Luffa Research Report
Post-harvest Bleaching of Luffa Sponges for Reduced
Stains Without Reduced Strength
Todd C. Wehner and Tammy L. Ellington
Department of Horticultural Science, North Carolina
State University, Raleigh, NC 27695-7609
Cucurbit Genetics Cooperative Report 19: 87-88
Sponges obtained from luffa gourds (Luffa aegyptiaca
Mill) have many uses ranging from household cleaning to personal
hygiene. Fruits are harvested from the vines after the skin of
the fruit has started to dry and turn brown. The seeds are shaken
out and the skin removed to reveal the sponge, which is the fibrous
skeleton from mesocarp of the fruit. The sponges may absorb brown
pigment from the skin causing discoloration of the sponge. Stained
sponges may have a lower market value. The objective of this study
was to evaluate bleach treatment to improve sponge appearance
and reduce staining without reducing sponge strength.
The experiment was a randomized complete block with
10 bleach soak durations and 2 replications. Sponges were harvested
from field performance trials at the Horticultural Crops Research
Station near Clinton, NC. After seeds and skin were removed from
the fruits, the sponges were grouped into stained and normal.
After rating the percentage of the total fruit surface that was
stained brown, they were submerged in a 10% bleach solution for
0, 1, 2, 4, 8, 16, 32, 64, 128, or 256 minutes. The bleach solution
in the soaking tank was replaced every 30 minutes to assure its
strength. After bleaching, the sponges were rinsed in clear water
for 30 seconds. The sponges were rated for whiteness after 3 days
of drying, and whiteness and strength after 127 days of aging
to determine the long-term effects of the bleach.
Each sponge was cut transversely into 3 pieces approximately
100 mm long, the length often used by sponge manufacturers. Two
of the sections were evaluated by 2 judges for sponge fiber strength,
each transversely tearing a separate section in 3 places. The
third section was evaluated for strength by a third judge using
a knife to make a transverse cut in two places. Strength ratings
were based on a scale of 1-9 (1-3=low, 4-6=moderate, 7-9=high
strength). The average of the three ratings was used to determine
the strength of the sponge (Table 1).
For heavily stained sponges, sponge strength decreased
as whiteness increased. However, there was a lot of variation
among sponges for strength, so the trend was not clear. Our recommendation
for sponges that are heavily stained is bleaching for 30 to 60
minutes. Bleaching for periods longer may decrease sponge strength.
Shorter bleaching time did not whiten the sponge adequately. There
was a tendency for the heavily stained sponges to be white after
bleaching (3 days), but then to darken later (127 days).
For the normal (unstained) sponges, whiteness increased
with bleaching time, and sponge strength had a slight tendency
to decrease after 64 minutes of bleaching. The recommendation
for sponges that are not heavily stained is bleaching for 30 to
60 minutes. Bleaching for longer periods of time decreases the
strength of the sponge.
Table 1. Sponge whitenessz and strength
of unstained luffa sponge gourds after 11 post-harvest treatments
rated before treatment and at 3 and 127 days after treatment.y
|
Bleach
|
Normal sponges
|
Stained sponges
|
|
treatment
|
Sponge whiteness
|
Strength
|
Sponge whiteness
|
Strength
|
|
(minutes)
|
Before
|
3 days
|
127 days
|
rating
|
Before
|
3 days
|
127 days
|
rating
|
|
0
|
80
|
80
|
72
|
5
|
45
|
45
|
20
|
6
|
|
1
|
90
|
90
|
90
|
9
|
5
|
5
|
10
|
2
|
|
2
|
85
|
95
|
95
|
8
|
35
|
75
|
90
|
6
|
|
4
|
85
|
97
|
100
|
5
|
20
|
65
|
60
|
5
|
|
8
|
95
|
100
|
100
|
7
|
55
|
90
|
70
|
6
|
|
16
|
75
|
100
|
100
|
9
|
10
|
100
|
70
|
4
|
|
32
|
85
|
100
|
100
|
7
|
10
|
100
|
35
|
8
|
|
64
|
80
|
100
|
100
|
8
|
35
|
100
|
100
|
8
|
|
128
|
90
|
100
|
100
|
4
|
0
|
100
|
65
|
6
|
|
256
|
85
|
100
|
100
|
5
|
5
|
100
|
95
|
4
|
z Percentage white, unstained area on the whole sponge
surface.
y Data are means of 3 ratings. |
