I’ve read that lye water made via wood ash is used very beneficially with corn in Mexico and South America and it increases the nutritional value of the corn quite effectively. I’ve also read that some healthier villages will use lye water to soak their beans in to do much of the same thing.
However, I’ve read in places too that using alkali water (baking soda) for soaking beans and such can also cause problems with destroying some vitamins which would be bad, but… it also destroys the phytates and tannins in beans and seeds that prevent the assimilation of vitamins, minerals and proteins which is very good.
One study (http://jn.nutrition.org/cgi/content/abstract/26/3/227) mentions the use of baking soda (sodium bicarbonate) in cooking peas and found there was no difference in the vitamin content when using it, though the peas cooked faster.
The study is a little old but it goes to some of the conflicting information I’ve found on the pros or cons of using alkali water for soaking.
From what I can gather, even though the levels of thiamine are reduced from the use of alkali water, the benefits from soaking of reduced toxins such as phytates, tannins and other anti nutrients which reside in the shell or hull of the bean significantly out weigh the loss of a B vitamin and may actually help the body absorb and use the vitamins and minerals in the beans, lentils and peas that would normally be blocked if soaking in an alkali water wasn’t performed.