1) Carrots contain several food matrix components that may affect carotenoid bioavailability. Evidence from a ferret model suggests that the crystalline form of carotenoids in carrot root chromoplasts and dietary fiber both negatively affect bioavailability (Zhou and others 1996). Detailed in vitro research modeling the gastric environment suggests that membrane‐bound carotenoids in spinach chloroplasts are more resistant to solubilization into oil than membrane‐bound and free crystalline carotenoids in the carotene bodies of carrots (Rich and others 2003a). However, blanching, which disrupts most of the organelles, increases solubilization of both β‐carotene and lutein from homogenized spinach by more than 60%, but was shown to have little effect on the solubilization of β‐carotene in carrot juice (Rich and others 2003a).
In raw carrot juice, cell walls are removed and the cellular structures containing chromoplasts are disrupted. Blanching of carrot juice further disrupts the membrane‐bound carotene bodies, but leaves carotene crystals intact (Rich and others 2003a). It was hypothesized that the carotene–carotene interactions in the crystals are more stable against solubilization than the lipoprotein–carotenoid interactions of the blanched spinach. This is in agreement with the observation that heating of carrot juice did not significantly increase carotene bioavailability in ferrets (Zhou and others 1996).
2) Torronen and others (1996) found a 45% bioavailability of β‐carotene in healthy women from daily intakes of 12 mg as either raw carrots or carrot juice for 6 wk.
that's roughly consistent with the previous study; while i am not surprised that heating carrot juice was not helpful, i am surprised to see no increase in bioavailability from juicing. that would perhaps go back to the first study, which points out that the carotenoids in carrots are mostly in between the cells, rather than within them - and that (1) breaking down the cell walls doesn't release them and (2) they're actually sensitive to heat, due to being outside the cell.
that would mean that pureed carrots are really only more bioavailable because the stuff that gets destroyed in your stomach anyways got stripped out - and you'd might as well eat the same fraction of them raw, instead. that is, pureed carrots are really just more concentrated, they're not really more bioavailable - and it doesn't really have to do with heat, or with granule size. because it's not actually inside the cell, at all...
so, as a source? they're lossy. low efficiency. that's how it is.
you'd might as well just go ahead and eat them raw - but chew them good.