Microwave irradiation enhances the in vitro antifungal activity of citrus by‐product aqueous extracts against Alternaria alternata

Abstract

Summary The effect of two lemon by‐product aqueous extracts at different concentrations (14, 7, 3.5 and 1 mg mL−1) was tested against the in vitro growth of Alternaria alternata. Prior to extraction, one batch of by‐product was dehydrated by freeze‐drying (untreated by‐product), while the other batch was treated by microwave irradiation in conjunction with freeze‐drying (microwave‐treated by‐product). High‐performance liquid chromatography (HPLC) was employed for the identification of individual phenolic compounds with potent antifungal activities. Both lemon by‐product aqueous extracts inhibited the mycelial growth and suppressed the spore germination of the fungus in a concentration‐dependent manner. In general, the extracts obtained from the microwave‐treated lemon by‐product displayed enhanced antifungal activity than those obtained from the untreated one. Scanning electron microscopy (SEM) revealed that both lemon by‐product extracts affected the hyphal morphology of the fungus. The antifungal activity of the extracts was attributed to their phenolic acid and ascorbic acid contents.

The Antifungal Activity of Gallic Acid and Its Derivatives against Alternaria solani, the Causal Agent of Tomato Early Blight

“…Moreover, numerous phenolic acids and phenolic-rich extracts exhibited high inhibitory effects on the radial growth of fungi [18,47]. Although considerable attempts have been made using naturally phenolic-rich products against Alternaria alternata [19][20][21][22][48][49][50][51], very few reports are available about their roles against A. solani. Nevertheless, the physiological and biochemical mechanisms behind this role are poorly understood.…”

Effect of drying techniques and operating conditions on the retention of color, phenolics, and antioxidant properties in dried lemon scented tea tree ( Leptospermum petersonii ) leaves

“…Previous research has shown several properties of plant derived phenolic compounds including antimicrobial (Bhuyan et al, 2017;Papoutsis et al, 2018), anti-inflammatory (Guo et al, 2014;Kazłowska et al, 2010), antioxidant (Papoutsis et al, 2017;Vuong et al, 2014), and bioactivities which lower the risk of cancer (Hsu et al, 2015;Ravishankar et al, 2013), cardiovascular diseases (Arts et al, 2001;Tangney & Rasmussen, 2013), and diabetes (Saravanan & Parimelazhagan, 2014;You et al, 2012). They can also help to boost up the immune system (Carlos et al, 2009;Reyes-Munguía et al, 2016).…”

Non-chemical treatments for preventing the postharvest fungal rotting of citrus caused by Penicillium digitatum (green mold) and Penicillium italicum (blue mold)

“…It has been shown the activities of enzymes such as POD, polyphenoloxidase (PPO), PAL, CHI, and β-1,3-glucanase, as well as the content of flavonoids are increased in the citrus peels after the application of the biocontrol agent Pichia membranefaciens (yeast), leading to lower P. italicum and P. digitatum growth in citrus (Luo et al, 2012). PAL is involved in phenolic compounds synthesis, which have the ability of altering fungal cell permeability, leading to macromolecule leakage (Papoutsis et al, 2018). On the other hand, both POD and PPO enzymes are responsible for the oxidation of phenolic compounds to quinones, which are also compounds with antifungal activities (Kanan & Al-Najar, 2009).…”