You generally have to contact the supplier or research online for the actual oils used.
Here we have a palm-based cooking oil, but mixed. So I emailed the company and they said it was palm and canola but wouldn't tell me the ratio - so with the saturated fat amounts for each oil and the amount for the mix itself, I could work out the actual mix of the two oils.
If the sap values for the two oils are pretty much the same, though, it's not critical. But if you have wildly different sap values you are more accurate with the measurements if you work it out
In principle you can't work out the oil proportions in shortening products by looking at saturated, monounsaturated and polyunsaturated numbers. Hydrogenated oils are incorporated into all of them in one way or another, and the specific effect of hydrogenation is to change how saturated the fats are.
The rest is ETA:
The problem is that you don't know the degree of hydrogenation or how it was done. The process can affect the balance of poly / mono / fully saturated in many different ways. So there's a mystery process you can't account for in your calculations.
However, it occurs to me that you could possibly work it out for a zero trans-fat shortening, if a few assumptions are true. First would be that only non-hydrogenated and fully hydrogenated oils are used to make the product. No partially hydrogenated because that would introduce trans-fat.
For Crisco, for instance, you can find the proportion of non-hydrogenated palm and soybean oils to give you the correct proportion of poly and monounsaturated. Then figure the proportion of fully hydrogenated soybean oil to get the right amount of saturated fat.
It turns out that about 1/3 each soybean, palm and fully hydrogenated soy gives you the right numbers and a SAP value of .138 for Crisco.
I know the label says there are "partially hydrogenated palm and soybean oils" in it, which would normally screw up our calculations, but in this case it might not be so. Our second assumption is that "partially hydrogenated" is for labeling purposes how they describe non-hydrogenated oil trans-esterified with fully hydrogenated oil (meaning the fatty acids are redistributed between the two oils).
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