Comparison of Antioxidant Capacities of Rosmarinate Alkyl Esters in Riboflavin Photosensitized Oil-in-Water Emulsions

Effects of rosmarinic acid esters on the oxidation kinetic of organogel and emulsion gel

Rosmarinic acid was esterified with ethanol, butanol, and hexanol to produce ethyl rosmarinate, butyl rosmarinate, and hexyl rosmarinate, respectively. The antioxidant capacities of the rosmarinic acid esters were evaluated in linseed oil, organogel, and emulsion gel during the initiation and propagation phases of peroxidation. Organogel control sample showed higher induction period and propagation period than those of linseed oil and emulsion gel control samples. Among linseed oil and organogel samples containing antioxidants, samples containing rosmarinic acid exhibited the highest antioxidant activity during the initiation phase, while rosemary extract containing butyl rosmarinate showed the highest antioxidant activity in the propagation phase. In emulsion gel, rosemary extract containing butyl rosmarinate showed higher antioxidant activity than those of rosemary extract containing ethyl rosmarinate or hexyl rosmarinate in the initiation and propagation phases. In addition, the investigated antioxidants showed lower efficiency in organogel and emulsion gel samples than those in linseed oil samples.

Lipophilized rosmarinic acid: Impact of alkyl type and food matrix on antioxidant activity, and optimized enzymatic production

In this study, the initial focus was on exploring the simultaneous impact of the oil-based food matrix and the polarity of rosmarinic acid derivatives on the antioxidant properties. Rosmarinic acid (RA) showed remarkable DPPH, FRAP, and ABTS radical scavenging activities, followed by methyl rosmarinate (MR) and ethyl rosmarinate (ER). In bulk oil, both conjugated dienes and p-AnV values reached a peak in the following order after 30 days: ER > MR > RA = BHT > control (no antioxidant). In the oil structured using monoacylglycerol, MR was more effective than ER and RA. For ethyl cellulose oleogel, emulsion, and gelled emulsion systems, RA was more effective. Additionally, after confirming the importance of the food matrix on the antioxidant activity of RA derivatives, the lipophilization of RA with ethanol was optimized as a model with Lipozyme 435 in hexane. A conversion yield of as high as 85.59% for ER was achieved, as quantified by HPLC-UV and confirmed by HPLC-DAD-ESI-qTOFMS.

Lipid oxidation in emulsions and bulk oils: a review of the importance of micelles

Lipid oxidation is a major cause of quality deterioration in food products. In these foods, lipids are often present in a bulk or in emulsified forms. In both systems, the rate, extent and pathway of oxidation are highly dependent on the presence of colloidal structures and interfaces because these are the locations where oxidation normally occurs. In bulk oils, reverse micelles (association colloids) are present and are believed to play a crucial role on lipid oxidation. Conversely, in emulsions, surfactant micelles are present that also play a major role in lipid oxidation pathways. After a brief description of lipid oxidation and antioxidants mechanisms, this review discusses the current understanding of the influence of micellar structures on lipid oxidation. In particular, is discussed the major impact of the presence of micelles in emulsions, or reverse micelles (association colloids) in bulk oil on the oxidative stability of both systems. Indeed, both micelles in emulsions and associate colloids in bulk oils are discussed in this review as nanoscale structures that can serve as reservoirs of antioxidants and pro-oxidants and are involved in their transport within the concerned system. Their role as nanoreactors where lipid oxidation reactions occur is also commented.

Investigation on the Double CutOff Phenomenon Observed in Protocatechuic Acid and Its Alkyl Esters under Various CAT-Based Assays

A strange cutoff phenomenon of a series of protocatechuic acid alkyl esters had been noticed using the conjugated autoxidizable triene (CAT) assay. Two parabolic shapes of antioxidant activities of protocatechuic acid alkyl esters described as ″the double cutoff effect″ have been speculated as a result of an oxidative driving force generated in the aqueous phase. The aim of this research was to investigate the double cutoff effect using various types of oxidation driving forces in different CAT-based assays. To further explain the phenomenon, the natural oxidation of conjugated autoxidizable triene (NatCAT) assay has been developed for the first time by relying solely on only the lipid autoxidation of tung oil-in-water (O/W) emulsions. In conclusion, NatCAT exhibited different antioxidant and oxidation patterns from both CAT and apolar radical-initiated CAT assays, and only one cutoff point was obtained. This discovery would lead to a greater understanding of the complexity of antioxidant/lipid oxidation dynamics in O/W emulsion systems.

Effects of plasma treatment on the oxidative stability of vegetable oil containing antioxidants

Plasma, the fourth stage of matter, is a partially or wholly ionized state of gas. Degree of lipid oxidation and effects of antioxidants were evaluated in bulk oils at plasma treatment. Significant changes in the conjugated dienoic acid were induced after 10 min of plasma treatment, which corresponded to treatment for 2.5 h at 100 °C and 48 h at 60 °C. Tocopherol stability in the stripped corn oil was significantly higher than that in medium-chain triacylglycerol after the plasma treatment. The antioxidant capacities of 10 μM of α-tocopherol and sesamol were higher than that of β-carotene, and synergistic effects among α-tocopherol, sesamol, and β-carotene were not observed. Added α-tocopherol and sesamol decreased CDA formation by 33 and 30% compared to control samples after plasma treatment. Moisture content in oils decreased significantly about 20% moisture after 6 min plasma treatment. Lipid oxidation could be an important issue in plasma-treated lipid-rich products.

Oxidative stability of extracts from red ginseng and puffed red ginseng in bulk oil or oil-in-water emulsion matrix

Background

Explosive puffing can induce changes in the chemical, nutritional, and sensory quality of red ginseng. The antioxidant properties of ethanolic extracts of red ginseng and puffed red ginseng were determined in bulk oil and oil-in-water (O/W) emulsions.

Methods

Bulk oils were heated at 60°C and 100°C and O/W emulsions were treated under riboflavin photosensitization. In vitro antioxidant assays, including 2,2-diphenyl-1-picrylhudrazyl, 2,2'-azinobis-3-ethyl-benzothiazoline-6-sulfonic acid, ferric reducing antioxidant power, total phenolic content, and total flavonoid content, were also performed.

Results

The total ginsenoside contents of ethanolic extract from red ginseng and puffed red ginseng were 42.33 mg/g and 49.22 mg/g, respectively. All results from above in vitro antioxidant assays revealed that extracts of puffed red ginseng had significantly higher antioxidant capacities than those of red ginseng (p < 0.05). Generally, extracts of puffed red and red ginseng had high antioxidant properties in riboflavin photosensitized O/W emulsions. However, in bulk oil systems, extracts of puffed red and red ginseng inhibited or accelerated rates of lipid oxidation, depending on treatment temperature and the type of assay used.

Conclusion

Although ethanolic extracts of puffed red ginseng showed stronger antioxidant capacities than those of red ginseng when in vitro assays were used, more pro-oxidant properties were observed in bulk oils and O/W emulsions.

Mass Transport Phenomena in Lipid Oxidation and Antioxidation

In lipid dispersions, the ability of reactants to move from one lipid particle to another is an important, yet often ignored, determinant of lipid oxidation and its inhibition by antioxidants. This review describes three putative interparticle transfer mechanisms for oxidants and antioxidants: (a) diffusion, (b) collision-exchange-separation, and (c) micelle-assisted transfer. Mechanism a involves the diffusion of molecules from one particle to another through the intervening aqueous phase. Mechanism b involves the transfer of molecules from one particle to another when the particles collide with each other. Mechanism c involves the solubilization of molecules in micelles within the aqueous phase and then their transfer between particles. During lipid oxidation, the accumulation of surface-active lipid hydroperoxides (LOOHs) beyond their critical micelle concentration may shift their mass transport from the collision-exchange-separation pathway (slow transfer) to the micelle-assisted mechanism (fast transfer), which may account for the transition from the initiation to the propagation phase. Similarly, the cut-off effect governing antioxidant activity in lipid dispersions may be due to the fact that above a certain hydrophobicity, the transfer mechanism for antioxidants changes from diffusion to collision-exchange-separation. This hypothesis provides a simple model to rationalize the design and formulation of antioxidants and dispersed lipids.

Impact of Hydrophobicity on Antioxidant Efficacy in Low-Moisture Food

The polarity and partitioning of antioxidants (AOX) in lipid dispersions and bulk oils have a large impact on efficacy, but this has not yet been studied in low-moisture foods. Using a homologous series of rosmarinic esters as AOX in crackers, we determined that efficacy increases with increasing hydrophobicity based on lipid hydroperoxide and hexanal generation. Confocal microscopy was used to determine the location of both lipids and AOX. Hydrophobic rosmarinic esters partitioned more closely with the lipid than rosmarinic acid, presumably placing the hydrophobic AOX at the site of oxidation reactions. Partitioning and efficacy of the intermediate polarity ester were affected by mode of incorporation (e.g., added to the water or to the lipid prior to dough formation). The synthetic AOXs propyl gallate, butylhydroxytoluene, and tert-butylhydroquinone gave similar results with the more hydrophobic BHT and TBHQ being more effective at reducing lipid hydroperoxide and hexanal generation than the more hydrophilic propyl gallate. These results provide important information on which AOX would be most effective in low-moisture foods.

Boosting antioxidants by lipophilization: a strategy to increase cell uptake and target mitochondria

PURPOSE

To explore the possibility to boost phenolic antioxidants through their structural modification by lipophilization and check the influence of such covalent modification on cellular uptake and mitochondria targeting.

METHODS

Rosmarinic acid was lipophilized by various aliphatic chain lengths (butyl, octyl, decyl, dodecyl, hexadecyl, and octadecyl) to give rosmarinate alkyl esters which were then evaluated for their ability (i) to reduce the level of reactive oxygen species (ROS) using 2',7'-dichlorodihydrofluorescein diacetate probe, (ii) to cross fibroblast cell membranes using confocal microscopy, and (iii) to target mitochondria using MitoTracker® Red CMXRos.

RESULTS

Increasing the chain length led to an improvement of the antioxidant activity until a threshold is reached for medium chain (10 carbon atoms) and beyond which lengthening resulted in a decrease of activity. This nonlinear phenomenon-also known as the cut-off effect-is discussed here in connection to the previously similar results observed in emulsified, liposomal, and cellular systems. Moreover, butyl, octyl, and decyl rosmarinates passed through the membranes in less than 15 min, whereas longer esters did not cross membranes and formed extracellular aggregates. Besides cell uptake, alkyl chain length also determined the subcellular localization of esters: mitochondria for medium chains esters, cytosol for short chains and extracellular media for longer chains.

CONCLUSION

The localization of antioxidants within mitochondria, the major site and target of ROS, conferred an advantage to medium chain rosmarinates compared to both short and long chains. In conjunction with changes in cellular uptake, this result may explain the observed decrease of antioxidant activity when lengthening the lipid chain of esters. This brings a proof-of-concept that grafting medium chain allows the design of mitochondriotropic antioxidants.