EFFECT OF BLANCHING TIME ON NUTRITIONAL QUALITY OF BUSH BEAN AT DIFFERENT POD AGE STAGES

J. Soil. Nature .1 (1): 15-21 (March 2007)
EFFECT OF BLANCHING TIME ON NUTRITIONAL QUALITY OF BUSH BEAN AT DIFFERENT
POD AGE STAGES
M. M. KHATUN1, N. SULTANA2, M. H. RAHMAN3 AND M. ASHADUSJAMAN4
1Scientific Officer, OFRD, BARI, Rangpur. 2Associate Professor, Dept. of Horticulture, BSMRAU, Gazipur-1706. 3Scientific Officer,
Hybrid Rice Project, BRRI, Joydevpur, Gazipur-1703. 4AGM, Supreme Seed Co. Uttara, Dhaka.
Accepted for publication: 8 February 2007
ABSTRACT
Khatun, M. M., Sultana, N., Rahman, M. H. and Ashadusjaman, M. 2007. Effect of Blanching time on Nutritional Quality of Bush Bean at
Different Pod Age Stages. J. Soil. Nature .1(1): 15-21
The study was conducted to find out the nutritional quality of pods harvested at different ages (10, 15 and
20 days after pod initiation) after blanching at 500c for 5, 10 and 15 minutes of bush bean genotypes.
Ascorbic acid, protein and dry matter retention percent were decreased as well as losses were increased
with the increase of blanching time, but total sugar content was increased with the increase of blanching
time. The highest 49.55 percent ascorbic acid retention was observed in V2 after 5 minute blanching and
91.00 percent losses were observed in V3 after 15 minutes blanching among all genotypes respectively.
Similarly, the highest 97.98 percent protein retention was found in V2 and lowest 90.68 percent protein
retention was observed in V4 after 5 minute blanching. On the other hand, V4 genotype was contained
higher percentage of protein retention after 10 and 15 minute blanching. Percent retention of protein was
higher in 20 days pod age for all genotypes. Dry matter retention was found 86.26 to 97.67%, 82.90 to
94.62% and 82.83 to 93.27% among genotypes when blanched at 5, 10 and 15 minutes respectively. But
total sugar content retention was observed 79.94 to 160.80%, 91.11 to 165.60% and 98.45 to 169.28% at 5,
10 and 15 minute after blanching respectively. The highest increasing sugar content was observed in V4 at
all blanching.
Key words: Pod age, Blanching time, Nutritional quality, Genotypes
INTRODUCTION
Popularity trends of bush bean are increasing day by day in Bangladesh due to its higher nutritive value, good
taste, export potentiality and wide range of use. To maximise nutritional quality and fulfill overseas market
demand of bush bean, it is important to harvest bush bean pods at different ages, as pod age is an important
factor for organoleptic and nutritional qualities. Post harvest losses of vegetable can be reduced by many
physical treatments. Among those treatments heat treatment is a common low cost method, known as blanching.
Blanching is known to delay chlorophyll loss in green tissue (Klein and Lurie, 1991; Paull, 1990). According to
Amiruzzaman (1994) blanching is an important step, which involves exposing the vegetables very quickly to
heat to inactivate naturally occurring enzymes and would prolong refrigerated and frozen storage of plant
materials. But heating can cause undesirable losses of visual and nutritive qualities. For maximum storage
sufficient heat treatment is needed to stabilize the product against enzymatic deterioration but at the same time it
is necessary to minimize quality losses due to heating. The optimization of blanching conditions implies a
concomitant between keeping the nutritional, organoleptical and structural quality of the food, and stability
during the storage as a result of enzyme inactivation. Considering the above facts the experiment objective is to
know the nutritional status of bush bean at different pod ages after blanching.
MATERIALS AND METHODS
The experiment was carried out in the laboratory of the Department of Horticulture, Bangabondhu Sheikh
Mujibur Rahman Agricultural University (BSMRAU), Gazipur, from December 2004 to March 2005. The bush
bean was grown in the Agronomy Research Farm, BSMRAU, Gazipur. The experiment was laid in Completely
Randomized Design with three replications. Four bush bean genotypes e.g. BB3 (Bush bean3), BB9 (Bush
bean9), BB13 (Bush bean13) and BB15 (Bush bean15) were used as plant materials. Bush beans from all
treatment combination were blanched at 500c for 5, 10 and 15 minutes. Ascorbic acid (%), Total sugar (%),
Protein (%) and Dry matter (%) were recorded on 10, 15 and 20 days after pod initiation. Bush bean genotypes
were designated as, V1=BB3, V2= BB9, V3= BB13, V4= BB15 and pod age stages were designated as M1=10
days after pod initiation, M2=15 days after pod initiation, M3=20 days after pod initiation
Ascorbic acid content was determined as per the procedure described by Pleshkov (1976). The total ascorbic
acid content was quantified by using the following formula.


© 2007 Green World Foundation (GWF)
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M. M. Khatun et al.
Ascorbic acid (mg/100g) = (T.F.V. 100)/Vw
Where,
Titrate volume of KIO3 ml
T=0.088 mg of ascorbic acid per ml of 0.001N of KIO3
F=Total volume of the sample extracted
V=Volume of the extract (ml) taken
W=Weight of the sample taken (g)
Sugar contents were estimated according to Somogyi (1952), using Bertrand A, Bertrand B and Bertrand C
solutions. Total sugar content was calculated comparing tabulated values. Before calculation of total sugar
factor of 0.4 KMnO4 was determined.
Total nitrogen and protein content of the collected sample was determined by Kjeldahl method using CuSO4 and
K2SO4 mixture (1: 9) as catalyst.
100
The total nitrogen was calculated by the following formula: %

N = 14 .007 × F × (T ? B )
(ml )
×
×
10 (
100 1000
ml )
w (g )
Protein was estimated by multiplying 6.25 to the value of total nitrogen.
Dry
weight
Dry matter (%) was calculated using this formula- % Dry matter
=
× 100
Fresh
weight

Procedure of blanching
Fresh harvested bush bean was blanched in hot water bath. Bush bean was immerged in hot water and covers the
pot. For immersion of bush bean Hot Water Bath was used. Blanching duration was counted after immerging the
bush bean in hot water. One-gallon water was used for each pound of bush bean. The same water was used only
two times because hot water can cause toughening of bush bean. Bush bean was cooled (to avoid boiling)
immediately after blanching in pans of ice cold water. Then bush bean was drained thoroughly.
RESULT AND DISCUSSION
Ascorbic acid
Ascorbic acid retention and losses of bush bean genotypes at three pod age stages after blanching are presented
in Table 1. it was found from Table 1 that with the increase of blanching time percent ascorbic acid retention
were decreased while at the same time losses were increased . Due to 5 min blanching, the highest (49.55%)
ascorbic acid retention was observed in V2where loss was 50.45%. The lowest retention (40.13%) was found in
V3 where loss was highest. After 10 and 15 minute blanching V2 also contained the highest retention percentage.
Considering pod age stages, the highest (48.79%) ascorbic acid retention was found in 20 days old pods and the
lowest was found in 10 days old pods at 5 minute blanching. In case of 10 and 15 minute blanching the highest
ascorbic acid retention was 30.42% and 19.81%, respectively. Regarding interaction effect, the highest retention
(60.00%) was found in V2 for 20 days old pods at 5 minute blanching. The lowest retention (8.64%) was
observed from V3 for 10 days old pods at 15 minute blanching. The prime reasons for ascorbic acid losses
during blanching might be due to the solubility in water, thermal destruction and enzymatic oxidations.
Lisiewaska et al., 2003 suggested the same reasons for ascorbic acid losses during blanching. In short term
boiling, water-soluble vitamins can be lost by leaching (Petersen, 1993).
Protein
It can be described from Table 2 that Percent retention of protein gradually decreased due to blanching. After 5
min blanching the highest (97.98%) protein retention was observed in V4 and the lowest (90.68%) was observed
in V2 (Table 2). Similarly, at 10 and 15 minute blanching V4 was also contain higher retention percent. Percent
retention of protein was higher in 20 days pod for all genotypes. In case of interaction effect between, the
highest (99.42%) protein retention was observed in V2 at 15 days old pods after 5 minute blanching and the
lowest (83.25%) protein retention was observed in V4 at 15 days old pods after 15 minute blanching. It may be
concluded that According to Vaintraub et al. (1979). It may be concluded that protein content decreased due to
heating, and after denaturation and digestion by pepsin and trypsin about 94.40% proteins are hydrolyzed.
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Effect of Blanching time on Nutritional Quality of Bush Bean at Different Pod Age Stages
Table1.Effect of blanching time (blanched at 500 C temp.) on ascorbic acid of bush bean genotypes at three pod
age stages
Treatments
5 min
10 min
15 min
Genotypes
Retention (%)
Loss (%)
Retention (%)
Loss (%)
Retention (%)
Loss (%)
V1 43.7 56.3 29.22 70.78 23.39 76.61
V2 49.55 50.45 32.50 67.50 24.02 75.98
V3 40.13 59.88 23.04 76.96 9.00 91.00
V4 42.19 57.81 30.33 69.67 18.08 81.92
Pod age
M1 42.63 57.37 26.19 73.81 17.41 82.59
M2 42.93 57.07 30.22 70.78 17.76 82.24
M3 48.79 51.21 30.42 69.58 19.81 80.19
Interaction
V1M1 42.31 57.69 36.92 63.08 26.46 73.54
V1M2 44.55 55.45 26.73 73.27 22.73 77.27
V1M3 44.55 55.45 22.73 77.27 20.45 79.55
V2M1 46.36 53.64 29.14 70.86 26.20 73.80
V2M2 45.51 54.49 27.19 72.81 19.25 80.75
V2M3 60.00 40.00 36.54 63.46 27.73 72.27
V3M1 37.50 62.50 20.00 80.00 8.64 91.36
V3M2 42.73 57.27 25.00 75.00 9.36 90.64
V3M3 40.91 59.09 24.91 75.09 9.09 90.91
V4M1 42.86 57.14 38.93 61.07 28.57 71.43
V4M2 38.93 61.07 26.43 73.57 11.07 88.93
V4M3 45.45 54.55 32.00 68.00 13.64 86.36

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M. M. Khatun et al.

Table 2 Effect of blanching time (blanched at 500 C temp.) on protein of bush bean genotypes at three pod age
stages
Treatments
5 min
10 min
15 min
Genotypes
Retention (%)
Loss (%)
Retention (%)
Loss (%)
Retention (%)
Loss (%)
V1 94.99 5.01 93.97 6.03 92.96 7.04
V2 90.68 9.32 88.57 11.43 87.14 12.86
V3 96.25 3.75 95.51 4.50 93.36 6.64
V4 97.98 5.02 95.91 4.09 95.88 4.21
Pod age
M1 94.50 5.50 93.35 6.65 93.25 6.75
M2 94.53 5.47 93.48 6.52 93.19 6.81
M3 95.63 4.37 93.66 6.34 93.71 6.29
Interaction

V1M1 96.04 3.96 94.59 5.41 94.30 5.70
V1M2 92.84 7.16 92.33 7.67 91.05 8.95
V1M3 96.15 3.85 95.05 4.95 93.57 6.43
V2M1 98.95 1.05 94.30 5.70 94.30 5.70
V2M2 99.42 0.58 99.42 0.58 98.84 1.16
V2M3 96.35 3.65 93.75 6.25 92.71 7.29
V3M1 97.22 2.78 97.22 2.78 92.78 7.22
V3M2 97.30 2.70 97.30 2.70 96.22 3.78
V3M3 93.33 6.67 92.31 7.69 91.33 8.67
V4M1 90.66 9.34 87.91 12.09 86.81 13.19
V4M2 89.04 10.96 85.35 14.65 83.25 16.75
V4M3 92.31 7.69 92.31 7.69 91.18 8.82

Dry matter

Percent retention of dry matter gradually decreased and percent losses were increased due to blanching time
increased (Table 3).Dry matter retention varied from 86.26 to 97.67%, 82.90 to 94.62% and 82.83 to 93.27%
among genotypes when blanched at 5, 10 and 15 minutes, respectively(Table 3). The genotype V1 contained the
highest amount of dry matter and the lowest retention was found in V2. Regarding pod age, dry matter retention
was higher in 20 days old pods, where losses were minimum. In case of interaction, the highest (98.75%) dry
matter retention was found from V4 for 20 days old pod at 5 minute blanching. From this Table it may be
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Effect of Blanching time on Nutritional Quality of Bush Bean at Different Pod Age Stages
concluded that dry matter retention decreased and losses were increased due to increased blanching time. This
might be due to loss of soluble solid during blanching (Tomasula et al., 1990). Lisiewaska and Kmiecik (1996)
found similar results and reported that blanching reduced of 9-10% dry matter in cauliflower.

Table 3. Effect of blanching time (blanched at 500 C temp.) on dry matter of bush bean genotypes at three pod
age stages

Treatments
5 min
10 min
15 min
Genotypes
Retention (%)
Loss (%)
Retention (%)
Loss (%)
Retention (%)
Loss (%)
V1 97.67 2.33 94.62 5.38 93.27 6.73
V2 86.26 13.74 82.90 17.10 82.83 17.17
V3 90.80 9.2 86.96 13.04 84.37 15.63
V4 97.56 2.44 93.61 6.39 90.62 9.38
Pod age
M1 90.17 9.83 86.13 13.87 85.63 14.37
M2 95.23 4.77 91.59 8.41 89.70 10.30
M3 96.80 3.20 93.25 6.75 90.45 9.55
Interaction

V1M1 97.50 2.50 91.40 8.60 91.20 8.80
V1M2 95.45 4.55 92.27 7.73 92.18 7.82
V1M3 99.00 1.01 96.88 3.13 95.31 4.69
V2M1 82.11 17.89 90.63 9.38 85.94 14.06
V2M2 88.24 11.76 85.29 14.71 85.29 14.71
V2M3 90.63 9.37 78.95 21.05 75.79 24.21
V3M1 94.68 5.32 89.36 10.64 89.36 10.64
V3M2 95.74 4.26 93.62 6.38 90.43 9.57
V3M3 94.68 5.32 80.00 20.00 76.00 24.00
V4M1 93.75 6.25 97.50 2.50 90.00 10.00
V4M2 98.00 2.00 98.75 1.25 93.75 6.25
V4M3 98.75 1.25 88.54 11.46 88.54 11.46

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M. M. Khatun et al.
Table 4. Effect of blanching time (blanched at 500 C temp.) on total sugar of bush bean genotypes at three pod
age stages

Treatments
5 min
10 min
15 min
Genotypes
Retention (%)
Increased (%)
Retention (%)
Increased (%)
Retention (%)
Increased (%)
V1 202.90 102.90 211.07 111.06 214.36 114.36
V2 179.94 79.94 195.63 95.63 214.63 114.63
V3 189.43 89.43 196.11 91.11 198.45 98.45
V4 260.80 160.80 265.60 165.60 269.28 169.28
Pod age
M1 191.53 91.30 196.14 96.14 204.86 104.86
M2 199.86 99.85 209.41 109.76 217.15 117.15
M3 235.30 135.30 243.75 143.75 251.69 151.69
Interaction

V1M1 181.82 81.82 187.50 87.50 190.91 90.91
V1M2 190.24 90.24 199.00 99.00 200.25 100.25
V1M3 250.42 150.42 261.27 161.27 267.11 167.11
V2M1 169.69 69.68 192.81 92.81 203.28 103.28
V2M2 169.59 69.59 192.98 92.98 216.37 116.37
V2M3 185.65 85.25 201.64 101.64 223.02 123.02
V3M1 231.48 131.48 235.45 135.45 238.10 138.10
V3M2 289.29 171.43 274.64 174.64 284.64 184.64
V3M3 271.43 131.48 279.79 176.79 285.71 185.71
V4M1 171.59 71.59 176.14 76.14 176.10 76.10
V4M2 176.68 76.68 176.68 76.68 182.57 82.57
V4M3 233.72 133.72 233.72 133.72 253.76 153.76

Total sugar

Increased percentage in total sugar with the increase of blanching duration was found in this study. Among
genotypes, increasing in total sugar varied from 79.94 to 160.80%, 91.11 to 165.60% and 98.45 to 169.28% at 5,
10 and 15 minute after blanching respectively (Table4). The highest increase was observed in V4 among all
blanching. Regarding pod age stages, the highest (151.69%) increasing was found in 20 days old pods at 15
minute blanching and the lowest (91.30%) in 10 days old pods after 5 minute blanching. In interaction effect,
the highest (285.71%) sugar retention was found in V3 for 20 days old pods after 15 minute blanching. From
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Effect of Blanching time on Nutritional Quality of Bush Bean at Different Pod Age Stages
this table it may be concluded that sugar content increased due to blanching. This might be due to increased in
sucrose and fructose during hot water treatment. W. Hu et al. (2004) found the similar results in the case of
sweet potato sucrose and glucose content increased due to hot water treatment (500C for 30 minute).

CONCLUSION
Ascorbic acid retention percent found to be decreased and losses were increased with the increase in blanching
time due to 5 minute blanching at 500c; the maximum (49.55%) ascorbic acid retention was recorded from V2
and the lowest in V3. But the minimum retention was observed from 15 minute blanching condition. In this case
20 days age stage contained maximum retention percentage of ascorbic acid. The highest (97.98%) protein
retention percentage was found in the genotype V4 at 5 min blanching condition and 20 days pod age stage. The
loss of protein due to blanching varied from 3.75-12.86% among genotype and 4.37-6.75% among pod age
stages. Dry matter retention was highest (97.67%) in V1 when blanched at 5 minute and loss was highest
(17.17%) after 15 blanching. Regarding total sugar, the highest retention (269.28%) was found in V4 among the
four bush bean genotypes. Total sugar retention percentage found to be increased with the advancement of
blanching time. So, the highest amount of nutrition was observed from 5 min blanching except total sugar, and
highest ascorbic acid, protein, dry matter and total sugar content was higher in 20 days pod.

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