Plant Cell Types, Fruits, and Carbohydrate Chemistry in Food Science

Parenchyma

Thin-walled, loosely packed cells responsible for storage, photosynthesis, and metabolic activity. Found in edible parts of fruits and vegetables; contribute to texture and juiciness.

Collenchyma

Elongated cells with unevenly thickened walls. Provide flexible support in growing tissues (e.g., celery stalks).

Sclerenchyma

Thick-walled, lignified cells that provide rigid support. Found in seed coats and gritty textures (e.g., pear stone cells).

Cellulose

Insoluble fiber; remains largely unchanged during cooking.

Hemicellulose

Partially soluble; breaks down with heat and alkaline conditions, softening plant tissue.

Pectic substances

Convert from protopectin (firm, immature) to pectin (gel-forming, ripe) to pectic acid (overripe, mushy). Affected by ripening and acid/heat exposure.

Climacteric Fruits

Continue to ripen after harvest; show a spike in respiration and ethylene production. Examples: Bananas, apples, peaches, tomatoes.

Nonclimacteric Fruits

Do not ripen further after harvest; minimal ethylene response. Examples: Strawberries, grapes, citrus fruits.

Refrigerate

Most berries, leafy greens, apples, carrots — slows respiration and spoilage.

Room temperature

Tomatoes, bananas, avocados (until ripe), onions — cold can damage texture or flavor.

Retaining Chlorophyll in Green Vegetables

Cook uncovered briefly to allow volatile acids to escape. Use boiling water and avoid prolonged cooking. Avoid adding acids (e.g., lemon juice) during cooking — they promote pheophytin formation (olive-green pigment).

Preventing Browning of Anthoxanthins

Strategies: Add acid (lemon juice, vinegar), cook with lid off, minimize heat exposure. Mechanism: Acid stabilizes white pigments and prevents enzymatic browning by lowering pH.

Acids in Fruits

Higher total acid concentration; fewer types (e.g., citric, malic).

Acids in Vegetables

Lower total acidity but more diverse acids (e.g., oxalic, isocitric).

Functional Roles of Soluble Fibers, Gums, Inulin

Improve texture and mouthfeel. Stabilize emulsions and foams. Enhance satiety and digestive health. Act as fat replacers or prebiotics.

Simple Carbohydrates

Mono- and disaccharides; sweet, quick energy, high solubility.

Complex Carbohydrates

Polysaccharides (starch, fiber); slower digestion, structural roles, less sweet.

Monosaccharide Composition of Disaccharides

Sucrose = Glucose + Fructose; Lactose = Glucose + Galactose; Maltose = Glucose + Glucose.

Starch Structure

α-1,4 and α-1,6 bonds; digestible, energy source.

Cellulose Structure

Glucose polymer; provides structural support.

Sweetness

Fructose > sucrose > glucose; heat can reduce perceived sweetness.

Hygroscopicity

Increases with humidity; affects texture.

Solubility

Fructose most soluble; temperature increases solubility.

Hydrolysis

Splits disaccharides into monosaccharides (e.g., sucrose → glucose + fructose).

Degradation

Breakdown under heat or acid.

Caramelization

Browning from sugar heating; flavor and color changes.

Maillard reaction

Sugar + amino acid → browning, flavor (non-enzymatic).

Crystalline Candies

Organized sugar crystals (fudge, fondant); smooth texture.

Amorphous Candies

No crystals (toffee, taffy); chewy or glassy.

Inversion

Hydrolysis of sucrose into glucose + fructose.

Nutritive Sweeteners

Provide calories and sweetness; include sucrose, glucose, fructose, honey, corn syrup.

Nonnutritive Sweeteners

Bitter aftertaste: Saccharin, stevia (some forms).

Amylose

Linear; forms firm gels, retrogrades easily.

Amylopectin

Branched; thickens but doesn't gel well, better freeze-thaw stability.

Influences on Starch Gel Strength

Amylose content, concentration, temperature, pH, sugar, fat, and agitation.

Milling Process

Grain cleaned, tempered, ground, and sifted; separates bran, germ, and endosperm.

Flour Types and Baking Behavior

Cake/Pastry: Low (~7-9%); All-Purpose: Medium (~10-12%); Bread: High (~12-14%).

Self-Rising Flour

Contains AP flour + baking powder + salt; substitution requires adjusting leavening and salt in recipe.

Gluten Development

Requires water + mixing; influenced by flour type, hydration, mixing time, fat/sugar (inhibit), salt (strengthens).

Functional Role of Baking Ingredients

Flour: Structure; Liquid: Hydration, steam; Fat: Tenderness, flavor; Sugar: Sweetness, browning; Eggs: Structure, emulsification; Leavening: Volume; Salt: Flavor, gluten control.

Leavening Sources

Air: Whipping, creaming; Steam: Liquid evaporation; CO₂: Baking soda/powder, yeast fermentation.

Baking Powder Substitute

Substitute: ¼ tsp baking soda + ½ tsp cream of tartar per tsp baking powder; mechanism: Acid-base reaction releases CO₂ for leavening.