Salt, Water and Vegetables

For this experiment I observed the variations in pH levels in six different samples of peas and I cooked broccoli and carrots in what seemed to be every conceivable way possible while evaluating the differences in the pH and color of the cooking liquid and vegetable color for the broccoli, as well as a sensory evaluation based on the timing of the carrots. 


"Effect of Heat and pH on Plant Pigments


Introduction
Many plant pigments, especially chlorophyll and the anthocyanins (a flavonoid), are sensitive to heat and changes in pH. Under favorable acid conditions, these pigments will exhibit an acceptable color, but when the pH is increased or decreased, the pigment may change to an undesirable color. This presents a sensory defect in the food. The objective of this exercise is to determine the effect of heat and pH on plant pigments.


Materials
Frozen peas, canned peas, vinegar, NaOH (1 N)


Chlorophyll Procedure


Sample A

1. Heat 2/3 cup of deionized water to boiling
2. Add approximately 2 1/2 tbsp of frozen peas
3. When the water returns to a boil, time for 7 min
4. Remove the sample from the water and place in a beaker

Sample B

1. Add 1/2 tbsp of vinegar to about 2/3 cup deionized water and determine the pH of the solution. Boil the solution.
2. Add approximately 2 1/2 tbsp of frozen peas
3. When the water returns to a boil, time for 7 min.
4. Remove the sample from the water and place in a beaker. 

Sample C

1. Add 1/2 tbsp of 1 N NaOH to 2/3 cup deionized water and determine the pH of the solution. Boil the solution. 
2. Add approximately 2 1/2 tbsp of frozen peas. 
3. When the water returns to a boil, time for 7 min.
4. Remove the sample from the water and place in a beaker

Sample D

Expose 2 1/2 tbsp of frozen peas to a cold mixture of 1/2 tbsp vinegar and 2/3 cup deionized water for 7 minutes without cooking.

Sample E

Expose 2 1/2 tbsp of frozen peas to a cold mixture of 2 g baking soda (NaHCO3) and 150 ml deionized water without cooking. 

Sample F

Set up a sixth beaker with canned peas."

Results

(Sample A: Boiled Peas)

pH N/A

• Color: charred, light green and dull green mixture
• Odor: faint smell of peas, not very strong
• Flavor: not too strong, tastes a bit charred because the bottom burnt a the end-- not enough water
• Texture: partially wrinkly 

(Sample B: Vinegar Water Boiled Peas)

pH 6.5

• Color: dull green and lighter dull green with a yellow tinge
• Odor: strong pea smell, faint vinegar smell
• Flavor: only slightly tastes pea-like (the familiar flavor) Just a hint of a sour sting.
• Texture: partially wrinkly, not very juicy

(Sample C: NaOH Water Boiled Peas)

pH 13.5

• Color: bright green-- doesn't look like its been boiled, but rather shocked or steamed
• Odor: doesn't smell much like peas, but also doesn't smell like anything else in particular
• Flavor: POISON!
• Texture: I didn't want to touch, but it looks wrinkly, like the other boiled peas

(Sample D: Vinegar Water Frozen Defrosted Peas in Cold Water)

pH 6.5

• Color: bright green, shiny
• Odor: you can smell the vinegar, but it doesn't mask the smell of the peas
• Flavor: vinegar adds a little twinge, but only so slightly. The peas taste slippery and fresh
• Texture: Round and bright. Pops in your mouth. Juicy.

(Sample E: Baking Soda and Water Peas Soaked)

pH 8

• Color: bright and consistent, but not as bright as sample D
• Odor: smells kind of funky, like rotten peas
• Flavor: these taste like normal, slightly watery peas
• Texture: big, round, bright, not as bouncy as sample D

(Sample F: Canned Peas, Drained)

pH 6.5

• Color: yellow-green bright color, dull tone
• Odor: strongest and smelliest of all!
• Flavor: not juicy, entirely different from fresh peas, skunky
• Texture: mushy and round/full

"Sensory Qualities of Carrots


Wash and peel the carrots. Cut into pieces about 2" long x 1/2" across.


For each of the methods below, weigh 100g of sliced carrots. Prepare according to assigned directions and serve for subjective evaluation of flavor. Note boiling times carefully. 


Oven roasted. Preheat oven to 400 F. Place 30 ml olive oil in a bowl and add 100 g carrot slices. Stir to coat with oil before placing on a baking sheet. Roast for 1 hour or until tender. 


Waterless, covered. Place 100 g carrots and 25 ml water in a heavy saucepan with a lid. Heat to boiling and continue boiling just until fork tender. Watch carefully and add water as necessary to prevent scorching. Note the time required.


100 ml water, covered. Place 100 ml water in a 1 qt saucepan. Heat quickly to boiling before adding carrots. Immediately add 100 g of carrots, cover and boil gently until fork tender. Note the boiling time required.


300 ml water, covered. Place 300 ml water in a 1 qt saucepan. Heat quickly to boiling before adding carrots. Immediately add 100 g of carrots, cover and boil gently until fork tender. Note the boiling time required.


100 ml water, uncovered. Place 100 ml water in a 1 qt saucepan. Heat quickly to boiling before adding carrots. Immediately add 100 g of carrots, cover and boil gently until fork tender. Note the boiling time required.

300 ml water, uncovered. Place 300 ml water in a 1 qt saucepan. Heat quickly to boiling before adding carrots. Immediately add 100 g of carrots, cover and boil gently until fork tender. Note the boiling time required.


Tender + 10 minutes, covered. Place 300 ml water in a 1 qt saucepan. Heat quickly to boiling before adding carrots. Immediately add 100 g of carrots, cover, and boil gently until fork tender, add 10 more minutes of boiling. Not the total boiling time.


Cold start, uncovered. Place 150 ml water and 100 g carrots in an uncovered 1 qt saucepan. Bring to a boil and continue boiling until tender. Not total cooking time. 


Stir-fry. Briefly heat 5 ml peanut oil in a heavy frying pan with a cover and add 100 g carrots. Stir briefly; cover, lifting to stir every 30 seconds. If carrots start to burn, add 10 ml water. Cook just until tender. Note the cooking time. 


Microwave oven. Place 100 g carrots and 25 ml water in a small, covered dish. Place in a microwave oven and cook for 1 minute and 30 seconds. Stir the carrots and cook covered another minute and 30 seconds. 


Steamer. Place 100 g carrots in steamer and add enough water to boil throughout the cooking period without being high enough to touch the carrots. Note the time required."


Results


Waterless, covered 

• Added 2 tbsp of water at 4 minutes, 10 sec
• Time: 1 min 50 sec to boil, 5 min 42 sec to cook
• Color: Smoothed, duller on the outside, fade inwards dark to light
• Odor: More carroty than uncooked, steam is strong
• Flavor: Not much flavor at first, flavor comes out in juice as it is chewed
• Texture: Soft-ish to bite into, tough to chew, still has a slight crunch

100 ml water, covered

• Time: 2 min 6 sec to boil, 7 min 46 sec to cook
• Color: Brighter than the waterless, smoothed, less color contrast, slightly green in the center
• Odor: More carroty than uncooked, not as much as the waterless
• Flavor: More consistent flavor from the start, but chewing enhances flavor by releasing juices
• Texture: More soft, not as chewy as waterless, but still not melt-in-your-mouth

300 ml water, covered 

• Time: 2 min 30 sec to boil, 8 min 2 sec to cook
• Color: Bright, smoothed, less color contrast than 100 ml, covered
• Odor: More carrot smell than uncooked, less than 100 ml, covered
• Flavor: Consistent medium carrot flavor from the first bite on
• Texture: More soft than 100 ml, still chewy

100 ml water, uncovered

• Add 3 tbsp water at 4 min 45 sec
• Add 2 tbsp water at 6 min 31 sec
• Add 2 tbsp water at 8 min 3 sec
• Add 2 tbsp water at 11 min 22 sec
• Time: 3 min 32 seconds to boil, 11 min 55 sec to cook
• Color: dull, charred, slightly bright in the center
• Odor: carroty, like the results of waterless, covered 
• Flavor: not as much flavor as any of the above or raw
• Texture: chewy, a bit crunchy, and just tender enough

300 ml water, uncovered

• Time: 3 min 19 sec to boil, 13 min 20 sec to cook
• Color: Brighter than mostly all of the other options, very slightly green in the center 
• Odor: Not as carroty as the others, steam enhanced the smell
• Flavor: Less flavorful, but still consistent, more mild
• Texture: Fleshy on the inside, crunchy bite, tougher on the outside 

Tender + 10 min, covered

• Time: 3 min 19 sec to boil, 13 min 20 sec to cook
• Color: Slightly darker, dulled the colors
• Odor: Deeper carroty smell, sweeter but not very strong
• Flavor: Sweeter with every bite until the last, which turns bitter
• Texture: Effortless to chew, smooth, but not quite melt-in-your-mouth

Cold start, uncovered

• Time: 2 min + 1 minute 30 sec --> 30 sec
• Color: Darker orange, fades inwards light to dark
• Odor: Charred 
• Flavor: Bitter/unpleasant aftertaste
• Texture: Still crunchy, easy outside, tough inside

Stir Fry

• Time: 3 min 35 sec to cook (4 min 20 sec to burn! oops)
• Color: Slightly charred, deep orange, light edges
• Odor: Smells deep and carroty, very cooked
• Flavor: Smokey and slightly sweet
• Texture: Oiled, crunchy, tender

Microwave oven

• Time: 1 min 51 sec to boil, 5 min 53 sec to cook
• Color: Bright, smooth coloring
• Odor: Hardly and odor, even with steam
• Flavor: Fresh taste, increasing flavor as you chew
• Texture: Easy to bite and chew, nice crunch, firm outside, easy inside

Steamer

• Time: 14 min 27 sec to cook
• Color: Vibrant consistency of color, almost totally smooth
• Odor: Fresh, carroty, sweet
• Flavor: Sweet, but not as sweet as oven roasted, flavor gradually disappears
• Texture: Starchy, easy to bite into , smooth and a bit grainy

Oven Roasted

• Time: 1 hour
• Color: Burnt, orange in the center
• Odor: Burnt, still very carroty
• Flavor: Extra sweet in the center, sweet-potato like, charred
• Texture: Chip-like, crunchy, gooey in the center

"Broccoli Sensory Qualities


Wash the broccoli (~2 lb) well. Chop all the stalks and flowers into segments 1/2" long and approximately 1/3" in diameter. Place the entire mixture in a large mixing bowl and stir to blend the stalks and flowers uniformly throughout. Randomly remove 50 g of the chopped broccoli for each of the following preparations.


Directions
Cook the broccoli according to the variation assigned (below). 
After cooking, remove the broccoli from the cooking liquid with a slotted spoon. Pour the cooking liquid into a glass beaker and place beside the plate of broccoli for evaluation. When the cooking liquid is cooled to room temperature, test the pH on the pH meter. 


Variations
Lid on, 5 minutes: In a covered 1-qt saucepan bring 1 cup of tap water to a boil; add 50 g chopped broccoli. Boil 5 minutes.


Lid on, 15 minutes: In a covered 1-qut saucepan bring 1 cup of tap water to a boil; add 50 g chopped broccoli. Boil 15 minutes.


Lid off, 5 minutes: In a covered 1-qt saucepan bring 1 cup of tap water to a boil; add 50 g chopped broccoli. Boil 5 minutes.


Lid off, 15 minutes: In a covered 1-qut saucepan bring 1 cup of tap water to a boil; add 50 g chopped broccoli. Boil 15 minutes. 

Cold water start, lid off: In an uncovered 1-qt saucepan, place 1 cup cold tap water and 50 g broccoli. Heat (uncovered) to a boil and continue to boil actively for 5 minutes Note total time for heating and boiling. {Start = 4 min 59 sec/End = 5 min 7 sec}


Distilled water, lid off: In an uncovered 1-qt saucepan, heat 1 cup distilled water to a boil; add 50 g chopped broccoli. Boil 5 minutes.


Microwave oven, uncovered: Place 50 g chopped broccoli in a small dish. Add 1 tbsp water. Cook in microwave oven for 1 min 30 sec. 


Microwave oven, covered: Place 50 g chopped broccoli in a small covered dish. Add 1 tbsp water. Cook in microwave oven for 1 min 30 sec. 


Steamer: Place 50 g chopped broccoli in a covered steamer containing enough water to boil throughout the steaming period, but without touching the broccoli. Note the time required for the stalks to become fork tender."


Results
*NC = No drastic (aka very noticeable) change


Lid on, 5 min

• Cooking liquid
• pH: 6.8
• Color: Murky, yellow, powdery/milky
• Vegetable color: Bright, but not as bright as microwaved

Lid on, 15 min

• Add 1 cup water at 10:00 minutes (It was burning!)
• Cooking liquid
• pH: 6.7
• Color: Dark brown, similar to the tone of a black tea
• Vegetable color: tinted brown, dark, dull color, looks over-cooked and wilted

Lid off, 5 min

• Cooking liquid
• pH: 6.5 (NC)
• Color: murky, light amber-toned when poured
• Vegetable color: Dark on tops and in leaves, fading inwards dark to light

Lid off, 15 min

• Add 1 cup water (It was burning!)
• Cooking liquid
• pH: 7
• Color: Dark amber-brown, deep gold when poured
• Vegetable color: Dull green, tinted brown, more consistent

Cold water start, lid off

• Cooking liquid
• pH: 6.5 (NC)
• Color: Clear, like plain water. No change. 
• Vegetable color: Bright, vibrant, dark tops, faded contrast

Distilled water, lid off

• Cooking liquid
• pH: 6.6 (NC)
• Color: Yellow-tinted, mostly clear
• Vegetable color: Dark and vibrant, strong lights and darks contrast

Microwave, uncovered

• Cooking liquid
• pH: 6.7
• Color: Mostly clear, faint, slight tint of yellow
• Vegetable Color: Bright and vibrant, stems had less variation in tone

Microwave, covered

• Cooking liquid
• pH: 6.6 (NC)
• Color: Mostly clear, faint, slight tint of yellow
• Vegetable color: SUPER bright, neon resemblance, dark contrast between the edges and the inside

Steamer

• Cooking liquid
• pH: 6.6 (NC)
• Color: Clear, no color change 
• Vegetable color: Bright, colors smoothly faded inwards from dark to light, subtle contrast except for the blooms 

Questions

1. How do vegetable textures and the color of chlorophyll change when plant tissue is subject to heat at various pH values?


When vegetables are boiled in acidic liquid they will be more likely to retain their original textural composition, just as a more basic liquid will allow for cooked vegetables to become more soluble. This is because hemicelluloses do not break down as easily in acidic solutions. Therefore, we can see from the broccoli experiment that a liquid that is fairly neutral will allow a vegetable to cook anywhere between 5 and 15 minutes before tender. A vegetable cooked in an acidic liquid could take hours before becoming tender. 


"Steam itself is also a somewhat acidic pH6". This shows why it took nearly 3x as long to steam the broccoli than it took the other effective techniques. The 15 minute long trials, both with the lid on and off, burn the broccoli and made it unpleasantly mushy. The faster a vegetable is cooked, the more vibrant its color will be. This explains why the microwave cooking was the brightest of all the options-- cooked in 1 minute and 30 seconds.


"Acidity dulls chlorophyll"
This makes sense because in the broccoli experiment, pH7 was the highest acidity and the least vibrant of the whole experiment. It was a very dull green with a consistent brown tint. 


Blanching a vegetable immediately after it is finished cooking prevents it from losing more of its color. 


When carrots are cooked, the heat alters the composition of the carrot itself, as well as the visual presentation. Beta-carotene changes the color from "red-orange" to more of a yellow. Green vegetables change much more noticeably because when a green vegetable is put into boiling water and vulnerable to heat, the space between the cells expand, releasing gasses that veil the original color and reveal it to be much brighter and vibrant than before when the gasses settle.


2. What chemical changes occur in the chlorophyll molecule in the various treatments?


When chlorophyll interacts with heat, its "carbon-hydrogen tail" disappears. This allows the pigment to "leak" into the cooking liquid. Dulling of the color of a vegetable happens when an acidic cooking liquid causes hydrogen to replace magnesium, resulting in a yellowish tinge. 


Cooking in alkaline water keeps vegetables bright because it lacks enough hydrogen ions to replace the magnesium + darken/dull the color. Baking soda eliminates the acidity in your liquid. This explains why sample E of the experiment with the peas was bright and consistent, despite its exposure to water. 


TRICK FROM THE BOOK: 
Don't dress your vegetable with something acidic, like lemon juice, until the very last minute. If you need to dress your vegetable immediately beforehand, coat with a tossing of butter or oil first to protect the acid from interacting with the vegetable. This will help your final presentation look vibrant and fresh!


3. Illustrate the chemical effects that changes in pH have on the structure of anthocyanin molecules and the color of anthocyanin solutions:


pH Acidic + Anthocyanin = reddish color
pH Neutral + Anthocyanin = "colorless or light violet"
pH Alkaline + Anthocyanin = "bluish" color


When heat is applied, the spaces that hold the pigment are broken and some pigment escapes, disintegrating. The pigment that did not escape become the new color, adapting to the cooked vegetable tissue. 


TRICK FROM THE BOOK:
To keep the colors of anthocyanin fruits and vegetables consistent when cooked, add an acid like lemon juice or vinegar because the acid bonds the ions, preserving the color. Also, using baking soda in pancake batter will keep blueberries from turning green!


4. Compare the pH of the various cooking liquids from broccoli variations. 


A. Does boiling modify the pH? If so, how?
Each of the results from the broccoli boiling variations were fairly neutral. They differed only slightly with the largest difference being the pH of the "lid off, 15 minutes" experiment-- pH7. All pH samples ranged from pH6.5-pH7.


B. Is there any difference in the pH of the distilled water and tap water? If so, what is the difference?
There was not much difference. In any way there was a slightly lower pH in the distilled than in the tap water. 


C. Does the pH of the cooking liquid change when a vegetable is heated in it? If so, what causes the change?
Yes, the pH of the cooking liquid can possibly change slightly because when a vegetable interacts with heat it can release the plants own natural acids, therefore altering the pH. 


D. Does use of a lid influence the pH of the cooking liquid? If so, why?
According to my results, the use of a lid resulted in a less drastic change in pH between 5 minutes cooking and 15 minutes cooking. I could not find an explanation for this in my studies and I think this may have been based on an alternate, unplanned element of the study. The lid on for 5 minutes was about 0.3pH higher than the lid off, and the lid on for 15 minutes was about 0.3 pH lower than the lid off. Since this is inconsistent, I found no clear explanation as to why the lid on/lid off produced these results. 


E. Does microwave cookery influence the color of chlorophyll? Give an explanation for your answer.
Yes, microwave cooking does influence the color of the chlorophyll. The faster and more evenly the vegetable cooks, the brighter the color will be!


TRICK FROM THE BOOK:
For microwaves and vegetables-- microwave radiation tends to dry out vegetables, so for every 1 minutes and 30 seconds, add 1 tablespoon of water to keep the vegetables crisp and steamed nicely. 


F. Does covering the vegetable in the microwave cookery modify chlorophyll color? Explain your answer. 
According to my results, the covering of the container did not change the chlorophyll color very much. The covered sample was a bit brighter than the uncovered, becoming almost a neon bright green. This is because the steam that is trapped with a cover on holds more contained heat, which releases more gasses that lie between the cells. When the gasses settle as they cool, they reveal the bright color. 


5. Describe the effects of the various treatments on the color, odor, flavor, and texture of the carrots and indicate the preferred techniques. What characteristics of carrots influenced your preference for cooking treatment? Explain. 


Preferred technique: flavor-wise, oven roasted was my favorite because it brought out the natural sweetness and held a melt-in-your-mouth texture that I enjoy when it comes to cooked carrots. I would have done 45 minutes instead of 1 hour, however, to prevent burning. Texture-wise, my favorite was the microwave oven. It was easy to bite and chew, but it still held a nice crunch that was firm on the outside and easy on the inside. 


My friends and I made the roasted broccoli recipe for part of the bi-bim-bop house dinner! Unfortunately, we ran out of broccoli and weren't able to make the multiple variations, but it was DELICIOUS. It really is a great recipe and I am sure I will make it again. 


Roasted Broccoli (America's Test Kitchen)
Serves 4


1 large head of broccoli (about 1 3/4 pounds)
3 tablespoons extra-virgin olive oil
1 tablespoon crushed garlic
1/2 teaspoon salt
1/2 teaspoon sugar


Adjust the oven rack to the lowest position, place a large rimmed baking sheet on the rack, and heat the oven to 500 degree F.


Cut the broccoli at the juncture of florets and stems. Cut the stalk into 2 to 3 inch lengths and each length into 1/2-inch-thick pieces. Cut the crowns into equivalent sized pieces. 


Mix the olive oil, garlic, sugar, and salt in a large mixing bowl. Add the broccoli and toss well. 


Working quickly, remove the baking sheet from the oven. Carefully transfer the broccoli to the baking sheet and spread into an even layer, placing the flat sides down.


Return the baking sheet to the oven and roast until the stalks are well browned and tender and the florets are lightly browned (9-11 minutes). 


Transfer to a serving dish and enjoy!


Variations to try: (salt omitted, sugar omitted, salt and sugar omitted)