A bigel is a semi-solid biphasic system where both the oleogel and hydrogel phases are structured. They have superior properties compared to mono-phase gels. Many studies have explored bigels for drug delivery; however, no studies have reported their use in foods to protect sensitive ingredients. In a previous work we successfully developed a novel bigel composed of a whey protein hydrogel and soy lecithin, stearic acid, and milk oleogel emulsion. The objective of this work was to successfully entrap Lactobacillus acidophilus and Bifidobacterium lactis in bigel matrices to enhance their viability during gastrointestinal digestion. The effect of physical structure and phospholipids on probiotic survival were tested through three different matrices. One with soy lecithin (phospholipid source) and stearic acid, one with just stearic acid (phospholipid-free), and one without any oleogelators (no structure). In vitro digestion tests were performed and probiotic counts over time were measured. Sample firmness was analyzed at 4 (refrigeration temperature) and 37°C (digestion temperature) to account for physical hardness differences. Finally, GC fatty acid analysis explored the extent of lipolysis during digestion. The results show that structured bigels successfully provided protection to probiotics during digestion. Compared to the control, the structured gels had ~50 and 5-10% greater probiotic survival at the end of gastric and intestinal phases, respectively. Lipolysis was actively occurring, and unstructured samples had about four-fold more free fatty acids than structured gels. It was shown that our novel bigel systems can be used to protect probiotics from harsh digestive tract conditions.
