Softening Rates of Fermented Cucumber Tissue: Effects of pH, Calcium, and Temperature

First-order softening rates for cucumber mesocarp tissue were determined as a function of pH (2.6–3.8), calcium (0–72 mM), and temperature (25–65°C). Fermented tissue, unlike blanched, nonfermented tissue, often showed two softening rates in first-order plots. A five–variable, empirical equation was derived (R²= 0.913) which predicted softening rates as a tunction of pH, calcium concentration, and temperature. Comparison of softening rates in tissue fermented with and without 18 mM added calcium indicated the softening rate depended upon the concentration of calcium present during the period of measurement and not upon previous history of calcium exposure.     

Effects of Salts Added After Cooking on the Texture of Canned Snap Beans

Soaking bean pods in NaCl solutions caused decreases in firmness and increases in Ca⁺⁺ solubilization as the NaCl concentration increased. CaCl₂ soak solutions increased firmness of pods previously softened by soaking in KCl solutions. Chlorides of Na⁺, K⁺, Li⁺, NH₄⁺, and Mg⁺⁺, and Na acetate caused softening. LiCl caused the most softening, while MgCl₂ caused the greatest solubilization of Ca⁺⁺. Salt-induced softening was accompanied by Ca⁺⁺ displacement. Firmness of salt-softened pods was further decreased by subsequent removal of the salt, indicating an electrostatic component as a minor factor in pod texture.     

pH Effect on Calcium Inhibition of Softening of Cucumber Mesocarp Tissue

The first-order rate of softening of cucumber tissue containing 1.5M NaCl with and without 20 mM added calcium ion was determined from pH 2.5 to 8.6 at 74°C. Calcium ion had little inhibitory effect on rate of softening when pH was above 5. Below pH 5 the relative effectiveness of calcium in reducing rate of softening increased as pH decreased. This behavior was opposite to that expected if calcium inhibited softening by cross-linking negatively charged pectin car-boxyl groups. This was more evidence against that mechanism as an explanation for inhibition of softening by calcium ion in plant tissues. A very large decrease in rate of tissue softening was observed at alkaline pH whether or not calcium was added.     

KCI, CaCI2, Na+ Binding, and Salt Taste of Gum Systems

Aqueous nonionic (0.3% w/v) and ionic (0.1% and 0.3% w/v) gum systems containing NaCl, or equal weights of NaCl plus KCl, or NaCl plus CaCl, were examined. At equivalent molar concentrations of added ions, ²³Na NMR transverse relaxation rates (R₂, set^?1) showed an increase in average Na⁺ mobility with the addition of K⁺ or Ca²⁺ to ionic gum systems. Correspondingly, salt taste increased with addition of KCl as determined by Decision Boundary modeling of subject identification data. Viscosity did not affect saltiness. Na⁺ was free to induce salt taste when K⁺ was bound to the gum. Enhancement of salt taste by KCl is due, in part, to competitive binding of Na⁺ and K⁺ in a system.     

Effect of Calcium Ions on the Thermodynamics of Cucumber Tissue Softening

Calcium ion was found to cause inhibition of softening in blanched cucumber tissue under acidic conditions due to a dominant effect of the calcium upon the entropy of activation for the softening reaction. This resulted in slower rates of softening despite a decline in the enthalpy of activation. Enthalpy/entropy compensation was found to occur. The isokinetic temperature for softening was 260 ± 9 K. An assumption was made that the hyperbolic inhibition of softening by calcium was due to saturation of a binding site by calcium. The dissociation constant for calcium from the proposed site was determined to be 1.5 mM at 30°C. This was considerably stronger binding than should occur if calcium was binding to pectin carboxyl groups under similar conditions. The apparent enthalpy and entropy for calcium binding were determined.     

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.     

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.     

Evaluation of malolactic-deficient strains of Lactobacillus plantarum for use in cucumber fermentations

In the fermentation of cucumbers, naturally occurring strains of Lactobacillus plantarum decarboxylate malic acid (MDC⁺) to form lactic acid and CO₂. Since CO₂ buildup in the brine contributes to bloater damage of the cucumbers, it is desirable to have strains of L. plantarum that do not decarboxylate malic acid (MDC^-1). Two MDC^- mutants, obtained by N-methyl-N′-nitro-N-nitrosoguanidine mutagenesis of different MDC⁺ strains, and their parent strains of L. plantarum wre evaluated in laboratory fermentations of filter-sterilized cucumber juice and of whole cucumbers as to growth rate, end-products, residual malic acid, and competitiveness with the natural flora. Effects of temperature (15 to 40°C) and NaCl concentration (0-6%) on growth in cucumber juice were determined. One MDC^-1 strain, designated MOP3-M6, was selected for further development because of its relative dominance in cucumber ferementations, high residual malic acid concentration after fermentation and greater salt tolerance as compared to its closest rival mutant culture. Growth lag and generation times averaged 1·6 and 1·2 times greater, respectively, for the MOP3-M6 mutant than its parent. However, this mutant may still have application as a starter culture for cucumber fermentation, particularly under relatively aseptic conditions.     

Relationship Between Degree of Pectin Methylation and Tissue Firmness of Cucumber Pickles

The relationship between pectin methylation and tissue firmness was examined in cucumber pickles exposed to pre-brining and brining treatments. Tissue treated with CaCl₂ prior to or during brining, blanched before brining or held at 2°C during brine storage resisted softening. Although all treatments reduced the degree of esterification (DE) of pectic substances, less demethylation occurred in treatments that protected against softening. Join point regression analysis of the data indicated that maximum firmness of mesocarp tissue was attained when the DE of pectins was 12.3 ± 1.2 or greater. Firmness declined concomitantly when the DE declined below 12.3 ± 1.2. Methods that protect against excessive demethylation of pectins appear to be important in retarding softening of cucumber pickle tissue during storage in brine.     

Calcium Chloride and Potassium Sorbate Reduce Sodium Chloride used during Natural Cucumber Fermentation and Storage

Cucumber fermentation characteristics and pickle quality were evaluated in brines containing equilibrium concentrations of 0-0.4% CaCl₂, 0-0.4% potassium sorbate and 0-10% NaCl. Changes in brine pH and acidity, cucumber texture and color, coliforms, lactic acid and total bacteria, yeasts and molds were followed over time. Results indicated that cucumber spoilage would eventually take place if NaCl or potassium sorbate were not present in the brine. The presence of CaCl₂ helped maintain cucumber firmness. A synergistic action between NaCl, CaCl₂ and potassium sorbate was seen, which allowed good quality pickles to be produced when moderate amounts of all three components were present in the brine (5% NaCl, 0.2% CaCl₂, 0.2% potassium sorbate).     

Thickening Agents Effects on Sodium Binding and Other Taste Qualities of Soup Systems

Low sodium chicken broth with NaCl added to provide Na⁺ concentrations in typical reduced Na⁺ soups (144 and 288 mg Na⁺/240 mL serving) was thickened with commonly used gum, starch, or flour food additives. Xanthan gum suppressed saltiness as the result of ionic binding of Na⁺, as determined by sensory evaluation and ²³Na NMR spectroscopy. Saltiness was affected by added NaCl (p = 0.0001), thickener (p < 0.01), and added NaCl* thickener (p < 0.01), and positively correlated with chicken and overall flavors (p = 0.0001). Cornstarch provided body, no suppression of salt taste, and the greatest salt enhancement of chicken and overall flavors. In complex food systems, temperature and other factors affected Na⁺ binding as measured by NMR pointing to the need for a new model.     

Na+ Binding as Measured by 23Na Nuclear Magnetic Resonance Spectroscopy Influences the Perception of Saltiness in Gum Solutions

Binding of Na⁺ in aqueous gum systems as determined by ²³Na nuclear magnetic resonance (NMR) spectroscopy and its relations to perceived saltiness were examined. Two levels of NaCl (0.1% and 0.2%) were added to two concentrations (0.1% and 0.3%) of two ionic (xanthan and kappa carrageenan) and two non-ionic (locust bean and guar) gum solutions. Saltiness perception was affected by the ionic properties of the gums. NMR transverse relaxation rates (R₂, see^?l) indicated Na⁺ was less mobile in ionic than nonionic systems. Ionic gums correspondingly suppressed saltiness perception- compared to nonionic gums. As Na⁺ increased in both ionic and nonionic systems, R₂ values converged and perceived saltiness equalized. Food components that bind Na⁺ may suppress saltiness perception, which may be important in low-sodium foods.     

Functionality of native and denatured cashew nut kernel protein isolates at isoelectric pH as a function of salt concentration

The reduced solubility of proteins near the isoelectric pH limits their use in food formulations whose pH lies in the range 5.0–6.0 because of poor functionality. In the present study, the effect of salt on the functionality of native and denatured cashew nut kernel protein isolates at the isoelectric pH was investigated. Both isolates showed improvement in their functional properties, but the improvement was greater for the denatured protein isolate. The solubilities of denatured and native protein isolates at the isoelectric pH increased from 26.4 g l^?1 and 64 g l^?1, respectively, without salt to maxima of 363 and 308 g l^?1, respectively, at 0.75 M salt concentration. The water binding capacity of the isolates increased with increase in NaCl concentration from 1.70 ml g^?1 to 1.77, 1.82, 1.92 and 2.2 ml g^?1 for denatured protein isolate and from 1.45 ml g^?1 to 1.65, 1.69, 1.82 and 1.97 ml g^?1 for native protein isolate at 0.25, 0.50, 0.75 and 1.0 M salt concentrations, respectively. When the properties of the isolates in 0.75 M NaCl solutions were compared with those in salt‐free water there were 15% and 116% increases in emulsifying capacity, 40‐fold and 45‐fold increases in emulsifying activity and 4.6‐fold and 40‐fold increases in emulsion stability for native and denatured protein isolates, respectively, whilst the corresponding foaming capacities increased from 4 to 5.5 and 0 to 8.9 ml g^?1 protein. Statistically, no difference in the foaming capacity of either of the isolates was observed above 0.5 M NaCl. The foam stability also exhibited similar behaviour. Copyright © 2004 Society of Chemical Industry     

Quality and nutritional value of strawberry fruit under long term salt stress

Modifications of fruit quality, in response to a long-term salt stress of four months, were studied in two strawberry cultivars differing in their sensitivity to salinity. The sensitive cv. Elsanta and the less sensitive cv. Korona were treated during two vegetation seasons with 0, 40 or 80 mmol NaCl/l in the nutrient solution. While mean fruit weight decreased, dry matter and contents of total soluble carbohydrates, as well as sweetness index of fruits, remained constant. Salt stress in both cultivars increased the antioxidant capacity, antioxidants pools (ascorbic acid, anthocyanins, superoxide dismutase) and selected minerals such as Na⁺, Cl⁻, K⁺, N, P and Zn²⁺, as well as lipid peroxidation. Furthermore, salt stress increased the contents of free and essential amino acids, especially in cv. Elsanta. The more tolerant cv. Korona was characterized by an increase of reduced glutathione and a better fruit taste. In salt-stressed fruits of cv. Elsanta, taste was significantly impaired.     

Physiological changes, phenolic content and antioxidant activity of Salvia officinalis L. grown under saline conditions

BACKGROUND: Hydroponic culture was used to investigate the effect of NaCl concentrations on the growth, nutrient uptake, phenolic content and antioxidant activity of Salvia officinalis L. leaves. The antioxidant capacity of the methanolic extract of S. officinalis was evaluated by using 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) radical scavenging test and β‐carotene‐linoleic acid bleaching assay. Physiological and biochemical parameters of S. officinalis were assessed after 4 weeks of salt treatment with 0, 25, 50, 75 and 100 mmol L^?1 NaCl. RESULTS: Plant growth exhibited a reduction of 61% at 100 mmol L^?1 NaCl. Assessment of Na⁺, K⁺ and Ca²⁺ and water contents of shoots and roots showed that S. officinalis is able to regulate Na⁺ concentration by active compartmentation in vacuoles. Salvia officinalis phenolics were increased in response to salinity at the threshold of 75 mmol L^?1 NaCl. This herb was also found to be able to achieve important DPPH^? quenching activity and to inhibit the β‐carotene‐linoleic acid bleaching notably enhanced by salt treatment. It is interesting to highlight the correlation between the phenolic and antioxidant activity, suggesting the involvement of these compounds in this activity. CONCLUSION: Salvia officinalis treated with 75 mmol L^?1 NaCl constitutes a potential source for production of secondary metabolites useful in several applications. Copyright © 2011 Society of Chemical Industry     

Contribution of amino acids to strawberry fruit quality and their relevance as stress indicators under NaCl salinity

Strawberry cvs Korona and Elsanta, differing in their sensitivity to salt stress, were exposed to 0, 40, or 80 mM NaCl in the root medium from the end of April to mid-August. Although fruits of both cultivars contained comparable amounts of Na⁺ and Cl⁻, fruit quality was more impaired in cv. Elsanta, as indicated by the larger reductions of fruit size and sugar/acid ratios. Malondialdehyde levels started to rise significantly at 40 mM NaCl in the more sensitive cv. Elsanta, but at 80 mM in cv. Korona. Total amino acid levels, especially contents of essential amino acids, rose significantly in both cvs. Salt stress also increased contents of free proline, asparagine, and glutamine. Their increases may contribute to osmotic adjustment. The results of the present study favour the interpretation that elevated levels of proline, asparagine and glutamine are indicative of salt stress damage.     

Mechanisms of Salt Tolerance Conferred by Overexpression of the HAL1 Gene in Saccharomyces cerevisiae

Overexpression of the HAL1 gene improves the tolerance of Saccharomyces cerevisiae to NaCl by increasing intracellular K⁺ and decreasing intracellular Na⁺. The effect of HAL1 on intracellular Na⁺ was mediated by the PMR2/ENA1 gene, corresponding to a major Na⁺ efflux system. The expression level of ENA1 was dependent on the gene dosage of HAL1 and overexpression of HAL1 suppressed the salt sensitivity of null mutants in calcineurin and Hal3p, other known regulators of ENA1 expression. The effect of HAL1 on intracellular K⁺ was independent of the TRK1 and TOK1 genes, corresponding to a major K⁺ uptake system and to a K⁺ efflux system activated by depolarization, respectively. Overexpression of HAL1 reduces K⁺ loss from the cells upon salt stress, a phenomenon mediated by an unidentified K⁺ efflux system. Overexpression of HAL1 did not increase NaCl tolerance in galactose medium. NaCl poses two types of stress, osmotic and ionic, counteracted by glycerol synthesis and sodium extrusion, respectively. As compared to glucose, with galactose as carbon source glycerol synthesis is reduced and the expression of ENA1 is increased. As a consequence, osmotic adjustment through glycerolsynthesis, a process not affected by HAL1, is the limiting factor for growth on galactose under NaCl stress. © 1997 John Wiley & Sons, Ltd.     

Biochemical Variations in Salt Soluble Fractions of Ultrasonicated Actomyosin Isolated from Broiler Breast-Muscle

Solubility and quality of actomyosin play crucial roles during storage and processing of a particular muscle type. We report here the effect of low intensity (20 kHz) ultrasonication on the solubility and some other biochemical properties of the actomyosin isolated from chicken breast muscle. Although there was an overall enhancement in the solubility of actomyosin during sonication, the major increase of ~61.55% occurred at 0.2M NaCl after 10–12 min of exposure. The distinctive feature of sodium dodecyl sulphate-polyacrylamide gel electrophoretic (SDS-PAGE) profiles of this fraction was the presence of free or non-interacting actin in considerable amount. Even at higher salt concentrations (0.4 and 0.5M NaCl), the protein solubility was almost twice as high as that of the corresponding controls. At low salt concentrations (<0.3 M NaCl or KCl) where the protein solubility was high, Ca²⁺-, K⁺(EDTA)- and Mg²⁺-ATPase activities were low. However, a remarkable increase in each of the enzymatic activities occurred at the salt concentrations higher than 0.3 M. More importantly, the high level of Mg²⁺-ATPase strongly indicated that actomyosin was reconstituted. The ultraviolet spectra also supported the reconstitution of actomyosin at high salt concentrations. These data suggested that ultrasonication caused conformational changes which modified properties of myosin and actin affecting the intermolecular relationships within actomyosin complex. The shift in the solubility and functional modifications of sonicated actomyosin provide some basis to explain the processing behavior of sonicated poultry meat. In addition, the low frequency sonication may be suggested as a non-destructive method to compare actomyosin extracted from various sources.     

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.     

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.