Luffa Research Report – Post-harvest Bleaching

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.