Chemical Changes in Fats & Oils: Lipid Oxidation

[@mostafamohamed3485]

Very helpful and excellent explain thank you

[@parthasarathyarumugam1181]

Thank you, nice presentation

[@lusanivhangani2768]

Glad you liked it! Thank you.

[@realchristopher4334]

Goodness me! I do not understand how the heck I can understand this! I am not even a chemist! The best explanation of a highly complicated or sophisticated concept! Visual aid helps me a lot but this visual aid is very clear and very detailed!

[@lusanivhangani2768]

Hello Real Christopher. I am glad you found the content of this video simple to understand. Thank you for the positive comment, it gave me a boost to do more🤗.

[@realchristopher4334]

​@@lusanivhangani2768 Ah ha! Makes sense now! I connected the dots! You are a scientist of Cape Peninsula University of Technology! Not some "tuition teacher" online. Many of those "teachers" complicate what is already complicated. Some of them oversimplify things to the extent that data becomes inaccurate or outright wrong. Simplify things but not any simpler.

[@DevastotraPoddar]

Very Nice explanation 👌 Short & Crisp..

[@lusanivhangani2768]

Thank you.

[@AlexD-ng2pn]

Great explanation. Thank you Dr.Vhangani. Could you explain how antioxidants play their role in lipid oxidation process?

[@lusanivhangani2768]

Good day Alex, Thank you for engaging with my content. In terms of your question, I usually use the Farmer's hydroperoxide mechanism to explain how antioxidant function to inhibit/prevent oxidation. Lets start at initiation - metal initiators that abstract the hydrogen can be chelated using antioxidants such as EDTA, prolonging the induction period. In the propagation stage, oxygen scavengers can react with oxygen . Free radical scavengers can donate hydrogen to alkyl, peroxyl or alkoxy radicals, to prevent them from stealing another Hydrogen from a new fatty acids

[@mostafamohamed3485]

Thank you very much

[@ukaszdebiec9564]

Thank you for your very nice video! I have one question - I heared once from food-production profesor that people can't smell oxidation of vegetable oils as they can do with animal fats. I'm wondering what he meant, from what i understand it might be, but you told that primary oxidation products can't be perceived. So maybe vegetable oils secondary oxidation products are mostly some products that also cant be detected easily by human and animals turn into something else like more alcohol less polymers or something like that? Or maybe its not about fats but other things that are in that products like amins because they are not "clear". Can you confirm / explain shortly that ? Thanks! BTW. My own experience from kitchen confirms that for example sunflower oil which is more unstaturated and hence unstable can stay for 1-2 years and you dont see that it changed, while egg fish or butter or anything else you can easily see and smell when its not fresh.

[@lusanivhangani2768]

Thank you for engaging with my content and for the question. In my own experience, I have come across a vegetable oil (sunflower) that oxidised, and produced an off flavour. However, this oil I had extracted (crude) myself ,and left at room temperature for 3 - 5 years. This experiment was for educational purpose for my students. The oil became rancid and started forming gums around the opening of the bottle (PET). I have never experienced any rancidity of animal fat, in the period of normal use. It would be interesting to get hold of the literature or research the Professor was using, it might be that that is another lipid phenomenon. But I surely stand by the notion of saturated fats are less prone to oxidation than their unsaturated counterparts'. In terms of your observations, just note that commercially sorls sunflower oil is refined first, and then added with the antioxidant TBHQ. Moreover, you probably had it stored under proper conditions. Fish on the other hand oxidises much quicker. Butter undergoes hydrolysis easily than oxidation, and whatever off-flavours you perceived were related to hydrolytic rancidity. There is another type of oxidation "photooxidation" that is seldom talked about, and it affects a lot of dairy products during display in retail shops. In the case of products that contain other food components other than just lipids, they would also accelerate oxidation due to presence of these other components. Lipid degradation is such a complex phenomenon. I hope I shed some light, but i have different experience and opinion from the Professor

[@MySelf-kz3md]

I like those stupid examples 😄. In fact those examples helps me to understand the concept. 😉 Thank you Ma'am 🤗

[@lusanivhangani2768]

Thank you too. I will keep "the stupid examples"

[@ivyvera3607]

Thank you so much for this video!! It was really helpful!

[@lusanivhangani2768]

I'm glad it was helpful. Thanks for watching.

[@hakimbourouba6155]

Thank uuuu 🌺

[@ukaszdebiec9564]

Oh i was also wondering that if oxidation and degradation of fats need Oxygen to happen, than vaccum-packaging of products like meats or someything and also keeping oils in glass bottles that are 100% full (no much oxygen inside) should stop this reaction and preserve this products. Or are there some other possibility to degradate fats without oxygen ?

[@lusanivhangani2768]

Thank you for engaging with my content. Regarding your question, the oxygen appears in the second step of the induction stage. Therefore in this case, without it oxidation will not proceed under the conditions of vacuum and maybe Modified and Controlled Atmospheric Packaging that you alluded to. But lets not forget in cases where the enzyme lipoxidase (lipoxygenase) is present and active in the product, it catalyses the reaction of an unsaturated fatty acid to directly form lipidhydroperoxides without the aid of oxygen. The formed peroxides will then further break down to continue the reaction provided the are initiators such as metals or higher temperature. So to answer your question directly, yes lipids can become rancid without the oxygen only if the enzyme lipoxidase is present.

[@secretstone8279]

Hi, thanks for the great video! I really enjoy it! I would like to ask about the measurement of secondary oxidation products. Commonly, we are using the P-ANV test to measure it. We were thaught that the P-ANV will be in increasing trend over a period of storage time, however, when we measuring the P-ANV in the oils samples, we found out that there were times where we observed the month 3 samples has lower P-ANV value than month 1 samples. Just wondering how could this happened? What is the best explanation on this phenomenon? Thanks!

[@lusanivhangani2768]

Thank you for taking your time to watch my videos, and giving feedback. Just a few questions: what type of oils did you work with? Were your storage conditions real time or accelerated? Reason being at high temperatures oils oxidise faster and form aldehydes and ketones which are then measured using P-anisidine value. However, continued storage under those conditions may lead to the next step of polymerisation of oxidation products (aldehydes and ketones) leading to increased viscosity (gummy/sticky). It might happen that the newly formed polymers do not represent the structure of an aldehyde or ketone, thus not being absorbed at 350 nm. Remember polymerisation is also a process, therefore, AV can reduce before the visual effects are perceived.

[@manoulaboub6380]

Thank you very much, It's very helpful 🥺❤

[@lusanivhangani2768]

You are welcome

[@nommoiyu3258]

Thank you for describing soo briefly. I have some questions Do lipid oxidation occur on esters of Fatty acid like tri, di, monoglycerides or on free fatty acid or on both ? And what's the relation between acid value and peroxide value of fat, is there a mathmetical relation ? Thank you ..

[@lusanivhangani2768]

Good day. Apologies for a late reply. Notification for this comment passed me. Yes, lipid oxidation will take place in any lipid (fatty acid) whether esterified or free. The acid value measures the fatty acids that broke/separated from the ester bond to form what we call (free fatty acids), the main reaction is on the ester bond, on the other hand, peroxide value is based on oxidation that took place on the actual hydrocarbon where ROOH was formed on the chain. These two are in directly related, since if a free fatty acid is formed, it's affinity is on the interface of the oil and air, thereby resulting in reduced surface tension, allowing oxygen to enter the oil and then cause oxidation, which will form ROOH (peroxides). The only mathematical relation I can say (based on my opinion) will be calculating the rate of peroxide formation between a pure lipid vs a lipid that has been hydrolysed to form free fatty acid.

[@SelamWorku-ro7jm]

❤

[@yallugly363]

Hello! Can I ask what will happen to the lipid’s properties if there was a simple chemical composition?

[@lusanivhangani2768]

Hi There. I'm assuming when you say "simple chemical composition" you referring to if the fatty acids were all saturated and maybe short chains. The same chemical reaction (lipid oxidation) will take place, the difference will be the onset of the reaction will be delayed for saturated fatty acids since it is takes more energy to abstract that hydrogen form saturated carbons. in some cases extreme conditions such as frying the oil/fat at high temperature repeatedly will accelerate the reaction. I hope this makes sense

[@yallugly363]

@@lusanivhangani2768 Thanks you very much❤️

[@yallugly363]

Oh wait, i meant to say simple chemical change not chemical compositin

[@lusanivhangani2768]

@@yallugly363 I'm glad i could be of help to you.

[@lusanivhangani2768]

@@yallugly363 Remember the extent of the chemical change depends on the extent on the factors, for instance the more the double bonds, the higher the temperature, the more the initiators such as sunlight and metals, the heightened the oxidation. Same applies when the fat/oil is stored at lower temperatures away rom direct sunlight, the lesser the change.