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This study aims to assess kinetic modelling of the solid–liquid extraction process of total polyphenolic compounds (TPC) from apple pomace (AP). In this regard, we investigated the effects of temperature and solvent (i.e. water, ethanol, and acetone) on TPC extraction over various periods. The highest TPC yield of 11.1 ± 0.49 mg gallic acid equivalent (GAE)/g db (dry basis) was achieved with a mixture of 65% acetone–35% water (v/v) at 60 °C. The kinetics of the solvent-based TPC extraction processes were assessed via first-order and second-order kinetic models, with an associated investigation of the kinetic parameters and rate constants, saturation concentrations, and activation energies. The second-order kinetic model was sufficient to describe the extraction mechanism of TPC from AP. This study provides an understanding of the mass transfer mechanism involved in the polyphenolic compound extraction process, thus facilitating future large-scale design, optimization, and process control to valorize pomace waste.

Apple pomace (AP) from the food industry is a mixture of different fractions containing bioactive polyphenolic compounds. This study provides a systematic approach toward the recovery and evaluation of the physiochemical and biological properties of polyphenolic compounds from AP. We studied subcritical water extraction (SCW) and solvent extraction with ethanol from four different AP fractions of pulp, peel, seed, core, and stem (A), peel (B), seed and core (C), and pulp and peel (D). The subcritical water method at the optimum condition resulted in total polyphenolic compounds (TPC) of 39.08 ± 1.10 mg GAE per g of AP on a dry basis compared to the ethanol extraction with TPC content of 10.78 ± 0.94 mg GAE/g db. Phloridzin, chlorogenic acid, and quercetin were the main identified polyphenolics in the AP fractions using HPLC. DPPH radical scavenging activity of fraction B and subcritical water (SW) extracts showed comparable activity to ascorbic acid while all ethanolic extracts were cytocompatible toward human fibroblast (3T3-L1) and salivary gland acinar cells (NS-SV-AC). Our results indicated that AP is a rich source of polyphenolics with the potential for biomedical applications.

AbstractIn this study, the solubilization of waste coarse wool as a precursory step for the large-scale valorization of keratin was investigated using a green deep eutectic solvent (DES) based on L-cysteine and lactic acid. The investigation was undertaken via the response surface methodology and based on the Box–Behnken design for four process variables of temperature (70–110 °C), dissolution time (2–10 h), the mass of L-cysteine (0.5–2.5 g) in 20 mL of lactic acid, and wool load in the DES (0.2–0.6 g). Temperature was the most significant process variable influencing keratin yield from the waste coarse wool. The optimum keratin yield (93.77 wt.%) was obtained at the temperature of 105 °C, 8 h dissolution time, with 1.6 g L-cysteine in 20 mL of lactic acid using 0.5 g of wool. This study suggests L-cysteine and lactic acid as a green solvent with the potential to scale up keratin recovery from waste wool without significant destruction in the structure of the recovered keratin.Graphical abstract

In line with the prevailing global interest in value extraction from biomass waste streams, the current study explored the technical feasibility of valorizing waste apple pomace (WAP) to produce high-value biochemicals of 5-hydroxymethylfurfural (HMF), lactic acid, and xylitol. Technical feasibility was demonstrated via a process simulation study that employed experimental data and incorporated previously reported approaches in the literature. Economic and environmental performances of the WAP based biorefinery were assessed using the internal rate of return (IRR) and the mass of greenhouse gas emission per unit mass of feedstock ( G F ) as sufficient performance indicators, respectively. The study was able to show that as the IRR value increased (better economic performance), the G F increased (poorer environmental performance). This suggested that the determination of the optimal condition of the environmental and economic performances would require the imposition of trade-offs. The preferred trade-off condition for enhanced economic and environmental performances was subsequently determined via multi-objective optimization, with a Pareto front containing non-dominated equally optimal solutions subsequently developed. The present work, therefore, provides an in-depth performance analysis of WAP based biorefinery as a waste management strategy. Notably, the proposed strategy of multiple product generation from biomass may be extended to other organic waste based biorefineries. Graphic Abstract

Subcritical water extraction (SWE) technology, as an environmentally sustainable technique, was applied to optimize the recovery of polyphenolic compounds from apple pomace (AP). Box–Behnken experimental design approach was used to investigate the effects of four process variables; extraction temperature (100-220 ºC), extraction time (30-120 min), mean sample particle size (500-1000 µm) and solid to solvent ratio (1-10 g/100 mL) on total polyphenolic compounds (TPC) yield. The SWE conditions for the optimal TPC of 39.08 ± 1.10 mg GAE per g of AP on dry basis (db) were determined to be temperature of 203.71 ºC, time of 75 min, solid to solvent ratio of 1 g/100 mL and a mean sample particle size of 500 µm. The temperature and solid to solvent ratio were determined as the most statistically significant process variables that influenced TPC yield. At the optimum conditions, antioxidant activity (% DPPH inhibition activity) of the polyphenolic extract was found in the range of 15.38–92.90% as compared to ascorbic acid (8.64–95.90%). The findings of this study proposed that SWE as a green and efficient technology provided significant advantage in term of polyphenolic compounds yield, and AP could be utilized as potential raw material for SWE of valuable antioxidant polyphenolic compounds.

In this study, the solubilisation of waste coarse wool as a precursory step for the large scale valorisation of keratin was investigated using a green deep eutectic solvent (DES) based on L-cysteine and lactic acid. The investigation was undertaken via the response surface methodology and based on the Box-Behnken design for four process variables of temperature (70-110 C), dissolution time (2-10 h), the mass of L-cysteine (0.5-2.5 g) in 20 mL of lactic acid, and wool load in the DES (0.2-0.6 g). The effect of variations in temperature was established to be the most significant process variable influencing keratin yield from waste coarse wool in the current work. An optimum keratin yield (93.77 wt.%) was obtained at the temperature of 105 C, 8 h dissolution time, with 1.6 g L-cysteine in 20 mL of lactic acid using 0.5 g of wool. This study suggests L-cysteine and lactic acid as a green solvent with the potential to scale up keratin recovery from waste wool without significant destruction in the structure of the recovered keratin. Competing Interest Statement The authors have declared no competing interest.