ASBC

Beer Samples. The beer samples were examined as part of the American Society of Brewing Chemists (ASBC) and Association of Official Analytical Chemists (AOAC) collaborative studies of NDMA in beer. Duplicate samples were analyzed by the column extraction procedure and the ASBC distillation procedure (35). The AOAC procedure (36) was similar, except that a larger sample (50 vs. 25 g) was examined and sulfamic acid was added to minimize artifactual formation of nitrosamines. Both methods utilize N-nitrosodipropylamine (NDPA) as an internal standard. 

For the AOAC beer samples, a 2 m x 2 mm glass column packed with 8.57o Carbowax 20 M + 0.857, NaOH on 100/120 mesh Chromosorb G was used at 130 C and a helium flow rate of 20 cc/min. Retention times of NDMA and NDPA were 4.5 and 12.2 min, respectively. For the ASBC collaborative study, a 1 m x 2 mm glass column containing 67, Carbowax 20 M-TPA on 100/120 mesh Chromosorb G was operated at 90 C with 20 cc/min helium flow rate. Retention times were 3.6 and 11.3 min for NDMA and NDPA, respectively. For determination of nitrosamines in amines, a 2 m X 2 mm, 107, Carbowax 20 M-TPA on 100/120 mesh Chromosorb G column was operated at 190 C with a carrier gas flow rate of 20 cc/min. Retention times were NPYR, 6.6 min NMOR, 7.4 min. 

Column Extraction. Results obtained by the standard ASBC distillation procedure and by Celite column extraction are compared in Table III. The ASBC method included... 

Table III, NDMA Concentrations Beer, Using ASBC Method and Celite Column Extraction...

Institute of Brewing American Society of Brewing Chemists (ASBC) European Brewery Convention... 

Scope a- and / - Acids in extracts and solutions a- and /3-Acids in hops, hop powders and conventional extracts Same as ASBC... 

Standardization p-nitroanilide of myri stic acid Calibration hop extract Same as ASBC... 

ASBC Methods. Hops 14. a-Acids and /3-acids in hops and hop extracts by HPLC (International... 

ASBC Methods Hops 15. Iso-a-acids in isomerized hop pellets by HPLC. 

Most of the latest publications on NRPS substrate specificity are focused on A domain specificity because their substrate screening is straightforward in terms of biosynthetic substrate form (free amino acids/fatty acids/aryl acids) and T domain substrates (one T domain). Four studies focus on substrate specificity of NRPS loading modules of microcystin biosynthesis,97 mycosubtilin biosynthesis,51 daptomycin biosynthesis,108 and leinamycin biosynthesis.108 The A domains of microcystin, mycosubtilin, and daptomycin biosynthesis initiation showed fatty acid specificity. The initial domain from leinamycin biosynthesis has D-amino acid specificity. Another paper presents the elucidation of aryl acid-specific AsbC adenylation enzyme from petrobactin biosynthesis.104... 

Figure 18 Adenylation enzyme AsbC from petrobactin biosynthesis has aryl acid specificity, (a) Petrobactin. (b) AsbC enzymology. AsbC adenylates native substrate 3,4-DHBA and tethers it to thiolation domain AsbD. (c) AsbC substrate tolerance characterized by LC-IT-MS (observed and calculated mass shifts of AsbD).

Because heat is transferred reversibly to B and C, equation (6.19) can be substituted for ASbc I... 

ASBC. 1992. American Society of Brewing Chemists, Inc. Zinc in wort and beer by graphite furnace atomic absorption spectroscopy. Journal of the American Society of Brewing Chemists 50(4) 158-159. 

ASBC Am. Society of Brewing Chemists CFR Code of Eederal Regulations (U.S.)... 

The ASBC [108] retain the second method of Ribgy and Bethune [110] as it provides a more accurate estimate of the iso-a-acids in beer. In this... 

The major ions are the cations potassium, sodium, magnesium and calcium with the anions chloride, sulphate, nitrate and phosphate. The level of toxic metals may be limited by law. In Britain the level of arsenic (1959) and lead (1979) may not exceed 0-2 mg/kg (ppm) and the Food Standards Committee have recommended limits of 7-0 ppm for copper and 5 0 ppm for zinc in both wine and beer. The EBC, ASBC and the Institute of Brewing all describe methods for the estimation of iron and copper in beer. In addition the EBC gives methods for calcium, nickel, potassium, sodium and zinc the ASBC for calcium and phosphorous and the Institute of Brewing for arsenic, lead and zinc. 

Both the EBC and the ASBC describe methods for determining the original extracts of beers. The apparent extract ( % w/w) is determined from the specific gravity of the filtered beer. Then 100-0 g of beer is distilled and the alcoholic content (A % w/w) is determined from the specific gravity of the distillate diluted to 100-0 g and the real extract (E r% w/w) is determined from the specific gravity of the residue diluted to 100-0 g. 

The principal higher alcohols found in beer are 3-methylbutanol (isoamyl alcohol), 2-methylbutanol aciive-eonyl alcohol), 2-methylpropanol (isobutyl alcohol), propanol, and phenethyl alcohol (Table 22.9). It is noteworthy that the levels of higher alcohols in home-brewed beer and wines is at least 10 times higher than those in the commercial products [61]. The major volatile constituents of beer are most conveniently examined by gas chromatography either of the beer directly or of the gas in the head space above the beer in bottle. The ASBC recommend direct injection on to a 20% Carbowax 20M column at 80°C. In order to identify and estimate the minor volatile constituents it is usually necessary to prepare a solvent extract of the beer or a distillate. It may be desirable to fractionate the solvent extract by adsorption chromatography before examination by capillary gas chromatography-mass spectrometry [43, 59]. 

Much of the sulphur dioxide present in beer is in a bound form, for example, as the acetaldehyde bisulphite compound. The classical (Monier-Williams) method for the estimation of sulphur dioxide, adopted by the Institute of Brewing, involves the removal of SO2 from acidified beer in a stream of carbon dioxide and nitrogen at 100 C. The gas is absorbed in hydrogen peroxide and the sulphuric acid formed titrated. In Britain sulphur dioxide is a permitted preservative in beers ( > 70 ppm), ciders, and wines ( > 150 ppm) and the Monier-Williams method is official. The EBC-ASBC adopt a more sensitive colorimetric method in which the colour restored to acid-decolourized rosaniline hydrochloride is measured. 

The ASBC describe such a method. Some representative values for British beers are given in Table 22.21 where the results are also expressed in kilojoules (1 kcal = 4 184 kJ). Many brewers of low carbohydrate lite beers declare the calorific value (e.g. 26-29 kcal/100 ml) on the label. Beer is also a source of B vitamins containing (values in ppb for lagers and top fermentation beers) biotin (7-18 11-12), nicotinic acid (4494-8607 7500-7753), pantothenic acid (1093-1535 1375-1808), pyridoxine (329-709 341-546), riboflavin (219-420 331-575), and thiamine (15-58 59-181) [117]. Folic acid and vitamin Bj are also present [10]. 

The ASBC also use a spectrophotometric method and define beer colour as 10 times the absorbance of beer measured in a 12 7 mm (0-5 in.) cell with monochromatic light of wavelength 430 nm. The absorbance at 430 and 700 nm is measured. If the absorbance at 700 nm is equal to or less than 0 039 times the absorbance at 430 nm, the beer is judged free of turbidity and the colour calculated from the reading at 430 nm. Otherwise the sample must be clarified before the colour can be measured. Comparisons of wort colours on EBC and ASBC mashes of the same malts gave the following regression equations ... 

The ASBC describe a modification of the Helm-Carisberg method. 

---