Lesson 07 Introduction to Drying and Dehydration - Part 1 PDF

Lesson 7 Introduction to Food Drying and Dehydration – Part 1 __ ROLENZ DERICK R. CRUZ Food Technology Department College of Industrial Technology Bicol University © 2021 Rolenz Cruz...

Lesson 7 Introduction to Food Drying and Dehydration – Part 1 __ ROLENZ DERICK R. CRUZ Food Technology Department College of Industrial Technology Bicol University © 2021 Rolenz Cruz All rights reserved. This work is an intellectual property of the FT16 Food Processing II author. Redistribution or sale of any part of this presentation First Semester, AY 2024-2025 © 2021 and lecture without prior consent of the author Rolenz is not Cruz allowed. © 2021 Rolenz Cruz All rights reserved. This work is an intellectual property of the author. Redistribution or sale of any part of this presentation and lecture without prior consent of the author is not allowed. © 2021 Rolenz Cruz  LESSON OUTCOMES At the end of the lesson, you should be able to: Demonstrate understanding on the principles of food drying and dehydration in terms of its effects on the general quality of food and relevant scientific theories on moisture migration. 3 © 2021 Rolenz Cruz Drying and Dehydration Dehydration is the removal of water from a product. The reasons for drying are to: – preserve the product – modify product texture – reduce transport weight The most important of these is preservation, or more precisely extension of shelf life. – This is achieved by reducing moisture to a level at which its availability for reactions is reduced, measured by a parameter called water activity. 4 © 2021 Rolenz Cruz Photo courtesy of Sous Vide Guy (2021) Water Activity Water Table. Water Contents of Various Foods – Most abundant component of food and is important to the stability of most food products. – A controlling factor in microbial spoilage, and also contributes to chemical and physical stability. – For this reason, it is commonly used as a preservation technique. control of used as a preservation water content technique 5 © 2021 Rolenz Cruz Water Activity Water Activity (Aw) – A measure of the availability of water to Formally, it is defined as the ratio of the partake in chemical reactions and water vapor pressure (𝒑𝒗 ) in a food to influence microbial growth that of pure water vapor (𝒑𝒔 ) at the – An expression of the reactivity of water in same temperature: a food – Indicates how tightly water is structurally or chemically bound – Related to, but not the same as, moisture content 6 © 2021 Rolenz Cruz Water Activity Aw can be measured by determining the RH in the headspace above a product in a sealed container. 7 © 2021 Rolenz Cruz Water Activity Important Points: During drying, the fraction of chemically bound water within the product increases, reducing the vapor pressure. Consequently, there is less free water available for chemical and microbial reactions. Generally, as moisture in the product is reduced, the Aw is also reduced. Thus, generally, in dried foods, deterioration reactions are slowed down and the product will last longer. Note that changing MC is a means to control Aw, and therefore it is Aw, not MC, which is of first importance in drying – especially in microbial and chemical stability of food. 8 © 2021 Rolenz Cruz Drying and Food Quality Dehydration may change a food product in several ways: Microbial Stability Limits of microbial growth are determined by Aw For example, – most bacteria need Aw > 0.90 – molds need Aw > 0.60 The exact Aw limit for a specific organism also depends on other factors such as pH, oxygen availability, the nature of solutes present, nutrient availability, and temperature. – Generally, the less favorable the factors, the higher the value of Aw required for growth. Figure. Water Activity and Food Stability Diagram. Adopted from Campbell-Platt (2009) 9 © 2021 Rolenz Cruz Review: Classification of Bacteria Based on Oxygen Requirement Based on Temperature 1. Aerobes (need oxygen for growth) 1. Psychrophiles – optimum at 10-14°C Microaerophile – need only small amount 2. Mesophiles – optimum at 30-37°C of oxygen 3. Thermophiles – optimum at 50-65°C 2. Anaerobes Obligate – oxygen prevents growth Based on Salt, Acid, Aw, & Osmotic P Facultative – can tolerate some degree of oxygen 1. Halophiles – requires salt 2. Acidophiles – requires low pH 3. Xerophiles – can grow at low Aw (dried foods) 4. Osmophiles – can grow at high osmotic P (high sugar foods) 10 © 2021 Rolenz Cruz  Aw Limits of Microbial Growth Figure. Growth of various microorganisms at different water activity conditions. Adopted from Roos (2003) 11 © 2021 Rolenz Cruz Drying and Food Quality Microbial Stability Effects of microbial action on quality may be: – Discoloration – Physical damage – Off-flavors & off-odors (spoilage microbes) – Food safety issue (pathogens which cause food- borne diseases) Reduction in Aw will increase the microbiological stability of the product, thus increasing shelf life. 12 © 2021 Rolenz Cruz Drying and Food Quality Chemical Stability Water may take part in chemical reactions as: – a solvent, providing a transport mechanism for reactants to come in contact with each other – a reactant, as a component consumed in the reaction – a product, for example, in non-enzymatic browning reactions, or – a modifier, for example by catalyzing or inhibiting reactions. 13 © 2021 Rolenz Cruz Drying and Food Quality Chemical Stability Drying T has an important effect on the rates of chemical reactions, so directly affects the quality of the dried product. At low moistures, a further preservation mechanism becomes significant. – As product moisture drops, solutes become more concentrated and therefore solution viscosity rises. – This makes it increasingly difficult for reactants to come together. 14 © 2021 Rolenz Cruz Drying and Food Quality Chemical Stability Some examples of important food chemical reactions include the following: 1. Enzymatic reactions, which are very slow at low Aw values, due to lack of mobility of the substances to diffuse. 2. Non-enzymatic browning, a water-dependent reaction with maximum reaction rates around Aw = 0.6 to 0.7. Water is also a reaction product. – Too much water inhibits the reaction by dilution – Too little gives inadequate mobility 15 © 2021 Rolenz Cruz Drying and Food Quality Chemical Stability Some examples of important food chemical reactions include the following: 3. Lipid oxidation, a reaction that is fast at both low and high values of Aw, slow at intermediate values. 4. Loss of nutrients, for example vitamin B or C losses due to breakdown at high T. 5. Loss of volatiles, for example flavors and aromas, from the product. 6. Release of structural water, which changes food texture. 16 © 2021 Rolenz Cruz Drying and Food Quality Physical Stability Microbiological and chemical stability both correlate with Aw, but physical deterioration correlates with MC. Some examples of physical effects include the following: 1. Softening of texture at high moisture, hardening at low moisture. 2. Differential shrinkage: outer layers shrink relative to inner layers, leading to either surface cracks or radial cracks. 3. Surface wetting effects: moisture works on the product surface to expand pores and capillaries. 4. Case hardening: a hydrophobic layer may be formed in oil-rich or proteinaceous products during rapid drying of outer layers, which traps moisture inside the product. 5. Cell collapse: cells may collapse if internal moisture is removed, leading to the product shrinking and the surface becoming wrinkled. 17 © 2021 Rolenz Cruz  Microbial Stability Chemical Stability Physical Stability Figure. Water Activity and Food Stability Diagram. 18 © 2021 Rolenz Cruz Hot Air Drying Most food dryers use heated air passed across a product to remove moisture. – Moisture is normally used as an indication of the progress of drying. – Again, from the preservation point of view, it is not moisture but Aw which must be controlled. Air holds a relatively small amount of moisture, normally less than Figure. Moisture content 1% by mass. versus time of drying – RH for the air – ratio of the actual VP (𝑝𝑣 ) to the maximum possible VP (𝑝𝑠 ) at the same T. – Saturated air has a RH of 1, often written as 100%. 19 © 2021 Rolenz Cruz  In cold water: Lower rate of evaporation (L to G) Lower rate of condensation (G to L) In warm water: Faster rate of evaporation (L to G) Faster rate of condensation (G to L) Other points: At equilibrium, evaporation rate = condensation rate. When evaporation rate is not equal to condensation rate, then relative humidity is not at 100%. When air is saturated with water vapor, that gives 100% RH. Saturation concentration of air increases with T. 1 2 3 4 5 20 © 2021 Rolenz Cruz Relative Humidity RH is a measure of the Aw of the air. – If a product sample is allowed to equilibrate with a small amount of air in a sealed container, then the air and the product will equilibrate with respect to both temperature and moisture. At equilibrium, the air RH is numerically equal to the Aw: If a food product comes in contact with: – air with RH > Aw then it will absorb moisture from the air – air with RH < Aw then it will release moisture to the air 21 © 2021 Rolenz Cruz Relative Humidity Here are some important consequences: – A product should be stored in a package or a storage environment where the RH is controlled. – Drying cannot reduce the Aw below the RH of the air used for drying the product. Aw can be also controlled by other methods: 1. Adding humectants, such as sugars, salts and glycerol, can bind available water – e.g. jams & jellies (sugar concentrates) 2. Freezing a product also reduces the available water for reaction (temporarily only). Cabinet Dryer (Aumax Industrial) 22 © 2021 Rolenz Cruz Product Equilibrium If we place a product in a jar and then seal it, the product & air will come to equilibrium over time. There are two forms of equilibrium occurring: 1. a thermal equilibrium, where the temperatures equalize, and 2. a moisture equilibrium, which occurs when the rate of evaporation from the surface of the product becomes equal to the rate of condensation. 23 © 2021 Rolenz Cruz Moisture Content The amount (or concentration) of water in a product is called the product MC. May be measured in two ways: 1. Wet basis (𝑀𝐶𝑤𝑏 ): mass of water divided by the total product mass 2. Dry basis (𝑀𝐶𝑑𝑏 ): mass of water divided by the dried solids only 𝑤𝑡 𝑜𝑓 𝑤𝑒𝑡 − 𝑤𝑡 𝑜𝑓 𝑑𝑟𝑦 100 𝑥 𝑀𝐶𝑑𝑏 𝑀𝐶𝑤𝑏 = 𝑥100 𝑀𝐶𝑤𝑏 = 𝑤𝑡 𝑜𝑓 𝑤𝑒𝑡 100 + 𝑀𝐶𝑑𝑏 𝑤𝑡 𝑜𝑓 𝑤𝑒𝑡 − 𝑤𝑡 𝑜𝑓 𝑑𝑟𝑦 𝑀𝐶𝑑𝑏 = 𝑥100 100 𝑥 𝑀𝐶𝑤𝑏 𝑤𝑡 𝑜𝑓 𝑑𝑟𝑦 𝑀𝐶𝑑𝑏 = 100 − 𝑀𝐶𝑤𝑏 24 © 2021 Rolenz Cruz Moisture Content For example, for a product containing 40 kg of water for a 100 kg sample, the moisture content is expressed as 40% on a wet basis. 100 𝑘𝑔 − 60 𝑘𝑔 𝑀𝐶𝑤𝑏 = 𝑥 100 = 𝟒𝟎% 100 𝑘𝑔 Since the mass of dry solids is 60 kg, this is equivalent to 40/60 or 67% dry basis. 100 𝑘𝑔 − 60 𝑘𝑔 𝑀𝐶𝑑𝑏 = 𝑥 100 = 𝟔𝟕% 60 𝑘𝑔 25 © 2021 Rolenz Cruz  Try This! Complete the table below: Total Mass Dry Product Dry Basis MC Wet Basis MC 𝑤𝑡 𝑜𝑓 𝑤𝑒𝑡 − 𝑤𝑡 𝑜𝑓 𝑑𝑟𝑦 𝑀𝐶𝑤𝑏 = 𝑥100 Product (kg) Mass (kg) (%) (%) 𝑤𝑡 𝑜𝑓 𝑤𝑒𝑡 100 50 𝑤𝑡 𝑜𝑓 𝑤𝑒𝑡 − 𝑤𝑡 𝑜𝑓 𝑑𝑟𝑦 𝑀𝐶𝑑𝑏 = 𝑥100 100 90 𝑤𝑡 𝑜𝑓 𝑑𝑟𝑦 100 20 100 𝑥 𝑀𝐶𝑑𝑏 100 20 𝑀𝐶𝑤𝑏 = 100 + 𝑀𝐶𝑑𝑏 50 40 100 𝑥 𝑀𝐶𝑤𝑏 20 85 𝑀𝐶𝑑𝑏 = 100 − 𝑀𝐶𝑤𝑏 26 © 2021 Rolenz Cruz Answers: Complete the table below: Total Mass Product Dry Product Mass Dry Basis MC (%) Wet Basis MC (%) (kg) (kg) 100 50 100 50 100 90 11.11 10 100 83.33 20 16.67 100 80 25 20 70 50 40 28.57 133.33 20 566.65 85 27 © 2021 Rolenz Cruz Answers: Total Mass Product Dry Product Mass Dry Basis MC (%) Wet Basis MC (%) (kg) (kg) 100 50 100 50 100 𝑘𝑔 − 50 𝑘𝑔 𝑀𝐶𝑑𝑏 = 𝑥 100 = 𝟏𝟎𝟎% 50 𝑘𝑔 100 𝑘𝑔 − 50 𝑘𝑔 𝑀𝐶𝑤𝑏 = 𝑥 100 = 𝟓𝟎% 100 𝑘𝑔 28 © 2021 Rolenz Cruz Answers: Total Mass Product Dry Product Mass Dry Basis MC (%) Wet Basis MC (%) (kg) (kg) 100 83.33 20 16.67 100 𝑥 20% 𝑀𝐶𝑤𝑏 = = 𝟏𝟔. 𝟔𝟕% 100 + 20% 100 𝑘𝑔 − 𝑿 𝑀𝐶𝑑𝑏 = 𝑥 100 = 20% 𝑿 𝑘𝑔 𝑋 = 𝟖𝟑. 𝟑𝟑 𝒌𝒈 29 © 2021 Rolenz Cruz Answers: Total Mass Product Dry Product Mass Dry Basis MC (%) Wet Basis MC (%) (kg) (kg) 70 50 40 28.57 100 𝑥 40% 𝑀𝐶𝑤𝑏 = = 𝟐𝟖. 𝟓𝟕% 100 + 40% 𝑿 − 50 𝑘𝑔 𝑀𝐶𝑑𝑏 = 𝑥 100 = 40% 50 𝑘𝑔 𝑋 = 𝟕𝟎 𝒌𝒈 30 © 2021 Rolenz Cruz Moisture Content Let 𝑚𝑝 be the initial mass of a product. If we dry the product from an initial moisture content of 𝑀𝐶𝑖 to 𝑀𝐶𝑓 (both wet basis), then a useful formula for calculating the mass of water removed is: 𝑀𝐶𝑤𝑏 𝑓 − 𝑀𝐶𝑤𝑏 𝑖 𝑚𝑤 = 𝑚𝑝 𝑥 1 − 𝑀𝐶𝑤𝑏 𝑖 How much moisture would I need to remove to dry 100 kg of wet product from 50% to 20% wb? 20% − 50% 𝑚𝑓 = 100𝑘𝑔 𝑥 = 𝟔𝟏. 𝟐𝟐 𝒌𝒈 1 − 50% 31 © 2021 Rolenz Cruz Try This! 1. How much moisture would I need to remove to dry 250 kg of wet product from 80% to 15% wb? 2. What is the final MC in wet basis if the amount of water removed is 80 kg with an initial MC of 70% of a 400 kg food sample? 3. If the mass of the water removed is measured to be 135 kg of a product which has an initial MC (in wet basis) of 95% and a final MC of 20%, what is the mass of the product prior to drying? 𝑀𝐶𝑤𝑏 𝑓 − 𝑀𝐶𝑤𝑏 𝑖 𝑚𝑤 = 𝑚𝑝 𝑥 1 − 𝑀𝐶𝑤𝑏 𝑖 32 © 2021 Rolenz Cruz Answers: 1. How much moisture would I need to remove to dry 250 kg of wet product from 80% to 15% wb? 15% − 80% 𝑚𝑓 = 250 𝑘𝑔 𝑥 = 𝟐𝟎𝟓. 𝟕𝟎 𝒌𝒈 1 − 80% 2. What is the final MC in wet basis if the amount of water removed is 80 kg with an initial MC of 70% of a 400 kg food sample? 𝑋 − 70% 80 𝑘𝑔 = 400 𝑘𝑔 𝑥 1 − 70% 𝑋 = 𝟓𝟔. 𝟐% 33 © 2021 Rolenz Cruz Answers: 3. If the mass of the water removed is measured to be 135 kg of a product which has an initial MC (in wet basis) of 95% and a final MC of 20%, what is the mass of the product prior to drying? 20% − 95% 130 𝑘𝑔 = 𝑋 𝑥 1 − 95% 𝑋 = 𝟏𝟔𝟐. 𝟗𝟑 kg 34 © 2021 Rolenz Cruz Overview Introduction to Drying & Dehydration – Part 1 We were able to demonstrate understanding on the principles of food drying and dehydration in terms of its effects on the general quality of food and relevant scientific theories on moisture migration. Introduction and Definition Drying & Food Quality Microbial, Chemical, and Physical Stabilities Hot Air Drying RH, PEq, MC Def’n, Evaporation, Psychrometry, D&WBTs Drying Theory VATs, H, DRPs, MM 35 © 2021 Rolenz Cruz END. __ ROLENZ DERICK R. CRUZ Food Technology Department College of Industrial Technology Bicol University 36 © 2021 Rolenz Cruz