Monday, February 4, 2008

Keeping limu: strategies and common sense

In ancient Hawai'i, seaweeds were a primary spice—a way of providing different flavors to foods.

(Image: The invasive but edible seaweed Gracilaria salicornia. Source: Hawaii Coral Reef Initiative Research Program.)

Most folks know about the role of various limu in fish dishes like poke. Seaweeds also could be used as a condiment, eaten alongside other foods rather than mixed with them.

The early Hawaiians would often have eaten their limu fresh or salted, said University of Hawai'i botany professor emeritus Isabella Abbot, but the realities of today's world are that folks seek something that seems fresh even though it may be several days old—so it will require some storage technology. And that's the problem challenged by Robert E. Paull and Nancy Jung Chen, of the University of Hawai'i's College of Tropical Agriculture and Human Resources.

They conducted extensive studies with one of the most popular seaweeds, Gracilaria.

Gracilaria comes in several forms in Hawai'i, several of them native, but one, Gracilaria salicornia, an imported, invasive one. The most commercially desireable form is known in Hawaiian as limu manauea and in Japanese as ogo. It is Gracilaria coronopifolia.

In the journal Postharvest Biology and Technology, Paull and Chen outlined their results.

They found that the seaweeds change in many different ways after collection. Among the changes are color, production of ethylene, leakage of fluids, and changes in protein content.

They studied using different temperatures, keeping the limu in light and dark, heat treatments and more.

They found that when kept just above freezing, the samples went limp and changed color after just one night. At 18 degrees Fahrenheit above freezing, the color changes occurred after a couple of days. A little warmer than that made little difference.

Their conclusion was that the best way to store it without special treatment was to keep it in darkness at about 61 degrees Fahrenheit, which is about 29 degrees above freezing. This didn't keep the limu usable beyond about four days, but the quality was better during the storage period.

The authors said they found that a five-minute hot dip in seawater at about 108 degrees Fahrenheit, followed by storage in 60-degree water would extend the useful life of some samples.

They said one of the best ways to keep limu for an extended period is one that seems like common sense: keep it submerged in seawater in darkness. This can extend its useful life from four days to four weeks.

“Seaweed submerged in seawater in the dark had an extended postharvest life” of about a month, the scientists said in their abstract.

That system works in part because it takes advantage of a natural characteristic of many seaweeds. One of the ways they reproduce is for pieces to break off, drift in the ocean for a while, and settle elsewhere. In order for that to work, they need to remain alive after breaking off.

They are hard-wired to survive for a long time while drifting in salt water.

If you're not in a position to haul around a bucket of water for your seaweeds, the best thing is to do preserve it in salt.

“That's what the Hawaiians did,” Abbott said.

© 2007 Jan W. TenBruggencate