In this work, novel ultrathin electrospun fibers from different blends of amaranth protein isolate (API) and the carbohydrate polymer pullulan, with or without the surfactant Tween80, have been developed and characterized. The solution properties and molecular organization of the electrospun structures were studied and correlated with the morphology of the obtained fibers. The presence of pullulan in the blends resulted in increased viscosity and lower conductivity of the solutions, related to a better chain entanglement and decrease in the polyelectrolyte protein character, respectively, both factors needed for fiber formation. Infrared spectral changes indicated that defectfree fibers were correlated with extended α-helical protein structures, which for the blends with greater protein contents, was only obtained upon surfactant addition. The thermal stability of the hybrid fibers was better than that of pure API and slightly increased upon surfactant addition, while the water stability of the blends was highly dependent on fiber composition. These structures have a great potential for the encapsulation of bioactives for functional food applications. HIGHLIGHTS Novel ultrathin electrospun fibres of amaranth protein and pullulan were developed Surfactant was needed to obtain defect-free fibres for high protein content blends FTIR can be unequivocally used to distinguish between defect-free and beaded fibres Thermal stability of the blends slightly improved with respect that of pure protein Water sensitivity of the fibres was highly dependent on blend composition Electrospinning, amaranth protein, pullulan, encapsulation, ultrathin fibers
Two bioactive compounds, quercetin and ferulic acid, were encapsulated using the electrospinning technique within hybrid amaranth protein isolate (API):pullulan ultrathin fibres. Initially, the composition of the encapsulation structures was optimized, both in terms of matrix components ratio and to maximize the bioactive loading. The morphology and thermal stability of the developed encapsulation structures were evaluated, as well as the encapsulation efficiency and distribution within the fibres of both antioxidant compounds. Moreover, the release characteristics and protection ability of the encapsulation structures during an in-vitro digestion study were investigated. Smooth ultrathin electrospun fibres were obtained in which the antioxidants were homogeneously distributed. Through this methodology, it was possible to incorporate within the API:pullulan fibres up to 10 and 20 % (by weight) of quercetin and ferulic acid, respectively, which were released in a sustained manner during in-vitro digestion, keeping to a greater extent their antioxidant capacity in comparison with the non-encapsulated compounds. HIGHLIGHTS Quercetin and ferulic acid were encapsulated using electrospinning Blends of amaranth protein isolate and pullulan were used as encapsulating matrices Sustained release of the antioxidants from the electrospun fibers was observed Encapsulation improved antioxidant capacity of bioactives during in-vitro digestion *Highlights (for review) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 2 AbstractTwo bioactive compounds, quercetin and ferulic acid, were encapsulated using the electrospinning technique within hybrid amaranth protein isolate (API):pullulan ultrathin fibres. Initially, the composition of the encapsulation structures was optimized, both in terms of matrix components ratio and to maximize the bioactive loading. The morphology and thermal stability of the developed encapsulation structures were evaluated, as well as the encapsulation efficiency and distribution within the fibres of both antioxidant compounds. Moreover, the release characteristics and protection ability of the encapsulation structures during an in-vitro digestion study were investigated.Smooth ultrathin electrospun fibres were obtained in which the antioxidants were homogeneously distributed. Through this methodology, it was possible to incorporate within the API:pullulan fibres up to 10 and 20 % (by weight) of quercetin and ferulic acid, respectively, which were released in a sustained manner during in-vitro digestion, keeping to a greater extent their antioxidant...
Amaranth protein isolate (API) ultrathin structures have been developed using the electrospinning technique. The effects of pH, type of solvent and surfactant addition on the spinnability, morphology and molecular organization of the obtained structures have been studied. Regarding the effect of pH on API electrospinning, capsule morphologies were only obtained at extreme pH values (i.e. pH 2 and pH 12), which allowed the solubilisation of the proteins, and the process was favoured when the solutions were previously heated to induce protein denaturation. Fibre-like morphologies were only obtained when the solvent used for electrospinning was hexafluoro-2-propanol, as this organic solvent promotes the formation of random coil structures and, thus, an increase in the biopolymer entanglements. Capsule morphologies were obtained from the API-containing formic acid solutions and this solvent was better for electrospraying than the acetic acid, probably due to the higher viscosity and lower surface tension of the solutions thereof. Addition of 20 wt.-% of Tween 80 considerably improved the formation of capsule-like structures from the formic acid solution, as this surfactant contributed to the formation of alpha helical structures. Similar results were obtained when combining the surfactant with the reducing agent 2-mercaptoethanol. However, denaturation of the protein structure was not sufficient for fibre formation through electrospinning, as the solution properties play a fundamental role in determining the morphology of the electrospun structures.
In this work, the ability of amaranth protein isolate (API):pullulan structures obtained through electrospinning for the photoprotection of bioactive compounds was studied. The model bioactive compound encapsulated was folic acid, due to its great sensitivity to UV light exposure. Addition of 100 mg of folic acid per g of biopolymer to the biopolymeric solution used for electrospinning resulted in increased apparent viscosity and, thus, in thicker electrospun fibers. Very high encapsulation efficiency was obtained (>95%) using this encapsulation technology and no specific chemical interactions were established between the vitamin and the matrix materials as inferred from FTIR analysis. Encapsulation within the API:pullulan structures increased thermal stability of folic acid, which may be useful for food processing applications. Furthermore, no degradation of the encapsulated compound was observed after 2 hours of UV exposure, while the characteristic UV-Vis spectrum from the photodegradation compounds of folic acid was observed after UV irradiation of the unprotected vitamin.
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