27 Rehydrated bamboo shoots produced were shown in Figure 15 and results of color
measurements of rehydrated bamboo shoots were shown in Table 10. Referred to Appendix 22, Appendix 23, and Appendix 24, both concentration of sodium metabisulfite and drying
temperature highly significant affected p0.01 L and a values. The L value of the sample blanched in 1.5 Na
2
S
2
O
5
solution was highly significantly higher p0.01 than the
sample blanched in water without addition of Na
2
S
2
O
5
and blanched in 0.5 Na
2
S
2
O
5
solution, while it was not significantly different p0.05 with the sample blanched in 1.0 Na
2
S
2
O
5
solution. In the other side, the lowest L value was found in sample dried at 70 ⁰C.
Table 10. Mean L, a, b values of rehydrated bamboo shoots
[Na
2
S
2
O
5
aq] used in
blanching L
a b
50 ⁰C
60 ⁰C
70 ⁰C
50 ⁰C
60 ⁰C
70 ⁰C
50 ⁰C
60 ⁰C
70 ⁰C
69.05 ± 4.39
Aa
60.80 ± 14.96
Aa
49.45 ± 1.14
Ba
4.39 ± 2.32
Aa
5.13 ± 2.03
Aa
11.91 ± 1.23
Aa
21.69 ± 2.70
Aa
24.68 ± 8.20
Aa
26.55 ± 4.84
Aa
0.5 71.44 ±
4.58
Aa
69.32 ± 9.92
Aa
53.00 ± 2.16
Ba
2.24 ± 0.92
Ab
5.15 ± 3.39
Ab
7.13 ± 0.20
Ab
22.92 ± 4.37
Aa
27.04 ± 5.32
Aa
22.90 ± 2.49
Aa
1.0 74.81 ±
5.98
Ab
74.38 ± 2.15
Ab
73.11 ± 9.41
Bb
1.92 ± 0.52
Ab
1.76 ± 0.36
Ab
7.10 ± 1.24
Ab
22.75 ± 4.89
Aa
27.54 ± 6.10
Aa
29.82 ± 1.20
Aa
1.5 79.81 ±
2.73
Ab
76.08 ± 4.39
Ab
78.21 ± 5.92
Bb
1.45 ± 0.75
Ac
1.78 ± 0.60
Ac
1.09 ± 0.73
Ac
28.98 ± 6.84
Aa
26.55 ± 6.22
Aa
30.31 ± 3.57
Aa
Values in the same row having the same letters A, B for each parameter were not significantly different p0.05. Values in the same column having the same letters a, b, c for each parameter were not significantly different
p0.05.
In contrast to result of L value, the sample blanched in 1.5 Na
2
S
2
O
5
solution had
the lowest p0.01 a value, while the highest L value was found in sample dried at 70 ⁰C.
A different tendency was found on b value of rehydrated sample. It was not significantly
affected p0.05 by both factors, the concentration of sodium metabisulfite and the drying temperature. Generally, rehydrated bamboo shoots had higher L value, lower a value, and
higher b value when compared with the dried one.
a b
c
Figure 15. Rehydrated bamboo shoots left-right: blanched in 0, 0.5, 1.0, 1.5 of
Na
2
S
2
O
5
solution; a dried at 50 ⁰C, b dried at 60 ⁰C, and c dried at 70 ⁰C
4.2.4 Rehydration Ratio
Dried bamboo shoots must be rehydrated for their final use. Rehydration is a complex process including physical and chemical changes due to pretreatment and drying which plays
a major role on quality of dried products. It is defined as a process performed in order to obtain an adequate reconstitution of raw material properties when dried products contact with
water. The cell wall of dried product absorbed water, softened, and returned to their original
28 shape, due to natural elasticity of the cellular structure, by placing dried product into the
water. There are some factors influenced the rehydration ability, i.e. chemical composition of product, pretreatments, drying techniques and conditions, composition and temperature of
rehydration medium Taiwo et al. 2002; Singh et al. 2006. Results of rehydration ratio of dried bamboo shoots were shown in Figure 16. The
rehydration ratio ranged from 2.6298 to 4.3105. Referred to Appendix 26, both factors, the concentration af sodium metabisulfite and the drying temperature, highly significant affected
p0.01 rehydration ratio of dried bamboo shoots, while interaction between both factors had no significant effect p0.05 on this parameters. The sample dried at 70
⁰C had the lowest p0.01 rehydration ratio when compared with the other temperatures, while there
was no significantly different p0.05 between the samples dried at 50 ⁰C and 60 ⁰C. It
could be inferred that bamboo shoots dried at 70 ⁰C for about 20 hours may cause irreversible
structural damages in the tissue and collapse of tissue capillaries, resulting in loss of channel for water uptake during rehydration. A rigid surface may also contribute in loss of
rehydration ratio. A similar observation was reported by Nimmol et al. 2007. These authors
observed that banana slices dried at lower temperatures 60 ⁰C
and 70 ⁰C had higher
rehydration ratio. It agreed with an observation done by Wickramarachchi and
Ranamukhaarachchi 2005. These authors reported that there was a reduction of rehydration
ratio with increase in temperature in banana blossoms.
Figure 16. Mean rehydration ratio of dried bamboo shoots
Blanching sample in 1.5 Na
2
S
2
O
5
solution produced higher rehydration ratio when compared with sample blanched in water and 0.5 Na
2
S
2
O
5
solution, while the sample blanched in 1.5 Na
2
S
2
O
5
was not significantly different P0.05 with the sample blanched in 1.0 Na
2
S
2
O
5
solution. It can be explained that starch does not gelatinize completely even at 100
⁰C, thus when materials containing starch are boiled, the starch granules at or near the surface gelatinize easily, but those in the interior of materials may not gelatinized. Moreover,
the addition of sodium metabisulfite may retard starch gelatinization within the materials during blanching, which kept water binding capacity during rehydration. Agustinah 2011
reported that soaking corn grits in sodium metabisulfite solution caused gelatinization
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
