Hello I was just wondering if you can mix expr...

Hello I was just wondering if you can mix expressed milk? I have expressed twice today and have chilled both in the back of the fridge (I can only seem to get 60ml or so at a time). I cant seem to find any solid info on mixing the two together, some websites say its fine if they are both chilled but the more trustworthy (like Australian Breast Feeding Assc) websites don't have any info on it so it leaves me wondering if it is safe? Thank you for your time. :D