Synergistic effect of milk solids and carrot cell wall particles on the rheology and texture of yoghurt gels

Abstract

There is growing interest to improve texture, flavour and health benefits of manufactured foods, particularly dairy based products, using natural fruit and vegetable fibre. In this study, we aimed to investigate whether cell wall particles (CWP) could be used to replace part of milk solids and still maintain the gel strength and texture of the yoghurt gel. Set yoghurts with total solids of 12% w/w were used as the benchmark. Effects of replacing milk solids with carrot CWP at 1 or 2% on the gelation kinetics, microstructure, rheological and textural properties of yoghurt gels were examined. Replacement of 1% milk solids by CWP produced gels with similar rheological properties to that of the 12% milk solid gel. Confocal images showed that most of the carrot CWP was individually embedded in the casein micelle network providing a ‘filler’ effect and synergistically contributed to the rheological properties of the yoghurt gel. However, replacement of 2% milk solids by CWP lowered the complex modulus (G*) of the gel. G* remained low even for the yoghurt prepared with 13% total solids where 2% milk solids were replaced by CWP. This is because CWP can also form a particulate network at 2%, thereby hindering the casein micelles to form a connected colloidal network. This was demonstrated by the delay of the peak in tan δ during fermentation. However, the texture analysis revealed that the substitution of 2% milk solids by CWP improved the firmness of the gel. In addition, whey loss was also reduced considerably when CWP was used to replace milk solids in the formulation, due to the ability of carrot CWP to hold more water than casein micelles.