A Comparative Evaluation of Bio-solvents for the Efficient Extraction of Polyphenolic Phytochemicals: Apple Waste Peels as a Case Study

Abstract

Apple peels were used as a model solid matrix for the comparative evaluation of aqueous mixtures of three biosolvents, including ethanol, 2,3-butanediol (butanediol) and glycerol, with regard to polyphenol recovery. The evaluation process was based on a step-by-step optimisation of the extraction, taking into consideration basic factors, including solvent composition, liquid-to-solid ratio and temperature. A further detailed description of the extraction capacity of each solvent was carried out using kinetics. Optimal solvent concentrations were 50 % (v/v), 50 % (v/v) and 70 % (w/v) for ethanol, butanediol and glycerol, respectively, while optimal liquid-to-solid ratio and temperature were 100 mL g -1 and 80°C for all solvents tested. The kinetic assay showed that extraction yields in total polyphenols obtained with these solvent systems displayed no statistical difference, although the overall extraction rate constant and diffusion coefficient were significantly higher for the extraction performed with 50 % (v/v) butanediol. The liquid chromatography-mass spectrometry examination of the extracts obtained under optimised conditions revealed that their polyphenolic profile was composed, in total, of 12 principal substances, but some qualitative differences among the extracts were also observed. The reducing power of the extract obtained with 50 % (v/v) ethanol was significantly higher, a finding attributed to possible synergistic effects among polyphenols.List of symbols C solv Solvent concentration (%, v/v or w/v) C TP Total polyphenol concentration (mg GAE L -1 ) dDensityEffective diffusion coefficient (m 2 s -1 ) h Initial extraction rate (mg g -1 min -1 ) kExtraction rate constant (g mg -1 min -1 ) P R Reducing power (lmol AAE g -1 ) R Particle radius (m) R L/S Liquid-to-solid ratio (mL g -1 ) t Time (min) t R Time required to enter the regular regime (min) T Temperature (°C) Y TP Yield in total polyphenols (mg GAE g -1 ) Y TP(s) Yield in total polyphenols at saturation (mg GAE g -1 )Greek letters e Dielectric constant (dimensionless)

Optimization of a Green Extraction/Inclusion Complex Formation Process to Recover Antioxidant Polyphenols from Oak Acorn Husks (Quercus Robur) Using Aqueous 2-Hydroxypropyl-β-Cyclodextrin/Glycerol Mixtures

“…This finding suggests that the amount of both glycerol and CD largely defined Y TP within the limits specified by the experimental design (Table 1). With regard to C gl , the results obtained were in accordance with previous investigations, which showed that increases in C gl up to 70% (w/v) favored polyphenol extraction from apple peels [8]. A similar trend was also reported for polyphenol extraction from two Artemisia species, where the higher yield was achieved with 90% (w/v) glycerol [9].…”

“…The three independent variables or factors studied were 2-hydroxypropyl-β-cyclodextrin concentration (C CD ), varying between 1% and 13% (w/v), glycerol concentration (C gl ), varying between 0% and 60% (w/v) and temperature (T), varying between 40˝C and 80˝C. Value ranges were chosen on the basis of preliminary experimentation and previous studies [8,9]. Each variable to be optimized was coded at three levels,´1, 0 and 1 ( Table 1).…”

Low-Transition Temperature Mixtures (LTTMs) Made of Bioorganic Molecules: Enhanced Extraction of Antioxidant Phenolics from Industrial Cereal Solid Wastes

“…All the LTTMs were used as 70% (v/v) aqueous solutions because water regulates (i) the polarity of the LTTM, providing, in general, higher extraction yields [11], and (ii) the viscosity of the LTTM, allowing for higher diffusivity. Since solid-liquid extraction is governed by diffusion, increased diffusivity results in a shorter time during which the maximum extraction yield can be achieved [20,21].…”

Ultrasound-Assisted Extraction of Polyphenolic Antioxidants from Olive (Olea europaea) Leaves Using a Novel Glycerol/Sodium-Potassium Tartrate Low-Transition Temperature Mixture (LTTM)

“…Yet, RL/S of 36.2 mL g −1 has also been reported [15]. It should be stressed that optima RL/S determined for polyphenol extraction with conventional solvents may reach up to 100-120 mL g −1 [20,21], but such With respect to C LTTM , it has been suggested that the amount of water required depends on the polarity of the solute (polyphenols), with flavonoid glycosides, such as rutin, being more soluble in LTTMs with a higher water proportion, compared with its aglycone quercetin [12]. On such a ground, it has been supported that the extraction of more polar compounds may require LTTMs with higher water analogy [13].…”

“…Yet, R L/S of 36.2 mL g −1 has also been reported [15]. It should be stressed that optima R L/S determined for polyphenol extraction with conventional solvents may reach up to 100-120 mL g −1 [20,21], but such high values have never been predicted for polyphenol extraction with LTTMs. As pointed out earlier, a minimum R L/S is always required for sufficient mixing, which would allow for attaining appropriate diffusivity and hence increased extraction yield.…”