In vitro study links coffee seed extract to broader activity, while loquat extract reduces Candida biofilm biomass

An in vitro comparative study found that an ethanolic extract of coffee (Coffea arabica) seeds had higher measured antioxidant, enzyme-inhibitory and antimicrobial activity than a loquat (Eriobotrya japonica) seed extract, while the loquat extract showed a notable effect against established Candida albicans biofilms. The results concern laboratory assays and do not establish clinical efficacy.

The researchers prepared 80% ethanol extracts from seeds collected in Saudi Arabia’s Jazan region, then quantified selected phytochemical classes and individual phenolics. Total phenolics, flavonoids, alkaloids and terpenes were measured with colorimetric assays, while HPLC–DAD was used to analyze phenolic compounds. The biological testing included DPPH and ABTS radical-scavenging assays, FRAP, inhibition of α-amylase, α-glucosidase and butyrylcholinesterase, antimicrobial testing against four bacterial reference strains and one yeast strain, biofilm assays, and cytotoxicity measurements in Caco-2 colorectal adenocarcinoma cells and Wi38 normal lung fibroblasts.

Coffee seed extract contained 172.46 ± 7.17 mg gallic acid equivalents per gram of dry extract for total phenolics, 157.36 ± 3.34 mg quercetin equivalents per gram for total flavonoids, 10.16 ± 0.27 mg/g of alkaloids and 12.41 ± 0.26 mg limonene equivalents per gram for total terpenes. The corresponding loquat values were 40.00 ± 1.58 mg GAE/g, 3.24 ± 1.02 mg QuE/g, 4.25 ± 0.24 mg/g and 2.30 ± 0.04 mg/g. Chlorogenic acid was the dominant measured phenolic in both extracts, at 63,681.37 ± 1,245.6 µg/g in coffee and 5,848.71 ± 98.3 µg/g in loquat.

The coffee extract recorded lower half-maximal inhibitory concentrations in the principal antioxidant and enzyme assays. Its reported IC₅₀ values were 0.42 ± 0.02 µg/mL for ABTS radical scavenging and 0.66 ± 0.03 µg/mL for DPPH, compared with 1.85 ± 0.06 and 2.10 ± 0.08 µg/mL, respectively, for loquat. Coffee also showed lower IC₅₀ values for α-glucosidase inhibition, at 10.20 ± 0.15 µg/mL versus 48.50 ± 1.10 µg/mL, and butyrylcholinesterase inhibition, at 3.20 ± 0.08 µg/mL versus 6.90 ± 0.12 µg/mL. These measurements demonstrate activity in the specific in vitro assays but do not establish the inhibition mechanism or effects in people.

Both extracts inhibited the tested microorganisms, although the quantitative endpoints generally favored coffee. The reported minimum inhibitory concentration of coffee extract against Staphylococcus aureus was 7.8 µg/mL, compared with 31.25 µg/mL for loquat extract. Against C. albicans, the corresponding values were 15.62 and 62.5 µg/mL. The study used reference strains, including Enterococcus faecalis, S. aureus, Escherichia coli, Salmonella typhi and C. albicans, rather than clinical or drug-resistant isolates.

Established-biofilm testing produced the study’s most prominent loquat result. At 75% of the minimum fungicidal concentration, loquat extract reduced measured C. albicans biofilm biomass by 94.12 ± 0.8%. Coffee extract reduced the same measure by 96.68%. These crystal-violet measurements cover both living and dead microorganisms and extracellular material, so they cannot by themselves distinguish inhibition of biofilm formation from cell killing. Parallel viability assessments indicated that the lowest tested concentrations were sublethal, but additional imaging and viability methods would be needed to characterize the effect more precisely.

In the cell assays, coffee extract showed differential cytotoxicity between the two tested cell lines, with a reported Caco-2 IC₅₀ of 78.5 ± 0.2 µg/mL and a Wi38 IC₅₀ of 181.3 ± 2.2 µg/mL, producing a preliminary selectivity index of 2.31. Loquat extract also reduced Caco-2 cell viability, but was more toxic to the normal fibroblast line. The study assessed one cancer cell line and one normal cell line over 48 hours; it did not establish broad anticancer activity, apoptosis, therapeutic selectivity or safety in humans.

Analysis of 12 phenolics quantified in at least one extract found strong inverse associations between chlorogenic acid concentration and several IC₅₀ measurements. Those correlations are compatible with chlorogenic acid contributing to the observed activity, but they do not demonstrate causation. The chemical analysis was limited to 18 phenolic standards, and a major chromatographic peak remained unidentified. Caffeine and loquat triterpenoids were not quantified, leaving their proposed contributions unconfirmed.

The study was also constrained by its use of one seed source and crude extracts, plus the absence of pharmacokinetic, animal or clinical testing. The findings therefore identify measurable in vitro differences between the two seed extracts. Coffee seed extract showed the broader set of stronger assay results, while loquat seed extract was distinguished by its reduction of established C. albicans biofilm biomass. Broader microbiological, chemical and in vivo studies are needed to determine how those laboratory observations translate beyond the tested systems.

Subject of Research: Comparative in vitro phytochemical and biological assessment of coffee and loquat seed extracts

Article Title: Comparative phytochemical characterization and in vitro biological activities of coffee (Coffea arabica) and loquat (Eriobotrya japonica) seed extracts

Article References: Al-Rajhi, A. M. H., Alsalamah, S. A., Almotayri, A. M., Almimoni, N. M., Zeleei, R. I., Al Abboud, M. A., Shater, A.-R. M., Mashraqi, A., Sahagi, E. M., Masmali, I., & Abdelghany, T. M. (2026). Comparative phytochemical characterization and in vitro biological activities of coffee (Coffea arabica) and loquat (Eriobotrya japonica) seed extracts. Scientific Reports, 16(1), Article 32073. https://doi.org/10.1038/s41598-026-72286-4

Image Credits: AI Generated

DOI: 10.1038/s41598-026-72286-4

Keywords: coffee seed extract, loquat seed extract, chlorogenic acid, antioxidant activity, enzyme inhibition, antimicrobial activity, Candida albicans, biofilm reduction, cell cytotoxicity, in vitro study, Comparative, phytochemical