Elsevier

International Dairy Journal

Volume 97, October 2019, Pages 25-30
International Dairy Journal

Rheological methods to analyse the thermal aggregation of calcium enriched milks

https://doi.org/10.1016/j.idairyj.2019.05.001Get rights and content

Abstract

The colloidal state of calcium enriched milks during heating and its microstructures were analysed through interpretation of rheometric data with the Brownian aggregation theory, which can be considered as complementary to the methods currently used. Viscosity was measured at 100 s−1 through temperature and time sweeps. It was observed that from 25 to 60 °C, viscosity slowly decreased as temperature increased; above 60 °C, viscosity sharply increased at different temperatures depending on the amount of CaCl2. From time sweeps, the aggregation of casein micelles was described through the Smoluchowski theory. The addition of CaCl2 at concentrations of 20–30 mmol kg−1 decreased the stability factor 5 to 6 orders of magnitude compared with non-enriched milk. Values of the fractal dimension indicated that aggregation yields disordered aggregates occluding high amounts of solvent. The methodology described may help to analyse colloidal stability and structures when different calcium salts are used for enrichment.

Introduction

The need for increasing population calcium intake has led to the development of a variety of calcium-enriched dairy products (Canabady-Rochelle et al., 2007, Janve and Singhal, 2018, Koutina et al., 2015). However, when the delicate mineral equilibria in milk are modified, different changes can occur. Particularly, the addition of calcium salts reduces the pH and influences the level of colloidal calcium phosphate, the proportion of caseins in the micellar and serum phases, the activity of Ca2+ and the ionic strength of the milk. Also, the hydration of casein micelles (CM) and the zeta potential are reduced (Famelart et al., 1999, Koutina et al., 2015, Philippe et al., 2003, Philippe et al., 2005). As a consequence, these changes can affect the heat stability of milk (Omoarukhe et al., 2010, On-Nom et al., 2012, Sievanen et al., 2008, Singh, 2004).

On the one hand, heat processing of calcium enriched milk is challenging from a technological point of view (Koutina, Christensen, Bakman, Andersen, & Skibsted, 2016). For instance, the sediment deposition or film formation in heat exchangers (recognised as fouling) are increased by the addition of calcium in milk (Bansal and Chen, 2006, Boumpa et al., 2008). Fouling reduces the process efficiency, can compromise the product by contamination, and needs a regular and more intensive cleaning (Hooper et al., 2006, Sadeghinezhad et al., 2013). In this case, calcium addition has a negative impact on heat processing of enriched milk.

On the other hand, the heat treatment of calcium enriched milk was proposed as a novel process that leads to milk coagulation and to formation of the so called “calcium-milk coagulum” (Koutina et al., 2016, Ramasubramanian et al., 2014). For instance, a fine gel network can be obtained by combining calcium addition to milk, pH adjustment and heat treatment (Koutina et al., 2016) or strong calcium-induced milk gels can be obtained using heat treatment at 70 °C (Ramasubramanian et al., 2014). In this case, calcium addition to milk can be advantageously used for making novel dairy products.

Therefore, there are many aspects that justify the study of the heat stability of milk as affected by calcium addition. The literature relating milk calcium supplementation, physicochemical changes and heat stability is vast and a wide variety of techniques has been used to fulfil this purpose (Dumpler and Kulozik, 2015, Jeurnink and de Kruif, 1993, Kaushik et al., 2015, Koutina and Skibsted, 2015, Koutina et al., 2016, Lin et al., 2018, Omoarukhe et al., 2010, On-Nom et al., 2012, Sievanen et al., 2008, Singh, 2004, Singh et al., 2007). However, the characterisation of calcium enriched milk during heating through rheological properties is still scarce and necessary. The aim of the present study was to analyse the rheological properties of calcium enriched milks during heating through the classical shear rate rheometry. Particularly, we intended to get additional information about the extent to which the stability of milks changes due to calcium enrichment and the microstructures obtained when the thermal aggregation begins after CM destabilisation and before gel formation.

Section snippets

Preparation of milk samples

Skim milk powder (SanCor Cooperativas Unidas Ltda., Sunchales, Argentina: 4%, w/w, moisture; 1.5%, w/w, fat; 35%, w/w, protein; 8.5%, w/w, ash; 31 mmol kg−1 calcium) obtained with a low heat treatment that reduces the level of denatured whey proteins was used. Milk samples were prepared at a level of 10% (w/w), following the manufacturer's recommendations. The required amount of powder was gradually added to purified water at 25 °C while stirring at moderate speed. Samples were sealed and

Thermal aggregation of CM according to the Brownian aggregation theory

The heating of milk at high temperatures leads to coagulation, which is a consequence of the loss of CM stability. In this sense, the surface properties of CM rather than the interior ones are likely to be important (Singh, 2004). As a result, the CM surface characteristics provide electrostatic and steric stabilisation (Dalgleish and Corredig, 2012, de Kruif, 1999, Horne, 2006). Heat treatment markedly modifies the serum phase environment around the CM. pH decreases, calcium phosphate is

Results and discussion

Fig. 1 shows experimental results obtained through Test A (temperature sweep). Two well differentiated temperature ranges were observed: (a) from 25 to 60 °C, where the viscosity slowly decreases as temperature increases; and (b) above 60 °C, where the viscosity sharply increases but at different temperatures depending on the amount of CaCl2 added.

It is widely recognised that equilibria in milk are affected by temperature. For instance, between 4 and 40 °C, among the expected changes that

Conclusions

In this work, we explored some rheological properties of calcium enriched milks during heating through shear rate rheometry. When the viscosity of milks was measured as function of temperature, it was observed that between 25 and 60 °C, the viscosity of all milks slowly decreases. This decrease of viscosity was analysed by an Arrhenius-type equation and, from the values of EA obtained, it was observed that the viscosity change with heating is similar for all cases studied. Also, the viscosity

Acknowledgements

This study was conducted with the financial support of Universidad Nacional del Litoral (project CAI+D: 504 201501 00051 LI) (Santa Fe, Argentina), Consejo Nacional de Investigaciones Científicas y Técnicas (project CONICET: 11220150100606) (Argentina), and Agencia Nacional de Promoción Científica y Tecnológica (projects ANPCyT: PICT 2015-365 and 2016-249) (Argentina).

References (36)

  • Y. Lin et al.

    Altering the physico-chemical and processing characteristics of high heat treated skim milk by increasing the pH prior to heating and restoring after heating

    Food Chemistry

    (2018)
  • P.G. Miller et al.

    The coagulation temperature of milk as affected by pH, salts, evaporation and previous heat treatment

    Journal of Dairy Science

    (1940)
  • N. On-Nom et al.

    Heat stability of milk supplemented with calcium chloride

    Journal of Dairy Science

    (2012)
  • M. Philippe et al.

    The effects of different cations on the physicochemical characteristics of casein micelles

    Food Chemistry

    (2005)
  • L. Ramasubramanian et al.

    The rheological properties of calcium-induced milk gels

    Journal of Food Engineering

    (2014)
  • G. Singh et al.

    Heat stability and calcium bioavailability of calcium-fortified milk

    Lebensmittel-Wissenschaft und -Technologie- Food Science and Technology

    (2007)
  • J.F. Vélez-Ruiz et al.

    Rheological properties of concentrated milk as a function of concentration, temperature and storage time

    Journal of Food Engineering

    (1998)
  • B. Bansal et al.

    A critical review of milk fouling in heat exchangers

    Comprehensive Reviews in Food Science and Food Safety

    (2006)
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