Acetic acid

The films prepared within this study were based on two natural polymers (hydroxypropyl)methyl cellulose (HPMC) (3600–5500 mPa.s), which was obtained from Sigma, Darmstadt, Germany, and chitosan (CS) from shrimp and other crustacean shells (viscosity 200–600 mPa.s, 0.5% in 0.5% Acetic acid, 20 °C; deacetylation value: 80%, molecular mass 1526.464 g/mol), which was purchased from TCI, Belgium. Lauric acid was obtained from Sigma, Darmstadt, Germany. Acetic acid was obtained from LachNer, Neratovice, Czech Republic. All other materials were at least reagent grade. Millipore Milli-Q water was used for the preparation of gels and buffer solutions. Lipase from Mucor miehei (M. miehei) was supplied by Fluka, Basel, Switzerland, and had a specific activity of 1.19 U/mg of protein (1 U corresponds to the amount of enzyme which liberates 1 μmol butyric acid per min at pH 8.0 and 40 °C using tributyrin as substrate).

Formic acid (98%, ≈26 M, p.a., Lach-Ner,
Czech Republic) was used for the formulation of photochemical media
of various molarities (M, i.e., mol L^–1). Nitric
acid (≥65%, semiconductor grade) and sodium formate were sourced
from Sigma-Aldrich; acetic acid (99.8%, p.a.) was from Lach-Ner. Deionized
water (DIW, <0.2 μS cm^–1, Ultrapur, Watrex)
was used for the preparation of all photochemical media. DIW was also
used for the serial dilution of all stock solutions (no acids added)
with the exception of mixed working standards that were prepared with
the required molarity of HCOOH to match that of the tested photochemical
medium. The specification of individual analytical standards and compounds
used as potential metal ion sensitizers is given in the Supporting Information. Mixed standards used
for PVG contained no more than three analytes (e.g., Ru³⁺, Re⁷⁺, and Ir³⁺; Ni²⁺ and Mo⁶⁺; Fe³⁺, Co²⁺, and W⁶⁺, etc.)
prepared in the photochemical medium in addition to possibly being
spiked with various metal ion sensitizers.
For some experiments,
the photochemical media were saturated with Ar (99.996% purity), O₂ (99.5%), or CO (99.9%) obtained from SIAD Ltd. (Czech Republic).

The trans-resveratrol standard (99%) along with commercialized standard of trans-ε-viniferin (95%) (Fig. 5) were purchased from Sigma-Aldrich (Prague, Czech Republic), while the cis-ε-viniferin was generated from trans-ε-viniferin standard by UV exposition (Spectroline, CV-10, New York, USA). All compounds were measured as solutions in isopropyl alcohol (Lach-Ner, Prague, Czech Republic, gradient grade) which was also used as extraction solvent along with ethanol (Lach-Ner, Prague, Czech Republic, gradient grade). Other solvents for HPLC were methanol (Lach-Ner, Prague, Czech Republic, HPLC gradient grade), acetic acid (Lach-Ner, Prague, Czech Republic, 99%), and ultrapure water. Gallic acid (Sigma-Aldrich, Prague, Czech Republic, ACS reagent), Folin-Ciocalteu reagent (Sigma-Aldrich, Prague, Czech Republic, 2 M with respect to acid), sodium carbonate (Lachema, Brno, Czech Republic, 98%), and ultrapure water (Ultrapur Watrex system, Prague, Czech Republic) were used for determination of total content of phenolic compounds in extracts.Figure 5

Structure of bioactive compounds extracted from wine waste.

Chitosan (medium molecular weight), agarose (routine use class), and Direct blue 1 were purchased from Sigma Aldrich (St. Luis, MO, USA). Sirius red F3B and Reactive blue 49 were purchased from Synthesia (Pardubice, Czech Republic). Acetic acid for the preparation of Chitosan solution was purchased from Lachner (Neratovice, Czech Republic). Disodium hydrogen phosphate, sodium dihydrogen phosphate, citric acid, and sodium hydroxide for the preparation of buffer solutions were purchased from Penta (Chrudim, Czech Republic).
The exact molecular weights of Chitosan and agarose were determined by means of size exclusion chromatography coupled with multiangle static light scattering, differential refractive index, and UV/VIS detection (SEC chromatographic system from Agilent Technologies, detectors from Wyatt Technology). The exact molecular weights were 251 ± 4 kDa for Chitosan and 146 ± 3 kDa for agarose.
The deacetylation degree of Chitosan was determined by potentiometric titration as described by Garcia et al. [62 (link)]. The degree was determined as 83.8 ± 0.2% mol.

Chitosan (medium molecular weight), agarose (routine use class) and copper(II) sulfate (p.a.) were purchased from Sigma Aldrich (St. Luis, MO, USA). Acetic acid for the preparation of Chitosan solution was purchased from Lachner (Neratovice, Czech Republic).
The exact molecular weights of Chitosan and agarose were determined by means of size exclusion chromatography, coupled with multiangle static light scattering, differential refractive index, and UV/VIS detection (SEC chromatographic system from Agilent Technologies, detectors from Wyatt Technology). The exact molecular weights were 251 ± 4 kDa for Chitosan and 146 ± 3 kDa for agarose.
Deacetylation degree of Chitosan was determined by potentiometric titration described by Garcia et al. [67 (link)]. The degree was determined as 83.8 ± 0.2% mol.

Folin-Ciocalteu reagent, (±)-6-hydroxy-2,5,7,8-tetramethylchromane-2-carboxylic acid (Trolox), gallic acid, 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,4,6-tris(2-pyridyl)-s-triazine (≥99.0%) were supplied from Sigma-Aldrich (Steinheim, Germany). 2,2′-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammoniumsalt (98%) was purchased from J&K, Scientific Ltd. (Beijing, China). Additionally, sodium carbonate anhydrous and ferric chloride hexahydrate were supplied from Centrohem (Stara Pazova, Serbia), while acetic acid (99.8%) and potassium peroxydisulfate were purchased from Lach-Ner (Neratovice, Czech Republic). Sodium acetate anhydrous was purchased from Kemika (Zagreb, Croatia). Ultra-pure water was obtained from a Milli-Q Plus system (EMD Millipore, Billerica, MA, USA). All other chemicals used were of analytical reagent grade.

The pesticide standards were purchased from Restek (Bellefonte, Pennsylvania, USA) and Lab Instruments (Castellana Grotte, Italy). HPLC-MS-grade acetonitrile, methanol, formic acid, and acetic acid were obtained from Lachner (Neratovice, Czech Republic). Sodium chloride, magnesium sulfate anhydrous, disodium hydrogen citrate sesquihydrate (C₆H₈Na₂O₈), and trisodium citrate dihydrate (C₆H₅O₇Na₃ × 2H₂O) were obtained from Lachner (Czech Republic). The graphitized carbon black (GCB), C18 sorbent, and primary and secondary amines (PSA) were supplied from Sigma-Aldrich (St Louis, Missouri, USA).
The selected citrus fruits were purchased from local markets in Belgrade, Serbia, in February 2022, and a total of 76 samples were analyzed (28 oranges, 26 lemons, 17 tangerines, and 5 grapefruits). Each fruit sample was analyzed as the whole fruit following European Union Guidelines Regulation, (EC) No. 396/2005 Annex [20 ]. During the survey, fruits were stored in fridges in labeled plastic bags at 4 °C until analysis.