HI 83742

Photometer Forthe Determination of Color and Total Phenols in Wine

Significance of Use Color determination of wine

Analytical techniques have become a valuable tool of modern wine mak-ers. Especially the definition and the processing techniques to obtain the desired wine color are of key importance. The right decisions taken dur- ing maturation of the grapes, processing, aging and blending, all strong- ly influence the final result of wine color.The color of wine is always read after the removal of suspended matter.there are mainly two color components present, yellow and red, but alsoa blue or green hue may appear. The color hue is the ratio between theyellow color concentrations over the red one, and is an indication about the degree of evolution.The yellow color in wine comes from the present of tannins (polymers offlavonoid-procyanidins type, and non-flavonoid phenols) and can be read without dilution. The increase of the yellow brown color in older wines is due to aging or oxidation. The red colors of wines are caused by free anthocyanins, copigments of anthocyannis, and polymerized phe- nolic compounds. The color of these pigments is pH dependent and can be intense dark. It is therefore necessary to dilute the wine sample taking care not to change the original wine pH. Hanna recommends using the special wine solvent to minimize possible errors due to dilution. HI 83742 is supplied with reagentsfor 5 tests, 2000 µl pipette, 200 µl pipette, 1 mL pipette, 3 mL pipette, 5 mL syringe, (2) cuvets with caps, tissue for wiping cuvets, 12 VDCpower adapter,(4) 1.5V AA batteries and instruction manualin a hard carrying case.

Reagents andAccessoriesOrdering information

Reagents

Phenol determination of wine

HI 83742-20 (20) Total phenols and color reagents Phenolic compounds are important for sever reasons since they (i) affect the color of the wine, (ii) have an astringent taste, (iii) may cause pungent odor, (iv) are a source of oxygen reduction, and (v) are sources of browning substances. Wine can contain a large varietyof phenolic compounds and with traditional analytical techniques itis difficult to distinguish between total phenols and specific phenols. Although some progress has been made with HPLC, the most com- mon analyses for total phenols remain the reaction of phenolic sub- stances with the Folin-Ciocalteu reagent. Other methods like the direct spectrophotometric determinations are less accurate, because in specific molar absorptivity, and color present of non phe- nolic substancesThe reaction between phenols and the Folin-Ciocalteu reagent involvesoxidation of the phenolic groups (R-OH) with a mixture of phosphotung- stenic acid ( H HI 83742-25 (20) Wine solvent Accessories DEMI-10 Bottle to prepare 10 liters of demineralized water HI 731318 (4) Cuvet tissues HI 731342 2000 µl pipette HI 731352 2000 µl pipette tips HI 731340 200 µl pipette HI 731350 200 µl pipette tips HI 740142 P (10) 5 mL graduatedsyringe HI 740144P (10) 5 mL graduatedsyringe HI 731321 (4) Glass cuvets
3 PW
12 O
40 ) and phosphomolybdenic acid (H
3 PMo
12 O
40 ) tothe quinoid form (R=O). The concomitant reduction of the Folin- Ciocalteu reagent causes a blue color in the sample that is proportional to the total phenolic content that, in turn, is expressed as g/L of Gallic Acid Equivalents (GAE).Another common method to express the phenol content is to report theFolin Index (FI) or Total Phenol Index. Simply multiply the read value ing/L of GAE times 25, to find the Folin Index Value. HI 710006 12 VDC power supply HI 740027P (10) 1.5V AA batteries

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