Well in your specific kombucha I won’t be able to tell you but I can give you some math that should help you figure it out and should be able to be used by any brewer to figure out the caloric effect of fermentation on your brews.
So just to hit you with the math right now and ill break it down later the equation to figure out the change in calories caused by fermentation you will use the equation.
OG = Original Gravity
FG = Final Gravity
V = Volume of ferment in ml
Version for Sucrose fermentable used by OP
((((-(OG - FG) * 131.25*0.789*(V /100))/46.07)/4) *342.3*4) +(((OG - FG) *131.25*0.789*(V /100)) *7)
Version for maltose fermentable in beer (treats Maltose as glucose for math purposes)
((((-(OG - FG) * 131.25* 0.789*(V/100))/46.07)/2) *180.16*4) +(((OG - FG) * 131.25* 0.789*(V/100)) *7)
If you replace the variables with your values and paste it into https://www.wolframalpha.com it will output the answer.
Now to break down what is going on here.
(OG - FG) * 131.25 = ABV – this is the equation for estimating the ABV of your brew using original and final gravity.
ABV*0.789 = ABW – this changed the ABV into ABW which is a weight as opposed to volume measurement of the alcohol in your brew.
ABW*(V /100) – this is the total grams of alcohol in your brew – I’ll refer to this as AT from here on out.
AT/46.07=Moles of Alcohol – this converts the grams of alcohol into moles of alcohol which is a count of the number of molecules of alcohol in your brew.
Moles of alcohol/4=Moles of Sucrose Fermented – the process of fermenting sucrose (which you used) creates 4 molecules of alcohol for each molecule of sucrose fermented so by dividing by 4 we get the number of sucrose molecules fermented.
Moles of Sucrose Fermented*342.3*4 = calories of sucrose fermented- by taking the moles of sucrose and multiplying by the molar weight we change the moles of sucrose into grams of sugar then multiply those my calories per gram we get the total amount of calories that those sugar molecules possessed.
Now for the second half this will be quick I promise.
You will notice that the other half looks very similar that is because it is just calculating the total weight of alcohol in the brew and multiplying that by the calorie content on alcohol per gram giving us the calorie content of the alcohol.
Last part bringing it all together.
So once we do all this math we get
(- calorie content of sugar that was fermented) + (calorie content of new alcohol)
This gives us the total change in calories created by fermentation.