Coffee grinder

Selected fruits were immediately washed with distillated water and placed in hermetical polystyrene boxes in which we added some liquid nitrogen in order to prevent oxidation reactions, before to be stored at −20 °C. Whole fruits (flesh and peel, 5 kg) were manually sliced into approximately 2 g pieces, frozen at −80 °C, and at once freeze-dried during 48 h with a pilot CryoTec freeze-dryer (Saint-Gély-du-Fesc, France) with a separated cold trap at −70 °C, and plate temperature set to −20 °C at a working pressure of 15 Pa. Freeze-dried fruit pieces were then placed in a desiccator containing P₂O₅ in order to prevent water sorption. After freeze-drying, fruit pieces were immediately grounded with a Moulinex coffee grinder (Moulinex, Ecully, France). A small amount of liquid nitrogen were added to prevent oxidation during grinding. Powders were stored in a desiccator containing P₂O₅ in order to prevent water sorption, and their residual water content was measured after 24 h at 105 °C. Particle size distribution of fruit powders was measured through dynamic light scattering with a Malvern Mastersizer 2000 apparatus (Malvern Instruments Ltd, Malvern, UK) in absolute ethanol.

The samples used in this study were grape stems from Mazuelo variety collected from the 2016 harvest in Navarra, in the north of Spain. Grapes were manually removed and the resulting stems were dried in a stove (Ing Climas, Barcelona, Spain) at 25 °C until constant weight. Later, dried grape stems were milled in a coffee grinder (Moulinex, Ecully, France) and sieved in a sieve of 300 µm. The resulting powder had brown color and a homogeneous particle size.

Extracts were obtained from grape stems of Mazuelo variety from the Estación de Viticultura y Enología de Navarra, in northern Spain (2016 harvest). Prior to extraction, the stems were oven dried (Ing Climas, Barcelona, Spain) at 25 °C until constant weight. They were subsequently ground in a coffee grinder (Moulinex, Ecully, France) and passed through a 300 µm sieve. To obtain the grape stem extract, the dried and ground stem was macerated in 50% v/v ethanol/water (solid/solvent ratio 1:100, w/v), for 24 h at 40 °C. After the incubation, the extracts were centrifuged (8000 rpm for 15 min), filtered and lyophilized. The characterization of the extract thus obtained was published in a previous work [8 (link)]. To perform the stability study, 50 mg of the lyophilized extract were stored in transparent (T) and in amber vials (A), at 25 °C and 40 °C for 6 months. The samples were stored under fluorescent lamps. Nine replicates were performed for each of the conservation conditions studied, and three vials of each type were taken every two months for characterization. At the end of each storage period, the samples were kept at −20 °C for subsequent analysis. Prior to analysis, the lyophilized extract in each vial was reconstituted in 10 mL of methanol.