## 3 Antioxidant Properties of C\({}_{30}\) Carotenoids
[38] synthesized aldehyde and carboxylic acid C\({}_{30}\) carotenoid derivatives along with 4,4'-diapolycopen-4,4'-dial using a carotenoid oxygenase (CrtOx, diapacoratonal synthase) from _S. aureus_ to produce oxygenated linear C\({}_{30}\) carotenoids. Methyl glucosyl-3,4-dehydro-apo-8'-lycopenoate (C\({}_{37}\)H\({}_{25}\)O\({}_{8}\)), a C\({}_{30}\) carotenoid from _Halobacillus halophilus_, underwent chemical mutagenesis to isolate its intermediate compounds through a novel biosynthetic pathway. The intermediates, hydroxy-3,4-dehydro-apo-8'-lycopene and methyl hydroxy-3,4-dehydro-apo-8'-lycopenoate, were identified as 8'-apo derivatives that differed from 4,4'-diapo derivatives due to the nonsymmetric placement of the methyl groups rather than through FPP synthesis. Diapacoratenoid end groups are usually susceptible to oxidation by free peroxyl radicals formed in lipid membranes, possibly enhancing their reactivity [57; 58]. The antioxidant activity of the three carotenoids was measured according to singlet oxygen quenching, with an IC\({}_{50}\) value of 5.1 \(\upmu\)M for methyl glucosyl-3,4-dehydro-apo-8'-lycopenoate, and 44 \(\upmu\)M and 79 \(\upmu\)M for its intermediates methyl hydroxy-3,4-dehydro-apo-8'-lycopenoate and hydroxy-3,4-dehydro-apo-8'-lycopenoate, respectively. The disparity between these three compounds was attributed to the lower hydrophobicity of the intermediate and to a greater number of conjugated double bonds ascribed to greater singlet oxygen quenching [27]. [PERSON] et al. [26] isolated methyl glucosyl-3,4-dehydro-apo-8'-lycopenoate, a C\({}_{30}\) glycocarotenoic acid ester, from the marine bacterium _P. maritimus_. The singlet oxygen-suppressing activity of this carotenoid yielded an IC\({}_{50}\) of 5.1 \(\upmu\)M which was more potent than that of astaxanthin (8.9 \(\upmu\)M) and \(\upbeta\)-carotene (>100 \(\upmu\)M). Another marine bacterium, _Rubritalea squanifaciens_, produces novel acyl glyocarotenoic acid called diapolycopen-dioic acid xylosyl ester, which exhibits similar singlet oxygen suppression with an IC\({}_{50}\) value of 5.1 \(\upmu\)M. The esters isolated from this study were the first C\({}_{30}\) carotenoids shown to have D-xylose groups, although others have reported acyl glucose within the compound structures. The potency of the antioxidant activity was attributed to the presence of carboxylic acids at either end of the aglycone structure [59]. The synthesis and isolation of rare and novel carotenoids from different types of bacteria, including lactic acid and marine bacteria, are steadily increasing the number of characterized carotenoids. Two novel C\({}_{30}\) carotenoids, 4-[2-O-11Z-octadecenyl-\(\beta\)-glucopyranosyl]-4,4'-diapolycopene-4,4'-dioic acid (IC\({}_{50}\) 3.6 \(\upmu\)M) and 4-[2-O-9Z-hexadecenyl-\(\beta\)-glucopyranosyl]-4,4'-diapolycopene-4,4'-dioic acid (IC\({}_{50}\) 3.2 \(\upmu\)M), isolated from Methyl-lobacterium strains, had antioxidative activities comparable to that of astaxanthin (IC\({}_{50}\) 4.1 \(\upmu\)M) and greater than that of \(\beta\)-carotene (IC\({}_{50}\) >100 \(\upmu\)M) [60]. Additionally, the antioxidant activity of the novel compound methyl 5-glucosyl-5,6-dihydro-apo-4,4'-lycopenoateyielded an IC\({}_{50}\) of 5.1 \(\upmu\)M from \({}^{1}\)O\({}_{2}\) suppression activity, while the IC\({}_{50}\) values of astaxanthin and \(\beta\)-carotene were 8.9 \(\upmu\)M and \(>\)100 \(\upmu\)M, respectively [61].