920 and 1800 ppm for 1000 and 2000 ppm addition rates, respectively. In the present study, the initial concentration of CO2 at 1000 and 2000 ppm did not have a significant impact on the residual CO2 content in butter granules formed from unaged cream
Conclusions
Carbonation of dairy cream with the fat phase in liquid state (i.e. 35 °C), prior to ageing, induced changes in processing variables and physical properties of the resultant butter. For unaged cream, carbonation at 1000 and 2000 ppm resulted in shorter churning time. The pH of cream (reflected by butter milk pH) was reduced as a result of carbonation but pH reduction without carbonation did not have any effect on churning time or physical characteristics of butter. Butter made from carbonated
Conflict of interest
There are no conflicts of interest regarding this paper.
Acknowledgements
This research was supported under Australian Research Council's Industrial Transformation Research Program (ITRP) funding scheme (project number IH120100005). The ARC Dairy Innovation Hub is a collaboration between The University of Melbourne, The University of Queensland and Dairy Innovation Australia Ltd (currently disbanned).
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