The probiotic yogurt market is strong not only because of appealing flavor and textural properties, but also because of the potential benefits that probiotics provide to the host. However, probiotic viability can be easily affected by the environment. Edible bigels, recently-developed soft materials, have shown effectiveness in delivering bioactive components to humans. Nevertheless, the application of bigel in food is lacking. The objectives of this study were 1) use bigel technology to improve the survival of probiotics in yogurt and 2) evaluate the physical and rheological properties of yogurt after bigel addition. In this project, bigels were prepared by homogenizing an oleogel (OGE: 16% wt/wt oleogelators (1:1 soy lecithin: stearic acid), 20% wt/wt milk (1:1 sterilized milk: probiotic milk), and 64% wt/wt soybean oil) and a hydrogel (HG: 25% wt/wt whey protein concentrate and deionized water). Lactobacillus acidophilus and Bifidobacterium lactis, suspended in milk, were incorporated into a bigel to evaluate probiotic viability in yogurt during storage. Different levels (10%, 14%, and 18%) of bigels were incorporated into yogurts, with (Swiss-style) and without (sundae-style) agitation, all samples were stored at 4°C. Probiotic viability was monitored via plate counts for six weeks. Rheological and textural properties were conducted. Spontaneous syneresis, liquid holding capacity, as well as the color and oil migration of the samples were measured.

The results showed the total counts of L. acidophilus and B. lactis entrapped in bigels were significantly higher than free bacteria in yogurt after three weeks and five weeks, respectively, which indicated probiotics could be effectively entrapped, and their survival enhanced, in bigel systems. The presence of phospholipids and whey protein in the bigel matrix enhanced probiotic survival. No significant difference in probiotics survival was found between yogurt styles, which indicated that the bigel macrostructure structure might not play a key role in protecting the probiotic viability in yogurt, but nano- and microstructure likely do. This study also illustrated that the incorporation of bigels into yogurt changed rheological and textural properties of yogurt without bigel, such as increased viscosity, thixotropy, yield stress and firmness, as well as reduced spontaneous syneresis and promoted liquid holding capacity, possibly by interactions of micro- and nano-structures of bigel with proteins in yogurt strengthened the gel structure of yogurt. The Sundae-style yogurt was more susceptible to the liquid loss compare with the yogurt without bigel, suggesting the bigel incorporation method was critical. Bigel technology shows a promising future for potential application in commercial yogurt to improve probiotic viability and yogurt stability.