**1. Introduction**

Carotenoids are the most common lipid-soluble pigments responsible for the colors of plants, animals, and microorganisms, and over 1100 different types of carotenoids have been characterized so far [1, 2]. Carotenoids can be divided into the following two groups: (1) carotenes,

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which are nonoxygenated molecules such as lycopene and β-carotene; (2) xanthophylls, which are oxygen-containing molecules such as astaxanthin and fucoxanthin (**Figure 1**) [3]. The daily consumption of carotenoid-rich foods would be beneficial for human health because of their high antioxidant, anticancer, and antiatherosclerotic activities [4–6]. Because carotenoids contain numerous conjugated double bonds, many kinds of geometrical isomers are theoretically possible (**Figure 1C**, **E** and **F**). In general, carotenoids in plants occur predominantly in the (all-*E*)-configuration, whereas the *Z*-isomers are present in the human body and processed foods in considerable quantity, for example, over 50% of total lycopene is present as the *Z*-isomers in serum and tissues [7–9]. Data from several studies have shown that the *Z*-isomerization of carotenoids induced changes in important properties, such as the bioavailability, antioxidant activity, and anticancer activity [10–13]. However, these outcomes vary depending on the type of carotenoid: there were cases where the beneficial effects of carotenoids increased or reduced by the Z-isomerization [10–15]. For example, *Z*-isomers of lycopene and astaxanthin have higher bioavailability than the all-*E*-isomers [12, 16], whereas *Z*-isomers of β-carotene have lower bioavailability than the all-*E*-isomers [14]. Furthermore, the results may depend on the evaluation method used. For instance, when the antioxidant activity of β-carotene was evaluated based on oxidation of the low-density lipoprotein (LDL), the all-*E*-isomer showed higher antioxidant activity than the 9*Z*-isomer [17], whereas the 9*Z*-isomer showed higher antioxidant activity when evaluated based on antiperoxidative activity [18]. Moreover, the beneficial effects of carotenoids differ between the *Z*-isomers. For example, when the antioxidant activity of fucoxanthin was evaluated in 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging activity assay, the order of activity was 13*Z*-isomer ≈ 13′*Z*-isomer > all-*E*-isomer > 9′*Z*-isomer [19]. The above findings indicate that a good understanding of the effects of *E*/*Z*-isomerization on functional changes is important for increasing the beneficial effects of carotenoid ingestion and for the industrial processing of carotenoids. The objective of this chapter is to highlight the impact of *E*/*Z*-isomerization of carotenoids on their bioavailabilities, antioxidant activities, and inhibitory effects against diseases, such as atherogenesis and cancer. Furthermore, aspects of the change factor of the carotenoid bioavailability and functionality, modification of the physicochemical properties of carotenoids by *E*/*Z*-isomerization, and *Z*-isomerization meth-

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

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The effects of *Z*-isomerization on the bioavailability and functionality of eight carotenoids have been investigated thus far, including: (1) the bioavailability and antioxidant activity of lycopene; (2) the antioxidant activity of α-carotene; (3) the bioavailability and antioxidant, antiatherogenenic, and antiatherosclerotic activities of β-carotene; (4) the bioavailability and antioxidant activity of astaxanthin; (5) the antioxidant and pro-apoptotic activities of canthaxanthin; (6) the antioxidant and anticancer activities of fucoxanthin; (7) the bioavailability and antioxidant activity of lutein; and (8) the antioxidant activity of zeaxanthin. The changes caused by *Z*-isomerization varied according to the parental carotenoid molecules tested and

Lycopene is an acyclic carotene (C40H56) that is principally responsible for the bright-red color found abundantly in vegetables and fruits such as tomatoes, guava, and watermelons [3, 9]. Lycopene shows an especially strong antioxidant activity among carotenoids [6] and can significantly reduce the risks for arteriosclerosis, atherogenesis, and many types of cancer (such as prostate and esophageal cancer) [4, 5]. Therefore, in recent years, the use of lycopene in health foods and supplements, and as a natural functional pigment has attracted attention. It is well documented that the bioavailability and antioxidant activity of lycopene are changed by *Z*-isomerization. Most previous findings have demonstrated that the *Z*-isomerization of

Data from both *in vitro* and *in vivo* tests have suggested that *Z*-isomers of lycopene are more bioavailable than the all-*E*-isomer. Testing conducted using a diffusion model [20], bile acid micelles [21, 22], human intestinal Caco-2 cells [23], and lymph-cannulated ferrets [21, 22] has provided strong evidence supporting the higher bioavailability of the *Z*-isomers. Moreover, in humans, the ingestion of foods rich in lycopene *Z*-isomers resulted in a measurable increase in blood lycopene concentrations compared to a sample abundant in the (all-*E*)-isomer [12, 24–27]. For example, Cooperstone et al. [12] investigated the effects of ingesting red tomato juice, which mainly contained (all-*E*)-lycopene (90% all-*E*-isomer) and *tangerine* tomato juice, which mainly contained *Z*-isomers of lycopene (94% *Z*-isomers), on plasma lycopene concentrations. Lycopene from the *tangerine* tomato juice showed approximately 8.5-fold greater bioavailability than lycopene from the red tomato juice. Unlu et al. [25] reported that when comparing two tomato sauces—one rich in all-*E*-lycopene (95% all-*E*-isomer) and the other rich in (*Z*)-lycopene (45% *Z*-isomers)—that the *Z*-isomer-rich tomato sauce was approximately

**2. Effect of** *Z***-isomerization of carotenoids on their bioavailabilities** 

the evaluation method employed. The findings are described in detail below.

ods used for carotenoids are also discussed in this chapter.

**and functionalities**

**2.1. Lycopene**

lycopene results in "positive" health effects.

**Figure 1.** Chemical structures of (A) (all-*E*)-lycopene, (B) (all-*E*)-β-carotene, (C) (all-*E*)-astaxanthin, (D) (all-*E*) fucoxanthin, (E) (9*Z*)-astaxanthin, and (F) (13*Z*)-astaxanthin.

and inhibitory effects against diseases, such as atherogenesis and cancer. Furthermore, aspects of the change factor of the carotenoid bioavailability and functionality, modification of the physicochemical properties of carotenoids by *E*/*Z*-isomerization, and *Z*-isomerization methods used for carotenoids are also discussed in this chapter.
