Lactic Acid Bacteria in Fermentation

Lactic Acid Bacteria in Fermentation: Comparison

Please note this is a comparison between Version 1 by Leonardo Sepúlveda and Version 2 by Karina Chen.

The term fermentation derives from the Latin ‘fervere’, which means to boil, due to the appearance produced by yeast on fruit or malt extracts, as a result of the production of carbon dioxide bubbles caused by the catabolism of the sugars in the extract. The most common concept of fermentation is the conversion of sugar into an organic acid, then into alcohol. It occurs naturally in many food types, and humans have used it since ancient times to improve the preservation and the organoleptic properties of food. This term is only used when referring to microorganisms (bacteria, yeasts, and fungi) to make useful products for humans such as biomasses, enzymes, primary and secondary metabolites, recombinant products, and biotransformed products used in industry. Fermentation is a catabolic process of incomplete oxidation, completely anaerobic, and its final product is an organic compound, where in the absence of oxygen, the final acceptor of the NADH electrons produced in glycolysis is not oxygen, but an organic compound that will be reduced to oxidize NADH to NAD+ . There are different types of fermentation, e.g., alcoholic, acetic, butyric, and lactic. The fermentation processes have some main purposes: (1) the enrichment of the diet by developing flavors, aromas, and textures; (2) food preservation through lactic acid, ethanol, acetic acid, and alkaline fermentations; (3) enrichment of foods with protein, amino acids, lipids, and vitamins; (4) decrease in cooking time and fuel requirements so that the loss of nutrients is less; and (5) it can produce nutrients or eliminate anti-nutrients; being the final product an organic compound that characterizes the types of fermentation.

solid-state fermentation
submerged fermentation
tannin-acyl-hydrolase
tannins
Lactiplantibacillus plantarum

1. Production of Tannases with Submerged Fermentation (SF)

Microorganisms require a controlled atmosphere to produce better final quality, ensuring optimal productivity and better benefits ^[1]. SF has some process characteristics which have slight advantages over control in solid-state fermentation, which are shown in

Microorganisms require a controlled atmosphere to produce better final quality, ensuring optimal productivity and better benefits [30]. SF has some process characteristics which have slight advantages over control in solid-state fermentation, which are shown in

Table 1

Table 1.

Advantages and disadvantages of submerged and solid-state fermentation.

Submerged Fermentation
Advantages	Reference	Disadvantages	Reference
Easier and the product is easy to recover	^[2]	[32]	The difficulty for the passage of oxygen in the liquid medium	^[3]^[4]	[33,34]
Sterilization facilitates the process and its control	^[5]	[35]	Detrimental to fungal growth	^[

4. Lactic Acid Bacteria (LAB) That Produce Tannases

Lactic acid bacteria (LAB) have important applications in the food industry and other sectors, as shown in

Table 3

, for the added value they give to products, influencing the taste, odor, texture, nutritional value, and sensory characteristics. The genus

Leuconostoc

Enterococcus

Streptococcus

Pediococcus

, and

Lactobacillus ^[12] LAB have been used in submerged fermentation to produce tannases ^[28]. They are made up of a large group of Gram-positive, non-sporulated bacteria and are the largest producers of lactic acid; they have preservative power because they have antimicrobial properties and have a high content of organic acids and bacteriocins that inhibit the growth of bacteria ^[34]. LAB are present in groups of microorganisms called starters or lactic cultures, where lactic acid is their main metabolite. LAB are unable to synthesize some vitamins, specific peptides, and amino acids for their growth but can produce antimicrobial substances known as bacteriocins and hydrogen peroxide ^[35]. They are mesophilic, but some can grow in refrigeration at 4 °C, and others at 45 °C, with a preference for an acidic pH (4–4.5), although sometimes tolerate up to pH 9. They play an important role in biotransformation because they can act on the isolation of new chains of tannases. Among the LAB, the first to be tested to produce tannases was

[42] LAB have been used in submerged fermentation to produce tannases [6]. They are made up of a large group of Gram-positive, non-sporulated bacteria and are the largest producers of lactic acid; they have preservative power because they have antimicrobial properties and have a high content of organic acids and bacteriocins that inhibit the growth of bacteria [58]. LAB are present in groups of microorganisms called starters or lactic cultures, where lactic acid is their main metabolite. LAB are unable to synthesize some vitamins, specific peptides, and amino acids for their growth but can produce antimicrobial substances known as bacteriocins and hydrogen peroxide [59]. They are mesophilic, but some can grow in refrigeration at 4 °C, and others at 45 °C, with a preference for an acidic pH (4–4.5), although sometimes tolerate up to pH 9. They play an important role in biotransformation because they can act on the isolation of new chains of tannases. Among the LAB, the first to be tested to produce tannases was

Lactiplantibacillus plantarum ^[28]. One of the least used microorganisms to obtain tannins through fermentation by LAB ^[36], there are reports that they degrade and hydrolyze natural tannins and tannic acid efficiently ^[37]. Their cell wall contains glycerol, teichoic acids, and peptidoglycans ^[38]. On the other hand,

[6]. One of the least used microorganisms to obtain tannins through fermentation by LAB [60], there are reports that they degrade and hydrolyze natural tannins and tannic acid efficiently [29]. Their cell wall contains glycerol, teichoic acids, and peptidoglycans [61]. On the other hand,

Lactiplantibacillus plantarum was used to produce tannases from olive mill residues using a basic medium, plus 100 mL supplementation with tannic acid as a carbon source and inoculated with 1.38 mg of cells which were incubated at 37 °C for 24 h ^[39]. It is an optional heterofermentative; it can produce lactic acid and other by-products such as acetate and ethanol, depending on its growing conditions and its carbon source ^[40].

was used to produce tannases from olive mill residues using a basic medium, plus 100 mL supplementation with tannic acid as a carbon source and inoculated with 1.38 mg of cells which were incubated at 37 °C for 24 h [13]. It is an optional heterofermentative; it can produce lactic acid and other by-products such as acetate and ethanol, depending on its growing conditions and its carbon source [62].

Lactiplantibacillus plantarum is the most widely used bacteria because it has the greatest yield on plant fermentations where tannins are abundant due to their strains having tannase activity ^[30], playing an important role in food microbiology and human nutrition for their fermentative power and probiotic functions. It also has effects on cholesterol levels, inhibiting inflammation by acting on interleukins IL-1α, IL-1β, IL-6, and tumor necrosis factor α ^[35]. The importance of the growth of

is the most widely used bacteria because it has the greatest yield on plant fermentations where tannins are abundant due to their strains having tannase activity [31], playing an important role in food microbiology and human nutrition for their fermentative power and probiotic functions. It also has effects on cholesterol levels, inhibiting inflammation by acting on interleukins IL-1α, IL-1β, IL-6, and tumor necrosis factor α [59]. The importance of the growth of

Lactiplantibacillus plantarum stands out in the technological and physiological characteristics of the probiotic strains, the amino acids valine, arginine, tyrosine, and tryptophan, pantothenic acid and nicotinic acid which are essential, as well as manganese and iron ^[41]. While the growth during a

stands out in the technological and physiological characteristics of the probiotic strains, the amino acids valine, arginine, tyrosine, and tryptophan, pantothenic acid and nicotinic acid which are essential, as well as manganese and iron [63]. While the growth during a

Lactobacillus fermentation occurs at a pH of 4.5 to 5.8 ^[35]. Tannase production with

fermentation occurs at a pH of 4.5 to 5.8 [59]. Tannase production with

Lactiplantibacillus plantarum occurs at 37 °C, with pH 6.0, within 24 h, with tannic acid as a carbon source and the presence of nitrogen ammonium sulfate ^[42]. Several studies have been carried out obtaining the optimized fermentation process with

occurs at 37 °C, with pH 6.0, within 24 h, with tannic acid as a carbon source and the presence of nitrogen ammonium sulfate [64]. Several studies have been carried out obtaining the optimized fermentation process with

Lactiplantibacillus plantarum with a maximum tannase activity of 6 U ml-1 ^[39].

with a maximum tannase activity of 6 U ml-1 [13].

Table 3.

Applications biotechnological of lactic acid bacteria (LAB).

Microorganism	Isolation Source	Application	Reference
Limosilactobacillus reuteri	Whole wheat sourdough	Antifungal activity against	Aspergillus niger	^[43]	[65]
Lactobacillus delbrueckii subsp. lactis	NRRL B-633,	Lactobacillus delbrueckii subsp. cremoris	NRRL B-634	, Pediococcus		acidilactici	NRRL B-1116,	P. pentosaceus	NRRL B-14009,	Leuconostoc		mesenteroides subsp	.	mesenteroides	NRRL B-1118,	Latilactobacillus sakei subsp. sakei	NRRL B1917,	Limosilactobacillus fermentum	NRRL B-1932,	Limosilactobacillus reuteri	NRRL B-14171,	Lactiplantibacillus plantarum	NRRL B-4496,	Lactobacillus acidophilus	NRRL B-4495,	Lacticaseibacillus casei	NRRL B1922,	Levilactobacillus brevis	ATCC 367,	Lacticaseibacillus casei	21/1,	Lactobacillus amylovorus	ATCC 33621,	Fructilactobacillus sanfranciscensis	ATCC 27651,	and Lacticaseibacillus rhamnosus	NRRL B-442.	-	Antimicrobials in vitro against	Escherichia coli	,	Staphylococcus aureus	,	Shigella sonnei	,	Pseudomonas fluorescens	,	Salmonella typhimurium	, or	Listeria monocytogenes^6][7]	[36,37]
^[	⁴⁴	^]	[66]	Efficiency in preventing the growth of other microorganisms	^[8]	[38]
Lactobacillus	spp.	-	Produces exopolysaccharides that have interesting film-forming properties and may be used to produce edible packaging.	^[45]	[67]	Homogeneity in culture media and control in temperature and pH	^[9]^[10]	[
Enterococcus mundtii	STw3839,40]		Tehuelche scallop (	Aequipecten tehuelchus	), Patagonian Argentinean clam (	Ameghinomya antique	), Patagonian blue mussel (	Mytilus edulis		platensis	), sea cucumber (	Hemiodema spectabilis	), geoduck (	Panopea		generosa	) and razor clam (	Solen tehuelchus	) of the Argentine coast
Reducing the development of native flora of fish paste.	^[	⁴⁶	^]	[68]	Better control of physicochemical parameters, more biomass growth in less time	^[11]	[41]
P. pentosaceus	FP3,	Ligilactobacillus salivarius	FP35,	Ligilactobacillus salivarius	FP25, and	E. faecium	FP51	Collected from 17 healthy infant feces samples in the hospital of Chiang Mai.	The use of these probiotics may be suitable as an alternative bioprophylactic and biotherapeutic strategy for colon cancer.	^[47]	[69]	Ease in determining biomass by simple filtration or centrifugation	^[3]	[33]
7	Lacticaseibacillus casei	, 27	Lacticaseibacillus paracasei subsp. paracasei	, 15	Lactiplantibacillus plantarum subsp. plantarum	, 7	Lactobacillus delbrueckii subsp. lactis	, 1	E. faecium	, and 1	Enterococcus lactis.	Traditional Italian cheeses.	These strains with proven in vitro properties are good candidates for novel probiotic-containing formulations and could be used to functionalize foods such as dairy fermented products.	^[48]	[70]	It is used for bioremediation of effluents in industries	^[12]	[42]
S. thermophilus	,	Lactococcus lactis	SL242,	Lactobacillus delbrueckii subsp. Lactis	SL28 and	Lactobacillus delbrueckii subsp. lactis	IO-1	-	Development method presented is natural and low-cost and allows for the production of clean-label and lactose-free dairy products without using commercial enzymes from recombinant microorganisms.	^[49]	[71]	Bacteria, yeasts, and fungi can be used depending on the objective
Streptococcus		salivarius	subsp	. thermophilus	,	Lactobacillus delbrueckii		subsp. bulgaricus	,	and Lactobacillus acidophilus	,	Acetobacter aceti	,	Bifidobacterium bifidum	,	B. adolescentics	,	B. longum	,	B. animalis^[7]	[37]
,	Lactobacillus acidophilus	,	Lactococcus lactis subsp.		cremoris	,	Propionibacterium freudenreichii	,	Enterococcus faecium		and Streptococcus salivarius subsp. thermophilus	Iprovit Bacterial Milk-Yogurt Starter™, Symbilact Vivo Starter™ and Provit Streptosan Milk Starter™	It requires less investment, less energy, and a simple means of fermentation. Better condition of bacterial control	^[13]	[26]
It is used on an industrial scale, nutrients, and oxygen dissolve easily in the medium and disperse throughout the bioreactor, so heat and mass increase efficiency	^[6]	[36]
Incubation time decrease, better control in the process	^[14]	[43]
Have a better performance, reduces costs and is sustainable, making it beneficial for the environment and the economy of production	^[15]	[44]
Solid-State Fermentation
Effective to produce enzymes	^[16]	[45]	Low O	₂	and CO	₂	transfer ratio, it is difficult to monitor, control, and scale. There is no uniformity in culture	^[2]	[32]
Effective to produce bioactive compounds	^[17]	[46]	Slower microorganism’s growth	^[18]	[3]
Lower demand for water and energy, easy aeration in the medium	^[3]	[33]	It is less efficient for the growth of microorganisms that require high water content	^[19]	[47]
Most used for agro-industrial waste. Economical and superior enzymatic performance	^[20]	[48]
There is less waste of water, simplicity	^[17]	[46]
They are much more efficient fermentations; their products are stable and can be easily recovered	^[6]	[36]

In submerged fermentation processes, nutrients are used, and some enzymes such as tannase, amylase, and glucoamylases are released, to name a few ^[7]. It is the most widely used type of fermentation in the industry due to its simplicity, and its final product is easier to recover. The development of microorganisms is typical, which gives rise to a dormancy phase, growth, stationary phase, and death phase. These phases are present in submerged and solid-state fermentation, divided into several types—batch, continuous, and fed—according to the input and output of the substrate and product, and are used for the bioremediation of industrial effluents ^[2]. In the SF, the initial water content and inoculum and substrate are important; the conditions of the culture medium can produce a wide range of bioactive compounds that have benefits for human health ^[8]. It is the most widely used in the food industry to obtain enzymes with different substrates and microorganisms.

In submerged fermentation processes, nutrients are used, and some enzymes such as tannase, amylase, and glucoamylases are released, to name a few [37]. It is the most widely used type of fermentation in the industry due to its simplicity, and its final product is easier to recover. The development of microorganisms is typical, which gives rise to a dormancy phase, growth, stationary phase, and death phase. These phases are present in submerged and solid-state fermentation, divided into several types—batch, continuous, and fed—according to the input and output of the substrate and product, and are used for the bioremediation of industrial effluents [32]. In the SF, the initial water content and inoculum and substrate are important; the conditions of the culture medium can produce a wide range of bioactive compounds that have benefits for human health [38]. It is the most widely used in the food industry to obtain enzymes with different substrates and microorganisms.

2. Production of Tannases Using Solid-State Fermentation

Solid-state fermentation is an effective method to produce microbial enzymes and bioactive compounds ^[17], allowing the accumulation high-value products. Its main products are enzymes produced using agro-industrial waste. Microorganisms grow by joining solid substrates, imitating their habitat, giving a fruitful result ^[21]. In this process, the substrate and nutrients can be reused, although this type of fermentation does not apply to bacteria because they require a high-water content ^[1]. However, it is much more attractive because its chemical and physical processes are low cost, simpler, and have better yields; it allows reproducible conditions similar to the environment in which microorganisms live ^[16]. Solid-state fermentation has advantages in terms of the final product concentration, has a lower water expenditure, requires less sterile conditions, and has a low repression effect ^[22]. It is a slightly more laborious process because the growth of the microorganism is slower; there is a low transfer of oxygen and carbon dioxide, heat removal, and it can easily be contaminated ^[2]. A fundamental stage is the culture media preparation to ensure the fermentation process productivity ^[23]. The problem that may arise is that the culture substrate is uneven, and changes in temperature, pH, humidity, and substrate concentration lead to making it less reproducible ^[24]. The water content is an extremely important parameter to produce the desired final product ^[25]. Growth is carried out on a solid substrate almost without water, but with enough to tolerate growth and metabolism. In solid-state fermentation, the particle size and the humidity level are the most critical factors, as well as the initial pH, substrate, aeration, temperature, inoculation, and incubation ^[26].

Solid-state fermentation is an effective method to produce microbial enzymes and bioactive compounds [46], allowing the accumulation high-value products. Its main products are enzymes produced using agro-industrial waste. Microorganisms grow by joining solid substrates, imitating their habitat, giving a fruitful result [49]. In this process, the substrate and nutrients can be reused, although this type of fermentation does not apply to bacteria because they require a high-water content [30]. However, it is much more attractive because its chemical and physical processes are low cost, simpler, and have better yields; it allows reproducible conditions similar to the environment in which microorganisms live [45]. Solid-state fermentation has advantages in terms of the final product concentration, has a lower water expenditure, requires less sterile conditions, and has a low repression effect [50]. It is a slightly more laborious process because the growth of the microorganism is slower; there is a low transfer of oxygen and carbon dioxide, heat removal, and it can easily be contaminated [32]. A fundamental stage is the culture media preparation to ensure the fermentation process productivity [51]. The problem that may arise is that the culture substrate is uneven, and changes in temperature, pH, humidity, and substrate concentration lead to making it less reproducible [52]. The water content is an extremely important parameter to produce the desired final product [53]. Growth is carried out on a solid substrate almost without water, but with enough to tolerate growth and metabolism. In solid-state fermentation, the particle size and the humidity level are the most critical factors, as well as the initial pH, substrate, aeration, temperature, inoculation, and incubation [12].

Figure 2

shows the production process of enzymes from agro-industrial waste through solid-state and submerged fermentation.

Figure 2.

Diagram showing the main enzyme production processes through solid-state and submerged fermentation (original source).

3. Microorganisms Used in Tannases Production

Tannases can be produced from microorganisms, plants, and animals, even though the most widely used microorganisms are fungi, yeasts, and bacteria.

Aspergillus

and

Penicillium

are the most used genera in tannase production; around 27 and 24 species, respectively, have been evaluated for tannase production.

Paecilomyces variotii is the best tannase producer using grape pomace as substrate ^[27]. Four species of

is the best tannase producer using grape pomace as substrate [54]. Four species of

Trichoderma

and three species of

Fusarium

have been also evaluated. Regarding bacteria,

Lactobacillus is the most studied ^[5], mainly

is the most studied [35], mainly

Lactiplantibacillus plantarum

, but

Bacillus

spp. and

Corynebacterium spp. have been also studied ^[28]. Lactic acid bacteria (LAB) degrade gallotannins to gallic acid, but they live under extreme conditions ^[29]. Bacteria can change and repair the membrane to reduce the effect of tannins on the digestive tract, increasing the number of unsaturated fatty acids, modifying their isomerization ^[30].

spp. have been also studied [6]. Lactic acid bacteria (LAB) degrade gallotannins to gallic acid, but they live under extreme conditions [25]. Bacteria can change and repair the membrane to reduce the effect of tannins on the digestive tract, increasing the number of unsaturated fatty acids, modifying their isomerization [31].

There are a variety of microorganisms that produce tannases that have been studied for a long time in terms of process, development, and application; the microorganisms for the activation and production of tannases are listed in

Table 2

Table 2.

Microorganisms used to produce tannases.

Microorganism	Reference
Aspergillus niger	^[28]	[6]
Enterococcus faecalis	^[31]	[55]
Aspergillus ficuum	^[32]	[56]
Achromobacter	^[32]	[56]
Corynebacterium	spp. and	Klebsiella pneumoniae	^[21]	[49]
Azotobacter		Lactiplantibacillus paraplantarum	^[33]	[57]
Aspergillus oryzae	^[31]	[55]
Lactiplantibacillus paraplantarum		Fusarium		Trichoderma	^[32]	[56]
The development of edible coatings containing LAB to wheat bread diminished the number of mesophilic aerobic and facultative aerobic bacteria in the bread crust and protected it from contamination of mycelium fungi of genera	Aspergillus	and	Penicillium	.	^[50]	[72]	Enterobacter cloacae
Lactiplantibacillus plantarum:	TL-1, TL-2, TP-2, TP-5, I-UL4, I 11, RG 11, RG 14, RS 5. 6	Pediococcus pentosaceus:	B12m9, TB-1, TL-3, TP-3, TP-4, TP-8. 2	^[21]	[49]

Pediococcus acidilactici
: TB-2, TP-6.
Tempeh-fermented

soybean cake, apai ubi-fermented

cassava, ikan

rebus-steam fish, budu-fermented fish sauce, tempeh-fermented	soybean cake and empeh-fermented soybean cake	LAB isolates possess versatile extracellular proteolytic system and have vast capability of producing various amino acids including as methionine, lysine, threonine and tryptophan.	^[51]	[73]

5. Agro-Industrial Wastes to Obtain Tannases

Agro-industrial wastes rich in polyphenolic compounds can be used as a source of carbon and energy so that the microorganism can develop and produce tannases. This section describes some research papers where they used agro-industrial waste to produce tannases with the help of microorganisms. For example, coffee pulp rich in polyphenolic compounds as a source of carbon and energy were evaluated through a solid-state fermentation process for tannase production. The authors concluded that the utilization of this wastes for tannase production has potential applications in the food industry ^[52]. In another study, solid-state fermentation was used for tannase production, using a medium containing pomegranate peels (10%) and other salts with pH adjusted to 7.0. These production conditions were compared to define the optimal ones, and various carbon sources, including Moringa cake, palm kernel, palm fronds, wheat straw, olive cake, and pomegranate peels were evaluated ^[53]. Tannase production from solid-state fermentation using coir waste as a substrate was performed. In the reactors, 10 g of the substrate were added and subsequently incubated at 30 °C for 48 h ^[54]. The tannase-biotransformed grape pomace extracts were evaluated to prove intestinal anti-inflammatory activity using an in vitro colon model. This research mentioned that the biotransformation improved the anti-inflammatory effect in Caco-2 cells, indicating that the application of a bioprocess in grape residues may contribute to the development of new ingredients and nutraceuticals with anti-inflammatory potential ^[55]. Various agricultural wastes (coffee husk, tamarind seed powder, bagasse, groundnut oil cake, wheat bran and rice bran) and solid substrates (bengal gram powder (

Agro-industrial wastes rich in polyphenolic compounds can be used as a source of carbon and energy so that the microorganism can develop and produce tannases. This section describes some research papers where they used agro-industrial waste to produce tannases with the help of microorganisms. For example, coffee pulp rich in polyphenolic compounds as a source of carbon and energy were evaluated through a solid-state fermentation process for tannase production. The authors concluded that the utilization of this wastes for tannase production has potential applications in the food industry [74]. In another study, solid-state fermentation was used for tannase production, using a medium containing pomegranate peels (10%) and other salts with pH adjusted to 7.0. These production conditions were compared to define the optimal ones, and various carbon sources, including Moringa cake, palm kernel, palm fronds, wheat straw, olive cake, and pomegranate peels were evaluated [75]. Tannase production from solid-state fermentation using coir waste as a substrate was performed. In the reactors, 10 g of the substrate were added and subsequently incubated at 30 °C for 48 h [76]. The tannase-biotransformed grape pomace extracts were evaluated to prove intestinal anti-inflammatory activity using an in vitro colon model. This research mentioned that the biotransformation improved the anti-inflammatory effect in Caco-2 cells, indicating that the application of a bioprocess in grape residues may contribute to the development of new ingredients and nutraceuticals with anti-inflammatory potential [77]. Various agricultural wastes (coffee husk, tamarind seed powder, bagasse, groundnut oil cake, wheat bran and rice bran) and solid substrates (bengal gram powder (

Cicer arietinum

), black gram flour (

Vigna mungo

L.), green gram flour (

Phasleolus aureus

), barley (

Hordeum vulgare

), millet flour (

Peninsetum glaucum

), ragi (

Eleusine coracana

), oats (

Avena sativa

), corn flour and rice flour) were evaluated to produce tannase by

Lactiplantibacillus plantarum ^[56]. In another study, agro-industrial wastes were shown to be generally rich in tannins and can be used as low-cost substrates for tannase production. Agro-industrial wastes as potential substrates were evaluated for enhanced tannase production using solid-state fermentation. Rice bran showed the highest tannase activity during solid-state fermentation, followed by brewer’s rice, spent coffee grounds, and desiccated coconut waste ^[20]. The cost-effective substrate

[78]. In another study, agro-industrial wastes were shown to be generally rich in tannins and can be used as low-cost substrates for tannase production. Agro-industrial wastes as potential substrates were evaluated for enhanced tannase production using solid-state fermentation. Rice bran showed the highest tannase activity during solid-state fermentation, followed by brewer’s rice, spent coffee grounds, and desiccated coconut waste [48]. The cost-effective substrate

Triphala

was used as a tannin and energy source for tannase production through solid-state fermentation. In this research, statistical experimental design with

Triphala at optimized conditions showed 6.1-fold higher tannase activity than that obtained in submerged fermentation ^[14]. Tannase production was optimized using pomegranate husk as a solid substrate. Easily available and low-cost substrates such as cow dung, coffee husk, apple peel, and pomegranate peel were initially screened for tannase production ^[57]. On the other hand, a cocktail of hydrolytic enzymes was performed by solid-state fermentation using as substrate a mixture of grape pomace and wheat bran. They concluded that the use of solid-state fermentation is a less costly alternative to obtain an enzymatic cocktail that can be used in the food industry ^[58].

at optimized conditions showed 6.1-fold higher tannase activity than that obtained in submerged fermentation [43]. Tannase production was optimized using pomegranate husk as a solid substrate. Easily available and low-cost substrates such as cow dung, coffee husk, apple peel, and pomegranate peel were initially screened for tannase production [79]. On the other hand, a cocktail of hydrolytic enzymes was performed by solid-state fermentation using as substrate a mixture of grape pomace and wheat bran. They concluded that the use of solid-state fermentation is a less costly alternative to obtain an enzymatic cocktail that can be used in the food industry [80].