Fruit juice gases

Acids, for example those in fruit juices, catalyze rust formation because they furnish H+(aq) to accept electrons from the iron, causing it to dissolve faster. Oxygen gas is necessary to oxidize Fe+S to Fe2Oa. The presence of water facilitates the migration of Fe+2 from the reaction site. The resulting reduction in Fe+2 concentration allows more to be formed. Support for these ideas comes from the frequent observation that when... 

Foods. The determination of antioxidants and food preservatives is a very active part of the gas chromatography field. Adaptations and sample types are almost limitless for example, analysis of fruit juices, wines, beers, syrups, cheeses, beverages, food aromas, oils, dairy products, decomposition products, contaminants, and adulterants. A detailed discussion of this field may be found in Chapter 9. 

Castane (31) suggests a method that is an alternative both to the enzymatic one and to gas chromatography. He uses a column, sulfonated styrene divinylbenzene resin in H+ form (Fast-Fruit Juice), 7 fim, 7.8 X 150 mm and a refractive index detector. The mobile phase, composed of H2S04 0.002 M, is maintained at 60°C. In this way he succeeds in separating and quantifying the ethanol in concentrations between 0 and 1% (v/v). The author also ascertains a reproducibility of 0.04% v/v and a repeatability of 0.07% v/v with a precision value of 0.55% v/v. 

Anon (2004c) Detection of syrup addition to apple juice by capillary gas chromatography recommendation No 4, in IFU Compendium of Analytical Methods for Fruit Juices and Nectars, Swiss Fruit Juice Union, Zug, Switzerland. 

The method is not only applicable to the EU-official aqueous and fatty food simulant but also to foodstuffs such as beverages and soft margarine. Indeed the collaborative trial included fruit juice, wine and sunflower oil. The level of migrated acrylonitrile is determined by headspace gas chromatography, preferably with automated sample injection and using a nitrogen specific detector, for instance an alkali flame ionization detector (AFID). This gives the method the necessary sensivity to meet the... 

Saraji, M. Mousavinia, F. 2006. Single-drop microextraction followed by in-syringe derivatization and gas chromatography-mass spectrometric detection for determination of organic acids in fruits and fruit juices. J. Sep. Sci. 29 1223-1229. 

A different mode of operation, characterised as bubble flow, is possible if the continuous phase is the liquid to be extracted. The liquid level is kept constant at the top of the column and the supercritical gas which is introduced at the bottom is bubbled through the liquid for extraction. This method is mainly used if small amounts of dense gas are sufficient for complete extraction, i.e. if the solvent ratio of dense gas/ liquid feed is around 1 kg/kg. Examples are the extraction of flavours from wine and fruit juice where only very small amounts of extract can be expected. 

Capella, R Lercker, G. Lerici, C. R. Aroma retention during freeze-drying of fruit juices volatiles behaviour evaluated by head-space gas chromatography. IV International Congress of Food Science and Technology 5b, 18 (1974)... 

Several years ago a flotation process for clarification of fruit juices was developed in Canada [6,6a]. The juice is enzymatically treated, bentonite is added and the mixture is impregnated with an inert gas (nitrogen, carbon dioxide). Then the liquid is pumped into an especially designed flotation tank in which the solids float to the top from where they can be skimmed off in concentrated form. The liquid is polished by filtration. This process was also tested in Europe. 

The fruit juice aroma is an aqueous liquid with a characteristic individual flavour and a chemical composition, depending on the type and the maturity of the fruit. The quality is judged by gas chromatography and sensorial tests. 

Instead by solvent extraction [207], aroma compounds from aqueous media, e.g. fruit juices, can even be separated and enriched by techniques of solid phase micro extraction (SPME), preferably from the headspace [208] , corresponding devices can often be directly connected to GC systems. These techniques provide the complete spec-tmm of the individual compounds of an aroma. As it will normally not be possible and even not necessary to analyse all components of the complex mixture, the separation of its main compounds may demand a multi-dimensional (MD) gas chromatographic system [209[ as displayed in Fig. 6.14 [210[. Examples for the multi-ele-ment/multi-compound isotope analysis by such systems will be given later (6.2.2.4.4, [211[) they can even integrate the identification of the compounds by molecular mass spectrometry and a simultaneous determination of the enantiomer ratios of isomers [210, 211 [. The importance of enantiomer analysis as a tool for authenticity assessment is extensively treated in chapter 6.2.3. 

Barden, T.J., Croft, M.Y., Murby, E.J., and Wells, R.J. 1997. Gas chromatographic determination of organic acids from fruit juices by combined resin mediated methylation and extraction in supercritical carbon dioxide. Journal of Chromatography A 785 251-261. 

Membrane contactors (MCs) are another interesting emerging membrane technology for desalination. MCs are devices that bring two phases (gas/liquid, liquid/liquid or liquid/gas/liquid) into contact at the entrance of pores (Fig. 2.1). MCs are today most commonly employed in the production of ultrapure water, wastewater treatments and water purification, as well as being used to control the concentration of several non-volatile solutes in aqueous solutions, such as salt and sugar in fruit juices and blood treatments. 

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