Physicochemical and microstructural properties of fermentation-induced almond emulsion-filled gels with varying concentrations of protein, fat and sugar contents

The influence of the protein, fat and sugar in almond milk on the formation of the acidic gel was investigated by determining their physicochemical and microstructural properties. The protein, fat and sugar in the almond milk were varied from 2% to 6%, 0.8%-7% and 0.6%-7%, respectively and fermented using Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophiles cultures to form a gel structure. Both protein and fat increased the gel strength, viscosity (stirred gel) and lightness of almond yoghurts as the concentration increased. The addition of protein content increased the cohesiveness (from 0.70 to 1.17), water holding capacity (from 28.75% to 52.22%) and D_4,3 value of particle size (from 32.76 μm to 44.41 μm) of almond yoghurt. Fat reduction decreased the firmness (from 6.56 g to 4.69 g), D_4,3 value (from 88.53 μm to 18.37 μm), and water holding capacity (from 48.96% to 27.66%) of almond yoghurt. With sugar addition, almond yoghurt showed increased adhesiveness, decreased lightness and a low pH, with no significant difference in firmness, particle size, and flow behaviour. The confocal images provided evidence that the fortified protein contents homogeneously entrapped fat globules resulting in a more stable gel network and increased fat content led to large fat globule formation resulting in a harder gel network, while the added sugar did not significantly affect the gel network. The results suggested that the protein fortification enhances the texture of almond yoghurt. The fat content of 7% with 3.5% protein showed poor consistency and gel strength of yoghurt. Sugar mainly contributed to bacterial metabolism during fermentation.