Frozen milk

I recently thawed some bm and my LO would not eat it. When I first started freezing it we thawed some and he ate it fine this is the first time I needed to since then, he is almost 4 months. We have had some issues with him refusing the bottle so is it possible that the milk taste different and that's why he will not eat it? There is no reason it should be bad. Would it still be ok to donate it if he will not take it? I have over 600 oz, I don't think I have it in me to throw it away! I planned to use it to make baby food once he starts solids. How do I know if he is just refusing or if it is spoiled.