**2.2. β-Carotene**

β-carotene is a cyclic carotene (C40H56) that is found abundantly in vegetables and fruits, and provides vegetables such as carrots and pumpkins with a deep orange-yellow color [3, 4]. As with other carotenoids, β-carotene has a high antioxidant capacity [6] and preventive effect against various diseases such as cancer and atherogenesis [4, 17]. Furthermore, β-carotene is very important as a retinol precursor, with a high conversion rate [3, 4]. It is also well documented that the bioavailability and antioxidant activity of β-carotene as well as its antiatherogenic activity are changed by *Z*-isomerization. Most previous studies have shown that the *Z*-isomerization results in "negative" effect for bioavailability. In contrast, β-carotene *Z*-isomerization has shown both "positive" and "negative" effects on antioxidant activity, depending on the evaluation method, and "positive" effects have been shown in terms of antiatherogenic activity.

1.5 times more bioavailable than the all-*E*-isomer-rich sauce. In general, the uptake of carotenoids into intestinal mucosal cells is aided by the formation of bile acid micelles [21, 22, 24, 27]. Thus, it is believed that because lycopene *Z*-isomers are more soluble in bile acid micelles than the all-*E*-isomer, they are preferentially incorporated into enterocytes and efficiently form chylomicrons [21, 22]. Indeed, very recently, several reports showed that the solubility of

by *Z*-isomerization [28–32]. However, Richelle et al. [33] showed by human oral-dosing tests that the (9*Z*)- and (13*Z*)-isomers were less efficiently absorbed than the 5*Z*- and all-*E* isomers

Several previous reports have shown that lycopene *Z*-isomers have higher antioxidant activity than the all-*E* isomer and that the relative activities of the isomers varied depending on the assay method [10, 11]. Böhm et al. [10] compared the antioxidant activity of (all-*E*)-lycopene with four unknown *Z*-isomers by measuring their abilities to reduce radical cations of 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (TEAC assay), and each *Z*-isomer showed higher antioxidant activity than the all-*E*-isomer. Müller et al. [11] evaluated the antioxidant activities of (all-*E*)-, (5*Z*)-, (9*Z*)-, (13*Z*)-, and (7*Z*,9*Z*,7′*Z*,9′*Z*)-lycopene using four different *in vitro* assay, namely the TEAC assay, the ferric-reducing antioxidant power (FRAP) assay, the peroxyl radical-scavenging capacity (PSC) assay, and the heme-induced peroxidation of linoleic acid in mildly acidic emulsions mimicking postprandial lipid oxidation in the gastric compartment (MbFeIII-LP) assay. No significant changes were observed among the isomers in the TEAC and FRAP assay. However, the lycopene *Z*-isomers showed higher antioxidant activities than the all-*E* isomer in the PSC assay (9*Z*-isomer > 5*Z*-isomer ≈ 7*Z*,9*Z*,7′*Z*,9′*Z*-isomer > 13*Z*-isomer > all-*E*-isomer) and in the MbFeIII-LP assay (5*Z*-isomer > all-*E*-isomer ≈ 9*Z*-isomer ≈ 13*Z*-isomer ≈ 7*Z*,9*Z*,7′*Z*,9′*Z*-isomer). In TEAC assay, Böhm et al. [10] found that *Z*-isomers of lycopene had higher antioxidant activity, but Müller et al. [11] concluded that no significant differences occurred among the isomers. These discrepant findings may be explained by the

fact that different concentrations of the isomers were used in each study [10, 11].

fied, further research in that field is expected in the future.

**2.2. β-Carotene**

Based on the above findings, *Z*-isomerization effectively promotes the beneficial effects of lycopene. Among the *Z*-isomers, (5*Z*)-lycopene would have the highest bioavailability [33] and antioxidant activity [11]. Furthermore, the 5*Z*-isomer has the highest stability of the *Z*-isomers [34–36]. Therefore, regarding lycopene, it is very important to increase the 5*Z*-isomer level and its ingestion. As the *Z*-isomerization method to increase (5*Z*)-lycopene efficiently, heating in some alkyl halides [37] and some kinds of oils such as sesame oil [9, 38], light irradiation with photosensitizers [39], and catalytic treatment [20, 40] were effective. Moreover, to our best knowledge, because the effect of ingesting *Z*-isomer-rich lycopene on inhibiting the development of diseases such as atherogenesis and cancer has not been clari-

β-carotene is a cyclic carotene (C40H56) that is found abundantly in vegetables and fruits, and provides vegetables such as carrots and pumpkins with a deep orange-yellow color [3, 4]. As with other carotenoids, β-carotene has a high antioxidant capacity [6] and preventive effect

(SC-CO<sup>2</sup>

) was significantly improved

lycopene in oils, organic solvents, and supercritical CO2

or were converted into 5*Z*- and all-*E* isomers.

142 Progress in Carotenoid Research

Data from several *in vitro* and *in vivo* tests have indicated that *Z*-isomers of β-carotene are less bioavailable than the all-*E*-isomer. For example, *in vivo* tests using Caco-2 cells, HSC-T6 cells, and liver microsomes [14], as well as *in vivo* tests using ferrets [41] and gerbils [42] have shown this phenomenon. In humans, the intake of *Dunaliella salina* and *Dunaliella bardawil* rich in (9*Z*)-β-carotene showed lower β-carotene bioavailability than foods rich in the all-*E*-isomer [43–48]. The effects of the *Z*-isomer content on the bioavailability were opposite between lycopene and β-carotene. Generally, after carotenoids are extracted from the food matrix and incorporated into mixed micelles, bioaccessible carotenoids can be internalized by enterocytes [21, 22, 24, 27]. The main absorption site of carotenoids is in the duodenum, and several proteins that are temporarily present at the apical membrane mediate selectivity in terms of carotenoid uptake [27, 49–51]. *In vitro* experiments with Caco-2 cells showed that carotenoid transport decreased in the following order: β-carotene ≈ α-carotene (50% inhibition) > β-cryptoxanthin ≈ lycopene (20% inhibition) > lutein: zeaxanthin (1:1) (7% inhibition) [49]. Because carotenoid *Z*-isomers have higher solubility than the all-*E*-isomers [28–32], they can incorporate into bile acid micelles more efficiency [21, 22]. Therefore, it is considered that *Z*-isomers of β-carotene have lower transport efficiency in Caco-2 cell than the all-*E*-isomers [13]. However, a few studies have suggested that *Z*-isomers of β-carotene have higher bioavailability than the all-*E*-isomers, as evaluated using human intestinal Caco-2 cells [52] and ferrets [53]. The use of different delivery systems with the cell model system and animal species might have caused discordant results [15].

Several studies have been conducted to compare the antioxidant activities of (all-*E*)-β-carotene and the *Z*-isomers, and the degree of antioxidant activity detected varied according to the assay method. Namely, the 9*Z*-isomer showed higher antioxidant activity than the all-*E*-isomer when evaluated in terms of the sensitivity to external oxidants [54], the antiperoxidative activity [18], and oral dose testing in rats [55]. However, the opposite results (or no significant differences) were observed when the antioxidant activities were evaluated by measuring the oxidation of LDL [17] or in TEAC assay [10, 56], and PSC assay [56, 57]. Rodrigues et al. [57] reported that β-carotene *Z*-isomers were less efficient as peroxyl radical scavengers than the corresponding all-*E*-isomers: the *Z*-isomers presented the values about 20% lower than that found for the all-*E*-isomer, and they addressed that the negative effect may be due to the decreasing of the orbital overlap. Based on the above findings, it is difficult to conclude whether antioxidant activity is enhanced by *Z*-isomerization of the all-*E*-isomer.

Moreover, as additional "positive" effects of β-carotene *Z*-isomers, it has been reported that the 9*Z*-isomer has higher antiatherogenic activity [58] and antiatherosclerotic activity [59, 60] than the all-*E*-isomer. On the other hand, there are other "negative" effects. Namely, β-carotene is a very important retinol precursor with a high conversion rate. The (all-*E*)- and (9*Z*)-β-carotene can be metabolized respectively to (all-*E*)-retinoic acid and (9*Z*)-retinoic acid [61, 62], both of which are active in gene regulation [63, 64]. However, the rates of cleavage of β-carotene isomers to vitamin A and the composition of the respective isomer metabolites vary, that is, (all-*E*)-β-carotene was the preferred substrate for cleavage to vitamin A when compared with the *Z*-isomers [61, 65, 66].

the antioxidant activity was 13*Z*-isomer > all-*E*-isomer > 9*Z*-isomer [81]. The results of these studies suggest that *Z*-isomers of astaxanthin, especially the 13*Z*-isomer, have higher antioxi-

Effects of *Z*-Isomerization on the Bioavailability and Functionality of Carotenoids: A Review

Most investigators have concluded that "positive" effects on the bioavailability and antioxidant activity occurred following astaxanthin *Z*-isomerization. Thus, the ingestion of astaxanthin *Z*-isomers could be effective in these terms. As with other carotenoids, *Z*-isomers of astaxanthin could be obtained by heating [81, 82] and catalytic treatment [76, 81, 83] of the

pink color found abundantly in egg yolk and various microbes such as *Bradyrhizobium* sp. and *Halobacterium* sp. [84, 85]. Canthaxanthin can significantly reduce the risk of cancer and neurodegenerative disorder [86, 87] and shows strong antioxidant activity [88], that is, canthaxanthin administration decreased mammary tumor volumes in mice [86] and exhibited antiinflammatory activities by increasing the activity of GPX and catalase, thereby reducing the production of IL-1, IL-6, and TNF-α [87]. Furthermore, canthaxanthin is widely used as feed for hens and fish to improve the egg yolk color and the body color, respectively [84, 89]. A few reports have shown the effect of canthaxanthin *Z*-isomerization on antioxidant activity and functionality. Venugopalan et al. [88] reported that (9*Z*)-canthaxanthin isolated from *Dietzia* sp. had higher antioxidant activity, as evaluated by performing DPPH radicalscavenging assay, superoxide radical-scavenging assay and fluorescence assay to detect reactive oxygen species generated in THP-1 cells. Moreover, the (9*Z*)-isomer exhibited higher pro-apoptotic activity than the all-*E*-isomer, which was evaluated in THP-1 macrophages [90]. The above literature indicates that *Z*-isomerization of canthaxanthin has "positive" effects. Canthaxanthin *Z*-isomerization can be achieved by heating and catalytic treatment [91, 92],

and brown seaweeds such as *Mactra chinensis* and *Undaria pinnatifida* [1, 93]. Fucoxanthin has high antioxidant capacity [94] and shows anticancer and antiangiogenic activities [95, 96]. For example, fucoxanthin remarkably reduced the viability of human colon cancer cell lines, such as Caco-2, HT-29, and DLD-1 cells [95]. In addition, fucoxanthin has antiobesity and antidiabetic effects [97–99], for example, administration of Wakame (*Undaria pinnatifida*) (which is rich in fucoxanthin) significantly suppressed body weight and white adipose tissue weight gain induced by the high fat diet in an obese murine model [98], which has attracted much attention recently in the food industry. The *Z*-isomerization of (all-*E*)-fucoxanthin can induce changes in the antioxidant and anticancer activities. Namely, Zhang et al. [19] reported that when the antioxidant activity of fucoxanthin isomers was evaluated by performing DPPH radical-scavenging and superoxide-detection assay, the following relative activities were observed: 13*Z*-isomer ≈ 13′*Z*-isomer > all-*E*-isomer > 9′*Z*-isomer. Evaluation by performing

) that is principally responsible for the orange-

http://dx.doi.org/10.5772/intechopen.78309

145

) that is found abundantly in edible shellfish

dant activity than the all-*E*-isomer.

Canthaxanthin is a xanthophyll (C40H52O2

and *Dietzia* sp. can serve as a source of (9*Z*)-canthaxanthin [88, 89].

Fucoxanthin is an allenic xanthophyll (C42H58O6

all-*E*-isomer.

**2.4. Canthaxanthin**

**2.5. Fucoxanthin**

Regarding β-carotene, considering that "positive" and "negative" effects are associated with *Z*-isomerization, it is considered important to use them properly depending on the situation. Besides, as the *Z*-isomerization method for (all-*E*)-β-carotene, heating [67, 68], light irradiation with photosensitizers [69], and catalytic treatment [70, 71] were well documented. Moreover, *Dunaliella salina* and *Dunaliella bardawil*, which contain a large amount of (9*Z*)-β-carotene, have been used as *Z*-isomer-rich materials [43–48].
