Isoflavones and Myoglobin in Meat Science

Isoflavones

• Isoflavones are polyphenolic compounds found in soybeans.
• They act like estrogen, classified as phytoestrogens.
• Primarily in glycoside form, converted to aglycones during fermentation/digestion.
• Soy isoflavone glycosides: genistin, daidzin, glycitin; aglycones: genistein, daidzein, glycitein.

Myoglobin

• Meat pigments include hemoglobin and myoglobin.
• Myoglobin gives meat its red color.
• In livestock, 90% of iron is in hemoglobin, 10% in myoglobin.
• In consumed meat, 95% of iron is from myoglobin.
• Myoglobin is a porphyrin structure with iron at its center.
• Globin (protein component) is a globular protein.

Changes in Meat Color

• Myoglobin combines with oxygen to form oxymyoglobin (pink) then metmyoglobin (brown).
• This reaction speeds up with heating.

Non-Enzymatic Browning

• Maillard Reaction: Sugars react with amino compounds to form brown pigments (melanoidins).
• Affects color, flavor, and aroma (e.g., bread, soy sauce).
• Factors influencing Maillard reaction: temperature, water activity, sugar type, pH, protein concentration, amino compounds.
• Caramelization: Sugars heat to form brown pigments (caramels). Common in high-sugar foods.

Enzymatic Browning

• Caused by polyphenol oxidase, which oxidizes foods to melanin.
• Related enzymes: monophenol oxidase, diphenol oxidase.

Control Measures for Browning

• Control oxygen levels.
• Inactivate enzymes.
• Add chelating agents (e.g., phosphates, EDTA) to bind metal cofactors.
• Use reducing agents (e.g., ascorbic acid, cysteine).
• Adjust temperature.
• Dehydrate the product.
• Apply irradiation.
• Utilize enzyme inhibitors.
• Employ high-pressure treatment.

Food Flavor

• Flavor involves taste, aroma, tactile sensations, pain, and temperature.
• Flavor influences food preference as much as color.
• Sensory evaluation was the primary method to determine food flavor. Flavor chemistry (aroma study) introduced the electronic nose and electronic tongue.

Electronic Nose and Tongue

• Detect odor/aroma components using a sensor array system (SAS).
• Qualitative and quantitative analysis through software, based on electrical signals.
• Human pathway: component-receptor binding, biochemical reaction, signal conversion, brain transmission.

Taste of Food

• Taste relies on sensory evaluation and analysis.
• Taste may be influenced by other taste components (volatile and non-volatile).
• 20th century: taste classification unified into four basic tastes.
• Basic tastes: sweetness, saltiness, sourness, bitterness.

Basic Taste Criteria

• Distinct receptors, different from other basic tastes, and cannot be replicated by combining other basic tastes.

Taste Perception in the Tongue

• Four basic tastes primarily detected in specific tongue regions:
  • Sweetness: front
  • Saltiness: near front
  • Sourness: middle
  • Bitterness: back

Taste Organs

• Taste receptors exist beyond the tongue (throughout the oral cavity).
• Taste components bind to various taste receptors on the tongue surface.
• Tongue contains papillae with taste buds (clusters of 50-150 taste receptors).

Taste Receptor Mechanisms

• Taste component contacts taste receptor.
• Biochemical reaction occurs.
• Chemical energy converts to electrical energy, transmitted to the brain.
• Sweet and bitter tastes use G-proteins for signal transmission.

Sourness and Saltiness

• Sourness (H+): blocks ion flow.
• Saltiness (Na+): permeates ion channels.

Taste Thresholds

• Absolute/sensitivity/recognition thresholds: minimum detectable concentration of a taste component.
• Basic taste minimum concentrations:
  • Sweetness: 0.02 M sucrose
  • Saltiness: 0.02 M NaCl
  • Sourness: 0.005 M HCl
  • Bitterness: 0.002 M quinine

Taste and Temperature

• Taste perception varies with temperature, with exceptions for sourness.
• Bitterness and saltiness thresholds increase with rising temperature.
• Sweetness thresholds decrease up to a certain temperature, varying with sweeteners.

Sweetness

• (AH/B) theory: describes how fructose interacts with taste receptors to produce a sweet taste. (Focuses on the hydrogen bonding interactions of specific hydroxyl groups of fructose and the receptor proteins)

Sucralose/Fructooligosaccharides

• Sucralose and fructooligosaccharides taste similar to sucrose.

Bitterness

• Bitterness is often undesirable but key in some food types (e.g., beer, tea).
• Bitter components: alkaloids, glycosides, amino acids/peptides, ketones.
• Bitter compounds in foods: quinine, theobromine, and caffeine.

Bitter Taste Components

• Beer bitterness: originates from the hop plant constituent Humulone undergoing isomerization (to Isohumulone).
  • Other bitter substances: Co-humulone and Ad-humulone.
• Citrus fruit bitterness: Flavonoids, naringin (glycoside), limonin.
  • naringin can be converted to naringenin by enzyme naringinase, removing the sugar portion.
  • Limonin bitterness can be reduced via cyclodextrin removal
• Amino acids/peptides: bitter, especially those high in hydrophobicity (Val, Leu, Ile, His, Tyr, Phe, Trp).

Saltiness

• Salt (NaCl) is the primary salty taste.
• Salty taste is influenced by cationic components of the salt.
• Anions influence or modify saltiness.
• Chloride (Cl-) has the lowest suppressive power.
• Salt affects other taste perceptions (sweet, sour, and bitter).

Sourness

• Sourness is due to organic acids (e.g., acetic, lactic, malic, citric, tartaric, ascorbic).

Hot/Pungent Taste

• Chili pepper heat: Primarily capsaicin and dihydrocapsaicin, derivatives of Guaiacol.
• Scoville scale: measures pungency/stimulation in chili peppers.
• Pepper (Piper nigrum) heat: Chavicine in unripe; piperine (less spicy) in ripe.
• Ginger heat: Gingerol, shogaol (phenylalkyl ketones) > zingerone (sweet).

Umami

• Umami is a savory, pleasant taste (Japanese for "delicious").
• Monosodium glutamate (MSG), first isolated in kelp.
• Nucleotides (e.g., from dried bonito) also contribute to umami.
• Other umami enhancers: hydrolyzed vegetable proteins, yeast extracts, soy extracts, peptides containing cysteine.

Astringency

• A taste causing a contraction feeling in the mouth.
• Caused by protein coagulation with astringent substances.
• Components: tannins, polyphenols, metallic salts, carbonyl compounds.
• Milk/cream can reduce astringency by binding polyphenols.

This quiz explores the roles of isoflavones and myoglobin in meat coloration and composition. Learn about phytoestrogens, the impact of myoglobin on meat's red color, and the Maillard reaction's significance in non-enzymatic browning. Perfect for food science enthusiasts or students!