hey everybody dr. Oh we talked about using heat before so we're gonna start by talking about cold just so you know this is kind of a miscellaneous video I'm going to cover cold pressure and desiccation or drying all in this video so they're all important but I didn't want to make several videos for each one so cold let's talk about refrigeration versus freezing freezing so refrigeration will work it inhibits metabolism doesn't kill organisms so the key word there is that low temperature like refrigeration has a bacteriostatic effect it'll keep microbes from growing or slow them from growing but it will not actually kill them so it's bacteriostatic not bacterial seidel now freezing if you get below minus 2 degrees Celsius or centigrade can actually kill some microbes but not all there are psycrow philic organisms actually love this temperature so we'll cover that in a different video but refrigeration is great at slowing microbes down by inhibiting their metabolism if you want to stop their metabolism of almost all organisms and kill some then you'd use freezing so you can even have ultra low temperature freezing though so you can you can there are freezers full of dry ice that can maintain things at negative 70 degrees or here I have a picture of using liquid nitrogen these tanks are going to maintain a temperature of a hundred and M sorry minus 196 degrees Celsius there so that's how we use cold to control microbes next we have pressure so you may not have heard about this much but it is being used in food I've seen it primarily used like in some like in deli meats and precooked meats but juices are where I've seen it used the most so high pressure can denature proteins and cause you know some cells to rupture just like using heat would but the advantage of using high pressure is that it appears to maintain the quality and shelf life of the food better than using heat at least in those situations the examples I gave you so it can kill if you want to say he can kill viruses parasites mold fungi all sorts of things so what's crazy about this is the amount of pressure it takes so it says there are a hundred to eight hundred that would be a mega pascals so the other term for using pressure to control microbial growth is Pascal ization instead of pasteurization I'll I'll put that on the screen but a hundred to eight megapascal sir he is a huge number right the atmospheric pressure at sea level is 0.1 of mega Pascal in that ballpark so I did the math 800 mega Pascal's would be over a hundred and sixteen thousand pounds per square inch think about like your car tire with 30 pounds per square inch or even our autoclave only uses 15 pounds per square inch so we're talking about massive amounts of pressure the same issues with lots of other much microbial control techniques it can kill the living vegetative cells good or well but it has a hard time with the endless pores just like most of the other ones so that's how you might use pressure or Pascal ization next we have desiccation or drying so the key here is that microbes and all living things can't have a metabolism without without water right so so drying just sucks the moisture sucks the water out of things and that slows the metabolism so the examples you have here would be like drying fruits like like making raisins or jerky those kind of things so pretty simple that be things like Sun drying it's far from making things sterile you're definitely not going to kill all the food spoilage organisms or the or the pathogens but it's better than nothing for sure the next thing you can do is just actually remove the moisture I mean you keep the liquid around but you remove the moisture or liquid from individual cells by adding salt or sugar is what that should say there so you reduce the water activity so you see a picture here this is this is a red blood cell but um if you put if you if you put a cell in the hypertonic environment it sucks all the moisture out of the cell and that slows or stops its metabolism so this would be like the you know the reason you know honey is almost all sucrose the reason that that that's why living cells don't live in it right there are still spores though which is why children under one shouldn't shouldn't consume honey so you add sugar to things like vegetables and making jams and jellies you add salt to like your canned goods so you're creating a hypotonic environment sucking the moisture out of these cells now the term which I do want you to know it's called plasmolysis so if you remove the moisture remove the water from a living cell it's called plasmolysis so that's going to be creating a hypertonic environment think about your canned goods from the grocery store mainly and then the last example here would be like awful ization so this is something that we don't doing the lab but we do get a lot of our supplies have have been layoffs allies like the DNA we use in our DNA based labs has been laughs alized and so I have all the bacteria we work with we buy lyophilized samples that we that we keep in our refrigerator and then we rehydrate them and warm them up and we want to use them so laughs Allah zation think like a rapid freeze drying under a vacuum so you're gonna you're gonna freeze dry these super quickly they call it snap freezing or snap snap frozen but then under a vacuum which is going to remove all the moisture so you basically you frozen this while you've dried it and that's what my authorization is okay so those are three more methods of microbial control using using pressure I don't remember the other one I did so cold pressure and removing water all right I hope this helps have a wonderful day be blessed