**3. Concentrations of melatonin in horticultural crops and its influential factors**

Although policies regarding the free sale, universal use and food supplement of melatonin are still controversial, most developed countries have classified melatonin as an over-the-counter drug and allowed it to be sold freely in pharmacy stores. Currently, melatonin is regarded as an over-the-counter medicine and health care product to relieve sub-health and improve sleep [11]. Some studies indicated that regular consumption of melatonin-rich foods can significantly improve human health [12–14]. In view of the health benefits of melatonin, more and more nutritionists begin to pay attention to the amount of melatonin in food, hoping that people can get more natural melatonin from daily food.

Two research groups identified melatonin in some edible plants in 1995. Vantassel et al. [15] have identified the presence of plant-derived melatonin in higher plants of morning glory (*Ipomoea nil* L.) and tomato (*Solanum lycopersicum* L.) by radio immunoprecipitation and gas chromatography-mass spectrometry analysis; this was also the first report of plant-derived melatonin in horticultural crops. Since then, melatonin has been isolated and identified in numbers of horticultural crops (**Table 1**). Melatonin levels are usually high in seeds and low in fruits in these edible organs of horticultural crops. According to the statistics, melatonin concentrations in various tissues of plants generally conform to the following rules from high to low: seeds, leaves, roots, flowers and fruits [16]. Moreover, the melatonin concentrations are not evenly distributed in the same tissue. Using white lupine (*Lupinus micranthus* Guss.) leaves as an example, the highest concentrations of melatonin are in the leaf tip, then in the middle leaf, and the least in the leaf base [17]. Through comparative analysis, the distributed gradient of melatonin is similar to the distribution of auxin, which indicates that these two indoleamine compounds may play similar or synergistic roles in plants [18].

The melatonin concentrations in horticultural crops are closely influenced by species, varieties, growing environment, cultivated methods, harvesting time and processing methods. As shown in **Table 1**, melatonin concentration in sweet cherry (13.46 ng g<sup>−</sup><sup>1</sup> ) is threefold higher than that in tomato. (4.1 ng g<sup>−</sup><sup>1</sup> ) [19]. In different varieties of tomato, the melatonin concentrations fluctuated greatly from 0.5 pg g<sup>−</sup><sup>1</sup> to 114.5 ng g<sup>−</sup><sup>1</sup> . This difference is largely influenced by the genotype of the variety itself. Climate and environmental factors in different years have significant effects on the melatonin concentrations of horticultural crops. For example, the melatonin concentrations of 'Marbone' tomato harvested in 2010 were six times higher than those in 2009, while the melatonin concentrations of 'Festival' strawberries harvested in 2010 were three times lower than those


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concentrations.

*Review of Melatonin in Horticultural Crops DOI: http://dx.doi.org/10.5772/intechopen.90935*

*The content of melatonin in horticultural crops [16].*

**Table 1.**

in 2009 [20]. The concentrations of melatonin in field-cultivated tomato were significantly higher than those in the phytotron-cultivated tomato, and higher than those in the vitro-cultivated tomato [21]. Riga et al. [22] found that fruit bagging can significantly increase the melatonin concentrations in most tomato varieties but reduce the concentrations of melatonin in pepper (*Capsicum annuum* L.). The dynamic change of melatonin concentrations in mammals is regulated by photoperiod and circadian rhythm; the change of melatonin concentrations in plants is also following an analogous pattern. Thus, the harvest time in one day also has an impact on the concentrations of melatonin in the product organs. Zhao et al. [23] showed that the melatonin concentrations of cherries picked at night were significantly higher than those when picked at day times. However, the peak value of melatonin concentrations in cherry fruits usually occurred at 14:00, when the temperature was the highest and the light was intense. This result suggests that melatonin is not only responding to the photoperiod but also involved in a photoprotective mechanism and free radicals scavenging against light damage during photosynthesis. Other studies have shown that the harvest time can also affect the melatonin concentrations in the organs of products. The concentrations of melatonin in cherry usually increase with fruit ripening [24]. The melatonin concentrations of mulberry leaves decreased with the maturity process [25]. The concentrations of melatonin initially increased and then decreased with the chili (*Capsicum annuum* L.) maturation [26]. Similarly with mammals, the highest melatonin concentrations usually exist in young tissues, followed by mature tissues, and then in aging tissues, which indicates that melatonin offers juvenile protection or acts as an aging antagonistic substance. Post-harvest processing has a great influence on the concentrations of melatonin in horticultural products. For example, Kirakosyan et al. [27] compared the melatonin concentrations of frozen, freeze-dried powder, juice and dried fruits of cherry. They found that the cherry juice and cherry dried fruits did not contain melatonin. However, melatonin was detected in frozen cherries and freeze-dried powder, and the melatonin concentrations in freeze cherry were significantly higher than those in freeze-dried fruits. These results indicate that melatonin is not stable and easily degrades upon destruction of the cellular structure during form processing. Yeast is beneficial to produce melatonin during grape wine making [28]. The melatonin concentrations of mulberry tea are only 15% of those in fresh leaves when deep processing of mulberry leaves for green tea and black tea takes place [25]. In addition, melatonin can be detected in most Chinese teas, such as Longjing tea and oolong tea. Therefore, the selection of varieties with high melatonin level, appropriate climatic conditions, reasonable use of bagging cultivation technology and determination of appropriate harvesting time is important to maintain the high melatonin concentrations in horticultural crops. For the fruit and vegetable deep processing products, appropriate processing technology should be considered to maximally maintain the natural melatonin in the products. However, there is still a lack of systematic research on the influence of these factors on melatonin

Walnut *Juglans regia* L. 3.5 (DW) Bell pepper *Capsicum annuum* L. 0.179–0.581 (DW)

**Common name Specie name Melatonin content (pg g<sup>−</sup><sup>1</sup>**

**)**

*Review of Melatonin in Horticultural Crops DOI: http://dx.doi.org/10.5772/intechopen.90935*


**Table 1.**

*Melatonin - The Hormone of Darkness and Its Therapeutic Potential and Perspectives*

**Common name Specie name Melatonin content (pg g<sup>−</sup><sup>1</sup>**

Sweet cherries *Prunus avium* L. 8000–120,000 (FW) Tart cherries *Prunus cerasus* L. 1000–19,500 (FW) White radish *Raphanus sativus* L. 657.2 (FW) Ginger *Zingiber officinale* Rose 583.7 (FW) Pomegranate *Punica granatum* L. 540–5500 (FW) Shungiku *Chrysanthemum coronarium* L. 416.8 (FW) Pineapple *Ananas comosus* L. 302 (FW) Chinese cabbage *Brassica rapa* L. 112.5 (FW) Cabbage *Brassica oleracea capitata* L. 107.4 (FW) Carrot *Daucus carota* L. var. sativa Hoffm. 55.3 (FW) Taro *Colocasia esculenta* L. 54.6 (FW) Apple *Malus domestica* Borkh. 47.6 (FW) Spinach *Basella alba* L. 38.7 (FW) Onion *Allium cepa* L. 31.5 (FW) Cucumber *Cucumis sativus* L. 24.6 (FW) Kiwi fruit *Actinidia Chinensis* 24.4 (FW) Strawberry *Fragaria* x *ananassa* Duch. 12.4 (FW) Asparagus *Asparagus officinalis* L. 9.5 (FW) Banana *Musa acuminata* Colla 8.9 (FW) Beet root *Beta vulgaris* L. 2 (FW) Tomato *Solanum lycopersicum* L. 0.5–114,500 (FW) Thyme *Thymus vulgaris* L. 38,000 (DW) Chinese liquorice *Glycyrrhiza uralensis* Fisch. 34,000 (DW) Coffee beans *Coffea* sp. 5800–6800 (DW) Feverfew *Tanacetum parthenium* L. 1700 (DW) Mulberry Morus *Morus alba* L. 1510 (DW) Black pepper *Piper nigrum* L. 1092 (DW) Kidney bean sprouts *Phaseolus vulgaris* L. 529 (DW) Aloe *Aloe vera* L. 516 (DW) White radish Raphanus *sativus* L. 485 (DW) Jujube *Ziziphus jujube* Lam. 256 (DW) White mustard seed Brassica hirta L. 189 (DW) Qin Jiao *Gentiana macrophylla* Pall. 180 (DW) Mustard seed *Brassica nigra* L. 129 (DW) Goji berry *Lycium barbarum* L. 103–530 (DW) Almond seed *Prunus amygdalus* Batsch 39 (DW) Sunflower seed *Helianthus annuus* L. 29 (DW) Anise seed *Pimpinella anisum* L. 7 (DW) Coriander seed *Coriandrum sativum* L. 7 (DW) Celery seed *Apium graveolens* L. 7 (DW)

**)**

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*The content of melatonin in horticultural crops [16].*

in 2009 [20]. The concentrations of melatonin in field-cultivated tomato were significantly higher than those in the phytotron-cultivated tomato, and higher than those in the vitro-cultivated tomato [21]. Riga et al. [22] found that fruit bagging can significantly increase the melatonin concentrations in most tomato varieties but reduce the concentrations of melatonin in pepper (*Capsicum annuum* L.). The dynamic change of melatonin concentrations in mammals is regulated by photoperiod and circadian rhythm; the change of melatonin concentrations in plants is also following an analogous pattern. Thus, the harvest time in one day also has an impact on the concentrations of melatonin in the product organs. Zhao et al. [23] showed that the melatonin concentrations of cherries picked at night were significantly higher than those when picked at day times. However, the peak value of melatonin concentrations in cherry fruits usually occurred at 14:00, when the temperature was the highest and the light was intense. This result suggests that melatonin is not only responding to the photoperiod but also involved in a photoprotective mechanism and free radicals scavenging against light damage during photosynthesis. Other studies have shown that the harvest time can also affect the melatonin concentrations in the organs of products. The concentrations of melatonin in cherry usually increase with fruit ripening [24]. The melatonin concentrations of mulberry leaves decreased with the maturity process [25]. The concentrations of melatonin initially increased and then decreased with the chili (*Capsicum annuum* L.) maturation [26]. Similarly with mammals, the highest melatonin concentrations usually exist in young tissues, followed by mature tissues, and then in aging tissues, which indicates that melatonin offers juvenile protection or acts as an aging antagonistic substance. Post-harvest processing has a great influence on the concentrations of melatonin in horticultural products. For example, Kirakosyan et al. [27] compared the melatonin concentrations of frozen, freeze-dried powder, juice and dried fruits of cherry. They found that the cherry juice and cherry dried fruits did not contain melatonin. However, melatonin was detected in frozen cherries and freeze-dried powder, and the melatonin concentrations in freeze cherry were significantly higher than those in freeze-dried fruits. These results indicate that melatonin is not stable and easily degrades upon destruction of the cellular structure during form processing. Yeast is beneficial to produce melatonin during grape wine making [28]. The melatonin concentrations of mulberry tea are only 15% of those in fresh leaves when deep processing of mulberry leaves for green tea and black tea takes place [25]. In addition, melatonin can be detected in most Chinese teas, such as Longjing tea and oolong tea. Therefore, the selection of varieties with high melatonin level, appropriate climatic conditions, reasonable use of bagging cultivation technology and determination of appropriate harvesting time is important to maintain the high melatonin concentrations in horticultural crops. For the fruit and vegetable deep processing products, appropriate processing technology should be considered to maximally maintain the natural melatonin in the products. However, there is still a lack of systematic research on the influence of these factors on melatonin concentrations.
