Integrated Efforts for the Valorization of Sweet Potato By-Products within a Circular Economy Concept: Biocomposites for Packaging Applications Close the Loop

Micaela Vannini,Annamaria Celli,Paola Marchese,Laura Sisti,Taihua Mu,Hongnan Sun,Andrea Saccani

doi:10.3390/polym13071048

Abstract

With the aim to fully exploit the by-products obtained after the industrial extraction of starch from sweet potatoes, a cascading approach was developed to extract high-value molecules, such as proteins and pectins, and to valorize the solid fraction, rich in starch and fibrous components. This fraction was used to prepare new biocomposites designed for food packaging applications. The sweet potato residue was added to poly(3-hydroxybutyrate-co-3-hydroxyvalerate) in various amounts up to 40 wt % by melt mixing, without any previous treatment. The composites are semicrystalline materials, characterized by thermal stability up to 260 °C. For the composites containing up to 10 wt % of residue, the tensile strength remains over 30 MPa and the strain stays over 3.2%. A homogeneous dispersion of the sweet potato waste into the bio-polymeric matrix was achieved but, despite the presence of hydrogen bond interactions between the components, a poor interfacial adhesion was detected. Considering the significant percentage of sweet potato waste used, the biocomposites obtained show a low economic and environmental impact, resulting in an interesting bio-alternative to the materials commonly used in the packaging industry. Thus, according to the principles of a circular economy, the preparation of the biocomposites closes the loop of the complete valorization of sweet potato products and by-products.

Highlights

The principles of a circular economy are based on the consideration that waste and pollution are precious resources of added-value molecules, that can be exploited to obtain new ingredients and materials, which can, at the end of their life, return to the ground [1]
Approximately 4.5–5.0 tonnes of fresh sweet potato residues are generated for every tonne of produced starch
While a small amount of the sweet potato residue by-products is used as low-value animal feed, most of it is thrown away, and becomes a major element of environmental pollution

Summary

Introduction

The principles of a circular economy are based on the consideration that waste and pollution are precious resources of added-value molecules, that can be exploited to obtain new ingredients and materials, which can, at the end of their life, return to the ground [1]. In the agricultural sector, food production leads to large amounts of waste that correspond to 140 billion tons of biomass, generated globally every year [2] These wastes are rich in valuable substances that can be further exploitable [3,4,5,6]; In addition to that, even the remaining residues after the extraction of all the precious substances can be valorized by finding a profitable way as an alternative to landfill or incineration [7,8]. Potato wastes have been used as a carbon source in the microorganism fermentation for the synthesis of bio-polyesters: it is reported that microorganisms, as Cupriavidus necator [18], Alcaligenes eutrophus [19], Bacillus cereus or Bacillus thuringiensis [20] produced polyhydroxyalkanoates (PHA) from potato waste

Methods

Results

Conclusion