Does freezing microorganisms such as probiotics kill them?

Question

Does freezing microorganisms such as probiotics kill them? If not, what is the process that allows them to "come back to life" after the temperatures are increased? As an example, lets say you freeze a yogurt (whether it be Greek, Australian, Turkish, Indian, Russian, European, or Western) and eat it while frozen. Would the probiotics in the yogurt "come back to life" and be beneficial? Specifically, I am referring to freezing refrigerated yogurts, and not products that are sold as "frozen yogurts". What's the biological basis for this?

Answer 1

Hi! so the good majority of microbes (spore forming bacteria can! Resilient buddies!) are not going to survive freezing. When frozen, the water in and around the cell transforms into ice crystals leading to 1) dehydration due to decrease in available water and 2) destruction of the cell membrane due to the jagged crystal edges. If you freeze your yogurt the liquid portion would form ice crystals leading your yummy probiotics to be turned to shreds. However while most microbes would not survive this, spore forming bacteria can. These bacteria can withstand extremes in temperature and moisture level through transforming from a vegetative state to a sporulating state (no growth, low moisture content). These bad boys will be able to be thrown in the freezer, survive and "come back to life" once warmed to a satisfactory temperature. As far as probiotics go, you are in luck! spore forming probiotics are on the rise due to their ability to survive past the low pH of the stomach to make it to the mother land in the gut.