Development and characterization of biphasic gels for potential application as semi-solid fat replacers in animal- and plant-based food products
Date
2022-05
Authors
Cho, Karin
Major Professor
Advisor
Acevedo, Nuria C.
Tarté, Rodrigo
Lamsal, Buddhi
Shi, Xiaolei
Sebranek, Joe
Committee Member
Journal Title
Journal ISSN
Volume Title
Publisher
Altmetrics
Abstract
Various oil structuring technologies have been explored to meet consumer demand for food products containing healthier fats and/or less total fat without reducing the food’s aesthetics and sensory attributes. Biphasic gels, also known as hybrid gels or bigels, are semi-solid systems consisting of generally immiscible phases. The aqueous and lipid semi-solid matrices are called hydrogel and oleogel, respectively. Although the use of biphasic gels has been explored for pharmaceutical applications, limited studies are available for food applications; therefore, this research focused on the development of edible biphasic gels. Two key objectives were identified for this work: 1) to develop and characterize the storage and freeze-thaw stability of an animal-containing biphasic gel, and 2) to develop and characterize a plant-based biphasic gel. The purpose for the two different formulations was to accommodate for rising dietary demands for plant-based products.
For the first study, the physical and chemical stability of the animal-containing biphasic gels were investigated. Biphasic gels consisted of a rice bran wax (RBW)-high oleic soybean oil (HOSO) oleogel and a porcine gelatin/aqueous buffer solution hydrogel. The gels were formulated with varying ratios of oleogel:hydrogel (OG:HG), which were 40:60, 50:50, 60:40, and 70:30, with fixed concentrations of each gelator: 7.5% RBW and 7% gelatin. The buffer solution included 1% of sodium benzoate and potassium sorbate as preservatives to inhibit mold growth during gel storage at room temperature. Since freezing is a common method of storage for food products, the freeze-thaw stability of the gels was also assessed by exposing all gels to one freeze-thaw cycle. The gels were evaluated using differential scanning calorimetry (DSC), rheology, confocal laser scanning microscopy (CLSM), spectrophotometry for peroxide value (PV) analysis, and a gravimetric test for liquid loss. All biphasic gels were stable for a minimum of approximately 6 months and the peroxide value of all samples remained below 10 meq/kg throughout the storage period. Micrographs of the gels showed that all gels had an oleogel-in-hydrogel microstructure, even if the oleogel was proportionally greater than the hydrogel. Furthermore, the rheological properties of the biphasic gels were greatly dependent on the ratio of OG:HG—biphasic gels with more OG showed a higher G', whereas those with higher HG showed a higher yield stress. In terms of freeze-thaw stability, all biphasic gels retained more liquid (water and oil) than the hydrogel, demonstrating the robust nature of biphasic gels. Overall, the findings from this study illustrated the stability of biphasic gels under freeze-thaw conditions and long-term storage at room temperature.
In the second study, plant-based biphasic gels were developed using the same oleogel formulation, but different hydrogel formulation without gelatin. This hydrogel formulation consisted of a mixture of κ-carrageenan, soy protein isolate (SPI), and different cation species (K+ or Ca2+) in a buffered solution. Based on observations from the first study, a higher OG:HG ratio led to more desirable characteristics in the biphasic gel; therefore, formulations with OG >50% were used for all biphasic gels. The effects of the two cations on the physical and chemical properties of the biphasic gels was also investigated. The gels were analyzed using rheology (amplitude sweep and temperature sweep), low field nuclear magnetic resonance (LF-NMR), Fourier transform infrared spectroscopy (FTIR), and confocal laser scanning microscopy (CLSM). Results showed that the type of cation in the hydrogel affected the rheological and thermal stability of the final biphasic gel. Gels containing Ca2+ had higher yield stress than K+ gels. Additionally, after melting and re-solidifying the biphasic gels, the Ca2+ gels were less able to immobilize water than K+ gels. These differences may be due to the mechanisms by which Ca2+ and K+ induce gelation of the κ-carrageenan and SPI matrix. When the microstructure was observed, it appeared that the 60:40 biphasic gels had a bi-continuous matrix, whereas the 70:30 biphasic gels appeared to have a hydrogel-in-oleogel matrix. This suggests that at 70% oleogel, the oleogel phase dominates and the bi-continuous matrix is lost. Additionally, slight differences in the hydrogel structure was observed depending on the cation used in biphasic gels. When Ca2+ was used, the hydrogel had thinner (less dense) mesh-like structures compared to when K+ was used. This difference in microstructure may account for the minor differences in G', G'', and yield stress, as well as their water holding behavior after melting and re-solidifying without shear.
This research has demonstrated the versatility of raw materials to develop biphasic gels for specific food applications, notably for animal-containing or plant-based products. In addition, the physical and chemical stability of the biphasic gel system has also been illustrated with the animal-containing gels, and further work should be performed to assess whether the plant-based gels have similar stability over time. The findings from this research sheds light on the behavior of the two phases in a biphasic gel system at the micro- and macroscopic scale.
Series Number
Journal Issue
Is Version Of
Versions
Series
Academic or Administrative Unit
Type
thesis