A 2026 study extracted grapevine buds with three water-glycol micellar systems and formulated the extracts directly into toners: the 1,2-pentylene glycol system recovered the most phenolics, showed the most complex particle-size distribution, and gave the clearest liquid.

The extraction medium is part of the formula

The study compared 1,3-propanediol, 1,3-butylene glycol, and 1,2-pentylene glycol in aqueous systems containing a non-ionic surfactant blend of polyglyceryl-4 laurate/sebacate and polyglyceryl-6 caprylate/caprate. Grapevine buds obtained from viticulture by-products were homogenized in each medium and macerated for 24 hours at room temperature, with the cycle repeated twice before pressure filtration. The extracts were then incorporated at 20% into model facial toner formulations. The plant lot, surfactant blend, and addition level were held constant across the three media, so the glycol was the only variable. All three glycols already have a place in toner formulas as humectants and, in the case of the butylene and pentylene glycols, as preservation boosters, which is what makes them candidates for double duty. The authors describe this as loan-extraction: part of the final formulation serves first as the extraction medium and returns with the extract, so no solvent has to be removed afterwards, and extraction performance and finished-formula behaviour have to be evaluated together rather than in two separate studies.

What each glycol delivered

The critical micelle concentration of the surfactant mixture fell as the glycol became more hydrophobic, in the order 1,2-pentylene glycol < 1,3-butylene glycol < 1,3-propanediol. A lower critical micelle concentration means the surfactant assembles into micelles at a lower dose, so more of the medium is micellar volume able to solubilise plant material. Total phenolic content and DPPH antioxidant activity followed the same order: highest with 1,2-pentylene glycol, close behind with 1,3-butylene glycol, lowest with 1,3-propanediol.

Dynamic light scattering told a different story. The 1,3-propanediol and 1,3-butylene glycol extracts showed monomodal distributions near 53 nm and 40 nm. The 1,2-pentylene glycol extract was bimodal, with populations near 15 nm and 726 nm and a polydispersity index of 0.908, meaning small micelles and much larger aggregates coexisted in the same liquid.

In the finished toners, viscosity increased only slightly relative to the controls, while turbidity and colour changed more clearly. The Zein number, used as an in vitro indicator of protein-denaturing capacity, fell in all three toner systems after the extracts were added, with the largest drop in the 1,2-pentylene glycol system; human tolerability and efficacy are separate questions for separate tests. Over 30 days at ambient temperature, none of the three toners containing 20% extract separated or sedimented.

The most complex particle population gave the clearest liquid

Turbidity, measured nephelometrically in NTU, is the result that needs explaining. The usual expectation is that a broader distribution with larger aggregates scatters more light and looks cloudier. The measurements ran the other way: the bimodal 1,2-pentylene glycol extract had the lowest turbidity at 1.7 NTU, and the monomodal 1,3-propanediol extract the highest at 7.3 NTU. After formulation, the pentylene glycol toner was still the clearest of the three extract-containing toners.

Scattering intensity depends on the refractive-index contrast between aggregate and medium and on how hydrated the particles are; size is only one variable. One plausible reading is that the 726 nm population in the pentylene glycol system consists of loose, water-rich aggregates whose refractive index sits close to that of the medium, while the 53 nm micelles in the propanediol system are numerous and compact enough to scatter more in total. Mean size, size distribution, scattering intensity, and visual clarity are four different quantities and deserve four separate entries in a formulation record. Within this study, 1,2-pentylene glycol delivered both the highest phenolic recovery and the lowest turbidity, 1,3-butylene glycol came close on recovery with a tidier size distribution, and 1,3-propanediol trailed on both.