Abstract
Seeds from Citrus species represent a relevant by-product of the juice industry and a potential source of bioactive compounds such as phenols and other antioxidants. Sprouting could be an intriguing idea to enhance the content of these compounds, as explored for other fruittree species. In this experiment, the sprouting performance, the concentration of total phenols and phenolic acids, and the antioxidant activity of seeds and sprouts were evaluated for bitter orange (Citrus aurantium L. seedlings), blonde orange (Citrus sinensis (L.) Osbeck cv.Biondocomune), sweet orange (Citrus sinensis (L.) Osbeck seedlings), lemon (Citrus limon (L.) Osbeck cv.Femminello), and mandarin (Citrus reticulata Blanco cv.Tardivo di Ciaculli). The germination was high for all genotypes except for mandarin, but it took 4–8 weeks. Sprouts did not differ among genotypes for size and generally had hard consistency of cotyledons and a bitter taste. The concentrations of total phenols and phenolic acids of seeds and sprouts varied with the genotype, while the antioxidant activity was not statistically different among treatments. Sprouting increased both the concentration of phenolic compounds and antioxidant activity but no correlation was found between them, suggesting that other antioxidants, besides phenols, are present. Given the slow germination and the bitter taste, Citrus sprouts appear unsuitable for homemade production aimed at direct consumption, while they may have perspectives for extraction of food additives, cosmetics, and pharmaceutics.
Highlights
Fruits from Citrus species represent a worldwide commodity of over 100 million metric tons per year [1]
The G was over 70% in three out of five Citrus genotypes, with bitter orange showing the highest value (90%) (Table 1) and mandarin the lowest one (19%)
The two methods revealed a significant increase of antioxidant activity passing from seeds to sprouts (Figure 2a,b), which apparently matchedwith the increase observed for phenolic compounds (Figure 1)
Summary
Fruits from Citrus species represent a worldwide commodity of over 100 million metric tons per year [1]. Citrus triterpenoids) and phenolic compounds, such as phenolic acids and flavonoids, tocopherols, and carotenoids, the effects of which on human health are well known [1,2]. P-coumaric, and ferulic acids are among the main representative phenolic acids in Citrus seed extracts [2]; the phenolic profile composition strictly depends on both genotyping and environmental factors [1]. This opens perspectives for exploiting these by-products as a source of bioactive compounds for food additives and supplements, cosmetics, and pharmaceutics [1,2,3]. Since the consumption of Citrus seeds in human nutrition is hampered mainly by the woody texture and the astringent and bitter taste, Agriculture 2020, 10, 33; doi:10.3390/agriculture10020033 www.mdpi.com/journal/agriculture
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