456
M. Honda
18.1.8 Z-Isomer of Carotenoids
Since carotenoids contain multiple conjugated double bonds, a large number of
geometric isomers are theoretically possible. In fact, Z-isomers of carotenoids are
widely present in plants, processed foods, and animal bodies. For example, more than
20% of total lycopene is present as the Z-isomers in some processed tomato products
such as tomato sauce and tomato soup (Honda et al. 2017a), and more than 30% of
total astaxanthin is present as the Z-isomers in human plasma (Coral-Hinostroza et al.
2004). Recently, ample studies have addressed that Z-isomers of carotenoids such as
lycopene and astaxanthin showed higher bioavailability and antioxidant activity than
the all-E-isomers (Cooperstone et al. 2015; Müller et al. 2011; Yang et al. 2017a).
For example, a human oral administration test reported by Cooperstone et al. (2015)
showed that Z-isomer-rich tangerine tomato juice (containing 94% total Z-isomer
content of lycopene) was over 8 times more bioavailable than an all-E-isomer-rich red
tomato juice (containing 10% total Z-isomer content of lycopene). On the other hand,
several studies have reported that Z-isomers of β-carotene showed less bioavailability
than the all-E-isomer (During et al. 2002; Gaziano et al. 1995). In fact, although a
great amount of the Z-isomers of lycopene (>50% of the total lycopene) and astaxanthin (>30% of the total lycopene) was present in human serum, the total amount of
β-carotene Z-isomers was less than 10% (Coral-Hinostroza et al. 2004; Stahl et al.
1992). In addition, although there are limited evidences, several carotenoid Z-isomers
exhibit higher bioactivities such as anti-cancer activity and anti-atherosclerosis effect
than the all-E-isomers. For example, (9Z)-β-carotene from the green halophilic alga
Dunaliella sp. would have higher anti-atherogenesis and anti-atherosclerosis effects
than the all-E-isomer (Harai et al. 2008; Relevy et al. 2015). Nakazawa et al. (2009)
reported that fucoxanthin Z-isomers showed higher anti-cancer activity than the allE-isomer, that is evaluated by measuring the potent inhibitory effects on human
promyelocytic leukemia cells (HL-50) and colon cancer cells (Caco-2). These functional changes between all-E-isomer and Z-isomers of carotenoids may be caused
by the change in the physicochemical properties such as solubility and crystallinity
(Honda et al. 2018a; Murakami et al. 2017), e.g., Honda et al. (2018a) reported that the
solubility in ethanol of astaxanthin containing 63.2% Z-isomer was approximately
700 times higher than that of the all-E-isomer, and (all-E)-astaxanthin was present
in the crystal state, while the Z-isomers were present in an amorphous state, that
was confirmed by differential scanning calorimetry (DSC), powder X-ray diffraction (XRD), and scanning electron microscopy (SEM) analyses. The effects of Zisomerization of carotenoids on the bioavailability, antioxidant activity, and bioactivity are summarized in Table 18.1. To my best knowledge, among the over 750
naturally occurring carotenoids, only approximately 10 carotenoids have been characterized in terms of the effects of Z-isomerization. Thus, there is still considerable
room for development of this research area.
M. Honda
18.1.8 Z-Isomer of Carotenoids
Since carotenoids contain multiple conjugated double bonds, a large number of
geometric isomers are theoretically possible. In fact, Z-isomers of carotenoids are
widely present in plants, processed foods, and animal bodies. For example, more than
20% of total lycopene is present as the Z-isomers in some processed tomato products
such as tomato sauce and tomato soup (Honda et al. 2017a), and more than 30% of
total astaxanthin is present as the Z-isomers in human plasma (Coral-Hinostroza et al.
2004). Recently, ample studies have addressed that Z-isomers of carotenoids such as
lycopene and astaxanthin showed higher bioavailability and antioxidant activity than
the all-E-isomers (Cooperstone et al. 2015; Müller et al. 2011; Yang et al. 2017a).
For example, a human oral administration test reported by Cooperstone et al. (2015)
showed that Z-isomer-rich tangerine tomato juice (containing 94% total Z-isomer
content of lycopene) was over 8 times more bioavailable than an all-E-isomer-rich red
tomato juice (containing 10% total Z-isomer content of lycopene). On the other hand,
several studies have reported that Z-isomers of β-carotene showed less bioavailability
than the all-E-isomer (During et al. 2002; Gaziano et al. 1995). In fact, although a
great amount of the Z-isomers of lycopene (>50% of the total lycopene) and astaxanthin (>30% of the total lycopene) was present in human serum, the total amount of
β-carotene Z-isomers was less than 10% (Coral-Hinostroza et al. 2004; Stahl et al.
1992). In addition, although there are limited evidences, several carotenoid Z-isomers
exhibit higher bioactivities such as anti-cancer activity and anti-atherosclerosis effect
than the all-E-isomers. For example, (9Z)-β-carotene from the green halophilic alga
Dunaliella sp. would have higher anti-atherogenesis and anti-atherosclerosis effects
than the all-E-isomer (Harai et al. 2008; Relevy et al. 2015). Nakazawa et al. (2009)
reported that fucoxanthin Z-isomers showed higher anti-cancer activity than the allE-isomer, that is evaluated by measuring the potent inhibitory effects on human
promyelocytic leukemia cells (HL-50) and colon cancer cells (Caco-2). These functional changes between all-E-isomer and Z-isomers of carotenoids may be caused
by the change in the physicochemical properties such as solubility and crystallinity
(Honda et al. 2018a; Murakami et al. 2017), e.g., Honda et al. (2018a) reported that the
solubility in ethanol of astaxanthin containing 63.2% Z-isomer was approximately
700 times higher than that of the all-E-isomer, and (all-E)-astaxanthin was present
in the crystal state, while the Z-isomers were present in an amorphous state, that
was confirmed by differential scanning calorimetry (DSC), powder X-ray diffraction (XRD), and scanning electron microscopy (SEM) analyses. The effects of Zisomerization of carotenoids on the bioavailability, antioxidant activity, and bioactivity are summarized in Table 18.1. To my best knowledge, among the over 750
naturally occurring carotenoids, only approximately 10 carotenoids have been characterized in terms of the effects of Z-isomerization. Thus, there is still considerable
room for development of this research area.