Kristie Leong M.D. is a family practitioner who believes in the power of nutrition and a healthy lifestyle to prevent and fight illness.
Broccoli is one of the most nutrient-dense vegetables around. Scientists now know that it contains compounds called glucosinolates that your body converts to chemicals with anti-inflammatory benefits. Some research suggests these natural compounds in broccoli have anti-cancer properties.
Three Reasons Why Broccoli Turns Yellow
Of course we all know broccoli should be green—but what if it's begun to turn yellow? You might wonder whether it's still safe to eat. Why does broccoli turn yellow, and should you eat it or toss it?
The short answer is that yellowing broccoli is still safe to eat. Although the yellow color may be less appetizing, a head of broccoli that has turned yellow is still safe to eat. So, what causes this unsightly change to this nutritious veggie?
Let's take a look at the three most likely culprits.
1. Natural Aging Process
The yellowing of broccoli is the result of the natural aging process. Just as all animals and plants age, broccoli does too. As it ages, the chlorophyll pigment that gives broccoli its green color breaks down. As this happens, the broccoli plant becomes less green in color and more yellow. You might see speckles of yellow around the florets and even the stalk.
Why the yellow color? As chlorophyll breaks down, another class of pigments in broccoli called xanthophylls becomes more prominent. Xanthophylls are a type of carotenoid, a class of compounds that give orange and yellow fruits and vegetables their color. As xanthophylls become more visible from chlorophyll breakdown, broccoli takes on a yellowish color.
2. Environmental Stressors
Another reason broccoli can turn yellow is stress. The most common reason for this is environmental factors, but it can be caused by pests, disease, and other things that stress the plant or compromise its health. Severe environmental stressors include:
- Too much rain
- Too little rain
- Too much sun
- Too little sun
- Too much fertilizer
- Too little fertilizer
- Sudden temperature changes
- Nutrient deficiencies
- Pest infestation
The same can apply to broccoli. Stress speeds up the aging process in plants, just as it does in animals. Any of these factors could speed up chlorophyll breakdown and cause broccoli to turn yellow prematurely.
3. Overcooking
If you cook broccoli too long, it can turn yellow. To avoid this, cook it until it's tender but not mushy. Overcooking will break down chlorophyll and give broccoli a yellow appearance. Cooking too long also reduces its nutrient content.
Can You Eat Yellow Broccoli?
Yellow broccoli is safe to eat, although it may taste more bitter than green broccoli. Cooking broccoli tends to enhance its bitterness. The best bet is to cut off any yellow part and cook or eat the rest raw.
If you’re shopping for broccoli at the grocery store and you see a head of broccoli with a lot of yellow, it’s best to look for a head that’s greener, not because it isn’t safe to eat but because the yellowing could make the taste more bitter.
Since broccoli is already somewhat bitter, although a pleasant kind of bitter, why enhance the bitterness by buying broccoli that’s already yellow? But if you grow your own, there’s no reason to waste it. You can still safely enjoy it.
Consider eating broccoli with some yellowing raw, since heat can enhance the bitterness. There are other perks to doing so. You’ll get more vitamin C if you eat broccoli raw since cooking destroys vitamin C.
However, since yellowing is a sign that broccoli is past its prime, you may get slightly fewer nutrients than if you ate greener, less mature broccoli. Yet broccoli that’s past its prime still retains all its fiber.
The Bottom Line
Broccoli turns yellow due to the natural aging process and the breakdown of the green pigment chlorophyll. If broccoli is stressed by the elements, it may “age” and turn yellow faster. This doesn’t make it unsafe to eat if the plant is still firm and shows no sign of rotting.
But you might not enjoy the taste as much. It may also have lost some of its nutritional value because it is past its prime.
Regardless of whether you’re eating brilliant green broccoli or broccoli with a little yellowing, use it as soon as you can to get the most nutrients from it. Also, don’t expose it to heat or cook it in too much water. Light steaming or sauteing are two of the best methods for cooking broccoli to preserve its nutrients.
References
Luo F, Cheng SC, Cai JH, Wei BD, Zhou X, Zhou Q, Zhao YB, Ji SJ. Chlorophyll degradation and carotenoid biosynthetic pathways: Gene expression and pigment content in broccoli during yellowing. Food Chem. 2019 Nov 1;297:124964. doi: 10.1016/j.foodchem.2019.124964. Epub 2019 Jun 8. PMID: 31253313.
Soundararajan P, Kim JS. Anti-Carcinogenic Glucosinolates in Cruciferous Vegetables and Their Antagonistic Effects on Prevention of Cancers. Molecules. 2018 Nov 15;23(11):2983. doi: 10.3390/molecules23112983. PMID: 30445746; PMCID: PMC6278308.
Yuan GF, Sun B, Yuan J, Wang QM. Effects of different cooking methods on health-promoting compounds of broccoli. J Zhejiang Univ Sci B. 2009 Aug;10(8):580-8. doi: 10.1631/jzus.B0920051. PMID: 19650196; PMCID: PMC2722699.
