23.3 Fruits, Vegetables, and Legumes: Classification, Market Forms, Quality, Storage, and Cookery

The Understanding Foods competency area (10% of Foods and Food Service Systems) asks examinees to explain the composition and properties of foods, classify food groups and market forms, explain ingredient functions and reactions during processing, and describe storage procedures. Pigment chemistry and browning are covered in the food pigments section.

Classification of Vegetables

Fruits are grouped as berries, drupes (mango, siniguelas), pomes (apple, pear), citrus (calamansi, dalandan, pomelo), melons, and tropical fruits (banana, papaya, pineapple, guava).

Market forms: fresh, frozen, canned, dried, juices, purees, and minimally processed (cut and packed).

Composition and Structure

• Water: about 70-95%, held in cell vacuoles; water pressure (turgor) makes produce crisp.
• Carbohydrates: sugars in fruits; starch in tubers and immature seeds; fiber (cellulose, hemicellulose, pectic substances, lignin).
• Pectic substances change with ripening: insoluble protopectin in unripe fruit becomes soluble pectin, and then pectic acid in overripe fruit, which softens the tissue.
• Nutrients: vitamin C, carotenes (provitamin A), folate, potassium, and phytochemicals.
• Organic acids (citric, malic, tartaric) give tartness.

Ripening, Selection, and Storage

Climacteric fruits (banana, mango, papaya, avocado, tomato, guava) show a burst of respiration and ethylene production after harvest and continue to ripen. Non-climacteric fruits (citrus, pineapple, grapes, watermelon) do not ripen further after picking, so they should be harvested ripe. Ethylene is the natural ripening hormone; the traditional practice of using calcium carbide (kalburo) to hasten ripening of mangoes releases acetylene and raises safety concerns.

Selection: firm, heavy for size, bright natural color, free from bruises, decay, and wilting.

Store ethylene-producing fruits away from leafy vegetables, which yellow and wilt when exposed to ethylene.

Cooking Fruits and Vegetables

Texture:

• Heat softens cellulose and dissolves pectin.
• Acid (vinegar, tomatoes, calamansi) keeps vegetables firm.
• Alkali (baking soda) makes vegetables mushy and destroys thiamine and vitamin C.
• Calcium firms tissue, which is why calcium chloride is used in canned tomatoes.
• Cooking fruit in sugar syrup helps it keep its shape; cooking in plain water makes it soft (as in sauces).

Flavor:

• The cabbage family (cabbage, broccoli, pechay) develops strong sulfur compounds when overcooked, so cook briefly.
• The onion family becomes milder and sweeter with longer cooking.

Nutrient retention:

• Wash before cutting; cut just before cooking into larger pieces.
• Use a small amount of water or steam, stir-fry, or microwave.
• Cook only until tender-crisp and serve promptly.
• Use cooking liquid in soups and sauces, as in sinigang and tinola.
• Cook green vegetables uncovered for the first few minutes to release volatile acids and keep their color.

Legumes

Dry legumes include mongo (mung beans), soybeans, kidney beans, garbanzos, black beans, and peanuts. They provide about 20-25% protein by dry weight (soybeans about 35-40%), plus fiber, folate, iron, and potassium.

Antinutrients and gas:

• Trypsin inhibitors and lectins are destroyed by thorough cooking; undercooked kidney beans can cause poisoning.
• Phytates reduce iron and zinc absorption; soaking, sprouting, and fermentation lower them.
• Raffinose and stachyose are not digested and are fermented in the colon, causing gas; soaking and discarding the water reduces them.

Preparing dry beans:

1. Sort and rinse.
2. Soak: long soak in cold water for 8-12 hours, or quick soak by boiling for 2 minutes and soaking for 1 hour.
3. Cook in fresh water until tender.

Old beans and hard water lengthen cooking time. Acidic ingredients such as tomatoes slow softening, so add them after the beans are tender. Baking soda speeds softening but destroys thiamine.

Soy products: soy milk; tofu and tokwa (soy milk coagulated with calcium sulfate or magnesium chloride and pressed); taho (soft tofu with syrup and sago); toyo (soy sauce); tausi (fermented black soybeans); and tempeh (fermented whole soybeans).

Mongo sprouts (togue) have more vitamin C than dry beans but must be kept cold and cooked because sprouts can carry bacteria. Peanuts and corn stored in warm, humid conditions can grow molds that produce aflatoxins, so store them dry and discard moldy or shriveled nuts.