All those people? You misunderstand me.
I never said they had to destroy the body. I was merely pointing out that in the Mass Effect universe memory, knowledge, experience and all these things are all linked to your genetic material and can be saved/stored/read. The Asari can read back through your heritage line when they meld with you (apparently). The thorian saved the 'essence' of the thorians by devouring their bodies. So on and so forth. This ability of 'preserving' organic knowledge is not something unique to the reapers and has been in the series since the very beginning.
The bodies of the protheans the Thorian devoured certainly were destroyed. The prothean's whom stored their knowledge and experience in the echo shards certainly ARE dead. No, you dont HAVE to destroy the body to save/store this information. I never said they had to.
You said you didn't see how they could preserve memories and knowledge by liquifying brains. I'm elaborating on the fact that they CAN in Mass Effect universe and pointing out examples, some direct and some not. The brain is irrelevant to the knowledge and memories, apparently. In Mass Effect all these things are biological markers, as Javik tells us.
Wiki quotes -
Asari:
An asari's melding ability extends to a mental connection as well, which Liara describes as being the true union between an asari and her partner. It allows the asari to explore her partner's genetic heritage and pass desirable traits on to any offspring. During mating an asari and her partner share memories, thoughts, and feelings. It is also possible for an asari to meld with another for the sole purpose of transferring thoughts, without reproduction.
Thorian:
"When the Protheans arrived and began building the metropolis that would eventually cover Feros, the curious Thorian studied them, likely made several of them into its thralls, and even absorbed them after they died, allowing them to become a part of its expanding consciousness.
From the Protheans, the Thorian's mind gradually absorbed the knowledge that would form the Cipher. "
Prothean:
"A unique attribute of Prothean physiology is an experiential exchange system based on physical touch. By touching something or someone, a Prothean could recall its experiences. This system can transfer complex ideas, with a Prothean being capable of learning a new skill or foreign language with a single touch."
Also take into account the prothean's Echo Shards. These 'echo shards' may not seem all that astonishing but consider this: these little pieces of technology are capable of storing memories, experiences, emotions, and knowledge. Not unlike the beacons themselves but seemingly more elaborate and with a broader scope of what it can store. Soldiers would pass them down from one to another to get glimpses of what life used to be. Individuals also seem to be able to place their own memories and experience into the shards by touching them, non protheans included.
Wiki quote:
“If you encourage Javik to relive it, he'll pass the Echo Shard to Shepard for him to add his memories to it”
To quote the wiki, again, on the reapers:
"Individuals who are determined to be suitable for processing are loaded onto Reaper Processors, where they are ushered into single-person pods. Once in the pods, the victims are dissolved into a raw genetic "paste" for ease of transport. This paste will then be used in the construction of a newborn Reaper, with the victims' minds being preserved to form the Reaper's gestalt consciousness. "
More quotes!
“This explains why the captured humans were rendered into their base components. Destructive analyst. They were dissected down to the atomic level. That data could be stored on an AI's neural network. The knowledge and essence of billions of individuals complied into a single synthetic identity. The ultimate goal would be to upload all humans into this reaper mind. “
It may also be worth mentioning the 'Virtual Aliens'. A species in Mass Effect lore that uploaded the minds of their civilization (one billion individuals) into a computer in order to survive a supernova. We are not talking about making mere copies of themselves, they were able to take their consciousness out of their physical bodies and store them safely in this virtual world. They can even swap places with other sentient being and control their bodies.
So yeah. They can preserve memories and experience from just the goo.