**1.5 Fermentations biochemistry**

Usually, fermentation is defined as an anaerobic process. Within the cucumber fermentation process, LAB and yeast convert glucose and fructose into lactic acid, ethanol, acetic acid, and CO2. The homofermentative LAB main pathway is breaking down of one six-carbon sugar (glucose) to produce two molecules of three-carbon lactic acid. More complex metabolism is used by Heterofermentative organisms. At the beginning, glucose is converted into CO2 five-carbon sugar phosphate, and furthermore degraded into lactic acid and a two-carbon compound, acetic acid or ethanol [32]. We shall concentrate here on vegetable fermentation biochemical features that link to quality of the product. So far, many researches are paying more attention in vegetables fermentation and storage, especially cucumbers, with reduced salt. Vegetable fermentations' chloride waste can be extremely reduced in case of reducing the required salt for fermentation and storage in order to exclude the desalting step before the conversion to final products. Many research studied the relationship between concentration and type of the salt [33]. Replacing

of NaCl with various cations and anions on fermentation of sugar in cucumber juice. The most interesting thing, fructose was the most preferred fermentable sugar to *Lactobacillus plantarum* more than glucose in most of experiments. Along with addition of different salts, the utilization of sugar was decreasing as anion or cation concentrations increasing. Lu et al. [33] and Zhou et al. [34] have identified various volatile ingredients in cucumbers that fermented with *Lactobacillus plantarum* (2% NaCl). About 37 volatile ingredients were determined, and as a result of fermentation, there was a little change in most of them. Inhibition of (E, Z)-2,6 nonadienal and 2-nonenal production was the most outstanding fermentation effect on cucumber volatiles [35]. Characterized trans- and cis-4-hexenoic acid as the strongest odors that specify the brine aroma properties of commercially fermented cucumbers in nearly 6% NaCl [36]. Illustrated that exposing the slurries (2% NaCl) of fermented cucumber to oxygen resulting in formation of nonenzymatic hexanal plus a series of trans unsaturated aldehydes with 5–8 carbon atoms that linked with oxidized odor intensity development the tissue of fermented cucumber. In the existence of light, about 100 μg/ml concentration of calcium disodium EDTA preserve nonfermented pickles against bleaching of pigments and lipid oxidation [14]. Although, when using this compound, there was a little reduction in pickles' firmness retention. Firmness retention in cucumbers fermentation and storage is a key quality issue. It is difficult to assure the firmness retention (in reduced salt fermented cucumbers) equal to what can be accomplished by fermenting and storage in 6% NaCl or more. Nevertheless, over many previous years there was a wide understanding for softening of cucumber tissue.

Fleming et al. [21] showed the importance of calcium in keeping fermented cucumbers' firmness. It was found that first-order kinetics is followed by the nonenzymatic softening of acidified, blanched cucumber tissue [37]. The mentioned kinetic manner made it reasonable to identify the activation of entropy and enthalpy of cucumbers' nonenzymatic softening, although that the chemical reactions in charge of softening were not known. At 1.5 M NaCl, both activation of entropy and enthalpy were high. Cucumber softening was inhibited by calcium because it reduced activation entropy too much into a limit that activation overall free energy was reduced [38]. This behavior of thermodynamic is resembled to that which occurs when changing conformation of polymers, just like in denaturation of protein. It is totally differed from the observed properties of pectin acid hydrolysis [39]. Figured out that pectin's acid hydrolysis rate was inefficient to be the reason for non-enzymatic softening the tissue of the cucumber [40]. Identified salt, temperature, and calcium concentrations combined effects on fermented cucumber tissue's softening rate. The softening kinetics of fermented cucumbers did not follow the first-order simple reaction. Just like the tissues of many other plants, cucumber possesses enzymes that have the ability to degrade the ingredients of plant cell walls, which may lead to changing in the texture.

In cucumbers, many activities of enzymes have been found such as exopolygalacturonase, pectinesterase, and endopolygalacturonase [41]. When fermenting or acidifying of cucumber, methyl groups are removed from pectin by pectinesterase [42]. Nevertheless, pectin's' enzymatic hydrolysis by polygalacturonases from cucumber has not been identified if it is a significant factor in fermented cucumbers' softening. Adding of fungal polygalacturonases into the tanks of fermentation, especially on the flowers attached to small cucumbers has been linked to the commercially importance of fermented cucumbers' enzymatic softening. Buescher and Burgin [43] developed a sensitive new method of diffusion plate to determine the activity of polygalacturonase in the brines of fermentation and found that alumino-silicate clay has the ability of adsorbing and removing the activity of polygalacturonase from the brines of fermentation that are recycled. Enzymes which could hydrolyze polysaccharides

**31**

*Cucumber Pickles and Fermentations*

*DOI: http://dx.doi.org/10.5772/intechopen.96052*

activities were found in olives, pears, and Semillon grapes.

of the cucumbers cell wall have not studied widely comparing with the enzymes that degrade pectin [45]. Showed that the activity of endo-β-1,4- gluconase in cucumber is inhibited under pH of 4.8 while endoglucomannan-splitting enzyme retains its activity under pH of 4.0 but is inhibited within the fermentation. In fresh cucumbers, they characterized 6 enzymes which hydrolyze p-nitrophenylglycosides of β-dglucose, β-d-galactose, α-d-galactose, β-d-xylose, α-d-mannose, and α-l-arabinose, which were inhibited throughout the fermentation. The enzymes that have the ability to hydrolyze the synthetic substrates are widespread in plants. Resemble enzymatic

Maruvada [44] and Takayanagi et al. [45] discovered the same p-nitrophenyl glycosidases detected by [44] in cucumbers. She reported undetectable levels in 2% NaCl brines throughout the first week of fermentation [46, 47]. Gathered calcium addition, fresh cucumbers' blanching relatively to enzyme inactivation, and a quick fermentation using a malolactic-negative *Lactobacillus plantarum* culture for cucumbers' fermentation and keeping a required texture in reduced (4%) sodium chloride concentration [48]. Found notable degradation products of glucosinolate in cucumbers fermented with *Lactobacillus sakei* compared to cucumbers manufactured with lactic acid bacteria starter cultures [49]. Reported that ascorbigen, a compound resulted from a degradation product reaction of indole glucosinolate (glucobrassicin) and ascorbic acid, is the cucumbers' dominant glucosinolate degradation product. Glucoraphinin existed in fresh cucumbers was converted over the fermentation into sulforphorane, however, sulforphorane was a relatively small glucosinolate degradation product in fermented cucumbers. There are many concerns about the biogenic amines' formation in cucumbers [50]. Reported that storing cucumbers up to 12 months led to the formation of tyramine. While very trace amounts of tryptamine, histamine, and spermine were determined. These findings were assured in a study on vegetable products which concluded that tyramine concentration was about 4.9 mg/100 g in canned cucumbers [51], and the same finding and the concentration reported by [50]. No health risk existed referring to these mentioned biogenic amine levels, with the possible exception that

individuals taking medications possessing monoamine oxidase inhibitors.

Compared to the fermentation of liquids such as beer, wine, and milk, unique problems are involved in the fermentation of whole vegetables. Structural integrity has to be preserved in whole vegetables, which is not a factor with liquids [52]. Tissue softening is also a serious defect that can be caused by pectinolytic enzymes of either microbial (primarily fungal) source [53] or of the cucumber fruit itself. Off-flavors and off-colors may result from improper methods of fermentation and handling. The cucumber pickle industry is faced with waste disposal, in addition to spoilage problems. These wastes consist of the salt used to prevent softening during fermentation and storage, and the organic wastes. Salt concentrations used greatly

Thus, after storing the brine, the excess salt must be leached from the cucum-

bers before they are processed into finished products. Disposal of this nonbiodegradable waste salt is a source of serious environmental concern. As the salt is extracted during leaching, soluble cucumbers, including desirable nutrients and flavor compounds, are also removed. These desirable components are not only lost, they must be degraded before being discharged into waterways. Discharge of salt and organic materials into municipal disposal systems typically entails an extra expense for pickle companies, since municipalities must charge for recovering the

**1.6 Fermented cucumbers-related problems**

exceed the 2–3 percent desired in the final product [54].

cost of handling such waste [55] (**Figure 3**).

#### *Cucumber Pickles and Fermentations DOI: http://dx.doi.org/10.5772/intechopen.96052*

*Cucumber Economic Values and Its Cultivation and Breeding*

understanding for softening of cucumber tissue.

plant cell walls, which may lead to changing in the texture.

of NaCl with various cations and anions on fermentation of sugar in cucumber juice. The most interesting thing, fructose was the most preferred fermentable sugar to *Lactobacillus plantarum* more than glucose in most of experiments. Along with addition of different salts, the utilization of sugar was decreasing as anion or cation concentrations increasing. Lu et al. [33] and Zhou et al. [34] have identified various volatile ingredients in cucumbers that fermented with *Lactobacillus plantarum* (2% NaCl). About 37 volatile ingredients were determined, and as a result of fermentation, there was a little change in most of them. Inhibition of (E, Z)-2,6 nonadienal and 2-nonenal production was the most outstanding fermentation effect on cucumber volatiles [35]. Characterized trans- and cis-4-hexenoic acid as the strongest odors that specify the brine aroma properties of commercially fermented cucumbers in nearly 6% NaCl [36]. Illustrated that exposing the slurries (2% NaCl) of fermented cucumber to oxygen resulting in formation of nonenzymatic hexanal plus a series of trans unsaturated aldehydes with 5–8 carbon atoms that linked with oxidized odor intensity development the tissue of fermented cucumber. In the existence of light, about 100 μg/ml concentration of calcium disodium EDTA preserve nonfermented pickles against bleaching of pigments and lipid oxidation [14]. Although, when using this compound, there was a little reduction in pickles' firmness retention. Firmness retention in cucumbers fermentation and storage is a key quality issue. It is difficult to assure the firmness retention (in reduced salt fermented cucumbers) equal to what can be accomplished by fermenting and storage in 6% NaCl or more. Nevertheless, over many previous years there was a wide

Fleming et al. [21] showed the importance of calcium in keeping fermented cucumbers' firmness. It was found that first-order kinetics is followed by the nonenzymatic softening of acidified, blanched cucumber tissue [37]. The mentioned kinetic manner made it reasonable to identify the activation of entropy and enthalpy of cucumbers' nonenzymatic softening, although that the chemical reactions in charge of softening were not known. At 1.5 M NaCl, both activation of entropy and enthalpy were high. Cucumber softening was inhibited by calcium because it reduced activation entropy too much into a limit that activation overall free energy was reduced [38]. This behavior of thermodynamic is resembled to that which occurs when changing conformation of polymers, just like in denaturation of protein. It is totally differed from the observed properties of pectin acid hydrolysis [39]. Figured out that pectin's acid hydrolysis rate was inefficient to be the reason for non-enzymatic softening the tissue of the cucumber [40]. Identified salt, temperature, and calcium concentrations combined effects on fermented cucumber tissue's softening rate. The softening kinetics of fermented cucumbers did not follow the first-order simple reaction. Just like the tissues of many other plants, cucumber possesses enzymes that have the ability to degrade the ingredients of

In cucumbers, many activities of enzymes have been found such as exopolygalacturonase, pectinesterase, and endopolygalacturonase [41]. When fermenting or acidifying of cucumber, methyl groups are removed from pectin by pectinesterase [42]. Nevertheless, pectin's' enzymatic hydrolysis by polygalacturonases from cucumber has not been identified if it is a significant factor in fermented cucumbers' softening. Adding of fungal polygalacturonases into the tanks of fermentation, especially on the flowers attached to small cucumbers has been linked to the commercially importance of fermented cucumbers' enzymatic softening. Buescher and Burgin [43] developed a sensitive new method of diffusion plate to determine the activity of polygalacturonase in the brines of fermentation and found that alumino-silicate clay has the ability of adsorbing and removing the activity of polygalacturonase from the brines of fermentation that are recycled. Enzymes which could hydrolyze polysaccharides

**30**

of the cucumbers cell wall have not studied widely comparing with the enzymes that degrade pectin [45]. Showed that the activity of endo-β-1,4- gluconase in cucumber is inhibited under pH of 4.8 while endoglucomannan-splitting enzyme retains its activity under pH of 4.0 but is inhibited within the fermentation. In fresh cucumbers, they characterized 6 enzymes which hydrolyze p-nitrophenylglycosides of β-dglucose, β-d-galactose, α-d-galactose, β-d-xylose, α-d-mannose, and α-l-arabinose, which were inhibited throughout the fermentation. The enzymes that have the ability to hydrolyze the synthetic substrates are widespread in plants. Resemble enzymatic activities were found in olives, pears, and Semillon grapes.

Maruvada [44] and Takayanagi et al. [45] discovered the same p-nitrophenyl glycosidases detected by [44] in cucumbers. She reported undetectable levels in 2% NaCl brines throughout the first week of fermentation [46, 47]. Gathered calcium addition, fresh cucumbers' blanching relatively to enzyme inactivation, and a quick fermentation using a malolactic-negative *Lactobacillus plantarum* culture for cucumbers' fermentation and keeping a required texture in reduced (4%) sodium chloride concentration [48]. Found notable degradation products of glucosinolate in cucumbers fermented with *Lactobacillus sakei* compared to cucumbers manufactured with lactic acid bacteria starter cultures [49]. Reported that ascorbigen, a compound resulted from a degradation product reaction of indole glucosinolate (glucobrassicin) and ascorbic acid, is the cucumbers' dominant glucosinolate degradation product. Glucoraphinin existed in fresh cucumbers was converted over the fermentation into sulforphorane, however, sulforphorane was a relatively small glucosinolate degradation product in fermented cucumbers. There are many concerns about the biogenic amines' formation in cucumbers [50]. Reported that storing cucumbers up to 12 months led to the formation of tyramine. While very trace amounts of tryptamine, histamine, and spermine were determined. These findings were assured in a study on vegetable products which concluded that tyramine concentration was about 4.9 mg/100 g in canned cucumbers [51], and the same finding and the concentration reported by [50]. No health risk existed referring to these mentioned biogenic amine levels, with the possible exception that individuals taking medications possessing monoamine oxidase inhibitors.
