Food Science: Fruits and Vegetables

Hello, RDs and RDs to be. Welcome to the RD exam ready podcast. I'm Zach Kaseberg, your tutor, coach and guide along the path to passing the RD exam. My biggest passion is to help RDs and RDs to be just like you to know how to effectively pass the CDR exam. And if that sounds like you then hey, you're in the right place. It's nice weather season where I live and that always brings about fresh fruits, fresh vegetables, herbs and all kinds of produce, overall tends to be outstanding. I want to dip our minds a little bit into the food science of produce, specifically our fruits and vegetables today to remember these and really know what we need to know for exam day. We don't really talk about food science of fruits and vegetables, but we always talk about the fruits and vegetables themselves. So to start, let's make sure we know what these are made up of. Even if you had the most base knowledge or knew nothing about fruits and vegetables, I could ask you to tell me fruits and vegetables are primarily made up of which macronutrient hmm. When I ask you that, you should say carbohydrates. And that's the truth that produces mostly made up of carbohydrates. But what type of carbohydrates is kind of the question because it's not all just sugar, right? It's not all the same. Carbs would include things like sugar, but it would also include things like your fibers, both digestible and indigestible in structure. A sugar that's found in fruits, for instance, would be in the form of monosaccharides and they would be the monosaccharide fructose, okay? Fructose would be the primary sugar that you find in fruits, for instance. As for vitamins and minerals, here's what should come to your mind. For fat soluble, you do have vitamin A. And of course, vitamin K. We know vitamin A is going to be nice and present, especially in those orange, in those red, those bell peppers, those oranges are really going to have a good amount of vitamin A in that beta-carotene that factors into that. And you know, from all of your warfarin educations and cumidine educations that vitamin K is also going to be found in things like leafy greens, for instance. So those will always come to your mind for the fat soluble vitamins. For water soluble, it would be things like vitamin C, folate, and for minerals and electrolytes, we would have potassium and magnesium. So your list of nutrients to remember would be carbs, of course, fiber, sugar, vitamin A, vitamin K, vitamin C, folate, potassium, and magnesium. Those are going to be your major ones to remember there. Now, plant cell walls are supported by fibrous compounds that are indigestible by humans. Think of the plant cell like a tiny factory surrounded by sturdy outer walls. The cell wall is the rigid outer layer that gives the plant its support, its shape, and protection. The main material in the cell wall is cellulose. Cellulose is a very strong fiber, and it acts like the framework of the cell. It is indigestible by humans, and it can't be broken down by our enzymes. But working alongside that cellulose is hemiscellulose, and hemiscellulose is also in that plant cell wall, and it connects those cellulose fibrous together, and adds both strength to that wall and flexibility. Another important thing that comes to a plant cell is pectin, pectin is the glue of the plant cells that holds everything together. It holds things like water and helps your plants stay nice and firm. It's also the same material and substance that's used to thicken things like jams, jellies, and make things thicker when it comes to plants. Now with pectin, one thing you're going to want to need to know for exam day is how pectin changes depending on the ripeness of a fruit or vegetable. When something is underripe, when we think of underripe, I would think of my favorite thing which is a green banana. A green banana contains a lot of what we call proto pectin, proto pectin, and what proto pectin which you should be thinking of is like the beginning, or a proto type is what I think of for proto pectin. This is the form of pectin that's going to be found in those underripe fruits. As it continues to ripen, that proto pectin will then turn into pectin. So pectin means the ripe fruits. This would be like a yellow banana in this case. As pectin continues to ripen though, and as those plants cell walls continue to break down, it's going to turn to pectic acid or that overripe fruit. That's going to be your kind of trick. Pectic acid would be like your brown, spotty banana, pectin would be your yellow banana, and proto pectin would be underripe. So keep those in mind because we're going to do a question on it later. As some plants mature, their walls develop lignin. Lignin is this hard woody material that makes stems and tree trunk strong and rigid, and lignin is what helps large plants to stand upright. A good example of this is asparagus or celery. Those would have a lot of lignin in them as they age and get older. They become very woody and kind of really tough and stringy. That's why if you bite into like a big, big thing of asparagus, like a large size spear, it's got a lot more woodyness than like a young asparagus spear that's kind of thin. Same goes for celery. The thing about it is despite it, if you want to cook that asparagus to death, that lignin is not going to be destroyed by boiling. It gets tougher as the vegetables age and won't be destroyed by boiling unfortunately. Now plants also produce gums in their cell wall. Gums are sticky substances that help protect damaged areas and retain moisture within the plant. And just inside that cell wall would be the cell membrane of the plant, which controls what enters and leaves the cell just like we talk about with our human cells as well. Inside the cell we obviously we have a nucleus which serves as that control center of the plant's DNA. You're going to have chloroplasts which going way back to your first ever biology class. Those chloroplasts would capture sunlight, transfer to energy, give off carbon dioxide and give plants their green color. Also within plant cells is these large central vacuals and what these are, it's like a big pod that stores water and helps maintain pressure inside the cell. And also stores some of our vitamins and minerals. Within a plant cell we're also going to have mitochondria. We know that as being the powerhouse of the cell, which is converting nutrients to usable energy. Cytoplasm is also going to be there which is like the jelly like fluid substance where all these structures really sit within them. So as we were talking about lignins and as we kind of talk about plant cell walls, I wanted to give a minute to introduce the topic of terrarium. Here you may have seen in a practice question before and if you have, think about what that question was asking. What terrarium is, is it's the force within the cell that pushes against the cell. And as vegetables age, they lose terrarium and they lose their rigidity. So really terrarium kind of corresponds to the amount of like water that's packed between cells. It's almost like the snappiness of a vegetable. A good example is celery. Celery lets really fresh right out of the store. When you snap it, it makes a snapping noise, right? It really snaps and pops. But if you leave celery inside your refrigerator for like two months, what happens? That celery actually isn't so rigid after that two months. It's actually quite rubbery and soft and limp. I would describe it as. What that is is that is the loss of terrarium. So it's losing that water. It's almost the evaporation of that water that's packed within those cells. So celery is a good example because as the celery age is, it loses that water and thus loses terrarium. So when you think terrarium, you're going to think very structured, strong and snappy types of fruits and vegetables. Another piece about terrarium, of course, age is affecting it like I said. But things like heat and humidity will also break down, trigger and make things a lot softer. Now in previous episodes, folks, we discussed plant pigments. We discussed phytochemicals, beta-carotene, flavonoids. We went through chlorophyll, talked through all the scenarios in which acid, base are going to affect those things. We're not going to spend our time on that today because we don't want to double up. But I do want you to make sure you have gone to watch that plant pigments kind of area, understand that and understand the phytochemicals that are found in fruits and vegetables. But instead, we're going to talk about ripening. When talking about fruits, specifically, you have both climax terric and non-climactic terric fruits. Now what are those? Climactic terric fruits will continue to ripen after they are picked. This would include fruits such as bananas, avocados, pears and tomatoes. They'll all continue to ripen after they've been picked. Non-climactic terric fruits are going to be things that stop ripening as soon as they're picked. Typically, when you pick them, you want to pick them at peak ripeness. They're going to be readily to go after. These would be things like grapes, berries, pineapple, melon. When you pick them at their peak ripeness, that's the peak ripeness. They're not continuing to get better with age in this case. That's what you would want to do with a non-climactic terric fruit or vegetable. Now a note about climactic terric fruits. They continue to ripen after being picked. Is that these fruits can give off ethylene gas. Ethylene gas. What that does is it helps to ripen things. It can be used artificially to add to fruits to ripen things quicker. So basically what you need to take for exam day is things like bananas and pairs that give off this ethylene gas. And this can be good if you want to ripen things quickly, but if you want to slow down that ripening, you would want to separate those ethylene producing things from the non-ethylene producing things. Or if you want to speed the ripening of something, put them close together. So this is why maybe it's not the smartest thing to put bananas near like your apples, it's going to continue to ripen that apple much faster than it would have under like ambience or refrigerated conditions. If you want to continue to slow the ripening of fruits, you need to maintain the highest level of quality of things like fruits and vegetables, and there are ways to go about doing that. You can slow down this ripening in oxidation in several ways. First off is by keeping those fruits and vegetables that can be stored in a refrigerator, in the refrigerator. For instance, you can pretty much store all fruits and vegetables, like apples, pears, green beans, all of those can go in the refrigerator. But there are exceptions of things you don't want to put under refrigeration. Make sure you know this list. Tomatoes, potatoes, bananas. All should be kept away from refrigeration. They should be held at room temperature in that case. One of the reasons is the heat or the humidity and the cold can really affect them and shock things a lot. Then being climactic, it's like, hey, go and keep them out of there with the exception of potatoes, this would not be climactic. You want to take all those other things and keep them under that refrigeration because they're going to oxidate slowly than they would at that room temperature. Once a fruit or vegetable also has had that cell wall or that plant cell wall broken or if you've sliced into it or cut it in any way, you've basically started the clock of oxidation at that point. You've seen this before with apples. If you slice an apple and then leave the apple sliced out all day, it browns. It has that enzymatic browning there. Make sure that you wash, cut, cook vegetables as close as you can to serve as time to maximize that vitamin and mineral content and to keep the highest quality. With the apple example or with other fruits and vegetables, there's other ways that you could try to slow down that oxidation. For instance, you've probably heard of the trick of using an acid as a way to kind of kill off those enzymatic browning. That's why, for instance, a lot of things like pre-sliced apples or pre-sliced pears. A lot of them are treated with an acid like vitamin C or a scorbic acid because that acid will kill off those enzymatic browning, the enzymes that would do that browning and it will slow that oxidation of things. You can also use things like citrus or acid to help prevent too much enzymatic browning in that case too. The best way to retain your vitamin and mineral content is to cook your fruits and vegetables until al dente. Do you know what that means? Al dente means to just tender. This would mean that I want to cook things like a green bean until it's a little bit, has some snap to it, but it's soft enough to chew. I don't want to cook it until it's a pureed mush, for instance, because that heat is really going to affect much of those fruits and vegetables. Let's talk more about that. There are methods I can go about with cooking fruits and vegetables to help retain as much vitamin and mineral content as I want. Things like steaming, grilling, broiling, stir frying and microwaving. These are the best ways to prepare your fruits and vegetables because why? They don't use excessive amounts of water. If you use a cooking method such as boiling things, you're really going to affect the vitamin and mineral content the most because a lot of those vitamins and minerals are going to be greatly affected by the boiling water. If you have to boil something, you want to make sure you're boiling it in a very small amount of water for a very short period of time to avoid that heat destruction of all of those water soluble vitamins, your minerals, and your fibers as well. Those will all just be destroyed by the boiling and you're not going to get anything you need out of that at that point. Now when it comes to food science, one piece is you always have to touch on your different grades of fruits and vegetables. That's a big key point to it too. So I want to make sure we just talk through our different grades a little bit and be familiar with those different products. So we're going to start with the processed fruits and vegetables a little bit and then we'll go into our fresh at that point. Starting with the process, this would be your frozen or your canned fruits and vegetables. You're going to start at your highest grade. Your highest grade in that point is going to be our US grade A fancy. US grade A fancy for a processed fruits and vegetables will be the highest grade, which makes sense. Grade A, the best, fancy the best. This would be the highest grade of fruits and vegetables. They're the most tender of fruits and vegetables, succulent, flavorful, and tend to be the most colorful. An example of this would be the highest quality that is reserved for things like fine dining establishments, Michelin star restaurants, and very high end stores would be using grade A. So we don't, you know, you me, if we chop in the store, we might not be getting the best of the best always. US grade B is going to be our next grade down for fruits. They would call this choice grade B and for vegetables, they would be called extra standard. Those are the different designations there. For this grade B, it would be slightly less tender and less colorful than fancy. And this is the majority of what you and I would see in our regular grocery stores. Grade C, US grade C, or standard, as it's also known, is going to be your third grade. So it's going to be just tearing down from here. These are going to be very mature fruits and vegetables, less tender, not much uniformity or shape or color. And these are really useful for things like soups, stews, and casseroles, but maybe you wouldn't want it as like a fresh design or a fresh vegetable that you're serving to someone might be better used if it's in like a process form. The last of it would be US grade D, sub standard, and this is going to be the lowest quality. For fresh, we're going to go back up to the top to the best of the best. US fancy. So nothing much changed here. US fancy would be the highest quality in grade for our fresh fruits and vegetables. Very uniform shapes and appearance, rarely seen in stores, and is reserved for fine dining and high end stores. US number one is our grade right below that. And US number one would be products that are fresh, tender, colorful, just not perfect. You may see some bruising lack of uniformity, maybe one little dimple or something like that, but this is still with the majority of what you and I are going to see in stores is US number one. So number one is still good. It's just one below fancy. US number two would be like a moderate intermediate quality. And then US number three is the lowest quality of fresh fruits and vegetables. This would have bruising present, lack of uniformity, no consistency in color. And really we do not often see these, but it is going to be a designation of a quality grade there. Now that you've really kind of trudge through all those fruits and vegetables and all the food science today, let's apply this to some practice questions and see what you remember. We want to use process of elimination to help us to get rid of the worst answers and choose the best answer that we feel good with. This is going to put you at the best odds of getting the question right on exam day, even if you don't know the answer. So let's try it out. Number one, as fruit changes from immature to overripe, protopectin chemical breaks down to a pectin, then pectic acid, B, pectic acid, and then depectin, C, oxalic acid, and then depectin, or D, pectin to oxalic acid. As fruit changes from immature to overripe, protopectin chemical breaks down to. So let's use process of elimination, see what we like, don't like, or just questionable on. For A, pectin, then pectic acid. So I think back to our discussion today, and I think back of the three stages of pectin we talked about. We talked about our green banana, which was protopectin, because we thought of the prototype. Next was pectin, and the third one was pectic acid. So per our kind of discussion we had today, I think A is a good fit. It would say that pectin, then depectic acid, I'm going to hold on to A, but see my other answers. B, pectic acid, and then depectin. No, I think it would go the opposite way. Pectin, then depectic acid, the pectic acid, would be our last step in the ripeness. So I would get rid of answer B, because I don't think it's a good fit. C, oxalic acid, and then depectin. I don't know much about oxalic acid. I could put a little question mark by it, depectin to oxalic acid. I don't know anything about that, and that one even seems like a weird one, because when we didn't talk about oxalic acid with pectin anyway, so I'm going to get rid of de. So now I had A, pectin, then depectic acid, or C, which I was a little bit questionable on. So for number one, its fruit changes from immature to overwrite, protopectin chemical breaks down to pectin, then pectic acid, answer A would be our best fit for this one. Number two, a strong fiber that acts as the framework of the plant cell wall and is indigestible by human enzymes. A, hemiscellulose, B, cellulose, C, lignan, or D, gum. A strong fiber that acts as the framework of the plant cell wall and is indigestible by human enzymes is known as. Let's use process of elimination to help us out. So I have a strong fiber indigestible to human enzymes. When I start with a hemiscellulose, we know it's a pretty strong fiber because we know it's kind of linked between the cellulose. So that fits the indigestibility piece I wonder about. I feel like maybe there could be some digestion of it, just not a whole lot. I'm gonna put a little question mark by hemiscellulose for right now. B, cellulose. Okay, I know cellulose is a strong fiber. I know it's indigestible by human enzymes and it really does serve as the framework for the plant cell wall. It's that strong fiber that really helps to hold it all together. I think B is a good fit and I'd like to hold onto that one. C, lignan. Lignin was that woody substance that was found in things like celery and asparagus. It kind of helps hold structure and framework certainly and isn't very digestible either. But I don't think it serves as the actual framework of the cell wall. I think it helps with the rigidity and helping things to stand up like our asparagus and celery. I don't think lignan feels like it's this answer and I think I'm gonna get rid of that one. Gums, the gums are present inside the plant cell wall and they help to retain moisture and have that thickening ability. But I don't think it would act as the framework because that doesn't sound like a very strong plant cell if it's held up by gums. So I'd get rid of D. So now I'm stuck between the hemiscellulose and cellulose. If I'm between those two, I wanna go with my best answer for me which felt like cellulose which would be our best answer. A strong fiber that acts as the framework of the plant cell wall and is indigestible by human enzymes would be known as cellulose in this example for number two. Number three, which vegetable should not be stored under refrigeration? A, potatoes. B, carrots. C, mushrooms. Or D, squash. Which vegetable should not be stored under refrigeration? Okay, let's see here. A, potatoes. I like potatoes as an answer. I don't store my potatoes in the refrigerator. Commonly when I go to the store, they're not stored in the refrigerator. I'm gonna hold on to potatoes as being one that should not be under refrigeration. B, carrots. I store my carrots in the refrigerator and they tend to do just fine with that. So I don't think carrots would be a good fit and I would wanna get rid of that one. Mushrooms, mushrooms would be my next one that I'd say. Mushrooms I can store in the refrigerator typically. So I would get rid of that one. In squash, I would also get rid of, 'cause I can store squash in the refrigerator as well. Which vegetable should not be stored under refrigeration would be answer A, potatoes. And one final fact today before we sign off about potatoes is remembering that potatoes also need to be protected from UV light. UV light affects potatoes in a very odd way. If you go to a store very early or very late in the day, you might notice they can't please like blankets over potatoes. The reason they do that is UV light affects potatoes and it creates this green toxic chemical. It's called so-lini. So-lini is this green toxic compound that comes into potatoes that are exposed to UV light. So that's your last little fun fact of food science for your fruit and vegetable discussion today. But that's a wrap today. For today's lesson students, I hope you watched, listen, learn and enjoy today's show. Remember, pass in this exam as a journey. We all need assistance along the way. Do yourself, do me a favor, hit the subscribe button, especially if you're on Apple Podcasts, Spotify, subscribe, let me know what you like about the show, comment, rate, review, join the mailing list that's located in this description, and look out for any upcoming live events on the RD exam ready YouTube. As always, happy studying to you RD to be, and I'll see you soon.