The mechanical properties of pectin films enhanced with polyphenol-rich fruit extracts were investigated. The scavenging and reducing activity of plant extracts incorporated into the pectin films were determined using bench assays, and their antioxidant activity was correlated with a high presence of polyphenols, which were predominantly comprised of flavonoids and anthocyanins. The pectin films generated from the extracts exhibited a range of mechanical properties; tensile strength (4.99 MPa - 6.91 MPa), elongation at break (45.8 % - 52.3 %), and stiffness (1835 g mm^-1 - 2765 g mm^-1). To investigate the underlying relationships between plant extract composition and mechanical properties, Projection to Latent Structures (PLS) models were developed. The PLS models revealed that extracts containing high sugar and polyphenol content increase the tensile strength and moisture content of films. The elongation at break of the films was improved or diminished depending on the profile of sugar, acids, and polyphenols in the fruit extracts. Furthermore, the structures and concentration of anthocyanins and flavonoids were identified to strongly influenced the elongation at break differences. By modifying the concentration of sugars, organic acids, and polyphenols, the mechanical properties of pectin-based films can be tuned for tailored applications as food packaging materials.

This study investigates the incorporation of anthocyanin-rich extracts from Mountain Pepper Berry (MPB) and Queen Garnet Plum (QGP) into pectin-based films to develop pH-sensitive indicators. Using glycerol as an extraction solvent, significant differences in anthocyanin composition were identified: MPB extracts contained a diverse range of anthocyanin species, with a total content of 267.13 ± 5.21 mg L⁻¹, compared to the predominantly cyanidin-based QGP extracts, with 222.14 ± 1.61 mg L⁻¹. Differences in anthocyanin structures were elucidated using UPLC-Q-ToF-MS/MS analysis. FTIR and UV-Vis spectroscopy were used to assess the compatibility of the extracts with pectin and the homogeneity of anthocyanins within the film structure. Mechanical testing revealed that MPB films exhibited superior tensile strength (8.53 ± 0.51 MPa), stiffness (2274 ± 158.64 gmm^− 1), and energy to failure (141.7 ± 16.23 J m^− 3) compared to QGP films, which had lower tensile strength (7.74 ± 0.32 MPa), stiffness (1947 ± 125.82 gmm^− 1), and energy to failure (115 ± 18.81 J m^− 3). Both film types displayed similar moisture content (MPB: 48.89%, QGP: 48.13%) and water vapour permeability, indicating comparable barrier properties. When exposed to volatile ammonia, QGP films showed a more pronounced colour change, attributed to their anthocyanin profile, with a notable shift from red to brown. This research highlights the potential of glycerol-extracted anthocyanins from Australian native fruits as functional additives in pectin films, offering promising applications for intelligent packaging with enhanced mechanical performance and responsive colour-changing properties. Graphical Abstract

High-throughput colourimetric assays are widely used to screen phenolic phytonutrients in foods and plants, supporting discovery, quality control, and preliminary nutraceutical assessment. This review summarises the historical development, operating principles, and limitations of phenolic-based benchtop methods, and reports practical guidance for defensible application. The following colourimetric approaches are critically evaluated: Folin–Ciocalteu for total phenolics; AlCl₃-based and alternative total flavonoid methods; the pH-differential procedure for total monomeric anthocyanins; and tannin assays including vanillin–HCl, butanol–HCl (Porter), DMACA, protein-precipitation, and hydrolysable-tannin (rhodanine/ellagic-acid) protocols. For each method, common biases are identified, matrix interferences, reagent cross-reactivity, oxidative artefacts, dependence on calibration standard, and the chemical meaning of the readout is clarified. A best-practice framework is proposed: define the analytical target; pair complementary assays; pre-clean extracts; justify standards and wavelengths; control oxidation; validate spike-recovery and conversion checks; and contextualise outcomes using functional measures. A consistent conclusion emerges: no single method quantifies “total tannins” or “total flavonoids” across diverse matrices, and transparent reporting with method triangulation is essential for comparability and credible nutraceutical interpretation. The guidance consolidated here aims to standardise practice, minimise over- and underestimation artefacts, and strengthen the evidentiary value of data in food and nutraceutical research.