The valorization of fruit-derived residues under the biorefinery concept has been a topic of interest in the last years due to the presence of high value-added substances in their composition. However, feasible alternatives for their implementation at an industrial level are still being developed since the abundance of pectin and extractives has made its biorefining challenging compared to conventional lignocellulosic residues. In this study, the sequential valorization of Orange Residues (OR) in a biorefinery was evaluated following the principles of biomass cascading and considering the composition of residual streams as a valuable input to maximize recovery after each processing step, without focusing on a sole product. To extract full value from the side-streams, fermentation with conventional and non-conventional yeasts was explored. The proposed biorefinery sequence produced essential oils, phenolic compounds, pectin, and fermentable sugars that were later converted to ethanol, xylitol, and single-cell protein. A detailed mass balance allowed to track compositional changes throughout the cascade and identify how extraction substances accumulate after each step, affecting further processing and side-stream utilization. The sequence proposed in this work extracted/transformed ∼85 % of the initial biomass into value-added products.

Residues from orange processing are being continuously generated in vast amounts due to the increasing demand for this fruit and its byproducts worldwide. The valorization of Orange Residues is challenging in contrast to conventional “lignocellulosic residues” since this fruit-derived biomass contains high amounts of pectin and an extractive fraction rich in sugars, essential oils, and polyphenols. The relative amounts of these fractions are highly influenced by the juice/pulp extraction process. Even though several studies have explored how to produce added value from this biomass, it is necessary to compare how different techniques and operating conditions influence the bioactive compounds that can be recovered and the remnant biomass after processing. This study compares essential oil extraction, solvent extraction, and acid hydrolysis for fermentable sugar and pectin production to elucidate a feasible sequence for a biorefinery from Orange Residues. From our results, it was proposed a technically feasible sequence that maximizes the yields of i) essential oils (0.70 ± 0.05 g/ 100 g DM) from steam distillation (4 h, 1500 W), ii) naringin (0.19 g/100 g DM), hesperidin (1.27 g/100 g DM), and glucose (3.9 g/100 g DM) from solid-liquid extraction (Ethanol 61.6 % (w/v), 45.8 °C, 155.5 min, and 5 % (w/v) biomass load), iii) pectin (25.24 g/100 g DM) from citric acid hydrolysis (pH 1.5, 90 °C, 82.1 min, and 5 % (w/v) biomass load), and iv) glucose (12.41 g/100 g DM) and xylose (10.13 g/100 g DM) from sulfuric acid hydrolysis (Sulfuric acid 0.68 % (w/v), 121 °C, 24.1 min, and 7.32 % (w/v) biomass load), in a biorefinery scheme.

Fruit waste (FW), mainly from agroindustry, is currently left behind in landfills despite its rich composition. The bioactive compounds (e.g., oils, polyphenols), carbohydrates, and lignin present in this biomass type require comprehensive characterization (i.e., identification and quantification) before they can be used as raw materials in biorefineries. This review collected information from scientific papers on FW compositional analysis methods and characterization data; the information needs to be compiled in a systematic, standardized, and comprehensive way to understand and quantify the true potential of FW as feedstocks for biorefineries. The information gathered in this review allowed us to identify the biomass fractions that could be valorized further depending on the kind of FW (peels, seeds, or seed vessels, and pomace or mixed residues). Fruit waste differs from conventional lignocellulosic biomass due to the presence of higher amounts (>5%) of extractives – pectin, and starch. This review describes current compositional analysis methodologies to identify possible strengths and weaknesses that could affect the adequate selection of valorization platforms. As no current methodology allows the composition of FW to be described thoroughly, this work identifies procedures applicable to biorefineries that use FW. Possible improvements are suggested to fill methodological gaps in the quantification of samples with large amounts of extractives and pectin. The standardization of methods for FW's quantification is fundamental for the adequate integration of different valorization platforms into biorefineries. It is essential to consider all the substances present in FW to exploit fully their potential for new value-added molecules, including oils, polyphenols, and pectin.

Compositional data on vegetable biomass is widely available from research papers and online databases. However, the high diversity of biomass characteristics and composition represents a challenge for researchers and companies willing to produce novel substances from residues, and that should decide on the best and most feasible options for their use as feedstocks. The present study constructed a database with information gathered from the proximate, ultimate, and chemical composition of different biomass residues that can be used for data analysis and classification to elucidate better how they can be valorized. Different data clustering techniques were implemented to determine how compositional data can be segmented. The identified groups, that contained residues with similar characteristics, allowed to have an insight into the valorization of these biomasses, which can be used as an initial tool for biorefinery design. The use of data clustering facilitated the identification of different types of biomasses in a systematic way, which until now has not been reported in the literature.