Analysis of Protein and Total Usable Nitrogen in Beer and Wine Using a Microwell Ninhydrin Assay

Abstract

In this study we present a ninhydrin based microwell assay that can be utilized in place of the traditional Kjeldahl method for the determination of the protein content of beer or wine. In addition, the assay is ideal for the determination of free amino acids in beer (FAN), a term understood and used by brewers, and yeast assimilable nitrogen (YAN) used by enologists. The assay only measures alpha amino acids and ammonia so other nitrogen sources are not detected, resulting in a 30% reduction in total protein of a variety of beers compared to the Kjeldahl method, which measures nitrogen from all sources. The results also showed that only 25% of the total "protein" in beer is actually derived from peptides larger than 3,500 Kd. Analysis of beer or wine with the microwell assay for total usable nitrogen was compared to the standard FAN and YAN methods and conditions were determined for maximal efficiency and precision. Superior results were obtained with low reaction volumes and a stable sodium acetate buffered ninhydrin reagent at pH 5.5. As an alternative, for use with cuvettes, a reduced volume FAN assay using the same pH 5.5 sodium acetate buffered ninhydrin reagent gave comparable results. The assay is economical, rapid, accurate and applicable to large numbers of samples.

Comparison of the Nutrient and Chemical Contents of Traditional Korean Chungtaejeon and Green Teas

“…It was found considerable variability in both total phenols (80.5-134.9 mg/g DW in black teas and 87-106.2 mg/g DW in green teas) and catechins (5.6-47.5, 51.5-84.3, and 8.5-13.9 mg/g DW in black, green, and fruit teas, respectively). These data [13,16] were comparable with our results. The contents of catechins were 11 and 16 mg/g DW in CTJ and GT, respectively.…”

“…Total amino acids were analyzed using ninhydrin assay [16] spectrophotometrically (Spectrophotometer Hewlett Packard, Model 8452A, Rockville, USA). Free amino acids were simultaneously separated in a HPLC system, using mobile phases of lithium citrate buffer with different pHs.…”

Quantification of the Maillard reaction product 6-(2-formyl-1-pyrrolyl)-l-norleucine (formyline) in food

“…Of the total beer nitrogen, 16-24 % was retained in the dialysis tubing. It is known from the literature that more than 75 % of ''protein'' in beer measured by the Kjeldahl method actually represents free amino acids and peptides which are lost during dialysis [34]. However, at least after worting, lysine residues are enriched in the high-molecular barley proteins, while the lowmolecular peptide fraction resulting mainly from hordein and glutelin hydrolysis is depleted in lysine [35], so that the concentrations of formyline and pyrraline in beer can roughly be estimated from the analysis of the retentate.…”

Extension the Shelf-Life of Fresh Golden Rainbow Trout via Ultra-Fast Air or Cryogenic Carbon Dioxide Super Chilling

“…Calibration curves were constructing by plotting values of peak height at 521.5 nm were measured using twin ray spectrophotometer UV-VIS Camspec, model M550 (Camspec Ltd, Sawston, Cambridge, United Kingdom), as they are printed on the instrumental chart in arbitrary units, versus known concentration of MDA in the final reaction mixtures. MDA in samples was calculated using formula: Free α-amino nitrogen: Firstly, an extraction of soluble proteins was made with help of buffer pH 7.3 homogenized with 2.5 g of meat and left for one night in refrigerator further developed by Abernathy [29]. The extract was diluted 20 times.…”