top of page
  • njikomes

Food Purity & Quality, Cooking Oils (Avocado, Olive, Vegetable Oil), Fruits & Vegetables, Nutrition


Full auto-generated transcript below. Beware of typos & mistranslations!

Nick Jikomes

The scientist and what your lab studies?


Selina Wang 6:11

Sure, I guess, depending on how, when we're talking about so I actually came to University of California in Davis for graduate school. And I study in the chemistry department doing physical organic chemistry work. And which is just another way to say that is using computational modeling to understand reaction mechanisms. And I loved it. I did that for five years. And towards the end of my PhD career, I started to think about what I wanted to do as a career. And a lot of people that was studying some similar to what I was doing would end up being a pharmaceutical company can study drug designs and other things. But somehow I always love foods, and I wanted to connect my knowledge and my passion together. So I decided to do a postdoc at the same university and in a different department, this time at department Food Science and Technology, which I didn't know even existed when I was an undergrad because not every university have such department. But luckily UC Davis has one of the best ones in the world. So I basically started learning about food science for chemistry. And at that time, it just so happened, California started investing, olive oil, olive oil crops for oil production. And given our university is big on agriculture, and there was a need to support this kind of work. And so they looked at me they say you're a chemist, right? And I say yes. And they said, great, you can study olive oil. And they didn't know that I was a physical organic chemist now exactly an analytical chemists, which is what they were thinking of. But you know, one can learn. So basically, we started learning how to study oil quality and purity. And that was a 2008. And that basically changed the trajectory of my my research interests and career pathway because, you know, started as a physical organic chemists who study very fundamental science to basically changing transitioning to more of a local camp chemists study very, very practical and applied work. And so several years later, I now is a faculty in the same department that I moved to. So that's all to say, I never left UC Davis after I came here for graduate school, I just moved to a different department, but what I'm doing now is far, far from far, far away from what I did for my PhD.


Nick Jikomes 9:42

So basically, you started out as like a hardcore, basic scientist, physical chemist. And, you know, through the path that you took, you became a food scientist using analytical chemistry and techniques from chemistry to actually understand food and food quality and things like that. Yes, yeah, yeah. And what, you know, what exactly is food quality? And how is it measured?


Selina Wang 10:09

That is a great question. Of course, a really depending on the crop, so the particular food we're talking about, right? And also, depending on where you are right, you know, because depending on what you can afford, you know, that's also something to take into consideration, right? And so it's hard to say, these are the standard parameters that we look for, for all the food because it really depends what we're talking about. Right. So if we go back to the olive oil example, when I, when we started, we look at parameters that's for quality, it's activation, right? Oxidation, because oil is mostly fats, and fats are, they're going to oxidize just with time, right. So obviously, there are factors such as light or temperature that will speed up the oxidation process, but it will just happen with time, even if you store it properly. So oxidation is something that we know that it will deteriorate this product, right. So that so for olive oil, for example, that will be a quality parameters. Now with other foods, let's say tomatoes, for example. Tomatoes, people want freshness, people want sweet people want next texture. So in those cases, organic acids or sugars may be part of the quality parameter. So it really depending on what consumers are looking for. And also keeping in mind what makes sense, right? You know, we don't want to generate so much food waste, because we set the bar of quality at a certain level. And that is sometimes unnecessary.


Nick Jikomes 12:14

I see so so when we think about food being fresh or food going bad. At a very basic level, what that means is chemistry has taken place, the chemical, the chemicals that are inside of a food, whether it's olive oil, or anything else, they've been changed in some way. And the way they change is going to depend on the food and the environment that it's embedded in. So you said in the case of olive oils, and probably other similar oils, are a really good measure of whether or not it's fresh, or it's gone bad is oxidation, because these oils are prone to be to being oxidized. And so what what causes this oxidation to happen as the presence of oxygen is heat? And, you know, why does it matter? Does it change the taste of the food? Is it purely like an aesthetic thing? Or does it also change other aspects of the chemistry in ways that can impact human health?


Selina Wang 13:08

Yeah, so oil is mostly made up triacylglycerols. So when oxidations occurred, these triacylglycerol will start breaking down, and then they will make compounds like peroxides. And peroxide itself doesn't have tastes or smells. So it's not something that we will experience. But you can further break down to small aldehydes. And those aldehydes actually have unpleasant smells such as rancidity. So if you have ever has stale walnuts, and you know, nuts tend to oxidize pretty quickly. So it has a smell that's almost kind of plasticky, and that is a smell of rancidity. Now people debate about the actual health risks of rancidity. But there hasn't been a lot of concrete data on that. And of course, you know, we're always careful about the concentration too, right? All of us, at some point have had rancid food. It's a natural part of living and our bodies also oxidizing, right? I mean, it's part of being alive. Yeah. And then yes, so, basically these fats, they will acidized in presence of oxygen. And this is why so for example, if you buy a bottle of olive oil and you want to open it, the oil will start deteriorating because once you open it, the oxygen can get into the headspace of the bottle so not into the oil but just in the in the empty part of the bottle in the headspace. And that or interact with the oil in the bottle and then speed up oxidation. So the oil that is completely closed has never been opened will have a longer shelf life compared to the oil once it's open. And this is always why when I talk with consumers about purchasing olive oil or any oil, in general is that don't buy a huge bottle if you live by yourself, and you will not be able to come soon the oil in six months, because once you open it, you're going to start axes, I think the oil right. And as you consume more and more oil, there's more and more empty space in the bottle. Yes. So then there's more and more oxygen that can get into the empty space, it will speed up the oxidation.


Nick Jikomes 15:51

So as you if you buy a bottle of olive oil, as soon as you open it, oxygen can get in and that oxidation of that oil will start to happen. And the oil will start to go bad as you consume more and more of the oil and it gets lower in the bottle, there's more space for more oxygen to get in. So the rate of oxidation increases as you go from the newly opened bottle to the nearly empty bottle.


Selina Wang 16:13

Exactly. And this is why I am a big proponent of the back the back in box. packaging for olive oil, which we've seen for wine, the box wine. People sometimes associate that with low quality, or using the word quality here, for one, but we know that's not true. But the if you had actually had box wine, a lot of them are actually quite good. But that that packaging system, right does not allow the oxygen to get in when you dispense with the liquid or the oil. So that's actually one of the best packaging system for oil and for for wine too. But the challenge with that is twofold. One is consumer perception consumer do not tend don't tend to associate that with high quality product, they still think glass is the way to go. And second is it's it's expensive for for processors to do.


Nick Jikomes 17:26

I see. And but you know, so going going back to the just the oxidation and rancidity question. When oils become oxidized, they go rancid chemically, what that means is the oils change and you start to get things like peroxides and aldehydes. Aesthetically, what's changing or on the sensory side is you can taste and smell the difference. Your olive oil will stop smelling like fresh olive oil, it'll start smelling bad, basically. And it will certainly taste rancid. And, you know, in terms of the health effects of this, you know, there's just two things I want to touch on here. You know, one, you know, our sensory systems evolved for a reason, right there, we're meant to be attracted to things that taste good. We're meant to avoid things that taste bad. And so you know, evolution has embedded in us the you know, the avoidance of things that taste rancid, because that can indicate either, you know, the presence of microbes or the presence of things like aldehydes, which we're probably not supposed to ingest. And so even though you said it hasn't been well studied whether these aldehydes and this rancid oil has health effects, it would be absolutely shocking to me if that wasn't bad for you, I mean, aldehydes you know, they're one of the primary things in cigarette smoke, that's bad for you, we know aldehydes are just bad. And so it sounds like you know, oxidized oil is not good. Is that a reasonable conclusion or you know, to draw.


Selina Wang 18:48

I would agree with that, although with a caveat that in a fresh, very fresh, very, very high quality extra virgin olive oil. It also has aldehydes because depending on what aldehydes we're talking about, they can actually be very pleasant aromas such as kind of grassy and green apple stone fruit, the kind of pleasant, volatile that one will want to experience from a very fresh extra virgin olive oil. Now and then the really interesting part of all this and it's complicated, the whole you know, the vault hose in includes is quite complicated. And the reason for that is because these volatiles they can behave very differently in depending on the concentration at a low concentration that can be pleasant, whereas ln the same compound at a high concentration, it becomes unpleasant or completely there. front can have sensory experience. And also depending on the matrix, so if they are in a more oil base matrix or more water base matrix, and then they would have a different smell as well. So,


Nick Jikomes 20:16

yeah, so So you know, some aldehydes can smell present pleasant at a low concentration that actually smell unpleasant at a high concentration. And presumably, they can also have different physiological effects in a concentration dependent manner as well, that would, that would be my guess.


Selina Wang 20:31

Yeah, yeah. And it's not exactly an area that's easy to study. So, you know, I think we're still, that's not me, per se, but scientists are still trying to learn more about it.


Nick Jikomes 20:44

Okay. I want to talk more about olive oil. It sounds like that's, that's been a major area of study for you. So before we get into like quality and freshness stuff a little bit more and adulteration and things like that. Can you give us a little bit more just about olive oil? So you know, I use a lot of olive oil. I love Olive oil. There's all different types of olive oil. There's right there's extra virgin olive oil, there's filtered and cold pressed olive oil. There's all these all of these different types of virgin, extra virgin, all that stuff. What are the basic types of olive oil? And what are those things actually refer to?


Selina Wang 21:19

Yeah, I wish it's not so confusing and complicated. And this also kind of depends on where you live. So in the US, if we're very fortunate, I think you agree that we have access to high quality products. And when you say that you cook a lot with olive oil, I'm assuming you are talking about extra virgin olive oil. And extra virgin olive oil is basically mechanically pressed or centrifuged oil, meaning that you think about how orange juice is made. So I'll just walk you through the process really quickly for extra virgin olive oil. Basically, you you harvest fruits at proper time. So before they become overripe, you process the fruit at the optimum time. And you bring them to the mill within ideally 24 hours. Because if you wait for too long, then the fruits can start fermenting. Ideally, I think most processor will do it six hours even. So you want that time to be as short as possible, bring into the mail. And they basically they can go through a washing process, although some people skip that part if the fruits are pretty clean, and you will go into the pastures with the skin and then the pits so the entire olives will go into the crusher, and basically grind it up into more or less like a paste. And then the pace will go into this thing, which is called a multiplexer. multiplexer is basically a equipment that needs this pace for about 45 minutes or an hour depending on the processor. And what happened during this mobilization process is the small oil droplets start to coil lace and forming large oil droplets. And then that goes into the centrifuge where the oil filters out. And everything else goes the other way as our oil byproduct. And that oil is extra virgin olive oil. So basically, it's there's no heat, there's no chemicals added. It's very much like how you make it's just


Nick Jikomes 23:44

a physical mechanical process of basically squeezing the oil out.


Selina Wang 23:48

That's right, that's right. So so that's that's extra virgin olive oil. And you know, do you still see bottles that says cold press? Actually, there's I don't know anyone is pressing the oil in California and very few in in other places too. But consumers research have shown that people associate high quality olive oil with the word cold press. So even though most of the oil is SAP is things centrifuged out the word cold pressed remains to be some bottles and


Nick Jikomes 24:31

so essentially they're just spinning it around very fast to separate the oil. There's no cold pressing happening in the way that people normally imagine. So that's basically just a marketing labor.


Selina Wang 24:43

Yeah, and you know, I much prefer centrifuged oil than a pressed oil because with a pressing it was actually very, very hard to make good oil because it's impossible to make those things clean to clean the process wearing this centrifuge. It's a much cleaner system.


Nick Jikomes 25:02

Okay, so you you sounds like you personally don't care about whether something's labeled cold pressed or not.


Selina Wang 25:08

Now, I, yeah.


Nick Jikomes 25:11

And what's so what's difference between virgin and extra virgin?


Selina Wang 25:16

Yeah, so that's in the US. Virgin. I don't really see any oil with Virgin on labels,


Nick Jikomes 25:27

you eat us pretty much all extra virgin olive oil.


Selina Wang 25:30

Yeah, I don't think in the US there's a market for virgin olive oil. But in terms of definition, basically olive oil or extra virgin olive oil is an olive oil that has no sensory defects. And virgin olive oil is an olive oil is an olive oil that can have a little bit of sensory effect. So olive oil is one of those very, very few food products that actually has sensory in the quality standards. You know, earlier, we talked about what is food quality, right? Most of the parameters are based on physical or chemical. Olive oil is very, very unique. In that sense. There's a physical, there's chemical, and then there's the sensory in the official standards. And the difference. Sure, there's a little bit of difference in there in terms of the chemistry standards between virgin and extra virgin. But mainly, it's the sensory, small sensory defect that is what makes an oil to be virgin instead of extra virgin.


Nick Jikomes 26:45

And so that just means the difference is really just fairly minor differences in the way they taste and smell. Yeah, is actually interesting. Okay, so we're now we know what extra virgin olive oil is. That's the thing you'll run into most of the time at at the store, when you buy it, at least in the United States. It's been, it's just olive oil that's been physically separated from from the rest of the stuff from the olives that it's derived from. But when I walked to the store, and I go buy olive oil, there's many different brands out there. And sometimes the prices vary a lot. Some of it's quite a bit more expensive than other stuff. So when we think about quality, not just in terms of the composition, or the freshness of the original material. Is there anything else to quality that we have to think about, like purity and whether or not it's been contaminated with other things in the process of actually making it?


Selina Wang 27:47

Yeah, yeah, there's a lot to cover there. Before we go into that they'll do you want to talk about refined olive oil? Oh, yeah, let's do that. Because that's part of the reason do you think that may cause the price differences to so refined olive oil is actually quite different from extra virgin olive oil as because he includes a completely separate processing step that is refining, soy, canola, soybean, vegetable oil, all those oils, without seeing on the labels, they're all refined, which is what gives them the light, pale, almost trans, transparent color, right. So where Extra Virgin Olive Oil still has the green hue and basically an oil that is what they call a lamb panty, which it means not fit for human consumption. And that can be oil that's made from really, really bad quality fruits. So the fruit that either has significant pest issues, or fruits that are so overripe that there's all kinds of sensory defects like fusty musty that come from fermentation of the fruit and and then they will go through the process we talked about for extra virgin right. And then after that process, they realized this oil is not extra virgin or Virgin. So you cannot sell it right. So, you will take this oil to refining to a refinery. And what happened during refinery is that they would basically use heat and sound chemicals to remove all the sensory defects and they will add something to neutralize the fatty acids in there so that it doesn't, it basically lowers the free fatty acidity and the you removes all the peroxide that we talked about from oxidation. So basically Eat the result is a very mild bland oil. And that is, that is what refined olive oil is. Now if you go to the supermarket and you buy in the US anyway, there's pure olive oil. And there's also extra light olive oil. And that is basically most consists of most refined olive oil and then you can tell by their color.


Nick Jikomes 30:29

I see. So if I'm hearing you correctly, when a food oil or cooking oil, whether it's olive oil or something else is refined, whether or not it says that on the bottle or not. When it's refined that basically means it was subjected to additional physical and chemical processing other than the the original process we talked about for something like extra virgin olive oil. And the reason it needed to be subjected to that additional processing that refinement is because the starting material was considered unfit for human consumption. Correct. So anytime an oil is refined, it's an oil that was processed physically and chemically from something that is considered unfit to put inside your body.


Selina Wang 31:16

Yes, or no one will want to eat it. Yeah.


Nick Jikomes 31:19

Okay. And so by default, that's a lot of vegetable oils. Yeah. And some olive oil.


Selina Wang 31:27

Yeah, yeah. So during this process, the negative sensory, the counter chemical compounds that are responsible for the negative sensory attributes are removed. But in the case of olive oil, the pigments are also removed. Right. So that's why it's not green anymore after it's refined, along with the antioxidants. So the natural phenolics they're also removed.


Nick Jikomes 31:55

So you're moving, you're moving bad things as well as good things. Yeah, that's right. Well, so here's, here's the next question I have now, in the process of refining a cooking oil, you have to subject the starting material to heat and other forms of chemical treatment, wouldn't that inevitably lead to some oxidation of the actual oil that's going to remain in there?


Selina Wang 32:22

So the process for refining has been worked out for a long, long time. And I think they're able to control the process where he based it basically very little natural oxidation is going to happen. So. So I, I, you know, because if you analyze the oil, after it's refined, it doesn't have really the oxidation markers that we usually look for there.


Nick Jikomes 33:02

Okay, so those things have been measured and fresh, refined oils. And when you initially crack open the bottle, there's no evidence of oxidized fats in there, right? I see. Okay, so So we did some background on there in terms of olive oil, and some other stuff about other oils. Now, let's talk about some of the work that you've done actually looking at olive oils that you've tested for things like purity and freshness, out in the wild, so to speak. So I believe you've done some studies where you've, you know, you've gone out and I think purchase some olive oils from different brands and things like that, and looked at, you know, whether the olive oil really is olive oil, and whether it has the properties that you would expect it to have based on how it's labeled. Can you can you tell us a little bit about that work?


Selina Wang 33:48

Yeah, so it was in 2008. And that was my postdoc work, when I really was just starting to learn about olive oil quality and purity. And at that time, there were scientists who work in Australia that they've been studying this for longer than we have. So we've learned how to do some of these chemical analysis from them. And I basically went to supermarkets all over California. And just like any consumer would, you know, stood in front of the aisle completely feel overwhelmed and confused and don't know what to buy. And but in this case, I just bought every single one of them and in three bottles or more, because we want to have duplicate samples, and or triplicate samples, and we brought them to the lab, we did quality analysis, which is mostly basically tell us if this oil is fresh, or it's oxidized. We also did purity analysis, which in this case, We follow the official methods for oil well, they're basically looking at their fatty acid profile, because fatty acids are the high the what's in the oil, basically. And each different oil, so vegetable oil, soybean oil, canola oil, or the different oil, they have different fatty acid profile. So by looking at that, you can see if he matches with olive oil, or a match is more like canola oil. And then in addition to that, we also look at their sterols. So cholesterol is the most common sterile that people know. But there's also many other plant sterols that's present. So similarly different seed oil or other type of oil have different sterols, composition and poor file. So comparing the one that is should be What should it look like for olive oil to canola soybean, you can see if this oil is actually made from olives, or it's adulterated with other oil. So those two are the primary primary methods that we use to analyze purity. And then we mentioned that sensory is part of the official standards for olive oil. So we also send samples to a train panel. So for this is not like you know what asked consumers and what they think about this oil? Do they like it? Or do they not like it, this is a trend sensory panel, where they basically calibrate themselves to be like analytical instruments. So they've been trained on given, say, rancidity, which is the most common one of the most common defects for olive oil, they are able to say on that zero to 10 scale, how rancid it is. And the panel is calibrated to the same degree, basically, and it requires at least a panelist to to participate. So we that's how we did the work. So we have quality, purity, and then from the lab and then work together with a sensory panel. And that work. We published it in 2010. And that's, you know, kind of started the whole thing about, I guess, raising people's awareness about food quality and potential fraud and these high value products.


Nick Jikomes 37:32

Yeah. So you tested all the products, and I'm guessing you did not find. I'm guessing you found some unsettling results.


Selina Wang 37:43

Yeah, my favorite one. So it's favorite, because it's shock value. It was actually the one so we did that, you know, study that we mentioned. I went to the supermarket. And then after that, I then work with the University dining services to look at the quality and purity of the food service oils. So the ones that restaurants purchase the one schools cafeteria or hospital cafeterias purchase from, right? Usually, the quality or purity from foodservice is worse than what we get from retailers that


Nick Jikomes 38:32

so basically places like schools and hospitals or things like that tend to use the lowest quality oils even lower than what a regular person is likely to purchase at the store.


Selina Wang 38:42

It's truly unfortunate. But it's a economic concern. Right.


Nick Jikomes 38:47

So I mean, so that would imply I mean, if this is an economic thing, right, is low quality highly correlated with the price.


Selina Wang 38:56

Now, always, not always, but I think it's because there's some people are just really, really greedy. So and we're seeing that in in different cases. But what will go back to that in a second. So the one sample we got through food service was this oil that was neon green, it almost looked like it will glow in the dark. And the green was hard to describe. You know, fresh olive oil will be green, but not that can be green. So when we got this oil, I just, I cannot wait to bring it to the lab. I just I wanted to learn everything about this oil.


Nick Jikomes 39:45

So just by looking at it, you were like What the hell is this? Exactly?


Selina Wang 39:50

Yeah. And so it turned out it was 70%, canola and 30 percent olive oil. But that is not the worst part. The worst part was he had artificial copper chlorophyll. So it's different from the actual natural chlorophyll that you will see in olive oil that makes extra virgin olive oil green. It was an artificial way added green color. So so you know it's it's the gold.


Nick Jikomes 40:27

So the manufacturer 70% canola oil 30% olive oil, and it's got this adulterant in it. So basically whoever manufactured this took something that was mostly canola oil, added an artificial version of chlorophyll to make it look green, which turned it into some kind of like, Teenage Mutant Ninja Turtle ooze color by your description, and then labeled it and sold it as olive oil. Yeah. Okay, yeah. Well, I mean, I think we'll get to questions about regulation later. But give us some there. I mean, that's one striking example. Can you give us some statistics here? So how many different types of olive oil? Did you look at? In the study? What percentage of them had a significant level of impurity? What percentage of them had a significant level of adulterants? Yeah, so


Selina Wang 41:13

I would say so first of all, this study was done 15 years ago, right. It's been 13 years since those reports are published, although I still get emails weekly from people who just read the report and and asked me what kind of what brand of olive oil issue by right. But I will say that the quality and purity of the olive oil available in the US has increased has gone up significantly. And actually, it's hard now. So I've been asked if I should repeat the study, because I think it's frustrating for some companies that people keep bringing up this study that was done 15 years ago, right. So there's some interest to do basically revisit and see if we will get the same results. My sense is not we will not.


Nick Jikomes 42:17

But but but you know, give us some guideposts here, like, you know, if you did this study back in, you know, 2010, it was published, if 10% of the samples had impurities in them, and we've gotten better from there. That's a very different story than if 60% of the samples in your original study had impurities, and we got a little bit better since then. So in the first study, knowing that this is a few years old, what percentage of samples had significant impurities or adulterants added to them? 50% 80% 5%?


Selina Wang 42:48

Yeah, no, I will say so in the report, we said about 68%. of imported, so any oil that did not were not made in the US did not meat, the USDA quality standards, meaning that they may be pure, but they were oxidized. And, and in terms of the oil that were not pure, it was definitely lower than the net percentage


Nick Jikomes 43:19

I see. So another way of saying that is at the time of the study around 2010, almost seven and 10 olive oil samples had either gone bad had some level of oxidation and or contained adulterants other types of oil inside of them. Yes,


Selina Wang 43:37

and I will say add to that, it's hard to use price as a quality indicator because there's a lot of times an oil that is actually really good. And, and that's why they were at the higher they were basically marked at a higher price point. But they don't sell right so they sit on the shelf at a grocery store for a long time. And the product sits there for six months, nine months. And it's oxidizing with all the light at the from the store. And also a lot of times they're not in an aisle that's very cool. So the richer the light is oxidizing the oil as they sit on a shelf. This is one of the reasons that I think that the oils that are higher in price sometimes do do not do well. And in you know


Nick Jikomes 44:43

it's not that it was a poor quality product when it was made. It's that the high price means people don't buy it for a long time and then sitting on the shelf is really the issue.


Selina Wang 44:53

Yeah, and the same the same reason I think contribute to a higher percentage of imported oil to be lower in quality compared to domestic oils? Because


Nick Jikomes 45:06

it takes extra time to get over here. Right? Okay, so So if you were to create a rubric for someone for how they should still go to the store and select which type if they want extra virgin olive oil, you know, what would you say it sounds like you would say, get something that's not imported, get something that is, what would you say?


Selina Wang 45:27

I will say freshness is key. So I will look for an oil that is made in the most recent harvest. Right? So if you choose to buy from California, you would look for harvest, and were in June now have to 2023. So your most recent harvest will be the fall of 2022. So that will be the most recent harvest?


Nick Jikomes 45:57

And is that printed, always printed on the label? Now always. So


Selina Wang 46:00

this is the tricky part, I think more and more producers. When 1015 years ago, very few, maybe one or two companies were doing that. But more and more people are realizing the importance of that information for consumers. So I would look for the most harvest the most recent harvest day. But also if the bottles didn't have it, you know, I kind of feel like well, maybe they don't want me to know. So that's fine. Yeah. So so that is most important to me, I actually buy oil from all different countries. I enjoyed the diversity in different origins, I also enjoy the diversity of different cultivars. So, you know, currently, the olive oil industry is kinda like, you go to a wine shop, and there's an aisle of red wine. And then there's the aisle of white wine, or maybe just one aisle that says wine, right. But in reality, right now you go to wine, there's different varieties wanting to choose from. So and it should be the same for olive oil, because they actually taste quite different there. And they may pair your cooking or baking differently too, because their sensory profile. So I, for me freshness is key. So I look for the most recent harvests, if it doesn't have that I'll go buy the best before date. So the oil that's as far away from its best before date, I also care about the price. So if it's a price that I can, I can buy other you know, different brands and that can give five bottles of those, you know that that's important to me too. And and then the packaging so I would avoid buying oil that's in plastic or clear plastic and usually most of oil now is in a dark green glass that's a good container or in a tin can. That's a good container and then we talked about back in the box that's a good container. But yeah, you I will enjoy I will avoid buying anything.


Nick Jikomes 48:20

So you want it to be in material that protects it from light


Selina Wang 48:25

right and then plastic is also porous so you will actually allow oxygen to get in as well.


Nick Jikomes 48:31

I see. Well so you said that you like the packaging where it's a bag in a box but isn't the bag made out of plastic?


Selina Wang 48:39

Yes, but there's actually a liner between the oil and the plastic.


Nick Jikomes 48:47

I see. Okay, so you want you want glass like tinted the tinted glass that filters out some of the light or you know metal metal a can or bag in a box that's better than clear glass and better than plastic bottle. Yes. Okay. So you want that for your container you want it to be as fresh as possible based on the harvest date or the sell by date anything else in terms of


Selina Wang 49:14

so size it right so if by it were you will be able to finish in three or four months


Nick Jikomes 49:22

ideally as small as reasonably possible


Selina Wang 49:25

as because the natural antioxidants will start decreasing right people buy olive oil for flavor and for health right so you the flavor it's at its best at the very beginning and the health benefits are also at its best at the very beginning. So you want to buy the bottle that you can finish consuming as early as possible.


Nick Jikomes 49:49

And how what are your feelings on the refined olive oil?


Selina Wang 49:54

I think there's a place for refined there you know for a while though the price of extraversion and refine, were very similar. And that is a little fact that was partially due to adulteration and other issues. I think that has improved quite a bit for olive oil. So if refined, olive oil is cheaper than extra virgin olive oil, which should be the case, then I think there's a place where we find olive oil as well.


Nick Jikomes 50:29

It's, you know, at the same time, though, based on what you told me about the refinement process, if the refined olive oil lacks the natural antioxidants that the unrefined olive oil has, wouldn't that mean that it's naturally going to go bad faster?


Selina Wang 50:42

So partially, yes, but also, the, the refined olive oil still has the same fatty acid profile as extra virgin olive oil, which means that it's mostly mono unsaturated fat, which is heart healthy, and it doesn't oxidize as fast as polyunsaturated fats. So buying olive oil itself still has a decent shelf life.


Nick Jikomes 51:17

I see. So olive oil in general, because it's high in monounsaturated fat and low and polyunsaturated fat has a shelf life that's longer than something that's mostly polyunsaturated fat.


Selina Wang 51:29

Yeah, so like macadamia oil.


Nick Jikomes 51:31

I see. Okay, so those are quality, you've got the harvest date, or the sell by date, you've got the type of container that it's in. And you've got the size of the bottle. Once you have these things at home, how do you store your olive oil, is it on the counter, is it in a cupboard is in the refrigerator?


Selina Wang 51:50

Yeah, so I would I store it in the cupboard. So you want to keep it away from light and heat, it's tempting to put it right next to the stove. But that is really really not a good place. And some people would store it in the fridge. But if you cook it every day, multiple times a day, that really is not a practical way of doing it because some part of oil could become cuckoo solidify. Right? Now, if you have fun. So for example, if you go to an olive oil tasting, which people do here in California, like they do for wine tasting, they go to an olive oil tasting, and you find this olive oil that you love, and you bought 10 bottles of it, and you bring them home, and there's no way you could finish using all 10 bottles, you may consider storing some of them in the freezer. And that is a way to preserve the antioxidants. That's


Nick Jikomes 52:57

so if you buy 10 bottles of something 10 small bottles, because we want to use it as quickly as possible. Once you open it. You can have the first one in the cupboard, and that's the one that you're using for your meal preparation. And then you will put the other nine in the freezer until it's time to use them.


Selina Wang 53:13

Yeah, and oil after you take the oil out of the freezer, you may never become fully liquids. But that's okay. That's just some waxes or that that is not a problem.


Nick Jikomes 53:25

I see. Okay. Interesting. Yeah, I think that's I mean, that's very useful. That's very useful. information. I think I didn't know most of this stuff until I looked at your work. What about other oils? I know that you've looked at other types of oil. And obviously, people use all different types oil, vegetable oils are very common. Avocado oil. There's many, many different types of vegetable oils. What can you say about some of these other oils? Or the you know, when you did the olive oil study or the problems that you saw with those olive oils that you purchased? Is that unique olive oils? Or is this more general issue?


Selina Wang 54:02

Yeah. So when we started studying olive oil, that was kind of considered to be the most high value product, right? So anytime there's a high value product, it's a risk for adulteration. And when I was working olive oil, I receive emails from people in the avocado oil industry from the hemp oil industry, where they have some concerns about quality and purity of the oils in their industry. So that's when I started considering taking on some of that work. We in in our lab, we take the approach that we're you know, we're not studying the health benefits, per se right. We look at the concentration of these natural antioxidants in there in terms of the chemical composition of in different oils. But we are not doing, say human clinical trials of these oils. But we what we do care about is the label should match with what is in the product. So, so that's where our work has been. And we have since expanded to avocado oil, which we have published a few papers on that. And I feel strongly about helping the industry to also develop standards, right, which is what's lacking for the avocado industry or the olive oil industry, we in 2014, at helped draft it. Along with other people in the industry, we drafted a standard for California, which is only applied to domestic producers in California, it's not a federal standards. So it's only a state standard. But that has helped a lot for the quality and purity of the products. So you know, having this kind of things I think helps the consumers to be more confident in the products they're purchasing. And we're hoping to do that for now avocado oil, but also other products in the future.


Nick Jikomes 56:21

And in some of the more recent studies that you've done avocado oil, what have been the results there in terms of purity and quality.


Selina Wang 56:27

Yeah, so in 2020, we published a paper basically about 80% of store bought avocado oil were either oxidized, or not pure. So


Nick Jikomes 56:42

very, a very similar result to the 2010 Olive Oil study.


Selina Wang 56:47

Very similar result, but there was in some cases. And I still remember that because I was sitting in the room that I'm in now with my graduate student, Hilary Green, who was the first author on all these work. And we're going through the data, and I saw something that I didn't see in all of my work with olive oil. That was I think there were some companies were just really taking advantage of the lack of standards and knowledge in avocado oil, because they were 100% soybean oil, people us extra virgin avocado oil.


Nick Jikomes 57:33

So they were literally just putting soybean oil in a bottle and calling it something else.


Selina Wang 57:38

Yeah, yeah. So in the case of all,


Nick Jikomes 57:42

which will who was that? That


Selina Wang 57:44

company actually is no longer in business. I think things are work.


Nick Jikomes 57:49

Who Who were they?


Selina Wang 57:53

I don't remember the name, but I can find out.


Nick Jikomes 57:57

Okay. Yeah, don't worry about okay, so they're no longer business. That's good. Okay, so what else? Did you


Selina Wang 58:04

not know me, but somebody did.


Nick Jikomes 58:08

So this does this, this is not a unique problem to 2010. And it's not a unique problem to olive oil.


Selina Wang 58:16

Yeah, so in olive oil, usually you see a blend of olive oil and something else. And in this case, it was 100% of the adulterant. And something that's refined being mislabeled as extra virgin, which has very different processing steps. So so that was very troubling. And also the price of that was very high. And we purchased it from one of the co op health stores in town. So people were paying for that product. I'm assuming we're trying not to buy soybean oil. I can, but likely, and in fact, after we publish the work, I receive a lot of emails from parents who wrote to me and said that they either they're their children's factors, or they're trying to avoid soybean oil for their children for a variety of reasons. And they feel completely helpless regarding what oil they should buy for because they were trying to use avocado oil in order cooking. And because my study which has a lot of fear in them, unfortunately,


Nick Jikomes 59:45

what what brands of avocado oil had the best purity and quality.


Selina Wang 59:51

So in our study, so I need to be very clear that we were not able to collect all the brands right So that's one of the things adding. In our first study in the paper, we didn't list the name of the brands. We had sample 12345.


Nick Jikomes 1:00:12

Bless. Yeah, we can talk about why that is.


Selina Wang 1:00:17

Yeah, but UC Davis follow up with a press release, where in that press release, they commented on the brands that were tested to be pure and not oxidized. And they it was Marianne, which we purchase from Costco. I think they still sell that at Costco, and chosen foods, which you can find that anywhere, basically.


Nick Jikomes 1:00:48

So that's one. That's one good one was that the only one,


Selina Wang 1:00:53

Marion and chosen foods?


Nick Jikomes 1:00:55

Those are like the two good ones that are easy to find? Very easy to find.


Selina Wang 1:00:59

There's other ones. But there are some that I know they're pure, but they happen to be oxidized, when we analyze them. And it could


Nick Jikomes 1:01:10

just be because they didn't sell in time they sit on the shelf, not necessarily because you know, the manufacturer did something wrong?


Selina Wang 1:01:17

Yeah. And there were after the study, some companies have reached out and asked, I, we published a lot numbers and all that information. So the company can trace the product. And they can see. And then some of them say, yeah, that that oil was old, we should have bought it off the shelf. So some company used it as a way to improve, which, you know,


Nick Jikomes 1:01:45

which, what were some brands that contain significant levels of adulterants?


Selina Wang 1:01:50

So I mentioned the company that is no longer in business. And


Nick Jikomes 1:01:59

I think it would be more useful for people to know the companies that are still in business.


Selina Wang 1:02:03

I know, I can't remember the name actually on top my head. I'm not trying to protect him, but I think I can't remember.


Nick Jikomes 1:02:12

Does that information anywhere? Now? Oh,


Selina Wang 1:02:19

yeah. This is this is


Nick Jikomes 1:02:21

boring. This is Yeah. But what's the point of doing this?


Selina Wang 1:02:25

This is part of the discussion that I think is worthwhile having, right? So as a researcher, right, so when we publish the paper, the goal of the work is to demonstrate the need for standards. Right. And we're not trying to police, the bad guys in the industry, right? We're developing chemical methods. And we are demonstrating there's a need for standards and our lab is working on developing these standards. And


Nick Jikomes 1:03:00

you're effectively not releasing data. I mean, that's what that's what we're talking about here. So you're you're not releasing data. What Yeah, correct. I mean, how do you how do you square that with your philosophy of science?


Selina Wang 1:03:18

So so we can debate about that? Right? Because Because if we did, you know, there's a lot of studies like this, people just list sample 12345. Right. I, there's so many studies like this. And but what I got was for the consumers, like you said, a lot of consumers feel the same way you did. Also, there's no way for them to know if the oil that was in them as a good brand. was either one either not included in the study, or they were bad, right? There's no way to tell that. Right. So I actually consulted this with university with a campus console. And this is this is what we decided on. I see. Yeah, it's


Nick Jikomes 1:04:18

any of these food companies contribute to the research funding and sort of the food science departments generally. So the


Selina Wang 1:04:25

first study we did it was funded by a company called de pasa. And we of course, we collected samples independently. And it turned out their oil was not one of the good ones that their oil was pure, but due to packaging their oil was when we analyzed it, it was not the results that they wanted to see. But they contribute Due to to some of the funding the first study, that was the only funding we receive. And the second study that we just released most recently, which was a very similar study, but this time we focus on the store brands, because I receive a lot of emails from consumers about what about all the store brands, right, which they tend to be a little cheaper and a little bit more accessible. So that's what the second study was, basically. And that was my student was funded on a fellowship, and we use our labs resources.


Nick Jikomes 1:05:37

So just to finish off on this, the decision not to publish the names of brands that are producing oils, with adulterants in them, is made by the University of California Davis.


Selina Wang 1:05:52

It was I consulted with them. I don't know if


Nick Jikomes 1:05:56

you consulted with your employer.


Selina Wang 1:06:00

So yeah, I think the I think the rationale, and I struggle a lot with this is the rationale is that is not we didn't do the study to find out who the bad guys are.


Nick Jikomes 1:06:19

I I comprehend what you're telling me. And I'm sure I'm sure the lawyers were to things carefully.


Selina Wang 1:06:29

Yeah, we we wanted to demonstrate that there's a need for standards. But I don't think we want to be in the position of policing.


Nick Jikomes 1:06:46

You're not in policing. So police enforce the law. That's that's what a police officer is, you would simply be publishing your findings. And that's what the process of doing sciences. I mean, we don't we need it. We don't need to dwell on it or agree. I just, I just don't personally understand it. It's it sounds like a legal argument to me not Yeah,


Selina Wang 1:07:06

I'm trying to find the perfect pitch. I don't know if we exist. I'm trying to find the perfect way of doing this. Because I don't think I don't, I will probably come across this again. So let me tell you what I did a second study based on what I learned from the first the first study. So I think many people feel the same way that you do for the first study. So in the second study, what we did is in the paper, we still have samples 12345 But there's a support supporting information where we list all the brands. But again, the brands are not tied to the sample number. So this time, you one would know what where the samples came from what samples we actually analyzed, but we're not saying what oil tested well, and


Nick Jikomes 1:08:06

so the information is there, it's just not in an actionable format. Correct. So going back to the olive oils briefly, because I forgot to ask you for that. What what brands of olive oils had high purity and high quality


Selina Wang 1:08:24

that was 15 years ago. So that's actually in that we took a different approach in that that was not peer reviewed. So the work of that California and imported olive oil study. It was not peer reviewed, it was published as an independent report by UC Davis all of center. So in there, it actually show how each of the brand did


Nick Jikomes 1:08:59

I see okay, so that's that's in there. Yeah. Okay. Um, I'll try to link to that in the episode description so people can look that up. So besides avocado oil, olive oil, has your lab studied any other types of cooking oils?


Selina Wang 1:09:14

Yeah, so we're we're interested in some refining process of different oils right. So we have been mostly looking at at extra virgin so mechanically pressed oil, which we continue to do we continue to study olive oil and avocado oil. But I'm also interested in refined oil because we will never be able to make enough extra virgin olive oil or avocado oil to feed the world. So if we can make Vegetable oil or other types of oil, healthier, a little better for us, either meaning a by changing the parameters slightly by imposing different quality limits our standards, we want to take a look at that which a lot of people have been studying vegetable oil has. And, you know, all different kinds of oil has been studied quite a lot in the US and outside the US. But that is an area that we're also thinking of, but most for. So that's one area, we're also focused a lot of our work currently on the byproduct. So the byproduct from making olive oil, and there's a significant amount of antioxidants that's in the byproduct that is not in the soil that we get to enjoy. So we want to find some valuable use in that. So there's a lot of work on that.


Nick Jikomes 1:11:13

And besides cooking oils, does your lab look at other types of foods?


Selina Wang 1:11:19

Yeah, we look at almonds, pistachios, walnuts, because naturally those foods are also high in lipids. So that was kind of an easy transition for us. But my job actually is to cover all the crops in California. So we also have projects on tomatoes, oranges, strawberries and pomegranates. I'm sure I'm forgetting a bunch of things, but basically every crop that is we have in California.


Nick Jikomes 1:11:57

I mean, is there anything any result that you can share with us that might be interesting to listeners around, you know, the purity or quality of those types of foods?


Selina Wang 1:12:06

For for wallets, so walnuts is one of those crops that suffer oxidation pretty commonly. And I think there's a few things that the industry can use help with. So that's basically, you know, storage packaging. So which we've been helping, we're trying to help them to monitor activation and predict, I'm coming out with chemical tools to predict oxidation and shelf life better for walnuts. And so this way, you know, because sometimes, and this happened, has happened to me, I don't know if has happened to you is you go to the store, you buy a bag of walnuts, and then to rancid when you buy it. So some so something has already happened to it. And we want to avoid that kind of experience for consumers. So so that's something we've been working on for walnuts. And everything is there's mislabeling issues for walnuts just like there is for our two things. Mostly there are walnuts that were made in China, that are mislabeled as California walnuts. So we've been developing chemical tools to differentiate California walnuts from Chinese walnuts or walnuts from other origins. So this is kind of a different type of fraud. It's not adulteration, but it's still fraud now for us.


Nick Jikomes 1:13:57

Yeah. And I mean, this is like, this seems to be a very widespread problem to me for just consumables of all kinds. Because, like all the work that you've shared with us about foods, you know, that's, you know, you have found the startling things that you found. You know, I know, this is also true for things like health supplements, people have found that the, you know, the labels of health supplements often don't match, they're not the right dose, or they're not even the right thing. I you know, I've worked in the cannabis industry for a number of years, and I've studied the laboratory testing methodologies, and results from that industry. And, you know, same issues apply there. And it's, I mean, if I remember correctly, when we were talking about the olive oil stuff, I think you said that, you know, a very large percentage of the oils that you tested didn't meet the standards that were already in place. And I understand you're trying to make new standards, but you can have as many standards and as as rigorous standards as you want. If no one is, you know, enforcing the standards, then then what's the point of it? So I guess I just want to ask you out what, you know, what are your thoughts on not just creating standards using some of the scientific work someone like you is doing? But how can we actually enforce standards in ways that ensure consumers are protected, and they're getting what they're paying for?


Selina Wang 1:15:15

Yeah, 100%. And sometimes I get very frustrated. In the case of olive oil, they are standards, they were standards before we started doing the work. The the difference of California standard is is mandatory. So the producers has to send their sample out to a third party lab, and get the lab results. And my lab will actually review these results. And we'll write a comprehensive report to the olive oil commission of California, which California Department of Food and Agriculture will reveal. So it's a mandatory monitoring program. Right. So that is very different from the voluntary standards that the USDA has. So I agree that standards without enforcement is not that useful. And currently, the industry, the California industry is has submitted a standard of identity petition to FDA, that is different from the USDA standard, and he can be enforced if it's approved. But I don't know how many years we'll have to wait before that will become available. And so far for avocado oil, there's no, there's no official standards. And I don't see, I don't see any enforcement. So


Nick Jikomes 1:16:57

I see. So basically, at the end of the day, the only way for a consumer to ensure that they're getting something that's high quality and they're getting what they paid for, is to use some of the tips that you gave around looking at harvest dates, being conscious of the type of bottle and the size of bottle or container that something's coming in, and actually to basically train yourself to learn what things should taste like. Because it's based on everything you've told me, you know, if someone's going to buy an oil, bottle of avocado oil, right now, it's within the realm of possibility that they might be buying a bottle of, you know, soybean oil, oil, or whatever. And the only way for them to know that would literally be to taste it and be able to tell the difference in themselves.


Selina Wang 1:17:42

Yeah, yeah. And that is true. And if you had a good if you have ever tasted or smell a fresh extra virgin olive oil, you will know what that is like, right? And then it's hard to go back to the rancid, oxidized oil. And in the case of avocado oil is more difficult, because most of the avocado oil in the US, unlike the olive oil industry, most of the avocado available to us in the US are refined, which means they're much more mild in their taste and smell. So it's hard to just try it and then see if it's pure, or if it's good quality. Right. I was in New Zealand a few months ago and they didn't have really a market for refined avocado oil. It was mostly extroversion an avocado oil, in that case, you can smell and taste if it's fresh or pure. But still extraversion avocado oil is a little bit more mild and he has different tastes and smart smell fun olive oil, extra virgin olive oil.


Nick Jikomes 1:19:09

Um, is there anything that you want to reiterate from from what we've talked about or any final thoughts you want to leave people with about food quality and purity and and how people as consumers should think about this and and you know, the ways maybe that they can use some of this work to be mindful consumers about about what they're actually buying?


Selina Wang 1:19:31

Yeah, so I think a lot of people who do research in this area are doing what they can to, to to help to move things forward. I think people get frustrated with people at USDA, FDA, or even me doing research. Right and and where me Making progress slowly. But resources is a challenge, right? So so for many of us, and for things like standards and enforcement, we also really require the members of industry to work together to want to improve, because it's a whole, it's a reputation of the entire industry, not just one brand, right. And this is partially why I, or we try to stay away from pointing out a particular brand, because really is trying to focus on the industry as a whole and trying to help the industry as a whole, rather than to create more problems and prevent the industry to work together. So, so I will say that, and, and then for for, you know, that's just coming from the researchers point of view. And for consumers, if it's, it's hard, but I think a lot of us may be disappointed that our food are not as pure or they don't meet, they don't, the labels are not always what they say they are. But I think, given the work that I have been doing that 15 years, the people I have talked to, and we're moving in a more positive direction the technologies are improving. So there will be able to help to detect quality and purity in a faster, better and cheaper way. Because that's one of the reason why we cannot or USDA cannot test every single lot of products that are coming to the US, right, because the testing is expensive, and it takes time. But I think as technology advances, we can apply that to our food supply chain and and food system. So it's a it's a big problem. But I think, you know, putting more technology in this area, and which is where now people at least, you know, people care more about their food, where it's coming from, and the quality and the purity and authenticity of that more than people had before. Right. So, so that's, you know, I am optimistic about this, even though you know, I do see things like what we have studied.


Nick Jikomes 1:22:58

All right, Dr. Selena Wang, thank you for your time. Thank you.





14 views0 comments
bottom of page