Water-starch complex analysis

FIGURE 16.17 Nonbranched/long chain branched glucans of potato starch dissolved in hot water-steam and 0.1 M NaOH 1.2 ml of the 18-mg/ml solution was separated on Sephacryl S-1000 (95 X 1.6 cm) 3-ml fractions were collected for further analysis normalized (area = 1.0) eluogram profiles (ev) constructed from an off-line determined mass of carbohydrates for each of the fractions branching index ( ) determined from iodine-complexing potential of individual 3-ml fractions flow rate 0.40 ml/ min V ,i = 75 ml, Vtot = 162 ml eluent 0.005 tA NaOH. 

APHA Method 4500-CL02-B, iodometric titration analysis, measures the concentration of chlorine dioxide in water by titration with iodide, which is reduced to form iodine. Iodine is then measured colorimetrically when a blue color forms from the production of a starch-iodine complex. The detection limit for this method is 20 pg/L (APHA 1998). 

A method of determining airborne iodine has also been reported.241 Here, iodine is absorbed into 5% aqueous KI and spectrophotometrically determined at 590 nm in the form of its complex with starch. This method is selective with respect to bromine and chlorine, and the sensitivity of this method is 0.25 mg of I2 per m3 of air. The concentration of the, 31I isotope in water can be determined by a method involving isotope exchange in the starch-iodine complex.242 Flow-injection determination of ascorbic acid (0.1-40 mg/mL) has been proposed.243 Iodine is generated in the flow system as I3- ions, which are in turn exposed to starch to produce a steady signal at 350 and 580 nm. Ascorbic acid provides inversed maxima which are measured. This method is recommended for analysis of ascorbic acid in fruit juice, jam, and vitamin-C preparations. Use of the blue complex has also been reported for determination of sodium dichloro-isocyanurate in air.244 Obviously the blue reaction is applicable in the determination of amylose, amylopectin, and starch,245-252 as well as modified starches.245,253-255... 

Several different analytical approaches have been proposed for the determination of acrylamide, The analysis of food samples presents a special challenge because of the high levels of matrix interferences, particularly in starch foods, r.arly method,s used GC or HPl.C in the determination.. Although these methods were successful in water, agricultural samples, and environmental samples, the selecliviiy was not sufficient for samples of ctxtkcd fotxls where the matrices arc quite complex. The most successful methods for food samples have involved MS coupled with GC or l.( separa tion methods. 

The use of NIR for process analysis and real-time analysis of complex samples is impressive. Grains such as wheat and com can be measured with no sample preparation for protein content, water content, starch, lipids, and other components. An NIR spectrometer is now commercially available on grain harvesting machines to measure protein, moisture, and oil as the grain is being harvested. The analysis is performed in real-time, as the... 

Near-infrared (NIR), the spectral region between 780 and 3000 nm, is characterized by broad and overlapping spectral peaks produced by the overtones and combinations of infrared vibrational modes. Figure 28.5 shows typical NIR absorption spectra of fat, water, and starch. Exploitation of this spectral region for in vivo analysis has been hindered by the same complexities of nonpulsatile tissue spectroscopy described above and is further confounded by the very broad and indistinct spectral features characteristic of the NIR. Despite these difficulties, NIR spectroscopy has garnered considerable attention, since it may enable the analysis of common analytes. 

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