Chocolate Science Exam 3

describe polymorphism

the ability of a substance to exist in multiple crystalline forms

specifics for cocoa butter

• 6 different polymorphic forms

• each form possesses a different melting point & level of stability

• form V is highly stable w/ a melting point of 33.8 degrees C

Tricylglycerol molecules

commonly known as TAGs, they are molecules w/ a glycerol backbone bonded to three fatty acid chains

Cocoa butter specifics for TAGs

TAGs are primarily symmetrical monounsaturated molecules; referred to as SOS (saturated-oleic acid-saturated) ^→ two fatty acids and in the middle a monosaturated molecule

Main TAGs in cocoa butter

• POSt (1 palmitoyl- 2 oleoyl-stearin) : most abundant 40.3%

• stOSt (1 stearoyl- 2 oleoyl- stearin) : 22.7% to 23%

• POP (1 palmitoyl- 2 oleoyl- palmitin) : 19.6% to 20%

3 methods for tempering chocolate

1. by hand: pour hot liquid chocolate onto cold marble slab → use spatulas to move the mass (initiates crystallization) → chocolate solidifies once stable seeds form

2. tempering machines: automation of tempering process; uses internal agitating mechanisms and precise sensors to maintain exact temperatures needed for crystal stability

3. Three Stage Thermal Sequence: manipulation of temperature over time

   1. Heat chocolate to 50 degrees C to melt all existing fat crystals

   2. Cool the mass to 27 degrees C to allow the formation of both stable (β) and unstable (β′) crystals

   3. Reheat mass to 30-32 degrees C to melt out the unstable crystals, leaving only the stable Form V crystals in the final liquid

Impact on Tempering Chocolate

1. Appearance and Snap → leaves chocolate shiny and the “snap” when broken

2. Mouthfeel and Melting → ensures chocolate melts at mouth temp. creating smooth texture

3. Prevention of fat bloom → incorrect tempering leaves a white/grey film that ruins the texture & look

4. Manufacturing efficiency → tempering ensures the chocolate contracts slightly as it solidifies, allowing it to release from molds easily

Physical Properties of Solid Chocolate

• defined by mass, volume, size, shape, and density

• deformation properties: describes the force required to change its shape

• Modulus of Elasticity: the extent of the deformation

Liquid Properties of Chocolate

• non-Newtonian fluid: a substance that changes its viscosity (thickness) and flow behavior when subjected to stress, force, or shear, rather than maintaining a constant viscosity like water

• apparent viscosity (resistance to flow)

• yield stress (the minimum force to make the liquid start moving)

Measuring Solids

• Compression and Tension Tests: measure stress (pressure in Pascals) versus strains (relative change in height)

• Flexure Test (Three point Bending): used to determine the Young’s Modulus (E), which represents the ratio of stress to strain. Quantifies the chocolate stiffness, its “snap”, and its fracture point

Measuring Liquids

• Rheometry: flow properties are measured by plotting shear stress (σ) against the shear rate (γ˙). The slope of the curve identifies the apparent viscosity

• Mathematicals models: frameworks like the Casson Model and the Herschel-Bulkley Model are applied to these measurements to precisely characterize the fluid’s behavior

Relevance of Measuring Physical Properties

• Engineering and Economics: critical for pumping calculations → select correct pump size & estimate energy costs for chocolate to move through the pipes

• Consumer Experience: measurements help relate objective instrumental data to the subjective human sensory experience

• Quality Assurance: serve as a check for the success of tempering, correct composition (ingredient ratios), and the microstructure (such as the presence of air bubbles)

Connection between Chemistry and Physics

• Molecular Basis: the physics of how chocolate melts is a chemistry of triacylglycerol (TAG) molecules

• Polymorphism: since there is 6 crystalline forms → each has a different melting point and stability

• Crystallization through Physics: Tempering uses controlled thermal sequences (physics) to ensure the chocolate reaches Form V → gloss and snap of chocolate

Ingredients and Composition (Abundance)

Chocolate is primarily composed of carbohydrates (sugars/starch), lipids (cocoa butter/lecithin), and proteins (enzymes/storage proteins), along with water and stimulants

Categories of Chocolate (Standard of Identity)

Defined by federal law (CFR Title 21) as Chocolate Liquor, Sweet Chocolate, Semisweet/Bittersweet Chocolate, Milk Chocolate, and White Chocolate based on specific fat/solid percentages

Methods to Characterize Composition

Chromatography (GC/LC) for sugars and aromas; HPLC for antioxidants; the Kjeldahl method for total protein; and Ether extraction for fat analysis

5 Components of Chocolate Liquor (Fat vs. Solids)

Fat Fraction: Triacylglycerols (TAGs). Cocoa Solids Fraction: Fiber, Starch, Theobromine, and Caffeine

Determination of Relative Sweetness

Measured by sensory panels relative to sucrose, which is the standard baseline with a value of 1.0

Function of Milk in Milk Chocolate

Milkfat softens texture; lactose adds sweetness and flavor precursors; and milk proteins reduce the perception of bitterness and astringency

The Maillard Reaction

A form of non-enzymatic browning where a sugar's carbonyl group reacts with a protein's amino group (optimal at 140-165°C) to create roasted flavor compounds like pyrazines

Main Nutrients in Chocolate

A complex mixture of carbohydrates (sucrose, starch, fiber), lipids (triacylglycerols, phospholipids), and proteins (enzymes, storage proteins), along with minerals, sterols, and stimulants like theobromine and caffeine

Nutrition Facts and Daily Values (DV)

Calculated against a standard 2,000-calorie diet; for a 40g serving of 70% dark chocolate, this includes 19g total fat (29% DV), 12g saturated fat (60% DV), and 17g total carbohydrates (6% DV)

Serving Size and Frequency

A proposed healthy serving is 4 squares (40g), integrated into a 2,000–2,500 calorie daily intake to ensure the overall diet remains balanced in proteins, carbs, and fats

Phytochemicals

Non-nutritive, health-promoting chemicals derived from plants; in cacao, these primarily refer to antioxidants like flavonoids

Role of Cacao Lipids in Health

Cacao contains C-18 fatty acids (stearic acid) and plant sterols, specifically β-sitosterol, which may contribute to health by inhibiting cholesterol absorption

Role of Non-Caloric Health-Beneficial Compounds

Includes flavonoids (catechin, epicatechin, and quercetin) that provide antigenotoxic and anticarcinogenic effects and help mitigate conditions associated with aging

How Antioxidants Work

They stabilize harmful free radicals (unstable atoms created when an electron is removed) by donating electrons to them, thereby preventing damage to DNA and proteins

Chemical Structure of Polyphenols and Flavonoids

Possess a C15​ (C6​−C3​−C6​) basic skeleton consisting of two benzene rings (A and B) joined by a three-carbon chain that forms a middle oxygen-containing ring (C)

Physiology and Psychology of Taste

Perception is a biosensing process where physical/chemical receptors (physiology) send signals to the brain, which then uses psychophysics to interpret those signals based on individual, social, and cultural effects

Principles of Taste, Texture, and Aroma

flavor is defined by Gustation (5 tastes: sweet, sour, salty, bitter, umami), Olfaction (ortho-nasal and retro-nasal aromas), and Texture (oral/hand feel and chemesthetic irritation like "heat")

Commonly Used Sensory Analysis Tests

(1) Hedonic Test: Uses a 9-point scale ("Like Extremely" to "Dislike Extremely") to measure consumer liking; (2) Difference Tests: Such as the Triangle Test, used to determine if a perceivable difference exists between samples

Human Senses vs. Laboratory Instruments

Humans follow a Receptor → Brain → Behavior flow, acting as complex biosensors, whereas instruments follow Sensor → Processor → Output; human panels must be "calibrated" through training to provide reproducible results

Requirements of Subjective Measurements

Requires highly controlled environments (booths/amber lighting) to prevent bias; the primary challenge is mathematically relating instrumental data (viscosity/size) to the actual subjective human experience using statistical tools like ANOVA

Cultural and Experiential Factors in Perception

Sensory perception is shaped by age, regional culinary history (e.g., exposure to "ethnic aisles"), and concepts or attitudes, such as the perceived health benefits of a product

Consumer Panel vs. Trained Panel

Consumer panels are used for affective testing to assess market liking and purchase likelihood without calibrating participants. Trained panels consist of selected members calibrated to a consistent lexicon to provide objective, reproducible assessments for quality assurance or product formulation

Two Common Sensory Analysis Experiments

(1) Hedonic Test: Uses a 9-point scale ("Like Extremely" to "Dislike Extremely") to measure preference. (2) Triangle Test: An analytical test where participants identify the different sample among three to determine if a statistically significant difference exists

Challenges of Quantitative Data from Subjective Measurements

The primary scientific hurdle is mathematically relating instrumental data (such as viscosity) to the actual human experience.

Mitigation of Cultural/Experiential Factors

managed in sensory analysis by using individual booths to avoid influence, amber lighting to mask distracting visual cues, and a standardized lexicon to ensure consistent language across different panelists