Effect of drying on the bioactive compounds, antioxidant, antibacterial and antityrosinase activities of pomegranate peel

Abstract

BackgroundThe use of pomegranate peel is highly associated with its rich phenolic concentration. Series of drying methods are recommended since bioactive compounds are highly sensitive to thermal degradation. The study was conducted to evaluate the effects of drying on the bioactive compounds, antioxidant as well as antibacterial and antityrosinase activities of pomegranate peel.MethodsDried pomegranate peels with the initial moisture content of 70.30 % wet basis were prepared by freeze and oven drying at 40, 50 and 60 °C. Difference in CIE-LAB, chroma (C*) and hue angle (h°) were determined using colorimeter. Individual polyphenol retention was determined using LC-MS and LC-MSE while total phenolics concentration (TPC), total flavonoid concentration (TFC), total tannins concentration (TTC) and vitamin C concentration were measured using colorimetric methods. The antioxidant activity was measured by radical scavenging activity (RSA) and ferric reducing antioxidant power (FRAP). Furthermore, the antibacterial activity of methanolic peel extracts were tested on Gram negative (Escherichia coli and Klebsiella pneumonia) and Gram positive bacteria (Staphylococcus aureus and Bacillus subtilis) using the in vitro microdilution assays. Tyrosinase enzyme inhibition was investigated against monophenolase (tyrosine) and diphenolase (DOPA), with arbutin as positive controls.ResultsOven drying at 60 °C resulted in high punicalin concentration (888.04 ± 141.03 mg CE/kg dried matter) along with poor red coloration (high hue angle). Freeze dried peel contained higher catechin concentration (674.51 mg/kg drying matter) + catechin and –epicatechin (70.56 mg/kg drying matter) compared to oven dried peel. Furthermore, freeze dried peel had the highest total phenolic, tannin and flavonoid concentrations compared to oven dried peel over the temperature range studied. High concentration of vitamin C (31.19 μg AAE/g dried matter) was observed in the oven dried (40 °C) pomegranate peel. Drying at 50 °C showed the highest inhibitory activity with the MIC values of 0.10 mg/ml against Gram positive (Staphylococcus aureus and Bacillus subtili. Likewise, the extracts dried at 50 °C showed potent inhibitory activity concentration (22.95 mg/ml) against monophenolase. Principal component analysis showed that the peel colour characteristics and bioactive compounds isolated the investigated drying method.ConclusionsThe freeze and oven dried peel extracts exhibited a significant antibacterial and antioxidant activities. The freeze drying method had higher total phenolic, tannin and flavonoid concentration therefore can be explored as a feasible method for processing pomegranate peel to ensure retention of the maximum amount of their naturally occurring bioactive compounds.Trial registrationNot relevant for this study.

Effect of oven drying on antioxidant activity, phenolic compounds, fatty acid composition and tocopherol contents of pomegranate aril and oils

“…On the other hand, drying process caused a decrease in gallic acid content of both Hicaznar (ranging from 111.232 mg/100 g to 45.313 mg/100 g) and 33 N 16Keben (varied from 66.036 mg/100 g to 52.737 mg/100 g) in comparison with control samples. The reduction of quantities of phenolic compounds during drying processes has also been observed in different studies (Mphahlele et al, ; Tontul & Topuz, ). It was observed statistically significant differences among phenolic compounds of Hicaznar pomegranate arils compared to control group ( p < 0.05).…”

“…Dried pomegranate peel contains phenolic acid (p‐coumaric), flavan‐3‐ols (+catechin,‐epicatechin), flavanone (hesperidin), flavonol (rutin), ellagitannin (punicalin) (Mphahlele, Fawole, Makunga, & Opara, ). Punicalin values of pomegranate peel changed between 559.60 and 888.40 mg/kg dw (Mphahlele et al, ), and punicalin is hydrolyzable tannin which is known to account for high antioxidant activity in pomegranate peel (Lin, Hsu, Lin, & Hsu, ; Sun, Tao, Men, Xu, & Wang, ; Tzulker et al, ). In another study, pomegranate juice contained 22.8 ± 0.69 μg/100 g vitamin A, 57.8 ± 0.59 mg/100 g vitamin C, and 0.07 ± 0.01 mg/100 g vitamin E (Anahita, Asmah, & Fauziah, ).…”

“…The highest punicalin (888.04 ± 141.03 mg CE/kg dw) and catechin (674.51 mg/kg dw) were found in oven drying at 60°C and freeze‐dried peels, respectively. In addition, high level of vitamin C (31.19 μg AAE/g dw) was observed in the oven‐dried (40°C) pomegranate peel (Mphahlele et al, ). The curent results are nealy in accordance with those obtained by Calin‐Sanchez et al (), Başlar, Karasu, Kiliçli, Us, and Sağdiç () and Poyrazoğlu et al, ().…”

Effect of microwave power on drying kinetics, structure, color, and antioxidant activities of corncob

“…Lowering the microwave power to the lowest level at 180 W caused an even higher reduction in the content of individual value. It has been observed that the high porosity of dehydrated products promotes greater contact of the material with oxygen, which makes the released antioxidants more prone to oxidative damage (Mphahlele et al, ). Carrying out drying at 180 W increased the required drying time by ∼50% compared to that at 300 W, which increased the exposure to oxygen and oxidative enzymes.…”

The ethanol extract from the rhodophyta Gloiopeltis furcata and its active ingredient docosahexaenoic acid improve exercise performance in mice

“…Therefore, proper drying methods are essential to preserve the cellular metabolites in harvested seaweed thalli. In food processing, freeze drying is commonly used to capture phenolic, tannin, and flavonoid compounds in the food (Mphahlele, Fawole, Makunga, & Opara, ). However, freeze drying is expensive and the drying capacity is smaller than for shade‐, sun‐, and oven‐drying.…”