| dc.description.abstract | Red Palm Oil (RPO) is a carotenoid-rich edible oil that can potentially be used as a source of natural provitamin A, especially β-carotene. However, the use of RPO nowadays is still limited because it is susceptible to storage damage (rancidity and decreased β-carotene content) and has high hydrophobicity (making it difficult to apply to water-based food systems). Emulsification of RPO in the oil-in-water (O/W) system is expected to overcome these weaknesses by protecting RPO from external factors and “carrying” RPO in different phases. Based on that, this study generally explored the potential of whey protein (WP)-stabilized emulsions to serve as “carrier systems” for RPO. To achieve the general objective, this study evaluated the physical properties and stability of the developed RPO emulsion and the stability of RPO’s β-carotene and lipids in it.
A literature review was conducted to review the potential for WP-stabilized emulsification to enhance the stability of RPO carotenoids. Based on the results, the low stability of carotenoids, including β-carotene, is related to their molecular structure, which consists of conjugated double bonds with high electron affinity. Carotenoid degradation is caused by interactions or reactions between the molecular structure and external factors such as oxygen, light, and heat. The study’s results indicated that O/W emulsions stabilized with WP have the potential to become an RPO carrier system.
RPO emulsification in this study was carried out using three types of WP emulsifiers (i.e., WPCa, WPCb, and WPI) at several concentration levels (i.e., 2.5%, 5%, 10%, and 15% w/v) by employing a catastrophic phase inversion technique. Thus, 12 WP-stabilized RPO emulsion systems were generated in this study. The physical properties of the emulsions were analyzed based on their droplet size characteristics, droplet charge characteristics, and rheological properties (flow behavior and dynamic viscoelastic properties). Then, the droplet size characteristics were further evaluated for change in the storage and centrifugation tests. The results showed that the characteristics and physical stability of the 12 RPO emulsions produced varied depending on the type and concentration of WP emulsifier used. Based on the droplet size, 4 of the 12 emulsions prepared were mini-emulsions (mean particle size (ADS) = 384.92–480.44 nm), while the others were macroemulsions (ADS = 653.44–2029.44 nm). The results showed that the physical stability of the RPO emulsion could be explained using the relationship between the droplet characteristics and their rheological properties. However, observation of the physical appearance is still necessary (i.e., presence or absence of creaming or “oiling off”). Based on the storage and centrifugation tests, it was found that the RPO mini-emulsion produced tended to experience destabilization through the coalescence mechanism. In contrast, the RPO macroemulsion underwent the Ostwald ripening mechanism. In addition, the RPO mini-emulsion had better physical stability than the RPO macroemulsion. Among the produced systems, the 15% WPCb-stabilized RPO mini-emulsion had the best physical stability with an initial ADS of 384.92±16.88 nm.
The stability of RPO’s β-carotene and lipids in the 15% WPCb-stabilized RPO mini-emulsion was evaluated using an accelerated shelf-life test approach by exposing the system to conditions that accelerate the rate of deterioration. Several other physical properties were also evaluated in the test, which included the color of the system surface, the size and charge of the droplets, and the rheological properties of the system. In the test, thermal and light exposures were applied at three intensity levels separately (i.e., (1) 35, 45, and 55 °C for thermal exposure and (2) 0, 5000, and 1000 lx for light exposure). The results showed that the RPO emulsion could significantly increase the stability of RPO β-carotene against light exposure but could not improve its stability against thermal exposure. The half-life of RPO β-carotene after emulsification increased significantly when exposed to high-intensity light, from 92.5 days to 268.9 days at 5000 lx (at 30 °C) and from 51.5 days to 268.1 days at 10000 lx (at 30 °C). Meanwhile, the half-life of RPO β-carotene after emulsification decreased when exposed to thermal, from 343.5 days to 254.3 days (at 30 °C and 0 lx). In addition, the tested RPO emulsion could reduce the sensitivity of RPO lipids to primary and secondary oxidation. However, the system had not been able to increase the stability of RPO lipids during storage. Based on the results, the stability of RPO’s β-carotene and lipids in the tested emulsion was related to the physical stability of the system. The RPO emulsion tested had an initial ADS of 375.43±0.97 nm, a polydispersity index (PDI) of 19.76±2.3, and a retention of β-carotene after emulsification of 86.24±3 %.
The results of this study, in general, have shown that the produced RPO emulsion can be an RPO “carrier system.” This dissertation has generated several novelties, as follows: (1) information proving the potential of WP-stabilized emulsions as RPO carotenoid carrier systems based on the properties, mechanisms, and factors related to carotenoid stability; (2) a technique that was able to emulsify RPO with stabilization by the WP as a single emulsifier, namely the catastrophic phase inversion technique; (3) RPO mini-emulsions and macro-emulsions with a high proportion of oil (30% v/v) stabilized with several types and concentration levels of WP, one of which has good physical stability up to 240 days, namely stabilized MSM emulsion with 15% WPCb; (4) the physical characteristics and information on the physical stability of the RPO emulsion produced based on their droplet size and charge characteristics and their rheological properties; (5) a model of the dominant destabilization mechanism in the produced emulsion, namely coalescence in the mini-emulsions and Ostwald ripening in the macro-emulsions; and (6) kinetic parameters of thermal- and photo-degradation of RPO’s β-carotene and lipids in the 15% WPCb-stabilized RPO emulsion produced. | id |
