A green extraction to recover polyphenol and polysaccharides from red bell pepper fruit by-products

The pepper fruit contains several phenolic compounds, mainly glycosides of apigenin, luteolin and chrysoeriol [1], and polysaccharides which have shown anticancer activity and anti-inflammatory properties in in vitro and in vivo tests [2]. The processing of fresh fruit and vegetables produces high quantities of waste (about 25%-60%), today known as agricultural by-products and not waste [3]. If the processes applied to treat these materials are ecological and sustainable, these by-products can become interesting as economical sources of valuable bioactive molecules. The by-products of red pepper (RPB) obtained from the processing of the fruit for the vegetable canning industry and consisting mainly of the discarded tops of the fruit and the seeds, have so far been little studied. The objectives of this study were to investigate the content of polyphenols and polysaccharides in the RPB by-product. Furthermore, in order to define an extraction process suitable for a scale-up, the Timatic® extractor was used, with water as the extraction solvent at a pressure of approx. 7 bars, applying different extraction cycles. The extraction time was 60 and 120 min, the temperature from 50°C to 90°C. All extractions were performed applying an RPB/solvent ratio of 1:20 (w/v). The phenolic content was determined by HPLC-DAD-MS, while size exclusion chromatography (SEC) and dynamic light scattering (DLS) were applied to study the molecular weight distribution of the polysaccharides. 1H-NMR was useful to determine galacturonic acid, methylation and degree of acylation after acidic hydrolysis according to Khatib et al 2021[4]. The phenolic content in RBP was low and reached max. 11.2 mg/g on dry extract. At the same time, the samples contained approx. 7%-10% of highly methylated polysaccharides determined on the dry aqueous extract. Five fractions were obtained from the pool of polysaccharides by adding increasing aliquots of ethanol at 0°C, of which Fraction 3 covered 40% of the total polysaccharides. The hydrodynamic volume of the main fractions was determined by SEC, which resulted close to 2000 kDa counting 80% of the total components detected. The acidic hydrolysis of polysaccharides by trifluoroacetic acid (TFA) allowed pointing out the presence of galacturonic acid. The 1H-NMR, used to verify the methylation and acylation grade of the fractions, confirmed the presence of O-methyl groups and O-acetyl groups in several fractions along with a high content of galacturonic acid indicating the presence of pectin. The extraction by hot water is suitable to recover up to 10 % of polysaccharides from RPB. This work describes a sustainable and green extraction process to obtain new functional food ingredients mainly based on polysaccharides from red pepper by-products.