Delayed Light Emission of Green Tea as a Means of Quality Evaluation (1)
Delayed Light Emission of Fresh Tea Leaves
1978 Volume 39 Issue 4 Pages 483-490
Details
1978 Volume 39 Issue 4 Pages 483-490
The DLE characteristics of chlorophyll of green tea leaves were investigated to use as a means of non-destructive and prompt estimation of the quality of the leaves.
By using the xenon flash lamp as an exciting light source, DLE characteristics of the fresh leaves were obtained as follows:
1. The DLE of fresh leaves presented a dark recovery phenomenon. Recovery of DLE intensity, under the decay periods of 1.0 and 2.0 seconds, was noticed after the dark period of 10 minutes (Fig. 3). The DLE intensity was independent of preillumination period (Fig. 2).
2. The peak of DLE spectrum of green tea leaf shifted toward a wavelength longer than 685nm, due to the self-absorption of the spectrum by chlorophyll (Fig. 4).
Considering this, DLE detector shoud be selected favorably.
3. The DLE of fresh leaves showed light saturation beyond the 1/4 relative exciting light intensity (Fig. 5). Leaf temperature did not affect the level of exciting light intensity needed for the saturation.
4. The leaf temperature has much to do with the DLE intensity of the leaf. The DLE intensity of fresh leaf has a peak at the temperature of 37°C (Fig. 6).
5. Each of ingredient values of leaf color (Hue, Value and Chroma) had a high correlation with DLE intensity of fresh leaf. The DLE intensity of fresh leaf increased with the change of Hue from yellow to green, Value from light to dark color and Chroma from bright to dull color, respectively (Fig. 7).
6. Chlorophyll content of fresh leaf has a linearity with the intensity of DLE. Therefore the quality of tea leaves, so much as the chlorophyll content is used as an index, could be estimated non-destructively and promptly by means of DLE (Fig. 8, Table 2).
Measurement of DLE of back side of a leaf is desirable than that of front side.
7. By using the ratio of (DLE intensity of back side of a leaf)/(DLE intesity of front side of a leaf) as an index of quality of the tea leaves together with the use of xenon flash lamp, the old leaves which remarkably degrade the quality of tea could be separated from young ones.
The mean values of the index were 1 for the young leaves and 1.4 for the old ones (Table 4).
