FST50 2024 Heat Preservation-annotated PDF

F S T 5 0 2 0 2 4 Heat Preser vati on Pasteurization and Sterilization_Part I Prof. Juliana Bell Food Science and Technology L e a r n i n g O b j e c t i v e s Pasteurization and Sterilization Thermal processing of foods (heat preser...

F S T 5 0 2 0 2 4 Heat Preser vati on Pasteurization and Sterilization_Part I Prof. Juliana Bell Food Science and Technology L e a r n i n g O b j e c t i v e s Pasteurization and Sterilization Thermal processing of foods (heat preservation) Thermal properties of foods Mechanisms of heat transfer Describe the effects of heat on microbial inactivation and food preservation Define heat inactivation parameters in food processes (D, z, and F) Reading: chapter 8 (Food Science)  Applications! Heat Preservation The use of heat to preserve foods has several applications!!! // Cooking, frying, baking, broiling...... Tender, palatable, destroy some microorganisms and enzymes _ longer shelf life vs. uncooked  Heat treatment _ Food Processing Industry Importance Advantages Disadvantages Control of processing Eating qualities Destruction of compounds conditions Preservative L o s s o f f l a v o r, c o l o r, Production of shelf-stable texture foods Destruction of antinutritional compounds Increased availability of some nutrients  Heat Transfer One of the most impor tant unit operations in the food industry 1 Heat Processing Desig n Determining a target processing outcome 2 Thermal Properties of Fo o ds Rate of heating, cooling, f reezing 3 Mechanisms of Heat Transfe r Calculate the rate of heat transfer 4 Effects of Heat on Targe t Co mp o unds Microorganisms, enzymes, f ood compo unds  T h e r m a l P r o p e r t i e s o f F o o d s accounti ng for changes Specific Heat Is the amount of heat needed to raise the temperature of 1kg of material by 1 Cp (function of the cons tituents o f fo o d/ mate r ial) S p e c i f i c H e a t Function of the composition and state of the material Cp = Water has a relatively high specific heat 4 “Cp of foods is strongly influenced by the 2 moisture content” 0 Cp (KJ/Kg.C) Water Water vapor Ice Carbohydrate Protein Fat T h e r m a l P r o p e r t i e s o f F o o d s accounti ng for changes Thermal Conductivity ( indicates the ability of a ma ter ial to conduct heat) Is the amount of heat co nducted per unit time through a unit thickness of the ma ter ial if a temperature gradient exists  T h e r m a l C o n d u c t i v i t y In foods, it is a function of the composition (cell structure, air entrapped between cells, moisture content) Impact of moisture content reduction on conduction of heat “Reduction on the 400 2 moisture content results in reduced thermal conductivity” 200 1 0 0 K (W/mK) K (W/mK) Aluminum Silver Steel Water Ice Strawberry Air Animal fat (9%, water) Animal fat (2% water)  T h e r m a l P r o p e r t i e s o f F o o d s accounti ng for changes Thermal Diffusivity It is a measure of a mater ial's ability to conduct heat relative to its ability to st ore heat  Heat Transfer One of the most impor tant unit operations in the food industry 1 Heat Processing Desig n 2 Thermal Properties of Fo o ds 3 Mechanisms of Heat Transfe r 4 Effects of Heat on Targe t Co mp o unds S e n s i b l e a n d L a t e n t H e a t Understanding the impact of energy addition in a system Sensible Heat Latent Heat Phase change Energy required to change Energy ____________ or Energy is used to change the______________ of a __________ by a substance the_____________________________ substance__________________ during a _________________________________ _________________ ______________________  Major Mechanisms! Modes of Heat Transfer Conduction Convection Radiation // // // molecular collision, via fluid movement no medium required physical contact  Major Mechanisms! Conductive Heat Transfer Tr a n s f e r o f e n e r g y Fo u r i e r ' s l a w Molecular collision Rate of heat transfer is directly proportional to the temperature gradient and the cross-sectional area  Major Mechanisms! Convective Heat Transfer Tr a n s f e r o f e n e r g y Newton's Law of Cooling Via movement of fluids The rate of heat transfer is proportional to the area, temperature difference, and convective heat transfer coefficient  Major Mechanisms! Radiative Heat Transfer Tr a n s f e r o f Stefan Boltzmann's equation Electromagnetic radiation through space The rate of radiative heat transfer is a function of the area, nature and the temperature of the 4 surface  Heat Transfer One of the most impor tant unit operations in the food industry 1 Heat Processing Desig n 2 Thermal Properties of Fo o ds 3 Mechanisms of Heat Transfe r 4 Effects of Heat on Targe t Co mp o unds M i c r o o r g a n i s m I n a c t i v a t i o n Change i n mi crobi al pop ulati on (ti me) First Order Kinetic Model N = Number of microbes at time t No = Original number of viable microbes (t = 0) dN/dt=-kN k = rate constant for natural ln (Log to base “e”) equation Microbiologists use base 10 (log, log10), not natural logarithms (ln) k’ = rate constant for Log to base 10 equation log N = log No - k’ t Effect of Heat on Microorganisms The preservative effect o f heat treatment Rate of destruction (1st o rde r reaction) Logarithmic order of de ath (Death rate curve)  Death Rate Curve D-time _ Decimal reduction time The heating time required to _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ of a specific microorganism at a const ant temperature  Two Implications _ DRT 1.The higher the number microorganisms of 2.The longer it takes to target number re d uc e to a 3.Microbial reduction _ lo 4.Infinite time _potentia g a rithmically cells ll y d estroy all  Understanding microbial Inactivation example dealized i  Understanding microbial Inactivation D time, or decimal reduction time (decreases the surviving population by ______ log cycle) Understanding microbial Inactivation  E f f e c t o f I n i t i a l P o p u l a t i o n S i z e Hi gher i ni ti al mi crobi al populati on Longer times needed to achieve a required reduction! M i c r o b i a l d e s t r u c t i o n Temperature Dependent Cells die more rapidly at higher temperatures! Thermal Death Time Curve Effects of Heat Treatment on Microorganism Inactivation Time-temperature dep e nd e nce Z value: is the temperature rise to achieve a _ _ _ _ _ _ _ decrease in the D value D value: heat resistance of mi croorganism Z value: resistance of a mi croorganism to changing temperatures  D and F value Relationship F-value Is the number of minutes to achieve a st ated reduction in a microbial population at a given temperature 10^3 to 10^2: F = ________ Reduce Microbial Popu lation from: 10^4 to 10^2: F = ________ 10^4 to 10^1: F = ________  F value, Process Lethality or Thermal Death Time ( TDT) F is the total time requir e in a microbial population d to achieve a stated reduction at a specific temperature F = N * D (D _ decima thermal death time (min),l reduction time (min), F_ reduction) N_ number of log cycle F is often expressed as: Z - z value of the microorganism T _temperature  F-value Fvalue, Process Lethality or Thermal Death Time (TDT) // The number of minutes required to destroy a specif ic number of spores at 121.1 when Z is 10  Factors Affecting Microorganisms Heat Resistance Ty p e o f m i c ro o rg a n i s m 1 Species and strains I n c u b a t i o n c o n d i t i o n s d u r i n g c e l l g row t h 2 o r s p o re f o r m a t i o n Temperature during spore formation, age of the culture 3 Culture medium used Mineral salts and fatty acids influence the heat resistance of spores 4 p H o f t h e f o o d , A w, c o m p o s i t i o n o f f o o d In general, bacteria are killed more rapidly at lower and higher pH values than in more neutral pH  Special!! Protective Effects of Food Constituents Several food constituents protect microorganisms against heat to various degrees High sugar concentration (protects bacterial spores) - canned fruits in a sugar syrup _ longer times/temperature Starch and protein _ act like sugar Fats and oils (protective effect on microorganisms) _ interfere with the penetration of wet heat