In a recent study published in Molecules, researchers characterised the bioactive agents within the food industry byproducts of pumpkins.

Study: Biological Activity of Pumpkin Byproducts: Antimicrobial and Antioxidant Properties. Image Credit: EvgeniiAnd/Shutterstock

Natural products are increasingly studied as sources of bioactive compounds. Nevertheless, vegetable-based meals are limited to solutions reminiscent of ready-to-use foods in modern societies. With a growing demand for these food products, a considerable quantity of byproducts is produced within the food industry and discarded along the method.

Research has recently been centered on promoting sustainability and exploring high-value compounds. For example, extracts from sweet potato leaves, primarily phenolic compounds, have been attributed with antioxidant, anti-diabetic, anti-mutagenic, anti-cancer, anti-inflammatory, cardioprotective, and hepatoprotective properties.

The production of formulations from pumpkin pulp is common within the food industry, generating a high quantity of peels, fibers, and seeds as byproducts. Although the pumpkin pulp is appreciated, its byproducts, which can contain polyphenols, polyunsaturated fatty acids, minerals, and carotenoids, are under-utilized or discarded.

Concerning the study

In the current study, researchers evaluated the byproducts of Algerian and Portuguese pumpkins to discover and characterize bioactive compounds.  Gold nugget pumpkin, Musquée de Provence, butternut squash pumpkins from local Algerian markets, and kabocha squash, common pumpkin, and butternut squash from local Portuguese markets were obtained.

Samples (of fibrous strands, seeds, and peels) were produced by segregating pulp from byproducts. These samples were lyophilized, crushed, and extracted by maceration. The phenolic composition was determined using high-performance liquid chromatography (HPLC) coupled to a diode array detector (DAD) and electrospray ionization/mass spectrometry (ESI/MS).

The antioxidant potential was assessed using the oxidative hemolysis inhibition assay (OxHLIA) in sheep red blood cells and the thiobarbituric acid reactive substance (TBARS) assay in porcine brain homogenates. Antimicrobial activity was investigated against bacteria (Yersinia, Staphylococcus, Escherichia, Pseudomonas, Enterobacter, Listeria, and Bacillus spp.) and fungi (Aspergillus spp.) by the p-iodonitrotetrazolium chloride method. Cytotoxicity was tested by sulforhodamine B (SRB) colorimetric assay in primary non-tumor porcine liver cells.

Findings

The authors identified eight (tentative) compounds from pumpkin byproducts that belonged to the flavonoid, flavan-3-ol, and phenolic acid families. Flavonoids were essentially the most abundant compounds detected, including the O-glycosylated derivatives of quercetin, isorhamnetin, and kaempferol. The peel of common pumpkin (from Portugal) had statistically higher quantities (9.4 mg/g) of phenolic compounds, followed by kabocha squash fibers (4.8 mg/g) and butternut squash peel (4.73 mg/g).

Epicatechin was essentially the most abundant compound. In Algerian pumpkins, most phenolic acids were identified within the fibrous strands of gold nugget pumpkin, and flavonoids were the best within the peels and seeds of Musquée de Provence. The gold nugget pumpkin peels and fibers had the best total phenolic compounds at 4.1 mg/g and three.93 mg/g, respectively.

The extracts from Portuguese kabocha and butternut squash seeds showed one of the best antioxidant activity within the TBARS assay, with half-maximal inhibitory concentration (IC50) values of 164 μg/mL and 185 μg/mL, respectively. The antioxidant activity was not significantly different from that of Trolox (positive control) with an IC50 of 139 μg/mL.

The findings in OxHLIA were comparable amongst samples, with IC50 values starting from 43 μg/mL to 96 μg/mL, roughly two to four-fold higher than for Trolox. Furthermore, Portuguese pumpkin samples had greater anti-hemolytic activity than Algerian samples. Interestingly, despite lacking anti-hemolytic activity, the extracts from gold nugget pumpkin seeds exhibited essentially the most potent inhibition within the TBARS assay.

All Portuguese pumpkin samples showed inhibitory activity against Y. enterocolitica, whereas those from Algeria inhibited S. aureus. All samples inhibited the expansion of A. brasiliensis, whereas extracts from the fibrous strands of Algerian pumpkins were protective against A. fumigatus. No sample was cytotoxic to porcine liver cells, even at the utmost tested concentration of 400 μg/mL.

Conclusions

In summary, the study characterised the bioactive compounds from pumpkin byproducts. The butternut squash extracts from each countries had essentially the most potent antioxidant activity, whereas gold nugget pumpkin seeds and butternut squash fibers showed the best antimicrobial activity. The common pumpkin from Portugal had the best and most diverse profile of phenolic compounds. Overall, the findings corroborate the importance of recycling food industry byproducts to be used in numerous industries, reminiscent of cosmetics and pharmaceutics.