Spray drying enzymes

Because of the long-term instability of proteins in aqueous solution, enzyme producers and formulators have attempted to produce stable solid enzyme formulations since enzymes were first used in detergents. Initially, commercially produced protease-containing detergents contained spray dried enzymes. As discussed earlier, proteases have the ability to digest themselves via autolysis and are often incompatible with surfactants. These problems are easily overcome by storing the... 

Relevant properties of dried enzymes are listed in Table 48.2. By modifying the spray-drying process, it is possible to alter and control the properties that are mentioned earlier for spray-dried enzymes. 

As it has been found that generally the loss in enzymatic activity increases when the water content in the spray-dried enzyme concentrate is lowered (Table 48.4), it is desirable that the product leaving the spray dryer has a moisture content of not less than 8%-10%, preferably about 20%. This results in extremely low outlet temperatures from the drying system combined with controlled second-stage drying that takes place within the static fluid bed at a lower temperature (40°C-50°C) to achieve the desired moisture content. The product from the dryer can be postcooled or postdried in a vibrating fluid bed. 

Figure 4 The different approaches to the production of carrier-free immobilized enzymes (A) crystallization (B) aggregation (C) spray-drying and (D) direct cross-linking. AGG, aggregates CLE, cross-linked dissolved enzyme CLEA, cross-linked enzyme aggregate CLEC, cross-linked enzyme crystal CSDE, cross-linked spray-dried enzyme CRY, crystals SDE, spray-dried enzyme.

Spray Congealing Spray dried enzyme powder can be incorporated into a molten fat or wax. This mixture is atomized through a rotary nozzle into a cooled chamber essentially equivalent to a spray drier tower. The atomized droplets cool, solidify into particles, and harden as they fall, resulting in round particles. A simplified box diagram of spray congealing process is shown in Figure 6.11. 

Dispersions Dispersions can be prepared from spray dried enzyme powder, or from an enzyme precipitate or crystal paste. The dried or partially dried powder is suspended in a suitable carrier such as glycols or glycol/water mixtures and preserved if needed. The dispersion may be visually clear or cloudy in appearance. As salts are commonly used to force the precipitation or crystallization of proteins, it may be difficult to remove or reduce the salt concentration prior to formulation. 

The first detailed description of the drying of products in spray form was mentioned in a patent of 1872 entitled Improvement of Drying and Concentration of Liquid Substances by Atomizing (2). However, this process found its first significant applications in the milk and detergent industries in the 1920 s (3). In current times, spray drying is utilized extensively in many aspects of our daily life from food products, cosmetics, and pharmaceuticals to chemicals, fabrics, and electronics. Typical pharmaceutical examples include spray-dried enzymes (such as amylase, protease, lipase, and trypsin), antibiotics (such as sulfathiazole, streptomycin, penicillin, and tetracycline) and many other active pharmaceutical ingredients, vitamins (such as ascorbic acid and vitamin B12), and excipients for direct compression (such as lactose, mannitol, and microcrystalline cellulose). 

Many proteins and peptides are susceptible to degradation upon spray drying due to relatively high temperatures. In a recent study, the effects of inlet and outlet temperatures on some spray-dried peptides and proteins were reported (46). In another study, enzyme activity was found to be susceptible to spray-drying temperature and only half of its activity remained after spray drying without additives at outlet temperatures <50°C (47). In this study, it was found that the activity of a formulation consisting of enzyme and mannitol was maintained at outlet temperatures <50°C and compromised at temperatures >50°C. Replacing mannitol with trehalose stabilized the spray-dried enzyme and its activity was maintained at 100% at an outlet temperature of 100°C. 

Casein hydrolyzates are produced from dried casein. With appropriate heat treatment and the addition of alkaHes and enzymes, digestion proceeds. FoUowing pasteurization, evaporation (qv), and spray drying, a dried product of 2—4% is obtained. Many so-called nondairy products such as coffee cream, topping, and icings utilize caseinates (see Dairy SUBSTITUTES). In addition to fulfilling a nutritional role, the caseinates impart creaminess, firmness, smoothness, and consistency of products. Imitation meats and soups use caseinates as an extender and to improve moistness and smoothness. 

Ultrafiltration (qv) (uf) is increasingly used to remove water, salts, and other low molecular-weight impurities (21) water may be added to wash out impurities, ie, diafiltration. Ultrafiltration is rarely used to fractionate the proteins because the capacity and yield are too low when significant protein separation is achieved. Various vacuum evaporators are used to remove water to 20—40% dry matter. Spray drying is used if a powdery intermediate product is desired. Tyophilization (freeze-drying) is only used for heat-sensitive and highly priced enzymes. 

Milk from cows contains 3.2% protein, about 80% of which is casein. Casein is isolated by a precipitation process from milk, involving heating, rinsing to remove whey, and drying to a powder. The yield is about 3 kg/ 100 kg skim milk. Rennet casein is obtained when the casein is precipitated by chymosin enzyme, also known as rennet, and acid casein is produced when precipitation is accomplished by acidification. Acid casein is usually found in the form of sodium caseinate or calcium caseinate, which are water-soluble salts. Caseinates are made by reacting NaOH or CaOH with a slurry of casein curd or powder and then spray drying (Southward, 2010). 

Soya Proteins. Early attempts to make albumen substitutes from soya protein also ran into problems. A bean flavour tended to appear in the finished product. A solution to these problems has been found. Whipping agents based on enzyme modified soy proteins are now available. The advantage of enzymatic modification is that by appropriate choice of enzymes the protein can be modified in a very controlled way. Chemical treatment would be far less specific. In making these materials the manufacturer has control of the substrate and the enzyme, allowing the final product to be almost made to order. The substrates used are oil-free soy flakes or flour or soy protein concentrate or isolate. The enzymes to use are chosen from a combination of pepsin, papain, ficin, trypsin or bacterial proteases. The substrate will be treated with one or more enzymes under carefully controlled conditions. The finished product is then spray dried. 

Spray-dried cells have a stable enzyme activity enabling easy storage and transport of the dehalogenase biocatalyst. 

Spray drying, employed preferentially for inexpensive enzymes on a mass scale, evaporates water by spraying the protein solution through a nozzle at high temperature, utilizing the Bernoulli effect. As contact times are short (on the order of less than 1 s), the enzyme is not deactivated. Not much modeling has been performed on this operation. 

An extreme case of covalent binding is cross-linking of enzymes. Instead of fixing the enzyme to a carrier, the enzyme acts as a carrier itself Enzyme aggregates or crystals, enzymes in a spray-dried form, or even enzymes in solution can be cross-linked. The immobilized enzyme is carrier free, that is the material is virtually pure enzyme and the negative effects of carriers can thus be avoided [10, 70]. 

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