Avocado seed starch as a non-traditional hydrocolloid for starch-citrate films prepared by reactive extrusion

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Avocado seeds are a starch-rich agro-industrial residue and a potential non-traditional hydrocolloid source for biodegradable film systems. This study examined how citric-acid reactive extrusion modifies the chemical, supramolecular, water-extraction, and functional properties of avocado seed starch films. Native Hass avocado seed starch showed 92.97 ± 0.25% purity, 41.94 ± 0.97% apparent amylose content, a B-type X-ray diffraction pattern, and gelatinization temperatures of 72.9–91.3 °C. Films were produced by single-screw reactive extrusion with glycerol and citric acid, followed by compression molding. A Resolution V fractional factorial design evaluated citric acid content, glycerol content, feed moisture, reactive-zone temperature, and screw speed. After ethanol washing of the extruded samples, ATR–FTIR and saponification/back-titration showed an ester carbonyl band near 1724 cm -1 and degree of substitution values of 0.032–0.064 in citric-acid-containing samples, whereas samples without citric acid showed values ≤0.0048. The water-insoluble fraction, swelling ratio, and water solubility ranged from 34.2 to 92.4%, 1.83 to 5.18 g/g, and 7.6 to 65.8%, respectively. XRD and DSC showed low relative crystallinity (4.03–9.72%) and apparent glass-transition temperatures of 28.6–81.7 °C. Higher citrate incorporation and water-insoluble fraction were associated with tensile strength and Young’s modulus up to 14.43 MPa and 707 MPa, respectively, and water vapor permeability as low as 4.69 × 10 -11 g m -1 s -1 Pa -1 . Citric-acid reactive extrusion therefore produced low-crystallinity starch-citrate films whose improved functional performance was associated with citrate incorporation and increased resistance to water extraction.