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.

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Pomegranate fruit, like other types of fresh horticultural produce, are susceptible to high incidence preharvest and postharvest losses and waste. Several studies have been done to improve the production and handling of pomegranate fruit to meet market standards, but little has been done in loss quantification, especially in the early stage of the value chain such as the packhouse. Therefore, the aim of this study was to quantify the magnitude of pomegranate fruit losses at the packhouse, identify the causes, and estimate the impacts of losses. The study was conducted on a case study packhouse in the Western Cape Province of South Africa from February to March 2020. The direct measurement method, which involved physical identification of the causes of loss on individual fruit, was used for data collection. Loss quantification involved the calculation of lost fruit proportional to the amount put in the packhouse processing line. The results showed that losses ranged between 6.74% to 7.69%, which translated to an average of 328.79 tonnes of pomegranate fruit removed during packhouse operation per production season at the investigated packhouse. This magnitude of lost fruit was equivalent to over ZAR 29.5 million (USD 1,754,984) in revenue, in addition to the opportunity costs of resources used to produce lost fruit.

While there is a growing body of scientific knowledge on improved techniques and procedures for the production and handling of quality pomegranate fruit to meet market demand, little is known about the magnitude of losses that occur at the farm and post-farmgate. This study revealed the amount of pomegranate fruit lost on the farm and the causes of loss and estimated the impacts of losses. The direct measurement method, which involved sorting and counting of individual fruit, was used since physical identification of the causes of fruit losses on individual fruit was necessary for data collection. Furthermore, qualitative data were collected by physical observation during harvesting and interaction with farm workers. At the case study farm in Wellington, Western Cape Province of South Africa, a range of 15.3–20.1% of the harvested crop was considered lost, as the quality fell below marketable standards for retail sales. This amounted to an average of 117.76 tonnes of pomegranate fruit harvested per harvest season in the case study farm, which is removed from the value chain and sold mainly at a low value for juicing and other purposes and translates to an estimated R10.5 million ($618,715.34) economic loss to the farmer. Environmental factors are the main causes of on-farm fruit losses. In the three pomegranate cultivars studied, sunburn and crack were identified as the leading cause of fruit loss, accounting for about 43.9% of all on-farm fruit losses. The lost fiber, carbohydrate, protein, iron and ascorbic acid contents associated with lost fruit were estimated to meet the daily recommended nutrition intake of 2, 9, 4, 2 and 24 people, respectively. Strategies to control and reduce pomegranate fruit losses and waste at the farm level should focus on environmental factors and mechanical damage since they account for the highest sources of fruit losses. This will ensure improved revenue to farmers, sustainable use of natural resources, reduction of the environmental impacts of the fruit industry, and more availability of quality fruit for nutritional security.