IV. RESULTS AND DISCUSSION
4.1 PRELIMINARY RESEARCH
Prior to main research, it was necessary to do some adjustment of process conditions. Some steps in this research were done with different methods. In addition, at this stage, it was also
determined drying time for bamboo shoots which were dried at the lowest temperature, i.e. 50 ⁰C.
Bamboo shoots used at this stage, as shown in Figure 9, were purchased in Chiang Mai. They are different with bamboo shoots used in main research, Dendrocalamus membranaceus Munro which
grows in the Doi Tung forest has not been able to be harvested during this stage.
Figure 9. Fresh bamboo shoots purchased in Chiang Mai
There are difficulties to handle bamboo shoots, besides many sheaths of overlapping protect bamboo shoots, it should be noted that they can be stored just for one day at ambient
temperature, thus there were two choices, either they were processed at the same day they were harvested or stored in the refrigerator 1-2
⁰C. Prior to both choices, bamboo shoots needed to peel for reducing their bulkiness and removing dirts on the sheaths. Moreover, there was
adjustment for peeling technique. Bamboo shoots should be peeled well. Thickness of peeled sheaths may influence final products. If they were not peeled well, there still remained sheaths
after drying, as shown in Figure 10. Thus, it needed to improve the peeling technique, due regard to yield obtained. After some experiments, it was obtained a good technique for applying in main
research, i.e. bamboo shoots were partially slashed from the bottom to the top of shoots and then the remaining sheaths were peeled in a counterclockwise motion into conical shape. Bamboo
shoots that were not directly processed, just peeled the outer sheaths and then packed in plastic bags before storing in the refrigerator.
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Figure 10. Peeled bamboo shoots left and dried bamboo shoots right
After peeling, bamboo shoots were trimmed, washed, drained, cut into same shape and size, and then dried. They were not subjected to any pretreatments in order to obtain an expected drying
time of untreated bamboo shoots. Bamboo shoots were dried until its moisture content got approximately 10 g water 100 g shoots, dry basis. The expected drying time was determined using
both initial and final desired moisture contents and would be further discussed. It was visually observed that making a hole inside bamboo shoots, two opposite holes on the
surface at the bottom, and four fine incisions at the top, allowed heated air flowing inside the bamboo shoots, thus the inside bamboo shoots can be dried well. Color change of bamboo shoots
was also visually observed. Dried bamboo shoots produced at this stage had dark reddish-brown color, as shown in Figure 11. This discoloration may be caused by enzymatic browning reaction
within the shoots during drying. As explained above that the shoots were not subjected to any pretreatments, thus browning-enzymes, peroxidase and polyphenoloxidase, can not be inactivated.
The enzymatic browning occured during drying as drying temperature applied, 50 ⁰C, insufficient to
inactivate the enzymes within the product. Mizobutsi et al. 2010 reported that polyphenoloxidase activity remained active for a period of 120 minutes at 40
⁰C and 50 ⁰C.
Figure 11.
Dried untreated bamboo shoots
4.2 MAIN RESEARCH 4.2.1 Moisture Content and Water Activity
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