Using a Flatbed Scanner and Automated Digital Image Analysis To Determine the Total Phenolic Content in Beer

Abstract

Here, students determine the total phenolic content in beers using the Folin–Ciocalteu assay. The Folin–Ciocalteu reagent is a yellow complex, in an alkaline medium; it reacts with phenols and non-phenolic reducing substances to form a blue complex. Quantitative analysis was carried out using absorbance measured at 765 nm (standard method) and digital images (proposed method). In the proposed method, samples were placed in a 96 microwell plate; then, a plate image was obtained with a flatbed scanner. The ImageJ plugin ReadPlate extracts red (R)-values from all wells of the scanned image at the same time; then, R-values were exported to a spreadsheet that converted these values to absorbances. Using absorbances obtained with R-values, the spreadsheet also provides standard calibration plots, limits of detection (LODs), limits of quantification (LOQs), and beer sample total phenolic contents. The proposed method and the standard method were compared using two-tailed significance tests; students observed that both methods provide equivalent results, that both methods were linear in a 2–10 mg L–1 gallic acid concentration range, and that both methods had close LODs and LOQs, 0.55 and 1.70 gallic acid mg L–1, respectively. Beer sample total phenolic contents were compared using one-tailed significance tests. This laboratory experiment provides an effective instrumental alternative to spectrophotometric methods, which can be especially beneficial, where purchasing and maintaining a spectrophotometer is a challenge, and it also presents to the students one-tailed and two-tailed significant tests.

Quantification of Nitrite in Food and Water Samples Using the Griess Assay and Digital Images Acquired Using a Desktop Scanner

“…Sensitivity is the slope of the calibration curve. − The standard method had a slope 3 times higher than the proposed method (Figure ), which means that the standard method is 3 times more sensitive than the proposed method in accordance with our later works. − …”

“…The DL (eq ) and the QL (eq ) may be calculated using “ s ” as the standard deviation of blank samples or using the standard curve, where “ s ” was the random error in the y -direction ( s y / x ) . We observed that these approaches underestimated DL and QL; thus, we used “ s ” as the standard deviation of the lowest concentration point on the standard curve ( n = 6).…”

“…In the Supporting Information, there is a spreadsheet that organizes the data taken from ReadPlate, convert it into an analytical signal (eq ), plot the standard curves, and calculate the concentration of samples as described in other works of our research group. − …”

“…Variances were compared using F test, and average values were compared using t test. Hypothesis tests were carried out using spreadsheets, as described in our previous papers. , …”

Analysis of Ethanol in Beer Using Gas Chromatography: A Side-by-Side Comparison of Calibration Methods

“…For the laboratory activity described here, beer was chosen as the complex chemical mixture to be analyzed, as most college students are familiar with and/or interested in beer. Indeed, a number of classroom and laboratory activities that focus on beer and brewing have been developed recently. − This experiment focused specifically on the determination of ethanol in a commercial beer sample using gas chromatography. Each class section performed four different methods of calibration (one calibration per group), and students used pooled data to calculate the ethanol concentration in the provided beer sample, for comparison to the labeled concentration and instructor data.…”