Food Preservation II: Food Stabilization by Chilling PDF

10/20/23 Food Preservation II Food Stabilization by Chilling Part I -...

10/20/23 Food Preservation II Food Stabilization by Chilling Part I - Refrigeration Asst. Prof. Dr. Hasika Mith Researcher-Lecturer Faculty of Chemical and Food Engineering Institute of Technology of Cambodia 2 1 2 1.1. Principle of refrigeration 1.1. Principle of refrigeration Ø The prepared produced supply chain Agent Food preservation and quality Primary Processor Retailer Consumer producer Pre- processor 3 4 3 4 1  10/20/23 1.1. Principle of refrigeration 1.1. Principle of refrigeration Chilling à to retard enzymatic, biochemical and microbiological activities What could be chilled? F The chilling does not destroy micro-organisms but prevent their development 5 6 5 6 Principle of food refrigeration 1.1. Principle of food refrigeration Refrigeration Cooling product between 0°C and RULES TO RESPECT : REFRIGERATING TRIPOD 15°C à Short term preservation of foods (a few days to a few weeks) Ø Raw materials of excellent quality Chemical effect : retard chemical reactions Ø Early implementation of a chilling treatment (maturation of fruits and vegetables, Ø Continuity of the cold chain hydrolysis reactions in meats). microbiological effect : depending on the level of temperature, some microorganisms can no longer grow. If T < +3°C, no more risk due to pathogenic or toxinogenic microorganisms. 7 8 7 8 2  10/20/23 1.1. Principle of food refrigeration 1.1. Principle of food refrigeration Refrigeration à good solution? Milk à after collecting à chilling at < 2h from 37°C to 5°C à maintained between 2°C to 4°C until arrival at factory by using double envelop tanks. Persimmons (kaki) Pasteurized milk is also refrigerated à preserve for 1 week at 0°C – 4°C. Fuyu – sensitive to heat Hachiya – resistant Pasteurized products à fruit juice heated and cooked foods by pasteurization à avoiding development of microorganisms surviving during heat treatment. Fruits and vegetables à as soon as possible after harvest Optimal temperature à avoiding important losses of water, risk of microbial contamination and slowing chemical reaction. for storage and Soft texture, browning and transport Chilling injury waterlogged appearance 9 10 9 10 Biosynthysis of ethylene C2H4 and intervention of oxygene, chilling, 1.1. Principle of food refrigeration injury and stresses in this biosythesis Maturation F autocatalytic synthesis of ethylene for climacteric Methionine fruit. Methionine adenosyltransferase - climacteric fruits (tomato, apple, pear, melon, bananas, SAM apricots) are characterized by a ripening-associated increase + Injury in respiration and in ethylene (phytohormone) production. ACC synthetase - Stress - Non climacteric fruits (citrus, grapes, strawberries, orange, O2 ACC pineapple) are characterized by the lack of ethylene- -- ACC oxydase Chilling associated respiratory peak and the signaling pathways - respiration bursts). C2H4 Anoxia n Very low concentration of C2H4 F accelerate maturation of R – C2H4 ( SAM : S-adenosylmethonine; ACC : acide 1- climacteric fruits and some non climacteric fruitsF senescence. aminocyclopropane 1-carboxylique; + stimulating action; - and -- inhibitory action) Biological action 11 12 11 12 3  10/20/23 1.1. Principle of food refrigeration 1.2. Cooling methods n Divers injuries or stresses (water deficit, bacterial or fungal attack) stimulate ACC synthetase and increase production of ethylene. n In anoxia (complete absence of oxygen), the synthesis of C2H4 is impossible, but accumulation of ACC and causes an increasing Cooling by forced Hydrocooling production of C2H4 when the organs return to ambient ventilation temperature. n In chilling, the enzymes are less active, temperature lowering reduces more activity of ACC oxidase than that of ACC synthetase. In the case of climacteric fruits, synthesis C2H4 is inhibited by Cooling by n Cooling by ice high concentration of CO2. Vacuum 13 14 13 14 1.2. Cooling methods Examples Quick cooling – Cooling by forced ventilation Foies Gras Ø Discontinuous device Rapid cooling cells: to cool down quickly the product à ~ 6°C à cooling product before freezing. Chilling chamber: to maintain the product at refrigerating temperature about 4°C. Multipurpose chamber: to serve for pre- refrigeration and maintain at refrigeration temperature. Advantages: less handling (unloading), Ø Continuous device product cooling time is long enough. Tunnels of pre-refrigeration: fast circulation Limits: over-equipped refrigerant group, of air at the interior of tunnel. they rotate at low speed during storage The products remain a few hours in the tunnel before sending to chilling chamber period or in refrigerated truck. 15 16 15 16 4  10/20/23 1.2. Cooling methods 1.2. Cooling methods Hydrocooling Cooling by vacuum Ø By immersion : fruits and vegetables are placed on cold water bath. It can predict the movement of fruits. The product is placed in vacuum chamber. The evaporation of water conducted at low temperature Avantages : due to vacuum. Necessary energy for change of state Good coefficient of heat exchange: quick cooling time Cleaning product is taken at product itself : thus product cooled down. Average installed cooling capacity Avantage : quick refrigeration (30 min) Limits : Limit : loss of water in product. This processus is then Risk of contamination, utilisation of disinfectants and reserved for product rich in water, risk of product fungicide in water bursting (tomato). System not adapted to all products Ø By spraying : passage of products under an ice water jet. Adapted for leafy products (salad...) coefficient of exchage less interested by comparison to immersion time of cooling is quick enough 17 18 17 18 1.2. Cooling methods 1.2. Cooling methods Cooling by ice Hydrocooler https://www.youtube.com/watch?v=gLLHnaMl3c4 Flake ice : often used to cool fish and seafoods Apple processing https://www.youtube.com/watch?v=TYSgUTNODo8 Precooling https://www.youtube.com/watch?v=azoGx5aegNc Salad https://www.youtube.com/watch?v=Ad6KcRxA_TU Leafy vegetables https://www.youtube.com/watch?v=7wQ08xBKXlU Carrot https://www.youtube.com/watch?v=aMTbQzQFFCo Control atmosphere https://www.youtube.com/watch?v=DQlTOxTaIqE Control atmosphere fresh fruits https://www.youtube.com/watch?v=pLMsesdQqmw 19 20 19 20 5  10/20/23 1.3. Chilling and conditions Refrigeration under controlled atmosphere 1.3. Chilling and conditions Refrigeration under controlled atmosphere Positive chilling Ø To modify the atmospheric composition of cooling chamber to + impoverishment of O2 in air prolong the preservation duration of fruits and vegetables. + enrichment of CO2 3 – 5% O2 3 – 5% CO2 90 – 94% N2 - Reducing O2 content C Reducing respiration : ü To avoid the browning and oxidation ü To slow the softening of fruits, loss of chlorophylls and production of ethylene. - Increasing CO2 C inhibition of enzymes responsible for respiratory chain and bacteriostatic effect. 21 22 21 22 Parameters of chilling chamber Parameters of chilling chamber 1.3. Chilling and conditions and refrigeration balance 1.3. Chilling and conditions and refrigeration balance Optimal temperature of refrigeration Air circulation Evacuation of releasing heat = conservation of 0 – 5°C : storage of products resistant to Homogenize temperature in the chamber chilling and obtain the cooling much faster. products by maintaining low temperature 5 – 10°C : storage of products sensitive Renew the air to eliminate the volatile to chilling harvest in temperate countries substances (aldehyde, esters) and gas Uncontrollable 10 – 15°C : storage of tropical or (ethylene). Food cooling loss Mediterranean products Parameters Frequency of renewing : Power of refrigerating of chilling 1500 – 2000 m3 C 2 changes per 24 h 15 – 30°C : normal or accelerated machine lightning maturation chamber 3000 – 4000 m3 C 4 changes per 24 h personnel Loading of chilling room transmission through wall Air renewing Door opening Relative humidity of chilling chamber Estimate the space between the Transpiration F water loss. Humidity walls and palettes for handling around 90%, do not exceed this value 200 kg/m3 for apples and pears (not favor microbial development). 400 kg/m3 for potatoes 23 24 23 24 6  10/20/23 1.3. Chilling and conditions Refrigeration under controlled atmosphere 1.3. Chilling and conditions Alteration of product during storage Ø Microbiological quality : Erwinia Ø Organoleptic quality : too much Advantages Limits responsible of dark spot on salad chilling à produce the brown ring leaves. Pseudomonas produce in apple. The atmospheric § To prolong duration of product § Complex method : controlling enzymes to hydrolyse the composition can create the brown preservation : + 40 – 60% / atmosphere, assuring the membrane of vegetables…etc spots on apples. normal refrigeration sealing of chambers (special § Better presentation of product membranes, absorbers, to sell generators) § Less loss of products § costly system 25 26 25 26 1.4. Application of refrigeration 1.4. Application of refrigeration Storage potential of horticultural produce in air at near-optimum storage temperature and Recommended pre-cooling methods for selected fruits and vegetables relative humidity Fruit Pre-cooling methods Vegetable Pre-cooling methods Class Storage life Degree of Commodity (weeks) perishability Apple Room, forced air, hydro-cooling Asparagus Hydro-cooling, package icing I 16 Very low Tree nuts and dried fruits 28 27 27 28 7  10/20/23 1.4. Application of refrigeration 1.4. Application of refrigeration Optimum storage temperature and humidity conditions for fresh fruits Optimum storage temperature and humidity conditions for fresh vegetables Vegetable Optimum Relative humidity Storage life Fruit Optimum Relative humidity Storage life Temperature ℃ % Temperature ℃ % Asparagus 2.2 95 – 100 2 – 3 weeks Apple – 1 to 4.4 90 – 95 1 – 12 months Broccoli 0 95 – 100 2 weeks Blueberries 2.2 90 – 95 2 – 3 weeks Cabbage 0 95 2 – 3 months Peaches 0.6 – 1 95 – 98 2 – 4 weeks Cucumbers 7.2 – 10 95 2 weeks Strawberry 0 90 – 95 5 – 7 days Eggplant 7.8 – 12.2 90 – 95 1 week Water melon 10 – 15.6 90 2 – 3 weeks Green beans 2.8 – 7.2 95 5 – 10 days Onions 0 70 2 – 3 months Potatoes 3.3 – 4.4 90 – 95 5 – 8 months Tomatoes 8.9 – 10 85 – 95 7 – 14 days 29 30 29 30 2.1. Principles of freezing Part II - Freezing Refrigeration Preservation ä Freezing / Deep-freezing 31 32 31 32 8  10/20/23 2.1. Principles of freezing 2.1. Principles of freezing v Microbiological quality : the products preserved for q Method of preservation that the temperature of several months (without microbial development) – product is reduced and maintained low, below the 0°C v Freezing does not destroy water activity reduction microorganisms but only prevent freezing point of food products. Pure water is their development v Nutritional and organoleptic quality : preserved q Conversion of liquid of food into ice crystals frozen at 0°C Food frozen below 0°C well the nutritional and organoleptic caracteristics (dissolved solids: sugars, acids…) (much better than sterilization) q Freezing / Deep-freezing = obstacles “cold” + “Aw” F Some particular mesures to be taken into account : v Microbiological quality : the products preserved for v Freezing does not destroy several months (without microbial development) – microorganisms but only prevent ü Raw material with excellent microbiological quality water activity reduction their development ü Strict hygiene condition during production (materials, local, personnels, handling) v Nutritional and organoleptic quality : preserved ü Control of temperature during production well the nutritional and organoleptic caracteristics ü Continuity of chilling chain to avoid regrowth of (much better than sterilization) microorganisms. 33 34 33 34 2.1. Principles of freezing Modification of product due to freezing 2.1. Principles of freezing 3 zones: T - Cooling to temperature slightly lower than the point of fusion (0ºC), before State change of pure water 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. Supercooling point – early nucleation - Cooling of ice, thermal diffusivity of water increases during state change. 0°C Temperature reduction of water Q = mcDT Liquid Mix of ice water water/ice Change of state (latent heat) Q = m.L Temperature reduction of ice Q = mc' DT time 35 36 35 36 9  10/20/23 2.1. Principles of freezing 2.1. Principles of freezing Crystals of solvent and solute appear simultanously for a particular T concentration of solute F eutectic concentration – eutectic temperature Four zones : State change of saline solution/ Cooling to temperature TC. biological tissue At Tc, incipient fusion temperature, apparition of pure ice crystals, increase of solution concentration (cryoconcentration) and decrease of Tc fusion point. From a concentration called eutectic, the solution crystalizes Pseudo (simultanously water and solute). The temperature remains constant until palier the whole solution becomes cristalized (zone slowing the temperature fall - vague « pseudo-palier ») Cooling the solidified ensemble 37 38 37 38 2.1. Principles of freezing 2.2. Freezing rate and product quality 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 39 40 39 40 10  10/20/23 2.2. Freezing rate and product quality Distribution and size of ice crystals 2.2. Freezing rate and product quality S Slow freezing S Quick freezing Big ice crystals at Smaller ice exterior of cells crystals faster rate slow rate growing of ice increase of concentration drawing water out of multitude of smaller ice less shrinking of reduction of degree of freeze crystals into the of frozen solution outside the cells by osmosis crystals at the interior + the cells damage (little change to texture/ intercellular tissue the cells exterior of cells less loss of nutrient when thawing) Advantage of quick freezing is to addition of this water to shrunken cells disruption of cell Much lesser preserve better quality of product the growing ice crystals + larger crystals structure exudate (distribution of ice and ice crystals) 41 42 41 42 2.3. Freezing methods/equipments Ø It depends on : Raw materials (nature of product) Plate Freezers Air Blast Freezers Temperature/pressure Packaging Sugar/salts Thickness/Contact surface of food product Immersion Evaporating Freezing systems-flow of air or Freezers Liquid Freezers refrigerant Refrigerant type 43 44 43 44 11  10/20/23 2.3. Freezing methods/equipments Plate freezers 2.3. Freezing methods/equipments Air blast freezer § Product is pressed by hydraulic ram between metal plates which have channels for refrigerant. Adapted for some foods, mainly bulk products § heat transfer at the surface gradually reduced with increasing thickness (50 mm max.). including beef quarters and fruits for further processing; frozen in rooms with or without forced air circulation. Refrigerant is air or forced air and cooled to – 30°C to – 40°C. Existing in batch or continuous equipment for food freezing Air blast freezers are the most classic and widely used due to their versatility : Food on metal trays § air is compatible with foods § possible to freeze in the same apparatus multitude Horizontal plate freezers Vertical plate freezers of different products. Usually 15 to 20 plates Mainly developed for freezing fish at sea Ü The air has tendency to wither the product surface Product placed on metal trays, manually Vertical freezing plates forming partitions pushed in between plates à high labor ð to pack the product and to spray water in a container with open top. content in loading and unloading operation. 45 46 45 46 2.3. Freezing methods/equipments Air blast freezer 2.3. Freezing methods/equipments Air blast freezer § Tunnel freezers are Tunnel freezer (Batch) flexible, packaged or unpackage products with different size and shape to § Overall operation economy of blast be frozen in freezer: weight losses during freezing stationary/push-through Tunnel for unpackaged products. freezers tunnels. § Primarily used for freezing - Improperly designed freezer: ≥ 5% packaged products. weight loss - Well-designed freezer: 0.5-1.5% weight loss Air blast freezers Fluidized bed Belt freezers freezers ü Minimization of dehydration loss - Low air temperatures/good heat § Belt freezers: single belt, multi-belt - Product individually frozen (Individual Quick Freezing) à applied to products with tendency transfer and spiral belt § Mainly used for freezing unpackaged to stick together (green beans, sliced carrots, products sliced cucumber…) - Independence of fluctuation in load - Reliability improvement (adapt for freezing 47 surplus water product) 48 47 48 12  10/20/23 2.3. Freezing methods/equipments Immersion Freezers 2.3. Freezing methods/equipments Evaporating liquid freezers Ø The immersion freezer consists Ø Direct contact immersion: tank Ø LN2 (liquid nitrogen) Freezer of a tank with a cooled freezing containing brine used to freeze medium (propylene, glycol, fishes (tuna) at sea (20% NaCl glycerol, sodium chloride, at -20ºC, possible to use a calcium chloride and mixtures of system of brine spraying). salt and sugar). Ø Indirect contact immersion Ø Fast temperature reduction (tight packaging): most through direct heat exchange commonly used for surface 1. Belt; 2. Spraying nozzles; 3. Fans; 4. Inlet; 5. Outlet; 6. Nitrogen tank supply line; 7. Regulating valve; when product is immersed or freezing “crust freezing” of 8. Temperature sensing unit; 9. Nitrogen gas exhauster sprayed. poultry to obtain a light surface color (final freezing is effected Liquid nitrogen (–196°C) to spray onto a single in a separate blast tunnel or belt freezer, used for products pre-cooling. § better coefficient of convection (rapid freezing) cold store), slow freezing of the Very high freezing rate to improve texture for § no consumption of energy of ventilation product core could affect quality certain fruits and vegetables, but cracking of § no desiccation of product and hazard. product surface if insufficient precautions Often used only for surface freezing (expensive osalty taste into product operation) oproblem of brine contamination 49 50 49 50 2.3. Freezing methods/equipments 2.3. Freezing methods/equipments Quick cooling / Deep-freezing of great Deep-freezing of meat Freezing of salmon Deep-freezing of spinach scallop 51 52 51 52 13  10/20/23 2.4. Thawing techniques 2.4. Thawing techniques v Exudation During thawing à fusion of ice crystals. A part of water is not re-absorbed by product, it Air thawing is called exudate. Exudate depend on : § freezing technique (slow/quick) Electric Air blast § maintaining temperature during storage methods thawing § thawing technique (quicker the thawing is, less exudate released) § presentation of pieces to be frozen (ex. minced meat à important quantity of exudate) Thawing techniques Exudate is responsible for : weight loss = financial loss creation of favorable medium for microbial development. organoleptic quality loss loss of nutritional compounds Vacuum watering thawing thawing 53 54 53 54 2.4. Thawing techniques 2.4. Thawing techniques v Still air thawing v Air blast thawing - Thawing duration is extremely - Air is ventilated with high humidity long (~ 90%) ° to improve the convection coefficient and avoid the desiccation - Rate of exudate from thawing of product. product by this method is relatively high (0,5 à 3%) - Cool air is forced at 4ºC, with ° not practically used. humidity ~ 70% ° to limit microbial development. Crossflow batch thawer 55 56 55 56 14  10/20/23 2.4. Thawing techniques 2.4. Thawing techniques Simple immersion thawer v Water thawing v Vacuum thawing This method is not normally applicable to - Products lies on racks inside a meat and with fish fillets or cut surfaces à container with air evacuation. waterlogging and flavor loss. - Water is allowed to evaporate freely Applicable for frozen whole fish even with from heated vessels inside the Spray thawer slight loss of pigments. container. Cheap and easy method of thawing (all - Condensation of water vapor at 18ºC types of whole fish) with clean water – 20ºC on product surface. supply. - Faster thawing than other surface Hygiene and intercontamination, T < 20ºC heating methods for products less ð to limit microbial development. than 10 cm thick. 57 58 57 58 2.4. Thawing techniques 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) 59 59 15