**1. Introduction**

Biocatalysis is a part of biotechnology that is inherently interdisciplinary and comprehensive, and its achievements are determined by the state of art in the fields of microbiology, molecular biology, biochemistry, chemical technology, and engineering sciences. Biocatalysis is a scientific field fully focused from the very beginning on practice, and the main task is to study and use only one selected enzymatic reaction for the purposeful target biotransformation of the initial reagent—substrate (S)—into the valuable product (P) demanded by the market [1]. Heterogeneous biocatalysis is a very important part of biocatalysis that is based on immobilized enzymatic active substances such as individual enzymes, whole microorganisms, and partially or completely disrupted microbial cells. Heterogeneous biocatalysis as an interdisciplinary sphere of professional activities, undoubtedly, has great scientific importance and commercial potential for industrial implementation, including the processing of renewable raw materials into valuable market products. In accordance with the 12 principles of green chemistry listed in [1, 2], biocatalytic processes satisfy all the requirements and provide environmentally friendly and energy-saving technologies that are a promising alternative to traditional chemical processes.

carbon aerogel. These lipase-active biocatalysts can effectively compete with traditional organic synthesis catalysts, and they are used in low-temperature processes carried out in unconventional anhydrous media such as interesterification of vegetable oils' triglycerides with ethyl acetate for producing ethyl esters of fatty acids (biodiesel and vitamin F) and esterification of fatty acids with aliphatic alcohols for synthesis of various esters used as fragrances, odors, emollients, and nonionic

*Heterogeneous Biocatalysts for the Final Stages of Deep Processing of Renewable Resources…*

**2. Glucoamylase-active heterogeneous biocatalysts for starch dextrin**

The glucoamylases (glucan 1,4-alpha-glucosidases, EC 3.2.1.3) hydrolyze the glycosidic bonds at the end of polymer (starch) or oligomer (dextrin) chains releasing glucose. The main areas of industrial application of these enzymes are as follows: (1) a large scale two-step hydrolysis of raw starch successively catalyzed by α-amylase then glucoamylase, for production of sweeteners such as treacle and glucose syrups used in food industry, and (2) large-scale processes of hydrolytic conversion of starch to fermentable sugars as feedstocks for the production of some commodity chemicals and the first-generation biofuel such as bioethanol. These industrial processes are conducted on an enormous scale. Although the enzymes involved are relatively inexpensive, they are used on a single-use, throw-away basis. As mentioned above, immobilization of enzymes ensures enzyme recycling that can

provide significant saving in the cost of final products not less than 20%.

ble raw materials into demandable sweeteners.

reason why this process has not been commercialized so far.

**5**

conversion—hydrolysis of dextrin (saccharification), following the stage of liquefication (dextrinization) of starch by amylases. It should be noted that the immobilization of glucoamylase (not amylase) is justified and appropriate because this enzyme converts relatively low molecular weight substrates such as dextrin (3– 5 kDa), and diffusion limitations can be overcome, in particular via design of employed reactor. The development of heterogeneous biocatalysts with high glucoamylase activity and operational stability is of great importance since they can serve as the basis for modern technology for deep processing of renewable vegeta-

The glucoamylases are the main enzymes used in the key second stage of starch

Back in 1970s, Corning Glass Co. carried out the fist pilot plant tests of a packedbed reactor filled with a heterogeneous biocatalyst prepared by covalent immobilization of glucoamylase on macroporous silica; the glucose productivity was 450 kg/ day. The main requirement for the commercial glucoamylase-active biocatalysts was a sufficiently high operational stability at pasteurization temperature of 60°C or higher. Inactivation half-times (t½) of the tested Corning Glass biocatalyst were 520, 150, and 75 h at 55, 60, and 70°C, respectively [4]. The best result described later in 2000 for a biocatalyst prepared by immobilization of glucoamylase on polystyrene was that t½ = 300 h at 50°C [5]. The best result described in the recent papers during 2008–2019 is that the glucoamylase immobilized by formation of cross-linked enzyme aggregates (CLEA) has "excellent recyclability, retaining over 45% of the relative activity after 24 runs" over a broad range of temperature (55–75°C) [6]. According to the opinion of the specialists working on the R&D projects of heterogeneous stage of saccharification the low thermal stability of the immobilized glucoamylase at elevated temperature (above 50°C) was the main

Reputedly, the inexpensive and available carbonaceous materials with appropriate texture parameters are promising supports for adsorptive immobilization of enzymes, in particular of glucoamylase, for the preparing of commercially

surfactants in food, perfume, and cosmetics industries.

*DOI: http://dx.doi.org/10.5772/intechopen.89411*

**hydrolysis**

Despite unique catalytic properties of soluble enzymes, such as 100% selectivity and high reaction rates under very mild, usually ambient conditions, as well as chemo-, regio-, and stereo-specificity, their industrial applications are limited due to the main disadvantages, namely, homogeneous conditions of periodic processes and inability to reuse enzymes that fall into wastewater. Immobilization of enzymes on/in support may overcome this drawback. Immobilization is defined as the fixation of enzymatic active substances onto/inside water insoluble solid supports, accompanied by retaining their enzymatic activity at a high level and their significant stabilization (up to 10<sup>3</sup> –105 times). Immobilization prevents the inactivation of enzymes and ensures their multifold reusability. The heterogeneous biocatalysts are prepared by immobilizing the enzymatic active substances. These biocatalysts are undoubtedly of great practical interest for widespread implementation in industrial periodic and continuous bioconversion processes using batch stirred-tank, packedbed, and novel types of vortex reactors specially designed for the heterogeneous diffusion-controlled biocatalytic processes in order to overcome diffusion limitations and enhance biocatalysts' productivity.

It is generally recognized that heterogeneous biocatalytic processes are more commercially attractive for large-scale implementation than homogeneous technologies due to considerable simplification and reduction (in 1.2–1.4 times) of the total production cost. Of course, the cost of the final product decreases with a decrease in the cost of the enzymatic active component of the biocatalyst, as well as the support and the method of immobilization. In order to reduce all expenses, both not purified enzymes but partially or fully disrupted, or whole nongrowing microbial cells, as well as inorganic support such as silica and carbon, and adsorptive immobilization are preferable for preparing commercial biocatalysts.

For successful commercialization of the heterogeneous biocatalytic processes, for example, the process of starch dextrin hydrolysis (saccharification), a biocatalyst has to convert 45% of the substrate during 15–20 min with the inactivation halftime (t½) of 30–120 days, which corresponds to 3–12 months operation of the reactor without reloading. A high value of t½ (50–100 days) is essential to increase productivity up to the recommended value from 100 kg to 10 tons of final product per 1 kg of biocatalyst [3].

Heterogeneous biocatalysts for two important bioconversion processes are briefly described here. One of the biocatalysts is glucoamylase immobilized by adsorption on mesoporous carbon support Sibunit™ type. This glucoamylase-active biocatalyst is used at the stage of starch saccharification, i.e., hydrolysis of dextrin to treacle and glucose syrups. The second of the biocatalysts is recombinant *T. lanuginosus* lipase immobilized on mesoporous silica KSK™ type and macroporous

*Heterogeneous Biocatalysts for the Final Stages of Deep Processing of Renewable Resources… DOI: http://dx.doi.org/10.5772/intechopen.89411*

carbon aerogel. These lipase-active biocatalysts can effectively compete with traditional organic synthesis catalysts, and they are used in low-temperature processes carried out in unconventional anhydrous media such as interesterification of vegetable oils' triglycerides with ethyl acetate for producing ethyl esters of fatty acids (biodiesel and vitamin F) and esterification of fatty acids with aliphatic alcohols for synthesis of various esters used as fragrances, odors, emollients, and nonionic surfactants in food, perfume, and cosmetics industries.
