While enjoying the fleshy and juicy guyabano fruit, I am carefully sorting out every seed passing thru my senses. Its not like tearing the flesh apart and flipping off every seed I see. I am taking in a whole chunk and spewing the seeds out.
The guyabano seeds are toxic but that is not the reason why I am sorting it out. I just never want my stomach to have extra load of indigestible thing. If I swallow a whole unbroken seed, it will just come out as whole and unbroken.
Guyabano seeds are toxic according to various studies. Here are some prominent search results:
The flesh of the fruit consists of an edible, white pulp, some fiber, and a core of indigestible, black seeds. (http://en.wikipedia.org/wiki/Soursop)
The compound annonacin contained in the seeds of soursop is a neurotoxin and it seems to be the cause of a neurodegenerative disease. The only group of people known to be affected live on the Caribbean island of Guadeloupe and the problem presumably occurs with the excessive consumption of plants containing annonacin. (http://en.wikipedia.org/wiki/Soursop)
Annonacin is a chemical found in some fruits such as the custard apple and Sour Sop (and others from Annonaceae family). It is a member of the class of compounds known as acetogenins. Reports have shown that regular consumption in rats (3.8 and 7.6 mg per kg per day for 28 days) caused brain lesions consistent with Parkinson’s disease. (http://en.wikipedia.org/wiki/Annonacin)
The seeds contain 45% of a yellow non-drying oil which is an irritant poison, causing severe eye inflammation. (http://www.hort.purdue.edu/newcrop/morton/soursop.html#Toxicity)
Guyabano seeds are pretty tough. Breaking it accidentally in between teeth is unlikely. Cracking the seed coat requires some concentration. My first trial was a failure and the second was a success. I got a slightly achy gum after.
Eating the fresh fruit possess no problem but the commercial processing does. Automatic seed remover and blender’s force might be enough to break the seed apart resulting to mixture to finish products. If my teeth could tear a seed apart, the more the heavy duty machines can. A friend of mine who worked in guyabano processing plant disagreed. He emphasized that it cannot be crumbled by a hammer. Maybe, they used a plastic hammer. See a guyabano seed after hammering.