Fundamental of Food engineering

Lecturer & Course Context

• Lecturer: Dr. Ernest (Food Science Group, UNSW).
  • Former UNSW B.Sc.(Food Sci & Tech) student, PhD in food safety.
  • Teaches food safety, food engineering; lab demonstrator & tutor.
• Week 5 of first-year/introductory Food Science course.
  • Preceded by Yong Wang’s industry-scale engineering lecture.
  • Audience mix: Food Science, Nutrition & Dietetics, General Science/Engineering, General-Ed students.
• Purpose of today’s lecture:
  • Give a “first taste” of core engineering & scientific principles behind turning raw commodities into safe, marketable food products.
  • No complex calculations in this subject—focus on concepts, vocabulary, where to look for equations later.

Why Food Engineering Matters

• Engineering (general): design & build components → larger functional system (columns, bridges, motors).
• Food engineering: assemble raw, often unsafe ingredients → safe, palatable, consistent foods.
  • Home cooking = small-scale food engineering.
  • Industrial scale introduces issues of force, scale-up, packaging, distribution.
• Core goals:
  • Safety (microbial, chemical, physical).
  • Shelf-life & quality retention.
  • Product diversity & added value.
  • Economic viability & consumer accessibility.
• Ethical dimension: Profit relies on consumer trust; unsafe food = loss of life and business.

Canonical Safety Example 1 – Pasteurisation

• Raw milk = high microbial load (faecal, soil, udder flora).
  • Drinking raw milk: illness risk; psychological discomfort.
• High Temp Short Time (HTST) standard in AU: 72^\circ\text{C},\;15\;\text{s}.
• Questions engineers must answer:
  • Temperature?
  • Time?
  • Post-heat contamination control?
  • Shelf-life prediction?
• Novel option: High-Pressure Processing (HPP)
  • Keeps product “fresh-like” but costly (\$7 L milk example).

Canonical Safety Example 2 – Commercial Sterilisation & Canning

• Three-step overview: Fill → Double-seam seal → Retort (cook).
• Double seam: lid curl + body flange rolled twice → hermetic seal (nothing in/out).
• Retort (pressure cooker): Steam at 121.1^\circ\text{C} (≡250^\circ\text{F}) for 2.88\,\text{min} (“botulinum cook”).
• Target organism: Clostridium botulinum
  • Spore former, anaerobic, common in veg/meat.
  • Lethal toxin dose \approx 30\,\text{ng} (≈ 10^{-6} of grain of salt).
• Correct process ⇒ theoretical infinite shelf-life; practical quality limits (rancidity, texture).

Key Engineering Concepts

1. Units & SI

• Quantity meaningful only with unit; standardisation prevents disasters (e.g., Air Canada “Gimli Glider” fuel mis-uniting).
• Base SI set (7): Mass M (kg), Length L (m), Time T (s), Temperature (K), Amount (mol), Electric current (A), Luminous intensity (cd).
• Most food-engineering variables derive from M,L,T:
  • Volume L^3, Density M/L^3, Acceleration L/T^2, Mass flow M/T, Energy (J) M L^2/T^2.
• Always convert to SI in calculations (e.g., 1\;\text{cm}=0.01\;\text{m}, 1\;\text{mL}=10^{-6}\;\text{m}^3).

2. Conservation Principles

• Mass: Total mass in system constant—only redistributed (ice → water = same g).
• Energy: Cannot be created/destroyed, only transformed (potential → kinetic; chemical → thermal).
• Implication: perform mass/energy balances on whole plant or single unit operation to size equipment, locate losses, design controls.

3. Heat & Mass Transfer

• Always moves high → low (temperature, concentration).
• Modes:
  • Conduction (solids), Convection (fluids), Radiation (EM).
• Heat exchangers: hot utility ⇌ cold food (counter-current plates/tubes) for pasteurisation, CIP, etc.

4. Fluid Dynamics & Rheology

• Viscosity \eta = resistance to deformation; energy ↑ → flow.
  • Water < Oil < Honey.
• Newtonian vs Non-Newtonian:
  • Newtonian: \tau=\eta\dot\gamma; linear (water, oil).
  • Shear-thinning (ketchup), shear-thickening (corn-starch “oobleck”), Bingham-plastic with yield stress (peanut butter, toothpaste).
• Laminar vs Turbulent Flow
  • Characterised by Reynolds number \text{Re}=\dfrac{\rho v D}{\mu}.
    • \text{Re}
  • Choice affects mixing, heat transfer, pipe fouling.

Unit Operations (Industrial “Recipe Steps”)

• Cooling/refrigeration (blast chillers, cold rooms) – slows reactions.
• Heating (ovens, retorts, UHT, fryers) – microbial kill, texture, flavour.
• Mixing (horizontal & planetary mixers, ribbon blenders) – create homogeneous phase.
• Separation (centrifuges, membranes, decanters) – density/size differences (e.g., cream separation).
• Drying (tray, tunnel, spray, freeze-dry) – water removal for a_w control.
• Packaging (cans, pouches, glass, multilayer composites) – barrier to O$2$, H$2$O, light, microbes; rising sustainability pressure.

Process Walk-Through – Fluid Milk

1. Farm – raw milk at ≈37^\circ\text{C}, laden with microbes.
2. Immediate cooling to \le 4^\circ\text{C} in bulk tanks (cold chain begins).
3. Transport in refrigerated tankers.
4. Pasteurisation (HTST 72^\circ\text{C}/15\,\text{s} via plate heat exchanger).
5. Homogenisation (often same line) – fat globule size reduction.
6. Fill & package into sterile HDPE bottles/cartons under hygienic conditions.
7. Refrigerated distribution (supermarket \le5^\circ\text{C}).
8. Consumer: cool bag → home fridge.

• Shelf-life ladder:
  • Raw (ambient) ~8 h
  • Raw (4 °C) 1–2 d
  • Past.+cold chain ≈7 d
  • UHT (room T) ≤6 mo (once opened, must be chilled).
• Critical control = time–temperature integrator & hygienic design.

Preservation & Novel Technologies (Links to Previous/Future Lectures)

• High-Pressure Processing (HPP): 400–600\,\text{MPa}, minimal heat, high cost.
• Pulsed Electric Fields, UV-C, Cold Plasma, Membrane filtration as emerging non-thermal options.
• Each balances safety, quality retention, energy use, capital cost, regulatory hurdles.

Ethical, Practical & Regulatory Implications

• Safety regulations (e.g., dairy HTST, canned-food botulinum cook) codified in national standards (FSANZ, FDA…).
• Allergen labelling accuracy (e.g., Nestlé “may contain tree nuts” non-compliance—must specify almond, hazelnut…).
• Environmental impact of processing & packaging → need for waste minimisation, recyclable/biobased materials.
• Consumer perception: “fresh is best” vs necessity of processing for public health & food security.

Study Connections & Real-World Relevance

• Thermodynamics & transport phenomena will re-appear in upper-year Food Engineering units.
• Microbiology (Week 3), Safety & HACCP (Week 2) provide biological rationale for heat/pressure settings.
• Packaging lecture (Week 7) deepens barrier & sustainability concepts.
• Industrial visits (Yong Wang) show scale-up of today’s principles.

Key Formulae & Numerical Facts to Remember

• Sterilisation target: 121.1^\circ\text{C},\;2.88\,\text{min} (F-value for C. botulinum).
• HTST milk: 72^\circ\text{C},\;15\,\text{s}.
• Lethal botulinum toxin dose: 30\,\text{ng}.
• Base SI conversions:
  • 1\;\text{cm}=10^{-2}\;\text{m} ; 1\;\text{mL}=10^{-6}\;\text{m}^3 ; 1\;\text{h}=3600\;\text{s}.
• Dimensional forms:
  • Volume =L^3, Density =M/L^3, Acceleration =L/T^2, Mass flow =M/T, Energy =M L^2/T^2.
• Reynolds number \text{Re}=\rho v D/\mu decides laminar vs turbulent.

Take-Away Messages

• Food Engineering = applied physics & maths for edible systems; it underpins safety, quality, economics.
• Always think in units, mass/energy balances, and “hot → cold, high → low” flows.
• Safety first: understand target hazards (e.g., C. botulinum) and design time–temperature or alternative regimes accordingly.
• Unit operations are industrial-scale “recipe steps” that can be recombined for any product.
• Emerging non-thermal technologies and sustainable packaging respond to consumer & environmental demands while retaining core engineering principles.