Abstract
Recently isolated spore-forming pigmented marine bacteria Bacillus indicus HU36 are sources of oxygenated carotenoids with original structures (about fifteen distinct yellow and orange pigments with acylated d-glucosyl groups). In this study, we evaluated the stability (sensitivity to iron-induced autoxidation) and antioxidant activity (inhibition of iron-induced lipid peroxidation) of combinations of bacterial HU36 carotenoids with the bacterial vitamin menaquinone MQ-7 and with phenolic antioxidants (vitamin E, chlorogenic acid, rutin). Unexpectedly, MQ-7 strongly improves the ability of HU36 carotenoids to inhibit FeII-induced lipid peroxidation, although MQ-7 was not consumed in the medium. We propose that their interaction modifies the carotenoid antioxidant mechanism(s), possibly by allowing carotenoids to scavenge the initiating radicals. For comparison, β-carotene and lycopene in combination were shown to exhibit a slightly higher stability toward iron-induced autoxidation, as well as an additive antioxidant activity as compared to the carotenoids, individually. HU36 carotenoids and phenolic antioxidants displayed synergistic activities in the inhibition of linoleic acid peroxidation induced by heme iron, but not by free iron. Synergism could arise from antioxidants interacting via electron transfer through the porphyrin nucleus of heme iron. Overall, combining antioxidants acting via complementary mechanisms could be the key for optimizing the activity of this bacterial carotenoid cocktail.
Highlights
Consumption of carotenoids may reduce the risk of developing chronic diseases associated with oxidative stress
Ultra-high performance liquid chromatography-mass spectrometry (UPLC-MS) analyses of the crude bacterial extract containing HU36 carotenoids were in agreement with the carotenoid composition described in the literature [24]
The analyses revealed more hydrophobic isoprenoids, e.g., the last major peak was attributed to MQ-7, a menaquinone with seven isoprenyl subunits (Supplementary Figure S1)
Summary
Consumption of carotenoids may reduce the risk of developing chronic diseases associated with oxidative stress. Bacillus indicus HU36 was initially selected for its high production of carotenoids, the resistance of its spores to UV radiation [22], and its probiotic properties [23] It was isolated from human feces and shown to synthesize yellow-orange pigments in variable proportions depending on whether the bacteria were present as vegetative cells or as spores [22]. The effect of the bacterial vitamin menaquinone MQ-7 (Scheme 1) on the stability and antioxidant properties of HU36 carotenoids was evaluated and compared with the effect on β-carotene. Combinations of carotenoids with similar structures (β-carotene and lycopene, Scheme 1) were evaluated to determine possible antioxidant interactions as compared to the cocktail of bacterial carotenoids.
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