By: Dawn Berkelaar
Published: 2019-04-26

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In EDN 142, we linked to several documents from Feed the Future, produced with support from USAID for the RAMA-BC (Resilient Agricultural Markets Activity — Beira Corridor) project. Another, slightly longer document by Zachary Hall describes how to germinate, soak and boil jack beans, to detoxify them and make them suitable for human consumption. This article summarizes that information. We encourage you to read the full document for more details.

Benefits of jack bean

Jack bean (Canavalia ensiformis) is an important green manure/cover crop plant. It improves soil, both through its high biomass production and through its relationship with nitrogen-fixing microorganisms in the soil. Jack bean seeds contain a number of antinutrients that repel pest insects and animals, which is helpful both in the field and when storing the beans. These traits, along with its drought tolerance, enable jack bean to grow in very poor soil. In the Beira Corridor in Mozambique, a single planting of jack bean can often produce two harvests. 

Antinutrient removal process

Antinutrients (described below) in the seeds of jack bean make them unsuitable for human food without treatment. Most legumes are made more digestible by soaking them for one day, then cooking them for one to three hours. Long treatment practices like these are common in Mozambique. However, jack bean contains some antinutrients that are only removed when the seeds germinate. Other antinutrients, which are somewhat reduced by cooking, are reduced even more by germination.

The germination process is not difficult, but it requires some planning. Jack beans can be germinated as follows: Soak beans for one day, then drain and wash them. Continue to wash them morning and night until they have germinated and the sprouts are one inch long (this usually takes two to four days). Finally, remove the seed coats—germination makes beans much easier to dehull—and cook the seeds for 90 minutes. See Figure 4 for pictures of the RAMA-BC process undertaken at ECHO.

EDN143 figure 4a Beginning of the soaking process, before the seeds have absorbed water and expanded.
EDN143 figure 4b After 24 hours of soaking. Note the increased size of the seeds. Shortly after this photo was taken, the seeds were drained and washed, then kept moist---but not submerged--- in the pot (with the lid on) for an additional 48 hours. During those 48 hours, the seeds were washed and rinsed at least twice daily, to keep them moist. 
EDN143 Figure 4c Fully sprouted seeds 48 hours after they were first drained and washed. The sprouts at this stage were approximately 2.5 cm (1 in) long.
EDN143 Figure 4d Fully sprouted seeds with seed coats removed. 
EDN143 Figure 4e Seed coats (left) and non-sprouted seeds (right) that were removed before boiling.
EDN143 Figure 4f Sprouted seeds that were boiled for 90 minutes, with the cooking water discarded. Several ECHO staff tried them, saying that the beans were filling and tasted good. 
Figure 4. Steps of the RAMA-BC jack bean detoxification method tried at ECHO in Florida. Source: Tim Motis

The paper lists a number of antinutrients in jack bean that are only removed by germination, or (in the case of concanavalin A) by germination along with soaking and boiling: 

  • Polyphenols and polyamines can bind with iron, making it unavailable.
  • Phytates can prevent iron, zinc and calcium from being used by the body.
  • Cyanide consumption can result in iodine deficiency and related disorders such as cretinism and goiter.
  • Concanavalin A is the most concerning antinutrient in jack bean, and blocks nutrients from being absorbed by the body in a number of ways. It is more heat resistant than other antinutrients, and is only partially removed by germination. Udedibie and Carlini (1998) showed that it could be removed by a combination of soaking (for 72 hours), breaking the beans into pieces, and cooking. The RAMA-BC approach achieves similar results by combining germination with soaking and boiling; in the boiling step, the beans naturally break into smaller pieces.

In Mozambique, the RAMA-BC project is undertaking “a behavior change campaign that includes trainings aimed at the adoption of germinating all beans and jack bean as a food crop.” This campaign includes spots on radio and TV, live demonstrations, trainings, and publication of various documents. So far, jack beans have been well-received as a high protein, good-tasting bean. 

This multi-step approach to detoxifying jack bean is most relevant for areas where access to alternative legumes is limited, and where people are already familiar with processing to remove antinutrients. If you experiment with this, be sure to follow all the steps as well as advice from physicians. To our knowledge, no adverse effects have been reported after eating jack bean seeds treated with this method. We are unaware of scientific reports of antinutrient levels in jack bean seeds that have been processed by the RAMA-BC method; however, the paper authored by Zachary Hall refers to numerous publications that support the effectiveness of the various parts of the process. 

References and further reading

Hall, Z. No date given. Germination as an effective method for processing jack bean for human consumption.

Udedibie, A.B.I. and C.R. Carlini. 1998. Crack and Cook: A Simple and Quick Process for Elimination of Concanavalin A (Con A) from Canavalia Seeds. Animal Feed Science and Technology 74:179-184.

For more about the effect of germination on the nutritional value of seeds, see the article “Effect of Sprouting on the Nutrition of Grain and Legume Seeds” in EDN 106.