Food Science Exam 2

oligosaccharides

• prebiotic function: fructo-oligosaccharides and galacto-oligosaccharides promote the growth of beneficial gut bacteria

• taste and texture modulation: fructo-oligosaccharides have mild sweetness (30-50% sweetness of sucrose) and improve mouthfeel in yogurt and beverages

• low caloric value: oligosaccharides are resistant to human digestion (used in low-sugar, low-calorie, and functional foods)

polysaccharides

digestible = starch

non-digestible = fiber

starch

• made of glucose units

• naturally occurs in plants as energy storage

• amylose: linear chains of a (1→4) linked glucose

• amylopectin: highly branched with a (1→4) and a (1→6) link

starch sources

cereal grains, legumes, potatoes

nutritional role of starches

digestible carbohydrate broken down into glucose in the small intestine (energy source)

functional properties of starches in food

thickening, gelation, texture modification, water binding (thickener, stabilizer)

starch gelatinization

starch is naturally present in the form of granules, when they are heated in the presence of water, they absorb water, swell, and lose their crystalline structure

• involves irreversible structural changes, such as amylose leaching, and results in increased viscosity and modification of texture

• during cooling, a semi-solid gel is formed (pudding, custard)

dietary fiber

• non-digestible polysaccharides found in plant-derived foods (resist digestion in the human small intestine)

• major types = cellulose, hemicellulose, pectin

cellulose

dietary fiber, linear polymer of glucose; provides structural support in plant cell walls

hemicellulose

dietary fiber, a heteropolymer, more branched and amorphous than cellulose

pectin

dietary fiber, rich in galacturonic acid, forms gels, important in fruits and used in jam/jelly making

physiological effects of dietary fiber

• consumption of viscous fibers delays gastric emptying and slows absorption (extends the feeling of fullness)

• helps regulate blood glucose levels

• promote gut heath by improving digestion and promoting regular bowel movement (prevents constipation)

• serves as a substrate for fermentation by gut microbiota

common sources of dietary fiber

fruits, vegetables, whole grains

dietary fiber recommendations

average, 1,3 grams fiber in 30 grams of vegetables (USDA)

water-holding and fat-binding

absorbs and retains water, improving moisture retention in baked goods and enhancing freeze-thaw stability in frozen foods (stabilizers, moisture retainers)

• binds fats or stimulate fat texture

texture modification effects

• improves viscosity and mouthfeel (thickeners)

• contributes to gel information (gelling agents)

• stabilizes emulsions (emulsifiers)

satiety and digestive health improvement

• add volume to low-calorie foods → bullying agents

• some soluble fibers stimulate beneficial gut bacteria → prebiotics

fiber intake and DRI values

adequate intake (AI) provided by the dietary reference intake (DRI) recommendations based on intake levels to protect against coronary heart disease

• men = 30-38

• women = 20-25

• average intake in US

  • men = 16-18

  • women = 12-14

ways to increase fiber intake

• select whole-grain breads (not just whole wheat)

• choose bread with 3+ grams fiber/serving

• eat the skins of fruits and vegetables

• choose fruit over fruit juices

• sprinkle ground flaxseed on cereals and baked goods

• limit consumption of highly refined white flour products

• use whole-grain pastas, crackers, cookies

proteins

macromolecules composed of long chains of amino acids

• polymers of amino acids

basic composition of proteins

carbon, hydrogen, oxygen, nitrogen, sometimes sulfur in sulfur-containing amino acids

structural support of proteins

proteins form body tissues such as muscle, skin, hair, and nails

• collagen in skin, keratin in Hari and nails, actin and myosin in muscle

enzymes

most are proteins that speed up chemical reaction in the body

• amylase: break down starch in saliva

• pepsin: digest protein in the stomach

transport proteins

move substances across membranes or throughout the body

• hemoglobin: carries oxygen in red blood cells

hormone, signaling and immune function of proteins

• some act as hormones that serve as chemical messengers, while others function as antibodies

• insulin = regulates blood sugar levels

• immunoglobulins = identify/neutralize pathogens

energy source (secondary role of proteins)

• provides 4 kcal/g, but the body prefers carbs and fats for energy; used during starvation, prolonged fasting, or low-carb diets

• risk of losing lean muscle mass if intake is inadequate

general structure of amino acids

central carbon atom is bonded to

• hydrogen atom

• amino functional group NH2

• carboxylic acid group - COOH

• R group (side chain) = rest of molecules

peptide bonds

formed between the carboxyl group of one amino acid and the amino group of another

• crucial process for forming the primary structure (linear sequence of amino acids) of proteins

dipeptide

2 amino acids (AAs) linked together

polypeptide

many amino acids linked in a chain

protein

one or more polypeptide folded into a functional structure

side chains

amino acid sequence and the properties of its side chains are key to protein folding (3D structure)

formation of proteins

1. amino acid sequence created a linear polypeptide chain (primary structure)

2. the secondary structure forms a helix, b-sheet

3. the tertiary structure is determined by the spatial folding of the secondary protein structure, driven by various side chain (r-group) interactions → 3D folding pattern

4. quaternary structure is formed when two or more tertiary structures assemble into a protein complex (not all proteins have it)

9 essential amino acids

• cannot be synthesized by the human body; must be obtained through diet

• if diet lacks essential amino acids, the body will quickly stop building proteins and start losing nitrogen, leading to the breakdown of muscle and other tissues

• 9 = histidine, isoleucine, leucine, lysine, methionine, phenylanine, threonine, tryptophan, valine

cysteine

• two molecules of cysteine can link together to form cystine via a disulfide bond

• disulfide bonds influence the texture of food

  • wheat proteins, glutenin and gliadin, are connected through disulfide bonds, which contribute to the formation of gluten (dough springiness)

monosodium glutamate (MSG)

• salt from glutamic acid (natural amino acid)

• enhances umami taste

• food containing high levels = instant noodles, flavored potato chips

• not found in nature

• produced through fermentation processes

protein denaturation

alternation of a proteins native structure without breaking its peptide bonds (unfolding of proteins)