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Introduction, • All foods and biomaterials need some form of, preservation to, – Reduce or stop spoilage, – Make them available throughout the year, – Maintain desired levels of nutritional and, bioactive properties for the longest possible, time span and, – Produce value added products, Shaikh Mussadique Ahmed
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Downstream processing, • Refers to the recovery of biomolecules from, natural sources such as animal or plant tissues, besides fermentation broth, • It is an essential step which determines final cost, of the product in the manufacture of, biomolecules e.g., – Antibiotics, vaccines, antibodies,, – Hormones (e.g. Insulin and human growth hormone), – Antibodies (e.g. Infliximab and abciximab), enzymes,, and, Shaikh Mussadique Ahmed, – Natural fragrance and flavor compounds
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Drying, • Air-drying is an ancient preservation method, • Foods are exposed to a continuously flowing, stream of hot air, • It involves simultaneous mass and heat, transport, • Moisture availability has a great impact on the, transfer of heat to microorganisms, • Consumer demand has increased for, processed products that keep more of their, original characteristics, Shaikh Mussadique Ahmed
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Drying Methods, • This requires the development of operations, that minimize the adverse effects of, processing, • There have been various advances in the, drying of foods with respect to quality,, rehydration, and energy minimization, • Some of the improvements and advancements, made leading to the new developments in, drying are discussed, Shaikh Mussadique Ahmed
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Intermittent batch drying, • By varying the operating conditions of a, drying process, – Airflow rate, – Temperature, – Humidity or, – Operating pressure, , • It can be monitored in order to reduce, the operating cost e.g. thermal input and, power input, Shaikh Mussadique Ahmed
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Intermittent batch drying, • The objective is to obtain high, energy efficiency without subjecting, the product beyond its permissible, temperature limit and stress limit, while maintaining high moisture, removal rate, , Shaikh Mussadique Ahmed
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Hybrid drying techniques, • May include either use of, –More than one dryer for drying of a, particular product (multi-stage drying), –More than one mode of heat transfer, –Various ways of heat transfer or, –Multiprocessing dryers, , Shaikh Mussadique Ahmed
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Hybrid drying techniques, • For particulate drying, – Variants of fluid bed or, – Fluid bed with some other techniques can be used, in series to achieve faster drying, , • For liquid feedstock, – Generally spray drying is followed by the fluid bed, dryer, , • To reduce moisture content to an acceptable, level which is not possible by spray dryer, alone, Shaikh Mussadique Ahmed
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Modified atmosphere drying, • The presence of oxygen results in various, unwanted characteristics in dried food, materials, – oxidation of the drying material, – destruction of its bioactive compounds, – browning, • O2 can be replaced by N2 or CO2, • In addition, it increases the effective moisture, diffusivities of some food products, Shaikh Mussadique Ahmed
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Superheated steam drying, • Superheated steam does not contain oxygen,, hence oxidative or combustion reactions are, avoided, • It also eliminates the risk of fire and explosion, hazard, • It allows pasteurization, sterilization and, deodorization of food and bio-products, • Net energy consumption can be minimized if, the exhaust (also superheated steam) can be, utilized elsewhere in the plant and hence is, not charged to the dryer, Shaikh Mussadique Ahmed
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Impinging stream drying, • In Impinging stream dryers, • The intensive collision of opposed streams, create a zone that offers very high heat, mass, and momentum transfers, • Hence rapid removal of moisture from surface, • Other advantages - low foot prints and high, robustness due to absence of moving parts, • Effective alternatives to flash dryers for, particulate materials with very high drying, loads, Shaikh Mussadique Ahmed
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Microwave drying, • Microwave oven has ability to heat food products, rapidly, conveniently and economically in a compact, space, • The primary drawback is its inability to heat, materials in a predictable and uniform manner, leading to, • -hot spots that damage the item being heated, • - cold spots - under heated or under processed,, thereby compromising product quality and, repeatability, • Microwave heating in combination with vacuum has, been used extensively for drying in pharmaceutical, Shaikh Mussadique Ahmed, processing
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Fig 1. Schematic diagram of a spray-drying process, , Shaikh Mussadique Ahmed
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Spray Drying • Allows preparation of stable and functional, powder products, • Can be implemented for large scale, throughputs, • Main disadvantages, • High installation costs, • Removal of aromatic volatiles, • Prone to damaging heat sensitive components, such as enzymes and probiotic bacteria, Shaikh Mussadique Ahmed
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Classification of dryers, •, •, •, •, •, •, •, , Mode of operation, Heat input-type, State of material in dryer, Operating pressure, Drying medium, Drying temperature, Relative motion between drying medium, and drying solids, Shaikh Mussadique Ahmed, • Number of stages
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Drying system, , •, •, •, •, •, •, , - post-drying stages, , Exhaust gas cleaning, Product collection, Partial recirculation of exhausts, Cooling of product, Coating of product, Agglomeration, etc., , • The optimal cost-effective choice of dryer will, depend on these stages, Shaikh Mussadique Ahmed
