Preserving fruit freshness with amyloid-like protein coatings

Abstract

Addressing critical challenges in perishable fruit preservation, including hydrophobic surface treatment, protective layer adhesion on complex cuticles, and synergistic integration of preservation components, here we present an eco-friendly amyloid-like protein coating strategy developed through computer-aided molecular simulation. This system employs phase-transitioned lysozyme as an adhesive layer bonded to fruit epicuticular wax, synergized with sodium alginate and cellulose nanocrystals to form a proteinaceous barrier. Validated across 17 fruit varieties, the coating extends shelf-life by 2-5-fold through microbial inhibition, moisture loss reduction, and rot delay, while maintaining 60-98% nutrient retention, surpassing chemical preservation efficacy without toxicity risks. With edible properties, easy washability, and low cost, the coating demonstrates universal applicability for post-harvest and fresh-cut fruits. Notably, it reduces carbon dioxide emissions by 90% versus refrigeration while achieving 2.5-fold longer shelf-life. These positions the amyloid-like protein coating as a practical and sustainable approach to mitigating global food waste issues.

Fig. 1. Schematic diagram illustrating the preparation of ALP coatings and their role in fruit preservation.

Phase-transitioned lysozyme, sodium alginate, and cellulose nanocrystals work together to enhance the ALP coating’s adhesion stability, mechanical strength, water and oxygen barrier properties, antibacterial performance, and antioxidant capabilities, thereby extending the shelf life of fruits. The ALP coating is washable, edible, cost-effective, reduces carbon emissions, and provides universal applicability in fruit preservation.

Fig. 2. Adhesion between fruits and ALP.

a Molecular dynamics (MD) simulations illustrate the interfacial adhesion between fruit wax and lysozyme as well as its amyloid-like variant. b Binding energy and contact area of lysozyme and amyloid-like lysozyme on the wax surface after simulation. c CD spectra of native lysozyme, PTL, and ALP. d The peeling strength of ALP coating and native protein adsorption layer during the 180° peeling test. Data are mean ± S.D. n  =  3 independent samples per group. e Optical images depicting ALP agent and native lysozyme solution interactions on fruit surfaces. f Sequential optical images showing a sessile ALP droplet on various fruit peels at time points t = 0 s and 60 s. Source data are provided as a Source Data file.

Fig. 3. Characterization of the ALP coating to show multifunctional fresh-keeping features.

a SEM images of ALP coating. Scale bar: 5 µm. b Mechanical properties of the ALP coating. c UV/vis transmission spectrum of the ALP coating, with the inset showing the ALP coating prepared on winter jujube. d The contact angle of a sessile water droplet on the ALP film as a function of time. e Water vapor transmission rate (WVTR) and Oxygen permeability (OP) of the ALP coating compared to common biopolymers used as a coating. f Respiration intensity of bare and ALP-coated cherry tomatoes at different storage times. g DPPH and ABTS radical scavenging activity of the ALP film. h Appearance of the ALP-coated and bare fresh-cut apple before and after 5 h of storage. i Antibacterial activity of lysozyme, cysteine, PTL, SA, CNC, and ALP on E. coli and S. aureus. j Weight loss and (k) stiffness of bare and lysozyme, cysteine, PTL, SA, CNC, lysozyme/SA, PTL/CNC, PTL/SA, and ALP-coated fresh-cut apples and winter jujubes at the end of storage. Different letters within each color indicate significant difference (p < 0.05). All data in Figs. 2f, g, 2i–k are mean ± S.D. n  =  3 independent samples per group. Statistical significance was determined by a two-tailed Student’s t test. The experiments in Fig. 2a were repeated independently at least three times with similar results. Source data are provided as a Source Data file.

Fig. 4. Effect of the ALP coating on ripening and sensory evaluation of non-climacteric and climacteric fruits.

a Photographs of bare and ALP-coated (spray coating) strawberries, loquats, winter jujube, and kumquats after different storage times. b Photographs of bare and ALP-coated (spray coating) cherry tomatoes, mangoes, nectarines, and bananas after storage. c Comparison of shelf-life between ALP-coated and uncoated fruits. d LDA discriminant analysis of e-nose data for bare and coated strawberries at the end of storage. Source data are provided as a Source Data file.

Fig. 5. Effect of the ALP coating on ripening and quality of fruits.

a ALP-coated fruits exhibit a significant reduction in the rate of weight loss and demonstrate enhanced preservation of stiffness, vitamin C (Vc), titratable acid (TA), and total soluble solids (TSS) relative to their uncoated counterparts. Data are mean ± S.D. n  =  3 independent samples per group. b Weight loss, (c) stiffness, (d) Vc content, (e) TA content, (f) TSS content, and (g) edible rate of bare and coated strawberries at different storage times at 23 °C and 50 % humidity. All data in Fig. 4b–g are mean ± S.D. n  =  3 independent samples per group. Statistical significance was determined by one-way ANOVA with Tukey’s multiple comparison test. Details (p-value) of statistical comparisons between groups are provided in the Supplementary appendix. Source data are provided as a Source Data file.

Fig. 6. The application of the ALP coating on the ripening and shelf-life of fresh-cut fruits.

a The impact of the ALP treatment on the appearance quality of fresh-cut apples was assessed at 4 °C and 50% humidity after 0, 6, and 10 days of storage. b Radar chart of e-nose data of bare and coated fresh-cut apples obtained at the end of storage. c LDA discriminant analysis of e-nose data for bare and coated fresh-cut apples at the end of storage. d Predictive results of e-nose data at the end of storage for coated fresh-cut apples in the LDA model. e The influence of the ALP treatment on the visual quality of fresh-cut fruit assortments was evaluated over a storage duration ranging from 2 to 10 days. Source data are provided as a Source Data file.

Fig. 7. The biosafety assessment of the ALP coating.

a Fluorescent images showing the ALP coating before and after cleaning with Congo red staining. b Water contact angle measurements on ALP-coated cherry tomatoes and bananas before and after cleaning. c Pathological examination results of heart, liver, spleen, lung, kidney, and intestine tissues. The control group was fed bare rat food, while the coated group was fed ALP-coated rat food. Results of (d) blood routine (white blood cell (WBC), neutrophil (Neu), lymphocyte (Lym), (e) liver function (alanine aminotransferase (ALT), aspartate transaminase (AST)), and (f) kidney function tests in both control and coated groups are presented (creatinine (CREA), blood urea nitrogen (BUN)). n  =  6 animals per group. Data are presented as a box and whisker plot (median, box:first and third quartiles, and whisker: minimum and maximum). All data in Fig. 6d–f are mean ± S.D. Statistical significance was determined by a two-tailed Student’s t test. The experiments in (a, c) were repeated independently at least three times with similar results. Source data are provided as a Source Data file.

Fig. 8. The sustainable assessment of ALP.

a Images showcasing cherry tomatoes stored in the fridge at 4 °C and coated at room temperature (23 °C and 50% humidity) on days 0, 4, and 8. b Life Cycle Assessment (LCA) of the ALP coating for preserving cherry tomatoes at room temperature (23 °C and 50% humidity) compared to refrigeration at 4 °C. The (c) weight loss and (d) Vc content of cherry tomatoes stored in the fridge at 4 °C and coated at room temperature (23 °C and 50% humidity) at different storage durations. Data are mean ± S.D. n  =  3 independent samples per group. Statistical significance was determined by one-way ANOVA with Tukey’s multiple comparison test. Source data are provided as a Source Data file.