Non-invasive Observation Methods

A non-invasive observation method is able to monitor the changes during the filtration process and is performed without removing the membrane from its module. This technique can minimize sample destruction, allowing more accurate visualization analysis compared with the invasive observation method previously discussed. 

Secretory cells filled with allelochemicals participate in the allelopathic relations. Their structure may be changed under various external factors that needs special methods for the observations. The application of non-invasive optical techniques to diagnose the physiological state of plants is one of the major problems of plant ecophysiology. 

Durian is one of the most commercially important fresh fruits in S.E. Asia, yet sorting immature from mature fruit by external measures is very difficult, so it is a prime candidate for non-invasive methods. Yantarasri and co-workers have sought correlations between soluble solids and sensory estimates of maturity with X-ray CT and NIRS measurements with moderate success but more recently they observed that MRI spin-echo image contrast at 0.5 T varied with the degree of maturity. Unfortunately no attempt was made to quantify relaxation time changes or separate oil-water peaks. However it was suggested that the contrast differences indicated signihcantly lower oil content in unripe durian compared to the ripe and overripe fruit. 

Dielectric spectroscopy or culture capacitance measurement is used as an on-line, non-invasive method for biomass estimation (see the chapter by Sonnleitner in this issue - the section on electrical properties) and responds mainly to living cells [43,44]. Observed difficulties in using the signal as a pure biomass concentration sensor, i.e. deviations from the simple correlation with cell density, were attributed to dependencies on the physiological state [43], and could be used to discriminate different populations in yeast cultures [45]. Connections with morphological features could be found for budding yeast... 

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