People have been using microorganisms in food preparations for thousands of years. One of the best examples of their uses is in winemaking, where yeasts ferment the sugars found in grape juice, and they convert it to wine. Technological advancements enabled researchers to understand that microbes can act as cell factories and suitable for various applications. What is even more interesting is that microorganisms produce a vast range of enzymes with many industrial applications. The employment of microbes for the production of commercial enzymes is the preferred option, as they can produce higher yields and are much cheaper compared to plants and animals. In addition, microbial enzymes are more stable than plant and animal enzymes, and thanks to their stability, they suit many industrial applications. This article will provide a brief and concise summary of the different enzymes produced by microbes and some of their industrial applications will be discussed.
Proteases. Proteases are enzymes that catalyze the hydrolysis of peptide bonds present in proteins and polypeptides. Proteases represent 60% of the enzymes the industry uses. The latter include the pharmaceutical, detergent, and food industry. Between 2014 and 2019, the annual growth rate of protease use was 5.3%, and it will continue to grow thanks to their applications in bioremediation processes and leather processing. Proteases can be classified based on their origin, nature, and catalytic activity of the reactive group in the catalytic site. However, the most common classification is into exopeptidases and endopeptidases. The main difference between these two groups is how they act on the polypeptide chain. Exopeptidases act on the ends of the polymerase chains, whereas endopeptidases act in the inner regions. It is possible to obtain proteases from animal, plant, fungal, and bacterial cells.
The food industry uses many plant proteases such as papain, bromelain, and ficin for various applications, including tenderization of meat and brewing.
Proteases are mainly used by the bakery and dairy industry as they can
- reduce the mixing time,
- decrease dough consistency and uniformity,
- improve texture,
- improve flavor characteristics, and also
- accelerate the ripening of cheese.
Lipases. Lipases catalyze lipid hydrolysis. They are located in the stomach and pancreas of animal species, although yeasts, fungi, and bacteria can produce them as well. Microbes produce the vast majority (approximately 90%) of commercially available lipases. The biofuel and detergent industries also use lipases.
The dairy industry, in particular, uses the properties of lipases to
- improve cheese flavor and
- as a processing aid to convert milk into several different kinds of cheeses.
In addition, lipases have many applications in alcoholic beverages, such as wine, to improve the aromatic profile of wines. Specific microbial-produced lipases such as those produced from Candida rugose have applications in single-cell protein, ice creams, and amino acid derivatives. Lipases also work for processing waste streams released from food industries.
Catalase. Catalase is a common enzyme found in nearly all living organisms exposed to oxygen (such as bacteria, plants, and animals) which catalyzes the decomposition of hydrogen peroxide to water and oxygen. It has great importance for cells as it can protect them from oxidative damage by reactive oxygen species. The preferred source of catalase production are microorganisms such as Aspergillus niger and Micrococcus luteus, mainly because of the advantages they offer, such as easy handling and rapid growth. Apart from these two organisms, a large number of organisms produce catalases. The latter include Bacillus spp, Enterococcus spp, and others. The fabric industry exploits the ability of catalase to remove hydrogen peroxide as they apply it to fabrics.
There are also several applications of catalase in the food industry:
- as a preservative, especially in the wine industry, as it can eliminate oxygen
- the bakery industry use it to remove glucose from egg whites,
- the dairy industry use it to eliminate peroxide from milk, and
- it work in food wrappers to prevent oxidation and control the perishability of food.
Pectinase. Pectinase is an enzyme that can break down pectin, a complex polysaccharide found in plant cell walls. The way pectinases work is by catalyzing the hydrolysis of glycosidic bonds in pectin polymers. Pectinases exist as pectin esterases, polygalacturonases, pectate lyase, and pectin lyase. Pectinases come from citrus fruits and other fruits and vegetables like pineapples, tomatoes, and apples. Several bacterial and fungal species produce pectinases. It is also possible to obtain pectinases from recombinant microorganisms.
Their industrial applications for the food industry include:
- juices with added pectinase have a more transparent appearance and filterability than enzyme-depleted counterparts
- reducing the turbidity of fruit juices
- haze generation of naturally derived fruit juices such as apple and banana,
- improvement of color and flavor of drinks.
Their effects in juice processing are so efficient that they can provide significantly better results than mechanical maceration.
Lactase. Lactase is the enzyme that breaks down the sugar lactose, a sugar found in milk. Lactase hydrolyses the disaccharide lactose into its monomers, i.e. glucose and galactose. Individuals with lactase deficiency experience intestinal symptoms when they consume dairy products (lactose intolerance). Lactose itself belongs to the family of β-galactosidase. Many organisms produce lactase. The latter include animals, plants, and microbes. However, microbes like fungi, yeasts, and bacteria are the preferred industrial source as they can provide high yields at a relatively low cost. Microbes can produce lactases able to perform at various pH ranges; hence, selecting specific lactase depends on its application. In the food industry specifically, the most popular classes of lactases are the thermostable and cold-active β-galactosidases.
They have wide applications in the dairy industry such as:
- reducing the lactose levels for lactose intolerant people,
- improvement of the scoopability and creaminess of ice creams by digesting lactose and
- sweetness improvement of dairy products.
Another primary application of lactase is lactose hydrolysis in whey. Whey is a byproduct of cheese production, and its main components are lactose, proteins, and minerals.
Peroxidase. Peroxidases are a large group of enzymes that play a role in various biological processes. They are mostly known for their ability to break down peroxides and for their ability to oxidize a variety of organic and inorganic compounds. Animal, plant, and microbial cells can produce peroxidase. In plants, they are primarily involved in lignification processes and defence mechanisms against damaged or infectious tissues. Again, as with most enzymes, the preferred organisms to produce them are microbes thanks to their easy handling and high yields. Many microorganisms produce peroxidases, and the best characterized is Phanerochaete chrysosporium. The main drawbacks of the industrial production of fungal peroxidases are mostly related to protein post-translational modifications. Because of their stability and wide range of applications, bacterial peroxidases are the preferred industrial peroxidases. The industry uses peroxidases to improve:
- color, flavor, and texture, or
- the nutritional quality of foods.
Peroxidases also work for treating industrial wastewater.
In particular, they can effectively oxidize phenols into less harmful substances.
Laccase. Laccases are oxidases that contain an active site consisting of four copper centers contained in bacteria, plants, and fungi. Laccases can oxidize a variety of phenolic substrates, and depending on the organism they produced. They can either play a role in lignin formation or degradation. These enzymes combine reducing substrate having four oxidized electrons with four reduced electrons for cleaving dioxygen bond in the presence of four copper atoms present in laccases. A few fungal species can produce them extracellularly as a product of their secondary metabolism, but bacterial species can produce high laccase yields.
- Laccase works for modification of color appearance of food and beverage industries or wine stabilization as an alternative to physical and chemical adsorbents.
- Furthermore, their ability to remove oxygen in the final step of beer production is helpful to the brewing industry because it extends the shelf life of beer.
- Additionally, commercially available laccases effectively reduce the formation of off-flavors in the brewing industry.
- In the bakery industry, laccases are used to enhance strength, stability and decrease stickiness, increasing the machinability of bread batter.
Cellulases. Cellulase is an enzyme produced by fungi, bacteria, and protozoans that catalyzes the decomposition of cellulose and other similar polysaccharides. Cellulases break down cellulose into beta-glucose or other short polysaccharides and oligosaccharides. Most commercial cellulases come from microbes. In food production, the most common cellulases come from the fungi Aspergillus and Trichoderma or from the bacteria Bacillus and Paenibacillus. Other industries use cellulases. These include the paper, textile, and detergent industries.
The juice industry uses cellulases combined with other macerating enzymes to increase process performance and yield and for more effective juice extraction, clarification, and stabilization.
Cellulases also reduce the viscosity of fruit nectar and puree, such as those obtained from apricot, mango, plum, papaya, pear, and peach. Cellulases also work for the extraction of flavonoids from flowers and seeds.
Additionally, they have other applications, such as for the extraction of phenolic compounds from grape pomace; they can improve the aroma and taste of citrus fruit and reduce their bitterness.
Finally, cellulases are suitable for olive oil extraction. Combined with other enzymes, they increase wine yield and quality.
Amylases. Amylases are enzymes that catalyze the hydrolysis of starch into sugars. Amylases are present in the saliva of humans and some other mammals, where it starts protein digestion.
Amylases have a variety of applications in the food industry, including:
- starch liquefaction, and
- as a digestive aid.
In baking, amylases can convert starch to smaller dextrins, which improves bread quality.
Other applications include starch liquefaction, where they break down starch into glucose and fructose syrups. During alcoholic fermentation, amylases convert starch to fermentable sugars. The latter process is helpful also during juice clarification. As with most enzymes, the preferred source is microbes, particularly Bacillus stearothermophilus, Bacillus amyloliquefaciencs, and Bacillus licheniformis.
Microbial enzymes can have a great range of different applications in the industry. Their ability to produce high yields and their relatively low production cost gives them a substantial advantage compared to plant and animal-derived enzymes. In addition, genetic engineering techniques can further improve production yields. Considering the vast number of microorganism in nature, more enzymes with very high potential and broader applications for the industry will probably appear soon.