Measurement of young coconut ( Cocos nucifera, L.) maturity by sound waves

Abstract

Sounds produced by tapping fresh young coconut fruits of ‘buko’ have been used by farmers/traders in the Philippines to differentiate their maturity levels. Considering the importance of identifying the three stages of ‘buko’ maturity (‘malauhog’ ‘U’; ‘malakanin’ ‘K’ and ‘malakatad’ ‘T’) a scientific basis for measurement of sounds produced by tapping of ‘buko’ was studied. Some physicochemical characteristics of ‘buko’ were analyzed to determine if sound waves could be associated with them. ‘Buko’ was also stored at ambient temperature for 12 days and changes in tapping sounds during this period were followed. Results showed that tapping sounds recorded on tapes (analog) can be converted to digital through the use of the analog-to-digital converter (ADC). Using the Fast Fourier Transformation the spectral magnitude of sound waves was computed and graphically presented in a coordinate system where frequency was the abscissa. The spectral magnitude of ‘U’ was found to be different from those of ‘K’ and ‘T’. The former produced what was described as a ‘solid’ sound while ‘K’ and ‘T’ gave ‘hollow’ sounds. Among the physical characteristics measured, only thickness of coconut meat (fruit endosperm) significantly identified ‘U’ from ‘K’ and ‘K’ from ‘T’. Chemical components of ‘buko’ meat such as crude fat and starch tended to increase with increasing maturity level while moisture content decreased significantly. Neither soluble solids or pH was significantly different between ‘U’, ‘K’ and ‘T’. But on storage, soluble solids decreased after the sixth day. The average of normalized magnitude spectrum for each of the maturity levels was computed to obtain the ‘average power’. There was a tendency for ‘U’ to have the lowest ‘average power’ compared to ‘K’ and ‘T’. For all maturity levels, ‘average power’ tended to rise with increased storage time.