Biorefinery of sunflower by-products: Optimization of twin-screw extrusion for novel biostimulants

Abstract

In view of improving the circularity and sustainability of crop production, sunflower by-products were extracted using twin-screw extrusion (TSE) to produce sunflower extract, a plant biostimulant that alleviates plant shoot development under salt stress conditions. The TSE process is a thermo-mechano-chemical pre-treatment method for the separation of liquid fraction from the biofiber. To improve the cost-efficiency of extraction, we determined the key procedure of TSE extraction within the production chain for biostimulants derived from sunflower bark and heads. This study scrutinizes sample preparation and extraction methods optimizing the sunflower by-product biorefinery, reducing energy input and maximal recovery of biostimulant activity. Optimal extraction conditions were obtained with starting material ground to a coarse size of 6 mm on average in alkaline aqueous solvent (pH 10) at a liquid-to-solid ratio of 5.5 injected at two different points using a 3 D length of reversed screw elements at the rotation speed of 200 rpm. These TSE settings provide a reproducible protocol for the biostimulant extraction from sunflower by-products. The optimized method contributes to improving the profitability of sunflower production and contributes to a more robust biostimulant extraction procedure.

Keywords: Biorefinery; Biostimulant; Optimization; Plant bioassay; Sunflower; Twin-screw extrusion (TSE).

Graphical abstract

Fig. 1

A biorefinery flowchart of sunflower by-products for biostimulants through twin-screw extrusion (TSE).

Fig. 2

Heatmap of Spearman's correlation coefficient of seven sunflower extracts derived from different tissues harvested in 2020 (mentioned in Table 1).

Fig. 3

Heatmap of Spearman's correlation coefficient of sunflower extracts using fourteen different TSE operation conditions from HSO+20 (mentioned in Table 2).

Fig. 4

All factors plot of R_MS (%) under six different TSE operation conditions with the optimal settings of feedstock coarseness (20 mm), liquid-to-solid ratio (5.5), pH (injected solvent) (7), water injection point (2), length of reversed screw (0.5 D), and screw rotation speed (150 rpm). TSE: twin-screw extrusion; R_MS: extraction yield in soluble molecules inside the clarified filtrate per kilogram of feedstock.

Fig. 5

All factors plot of SME under six different TSE operation conditions with the optimal settings of feedstock coarseness (6 mm), liquid-to-solid ratio (2.5), pH (injected solvent) (12), water injection point (1), length of reversed screw (0.5 D), and screw rotation speed (150 rpm). TSE: twin-screw extrusion; SME: specific mechanical energy.

Fig. 6

All factors plot of True leaf (%) under six different TSE operation conditions with the optimal settings of feedstock coarseness (6 mm), liquid-to-solid ratio (5.5), pH (injected solvent) (12), water injection point (2), length of reversed screw (3 D), and screw rotation speed (150 rpm). TSE: twin-screw extrusion; True leaf (%): percentage of plants with the first pair of true leaves.

Fig. 7

All factors plot of SA under six different TSE operation conditions with the optimal settings of feedstock coarseness (6 mm), liquid-to-solid ratio (5.5), pH (injected solvent) (12), water injection point (2), length of reversed screw (3 D), and screw rotation speed (150 rpm). TSE: twin-screw extrusion; SA: total shoot area.

Fig. 8

Material flow analysis and energy cost of sunflower conversion into lyophilized powder used as biostimulants. ^a The Twin-screw extrusion (TSE) operation conditions were of the O14 trial conducted from the HSO+20 sunflower feedstock (Table 3). ^b Screw profile 7 was described exhaustively in Fig. S1^c Energy consumption during TSE was estimated by means of specific mechanical energy (SME). ^d Lyophilized powder yield was calculated based on the extraction yield (R_MS (%)). TSE: twin-screw extrusion; R_MS: extraction yield in soluble molecules inside the clarified filtrate per kilogram of feedstock.

Fig. 9

Heatmap matrix on the biostimulant efficacy of sunflower-derived extracts, known antioxidants, and commercial biostimulants. ^a SBE18 was referred to the bioassay batch 4 (Table S2). Asterisk (∗) indicates the statistical significance (p < 0.05 at 95 % confidence interval) compared to blank under control or salt stress conditions. ( × ) denotes missing data. The concentration of 0.5 g/L was used for both SBE18 and other sunflower extracts. The codes for sunflower extracts are shown in Table 1, Table 3. SA: shoot area; GSH: glutathione; AsA: ascorbic acid.