Save the environment and protect your skin while doing it – the 'cherry on top'

By Hugo Francisco de SouzaReviewed by Benedette Cuffari, M.Sc.Oct 16 2023

In a recent study published in Foods, researchers investigate environmentally friendly and sustainable uses for processed tart cherry (Prunus cerasus L.) waste. Their study focused on cosmetic applications, including optimizing the extraction of bioactive metabolites from cherries and their beneficial impacts on human skin.

Study: Tart Cherry (Prunus cerasus L.) Pit Extracts Protect Human Skin Cells against Oxidative Stress: Unlocking Sustainable Uses for Food Industry By-products. Image Credit: Serhii Ivashchuk / Shutterstock.com

Cherries and the burden of environmental waste

Cherries, especially those belonging to the species Prunus avium L. and P. cerasus L., are processed in significant amounts. In fact, the United States Department of Agriculture (USDA) National Agricultural Statistics Services (NASS) reported an astounding 275,000 tons of Prunus avium L. and 114,600 tons of P. cerasus L. cherries processed in 2022 alone.

Over 90% of cherries are processed by the food industry to produce juice, brined products, and wine. This leads to the generation of byproducts, including cherry pomace and cherry pits (CP), almost all of which are burned or discarded.

Conventional waste results in environmental pollution of the soil, water, and air through greenhouse gas emissions, in addition to economic loss due to the disposal of organic resources that could otherwise be reused or recycled.

The skin is an individual's first line of defense from biological pathogens, nonbiological environmental pollutants, and ultraviolet (UV) radiation. Long-term exposure to UV radiation can result in skin inflammation and the generation of harmful reactive oxygen species (ROS), which induce cellular damage and can result in early aging, skin conditions like psoriasis and cancer.

Polyphenols, one of the largest classes of plant-derived metabolites, have been shown to exert antioxidant activity in vitro, potentially reducing skin inflammation. Cherries are rich in polyphenols and, as a result, could be a source of novel cosmetic products. Although previous studies have investigated the benefits of cherry byproducts from the stems and seeds, the antioxidant activity of CP still needs to be evaluated.

About the study

In the present study, researchers developed a novel method of extracting bioactive compounds from tart cherry (P. cerasus L.) CP and evaluated the cytotoxic and anti-inflammatory properties of these bioactives using human keratinocyte (HaCaT) cells. Tart cherry pits obtained from Peterson Farms in Michigan were oven-dried and ground into pit powder. Extraction was achieved through the conventional extraction using 100% water and the novel extraction approach using water:ethanol in a 1:1 ratio.

Extractions were performed at 150 °C with a solid-to-liquid ratio of 30 g of pit powder in 300 mL of liquid to produce CP water (CPW) or CP ethanol (CPE). CPW and CPE were then subject to centrifugation, and the resultant supernatant was used in analyses.

A double-beam Lambda 365 UV-Vis spectrophotometer was used to quantify the polyphenol (TP), antiradical powder (ARP), and flavonoid (TP) content of the supernatant. For increased accuracy of TP quantification, the colorimetric Folin-Ciocalteu assay (TP) was employed. Simultaneously, a second colorimetric assay was performed to investigate the in vitro antioxidant activity of TP, TF, and ARP against 2,2-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS).

Metabolomic analyses were carried out using liquid chromatography-mass spectrometry (LC-MS/MS). Individual polyphenol quantification was achieved using a UV-visible spectrophotometer with dimethyl sulfoxide (DMSO) as the reference solution.

HaCaT and mouse fibroblast (NIH3T3) cells were treated with varying concentrations of CPW and CPE or a combination of extracts and hydrogen peroxide (H₂O₂) for cell viability assays and ROS activity assays, respectively.

Intracellular ROS activity was measured using fluorescence microscopy. RNA isolation and real-time-polymerase chain reaction (RT-PCR) analyses were also performed to identify HaCaT and NIH3T3 genes that were up- or down-regulated following extract treatment.

Study findings

The novel water:ethanol extraction protocol was significantly superior to the conventional water-alone protocol. Adding ethanol into the mixture resulted in a 2.1-fold increase in TP yield from the same starting quantity of CP.

As noted through ARP assays, CPE was associated with about 2.5-fold more significant antioxidant activity as compared to CPW. CPE antioxidant superiority was confirmed through the ABTS assays, which found a 2.4-fold increase in activity as compared to CPW. Both extraction protocols revealed almost 10-fold TP content measurements compared to previous studies on other natural plant-derived sources of TP.

LC-MS/MS results identified and quantified multiple caffeoylquinate ester isomers, hydroxycinnamic acids, and flavonoids. CPE extracts depicted higher concentrations of compounds than CPW. Lyophilized CP extracts similarly exhibited higher concentrations of bioactives than liquid extracts, thus suggesting future industrial optimizations in extraction protocols.

Upon comparing CPW and CPE UV-Vis spectra, similar results were obtained corresponding to the peaks for apigenin, quercetin, and chlorogenic acid. These results confirm the abundance of flavonoids and coumaroyl derivatives in CP and CP extracts.

CP extract concentrations between 50-400 nM did not induce toxicity in HaCaT cells and NIH3T3 fibroblasts, even after 48 hours of incubation. When testing the impacts of common pure phenols detected during CP extract characterization, only apigenin and catechin were found to adversely impact cell viability at 100 µM or greater concentrations, which was more than 50-fold higher than those found in CP extracts.

Both CPW and CPE significantly decreased ROS levels in HaCaT cells treated with H₂O₂.

CP extracts were efficient in protecting cells against LPS-induced nitric oxide production, which was verified by 2’-7’-Dichlorodihydrofluorescein diacetate (DCF-DA) staining assays. RT-PCR assays revealed that H₂O₂ treatment reduced the catalase (CAT) and superoxide dismutase (SOD1) expression levels in HaCaT cells. CPE and CPW pretreatment rescued HaCaT cells from these effects.

Conclusions

In the present study, researchers aimed to find alternative uses for the byproducts of cherry processing, thereby reducing the environmental and economic burden of the millions of tons of byproduct waste polluting the ecosystem every year. To this end, they devised a novel method of extracting natural bioactives from CP, which was found to be between two- and three-fold more efficient than conventional extraction protocols.

CP extracts are rich in metabolites that can effectively reduce skin oxidative stress caused by pollution and extended UV exposure, thereby preventing dermatological ailments, including early aging, psoriasis, and even cancer.