29 temperature increased. Vega-Gàlvez et al. 2008 also found that immersing the sample in
sodium metabisulfite solution and decreasing the drying temperature could be alleviated the damages to cellular structure in red bell pepper. Moreover, this result agreed with an
observation done by Muchtadi and Adawiyah 1996. These authors observed that blanched bamboo shoots had higher rehydration ratio than unblanched one, while the highest
rehydration ratio was found in the sample blanched in sodium metabisulfite solution.
4.2.5 Dimensional Changes Shrinkage
Drying leads to volumetric changes upon water loss which are expressed as shrinkage. Shrinkage is defined as a relative or reduced dimensional change of volume, area, or
thickness. It has a negative impact on quality of dried products. Change in shape, in some cases, is a negative impression in some consumers. If the extension of shrinkage during
drying can be controlled, the quality of dried products may be improved Aguilera 2003; Mayor and Sereno 2004.
Change in the volume shrinkage of bamboo shoots was shown in Table 11. Generally, a quite high change in volume occured during drying due to high initial moisture
content of bamboo shoots. Shrinkage increases with the volume of water removed. The more water contained in the food, the more moisture gradient within the food, resulting in the more
hidro-stresses occured in the food. The highest shrinkage, 72.10 ± 7.21,
was found in the sample blanched in 0.5 Na
2
S
2
O
5
solution and then dried at 50
⁰C and the lowest shrinkage, 65.55 ± 9.13,
was found in the sample blanched in 1.5
Na
2
S
2
O
5
solution and then dried at
50 ⁰C. While
there was no significantly difference p0.05 among the samples on the shrinkage. The results also showed that both factors, the concentration of sodium
metabisulfite and the drying temperature, had no significant effect p0.05 on the shrinkage of bamboo shoots, referred to Appendix 28.
Table 11. Mean shrinkage of bamboo shoots
Changes in volume of bamboo shoots dried at 50 ⁰C were slightly higher p0.05
than in bamboo shoots dried at 60 ⁰C and 70 ⁰C. A similar observation was reported by
Hofsetz et al. 2008, sliced banana dried at 150 ⁰C for 12 minutes had less shrinkage when
compared with sliced banana dried at 70 ⁰C for 5 hours. Pimpaporn et al. 2007 also
investigated that more extensive shrinkage was found on the potato chips dried at lower temperature, 70
⁰C, than the potato chips dried at 80 ⁰C and 90 ⁰C. Shrinkage occurs first on the surface of material and gradually moves inward with
drying time. At high temperature, the moisture content on the surface became lower. It might induce a rubbery to glass transition and resulted the rigid outer layers, thus their final volume
was fixed early and did not change with further water loss during final stages of drying process Wang and Brennan 1995; Maskan 2001; Mayor and Sereno 2004. At lower
[Na
2
S
2
O
5
aq] used in blanching
Mean shrinkage 50
⁰C 60
⁰C 70
⁰C 71.94 ± 5.94
69.55 ± 1.24 66.00 ± 2.90
0.5 72.10 ± 7.21
68.69 ± 5.83 66.48 ± 2.25
1.0 65.55 ± 11.22
67.42 ± 5.38 68.85 ± 3.51
1.5 65.55 ± 9.13
68.28 ± 9.83 68.76 ± 0.93
30 temperature, the material took more time to be dried, therefore, contractile stresses occured in
the cellular become longer which may intensify the changes in volume. Nassiri and Heydari 2012 also stated that more shrinkage has been occured at lower temperature.
4.2.6 Texture of Dried and Rehydrated Bamboo Shoots
