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Table 1 Formulas for blank-correction of raw absorbance data

From: Screening natural product extracts for potential enzyme inhibitors: protocols, and the standardisation of the usage of blanks in α-amylase, α-glucosidase and lipase assays

Method

Formula for blank-correction

α-glucosidase assay

α-amylase and lipase assays

1

\({\text{A}}_{\text{test}} - {\text{A}}_{\text{buffer blank}}\)

\({\text{F}}_{\text{test}} - {\text{F}}_{\text{buffer blank}}\)

2

\({\text{A}}_{\text{test}} - {\text{A}}_{\text{substrate blank}}\)

\({\text{F}}_{\text{test}} - {\text{F}}_{\text{substrate blank}}\)

3

\({\text{A}}_{\text{test}} - {\text{A}}_{\text{sample blank}}\)

\({\text{F}}_{\text{test}} - {\text{F}}_{\text{sample blank}}\)

4

\({\text{A}}_{\text{test}} - ( {\text{A}}_{\text{buffer blank}} {\text{ + A}}_{\text{sample blank}} )\)

\({\text{F}}_{\text{test}} - ( {\text{F}}_{\text{buffer blank}} {\text{ + F}}_{\text{sample blank}} )\)

5

\({\text{A}}_{\text{test}} - ( {\text{A}}_{\text{substrate blank}} {\text{ + A}}_{\text{sample blank}} )\)

\({\text{F}}_{\text{test}} - ( {\text{F}}_{\text{substrate blank}} {\text{ + F}}_{\text{sample blank}} )\)

6

\({\text{A}}_{\text{test}} - [\left( {{\text{A}}_{\text{substrate blank}} - {\text{A}}_{\text{buffer blank}} } \right){\text{ + A}}_{\text{sample blank}} ]\)

\({\text{F}}_{\text{test}} - [\left( {{\text{F}}_{\text{substrate blank}} - {\text{F}}_{\text{buffer blank}} } \right){\text{ + F}}_{\text{sample blank}} ]\)

  1. A and F refers to absorbance and fluorescence respectively
  2. Atest = the absorbance of treatment wells (enzyme + substrate + plant extract), positive control wells (enzyme + substrate + positive control acarbose) and negative control wells (enzyme + substrate + vehicle)
  3. Abuffer blank = the absorbance of the buffer-only blank used to determine the absorbance due only to the buffer
  4. Asubstrate blank = the absorbance of the substrate blank (substrate + buffer)
  5. Asample blank = the absorbance of the sample blank, positive control blank, or negative control blank
  6. Ftest = the fluorescence of treatment wells (enzyme + substrate + plant extract), positive control wells (enzyme + substrate + positive control acarbose) and negative control wells (enzyme + substrate + vehicle)
  7. Fbuffer blank = the fluorescence of the buffer-only blank used to determine the absorbance due only to the buffer
  8. Fsubstrate blank = the fluorescence of the substrate blank (substrate + buffer)
  9. Fsample blank = the fluorescence of the sample blank, positive control blank, or negative control blank (Please see note below)
  10. Note on sample blanks: In this study, each “test sample” (i.e. extracts, positive control (acarbose or orlistat), and negative control (vehicle) were given their own sample blank. The sample blank for the positive control, which may also be referred to as the “positive control blank” contained buffer + positive control. The sample blank for the negative control, which may also be referred to as the “negative control blank” contained buffer + negative control (vehicle). In methods 3–6, the positive and negative controls were blank-corrected using their respective positive control “sample” blank and negative control “sample” blank