13
3.3.1.2 Adjustment of Drying Procedure
Prior to main research, it was needed some adjustments throughout the process, started from peeling until drying process. Besides, determination of
drying time of unpretreated bamboo shoots was also done in this stage.
3.3.2 Main Research 3.3.2.1 Drying Procedure
Drying experiment was performed using laboratory scale-tray drier Klue Nam Thai, Nicy Co. Ltd. The drier is capable of providing any desired drying
temperature and constant air velocity. Airflow was adjusted by the fan speed control and the air velocity was recorded by hot wire anemometer. Air velocity
used in this study was 1.0
m s
by applying fan speed about 625 rpm 25 out of 60; 60 is equivalent to 1400 rpm. Relative humidity at various locations around the
system was also measured by a thermo hygrometer Digicon DM-760.
Figure 7. Sample preparation
Storing, 0-2 ⁰C
Pre-cooling, 25 ⁰C
Fresh bamboo shoots D. membranaceus Munro
Peeling Washing
Cutting Draining, 15’
Blanching in Na
2
S
2
O
5
aq; 90-100
⁰C; 10’ Drying
Dried bamboo shoots MC 10
14 Experiment was carried out approximately an hour after the drier turned
on to reach its steady state condition. All samples were loaded onto a tray. Each concentration of sodium metabisulfite was presented by five samples. They were
set into four groups, i.e. 0, 0.5, 1.0, and 1.5. Position of each sample and each group was also rotated every 12 hours. Prior to drying, each group was
weighed to same total weight and a sample of each group was taken for initial moisture content determination. Drying was applied until total weight of samples
reduced to a level corresponding to moisture content of about 10 dry basis. The final total weight was obtained by calculation from initial moisture content
and initial total weight of sample. The weight loss was monitored by digital balance with accuracy of 1 g. The drying experiment was conducted at three
drying temperatures of 50 ⁰C, 60 ⁰C, and 70 ⁰C in triplicates for statistical
purpose. After drying was complete, the samples were allowed to condition at
ambient temperature for 30 minutes. The conditioning process was applied to evenly distribute minimal residual moisture throughout all samples. It may
reduce mold spoilage. After conditioning, one of samples were taken to determine its moisture content. It was done to obtain and confirm actual final
moisture content of the dried shoots. Remaining samples were packed in plastics, labeled with name of product, date, concentration of sodium
metabisulfite used, and drying temperature applied. The plastics were sealed tightly and stored in a dry and dark place.
3.3.2.2 Physical, Chemical, and Sensory Analyses 3.3.2.2.1 Determination of Moisture Content AOAC 1995
Moisture content of the sample was determined by drying milled sample ~2 g for 24 hours at 105 ± 0.5
⁰C to a constant mass. Analysis was done in triplicates duplo for each replication for
sample before drying initial moisture content and sample after drying final moisture content. Average moisture content in dry
basis, expressed in percents, was calculated using the following equation:
w =
m
−
m m
× 100
where: m
1
= mass of sample before drying g m
2
= mass of sample after drying g
3.3.2.2.2 Water Activity Measurement
Water activity of dried bamboo shoots was measured using water activity meter Novasina AWC500. Approximately 3 ± 0.01 g
of milled dried sample was placed in a container of a
w
meter and
15 then the a
w
meter was tightly closed. The sample was left in a
w
meter until obtained a constant value of a
w
. The determination was done in triplicates and duplo per each replication.
3.3.2.2.3 Color Measurement Hunter Lab
Color of dried and rehydrated samples were measured using Chromameter Hunter Lab ColorQuest XE. The instrument
Illuminant D65, 10 ⁰ Observer, ASTM E308 was calibrated with
black and white reference tiles through L, a, and b values, taking as standard values of the white background tile L 93.47, a -0.95,
b 0.53. Analysis of color values was done six times duplo for each part: bottom, middle, and top. Three parameters, i.e. L
lightness, a redness, b yellowness, were used to study the color changes. L refers to lightness of the sample and ranges from
black 0 to white 100. Negative value of a indicates green, while the positive one indicates red-purple color. Negative value of b
indicates blue, while the positive one indicates yellow color.
3.3.2.2.4 Determination of Rehydration Ratio Doymaz 2008, modified
A dried sample was weighed using digital balance with accuracy of 0.1 and soaked into distilled water 25-26
⁰C with a 1:100 ratio at room temperature ± 26
⁰C for 12 hours. After rehydration, the sample was taken out and drained for 5 minutes, and
then adhering water was absorbed carefully using tissue paper. After that, the rehydrated sample was weighed. Analysis was done in
triplicates and duplo for each replication. The rehydration ratio RR was calculated as following:
RR = m
m
where: m
R
= mass of rehydrated sample g m
d
= mass of dried sample used for rehydration g
3.3.2.2.5 Determination of Dimensional Changes Shrinkage Dehkordi 2010, modified
Sample height and diameter before and after drying were measured. Both height and diameter were measured using a steel
caliper with accuracy of 0.02 mm. The measurement were carried out at three different areas on each sample. Shrinkage was expressed
as a percentage change in volume of sample. Both dried and
16 rehydrated bamboo shoots were assumed as cones. Dimensional
changes shrinkage was calculated as following:
=
−
× 100
where: V = volume of sample before drying cm
3
V
t
= volume of sample after time t of drying cm
3
3.3.2.2.6 Texture Analysis
Texture analyzer TA.XTPlus, Stable Micro System, UK fitted with a knife blade probe was used. Dried and rehydrated
bamboo shoots were cut into pieces of uniform size and shape 30 mm x 5 mm x 5 mm. Each sample was aligned vertically on the
central of heavy duty platform HDP90. Three measurements were carried out on each sample. TA.XTPlus settings can be seen in the
Table 2.
Table 2. TA.XTPlus settings
Mode Measure Force in compression
Option Return to start
Pre-Test Speed 2.0
mm s
Test Speed 2.0
mm s
Post-Test Speed 10.0
mm s
Distance 5 mm
Trigger Type Auto – 5g
Data Acquisition Rate 200 pps
The analysis was performed in triplicates. Firmness of dried and rehydrated bamboo shoots were automatically computed from
curves using texture analyzer software macro Texture Exponent 32 Stable Micro System.
3.3.2.2.7 Determination of Total Residual Sulfites AOAC 1970; FAO JECFA 2006
Approximately 0.2 g of the milled dried bamboo shoots to the nearest mg, added to 50.0 ml of 0.1 N iodine in a glass-stoppered
flask, and the flask was stoppered. It was allowed to stand for five minutes in the dark, and then 1 ml of hydrochloric acid added. After
that, the excess iodine was titrated with freshly standardized 0.1 N sodium thiosulfate Na
2
S
2
O
3
. Approximately 2-3 ml 0.5 starch indicator solution was added as the end point was approached light-
straw color, and then the titration was continued until the blue color disappeared. Each ml of 0.1 N iodine is equivalent to 3.203 mg of
17 sulfur dioxide. Total residual sulfites, expressed in SO
2
, was calculated as follows:
SO ppm = V
−
V m
× N Na S O × 3.203 mg × 1000
where: V
1
= volume of 0.1 N Na
2
S
2
O
3
to titrate blank ml V
2
= volume of 0.1 N Na
2
S
2
O
3
to titrate sample ml m = mass of milled dried bamboo shoots used g
3.3.2.2.8 Determination of The Best Sample Zaboj 2002; DFPNI 2010, modified
In this study, sample catagorized as the best one was the sample with good color of dried and rehydrated forms high L
value, low a value, and high b value, high rehydration ability, good texture high firmness on dried form and similar firmness on
rehydrated form when compared with the fresh form, and low total residual sulfites.
The best sample was chosen based on arbitrary weighting method. The process of deriving weights and scores was depicted on
Figure 8.
Figure 8. Weighting method to determine the best sample
There were four attributes chosen, i.e. color including L, a, and b values of dried and rehydrated bamboo shoots, rehydration
ratio, dimensional changes shrinkage, and firmness dried and rehydration bamboo shoots. Each attribute had a weighted factor, as
shown in Table 3. The weighted factors were determined with regard to the desired quality of product, as mentioned above.
The largest part of dried products is rehydration. Almost dried products including dried bamboo shoots must be rehydrated before
Identification of attributes Weighting
Scoring
Interpreting Calculating
The best sample
18 final using Jayaraman and Das Gupta 1995; Lewicki 1998; Taiwo
et al. 2002; Krokida and Philippopoulos 2005; Singh et al. 2006; Ramallo and Mascheroni 2012. Due to its major role, rehydration
ratio was given 40 of total weighted factors. Besides rehydration ability, texture firmness also plays major role on quality of dried
products Bourne 2008; Vega-Gàlvez et al. 2008; Marzec et al. 2010; Bonazzi and Dumoulin 2011. Firmness was also given 40
of total weighted factors. Color is also important quality parameter that influences
consumer acceptance Krokida and Marinos-Kouris 2003; Kulshreshtha et al. 2009. Color had 30 of total weighted factors,
20 for dried form and 10 for rehydrated form. It was considered that rehydrated bamboo shoots may be futher processed and the
shoots may also be mixed with other materials during cooking. Thus, color of rehydrated product was given 0.1. In the other side,
the color of dried form was given 0.2. The color of dried bamboo shoots produced at the lab was expected better than existing
commercial dried bamboo shoots, thus the color of dried form was considered more important than the color of rehydrated form and
given 0.2. On the contrary, shrinkage is an undesired attribute. It has a negative impact on quality of dried products Aguilera 2003;
Mayor and Sereno 2004. Thus, shrinkage or dimensional change was given -0.1.
Table 3. Weighted factors
Attribute Weighted factor
L_dried 0.2
a_dried -0.2
b_dried 0.2
L_rehydrated 0.1
a_rehydrated -0.1
b_rehydrated 0.1
Rehydration ratio 0.4
Shrinkage -0.1
Firmness_dried 0.2
Firmness_rehydrated 0.2
Total 1.0
Mean value of each attribute was determined as a score. Thus, weighted score was obtained by multiplying the determined
weighted factor by mean value of the attribute. The best sample was sample which had the highest total weighted score. Yet, it should be
considered that the sample chosen as the the best sample had to have total residual sulfites less than 2500 ppm SO
2
.
19
3.3.2.2.9 Sensory Analysis
Sensory analysis was carried out on the best sample. The best sample produced at the lab and commercial dried bamboo shoots
purchased in Mae Sai were tested using hedonic rating. Before testing, both samples were soaked into distilled water 25-26
⁰C at room temperature ± 26
⁰C for 12 hours and then boiled for an hour. After that, the samples were cut into same shape and size 50
mm x 5mm x 5 mm. Both samples were presented in pairs according to the predetermined order. They were also coded by 3
random numbers. Thirty five untrained panelists Lawless and Heymann 1998
were asked to give preference score of the attributes on a scale from 1 to 5. Criteria for each attribute tested, including color, aroma,
taste, texture, and overall, was shown in Table 4.
Table 4. Category scales for rating hedonic test
Scale Criteria
1 Dislike extremely
2 Dislike moderately
3 Neither like or dislike
4 Like moderately
5 Like extremely
3.3.3 Experimental Design
Kategori