Alpha-Acid Unit

The amount of bitterness that a hop will add to a beer is a function of its alpha acid content, which is often listed as a percentage on the package label. Different homebrewers use different methods of gauging the expected bitterness of the beer. The method that we use is the alpha acid unit (AAU), which is described in Charlie Papazian s book, The Complete Joy of Homebrewing. One AAU is equal to one percent alpha acid per ounce. On this scale, an ounce of hops with 5% alpha content is said to contribute 5 AAUs of bitterness. A recipe that lists hop additions in AAUs is better than one that lists hop additions in ounces because it makes it easier for the brewer to substitute hop varieties. For example, if a recipe calls for 7 AAUs of a hop such as Clusters, the brewer can easily add a bit more of a lower alpha content hop or a bit less of a higher alpha content hop. 

Figure 10.12 Schematic representation of alpha helix. Hydrogen bonds (dotted) connect carbonyl oxygens (red) to amino nitrogens (blue) four amino-acid units down the chain.

The polyuronides are polysaccharides that yield uronic acid on hydrolysis. The most important of these are the pectins. Pectins are found in most plants, particularly fruits. They are extracted in commercial quantities and used to make jellies and to alter the consistencies of foodstuffs. Citrus pectin is mainly a partially methylated polygalacturonic acid, where the alpha—1,4-galacturonic acid units are present. Other pectins are arabans (polyarabinose) and galactans (polygalactose). 

As a quantitative criterion for the degree of bitterness the European Bitterness Unit (EBU) is accepted by the European Brewery Convention (90-93). These EBU values are obtained by measuring the absorbance of a beer iso-octane extract at 275 nm, the absorption maximum of the iso-alpha acids. In practice this value is determined as follows 10 ml degassed beer is acidified with 1 ml HCI 3 N and extracted with 20 ml iso-octane. Subsequently, the absorbance of the extract is measured at 275 nm in a quartz tube of 10 mm length the bitter degree according to the EBC norms is found by application of the formula ... 

Fluorinated ether-containing dicarboxyhc acids have been prepared by direct fluorination of the corresponding hydrocarbon (17), photooxidation of tetrafluoroethylene, or by fluoride ion-cataly2ed reaction of a diacid fluoride such as oxalyl or tetrafluorosuccinyl fluorides with hexafluoropropylene oxide (46,47). Equation 8 shows the reaction of oxalyl fluoride with HEPO. A difunctional ether-containing acid fluoride derived from HEPO contains regular repeat units of perfluoroisopropoxy group and is terminated by two alpha-branched carboxylates. 

Specialty sulfonic acid-based surfactants make up a rather large portion of surfactant production in the United States. Approximately 136,000 metric tons of specialty sulfonic acid-based surfactants were produced in 1992, which included alpha-olefin sulfonates, sulfobetaines, sulfosuccinates, and alkyl diphenyl ether disulfonates (64). These materials found use in the areas of household cleaning products, cosmetics (qv), toiletries, emulsion polymerization, and agricultural chemical manufacture. 

Figure 1.1 The amino acid sequence of a protein s polypeptide chain is called Its primary structure. Different regions of the sequence form local regular secondary structures, such as alpha (a) helices or beta (P) strands. The tertiary structure is formed by packing such structural elements into one or several compact globular units called domains. The final protein may contain several polypeptide chains arranged in a quaternary structure. By formation of such tertiary and quaternary structure amino acids far apart In the sequence are brought close together in three dimensions to form a functional region, an active site.

Fig. 5.12 (a) Synaptic types along dendritic spines of M/T and GC units uni-, and bi-directional junctions, (b) Transmitter systems at a reciprocal synapse, Mitral-Granule cell junction. [Glu, glutamate (R, receptor) GABA, y-aminobutyric acid (R, receptor) E, intracellular effector and aAR, alpha-adrenergic receptor.]. (From Hayashi et al., 1993.)... 

Amino acids, as the name suggests, contain two fundamental units an amino group, —NH2, and a carboxylic acid group, —COOH. For those amino acids that occur in proteins, the amino and carboxylic acid groups are attached to the same carbon atom. This carbon atom is termed the a (alpha) carbon atom. These amino acids are, reasonably, called a-amino acids. 

The more stable carbohydrate constituent of wood is assumed to be almost pure alpha cellulose. This is shown by the fact that 94-96% of the reducing materials, obtained in the later stages of hydrolysis, is fermentable. High temperatures and longer periods of time are required for the hydrolysis of the stable cellulose when dilute acid is used. If strong acid (72% sulfuric, 45% hydrochloric, 85% phosphoric) is used, the cellulose dissolves and then is converted into smaller units. Both of these procedures have been studied by many experimenters. 

The FDA defines maltodextrin (C5Hi2O5)n 0 (CAS. Reg. No. 9050-36-6) as nonsweet, nutritive saccharide polymers that consist of D-glucose units linked primarily by alpha-1-4 bonds and that have dextrose equivalence (DE) less than 20. They are prepared as white powders or concentrated solutions by partial hydrolysis of corn starch with safe and suitable acids and/or enzymes (48FR51911, Nov. 15, 1983). 

Manthey, F.A., Lee, R.E., and Hall, C.A., III 2002a. Stability of alpha-linolenic acid in macaroni containing ground flaxseed. In Proceedings of the 59th Flax Institute of the United States , pp. 14—20. Fargo, ND. 

In further work, Strepkov obtained99 labiose in crystalline form, of m.p. 126-8°, [c ]d + 136.7° (in water, air-dry basis). Labiose is completely hydrolyzed by invertase at 47-8° in 20 hours, and by 1% hydrochloric acid at 68-70° in 10 to 12 minutes, to give one molecular proportion of D-galactose and two molecular proportions of D-fructose. Labiose is not hydrolyzed by almond emulsin, and it is fermented but little by pressed yeast. Strepkov concluded that labiose is related to the alpha series ( ) and that, probably, the D-galactose unit is in the center of the molecule. 

From a structural viewpoint, a polypeptide is composed of planar peptide units as shown in Figure 2.8. The usefulness of considering the peptide unit as opposed to the amino acid is that the peptide unit is almost planar as opposed to the amino acid, which has atoms that are in more than one plane. To illustrate this point, the coordinates of atoms in the peptide unit are given in Table 2.2 and nonbonded atoms cannot be closer than the sum of the minimum atomic distances (Table 2.3). Note that all the atoms from the first alpha carbon (Ca) to the second alpha carbon do not have a z-coordinate. These coordinates come from X-ray diffraction studies on proteins and represent the average coordinates found among many pro-... 

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