Asparagus (Asparagus officinalis L.) is a popular vegetable consumed in many regions of the world. It was previously used as a traditional medicine in both Europe and Asia and as a tonic, antipyretic, antitussive, hair-growth stimulant, and diuretic drug in Chinese herbal medicine (Shao et al., 1997; Wang et al., 2003).
The functional components of asparagus have recently been attracting increasing attention for adding a high value to agricultural products. Asparagus spears contain abundant functional components such as saponin and phenol carboxylic acids (Chin et al., 2002; Hartung et al., 1990; Wang et al., 2003). Of these, rutin (quercetin rhamnosyl glucoside) has been reported to have anti-inflammatory, antitumor, and antiviral activities (Calabro et al., 2005; Heellerstein et al., 1951) as well as a high radical-scavenging capacity and roles in strengthening capillary blood vessels and inhibiting arteriosclerosis (Guo et al., 2007). The rutin content of asparagus [300–700 mg·kg−1 fresh weight (FW)] is similar to that of buckwheat (Maeda et al., 2005), and 75% of the antioxidant activity of asparagus is derived from rutin (Tsushida et al., 1994). Based on these findings, asparagus should be promoted as a rutin source and cultivation techniques to increase the rutin content may be developed in the near future.
Asparagus spears rapidly elongate and may grow by more than 10 cm a day (Maeda, 2008), requiring collection two to three times a day in the harvest season. Spears are harvested when ≈30 cm long, are trimmed to 25–27 cm (the release specification in the Nagano Prefecture, the main production area in Japan) in conventional cultivation (Motoki, 2003), and the trimmings are discarded. As the spears mature, the spearheads become loose and lose marketability. Therefore, their rapid growth may lead to a slight delay in harvesting, resulting in the whole spear being discarded. The quality of asparagus rapidly decreases during prolonged growth or after harvest (Kitazawa et al., 2011; Liu and Jiang, 2006), and an investigation of the changes in the composition and quality under various conditions is necessary to maintain quality and functional value. The rutin content and SSC of spears vary depending on the harvest season (Maeda et al., 2008), and the rutin concentration is reported to be highest in the spearhead (Chin et al., 2002; Maeda, 2008). However, there are no reports measuring the rutin content in the off-specification spears, i.e., in spears that are discarded for being too long after delayed harvest during normal cultivation. Normally, when the harvest is delayed and the spearhead loosens, the entire spear is discarded. However, if the rutin content of the discarded spear or the trimmed portion is high, then a new value for the asparagus normally discarded for being of poor quality may be realized.
In this study, we investigated the influence of spear length at harvest and position in the spear (from the base to the spear tip) on rutin content. We also investigated the effect of these factors on a quality index based on appearance, spearhead tightness, and SSC (Brix value), which is closely associated with flavor (Kohmura and Watanabe, 2005).
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