The use of principal component analysis and self-organizing map to monitor inhibition of calcium oxalate crystal growth by Orthosiphon stamineus extract

The modified Schneider's gel slide method is used to monitor the inhibitory effect of 50% methanol extract of Orthosiphon stamineus on the growth of calcium oxalate crystals. The images of crystals grown in the gel were captured at 1, 2, 3, 4 and 24 h with digital camera and image analysis was carried out. A total of nine variables relating to size and shape parameters were calculated and six were used for further analysis. Principal component analysis (PCA) and self-organizing map (SOM) were applied in the visualization of the size and shape distribution of the produced crystals using the following six variables: area, convex area, aspect ratio, equivalent diameter, roundness and full ratio. The results indicate that the modified gel slide method with the use of PCA and SOM to reduce the dimensionality of the data allowed an intuitive presentation of the differences in the studied inhibitors. The decrease in crystal growth for the extract and positive control of sodium citrate was clearly evident in the principal component scores and also on the location in the SOM. Evidence about the decrease in growth was also provided by an inhibition index of 0.290 for the extract and 0.255 for the positive control.