Blanching Pre-Treatment Promotes High Yields, Bioactive Compounds, Antioxidants, Enzyme Inactivation and Antibacterial Activity of ‘Wonderful’ Pomegranate Peel Extracts at Three Different Harvest Maturities

Abstract

‘Wonderful’ pomegranate (Punica granatum L.) peel contains a wide range of phytochemicals including vitamins, dietary fibre, phenolic compounds, and antioxidant properties. Yet, it is often used as animal feed or discarded in landfills, which is not the best eco-friendly way to utilize this phenolic-rich bioresource. Finding novel ways of utilizing pomegranate peel waste could prove a more profitable and eco-friendlier alternative that is far more beneficial to the economy. Adding a blanching pre-treatment step at optimal conditions prior to processing of pomegranate peel aids in the inactivation of quality changing enzymes such as polyphenol oxidase (PPO) and peroxidase (POD), which are accountable for the degradation reactions that cause breakdown of nutrients and phytochemicals. This study aimed to determine the effect of blanching at 80 °C for 3 min on the yield, polyphenol content, antioxidant properties, enzyme inactivation, and antibacterial activity of ‘Wonderful’ pomegranate peel ethanolic extracts from three different harvest maturities (unripe, ripe, and over ripe), including a comprehensive characterization and quantification using liquid chromatography-mass spectrometry (LC-MS). The blanched unripe peel extracts exhibited the highest total phenolic content, total tannin content, 2,2-diphenyl-1-picryl hydrazyl (DPPH) antioxidant activity, 2,2-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid (ABTS) radical scavenging activity and ferric ion reducing antioxidant power (FRAP) at 14.0 mg gallic acid equivalent (GAE)/g dry mass (DM), 1.0 mg GAE/g DM, 359.1 µmol Trolox/g DM, 912.2 µmol Trolox/g DM and 802.5 µmol Trolox/g DM, respectively. There was significant (p < 0.05) decrease in PPO and POD activity of all blanched pomegranate peel extracts. The blanched unripe peel extracts had the lowest PPO activity at 0.2 U/g fresh weight (FW), with a 70% PPO inactivation compared to ripe and over ripe harvest, whereas the highest POD inactivation was recorded at 67% in over ripe peel extracts. All blanched peel extracts, irrespective of harvest maturity, had minimum inhibitory concentration (MIC) values at 160 µg/mL against all four bacteria strains tested, which included two Gram-positive bacterial strains (Bacillus subtilis ATCC 6051 and Staphylococcus aureus ATCC 12600) and two Gram-negative bacteria (Escherichia coli 11775 and Klebsiella pneumonia ATCC 13883). A total of 25 metabolites including phenolic acids (4), organic acids (1), flavonoids (4), ellagitannins (13), and other polyphenols (3) in all three pomegranate peel samples were tentatively identified after LC-MS profiling. The blanched unripe peel extracts showed significantly higher punicalin α and β, β punicalagin, catechin, epicatechin content at 414 mg/g, and 678 mg/g, 151 mg/g, 229 mg/g, respectively, compared to peel extracts from other harvest maturities. This study provides supportive information for the commercial utilization of pomegranate fruit peel as source of value-added ingredients for the development of novel food, cosmetics, and pharmacological products.

Protection of antioxidants in pitaya (Hylocereus undatus) peel: effects of blanching conditions on polyphenoloxidase, peroxidase and antioxidant activities

“…Thus, the activation energy of PPO was higher than that of POD. The higher thermal stability of PPO compared to that of POD was also reported for pomegranate peel (Magangana et al, 2021), pineapple puree (Chakraborty et al, 2015) and peach (Lopes et al, 2014). In contrast, some studies demonstrated that POD was more heat resistant than PPO for red bell pepper (Wang et al, 2016) and coconut water (Chutia et al, 2019).…”

Compositions and Biological Activities of Pomegranate Peel Polyphenols Extracted by Different Solvents

“…Compounds 6 , 7 , and 11 with the molecular ion [M + H] + of m / z 595 were identified as kaemperol-3-o-rutinoside [ 18 ]. They were decomposed in various routes.…”

Micro-Encapsulation of Phytochemicals in Passion Fruit Peel Waste Generated on an Organic Farm: Effect of Carriers on the Quality of Encapsulated Powders and Potential for Value-Addition

“…The peels were cut into uniform sizes (4 × 4 mm) and then oven-dried (EcoTherm Economy, Labotec, Cape Town, South Africa) at 50 °C to a constant mass. The dried peels were ground into a fine powder (<1 mm particle size), mixed with 70% ( v / v ) ethanol according to Magangana et al [ 18 ], and then sonicated using an ultrasonic cleaner (Labotec, Sonic Clean, Johannesburg, Gauteng Province, South Africa) at 0 °C for 25 min. The passion fruit peel extracts (PFPE) were filtered using Whatman filter paper No.…”

“…The PFPP extracts for LC-MS/MS analysis and the profiling of the phenolic compounds were performed using the methods described by Magangana et al [ 18 ]. The phenolic compounds were profiled on a Waters Synapt G2 Quadrupole time-of-flight (QTOF) mass spectrometer (MS) connected to a Waters Acquity ultra-performance liquid chromatograph (UPLC) (Waters, Milford, MA, USA).…”