Date of Award
Master of Science
Food Science and Human Nutrition
Food Science and Technology
Nuria C. Acevedo
Phospholipids (PL) have been shown to bind to probiotics and increase their viability. However, phospholipids are readily prone to oxidation, which hinders their use in dairy products. The objectives of this study were to 1) produce and characterize semisolid soy lecithin (SL): stearic acid (SA) oleogels (LOG) and oleogel emulsions (LOGE) and 2) evaluate the viability of Lactobacillus acidophilus and Bifidobacterium lactis in the aqueous phase of LOGE. Oleogels were developed with 1 wt% water, and two gelator concentrations (20 wt% and 30 wt%) with SL:SA ratios (0:10, 3:7, 5:5, 7:3, 10:0). The same SL:SA proportions were used to prepare LOGE with 10 wt% and 20 wt% of water. Small (SAX) and wide (WAX) angle x-ray diffraction studies and polarized light microscopy were conducted to determine the nano- and microstructure of the samples. The hardness of the samples was analyzed by using a texture analyzer and the thermal properties with a differential scanning calorimeter. The results indicate that LOG were primarily formed through the entanglement of bundles of reverse worm-like micelles of SL. In contrast, LOGE were structured mainly through SA bilayers that interacted in a synergistic fashion with the SL reverse micelles network to stabilize the three dimensional network. The hardness of the LOG and LOGE increased with an increase in SA; however, in samples containing both SL and SA, LOGE were harder than LOG, demonstrating that the oleogelators have a synergistic effect.
Accelerated oxidative stability test of the oleogel emulsions were determined through measurement of peroxide value (PV) upon 5, 15, 30, and 45 days storage at room temperature (25°C). The physical and microstructural characteristics of the LOGE delayed the oxidation rate of the systems by preventing interaction between lecithin and other molecules prone to oxidation and radical species. Probiotics were inoculated into LOGE with 20% solids (5:5 SL: SA) and 10% water. LOGE were stored at 4°C aerobically, and plate counts were conducted for six weeks to determine the viability of the probiotics. The counts were compared to those of three controls: canola oil plus water, MRS broth, and MRS broth supplemented with SL. Counts were greater in LOGE than canola oil plus water controls.
The novel LOG and LOGE formulated with SA can be used as a more stable alternative to SL oleogels, particularly when the objective is to achieve semi-solid characteristics. With the potential of reduced phospholipid oxidation and increased probiotics survival, incorporation of LOGE into yogurt shows promise.
Gaudino, Nicole, "Development of lecithin-based oleogels and oleogel emulsions with stearic acid capable of enhancing probiotic viability and delaying oxidation" (2018). Graduate Theses and Dissertations. 17189.