Thermal Processing

Introduction

• Foods are highly reactive systems: Chemical/bio reactions=> post harvest and processing

• The systematic study of reactions in foods=> food chemistry and food biochemistry.

• the rate of reactions => food process engineer

Introduction

• Thermal processing involves heating food, either in a sealed container or by passing it through a heat exchanger, followed by packaging.

• Important=>to ensure that the food is adequately heat treated and to reduce post processing contamination (ppc).

• Important=> be cooled quickly

Reasons for Heating Foods

• The two most important issues : food safety and food quality.– Inactivate pathogenic or spoilage microorganisms, – inactivate enzymes to avoid the browning of fruit by

polyphenol oxidases and minimize flavour changes resulting from lipase and proteolytic activity.

– induces physical changes and chemical reactions: starch gelatinisation, protein denaturation or browning, which in turn affect the sensory characteristics, such as colour, flavour and texture, either advantageously or adversely.

Food safety• Variation heat resistance of pathogens:

– heat-labile, such as Campylobacter, Salmonella, Lysteria and of more recent concern Escherichia coli 0157, which are inactivated by pasteurisation,

– greater heat resistance is Bacillus cereus, may survive pasteurisation and also grow at low temperatures.

– heat-resistant pathogenic bacterial spore is Clostridium botulinum. • Spoilage bacteria : yeasts, moulds and gas-producing and souring

bacteria. • the most heat-resistant being the spores of Bacillus stearothermophilus.• The heat resistance of any microorganism depends on pH, water

activity, chemical composition of foods. • After processing, it is very important to avoid reinfection of the product

(ppc)

Food quality

• Quality issues : – minimising chemical reactions – loss of nutrients– Ensuring acceptable sensory characteristics

• conflicts between safety and quality issues. • important to understand reaction kinetics:

– microbial inactivation– chemical damage– enzyme inactivation– physical changes.

• Calculation of thermal processing for the destruction of microorganisms

• Optimization of thermal processes with respect to quality

• Optimization of processes with respect to cost• Prediction of the shelf life of foods as a function of

storage conditions• Calculation of refrigeration load in the storage of

respiring agricultural produce• Development of time-temperature integrators.

the most important applications of reaction kinetics in food engineering

Two groups Reactions in food processing

• Desirable or induced reactions: The pyrolysis of carbohydrates during coffee roasting, the hydrolysis of collagen when meat is cooked and, the hydrogenation of oils to produce solid fats, etc

• Undesirable reactions: Maillard-type browning in lemon juice, onset of rancidity as a result of lipid oxidation in nuts and crackers and, spoilage reactions induced by microorganisms, dsb

Reaction order

• n = reaction order• k=rate constant• C=concentration• t=time• n=0 => Zero order, not very common, non-enzymatic

browning, caramelization and lipid oxidation• n=1=> first order, many phenomena, thermal

destruction of microorganisms, non-enzymatic browning.

Effect of temperature on reaction kinetics

Reaction Kinetics

• Microbial Inactivation– three distinct periods: a heating period, holding period and

cooling period. – all three periods may contribute to the reactions. The

holding period is the most significant. • Heat Resistance at Constant Temperature

– When heat inactivation studies are carried out at constant temperature, it is often observed that microbial inactivation follows first order reaction kinetics i.e. the rate of inactivation is directly proportional to the population.

• Every microorganism has its own characteristic heat resistance and the higher its D value, the greater is its heat resistance.

• Heat resistance is also affected by a wide range of other environmental factors, such as pH, water activity and the presence of other solutes, such as sugars and salts.

• Example: for an organism with a D70 value of 10 s, heating for 10 s at 70 C will achieve a 90% reduction in the population, 20 s heating will achieve 2D (99%), 30 s will achieve 3D (99.9%) and 60 s will achieve 6D (99.9999%) reduction.

PHE

contoh• In the counter-current heat exchanger, milk is cooled from 73ºC to 38ºC at the rate

of 2500 kg/h, using water at 15ºC which leaves the heat exchanger at 40ºC. The pipework 2.5 cm in diameter is constructed from stainless steel 3 mm thick; the surface film heat transfer coefficients are 1200 W/m2K on the milk side and 3000 W/m2K on the water side of the pipe. Calculate the OHTC and the length of pipe required.

Penentuan waktu pemanasan

• Untuk tujuan food safety, waktu pemanasan dapat diprediksi menggunakan berbagai persamaan

• Un-steady state heat transfer• Kinetika pembunuhan m.o

Pindah panas un-steady state

• Laju aliran panas berubah dengan waktu• Pendugaan waktu dapat disederhanakan

menggunakan berbagai persamaan dan chart• Parameter yang perlu diketahui : faktor suhu,

biot number, fourier number

Contoh

Process lethality• There are two types of bacterial populations of concern in canned food

Sterilization : to reduce the population of organisms of public health significance and to avoid economic losses from spoilage-causing bacteria of much greater heat resistance in low acid food

• The organism : Clostridium botulinum (a safe level of survival probability 10–

12, or one survivor in 1012 cans processed/12 D concept for botulinum cook. • the highest D121 value known for this organism in foods is 0.21 min, the

minimum lethality value for a botulinum cook is F = 0.21×12 = 2.52 min• Most food companies accept a spoilage probability of 10–5 from mesophilic

spore Clostridium sporogenes• Max D121 value 1 min; F = 1.00 × 5 = 5.00 min• thermophilic spoilage is a concern, the target value for the final number of

survivors is usually taken as 10–2,

Lethality Values (Fo) for Commercial Sterilizationof Selected Canned Food Products

Kinetika kematian mikroorganisme

• Waktu pemanasan bergantung kepada jumlah mikroba awal dan mikroba akhir yang diinginkan

• t= D log(No/N)• Dengan acuan suhu standar 121oC• Fo= D121 Log (No/N)• Fo = t.10(T-121)/z

• Untuk suhu tidak konstan, Fo=∫ t.10(T-121)/z

Contoh• Suatu proses pemanasan makanan catan suhu di pusat panasnya

(thermal center) adalah sbb: Waktu

(menit)Suhu oC Waktu Suhu

0 80 (26,7) 40 225 (107,2)

15 165 (73,9) 50 230,5 (110,3)

25 201 (93,9) 64 235 (112,8)

30 212,5 (100,3)

• Jika nila Fo untuk Cl. Botulinum 2,45 menit dan z:18oF, apakah proses tersebut diatas telah memenuhi?

• Hitung nilai 10(T-250)/z pada berbagai waktu• Menit ke 0; 10(T-250)/z = 10(80-250)/18 = 3,6x10-10 •

Waktu Suhu 10(T-250)/z luasan

0 80 3,6 x 10-10

15 165 1,9 x 10-5 15x...

25 201 0,00189 10 x ...

30 212,5 0,00825 5 x 00,00507

40 225 0,0408 10 x 0,0245

50 230,5 0,0825 10 x 0,06165

64 235 0,1465 14 x 0,1145

Aseptic Processing

• Material condition : pumpable• Process : a continous process involving separate

sterilization of a pumpable food, containers, and closures followed by the cooling of the food and filling and sealing in containers under a sterile environment

• Products : mostly acid food• Size of package : ranged from consumer-size retail

packs of a few grams (60–180 g) to bulk storage containers up to more than about 4–6 m3

• The aseptic packaging system achieves this room-temperature shelf stability by filling a sterilized package with a sterile food product within the confines of a hygienic environment.

• This remarkable packaging system allows :– perishable products could be distributed and stored

without refrigeration for periods up to six months or more– No preservatives and/or refrigeration to achieve a long

shelf life.• Other advantages :

– Lightweight container, – space-efficient block shape, – easy-open, easy-pour, and reclosable features – no exposed sharp edges, – easy to crush

Comparation

aseptic process traditional canning hot-fill canning

•Product is sterilized outside the package using an ultra-high temperature process that rapidly heats, then cools, the product before filling. •The processing equipment allows the time (generally 3 to 15 seconds) and temperature (195° to 285° F) to be tailored to place the least amount of thermal stress on the product, while ensuring safety. •This flash-heating-and-cooling aseptic process substantially reduces the energy use and nutrient loss associated with conventional sterilization.

requires products to be heated in the container for 20 to 50 minutes.

Hot-fill canning uses the heat of the product to sterilize both the product and the package, a process which takes 1-3 minutes for heating and another 7-15 minutes for cooling

Isn’t the aseptic package an example of excessive packaging?

• the aseptic package is an excellent example of minimal packaging.

• Comparation by weight– An aseptic package is typically 95 percent beverage to 5

percent packaging. – PET bottles are 95 percent product to 5 percent packaging; – steel cans are 89 percent product to 11 percent packaging;

and – glass bottles are 65 percent product to 35 percent

packaging.

What products are available in aseptic packages

• In USA : milks, juices, tomatoes, soups, broths, tofu, soy beverages, wines, whipping cream, teas.

• In UE : pasteurized milk and yogurt drinks to fruit-based desserts and sauces.

• The bulk storage : need refrigeration.• Bulk storage : tomato paste storage and shipment

(190 L drums), banana puree, rail car and truck containers) and 378,000 L tanks for storage of soy sauce and other liquids.

Assembled aseptic processing system

Aseptic packaging material• Packaging material: high-quality

paperboard, polyethylene, and aluminum. • Paper (70 percent) provides stiffness,

strength and the efficient brick shape to the package.

• Polyethylene (24 percent) on the innermost layer forms the seals that make the package liquid-tight. A protective coating on the exterior keeps the package dry.

• Aluminum (6 percent) forms a barrier against light and oxygen. This ultra-thin layer of foil eliminates the need for refrigeration and prevents spoilage without using preservatives.

• The aseptic package contains a total of six layers in this order: polyethylene, paper, polyethylene, aluminum foil, polyethylene, and polyethylene.

Filling and sealing

Aseptic processing

– Container•

Product

• Aseptically packed product

Sterilization Sterilization

Aseptic environment

Thermal proccesing of product

• The thermal sterilitization depend on: (1) nature of the food (e.g., pH and water activity); (2) storage conditions following the thermal process (refrigerated versus room temperature); (3) heat resistance of the microorganisms or spores; (4) heat transfer to the food; and (5) the initial load of microorganisms.

Approximations of heat processes for destruction of C. botulinum and commercial

sterility

Heating unit in aseptic processing

Predicting process temperature

T = process temperature (°C) measured at the end of the hold tube, TR = reference temperature (°C), Z = temperature (°C) change necessary for the D-value to change by a factor of 10 or for 1-log or 90% reduction, t = hold time (minutes or seconds) calculated from flow rate and tube diameter, and F = sterilizing value needed to achieve commercialsterility for the product

• rapid heat transfer rate in heating and cooling : minimizes undesirable changes in the taste and nutritional quality of the resulting product.

• Continuous process: produces uniform product quality that does not depend on the size of a container,

• This attribute is especially important for products containing heat-sensitive ingredients and highly viscous products with poor heat transfer properties

Sterilization of packaging material• 3% of total m.o on surface material are spores• Plastic film and paperboard laminated on reels: assumed 1000 m.o/m2

and 30 spores• Cup : 3000• Method of sterilization :

– Irradiation• UV• IR• Gamma

– Heat• Steam• Hot Air

– Chemical treatment• Hydrogen peroxide• Peracetic acid• Ethylene oxide

Irradiation• Reqirement for packaging materials:

– smooth surface– Free from dust– Irradiation resistance

• UV : 200-315 nm, most effective of microbial destruction 250-280 nm

• IR : max temp 140oC• Gamma rays from Co 60 or Cesium 139, dose of 20

kGy can sterilize 105 spores of B. stearothermophillus

Heat

• Steam : – most reliable sterilant– Need high pressure– Need to remove air– Condensation of steam

• Hot Air :– High temperature can be reached at atmospheric

pressure– Need more time to sterilize

Chemical treatment• Hydrogen peroxide : 20% concentration at 80oC for

15 s• Concentration in food not more than 100 ppb

– Dipping– Spraying– Rinsing

• Paracetic acid:– Effective against aerob and anaerob m.o– 1% solution, eliminate 107-108 for 5 min 20oC

• Ethylen oxide– Toxic gas that can penetrate porous material

Indicator

Sterilization medium Indicator organism

Steam B. stearothemophillus

Dry heat B. polymyxa

H2O2 and heat B. stearothemophillus

H2O2 and UV B. Subtilis

Ethylene oxide C. sporogenes

Gamma irradiation B. pumilus

Filling and Packaging• The sterilization to the films is done by the

soak in H2O2 liquor and dried by the aseptic air, and with the shining of UV lights.

• The aseptic environment is made by the H2O2 atomizer and the UV lights.

• The machine can be linked with the UHT sterilizing machine, and CIP system to make up a automatic production line for commercial required aseptic liquid products.

• The filling environment is sterilized by heat or chemicals. After sterilization, the environment

• is maintained sterile using filtered air or inert gas (Clark 2004). The filters

• must be sterilized and validated to assure that there is no recontamination of the sterile

• environment.