Abstract
Helianthus annuus L. seed hull is an abundant waste of the edible oil industry. To envisage potential applications of this waste, here, we aimed to analyze the chemical composition of milled sunflower hulls (SP), constituted mainly by 210 μm (51.4%) and 420 μm (27.6%) average mesh particle sizes. SP contained almost 30% of cellulose, 26.4% of lignin, 38.5% of neutral sugars, mainly hemicelluloses, and only 1.3% of proteins. The important lignin content and low pectin content (4.0% of uronic acids) present in SP were both ascribed to its low hydrophilic behavior and hydration capacity. Phenolic compounds were mostly proanthocyanidins (168 mg/100 g SP), with lower amounts of extractable (31.4 mg/100 g SP) phenolics (O-caffeoylquinic acid), all of them associated with the DPPH radical scavenging capacity (95 mg ascorbic acid equiv./100 g) and ferric reducing power (FRAP: 152 mg ascorbic acid equiv./100 g) shown by SP. Esterified ferulic acid (52.9 mg/100 g SP) was also found, mostly as monomers and trimers. SP of 53 μm particle size was then assayed as a filler (0, 5, 8, and 12% concentrations) in calcium low methoxyl pectin-based films, which showed antioxidant capacity (DPPH and FRAP assays) in an SP-concentration-dependent manner. SP showed homogeneous dispersion in composite films equilibrated at 57.7% relative humidity. Water content decreased while film thickness increased with SP concentration. When loaded at a 12% level, the presence of 53-μm SP decreased the water vapor permeability and increased the normal stress at film fracture. Sunflower hulls can then be applied to the development of active materials like 12% SP film, which can be proposed as a food slice antioxidant separator to be investigated in a future work.
Highlights
Sunflower (Helianthus annuus L.), which belongs to the family Asteraceae, is an annual short season herbaceous crop with more than 70 species known worldwide
Results showed that Seed Hull Powder (SP) was chemically constituted by 1.3% w/w of proteins, almost 30% of cellulose and 26.4% of lignin, 4.0% of uronic acids of pectins, and 38.5% of neutral sugars, which can comprise mainly the monosaccharides that constitute the hemicelluloses, and low proportions corresponding to the rhamnogalacturonans of pectins (Table 1)
We found that proanthocyanidins were the main components of the extractable phenolic compounds of SP, with a total content of 168 mg/100 g SP (Table 3)
Summary
Sunflower (Helianthus annuus L.), which belongs to the family Asteraceae, is an annual short season herbaceous crop with more than 70 species known worldwide. Advanced valorization strategies, especially those based on green chemical technologies, can diversify the generation of multiple products by extraction of valuable components or chemicals [7, 8]. In this context, the sunflower hulls remaining after oil extraction can constitute an alternative carbon source of useful biopolymers and natural antioxidants for materials, dietary fibers, additives, and/or ingredients for food preservation. Toxicity analysis of sunflower hull based on the brine shrimp lethality assay has shown chronic toxicity as low as 1 g/mL [6] This is an extremely important quality since this waste can be applied to the development of edible materials such as active films. A localized activity of the food preservative loaded in films can be the way to achieve higher efficiency and to enhance availability [10]
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