Food Stabilisation by Water Elimination PDF 2022-2023

6/14/23 Food Stabilisation by water elimination Dr. MITH Hasika 2022-2023 1 Food stabilization by water elimination?...

6/14/23 Food Stabilisation by water elimination Dr. MITH Hasika 2022-2023 1 Food stabilization by water elimination? Suspension Spices Fruits (milk) 2 2 1  6/14/23 Water elimination (Drying) - One of the oldest methods of preserving food. - Removes moisture stops the growth of bacteria, yeasts & molds that normally spoil food. - Drying involves the application of heat to vaporize moisture and some means of removing water vapor after its separation from the food products. - A combined and simultaneous heat and mass transfer operation for which energy must be supplied. Dried food product: - Reduction in weight and volume, minimizing packing, storage, and transportation costs and enables storability of the product under ambient temperatures. Food stabilization by water elimination 3 3 Objectives of water elimination ü Drying technique à most abundant and oldest method of food preservation for perishable products. Ø to stabilize food products F Slow down or stop development of microorganisms and enzymatic activities F Osmotic pressures play important roles in biological mechanisms of exchange through living cell wall. - divers foods (meat, vegetables, rice, pasta, milk, …) - agricultural products (corn, luzernes or alfalfa, grains…) - cured products, cheese - Co-products (sweets, whey…) Ex. Milk powder could be preserved for many years 4 4 2  6/14/23 Objectives of water elimination Ø to reduce the cost (concentration) F for storage (ex. milk powder), transportation (international trade), handling Ø to make functional - instant coffee or porridge, precooked porridge/soup, purée flake (potato) … 5 5 Ø South America : large production of orange Ž concentrate juice Factory in Europe Barrel of concentrate juice Orange juice from concentrate Brazil Spain (Factory) ž France ž 100% pure orange juice (organoleptic quality) § Via drying à food caracteristics appreciated by consumers (fruits, vegetables, dairy products, fish, soup…) 6 6 3  6/14/23 Inconvenience of dehydration § Risks of quality alteration (nutritional and/or organoleptic) of product : loss of vitamines, loss of aroma, browning, insolubilization of proteins … § High cost of product (energy consumption) § Dried products often face competition from other products Ex : Orange juice from Brazil Vs Orange juice from Spain Nestcafé Vs fresh coffee (drying Ž powder) Milk in powder Vs sterilized milk 7 7 Basic Principle of Drying n The water may be contained in the solid in various forms like free moisture or bound form which directly affects the drying rate. n Moisture content is expressed either on dry or wet basis, e.g. moisture content in wet (𝑊" ) basis is the weight of moisture per unit of wet material. 𝑴𝒔𝒂𝒎𝒑𝒍𝒆 𝒃𝒆𝒇𝒐𝒓𝒆 𝒅𝒓𝒚𝒊𝒏𝒈 6𝑴𝒅𝒓𝒆𝒊𝒅 𝒔𝒂𝒎𝒑𝒍𝒆 𝑾𝒘 = 𝑴𝒔𝒂𝒎𝒑𝒍𝒆 𝒃𝒆𝒇𝒐𝒓𝒆 𝒅𝒓𝒚𝒊𝒏𝒈 𝒙 𝟏𝟎𝟎 and on dry basis (𝑊: ), is expressed as the ratio of water content to the weight of dry material 𝑴𝒔𝒂𝒎𝒑𝒍𝒆 𝒃𝒆𝒇𝒐𝒓𝒆 𝒅𝒓𝒚𝒊𝒏𝒈 − 𝑴𝒅𝒓𝒆𝒊𝒅 𝒔𝒂𝒎𝒑𝒍𝒆 𝑾𝒅 = 𝒙 𝟏𝟎𝟎 𝑴𝒅𝒓𝒊𝒆𝒅 𝒔𝒂𝒎𝒑𝒍𝒆 Food stabilization by water elimination 8 8 4  6/14/23 Relationship between wet-weight and dry-weight basis } Although the most convenient way to express moisture for mathematical calculations is on dry basis but for agricultural products moisture content normally is expressed in wet basis. Food stabilization by water elimination 9 9 Mechanism of drying n Drying basically comprises of two fundamental and simultaneous processes: 1. Heat is transferred to evaporate liquid and 2. Mass is transferred as a liquid or vapor within the solid and as a vapor from the surface The factors governing the rates of these processes determine the drying rate. n The different dryers may utilize heat transfer by convection, conduction, radiation, or a combination of these. Food stabilization by water elimination 10 10 5  6/14/23 Typical drying curve n A-B: Warm up periode. When some materials are placed in a dryer, they may take a short period to time to warm up. n B-C: The surface may be covered with a film of water that is evaporated at a uniform rate and water from the inside of the material moves to the surface by diffusion. n C-D: The rate at which water is evaporating becomes slower. Food stabilization by water elimination 11 11 Drying stages for an actual food material based on weight n At 6-7h: there was enough water on the surface of the material to support a constant rate of evaporation (i.e., the constant rate drying period). n At 8h: diffusion of moisture from inside the material was not sufficient to replenish the moisture on the surface and the falling rate drying period began Food stabilization by water elimination 12 12 6  6/14/23 Factors affecting drying q Properties of the Product: Spheres, Cylinders, Flat Plates or Slabs Ex: Berries and peas (drying rate is controlled by its radius, or half its diameter. This is because water must move from the centre of the sphere along its radius to reach the surface where it will be removed). Ex: whole carrots (The main difference between drying spheres and cylinders is the ratio of their surface area to volume which is higher in the case of the cylinders). q Size or Thickness of the Material q Composition, Structure, and Porosity q Initial Moisture Content q Surface Characteristics Ex: cranberries that have a waxy cuticle, or outer coating q Amount of Surface Available for Moisture Loss q Seasonal Variation of Materials q Differences in Varieties of Materials Food stabilization by water elimination 13 13 Factors affecting drying kinetic q Temperature q Air velocity Effect of temperature on drying kinetic Effect of air velocity on drying kinetic Food stabilization by water elimination 14 14 7  6/14/23 Factors affecting drying kinetic q Effect of surface characteristic on drying q Comparaison of water removal from whole and halved hot yellow pepper Food stabilization by water elimination 15 15 Factors affecting drying kinetic q Thickness of apple slices Effect of thickness on drying of apple slices Food stabilization by water elimination 16 16 8  6/14/23 Exercise 1 n Consider a food material with a dry basis moisture content of 8.09 grams of water per gram of dry solids. What is its wet basis moisture content? Answer: 88,99% Food stabilization by water elimination 17 17 Exercise 2 n A processor has 890 kg of mangoes with a moisture content of 85% on a wet basis. Calculate the weight of water and solids present. Answer: Weight of water= 756,5 kg Solid weight=133,5 Kg Food stabilization by water elimination 18 18 9  6/14/23 Exercise 3 n A processor has 500 kg papaya with a moisture content of 87% (wet basis). Calculate how much water must be removed to dry the papaya slices to a final moisture content of 10% (wet basis). How much final product will be obtained? Answer: M_water= 427,78 kg M_solid= 72,22 Kg Food stabilization by water elimination 19 19 Exercise 4 n A processor needs 200 kg of dried tomatoes with a final moisture content of 11% wet basis. The ripe tomatoes used for drying have a moisture content of 94% wet basis. How much fresh tomatoes would be need? Answer: M_fresh tomatoes = 2966,66 Kg Food stabilization by water elimination 20 20 10  6/14/23 Effects of drying on finished products q Nutritional Degradation q Loss of Structural Integrity q Reduction in Functionality q Flavour and Aroma Changes q Colour Changes q Loss of Nutrients by Water Leaching q Case Hardening Food stabilization by water elimination 21 21 Drying system used in the food industry q Sun drying q Solar drying q Freeze drying q Spray drying q Hot air drying q Microwave q Oven dryer q So on… Food stabilization by water elimination 22 22 11  6/14/23 Sun drying q The food stuffs are dried under the sun. (+): low cost (-): Spoilt product due to rain, wind, moisture and dust, loss of product due to birds and animals, deterioration in the harvest crops due to decomposition, insect attack and fungi contamination. 23 23 Solar drying (+): Clean, hygienic, time and energy saving, occupy less area, improve product quality, prevent from rain and humidity. 24 24 12  6/14/23 Passive solar drying n Passive dryers use only the natural movement of heated air. They can be constructed easily with inexpensive, locally available materials which make them appropriate for small farms where raw construction material such as wood is readily available. Ex: Cabinet dryer: Ø Limitation of cabinet dryer: q Due to its small capacity its use is limited to small scale applications. q Discolouration of crop due to direct exposure to solar radiation. q Moisture condensation inside glass covers reducing its transmittivity. q Sometimes the insufficient rise in crop temperature affecting moisture removes. q Limited use of selective coatings on the absorber plate. 25 25 Passive solar drying 26 26 13  6/14/23 Active solar drying Ø The crop is not directly exposed to solar radiation to minimize discolouration and cracking on the surface of the crop. Ø The separated unit termed as solar air heater is used for solar energy collection for heating of entering air into this unit. n The active solar dryers solar energy and motorized and fans/pumps for air circulation. All active solar dryer are, thus, by their application, forced convection dryer. n In a integral type active dryers, the solar collector forms an integral part of the roof/wall of the drying/storage chamber. A distributed type active solar dryer is one in which the solar collector and drying chamber are separate units. Mixed- mode type dryer are rather uncommon designs and it combines some features of the integral and distributed type. 27 27 Oven drying q Oven dryer: Fixable temperature and time and energy consumption -> costly Ø Lab scale: small quantity, study drying kinetic of foodstuffs, incubtor Ø Industrial scale: large quantity 28 28 14  6/14/23 Freeze-drying q Freeze drying/lyophilization: a water removal process typically used to preserve perishable materials, to extend shelf life or make the material more convenient for transport. Freeze drying works by freezing the material, then reducing the pressure and adding heat to allow the frozen water in the material to sublimate. Food stabilization by water elimination 29 29 Spray drying q Spray drying is a method of producing a dry powder from a liquid or slurry by rapidly drying with a hot gas. This is the preferred method of drying of many thermally-sensitive materials such as foods and pharmaceuticals. 30 30 15  6/14/23 Microwave q Microwave: an electric oven that heats and cooks food by exposing it to electromagnetic radiation in the microwave frequency range. (+) :Shorter drying time, retains the nutrients, the texture of food, color (-): Taste will change, compared to cooking in a stove. Food stabilization by water elimination 31 31 Lyophilisation (Freeze-drying) 32 32 16  6/14/23 Freeze dried products Freeze dried durian Freeze dried fruits Freeze dried rice grass juice powder Freeze dried banana 33 33 Conventional dried products Hot air dried orange Mango flakes or powders at different particle sizes obtained from Refractance Window (RW) drying, freeze drying (FD), drum drying (DD), and spray Sun dried banana drying (SD). Source: Caparino et al., 2012. 34 34 17  6/14/23 Conventional vs Freeze drying Conventional drying Freeze drying Successful for easily dried foods Successful for most foods but limited to those that (vegetables and grains) are difficult to dry by other methods Meat generally unsatisfactory Successful with cooked and raw meats Temperature range 37–93ºC Temperatures below freezing point Atmospheric pressures Reduced pressures (27–133 Pa) Evaporation of water from surface of food Sublimation of water from ice front Movement of solutes and sometimes case Minimal solute movement hardening Stresses in solid foods cause structural Minimal structural changes or shrinkage damage and shrinkage Slow, incomplete rehydration Rapid complete rehydration Solid or porous dried particles often Porous dried particles having a lower density than having a higher density than the original original food food Odour and flavour frequently abnormal Odour and flavour usually normal Colour frequently darker Colour usually normal Reduced nutritional value Nutrients largely retained Costs generally low Costs generally high, up to four times those of conventional drying Source: Fellows, 2000. 35 35 Definition Freeze drying is a process of removing water in foods by sublimation under vacuum. The transformation directly of ice to a gas phase without passing through a liquid phase is called ‘sublimation’. Sublimation of ice can occur when the vapor pressure and temperature are lower than the triple point (4.58 mm Hg, 0 oC) (Welti-Chanes et al., 2004) 36 36 18  6/14/23 Phases of Water There are three phases of water: 37 37 Triple Point of Water Liquid (water) Solid (ice) Gas (vapour) Phase diagram of water as a function of Possibly exist of temperature and pressure Source: Welti-Chanes et al., 2004 3 phases 38 38 19  6/14/23 Phases of water Sublimation 39 39 Freeze dryer System Freeze dryer consists of a drying chamber, a condenser, a vacuum pump and a heat source as presented in the Figure. The sample is placed, in the chamber where heating/cooling temperature takes place, on the tray with the temperature-controlled shelves. The pressure is controlled by vacuum pump. Condenser is responsible for cooling and collecting water vapor which release from frozen product. That water vapor is collected on condensing surface and turned into Shemar of simple freeze dryer ice crystal which is going to be system removed from the system (Welti- Source: Welti-Chanes et al., 2004 Chanes et al., 2004). 40 40 20  6/14/23 Freeze dryer System 41 41 Drying Stage n The freeze drying process has three important stages: i) the freezing stage, ii) the primary drying or sublimation stage, iii) the secondary drying stage. 42 42 21  6/14/23 Drying Stage n The freezing stage: the products to be dried must be frozen below the solidification temperature which the material is in a frozen state. n The primary drying stage: in this stage the frozen solvent or water is removed by sublimation under vacuum. 43 43 Drying Stage n The secondary drying stage: this is the final stage of drying. The purpose of this stage is to remove unbound or sorbed water, and the water vapor is transported through the pores of material that is dried (Liapis and Bruttini, 2007). 44 44 22  6/14/23 Heat & Mass transfer in freeze drying A coupled heat and mass transfer process occurs within the product Conduction Microwave: deeply penetrate, more effective and uniform heating 45 45 Influence of Parameters 1. Freezing n Slow freezing rates allow the growth of large ice crystals leading to larger pores, higher mass flow, and thus to shorter freeze drying time 46 46 23  6/14/23 Influence of Parameters 2. Heat flux n If the drying proceeds too rapidly (high heat flux), the product may melt, collapse, or can be blown out of the container, n This may cause degradation of the product, and will change the physical characteristics of the dried material n Dry cake to char or shrink 47 47 Influence of Parameters 3. Chamber Pressure n Chamber pressure affects the transport properties, thermal conductivity and water vapor diffusivity. n Thermal conductivity of the dry layer is higher at higher chamber pressures 48 48 24  6/14/23 Influence of Parameters 4. Temperature Low temperature will reduce aroma loss; If the temperature of ice in the condenser is higher than product’s temperature, water vapor will tend to move toward the product, and drying will stop; When freeze-drying temperature is high enough, the product cake suffers a drastic loss of its structure and is said to have suffered collapse. This phenomenon occurs when the solid matrix can no longer support its own weight, leading to drastic structural changes shown as a marked decreased volume, increase in stickiness of dry powders, loss of porosity 49 49 Changes after drying n Total phenolic compounds of fresh and freeze-dried fruits. Shofian et al. 2011 50 50 25  6/14/23 Changes after drying n Ascorbic acid content of fresh and freeze-dried fruits. Shofian et al. 2011 51 51 Changes after drying n β-carotene content of fresh and freeze-dried fruits. Shofian et al. 2011 52 52 26  6/14/23 Changes after drying Shofian et al. 2011 53 53 Limitation of Freeze Drying n Expensive process n Large operation time n Large amount of energy (require to freeze product, heat the frozen product to sublimate ice, condense water vapor, maintain the vacuum pressure. 54 54 27