PECTIC SUBSTANCES AND FIRMNESS OF CUCUMBER PICKLES AS INFLUENCED BY CACL2, NACL AND BRINE STORAGE1

The effects of brine treatments (CaCl₂ and NaCl) and storage on pectic substances and texture of cucumber pickles were examined. Firmness of cucumber pickles was closely associated with the solubility characteristics and degree of esterification (DE) of pectic substances. Brining, storage, time of CaCl₂ addition and concentration of NaCl and CaCl₂ were all observed to influence the characteristics of pectic substances. Important to preventing softening was maintenance of pectic substances not extractable (NXP) by conventional methods, i.e., by water (WSP), the chelator sodium hex-ametaphosphate (CSP), and dilute alkali (OHSP). Erosion of NXP consistently resulted in increased levels of CSP and reduced firmness. Reducing the amount of demethylation of pectins was also associated with maintaining firmness. Although the DE declined rapidly during brining, tissues from treatments that enhanced firmness had pectic substances with the highest DE. CaCl₂ added to brine at the beginning of fermentation was most effective in preventing the demethylation of pectins and solubilization of NXP. In contrast, delayed addition of CaCl₂ and storage in low NaCl concentration (5% or less) caused greater pectin demethylation, erosion of NXP with concomitant increases in CSP and tissue softening.     

Fermentation of Cucumbers Brined with Calcium Chloride Instead of Sodium Chloride

ABSTRACT: Waste water containing high levels of NaCl from cucumber fermentation tank yards is a continuing problem for the pickled vegetable industry. A major reduction in waste salt could be achieved if NaCl were eliminated from the cucumber fermentation process. The objectives of this project were to ferment cucumbers in brine containing CaCl₂ as the only salt, to determine the course of fermentation metabolism in the absence of NaCl, and to compare firmness retention of cucumbers fermented in CaCl₂ brine during subsequent storage compared to cucumbers fermented in brines containing both NaCl and CaCl₂ at concentrations typically used in commercial fermentations. The major metabolite changes during fermentation without NaCl were conversion of sugars in the fresh cucumbers primarily to lactic acid which caused pH to decrease to less than 3.5. This is the same pattern that occurs when cucumbers are fermented with NaCl as the major brining salt. Lactic acid concentration and pH were stable during storage and there was no detectable production of propionic acid or butyric acid that would indicate growth of spoilage bacteria. Firmness retention in cucumbers fermented with 100 to 300 mM CaCl₂ during storage at a high temperature (45 °C) was not significantly different from that obtained in fermented cucumbers with 1.03 M NaCl and 40 mM CaCl₂. In closed jars, cucumber fermentations with and without NaCl in the fermentation brine were similar both in the chemical changes caused by the fermentative microorganisms and in the retention of firmness in the fermented cucumbers.     

Softening of Cucumber Pickles by Cx-Cellulase and Its Inhibition by Calcium

The effects of polygalacturonase free Cx-cellulase alone or in combination with CaCl₂ on softening of cucumber pickles during brine storage were examined. Treating Cx-cellulase preparations with urea eliminated polygalacturonase activity. Pickles exposed to Cx-cellulase remained firm for 4 months. After 4 months, Cx-cellulase mediated softening became apparent. Calcium substantially increased firmness. Cx-cellulase did not reduce the level of firmness attained in pickles exposed to calcium during 12 months of storage.     

Catalase, Lipoxygenase, and Peroxidase Activities in Cucumber Pickles as Affected by Fermentation, Processing, and Calcium Chloride

Catalase, lipoxygenase, and peroxidase activities were determined in tissues and brines of pickling cucumbers during fermentation, storage, and after processing. Lipoxygenase and catalase were inactivated within three days of exposure to fermentation brines. Peroxidase activity was relatively unaffected by the first three days of brining, but it declined during fermentation, storage, and after processing. CaCl₂ reduced the loss of peroxidase activity in tissue and brine during fermentation and storage. Alum in post-desalting brine reduced peroxidase activity in processed pickles although CaCl₂ ameliorated its efficacy. No activity of catalase, lipoxygenase or peroxidase was detected in cucumber juice extracts fermented by four different lactic acid bacteria.     

Effect of Calcium Chloride and Alum on Fermentation, Desalting, and Firmness Retention of Cucumber Pickles

The effects of CaCl₂ in cucumber pickle fermentation and storage brines on fermentation, desalting and retention of mesocarp firmness after processing were determined. Also, the influence of post-desalting treatments with alum and CaCl₂ on firmness of processed pickle was evaluated. Fermentation and desalting were unaffected by CaCl₂ treatment of fermentation brines. However, exposure of pickles to CaCl₂ during fermentation and brine storage substantially reduced softening after processing. Post-desalting treatment with alum and/or CaCl₂ of pickles not previously exposed to CaCl₂ also reduced softening. Retention of firmness was maximized in pickles processed from fermentation and storage brines containing CaCl₂ and treated with alum or CaCl₂ after desalting.     

Effects of Sodium Chloride Concentration on Firmness Retention of Cucumbers Fermented and Stored with Calcium Chloride

The firmness of cucumbers brined at 0.2% CaCl₂ was retained during fermentation (1 month) and storage (12 months) when 2.6, 4.2 or 5.8% NaCl also was present. Firmness retention was not improved (P≥0.05) during storage by increase in NaCl concentration to 11.9% after fermentation. In the absence of added NaCI, cucumbers were firm after fermentation, but firmness was reduced during storage to 69% of initial for whole cucumbers, 64% for mesocarp tissue, and 32% for endocarp tissue. Addition of uncharacterized softening enzymes. extracted from debris collected at a cucumber grading operation, resulted in softening of cucumbers brined at 1.8% NaCl in the absence of added CaC1₂. Addition of CaCl₂ reduced but did not eliminate softening by ths extract. Results indicated that the firmness of brined cucumbers could be retained at appreciably lower NaCl concentrations than those traditionally used but that the lower limit of NaCl required to prevent softening by possible contaminating enzymes is yet to be established.     

CELL WALL CHARACTERISTICS AND FIRMNESS OF FRESH PACK CUCUMBER PICKLES AFFECTED BY PASTEURIZATION AND CALCIUM CHLORIDE1

Changes in cell wall pectic substances, degree of pectin methylation, bound Ca⁺⁺, neutral sugar composition, and firmness were determined in mesocarp tissue of pasteurized and nonpasteurized fresh pack cucumber pickles. Large changes in solubility characteristics of pectic substances occurred in cell walls of nonpasteurized pickles that were attenuated by pasteurization. In particular, water and alkali soluble pectins declined, and nonextractable pectins increased during the first month of storage. The major changes in pectic substance solubility appeared to be related to reductions in the degree of pectin methylation with a minor influence of CaCl₂. Galactose in cell walls of nonpasteurized pickles was substantially reduced, and the reduction in galactose was hindered by CaCl₂ or pasteurization. The amount of bound Ca⁺⁺ appeared to be associated with tissue firmness after one month in storage, since firmer tissue had more cell wall bound Ca⁺⁺. While firmness was associated with the amount of bound Ca⁺⁺, the amount of bound Ca⁺⁺ was dependent on the supply of Ca⁺⁺ and the degree of pectin methylation.     

Fermentation of Cucumbers Without Sodium Chloride

Cucumbers were successfully fermented and stored in the absence of sodium chloride (salt) under laboratory conditions, provided the fruit were blanched (3 min, 77°C) before brining in a calcium acetate buffer and the brine inoculated with Lactobacillus planturum. Bloater formation was prevented by blanching even when brines were not purged of CO₂. Firmness of cucumbers was similar in salt-free brines or those containing salt after 1 mo, but firmness of salt-free cucumbers was lower after storage for 12 mos. Under pilot-scale, commercial conditions, however, the cucumbers were severely bloated, and the firmness was unacceptable after storage for 7 mo, due apparently to Microbial recontamination after blanching.     

Firmness and Cell Wall Characteristics of Pasteurized Jalapeño Pepper Rings as Affected by Preheating and Storage

Changes in cell wall pectic substances, degree of pectin methylation, bound calcium and firmness were determined in preheated and nonpreheated fresh pack jalapeño pepper rings stored for 5 mo. Pepper rings preheated for 60 min at 50°C in a brine solution (8% NaCl and 0.2% CaCl₂, were firmer, had more nonextrctable pectins (NXP), more bound calcium, less water-soluble and chelator-soluble pectins (CSP), and less pectin methylation than nonpreheated pepper rings. The greater formation and maintenance of nonextractable pectins, which resisted acid hydrolysis during pasteurization and storage is probably an important factor in firming.     

Relationships Among Cell Wall Constituents, Calcium and Texture During Cucumber Fermentation and Storage

Demethylation of pectin was the major change in cell wall constituents which occurred during controlled fermentation of cucumbers. The average degree of polymerization of the pectin was 402 residues. This did not change until 6 months after brining. Galactose, xylose, glucose, mannose, and arabinose were present in order of decreasing abundance in the mesocarp cell walls. These noncellulosic neutral sugars did not change during cucumber fermentation and storage. Mesocarp firmness increased when pectin was demethylated, but the firmness subsequently decreased. Calcium chloride at 20 and 40 mM prevented firmness loss compared to fresh cucumbers during 11 months of storage.     

Bound Cations in Cucumber Pickle Mesocarp Tissue as Affected by Brining and CaCl2

The effects of brining, fermentation, storage, time of CaCl₂ addition and concentration of NaCl and CaCl₂ on Ca⁺⁺, Mg⁺⁺, Na⁺, and K⁺ bound to middle lamella-cell wall material of cucumber pickle mesocarp tissue were examined. Changes in the amount of each bound cation occurred rapidly during the first 2 days of brining; levels then remained relatively stable during fermentation and storage if concentrations of NaCl or CaCl₂ in brines were not altered. NaCl reduced levels of bound Ca⁺⁺, Mg⁺⁺, and K⁺, and the presence of CaCl₂ increased the amount of bound Ca⁺⁺ by displacing the other cations. Delayed addition of CaCl₂ to brines enhanced the content of bound Ca⁺⁺, indicating that levels of bound Ca⁺⁺ may not be related to maintenance of firmness.     

Changes in Pectic Substances and Enzymes during Ripening and Storage of "Keitt" Mangos

The relationship of the distribution of pectic substances to tissue softening was examined in ripening mangos at four stages of ripeness. Water-soluble and alkali-soluble pectin declined and ammonium oxalate soluble pectin increased as the mango lost its firmness and became soft. Polygalacturonase and cellulase activities of cell wall preparations increased markedly during ripening. The decline in alkali-soluble pectin and the increase in polygalacturonase activity correlated well with the loss of firmness. Alkali-soluble pectin declined slowly in ripe mangos stored at 4°C. This decline correlated with loss of firmness of the stored mangos. The cellulase activity of cell wall preparations from ripe mangos increased during 4°C storage and the increase correlated with the decrease in firmness.     

Pectinesterase Activity, Pectin Methylation, and Texture Changes During Storage of Blanched Cucumber Slices

Pectin methylation in blanched cucumber slices after 6 months’storage in acid brine (pH 3.7) ranged from 9% (no blanch) to 48% (99°C, 3 min blanch). An 81°C blanch caused complete pectinesterase inactivation, but 15 - 20% reactivation occurred during storage. After a 99°C blanch, only slight reactivation was observed. Pectinesterase was not inactivated at 66°C or less, but up to 85% of the activity was lost during storage. Firmness changes were complex. A clear relationship between pectin methylation and firmness changes was not observed. A 66 or 81°C blanch resulted in best firmness retention. Calcium ion was very effective in prevention of firmness loss regardless of the extent of pectin methylation.     

Compartmentalization of lactic acid bacteria and yeasts in the fermentation of brined cucumbers

Lactic acid bacteria were distributed between the brine and cucumbers in brine-fermented cucumbers. The percentage of bacterial cells located within the cucumbers, of the total cells produced, varied from c. 8–51%, depending upon: (1) gas exchange treatment of the cucumbers before brining and (2) time of inoculation with Lactobacillus plantarum after brining. Oxygen exchange of the cucumbers before brining, and early inoculation of the brine, resulted in higher percentages of cells within the fermented cucumbers. Nitrogen exchange of the cucumbers before brining, and delay in inoculation of the brine for 2 days after brining resulted in lower percentages of cells within the cucumbers. No evidence was found to indicate that yeast cells were present within fermented cucumbers, even when the brines were inoculated with Saccharomyces cerevisiae and the cucumbers had been O₂-exchanged prior to brining. Yeasts, because of their greater size than bacteria, appear to be excluded from the cucumber interior.     

Fermentation of Cucumbers in Anaerobic Tanks

A procedure was developed and tested for fermentation of cucumbers at low concentrations of NaCl in experimental, anaerobic tanks. The procedure included washing of the cucumbers, use of a buffered cover brine composed of 0.045M calcium acetate, sodium chloride to equilibrate at 2.7% or 4.6%, Lactobacillus plantarum culture, and N₂ purging to remove dissolved CO₂. The fermentations were predominantly homofermentative, lactic acid accounting for 95% of the cucumber sugars fermented. Firmness retention of the fermented cucumbers during storage for 1 year was improved by heating packaged products to 69°C before storage, but firmness retention was acceptable in un-heated products.     

The impact of collagen on softening of grass carp (Ctenopharyngodon idella) fillets stored under superchilled and ice storage

The objective of this work was to study the impact of collagen on softening of grass carp (Ctenopharyngodon idella) fillets during chilled storage. The fillets were stored under superchilling (?1.5 ± 0.2 °C) and with ice (0.2 ± 0.1 °C) for 21 days, and texture properties, collagen and the related enzyme activities were measured. Results showed that firmness and collagen content were strongly influenced by storage temperature and time. Fillet firmness decreased by 32.3% (superchilling) and 49.6% (ice stored) of the initial values after 3 days of storage, respectively. Total collagen content decreased with time, but different collagen fractions showed variations. Collagen degraded to different extents depending on storage conditions as indicated by SDS‐PAGE and amino acid analysis. In addition, collagenase activity declined significantly during the first 3 days, followed by a slow increase. This study demonstrated that collagen degradation was involved in grass carp fillet softening and provided useful information for fillet quality improvement.     

Influence of Processing Methodology on Quality of Cucumber Pickles

A study was conducted on the influence of fruit size, blanch temperature, treatment with calcium, and type of acid in cover brine on quality attributes and carbohydrates in nonfermented and fermented cucumber pickles. Firmness was improved by blanching, especially in CaCl₂ solution in both fermented and fresh-pack pickles. Fermentation and acetic acid brine treatments produced the firmest pickles. Size of fruit and length of storage affected quality attributes. The carbohydrate fractions, water-soluble pectin and sodium hexametaphosphate-soluble (SPS) pectin, were correlated with shearpress and sensory firmness. It was concluded that method of processing had a significant effect on quality of pickles.     

Evaluation of enzymatic and non-enzymatic softening in low salt cucumber fermentations

Retention of a firm, crisp fruit texture is a major consideration for pickled vegetables including pickles made from fermented cucumbers. It is known that cucumbers soften rapidly when fermented at low salt concentrations (<0.5 M) without added calcium. This study has shown that there is non-enzymatic softening in low salt fermentations because cucumbers soften even when heated sufficiently to inactivate pectinesterase and several glycosidases that can hydrolyse glycosidic linkages that are present in cell wall polysaccharides. Though pectinesterase activity declines and these glycosidases lose activity within the first week of fermentation there is generally greater loss of cucumber tissue firmness when enzymes are not inactivated by heat. While heating cucumbers prior to fermentation reduces softening during subsequent storage, a heat treatment after 2 weeks of fermentation does not reduce softening. This result suggested that the enzymatic reactions responsible for softening occur early in the fermentation process even though the softening does not become evident until later in the storage period. Despite the evidence of an enzymatic component of tissue softening in low salt cucumbers, softening could not be associated with specific enzymes.     

Effects of Various Treatments on the Quality of Salt-Stock Pickles from Commercial Fermentations Purged with Air

Large scale commercial trials were conducted of various treatments to be used for preventing sporadic softening of pickles due to air-purging of natural fermentations. A total of 220 cucumber fermentations located at 9 different stations and 8 pickle manufacturing companies were studied. Seven different treatments were tested which involved either limitation of oxygen in the brines for 1 or 2 days after brining or addition of potassium sorbate to brines to inhibit the development of molds. Good quality salt-stock pickles were found in all tanks examined of all treatments. However, the addition of 3 lb of potassium sorbate per 1000 gal of tank volume (?0.035%) to acidified (0.05% acetic acid) brine and constant air-purging resulted in salt-stock with the lowest incidence of all types of bloater (hollow pickle) damage.     

Secondary metabolism associated with softening of shiitake mushroom (Lentinula edodes) induced by O2 depletion and CO2 accumulation

It is difficult to preserve fresh shiitake mushroom (Lentinula edodes (Berk.) sing) partly because of the rapid deterioration of texture (softening or lignification). In this study, we developed a storage model in which tissue softening was induced to analyse the relationship between changes in firmness and alterations in cell wall chemical components as well as their metabolism. The results showed that the treatment group accumulated more CO₂ and contained less O₂ because of the poorer permeability in package. The contents of glucan and chitin in the treatment group decreased from 241.3 ± 13.2 mg g^?1 and 46.3 ± 1.2 mg g^?1 to 157.3 ± 11.2 mg g^?1 and 18.0 ± 1.0 mg g^?1 (P < 0.05) with the accumulation of CO₂. The activities of major cell wall degradation‐related enzymes were enhanced in the softening model, and the expression levels of major genes that encode enzymes related to cell wall degradation were upregulated. Our results suggested that the softening of shiitake mushrooms induced by high CO₂ was associated with the degradation of polysaccharides and glycosaminoglycan and that these changes were systematically regulated by alterations in the activities and expression levels of related enzymes and genes.