Abstract
Several studies have shown that UV-C (ultraviolet C) irradiation promotes the bioactive compounds and antioxidants of fresh fruits and vegetables. The aim of this study was to apply UV irradiation in dried lemon pomace powder for enhancing its phenolic content and antioxidant properties, thus more bioactive compounds should be available for extraction and utilization. Lemon pomace dried powder was placed under a UV lamp and treated with dosages of 4, 19, 80 and 185 kJ·m−2, while untreated powder was used as a control. UV-C irradiation significantly affected the total phenolic content, total flavonoid content, proanthocyanidins, and antioxidant capacity measured by cupric reducing antioxidant capacity (CUPRAC) and ferric reducing antioxidant power (FRAP) of the lemon pomace dried powder, while it did not affect the vitamin C content. UV-C irradiation of 19 kJ·m−2 resulted in 19% higher total phenolic content than the control, while UV-C irradiation of 180 kJ·m−2 resulted in 28% higher total flavonoid content than the control. The antioxidant capacity was reduced when UV-C irradiation more than 4 kJ·m−2 was applied. The results of this study indicate that UV-C treatment has the potential to increase the extraction of bioactive compounds of dried lemon pomace at relatively high dosages.
Highlights
Lemon (Citrus limon L.) is an important Citrus species with a strong commercial value and generates a large amount of waste
UV-C treatment had a significant effect on the total phenolic content of the dried lemon pomace powder aqueous extracts (Figure 2A) (p < 0.05, CV = 5.46%)
The increased total phenolic content of the treated powder could be attributed to the increased phenylalanine ammonia lyase activity, which is a key enzyme for phenolic compound synthesis in plant tissues, since it catalyzes the conversion of L-phenylalanine to ammonia and trans-cinnamic acid, which is the initial step for the synthesis of polyphenols [20]
Summary
Lemon (Citrus limon L.) is an important Citrus species with a strong commercial value and generates a large amount of waste. Phenolic compounds are the most abundant secondary metabolites synthesized by plants through the shikimate pathway [7] as a response to external stresses, such as ultraviolet radiation, wounding, aggression by pathogens, parasites and predators, in addition, they contribute to the color of plants [8,9]. Several treatments, such as heat treatment using electric oven [10,11], electron-beam irradiation [12], Foods 2016, 5, 55; doi:10.3390/foods5030055 www.mdpi.com/journal/foods. Arcas et al [18] mentioned that
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