Volume 186, 1 November 2015, Pages 119–122
ISPMF 2015: International Symposium on Phytochemicals in Medicine and Food (Shanghai, China, June 26th –29th, 2015)
Highlights
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- In contrast with most fruit and vegetables, the fresh-cut CWC presents etiolation.
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- Eriodictyol, naringenin, sucrose and ethyl d-glucoside were isolated from CWCs.
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- The CWC etiolation was linked to the presence of eriodictyol and naringenin.
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- We isolated for the first time eriodictyol and naringenin from the fresh-cut CWC.
Abstract
Fresh
cut Chinese water-chestnut is a popular ready-to-eat fresh-cut fruit in
China. However, it is prone to etiolation and the chemicals responsible
for this process are not known yet. To address this problem, we
extracted phytochemicals from etiolated Chinese water-chestnut and
separated them using MPLC and column chromatography. Four compounds were
obtained and their structures were determined by interpretation of UV,
TLC, HPLC and NMR spectral data and by comparison with reported data. We
identified these compounds as eriodictyol, naringenin, sucrose and
ethyl d-glucoside. Among those,
eriodictyol and naringenin were both isolated for the first time in
fresh-cut Chinese water-chestnut and are responsible for the yellowing
of this fruit cutting.
Keywords
- Chinese water-chestnut;
- Etiolation;
- Purification;
- Structural identification
1. Introduction
Because
of their convenience as ready-to-eat products and the health benefits
derived from their consumption, fresh-cut fruits and vegetables have
rapidly gained economic importance (Pradas-Baena, Moreno-Rojas, & Luque de Castro, 2015). The Chinese water-chestnut (CWC, Eleocharis tuberosa) is one of the most popular hydrophytic vegetables in China because of its unique taste ( Peng & Jiang, 2003)
and it is usually peeled before being eaten. Sometimes, the CWC is also
washed, peeled, sliced and packaged before being marketed as a
ready-to-eat product. However, most of fruit and vegetables turn brown
after being peeled ( Sagar & Kumar, 2010), such as apples ( Luo, Lu, Zhou, & Feng, 2011), pears ( Gomes et al., 2014) and potatoes ( Zvitov-Ya’ari & Nussinovitch, 2014).
In contrast with other fruit and vegetables, fresh-cut CWC is prone to
etiolation, reducing its shelf life and its commercial value ( Ma et al., 2010, Oms-Oliu et al., 2010 and You et al., 2012).
More that, the safety for human consumption of the etiolated component
is also worth considering. Most studies report on the CWC yellowing is
due to enzymatic browning and its inhibition ( Peng et al., 2008 and You et al., 2012; Zvitov-Ya’ari & Nussinovitch, 2014, Zhou, Li, Wu, Fan, & Ouyang, 2015),
however, to date, there are no reports specifically on the chemicals
controlling CWC yellowing. In general, the enzymatic browning reaction
is mediated by polyphenol oxidases (PPO) and requires oxygen and
phenolic compounds and is triggered by the enzymatic oxidation of
monophenols into o-diphenols and quinones, which further undergo further
non-enzymatic polymerization leading to the formation of pigments ( Gao, Zhao, Duan, & Tao, 2014; Zhou et al., 2015).
Cutting fruit and vegetables not only makes oxygen available, but also
disrupts the subcellular departmentalization of the enzyme and
substrates. In the plant tissues, only compounds as such as catecholase,
chlorogenic acid, dihydroxyphenylalanine and tyrosine act as substrates
for PPO ( Walker & Ferrar, 1998).
Fresh-cut CWC contains tyrosine, gallic acid, chlorogenic acid and
2,4-dihydroxy-cinnamic acid during the early days of storage ( Tong, 2005). In addition, fresh-cut CWC contains phenolic compounds, mainly dopa and epicate ( Pan & Chen, 2008), but only at low concentration ( You et al., 2007).
However, neither of them can be detected in the subsequent storage
period. PPO and Peroxidase (POD) are also closely associated with
browning of fresh-cut fruit and vegetables ( He & Luo, 2007)
and they are also present in fresh-cut CWC. With the extension of
storage time, PPO shows a downward trend while the POD showed a rising
trend, even tough the extend of this change is very small ( Pan & Chen, 2007). By contrast in potatoes, the activity of POD and PPO is much lower ( Pang & Zhang, 2002). Exogenous salicylic acid inhibits the browning of fresh-cut CWC ( Peng & Jiang, 2006),
but it has no significant effect on the activity of PPO and POD.
4-hexyl benzodiazepines can inhibits the activity of PPO, but cannot
prevent effectively CWC yellowing ( Tong, 2005). All previous research implies that CWC yellowing is different from enzymatic browning.
Therefore,
in order to clarify and control the mechanism of fresh-cut CWC
etiolation and to control as well as to evaluate the safety of the
etiolation components, we had to identify the chemicals involved in CWC
etiolation. In this study we extracted, purifies, and identified the
chemicals involved in etiolation from flesh of fresh-cut CWC by mean of
NMR analysis.
