Phosphates in wines

The content of phosphates in wines usually varies between 50 and 1000 mg/L (as P043 ) with a lower concentration in white wines as compared to the red ones (Garoglio, 1981 Zee et al., 1983 Ough and Amerine, 1988). Flak and Schaber (1989) did not find significant... 

Metrohm Application Note S-12, Determination of lactate, chloride, nitrate, sulfite and phosphate in wine, Metrohm Ltd, Hcrisau, Switzerland, 1999. 

Metrohm AG, 1C Application Note No. S-12 Determination of Lactate, Chloride, Nitrate, Sulfite, and Phosphate in Wine. Metrohm AG, Herisau, Switzerland. 

The simultaneous determination of sulfite and phosphate in wine was proposed by Yao et al. (1994), where a FI A system was coupled with amperometric detection. In this approach two different reactors with immobilized sulfite oxidase and co-immobilized purine nucleoside phosphorylase-xanthine oxidase were incorporated in a parallel configuration. The enzymatically generated hydrogen peroxide was selectively detected on a poly(l,2-diaminobenzene)-coated platinum electrode. Because of the different residence times at each channel, two different peaks could be obtained, the first corresponding to sulfite and the second to phosphate. Using this system, the analytes could be simultaneously analyzed with a linear range of 1 x 10 -2 x 10 M (sulfite) and 2 x 10 -5 x 10 M (phosphate) and a sample throughput of 30 Mb... 

Yao, T., M. Satomura, and T. Nakahara, 1994. Simultaneous determination of sulfite and phosphate in wine by means of immobilized enzyme reactions and amperometric detection in a flow-injection system. Talanta 41 2113-2119. 

Iron. Excess iron in wines causes cloudiness, interferes with the color, and can impair flavor. The mechanism of ferric phosphate precipitation has been intensively studied, and numerous colorimetric methods have been developed. For routine purposes the color developed with thiocyanate is adequate (6,9), but many enologists prefer the orthophenanthro-line procedures (3, 4, 6, 22). Meredith et al. (Ill) obtained essentially the same results for iron using 2,4,6-tripyridyl-s-triazine (TPTZ) to develop the color. Atomic absorption spectrophotometry can be used but, as with copper, corrections for reducing sugar and ethanol are necessary (51). 

Phosphorus is present in wines as phosphates of calcium, potassium, magnesium, etc., and also in organic form, probably as acid glycerophosphate of potassium and calcium. The addition of phosphate, which sometimes replaces plastering, naturally increases the quantity of phosphorus present. 

Phosphoric acid. The amount of this acid naturally present in wines is o-2-o-6 gram (P2Oa) per litre. Addition of dicalcium phosphate is sometimes made to wine and in this case the proportion of P2Oa may be increased to 1-5 gram per litre, the ash also being considerably augmented. 

Cvetkovic and coworkers [74] evaluated a mixed Ni and Sr nitrates matrix modifier for the determination of Se in wines by Zeeman ET-AAS. Samples were heated on a boiling water bath with small amounts of HNO3 and H2O2. To eliminate interferences, especially sulfates and phosphates, Se was complexed with APDTC and extracted into methylisobutyl ketone (MIBK) and the graphite furnace temperature program was optimized for both aqueous and organic solutions. Selenium concentrations up to 0.93 pg l-1 were detected in wines from the Republic of Macedonia. 

Citric acid is used in soft drinks, candies, wines, desserts, jellies, jams, as an antioxidant in frozen fruits and vegetables, and as an emulsifier in cheese. As the most versatile food acidulant, citric acid accounts for about 70 percent of the total food acidulant market. It provides effervescence by combining the citric acid with a biocarbonate/carbonate source to form carbon dioxide. Citric acid and its salts are also used in blood anticoagulants to chelate calcium, block blood clotting, and buffer the blood. Citric acid is contained in various cosmetic products such as hair shampoos, rinses, lotions, creams, and toothpastes. More recently, citric acid has been used for metal cleaning, substituted for phosphate in detergents, for secondary oil recovery, and as a buffer/absorber in stack gas desulfurization. The use of sodium citrate in heavy-duty liquid laundry detergent formulations has resulted in a rapid increase in the use of citric acid. 

Analysis of Phenolic Compounds. A Hewlett-Packard (Palo Alto, CA) Model 1090 HPLC System, was used to determine the levels of specific phenolic components. The HPLC system was equipped with a ternary solvent delivery system, a diode array UV-VIS detector, and HP ChemStation software for data collection and analysis. Full chromatographic traces were collected at 280, 520, 316, and 365 nm, and spectra were collected on peaks. The stationary phase was a Hewlett-Packard LiChrosphere C-18 coliram, 4mm X 250 mm, with 5 pM particle size packing. Operating conditions include an oven temperature of 40 C, injection volume of 25 pL, and flow rate of 0.5 mL/minute. The mefriod was based on a previously published method for phenolic components in wine (30) and used the modified solvent gradient shown in Table II. Solvent A was 50 mM dihydrogen ammonium phosphate, adjusted to pH 2.6 with orthophosphoric acid. Solvent... 

Organic acid content in wine has an important impact on organoleptic characteristics of the wine. a-Hydroxy acids (tartaric, malic, lactic, and citric acids) are mainly responsible for these characteristics. Other acids in wines include acetic, ascorbic, gluconic, and sorbic acids, as well as sulfite, sulphate, phosphate, and malonate (Masar et al., 2001). 

Figure 14.4 Separation of organic acids (as anions) and inorganic anions in wine (reproduced with permission of Dionex). Conditions column, 25cm x 4mm i.d. and precolumn stationary phase, lonPac AS11-HC mobile phase, 1.5 ml min nonlinear gradient from 1 mM to 60mM NaOH and from 0 to 20% methanol temperature, 30°C conductivity detector after packed suppressor. Peaks 1 = lactate 2 = acetate 3 = formate 4 = pyruvate 5 = galacturonate 6 = chloride 7 = nitrate 8 = succinate 9 = malate 10 —tartrate 11—fumarate 12 —sulfate 13 = oxalate 14 = phosphate 15 —citrate 16 = isocitrate 17 = c/s-aconitate 18 = frans-aconitate.

Consider just a few cases of aqueous equilibria. The magnificent formations i n limestone caves and the vast expanses of oceanic coral reefs result from subtle shifts in carbonate solubility equilibria. Carbonates also influence soil pH and prevent acidification of lakes by acid rain. Equilibria involving carbon dioxide and phosphates help organisms maintain cellular pH within narrow limits. Equilibria involving clays in soils control the availability of ionic nutrients for plants. The principles of ionic equilibrium also govern how water is softened, how substances are purified by precipitation of unwanted ions, and even how the weak acids in wine and vinegar influence the delicate taste of a fine French sauce. In this chapter, we explore three aqueous ionic equilibrium systems acid-base buffers, slightly soluble salts, and complex ions. 

The calcium cation produces many relatively insoluble salts. The most insoluble is calcium oxalate. Oxalic acid is used to demonstrate the presence of calcium in a liquid as it causes turbidity and precipitation. Calcium tartrate is also relatively insoluble, especially in the presence of ethanol (Section 1.6.5). In the same way, calcium gluconate and mucate, present in wine made from botrytized grapes, are reputed to be responsible for crystalline turbidity (Section 1.2.2). Calcium concentrations in white wines are between 80 and 140 mg/1, while they are slightly lower in red wines. The calcium content may increase following deacidification with calcium carbonate. As calcium is divalent, it is more energetically involved than potassium in colloid flocculation and precipitation, e.g. ferric phosphate, tannin-gelatin complexes, etc. 

There may be a few tens of mg/1 of inorganic nitrogen in wine after aging on the lees, or even after malolactic fermentation. Indeed, lactic bacteria do not assimilate ammonia nitrogen and may even excrete it. It is prudent to add diammonium phosphate in conjunction with thiamin pyrophosphate to wines intended for a second fermentation in sealed vats or in the bottle. 

Among the colloids found in wine, proteins and cellulose fibers are positively charged, while yeast cells and bacteria, colloidal coloring matter, ferric phosphate, copper sulfide, ferric ferrocyanide and bentonite are negatively charged. 

Colloids have a relatively large surface area, so they may act as adsorbents. Colloidal sediment formed in wine dne to natnral settling or treatment generally contains varions snbstances that were not involved in the colloidal floccnlation mechanisms that caused the deposit. Thus, for example, ferric phosphate deposits frequently contain calcinm. At one time, it was even snpposed that ferric-calcinm casse had occnrred. In fact, the calcinm is not involved in floccnlation as an electrolyte, bnt is rather fixed by adsorption. 

Repeated racking produces the clarity required in wine, especially if it is aged in the barrel. Of course, the most important aspect of racking is the decanting process, which eliminates waste from the wine (yeasts and bacteria, grape fragments, potassium bitartrate, ferric phosphate and cuprous sulfide). 

Cold stabilization is also partially effective in preventing other types of colloidal precipitation. It helps to prevent ferric casse by insolubilizing ferric phosphate in white wines and ferric tannate in reds. However, even after aeration to promote the formation of the Fe + ions involved in these mechanisms, only small quantities of iron are eliminated. Fining at the same time as cold stabilization improves treatment effectiveness but is never sufficient to prevent ferric casse completely. 

Phosphate additives are especially useful in the production of alcoholic beverages. This is because of their ability to form stable soluble complexes with troublesome Fe +, Cu % Ca and other cations which need not then be removed. Polyphosphates prevent clonding or hazing in wine and beer. 

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