Storage stability of sodium caseinate stabilized oil-in-water emulsions as affected by severe heat treatment and storage temperatures

Wednesday, July 23, 2014: 11:15 AM
3501C (Kansas City Convention Center)
Yichao Liang , Massey University, Palmerston North, New Zealand
Graeme Gillies , Fotnerra Research and Development Centre, Palmerston North, New Zealand
Hasmukh G Patel , South Dakota State University, Brookings, SD
Lara Matia-Merino , Massey University, Palmerston North, New Zealand
Aiqian Ye , Riddet Institute, Palmerston North, New Zealand
Matt Golding , Riddet Institute, Palmerston North, New Zealand
Abstract Text:

Oil-in-water emulsions are an important basis of many food products such as soup, sauces, salad dressing, processed cheese and whipped cream. In many cases, liquid emulsions are processed at high temperature (e.g., retort or UHT processing) and maybe stored at different temperatures. There is little information on how high heat treatment and storage temperatures influence the creaming stability of caseinate-stabilized emulsions. 

In this study, we investigated the effects of heating and storage conditions on the structural, mechanical and rheological properties of caseinate-stabilized emulsions. The stock emulsion was prepared by mixing a reconstituted sodium caseinate solution (2% w/w) with 60% w/w oil and subjecting it to a high pressure homogenization. Caseinate solutions of different concentration were heated separately at 120 °C as a function of time up to 60 min. These heated caseinate solutions were then mixed with the stock emulsion in different ratios to form the model emulsions with 1−8% protein. The creaming stability of unheated emulsions was determined between 20 and 60 °C. All experiments were carried out at least in duplicate.

The creaming kinetics determined by Turbiscan showed that the phase separation of model emulsions was markedly dependent on the duration of the heat treatment. The differences between unheated and heated emulsions were attributed to the heat-induced physicochemical changes in sodium caseinate nanoparticles. At low and moderate caseinate concentrations (2% and 4% respectively), the droplet−droplet interactions were weakened while the droplet−droplet interactions increased at high Na-CN concentration (6%) by the addition of heated sodium caseinate. It seems that the former structural change is predominantly due to reduced depletion attraction, whereas both reduced depletion attraction and decreased continuous phase viscosity influenced the later structural change. Unheated emulsions stored at higher temperature (60 °C) resulted in an accelerated phase separation compared to those stored at lower storage temperatures.  The main cause was attributed to the weakened depletion energy and decreased viscosity at accelerated temperatures. Both changes lead to a rapid droplet network formation and rearrangement.

Keywords: emulsion, heat-induced degradation, depletion flocculation