Review for Exam #2

Outline

• Barrier properties and permeation• Shelf life• Aseptic processing and packaging• Packaging for microwaves

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Barrier Properties and Permeation

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Barrier Properties• Goals of barriers

– Minimize gas, moisture, light, and odor movement– In some cases, movement is desired

• Two mechanisms of gas movement across plastic– Pore effect

• Movement through microscopic pores, pinholes, cracks• This effect decreases with increasing thickness of plastic

– Solubility-diffusion effect• Gas dissolves at one end, diffuses, and is desorbed at other end• Henry’s law of solubility• Fick’s laws of diffusion (First & second law)

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Steady State Diffusion across a SheetAt steady state and for low concentrations:F = -D (dc/dx) = D (c2 – c1)/LF: Gas transmission rate (GTR) in m3/m2 s OR

Water vapor transmission rate (WVTR) in kg/m2 sFrom Henry’s law, c = S pThus, F = -DS (p2 – p1)/LAlso, F = Q/AtQ: Quantity of permeant (m3 gas OR kg moisture)Thus, Q/At = DS (p2 – p1)/L P = DS & p = p2 – p1

Thus, P = QL/(A t p) = FL/p where, F = Q/A tP: Permeability coeff. (kg m/m2 s Pa OR cc m/in2 day mm Hg)

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Permeability Coefficient (P)• P = DS

– Product of diffusion coefficient (D) & solubility coefficient (S)

• Q: Amount of permeant, kg or m3

• L: Thickness of package, m• A: Surface area of package, m2

• t: Time, s• p: Partial pressure difference btwn inside & outside, Pa• F = Q/At = OTR or WVTR in m3/m2 s OR kg/m2 s

– OTR: Oxygen transmission rate– WVTR: Water vapor transmission rate

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Effective Permeability (Pe)

When a laminate/composite is created, the effective permeability of the package is given by:

L1, L2, ….: Thickness of each layerP1, P2, ….: Permeability coefficient of each layer

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Effect of Temperature on PermeabilityThe dependence of the permeability coefficient of a film to temperature is given by the following equation:

Writing the above equation for 2 temperatures, we get:

Dividing one equation with the other, we get:

T1, T2: Temperatures in KelvinP1, P2: Corresponding permeability valuesEp: Activation energy of the film for permeation of a specific constituent, J/molR: Universal gas constant (= 8.314 J/mol K = 1.987 cal/mol K

= 82.06 atm cm3/mol K = 1.314 atm ft3/mol K)8

Shelf Life Studies

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Shelf Life and Product Deterioration• Factors affecting shelf life

– Formulation (Functional ingredients, pH, O2 content aw)– Processing (Time-temperature)– Packaging (Barrier properties of package)– Handling of package (Compromising package integrity)– Storage (Temperature, relative humidity, light -- UV)

• Forms of deterioration during storage– Microbial (Spoilage organisms – gas, odor, instability)– Enzymatic (Color/odor change, product breakdown)– Chemical (Lipid oxidation, flavor changes)– Nutritional (Vitamin and antioxidant degradation)– Physical (Staling, caking, texture change, melting, settling)10

Techniques to Determine Shelf Life

• Literature values– Similar product

• Turnover time– Monitor sales at retail store to determine time taken to

sell a batch• End point study

– Samples from retail store taken periodically and tested• Accelerated shelf life testing (ASLT)

– Temperature (high & cycling), O2, RH, UV, shaking11

Accelerated Shelf Life Testing (ASLT)• Select at least 3 elevated temperatures 5+ °C apart• Determine shelf life at these temperatures• Plot shelf life (log scale) on y-axis and temperature on

x-axis• Extrapolate graph to determine shelf life at desired

temperature

Other Tests: Cycling temperature between 0 °C and room temp; controlled shaking; high oxygen; high humidity

Temperature

Shel

f Life

(Log

Sca

le)

**

*

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Other Factors in ASLT• Cycling product between 0 °C and room temp.

– Accelerates watery separation in starch-thickened foods– Absence of separation after 30 cycles over 2 months

suggests product will be stable for 2 years at room temp.• High oxygen or high humidity atmosphere

– Used for some products• Controlled shaking

– 250-300 strokes per minute for several hours• Used to check for separation in unstable emulsion products

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Sensors to Monitor Shelf Life• Critical temperature

– Response only when temperature goes above or below a pre-set value (Eg., 3M MonitorMark Freeze/Thaw indicator)

• Partial history– Time-temperature history is obtained after a certain

temperature is attained (Eg., 3M MonitorMark extended response indicator; chemical melts on wick and diffuses as a function of time)

• Full history– Continuous time-temperature history from beginning

(Eg., LifeLines Freshness monitor, IPOINT time temperature monitor, Vitsab single & triple dots) 14

Time Temperature Integrators (TTIs)• Characteristics of TTIs

– Inexpensive, easy to prepare, incorporation does not alter heating rate, experiences same time-temperature history as product, easy to recover, yield accurate information

• Classification of TTIs– Based on working principle

• Biological, chemical, physical– Type of response

• Single, multiple– Origin

• Intrinsic, extrinsic– Application

• Dispersed, permeable, isolated– Location

• Volume averaged, single point 15

Aseptic Processing and Packaging

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Aseptic Processing System

BPV

HoldingSection

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Ultra High Temperature (UHT)• The term UHT is used interchangeably with Aseptic• All pathogenic and spoilage organisms

(including spores of C. botulinum) are killed• Thermophilic organisms may survive• Commercially sterile product• 284 °F (140 °C) for 4 s• Shelf life: 1-2 years• UHT/Aseptic processing covered under

– 21CFR108, 21CFR113, 21CFR114

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Advantages of Aseptic Processing

• Rapid heat treatment• Improved product quality• Long shelf life of product• No need for refrigeration• Flexible package type• Less overall energy requirement• Easy adaptability to automation• Fewer operators needed

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Disadvantages of Aseptic Processing

• Slower filler speed• Higher initial cost• Need for better control of raw ingredients• Need for better trained personnel• Need for better control of process variables• Stringent validation protocol

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Aseptic Packaging: Types of Systems• Can systems

– Metal, composite• Bottle systems

– Glass, plastic• Sachet & pouch systems

– Form-fill-seal, layflat tubing• Cup systems

– Form-fill-seal, preformed cups• Carton systems

– Form-fill-seal, prefabricated cartons• Bulk packaging systems

– Metal drum, bag-in-box 21

Types of Aseptic Packages• Metal cans

– Dole system (superheated steam sterilization)

• Metal bags– Preformed (and irradiated) sealed bags

• Paperboard laminates– Form-fill-seal cartons– Preformed cartons

• Plastic cups– Preformed cups– Thermoform-fill-seal

• Plastic pouches– Form-fill-seal (similar to cartons)

• Plastic bottles– Preformed– Blowmold-fill-seal 22

Aseptic Packaging(Sterilization of Food Contact Surface)

• Radiation– UV-C, infrared, ionizing

• Heat– Saturated steam, superheated steam, hot air, hot air &

steam, extrusion• Chemicals

– Hydrogen peroxide, peracetic acid, ethylene oxide

Note: A 4D, 6D, or 12D process is delivered depending on type of product; ~3% of microorganisms on package are spores; ~30-90 spores per m2 is assumed

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Sterilization of Package• Radiation

– UV-C (250-280 nm)– Infrared (mainly for smooth, even surfaces -- lids)– Ionizing radiation (Co-60, Cs-137, e-beam)

• Heat– Saturated steam (165 °C for ~2 s)– Superheated steam (~225 °C for ~40 s)– Hot air (315 °C; surface reaches ~145 °C for ~3 min)– Hot air & steam– Extrusion (~180-230 °C for ~3 min)

• Chemicals– Hydrogen peroxide (30% conc. at ~80 °C)– Peracetic acid – PAA (1% conc.; ~20 °C)– Ethylene oxide 24

Package Sterilization (Radiation)• UV-C

– 250-280 nm is used (optimum effectiveness at 253.7 nm); applicable only to smooth, even surfaces

• Infrared– Applicable only to smooth, even surfaces

• Aluminum lid coated with plastic laquer

• Ionizing radiation– Co-60 or Cs-137 at 25 kGy (2.5 Mrad)– 100 keV of electron beam– Use: Empty sealed containers such as bag-in-box

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Package Sterilization (Heat)• Saturated steam

– 165 °C and 600 kPa for 1.4 s (cups) or 1.8s (lids)– Disadvantages

• Need for high pr., need to remove air to inc. heat transfer, and dilution of product as steam condenses

• Superheated steam– 220-226 °C for 36-45 s

• Hot air– 315 °C (Tsurface ~145 °C for ~3 min; acidic products only)

• Hot air & steam– Hot air blown through nozzle to heat base & walls uniformly; used

for PP cups which are stable up to 160 °C

• Extrusion– 180-230 °C for ~3 min; yields 3-4 log kill; ok for acidic products 26

Package Sterilization (Chemicals)• Hydrogen peroxide

– Dipping, spraying, rinsing with or without UV-C or heat– 80 °C and 30% concentration is needed– Residual peroxide < 100 ppb at fill and < 1 ppb in 24 hrs

• Peracetic acid (PAA)– Produced by oxidation of acetic acid by hydrogen peroxide– Effective even at 20 °C; 1% soln yields 7-8 log kill of most

resistant spores in 5 min at 20 °C; max usable temp. is 40 °C

• Ethylene oxide– It is a toxic gas that can penetrate porous materials and hence

used for paperboard cartons27

Verification of Sterilization• Inoculate the web, cup or lid with test organism of

desired concentration and let it dry– B. stearothermophilus strain 1518 is used for superheated

steam, peroxide + steam, extrusion– B. polymyxa is used for dry heat– B. subtilis strain A is used for peroxide + UV– C. sporogenes PA 3679 is used for ethylene oxide– B. pumilus is used for gamma radiation

• Run the system as in a commercial run with containers having a growth medium

• Test for survivors28

Types of Packaging Systems• Cans

– Superheated steam at 225 °C for 40 s sterilizes can and ends– Composite can: 143 °C for 3 min; steam could delaminate paper

• Bottles– Glass, plastic (non-sterile), sterile blown plastic, single station blowing, filling,

and sealing

• Sachet and pouches– Form-fill-seal (vertical or extruded blown film layflat tubing)

• Cups– Preformed (H2O2 for ~3 s), form-fill-seal (Polystyrene heated to ~130-150 °C)

• Cartons– Form-fill-seal, prefabricated (peroxide sterilization)

• Bulk packaging– Metal (steel with tin coating) drum (55 gal) with double-seamed ends; filling

through threaded hole with cap swaged after filling– Bag-in-box 29

Testing of Package Integrity• Destructive tests

– Teardown• Flaps unfolded and pr. applied to test tightness of transverse seals• Quality of transverse and longitudinal seals are tested by carefully pulling

apart seals – if seal is good, PE layers will be removed and Al foil laid bare in sealing zone

– Electrolytic• Brine is inside and outside insulating package; voltage applied across

package; presence of holes in package causes a flow of current– Dye

• 0.5% Rhodamine B in isopropanol is applied to seal areas; after 5 mins, it is cabinet dried overnight; any sign of pink inside flaps indicate holes in PE

– Biotests• Fill package with nutrient broth and seal it; place it in a medium containing

the test organism; after contact time, incubate and check for survivors in broth

• Non-destructive tests– Visual OR aided video inspection, automatic profile scanning 30

Packaging for Microwaves

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Components of a Microwave Oven• Power supply

– Convert 110 V to high voltage for magnetron• Magnetron

– Generates microwaves• Circulator

– Prevents reflected waves from reaching magnetron and damaging it

• Waveguide– Metal enclosure that guides waves into cavity of oven

• Wave- or mode-stirrer– Distributes microwaves randomly into oven cavity

• Oven cavity– Food is placed here 32

Factors Affecting Microwave Heating

• Dielectric constant (’)– Ability of a material to absorb microwaves

• Dielectric loss factor (’’)– Ability of a material to convert absorbed microwave

radiation into heat• Loss tangent (Tan )

– Tan = ”/’

Note: Frequency, temperature, and composition of food affect dielectric properties33

Depth of Penetration of Microwaves

• Electromagnetic waves are attenuated as they impinge on a dielectric material– Power decreases from surface to interior

• Depth of penetration refers to distance from surface where the power is 1/e (~37%) of that at the surface

Rule of thumb: If the smallest dimension of the object is greater than 4 times power penetration depth, then heating will occur only near the surface and interference effects will be small

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Classification of Packaging Materials for Microwaves• Transparent

– Most plastics, paper, ceramics, glass

• Absorbent– Thick organic coatings

• Powdered or flaked lossy substance mixed with a binder (eg., a copper flake in an organic base) and coated onto a substrate

– Chemceptors• Salt solution; salt dissociates in water; solution becomes semi-conducting, causing it to heat in

a microwave field; when enough water has been driven off, heating stops

– Thin organic coatings• Al particles are applied (at < 100 A°) to a heat resistant polyester film which is adhesive

laminated to a low loss, temperature-stable substrate (bleached paperboard)

– Dual mode susceptors• Materials that heat by both electric and magnetic fields

– Fibrous susceptors• Moisture permeable material which can be tailored to the surface heat flux, interior cooking,

moisture venting, and flavoring needs of the particular food

– Flake-coated susceptors• Flake in a polymer medium which is printed onto a polyester film 35

Classification of Materials from an Electromagnetic (EM) Standpoint

• Conductors• Reflect EM waves just like a mirror reflects light• Used as electrodes, applicators, and waveguides

• Insulators• Reflect and absorb small amount of EM waves• Transparent

• Dielectrics• Between conductors and insulators• Foods, water, oils, etc.

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Focusing and Shielding

• Focusing– For a spherical object, microwaves get focused at the center– For objects with sharp corners, microwaves concentrate at the

corners• Over-heating or drying can occur here

• Shielding– Use of metals at corners of package to prevent over-heating

• Metals reflect microwave energy

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