**6. Applications of acidic pectinases in food technology**

Pectolytic enzymes can be grouped into two categories according to their optimum pH values. The first one includes acidic pectinases that have optimum activity at pH 3.0–5.5 and 30–50°C. This group of enzymes is generally secreted by fungi, especially *Aspergillus sp*., and rarely secreted by bacteria. The second group is alkaline pectinases, which are typically bacterial pectinases and rarely secreted by fungi. The optimum pH values for this group of enzymes fluctuate from 8.0 to 10.5, while optimum temperatures are ranged from 45 to 75°C [46].

In the field of food technology, acidic pectinases are routinely used to increase the proportion of juice extraction by mechanical pressing or crushing [9, 47, 48], to increase filtration efficiency and clarification of fruit juice. These are mandatory operations for fruits and vegetables rich in pectic substances such as citrus and

#### **Figure 6.**

*PDB Image of Pectin Lyase B from A. niger at 1.7 Å resolution [45] Available from: https://www.ncbi.nlm.nih. gov/Structure/pdb/1QCX. Code of colours: Beta strands in green, loops in blue, alpha hélix in red.*

tomato, as well as for liquefaction. Specialised pectolytic enzymes that act only upon the middle lamella (macerating enzymes) can be used to prepare products focused on preserving the integrity and shape of the plant cells. These enzymes keep the pulp juice with the taste and flavour of the original fruit. Pectinases can also be used in protoplast fusion technology [49]. Therefore, a wide variety of objectives that require the addition of pectolytic enzymes have been reported according to the purpose of the technological process.
