Phytochemicals are plants or fruits derived chemical compounds. "Phytonutrients" refer to a phytochemicals or the compounds that comes from edible plants. There are abundance evidences from epidemiological studies saying that the phytochemicals present in fruits and few vegetables can significantly lower the risk of a cancer which is probably due to anti-inflammatory and polyphenol antioxidant effects. Phytochemicals are been used as a drugs for millennia example, Hippocrates in the four hundred BC used for the prescription of willow tree leaves, to abate fever. Salicin, with the potent anti inflammatory and pain relieving properties, was extracted from White Willow Tree, and then later synthetically was produced to become staple over counter drug named Aspirin.
The one of the best drug for the cancer treatment Taxol, used worldwide is phytochemical which is extracted and then purified form pacific yew tree.

There are currently a lot of other phytochemicals which have potent medicinal properties which are in the clinical trials to be tested for variety of diseases. Lycopene for example, from tomotoes is under clinical trials to be tested for the cardiovascular diseases and for prostate cancer.Trial tests have proved that lycopene helps in improving blood flow through heart and the clinical studies suggest a anti cancer activity against the prostate cancer. Lutein and zeaxanthin derived from spinach have shown through the clinical trials that it directly improve the human visual performance.

Studies have proven that intake of broccoli and tomatoes in your diet helps to inhibiting the growth of prostate cancer more effectively than campared to the leading drug specially made for this purpose.

Many phytochemicals are assumed to be destroyed / removed by the modern food processing technique which may possibly includes cooking.Due to this it is assumed that industrial processed food in not as benefitial as compared to natural food. Interestingly, lycopene, which is phytonutrient that is found in tomatoes which is concentrated in the processed food such as ketchup and spaghetti sauce are good source of lycopene.

Food stuff containing high phytonutrients are:-
soy - protease inhibitors, saponins, beta sitosterol, isoflavones, phytic acid
tomato - beta carotene, lycopene, vitamin C
broccoli - vitamin C, 3,3'-Diindolylmethane, lignans, sulphoraphane, selenium
garlic - limonene, thiosulphonates, quercitin
flax seeds - lignans
citrus fruits - monoterpenes, cryptoxanthin, coumarin, vitamin C, oxalic acid, ferulic acid
blueberries - lignans, tannic acid, anthocyanins
sweet potatoes - beta carotene
chilli peppers - capsaicin
legumes: peas,beans, lentils - saponins, omega fatty acids, catechins, lutein,quercitin, lignans
Apples - catechins, quercetin, tartaric acid
Açaí berries - anthocyanins, vitamin C, omega-3, Beta-sitosterol, omega-6.

Possibly one of the highest-scoring fruit for the antioxidant ORAC values, though results may vary between 5,800 μmol TE per 100 grams - 53,600 μmol TE per 100 grams.
Dried apricots
Artichoke - caffeic acid, silymarin, ferulic acid
Brassicates: cabbage, kale, cauliflower - lutein, brussels sprouts,
Carrots - beta-carotene
Cocoa - flavonoids, epicatechin
Cranberries - ellagic acid, anthocyanins
Eggplant
Gac - beta-carotene, lycopene
Pink grapefruit - lycopene
Red grapes and the wine - resveratrol, quercitin, ellagic acid, catechins