Safflower-Enriched Edible Coating Keeps Cheese Below Safety Threshold for 21 Days

A whey protein isolate coating infused with safflower (Carthamus tinctorius L.) flower extract kept inoculated Malatya cheese below the 5 log CFU/g microbial safety threshold for a full 21 days of refrigerated storage, while uncoated cheese crossed that limit within 7 days, according to a study published on 15 August 2026 in the open-access journal Food Safety and Risk.

The coating system combines whey protein isolate, glycerol as a plasticizer, and guar gum with varying concentrations of methanol-extracted safflower flower extract, applied to cheese by immersion. Four formulations, labeled EC1 through EC4, contained increasing amounts of the extract, with EC4 representing the highest concentration. The researchers prepared the extract using a Soxhlet apparatus, extracting 10 grams of dried, powdered flowers with 150 milliliters of methanol for six hours before removing the solvent with a rotary evaporator. The flowers themselves came from the registered Turkish “Dincer” safflower variety, cultivated from seed in climate-controlled rooms and greenhouses at the university over roughly three months before harvest, drying, and grinding.

The central storage experiment used deliberately contaminated cheese samples. Circular pieces of Malatya cheese, each weighing 10 ± 2 grams, were sterilized with UV-C light and then inoculated on the surface with liquid cultures of Escherichia coli and Candida albicans, two microbial indicators chosen for the challenge test. After the microorganisms were fixed by a brief incubation at 37 °C, the samples were dipped in the coating solutions and stored either at refrigeration temperature (+4 ± 1 °C) or at room temperature (+20 ± 2 °C) for 21 days. Viable cell counts were tracked throughout the storage period and compared against the 5 log CFU/g safety threshold.

The results showed a clear concentration-dependent protective effect. In the uncoated control group, both E. coli and C. albicans proliferated rapidly under refrigeration, with the microbial load exceeding the critical 5 log CFU/g threshold by day 7. In contrast, cheese coated with the EC4 formulation, the one carrying the most safflower extract, remained below that limit throughout the entire 21-day storage period. Based on this comparison, the authors calculate a 14-day extension of shelf life relative to the uncoated control. At room temperature, E. coli counts rose sharply in the control group while the EC4 coating effectively inhibited bacterial proliferation, and C. albicans levels in the EC4 group stayed low, reaching their lowest value on day 21. Counts in the EC3 and EC4 groups were significantly lower than the control at days 7, 14, and 21 (p < 0.05).

The authors attribute the protective action to safflower phenolics gradually diffusing from the coating matrix to the cheese surface, where they can interact with microbial cell membranes, cause leakage of cellular components, and suppress metabolic activity. Spectroscopic and thermal analyses supported this gradual-release interpretation: FTIR, TGA, and DSC measurements revealed hydrogen bonding within the coating matrix and improved stability, which the authors suggest enables slow release of the bioactive compounds rather than a single burst.

Alongside the cheese challenge test, the team measured the intrinsic biological activities of the coating solutions. In the DPPH radical scavenging assay, antioxidant activity rose with increasing safflower extract concentration across the EC1 to EC4 formulations, with EC4 showing the highest scavenging capacity and the extract reaching 92.9% DPPH scavenging activity. The control coating without extract showed notably low antioxidant capacity. The authors link this behavior to hydrogen-donating flavonoids and phenolic acids in safflower flowers, including carthamin, quercetin, and chlorogenic acid, which neutralize free radicals through electron-transfer and radical-quenching reactions and could help retard oxidative degradation in the cheese during storage.

Antimicrobial performance was more modest. In disk diffusion tests against ten microbial strains, including Staphylococcus aureus, Pseudomonas aeruginosa, Bacillus subtilis, Klebsiella pneumoniae, Streptococcus pyogenes, Enterococcus faecalis, and C. albicans, both the safflower extract and the coating showed lower activity than the cefadroxil antibiotic used as a positive control. The coating was effective against some bacteria such as E. coli but showed limited effect against naturally resistant organisms like P. aeruginosa and C. albicans, a difference the authors attribute to cell wall structure, biofilm formation capacity, and metabolic defense mechanisms that reduce susceptibility to plant-derived phenolics. In macrodilution broth tests, the minimum inhibitory concentration of the flower extract was 5000 ppm (equivalent to 5000 µg/mL) for both E. coli and C. albicans, a value the authors themselves describe as relatively high compared with more potent herbal extracts such as oregano or olive leaf.

The study also has statistical limitations that the authors disclose openly. While the physicochemical assays, including MIC, disk diffusion, and DPPH measurements, were analyzed with ANOVA at a significance threshold of p < 0.05 in triplicate, the storage-period microbiological data could not support a full ANOVA with Tukey post-hoc testing for every treatment-by-day combination, because some groups showed very low or zero variance. Those storage results were therefore evaluated descriptively using means and standard errors, and the authors note that statistical comparisons were conducted only for datasets meeting the necessary replication requirements. Readers should weigh the shelf-life findings accordingly, as the strongest inferential statistics apply to the in vitro assays rather than the full storage dataset.

Context matters for interpreting the model system. Malatya cheese is a semi-hard brine cheese traditionally made from cow, sheep, or goat milk, shaped with cheesecloth and scalded in hot whey at 75–85 °C, a step that reduces microbial load but also alters the cheese’s microbiological and biochemical properties. The challenge test used UV-sterilized, deliberately inoculated samples rather than naturally contaminated commercial cheese, so the results demonstrate efficacy against two specific inoculated indicators under controlled conditions, not against the full natural spoilage community of real cheese. The authors also note that the coating’s antimicrobial efficacy was moderate overall, and that the abstract frames the work as a first report highlighting potential rather than a validated industrial solution.

Looking forward, the authors propose several optimization routes: increasing the phenolic yield of the safflower extract, improving its diffusibility within dairy matrices, and testing synergistic combinations with other natural antimicrobials or nano-encapsulation strategies to boost bioactivity. They position safflower-enriched whey protein coatings as a sustainable alternative to synthetic preservatives that could help reduce post-harvest losses in the dairy industry, while acknowledging that further development and validation would be needed before any industrial application. For now, the study stands as a proof of concept that a plant-extract-enriched edible coating can substantially delay the growth of inoculated E. coli and C. albicans on a traditional cheese under refrigerated storage, extending the time before counts cross a recognized safety threshold from 7 days to at least 21 days in this experimental model.

Subject of Research: A whey protein isolate and guar gum edible coating enriched with safflower flower extract tested for antimicrobial and antioxidant preservation of Malatya cheese

Article Title: Innovative active edible coating with safflower (Carthamus tinctorius L.) extract for microbial inactivation and shelf life extension of cheese

Article References: Güler, E. A., & Özbey, E. (2026). Innovative active edible coating with safflower (Carthamus tinctorius L.) extract for microbial inactivation and shelf life extension of cheese. Food Safety and Risk, 13(1), Article 33. https://doi.org/10.1186/s40550-026-00158-w

Image Credits: AI Generated

DOI: 10.1186/s40550-026-00158-w

Keywords: edible coating, safflower extract, Carthamus tinctorius, whey protein isolate, Malatya cheese, food safety, antimicrobial activity, antioxidant activity, shelf life, E. coli, Candida albicans, dairy preservation