Solvent extractions and spectrophotometric protocols for measuring the total anthocyanin, phenols and antioxidant content in plums

Total monomeric anthocyanins from six commercial plum varieties were extracted using two protocols, viz methanol/water extraction through end-over-end shaking and ethanol/water extraction in a shaking water bath; adapted from the Australian Wine Research Institute (AWRI) standard method. Anthocyanins were determined using the Association of Official Analytical Chemists (AOAC) standard protocol and a modification of the AWRI method. The mean relative standard deviation was found to be similar between methods, at 13.5% and 9.9%, respectively. On average, the anthocyanin concentrations given by the AWRI method were 27% higher than those obtained using the AOAC standard method. This was attributed to the AWRI method not correcting for haze or matrix interference, but estimating the anthocyanin concentration from the absorbance at a single wavelength. Anthocyanin measurements on the two extractions using the same measurement protocol supported this, indicating that the methanolic extracts gave a higher anthocyanin yield than the ethanolic extracts. Furthermore, HPLC profiling of the anthocyanin content demonstrated significantly more anthocyanins were extracted through the methanol extraction protocol. The methanol/water extraction protocol and AOAC standard method are much simpler to perform than the AWRI method and appear to be at least as precise. Thus this extraction and spectrophotometric protocol is well suited to future work on plum matrices. The extraction method is also more suitable for the subsequent photometric and/or HPLC determination of phenolic and total antioxidant contents.