Microstructure, rheology and storage stability of low-fat yoghurt structured by carrot cell wall particles

Plant cell wall particles derived from fruits and vegetables are natural fibre materials with a low calorie content that can be used as a healthy alternative to gum stabilisers and starches for structuring low-fat yoghurt. In this study we investigated the effect of cell wall particle (CWP) addition on the gelation kinetics, viscoelastic properties, microstructure, texture and whey loss of the set yoghurt gels as a function of CWP concentration, particle size and storage time. Three particle sizes of dried carrot CWP (d0.5 = 34, 71 and 80 μm) were produced from an industrial carrot pomace. Rehydrated CWP was added to skim milk prior to acidification. The results showed that the addition of carrot CWP accelerated the rate of pH reduction and induced earlier gelation. The gel viscoelastic properties were enhanced with increased CWP concentration. This was accompanied with progressive reduction in the whey loss. The smallest cell wall particles (d0.5 = 34 μm) gave better gel strength and lower whey loss compared to the larger CWP particles, possibly due to higher contact between the CWP and casein particles thus contributing to the stronger gel network. The CLSM images of yoghurt gels containing CWP showed that carrot CWP occupied the void space within casein particle network. The enhanced gel strength and reduced whey loss achieved by the addition of CWP were maintained throughout the 28 day storage period. The reduction of fermentation processing by almost 1 h, yet still achieving good gel properties for the yoghurt type product could be a significant benefit from a manufacturing point of review.