Food Stabilization by Chilling: Freezing - PDF

4/30/24 Food Stabilization by Chilling Part II - Freezing MITH Hasika, PhD...

4/30/24 Food Stabilization by Chilling Part II - Freezing MITH Hasika, PhD Faculty of Chemical and Food Engineering [email protected] 2022 – 2023 1 Principles of freezing Refrigeration Preservation ä Freezing / Deep-freezing By Dr. Mith Hasika Food Stabilization by Freezing 2 2 1  4/30/24 Principles of freezing q Method of preservation that the temperature of product is reduced and maintained low, below the freezing point of food products. q Conversion of liquid of food into ice crystals q Freezing / Deep-freezing = obstacles 0°C “cold” + “Aw” q Preservation is attained by combination of a temperature Pure water is reduction and a water activity frozen at 0°C reduction. Food frozen below 0°C (dissolved solids: sugars, acids…) By Dr. Mith Hasika Food Stabilization by Freezing 3 3 Principles of freezing Water crystallization (water immobilization) Augmentation of dissolved solute concentration Reduction of Aw By Dr. Mith Hasika Food Stabilization by Freezing 4 4 2  4/30/24 Principles of freezing Preserving effect of freezing Reduction of water activity of Thermal effet – cooling the treated product F inhibition of products until it reaches the zones microbiological activity and slow of temperature, for that all down the enzymatic reaction. biological activities are considerably reduced. o Freezing < -12°C à bacteria o Deep-freezing < -18°C à bacteria, yeasts and moulds (inhibition of microbial development) By Dr. Mith Hasika Food Stabilization by Freezing 5 5 Principles of freezing Advantages w Microbiological quality : preserve the products for several months (without microbial development) – water activity reduction w Nutritional and organoleptic quality : preserved well the nutritional and organoleptic caracteristics (much better than sterilization) Limits à Freezing does not destroy microorganisms but only prevent their development F Some particular mesures to be taken into account : ü Raw material with excellent microbiological quality ü Strict hygiene condition during production (materials, local, personnels, handling) ü Control of temperature during production ü Continuity of chilling chain to avoid regrowth of microorganisms. By Dr. Mith Hasika Food Stabilization by Freezing 6 6 3  4/30/24 Physical aspects of freezing Formation of ice Dessication of frozen foods Ice crystal size Change in ice crystal size in frozen foods during storage Completion of freezing Thermal radiation in Dimensional changes frozen food storage By Dr. Mith Hasika Food Stabilization by Freezing 7 7 Germany, Great Britain, France 1553 million tons/year By Dr. Mith Hasika Food Stabilization by Freezing 8 8 4  4/30/24 Dessication of frozen foods § During freezing Proportion of water of a product Product enclosed in water-vapor proof without packaging à evaporate package à no moisture escape from during freezing packet Faster freezing à smaller amount Air gap between surface of product of evaporated water and internal surface of package à same extent as moisture evaporates H2O from the product H2O H2O H O 2 H2O H2O H2O H2O H2O H2O Unpackaged product Packaged product By Dr. Mith Hasika Food Stabilization by Freezing 9 9 Physical aspects of freezing Modification of product due to freezing T State change of pure water Supercooling point – early nucleation O°C Liquid Mix of ice water water/ice time By Dr. Mith Hasika Food Stabilization by Freezing 10 10 5  4/30/24 Physical aspects of freezing Modification of product due to freezing 3 zones: - Cooling to temperature slightly lower than the point of fusion (0ºC), before returning to point of fusion after early nucleation = phenomena « supercooling ». - Palier of temperature at fusion point during state change process. Liquid water – ice biphasic equilibrium. - Cooling of ice, thermal diffusivity of water increases during state change. Temperature reduction of water Q = mcDT Change of state (latent heat) Q = m.L Temperature reduction of ice Q = mc' DT By Dr. Mith Hasika Food Stabilization by Freezing 11 11 Physical aspects of freezing T State change of saline solution/ biological tissue Tc Pseudo palier By Dr. Mith Hasika Food Stabilization by Freezing 12 12 6  4/30/24 Physical aspects of freezing Crystals of solvent and solute appear simultanously for a particular concentration of solute F eutectic concentration – eutectic temperature Four zones : Cooling to temperature TC. At Tc, incipient fusion temperature, apparition of pure ice crystals, increase of solution concentration (cryoconcentration) and decrease of fusion point. From a concentration called eutectic, the solution crystalizes (simultanously water and solute). The temperature remains constant until the whole solution becomes cristalized (zone slowing the temperature fall - vague « pseudo-palier ») Cooling the solidified ensemble By Dr. Mith Hasika Food Stabilization by Freezing 13 13 Physical aspects of freezing By Dr. Mith Hasika Food Stabilization by Freezing 14 14 7  4/30/24 1. Incipient Fusion Temperature, TC (ºC) Law of Raoûl kw : cryogenic constant of water (18.6 C.G.S) C' TC = - k w. C’ : mass of solute (g) dissolved in 100g water M M : molar mass of solute Exemple : In case of beef meat with humidity 74%, calculate incipient fusion temperature, as knowing molar mass of beef meat 723.5. Solution : Mass of solute (g) dissolved in 100g water 1 - 0,74 C' = ´100 = 35,1g / 100 gH 2O 0,74 Incipient fusion temperature 35,1 TC = -18,6 ´ = -0,9! C By Dr. Mith Hasika 723,5 Food Stabilization by Freezing 15 15 Proposed by Levy (1979) : æ1 ö Beef and sea fish : TC = -3ç - 1÷ èW ø Pork : TC = -0,9! C 1 Lamb : TC = -0,75 -1 W Equation proposed by Levy, temperature of beef meat with 74% humidity : æ 1 ö TC = -3ç - 1÷ = -1,05! C è 0,74 ø Incipient fusion temperature of some products : meat, fish : - 1ºC peas : -1,1ºC pears : -2,4ºC Concentrate of orange juice, 80 Brix : -6ºC By Concentrate Dr. Mith Hasika of apple juice, 80 Brix : by-10ºC Food Stabilization Freezing 16 16 8  4/30/24 2. Proportion of freezed water Equation of Bartlett (1944) : L : latent heat of fusion 6003 J.mol-1 R : ideal gas constant 8,314 J.mol-1.oK-1 Læ 1 1ö LnX = ç - ÷ T0 : fusion temperature (273,1oK) R çè T0 T ÷ø T : product temperature X : molar fraction of non-freezed water E 18 18 SX E : content of non-freezed water in product X = ÞE= E + S M (1 - X ) S : content of dry soluble extract 18 M Content of ice in product : G = W - E Total water (humidity) G Proportion of freezed water : Y = By Dr. Mith Hasika W Food Stabilization by Freezing 17 17 Empirical equation of Chen : S RT02 TC - T G=.. M L (T - T0 )(TC - T0 ) Empirical equation for equivalent molar mass of solute : 535,4 Beef : M = W 404,9 Morue : M = W 200 Orange and apple juices: M = 1 + 0,25S By Dr. Mith Hasika Food Stabilization by Freezing 18 18 9  4/30/24 Exercise: Determine the proportion of freezed water in beef of 74% humidity freezed at -15ºC. Knowing that L = 6003 J.mole-1 R = 1,94 cal.mol-1.K-1 By Dr. Mith Hasika Food Stabilization by Freezing 19 19 Physical aspects of freezing Ø One of key issues in maintaining the shelf-life and quality tributes of frozen foods is ice crystallization. Ø Quality changes during the freezing process are related to the way in which ice crystals are made to grow. Freezing Quality ? Freezing rate Ice crystallization By Dr. Mith Hasika Food Stabilization by Freezing 20 20 10  4/30/24 Physical aspects of freezing Distribution and size of ice crystals S Slow freezing Big ice crystals at exterior of cells slow rate growing of ice increase of concentration drawing water out of crystals into the of frozen solution outside the cells by osmosis intercellular tissue the cells addition of this water to shrunken cells disruption of cell the growing ice crystals + larger crystals structure By Dr. Mith Hasika Food Stabilization by Freezing 21 21 Physical aspects of freezing Distribution and size of ice crystals S Quick freezing Smaller ice crystals faster rate multitude of smaller ice less shrinking of reduction of degree of freeze crystals at the interior + the cells damage (little change to texture/ exterior of cells less loss of nutrient when thawing) Advantage of quick freezing is to Much lesser preserve better quality of product exudate (distribution of ice and ice crystals) By Dr. Mith Hasika Food Stabilization by Freezing 22 22 11  4/30/24 # Assignment 1. What is cryogenic freezing? 2. What are the advantages and disadvantages of cryogenic freezing? By Dr. Mith Hasika Food Stabilization by Freezing 23 23 Freezing rate/time Ø It depends on : Raw materials (nature of product) Temperature/pressure Packaging Sugar/salts Thickness/Contact surface of food product Freezing systems-flow of air or refrigerant Refrigerant type 24 By Dr. Mith Hasika Food Stabilization by Freezing 24 12  4/30/24 Freezing rate/time q allow to determine the time (for batch apparatus) or the speed of products to be applied (continuous apparatus) q Sizing of freezers requires knowledge of freezing rate relating to treated products. - Freezer, characterized by : - Product, characterized by : Ÿ its cooling capacity Q! Ÿ humidity Ÿ temperature of refrigerant T Ÿ its thermal conductibility λ ¥ Ÿ its coefficient of transfer (h) Ÿ its specific heat C Ÿ its density ρ Ÿ its geometric (surface, volume …) Ex. transferring surface “ ’ heat transfer “ By Dr. Mith Hasika Food Stabilization by Freezing 25 25 Freezing equipments Type of freezers Plate Freezers Air Blast Freezers Immersion Evaporating Freezers Liquid Freezers By Dr. Mith Hasika Food Stabilization by Freezing 26 26 13  4/30/24 1. Plate Freezers Product is pressed by hydraulic ram between metal plates which have channels for refrigerant. Slight pressure is applied to improve the contact between surface of food and the plates, and thereby increases the rate of heat transfer. Increasingt thickness of product à heat transfer at the surface gradually reduced à limited thickness of max. 50 mm. Two main types of plate freezer: - horizontal plate freezer - vertical plate freezer By Dr. Mith Hasika Food Stabilization by Freezing 27 27 1. Plate Freezers Ø Horizontal plate freezer Usually 15 to 20 plates Product placed on metal trays, manually pushed in between plates à high labor content in loading and unloading operation. Possibly automatic operation Food on metal trays By Dr. Mith Hasika Food Stabilization by Freezing 28 28 14  4/30/24 1. Plate Freezers Ø Vertical plate freezer Mainly developed for freezing fish at sea Vertical freezing plates forming partitions in a container with open top. Operation is usually mechanized; discharge of product by short hot gas defrost at the end of freezing cycle and the use of compressed air to force the product out. By Dr. Mith Hasika Food Stabilization by Freezing 29 29 2. Air Blast Freezers Adapted for some foods, mainly bulk products including beef quarters and fruits for further processing; frozen in rooms with or without forced air circulation. The refrigerant is air or forced air and cooled to – 30°C to – 40°C across the evaporator of a refrigeration system. In batch equipment, food is stacked on trays in room or cabinets. Continuous equipment consists of trolley stacked with trays of food or on conveyor belts which carry the food through an insulated tunnel. Air blast freezers include: Air blast freezer - tunnel freezers arrangement - belt freezers showing the cooler - fluidized bed freezers acting as an air diffuser By Dr. Mith Hasika Food Stabilization by Freezing 30 30 15  4/30/24 2. Air Blast Freezers Tunnel freezer (Batch) Tunnel freezers Air blast Belt freezer Fluidized freezers s bed freezers By Dr. Mith Hasika Food Stabilization by Freezing 31 31 2. Air Blast Freezers Avantages Air blast freezers are the most classic and widely used due to their versatility : § air is compatible with foods § possible to freeze in the same apparatus multitude of different products. Limites § weak coefficient of superficial heat transfer (speed 0.2 cm/h) § the fan must blow the air with important volume to absorb the heat released by the frozen products. Ü The air has tendency to wither the product surface ð to pack the product and to spray water By Dr. Mith Hasika Food Stabilization by Freezing 32 32 16  4/30/24 2. Air Blast Freezers Tunnel freezer (Batch) Ø Tunnel freezers § Product is place on tray, stand in or pass through tunnel in racks or trolleys § Racks/trolleys moved in/out of freezers by manual/forklift truck (stationary tunnels); push-through the tunnels with pushing mechanism (push-through tunnel) or are carried through by driving equipment, chain driver (carrier freezer) or slid through (sliding tray freezer) § It can be used also for freezing hanging meat carcasses carried on a suspension conveyor. By Dr. Mith Hasika Food Stabilization by Freezing 33 33 2. Air Blast Freezers § Tunnel freezers equipped with refrigeration coils and fans, Push-through tunnel circulating the air over the freezer products in a controlled way. 1. Trolleys with trays § Tunnel freezers are flexible, 2. Reversing fans packaged or unpackage 3. Air coolers products with different size and 4. System of baffles shape to be frozen in allowing adjustment of stationary/push-through the air flow. tunnels. § Primarily used for freezing packaged products By Dr. Mith Hasika Food Stabilization by Freezing 34 34 17  4/30/24 2. Air Blast Freezers § Belt freezers could be: - single belt Ø Belt freezers - multi-belt (position above each other in the same/opposite position) - spiral belt (belt up to 30 tiers above each other stacking and wound round a rotation drum) § Mainly used for freezing unpackaged products Single belt freezer 1. Insulated wall of the tunnel; 2. De-watering vibrator; 3. Loading hopper; 4. Belt drying system; 5. Variable speed belt (open mesh belt); 6. Product spreader; 7. Air agitation zone; 8. Evaporator; 9. High velocity air; 10. Variable air flow fans; 11.ByDefrost Dr. Mith Hasika water; 12. Refrigerant piping; 13.Belt speed changer; 14. Unloading hopper Food Stabilization by Freezing 35 35 2. Air Blast Freezers Ø Belt freezers Multi-belt freezer https://www.youtube.com/wa tch?v=q4meb5tcM6U By Dr. Mith Hasika Food Stabilization by Freezing 36 36 18  4/30/24 2. Air Blast Freezers Ø Belt freezers Spiral freezer By Dr. Mith Hasika Food Stabilization by Freezing 37 37 2. Air Blast Freezers Ø Fluidized bed freezer § Particles of fairly uniform shape and size are subjected to an upward air stream § Air velocity depends on characteristics of products § Particles floats in the air stream à separation of particles; surrounded by air and free to movement à the mass of particles behaves like a fluid By Dr. Mith Hasika Food Stabilization by Freezing 38 38 19  4/30/24 2. Air Blast Freezers Ø Fluidized bed freezer 1. Unfrozen product conveyer; 2. Product trough; By Dr. Mith Hasika 3. Frozen productFood discharge; 4. Air coolers; 5. Fan Stabilization by Freezing 39 39 2. Air Blast Freezers Ø Fluidized bed freezer § By comparison to belt freezer, some advantages of fluidization principle use: - The product is individually frozen (Individual Quick Freezing-IQF) à applied to products with tendency to stick together (green https://www.youtube.com/watch?v=MXd3XLT0j7M beans, sliced carrots, sliced https://www.youtube.com/watch?v=mgEc_aDep0c cucumber) - Independence of fluctuation in load - Reliability improvement (adapt for freezing surplus water product) By Dr. Mith Hasika Food Stabilization by Freezing 40 40 20  4/30/24 2. Air Blast Freezers § Overall operation economy of blast freezer: weight losses during freezing for unpackaged products. - Improperly designed freezer: ≥ 5% weight loss - Well-designed freezer: 0.5-1.5% weight loss ü Minimization of dehydration loss - Low air temperatures/good heat transfer 41 By Dr. Mith Hasika Food Stabilization by Freezing 41 3. Immersion Freezers Ø The immersion freezer consists of a tank with a cooled freezing medium such as propylene, glycol, glycerol, sodium chloride, calcium chloride and mixtures of salt and sugar. Ø The product is immersed in the solution or sprayed while being conveyed through the freezer, resulting in fast temperature reduction through direct heat exchange. By Dr. Mith Hasika Food Stabilization by Freezing 42 42 21  4/30/24 3. Immersion Freezers Ø Direct contact immersion with tank containing brine solution used to freeze fishes (tuna) at sea Ø The products are immersed in a tank containing brine of 20% NaCl at -20ºC, possible to use a system of brine spraying. Ø Indirect contact immersion (tight packaging) : most commonly used for surface freezing “crust freezing” of poultry to obtain a light surface color (final freezing is effected in a separate blast tunnel or cold store), slow freezing of the product core could affect Food By Dr. Mith Hasika quality and hazard. Stabilization by Freezing 43 43 3. Immersion Freezers Ø Avantages § better coefficient of convection (rapid freezing) § no consumption of energy of ventilation § no desiccation of product Ø Limites § salty taste into product § problem of brine contamination By Dr. Mith Hasika Food Stabilization by Freezing 44 44 22  4/30/24 4. Evaporating Liquid Freezers Ø LN2 Freezer Liquid nitrogen at –196°C to spray onto a single belt freezer à used to pre-cooling of products Very high freezing rate results in improved texture for certain fruits and vegetables But cracking of product surface if insufficient precautions Often used only for surface freezing, if final freezing to be carried out à 1 to 1.5 Kg/Kg of product (expensive operation) For certain productions, especially in-line processes, low investment and simple operation make this method economical. By Dr. Mith Hasika Food Stabilization by Freezing 45 45 4. Evaporating Liquid Freezers Ø LN2 Freezer 1. Belt; 2. Spraying nozzles; 3. Fans; 4. Inlet; 5. Outlet; 6. Nitrogen tank supply line; 7. Regulating valve; 8. Temperature sensing unit; 9. Nitrogen gas exhauster By Dr. Mith Hasika Food Stabilization by Freezing 46 46 23  4/30/24 4. Evaporating Liquid Freezers By Dr. Mith Hasika Food Stabilization by Freezing 47 47 4. Evaporating Liquid Freezers Ø LFF (liquid fluorocarbon freezant) Freezer Freezant is purified dichlorodifluoromethane with boiling point of –30°C Product introduced into the container and dropped into flowing stream of freezant, followed by horizontal freezng belt and discharge conveyor brings the product up and out of freezer The surface is frozen instantaneously with extremely good heat transfer Fluorocarbon leaves only small residues in most products On contact with product, the freezant evaporates à recovery of vapors by condensation on the surface of refrigerator (slight loss) By Dr. Mith Hasika Food Stabilization by Freezing 48 48 24  4/30/24 4. Evaporating Liquid Freezers 1. Product input conveyor 2. Freezing conveyer 3. Frozen product exit conveyor 4. IQF bath 5. Spray nozzles 6.Condenser By Dr. Mith Hasika Food Stabilization by Freezing 49 49 Examples Quick cooling – Foies Gras By Dr. Mith Hasika Food Stabilization by Freezing 50 50 25  4/30/24 Examples By Dr. Mith Hasika Food Stabilization by Freezing 51 51 Examples Deep-freezing of great scallop By Dr. Mith Hasika Food Stabilization by Freezing 52 52 26  4/30/24 Examples Chilling/deep-freezing of meat By Dr. Mith Hasika Food Stabilization by Freezing 53 53 Examples Quick chilling of Salmon Curve of chilling time By Dr. Mith Hasika Food Stabilization by Freezing 54 54 27  4/30/24 Storage During the storage period, the following hazard to quality of frozen food must be avoided: - Low relative humidity in the cold store - Retention beyond the expected storage life - Fluctuation in temperature (both during storage and in the process of loading, unloading, and dispatching vehicles) - Physical damage to the product or packaging during the course of storage or handling - Contamination of product by foreign bodies or vermin By Dr. Mith Hasika Food Stabilization by Freezing 55 55 Thawing a. Physico-chemical and microbiological aspects of thawing v Exudation During thawing à fusion of ice crystals. A part of water is not re-absorbed by product, it is called exudate. Exudate depend on : § freezing technique (slow/quick) § maintaining temperature during storage § thawing technique (quicker the thawing is, less exudate released) § presentation of pieces to be frozen (ex. minced meat à important quantity of exudate) Exudate is responsible for : weight loss = financial loss creation of favorable medium for microbial development. organoleptic quality loss loss of nutritional compounds By Dr. Mith Hasika Food Stabilization by Freezing 56 56 28  4/30/24 Thawing v Physico-chemical phenomena Thawing with the most concentrated solution, then thawing the pure ice. Reaction of degradation start at -5ºC à quick thawing to pass rapidly the zone of critic temperature. v Microbiological phenomena The thawing take place on the product surface à favourable condition for microbial development (Ex. In fresh meat, microbial load is 2 log cells per gram, so on surface, microorganisms could attain upto 3 to 7 log cells per gram). ð Do not re-freeze the food products defrosted at ambient temperature (too much contaminated) ð Defrosting in refrigerating condition is recommended. By Dr. Mith Hasika Food Stabilization by Freezing 57 57 Thawing b. Thawing techniques Air thawing Electric Air blast methods thawing Thawing techniques Vacuum watering thawing thawing By Dr. Mith Hasika Food Stabilization by Freezing 58 58 29  4/30/24 Thawing v Still air thawing - Thawing duration is extremely long - Rate of exudate from thawing product by this method is relatively high (0,5 à 3%) ° not practically used. By Dr. Mith Hasika Food Stabilization by Freezing 59 59 Thawing v Air blast thawing - Air is ventilated with high humidity (~ 90%) ° to improve the convection coefficient and avoid the desiccation of product. - Cool air is forced at 4ºC, with humidity ~ 70% ° to limit microbial development. Crossflow batch thawer By Dr. Mith Hasika Food Stabilization by Freezing 60 60 30  4/30/24 Thawing v Water thawing This method is not normally applicable to meat and with fish fillets or cut surfaces à waterlogging and flavor loss But applicable for frozen whole fish even with slight loss of pigments Cheap and easy method of thawing (all types of whole fish) with clean water supply - water immersion - water spraying Hygiene and intercontamination, T < 20ºC ð to limit microbial development By Dr. Mith Hasika Food Stabilization by Freezing 61 61 Simple immersion thawer Spray thawer By Dr. Mith Hasika Food Stabilization by Freezing 62 62 31  4/30/24 Thawing v Vacuum thawing - Products lies on racks inside a container with air evacuation. - Water is allowed to evaporate freely from heated vessels inside the container. - Condensation of water vapor at 18ºC – 20ºC on product surface. - Faster thawing than other surface heating methods for products less than 10 cm thick. By Dr. Mith Hasika Food Stabilization by Freezing 63 63 Thawing v Electrical methods Three electrical methods for thawing frozen fish (at present none is used commercially and equipment is not readily available). - Dielectric heating - Electrical resistance heating - Microwave heating: quick but problem (cooked) By Dr. Mith Hasika Food Stabilization by Freezing 64 64 32  4/30/24 By Dr. Mith Hasika Food Stabilization by Freezing 65 65 33