Functionalization of pectin-depleted residue from different citrus by-products by high pressure homogenization

In the valorisation of fruit and vegetable by-products by high pressure homogenization (HPH) into texturizing ingredients, the source of the by-product is an important determining factor. This study aims to demonstrate the valorisation potential of citrus residues after acidic pectin extraction (AR) and to investigate differences between citrus species (lemon, orange, grapefruit) and fruit parts (peel and pulp) as the source of the residues. Based on the results, pectin extraction is favourable in improving the storage modulus (G′) of the residue. However, residual pectin content in the different ARs, as indicated by pectic monosaccharides (e.g., GalA, Rha, Fuc), did not correlate to G′ after HPH. The G′ of all ARs suspensions, regardless of the source, improved significantly after HPH at 20 MPa. After HPH, fragmentation and subsequently aggregation of particles were observed from the particle size reduction and microscopy visualization. Particle morphology and size did not correlate with the G′ of the suspensions. Residual pectin's Rhamnogalacturonan-I contribution and degree of methyl-esterification, protein content, and glucose content related to hemicellulose were correlated to the G′ of the suspensions before HPH. However, after HPH, no correlation was found between G′ and these characteristics, likely due to changes on the structure of the particles. The results highlight the high potential of all the citrus ARs from the different sources to be functionalized as texturizing ingredients. However, the peel AR from grapefruit and lemon exhibited better rheological properties and may be considered as better sources compared to the other citrus by-products.