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I have some crenellated seeds with which I make jewellery and I need to remove the remaining fruit flesh from them. I have tried lots of things including ammonia, vinegar, bleach and a ultrasonic jewellery cleaning machine. the only thing that works is a wire brush which takes forever and results in grazed fingers. I wondered if some solution of the hydrochloric acid I use in the pool would work. If so, what concentration should I use and how long should the seeds be immersed in it? If not, what do you think would work?

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  • $\begingroup$ I'd be inclined to try something like a AC waterpik. The AC version has more power than the battery operated one. $\endgroup$ – MaxW Apr 13 '16 at 3:04
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It depends highly on the seed and the fruit flesh, but using hydrochloric acid to clean off the "jelly" from freshly collected tomato seeds is a recognized laboratory protocol. That protocol uses a 1:1 mix of concentrated HCl and water for 20 min., followed by a 20 min wash in 10% w/v trisodium phosphate to neutralize the acid.

Depending on what sort of flesh is covering the seeds, it may take different amounts of time and different strengths of acid to accomplish the job. You will likely have to experiment a bit. Start "gentle" (as in, less concentrated acid) and work your way up. - You probably don't want conditions that results in complete flesh removal, but rather ones where gentle agitation (e.g with an old toothbrush) after neutralization will dislodge the flesh. - Viability of the seeds will also vary depending on the exact protocol and how tough the seeds are, though it doesn't sound like you need the seeds to be able to germinate afterwards.

As always, when working with concentrated acids and bases, use of proper safety equipment is highly recommended - even for acids and bases they sell in the hardware store.

For the chemical perspective, concentrated acid solutions catalyze the hydrolysis of peptide, ester and glycosidic bonds of the polymers that make up the flesh of the fruit surrounding the seeds. With the polymers degraded, they more easily dissolve in solution. (This is also the reason that our stomachs have hydrochloric acid in them.) The cellulose that makes up the seed coat is recalcitrant to degradation, and so remains untouched to the "mild" acidic conditions.

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    $\begingroup$ Great reference! // One mystery here is how large the seeds are. I was thinking of something like a peach pit. The more flesh is removed prior to the acid bath, the better the acid bath will work. Also 50% HCl isn't really something for casual home use. There are some real safety concerns. $\endgroup$ – MaxW Apr 13 '16 at 21:40
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Thanks for your help. I tried a 1:1 acid/water bath for 20 mins followed by 20 mins in a caustic soda solution to neutralise the acid. This worked fine, the dirt and flesh came off easily with a wire brush. I then tried just putting them in caustic soda for 20 mins followed by a thorough flushing with water. This also worked perfectly! When I find the ultrasonic jewellery cleaner I will try that instead of the wire brush. I appreciate your help. The seeds, by the way, are quandong seeds, they have very deep crenellations.

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