Hydrolysis time

Residual aromatic ether concentrations are determined from the absorbance at 278 mfi of the crude reduction products in methanol solution. Steroidal ether concentrations of 1 mg/ml are employed. The content of 1,4-dihydro compound is determined, when possible, by hydrolysis to the a, -unsaturated ketone followed by ultraviolet analysis. A solution of the crude reaction product (usually 0.01 mg/ml cone) in methanol containing about 1/15 its volume of water and concentrated hydrochloric acid respectively is kept at room temperature for 2 to 4 hr. The absorbance at ca. 240 mfi is measured and, from this, the content of 1,4-dihydro compound can be calculated. Longer hydrolysis times do not increase the absorbance at 240 mp.. 

The next stage is neutralization of the alkenesulfonic acids with NaOH yielding water-soluble sodium alkenesulfonates, and hydrolysis of the sultones leading to sodium 3-hydroxyalkanesulfonates and sodium 4-hydroxyalkanesulfon-ates. The proportion of the latter two compounds in the mixture will depend on the conditions employed in the aging step. A hydrolysis temperature of 150-160°C and a hydrolysis time of 40-45 min ensures virtually complete hydrolysis of sultones 1,3-sultones will be present in ppb quantities and 1,4-sultones in ppm quantities. 

A general feature of optimum sample preparation is that maximum recovery of the analyte is observed. Consider a graph of recovery vs. variation in one experimental condition. Figure 5 shows such a graph, with temperature as the experimental variable. The curve exhibits a maximum and a decline on either side of the maximum. The assay will be most reproducible at the point of zero slope, i.e., at the maximum recovery, because small variations in conditions will not affect the result. In hydrolysis of a protein to its constituent amino acids, for example, it will be found that at very high temperatures or long hydrolysis times, degradation of the product amino acids occurs, while at low temperatures or short hydrolysis times, the protein... 

Albin, D. M., Wubben, J. E., and Gabert, V. M., Effect of hydrolysis time on the determination of amino acids in samples of soybean products with ion-exchange chromatography or precolumn derivatization with phenyl isothiocyanate,. Agr. Food Chem., 48, 1684, 2000. 

A more recent, extended study of purine synthesis via polymerisation of ammonium cyanide, described at the beginning of this section, showed that the yield of adenine from the non-hydrolyzed solution was only slightly temperature dependent. Shorter hydrolysis times for the insoluble polymerisation products led to higher adenine yields. When the solution is hydrolyzed at pH 8, the adenine yield is comparable to the value of 0.1% found for acidic hydrolysis (a model for the primeval ocean ). Increasing the hydrolysis time has no effect on the adenine yield because of its greater stability at pH 8. Hydrolysis of the black NH4CN polymer under acidic or neutral conditions results in an adenine yield of about 0.05% (Borquez et al., 2005). 

In real process not all of the accessible -OR groups have to hydrolyze to the -OH form. In fact, the longer the hydrolysis, the larger amount of the Si-OR groups undergoes hydrolysis to the Si-OH form. Thus, the three-dimensional extent of the silicate network is a direct result of the hydrolysis time. 

Figure 5. Contact angle 6 of phenylurethanated Visking film as a function of hydrolysis time (O) receding (9) advancing (-------) unreacted film...

The results of multi stage enzyme treatment suggests that further study of cellulase action is fully warranted. One hopeful area would be to decrease the hydrolysis time and enzyme concentration, and increase the number of stages. Another approach would be to remove the sugars by some other means, such as dialysis or fermentation (20). 

Hydrolysis Experiments. The substrate in the hydrolysis experiments included alkali-extracted beechwood 4-O-methylglucuronoxylan, DMSO-extracted acetylated beechwood 4-O-methylglucuronoxylan, alkali-extracted wheat straw arabinoxylan and acetylated or deacetylated xylo-oligomers from steaming of birchwood (24). Deacetylation was carried out by incubating the freeze-dried xylo-oligomers in ammonia vapor overnight. Substrate concentration was 10 gl— 1, temperature 45° and hydrolysis time 24... 

Table II. The effect of a-arabinosidase on the hydrolysis of wheat straw arabinoxylan. Substrate concentration 10 gl-1, initial pH 4, temperature 45° C, hydrolysis time 24 h...

Type of wood product Hydrolysis time, hrs. Yield of sugar, % Sugar concentration, %... 

The introduction of microwave radiation energy (in specially designed pressurized instruments) for hydrolysis of protein samples allowed a reduction of the overall hydrolysis time from many hours to a few minutes [205-209]. Joergensen and Thestrup [210] hydrolyzed food proteins containing carbohydrates, lipids, nucleic acids, and minerals, with HCl in a microwave oven at 150°C for 10-30 min, obtaining results similar to those of conventional hydrolysis. 

Figure 7. Emulsifying activity (expressed as volume percentage of the emulsified layer) of pepsin hydrolysates of soy protein as a function of pH and hydrolysis time. No hydrolysis (A) 2 h ( ) 8 h (X) 17 h ( ) 24h(O) (39).

Suggested changes would be to increase the percentage of solution A at the beginning if retention times are excessively long or decrease it at 20 min if there is incomplete resolution. It is not unusual to have minor amounts of unhydrolyzed anthocyanins glycosides in the sample. If amounts are excessive, increase the hydrolysis time or decrease the amount of sample subjected to hydrolysis. 

Amino acid Grams of amino acid residues per 100 g of protein4 in hydrolysis time of Moles of amino acid/ mole of protein MW 38,000 Nearest integral No. of residues/ mole of protein 1... 

There have been many studies for the optimization of conditions for the standard acid hydrolysis, but only a few of the more recent examples (24,27-29) are referenced here. These studies address the influence of various hydrolysis parameters on the accuracy of amino acid recoveries. Topics include acid-to-protein ratio, hydrolysis time, hydrolysis temperature, and the use of sealed tubes vs. open reflux. There is also evidence of a wide variety of techniques for the deaeration (very important ) of the sample, including vacuum, nitrogen purging, freeze/thawing, and combinations thereof. All of these issues have already been thoroughly reviewed in earlier... 

AM Rowan, PJ Moughan, MN Wilson. Effect of hydrolysis time on the determination of the amino acid composition of diet, ileal digesta, and feces samples and on the determination of dietary amino acid digestibility coefficients. J Agric Food Chem 40 981-985, 1992. 

M Rudemo, S Bech-Andersen, VC Mason. Hydrolysate preparation for amino acid determinations in feed constituents. 5. The influence of hydrolysis time on amino acid recovery. Z Tierphysiol Tierernaehr Futtermittelkd 43 27-34, 1980. 

B Lucas, A Sotelo. Effect of different alkalies, temperature, and hydrolysis times on tryptophan determination of pure proteins and foods. Anal Biochem 109 192-197, 1980. 

Figure 5. 2H-NMR spectra of DABES adsorbed on silica from a 2% solution in a 10 1 acetone-water mixture for hydrolysis times of (A) 1.75 h, (B) 3 h, and (C) 1 day. The full-width at half-heighi of each is given in the Figure.

Some of the fibers in each batch were aged in humid air, in deionized (DI) water, or in silane solution. All of the aging was carried out at 35°C for 30 days. A commercial (Blue-M) controlled atmosphere chamber held the relative humidity (RH) at 70% and the temperature at 34°C. The silane solutions were prepared by adding the requisite amount (1% by volume) of unhydrolyzed y-APS (A-1100 Union Carbide) to triply distilled water or to acetic acid solution. A hydrolysis time of approximately 8 h was allowed prior to adding fibers to the solution. This yielded solutions at pH 10 and pH 4, respectively. The fibers were suspended in Nalgene containers, where the glass surface area-to-solution volume ratio was fixed at 50 cm1. In all cases, the fibers were dried in air at 75°C and the solutions were analyzed for their Si, Al, Ca, and B contents. Table 1 presents the results of these solution analyses. 

The reaction product solidifies if it is allowed to stand too long in the reaction flask, thus causing difficulty with the hydrolysis. Time will be saved if the acid is added immediately after the addition of the carbon dioxide is completed. A rather concentrated acid solution is used in order to keep the volume of the water layer as small as possible. 

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