Malic Acid as a Source of Carbon Dioxide in Cucumber Juice Fermentations

The degradation of malic acid to lactic acid and CO₂ during fermentation of cucumber juice was investigated. This malolactic reaction was the major source of CO₂ when cucumber juice was fermented by Lactobacillus plantarum. It may also be an important CO₂ source in controlled cucumber fermentations. In addition to CO₂ production, the degradation of malate served to buffer the fermentation and increase sugar utilization. The pH after 7 days’fermentation was 2.8 when 13 mM malic acid was present in the juice and 4.1 with 135 mM malic acid. In the same fermentations, 52% of the sugars were degraded with the low malic acid concentration while complete sugar utilization was observed with the highest malic acid level.     

Malic Acid Degradation and Brined Cucumber Bloating

Bloater formation of brined cucumbers increased as more malic acid was degraded to CO₂ and lactic acid. CO₂ production by the brined cucumber, unrelated to malic acid degradation, was 12.5 mM. This was just sufficient to bring cucumbers to the point of bloating. CO₂ from malic acid provided the marginal increase required to cause significant bloating. Fermentation with a strain of Lactobacillus plantarum, which did not degrade malic acid, prevented cucumber bloating. Oxygen exchange of cucumbers before brining increased the amount of CO₂ required to initiate bloating damage by 8 mM. Nonmalic acid-degrading starter cultures and/or oxygen exchange may be useful alternatives to CO₂ purging from brines to prevent bloater damage.     

Evaluation of Fermentative Bacteria in a Model Low Salt Cucumber Juice Brine

Bifidobacterium bifidum, Lactobacillus casei, Lactobacillus plantarum, Lactococcus diacetylactis, Leuconostoc mesenteroides, Leuconostoc oenos, Pediococcus pentosaceus and a mixed culture of Propionibacterium shermanii and P. pentosaceus were used to ferment a model low salt (2.5% NaCl) cucumber juice brine at 22–26°C for 39 days. Percent sugar fermented ranged from 16.2 to 87.7. Substrates were citric acid, fructose, glucose and malic acid. Fermentation products quantitated were acetic acid, acetoin, ethanol, lactic acid, mannitol, and propionic acid with percent carbon recovery varying from 71.1 to 101.1. Final pH ranged 3.24 to 4.12. Each fermentation differed quantitatively in substrates and products formed suggesting use of these bacteria as cultures to ferment low salt brined cucumbers and generate a variety of unique organoleptic properties.     

Malolactic fermentation in sea buckthorn (Hippophaë rhamnoides L.) juice processing

Malolactic fermentation (MLF) traditionally used in winemaking was applied to sea buckthorn to reduce the high sourness of the berry juice. Chemical and microbiological aspects, as well as sensory properties of the juice during MLF were studied in order to develop an optimal process. In 1:1 water diluted juice with malic acid content of 15 g/l and pH 2.8, efficient conversion of l-malic acid to l-lactic acid was achieved with direct inoculation of unadapted Oenococcus oeni at a cell density of 10⁹ CFU/ml. The rapid malic acid degradation was performed by non-growing bacterial cells without loss of sugars, vitamin C, or pulp oil. More than 50% of the initial malic acid was metabolized to lactic acid and CO₂ already in 12 h of fermentation and a significant decrease in sourness and astringency was noticed. In 24 h fermentation, pH value was increased to 3.1 and only 3 g/l malic acid remained in the juice. Prolonged fermentation had only minor effect on malolactic reaction, but off-flavor of the juice began to increase.     

CONTROLLED ATMOSPHERE STORAGE AFFECTS QUALITY AND CHILLING SUSCEPTIBILITY OF CUCUMBERS

Controlled atmospheres (CA) maintained the quality of cucumbers better than conventional refrigerated storage at 5C. Elevated levels of CO₂ (3%) and decreased concentrations of O₂ (1 and 15%) also increased the tolerance of cucumbers to chilling exposure. The content of sugars, including fructose and glucose; and organic acids, particularly malic acid, were maintained at higher levels in CA-stored cucumbers than in air-stored samples. The respiration rates (measured as CO₂ production) of cucumber fruit during storage at 5C were markedly suppressed under CA conditions. Contrary to reports in the literature, CA storage was found to be beneficial in reducing chilling injury and maintaining cucumber quality.     

Effects of Fruit Size on Fresh Cucumber Composition and the Chemical and Physical Consequences of Fermentation

ABSTRACT: The composition of pickling cucumbers varied with fruit size, which affected buffer capacity, sugar utilization, terminal pH, and texture of the fermented fruit. We found that as cucumber size increased (from less than 27 to 51 mm in dia), malic acid, pH, buffer capacity, and dry matter content decreased, and glucose and fructose contents increased. Fruit firmness and bloater damage were greater in large than in small, fermented, whole cucumbers. Blanching (75 °C, 30 s) had little effect on the fermentation and prevention of bloater formation in finished products, regardless of fruit sizes. It was demonstrated that cucumber juice can serve as a model system for studying the metabolic, but not the physical (texture, bloater damage), consequences of lactic acid bacteria chosen as starter cultures for cucumber fermentation.     

Equilibration of Solutes in Nonfermenting, Brined Pickling Cucumbers

The equilibration of solutes between whole cucumbers and the brine in which they were held was found to be consistent with a diffusion-controlled first-order rate process. First-order rate coefficients for attainment of equilibrium (K_D) for sugar and malic acid (initially in cucumbers) and NaCl and lactic, tartaric, acetic and formic acids (initially in brine) varied up to threefold among four cucumber lots. However, the ratios of K_D values among solutes were not significantly different (P>0.05). K_D values increased as cucumber size decreased. Peeling increased K_D values 3.7- to 11.1-fold. Temperature dependency was greater for solute movement out of [apparent activation energies (E_a) of 6.5 and 6.3 kcal/mole for malic acid and sugar] than into (apparent E_a of 4.5 and 4.2 kcal/mole for NaCl and lactic acid) cucumbers. The equilibration-prediction model used may be helpful in studying rate limiting factors in the fermentation of brined vegetables and in other food preservation processes where solute movement is important.     

Viability of commercial cucumber fermentation without nitrogen or air purging

BackgroundBloated cucumber defect, resulting from the accumulation of the biologically produced carbon dioxide (CO₂) in the fruit, reduces yield and economic gains for the pickling industry worldwide. It was the aim of this review to identify commonalities among effective strategies to reduce bloater defect and determine the theoretical viability of commercial cucumber fermentations without bloater defect and/or purging.Scope and approachThis article summarizes the known causes of fermented cucumber bloating defect, including sources of CO₂, and the strategies developed to mitigate the production of the carbonic gas such as controlled fermentation, inoculation of selected starter cultures, cover brine acidification and reformulation and the application of air or nitrogen purging.Key findings and conclusionsIt was understood that microbial activity during fermentation, cucumber tissue respiration, as well as the pressure in the fruits and fermentation tanks, ambient temperature and cover brine composition, impact the levels of dissolved CO₂ in the system. Although the biological conversion of oxygen to CO₂ reduces the cucumbers internal gas pressure, the dissipation of the gas from the tissue is reduced by brining. Once the gas accumulates in the cucumber tissue in concentrations high enough to displace it, the irreversible formation of hollow cavities or bloaters occurs. Residual CO₂ is produced by acid-preserved cucumbers, presumably by tissue respiration, which results in the absence of bloating. Thus, microbial activity seems to contribute most of the CO₂ needed for cucumbers to bloat. It is speculated that colonization of the internal cucumber tissue by indigenous microbes, in particular aerobic gram-negative bacteria, results in the localized production of CO₂ causing bloating defect early in the fermentation. It is concluded that effective manipulation of the microbiota, reduction of dissolved oxygen levels and the use of adequately selected starter cultures may enable cucumber fermentations of acceptable quality without purging.     

Preparation of a Lactobacillus plantarum starter culture for cucumber fermentations that can meet kosher guidelines

A method is described for growth of a Lactobacillus plantarum starter culture in jars of commercially available pasteurized fresh-pack kosher dill cucumbers so that jars can be used to inoculate commercial scale cucumber fermentation tanks. A procedure is also described to transfer lactic acid bacteria from frozen storage in MRS broth into cucumber juice and commercial jars of kosher dill cucumbers so that a selected strain of lactic acid bacteria can be kosher certified for commercial fermentations in processing plants that operate under kosher certification. The strain of L. plantarum used in these experiments grew to maximum cell numbers in 4 d at 20 to 25 °C and then maintained viable cell numbers for 2 wk at >10(8) CFU/mL so the culture was suitable for inoculation of fermentation tanks. Refrigeration of jars of culture after they grow to maximum numbers minimizes die-off of cells sufficiently so that a pure culture can be maintained by aseptically transferring brine containing viable bacteria to a new pH-adjusted jar only once every 4 mo. PRACTICAL APPLICATION: This report describes a method to prepare a lactic acid bacteria starter culture suitable for kosher vegetable fermentations.     

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.     

Commercial Scale Cucumber Fermentations Brined with Calcium Chloride Instead of Sodium Chloride

Development of low salt cucumber fermentation processes present opportunities to reduce the amount of sodium chloride (NaCl) that reaches fresh water streams from industrial activities. The objective of this research was to translate cucumber fermentation brined with calcium chloride (CaCl₂) instead of NaCl to commercial scale production. Although CaCl₂ brined cucumber fermentations were stable in laboratory experiments, commercial scale trials using 6440 L open‐top tanks rapidly underwent secondary cucumber fermentation. It was understood that a limited air purging routine, use of a starter culture and addition of preservatives to the cover brine aids in achieving the desired complete cucumber fermentation. The modified process was used for subsequent commercial trials using 12490 and 28400 L open‐top tanks packed with variable size cucumbers and from multiple lots, and cover brines containing CaCl₂ and potassium sorbate to equilibrated concentrations of 100 and 6 mM, respectively. Lactobacillus plantarum LA0045 was inoculated to 10⁶ CFU/mL, and air purging was applied for two 2–3 h periods per day for the first 10 d of fermentation and one 2–3 h period per day between days 11 and 14. All fermentations were completed, as evidenced by the full conversion of sugars to lactic acid, decrease in pH to 3.0, and presented microbiological stability for a minimum of 21 d. This CaCl₂ process may be used to produce fermented cucumbers intended to be stored short term in a manner that reduces pollution and waste removal costs.     

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.     

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.     

Role of Gas Diffusion in Bloater Formation of Brined Cucumbers

A method was developed to measure diffusion rates of CO₂ and N₂ through fresh and brined cucumber tissue to examine the role of gas diffusion in bloater formation. The diffusion rate of CO₂ was 3.2 times greater than N₂ through fresh and 2.4 times greater than N₂ through brined cucumber tissue. The ratio of the diffusion rates of CO₂ to N₂ through brined cucumbers was not significantly altered from that of fresh fruit. Solubility of gases was determined to be a factor governing the rate and extent of bloater damage. Maximum rates of increase in expansion volume of N₂-exchanged cucumbers was 0.42, 1.30, and 11.90% hr^?1 for brines purged with Ar, CO₂, and SO₂, respectively, and 0.89% hr^?1 for Ar-exchanged fruit following purge of the brine with CO₂.     

Mass Transfer and Solute Diffusion in Brined Cucumbers

ABSTRACT: The exchange of malic acid, lactic acid, NaCl, and sugar between cucumber and cover brine was monitored over a course of 16 days for 5 sizes of cucumbers. Experimental results showed that sugar exchange between cucumbers and cover brine was the slowest. In comparison to Ficks diffusion equation, the exponential equation better described the movement of solutes during the brine fermentation of cucumbers. Diffusion coefficient of sugar was estimated to vary from 1.80 × 10–9 to 9.18 × 10–9 m2/s. Solute sorption rate from the exponential model varied from 0.0204 to 0.233 h-1 and decreased with increase in cucumber size and solute molecular weight.     

乳杆菌有机酸耐受性及发酵果蔬汁性能分析

选择3株从醋醅中筛选得到的高性能乳杆菌,考察培养基中不同浓度和种类有机酸对其发酵的影响,并比较其对12种典型果蔬汁的发酵效果.结果表明鼠李糖乳杆菌LR-S、植物乳杆菌LP-D和植物乳杆菌LP-F分别对苹果酸、柠檬酸和酒石酸具有较好的耐受,进而对这些有机酸为主体的果蔬原料发酵更具优势.在桑葚汁等有机酸复杂的原料中双菌顺序...     

Survival of Escherichia coli O157:H7 in cucumber fermentation brines

Abstract: Bacterial pathogens have been reported on fresh cucumbers and other vegetables used for commercial fermentation. The Food and Drug Administration currently has a 5‐log reduction standard for E. coli O157:H7 and other vegetative pathogens in acidified pickle products. For fermented vegetables, which are acid foods, there is little data documenting the conditions needed to kill acid resistant pathogens. To address this knowledge gap, we obtained 10 different cucumber fermentation brines at different stages of fermentation from 5 domestic commercial plants. Cucumber brines were used to represent vegetable fermentations because cabbage and other vegetables may have inhibitory compounds that may affect survival. The 5‐log reduction times for E. coli O157:H7 strains in the commercial brines were found to be positively correlated with brine pH, and ranged from 3 to 24 d for pH values of 3.2 to 4.6, respectively. In a laboratory cucumber juice medium that had been previously fermented with Lactobacillus plantarum or Leuconostoc mesenteroides (pH 3.9), a 5‐log reduction was achieved within 1 to 16 d depending on pH, acid concentration, and temperature. During competitive growth at 30 °C in the presence of L. plantarum or L. mesenteroides in cucumber juice, E. coli O157:H7 cell numbers were reduced to below the level of detection within 2 to 3 d. These data may be used to aid manufacturers of fermented vegetable products determine safe production practices based on fermentation pH and temperature. Practical Application: Disease causing strains of the bacterium E. coli may be present on fresh vegetables. Our investigation determined the time needed to kill E. coli in cucumber fermentation brines and how E. coli strains are killed in competition with naturally present lactic acid bacteria. Our results showed how brine pH and other brine conditions affected the killing of E. coli strains. These data can be used by producers of fermented vegetable products to help assure consumer safety.     

Preservation of acidified cucumbers with a combination of fumaric acid and cinnamaldehyde that target lactic acid bacteria and yeasts

The naturally occurring compound, fumaric acid, was evaluated as a potential preservative for the long-term storage of cucumbers. Fumaric acid inhibited growth of lactic acid bacteria (LAB) in an acidified cucumber juice medium model system resembling conditions that could allow preservation of cucumbers in the presence of sodium benzoate. Forty millimolars of fumaric acid were required to inhibit growth of an extremely aciduric Lactobacillus plantarum LA0445 strain at pH 3.8. Half of this concentration was required to achieve inhibition of L. plantarum LA0445 at pH 3.5. As expected growth of the spoilage yeasts Zygosaccharomyces globiformis and Z. bailii was not inhibited by fumaric acid at near saturation concentrations in the same cucumber juice medium. To usefully apply fumaric acid as a preservative in acidified foods it will be necessary to combine it with a food grade yeast inhibitor. The antimicrobial agent, cinnamaldehyde (3.8 mM) prevented growth of Z. globiformis as well as the yeasts that were present on fresh cucumbers. Acidified cucumbers were successfully preserved, as indicated by lack of yeasts or LAB growth and microbial lactic acid or ethanol production by a combination of fumaric acid and cinnamaldehyde during storage at 30 °C for 2 mo. This combination of 2 naturally occurring preservative compounds may serve as an alternative approach to the use of sodium benzoate, potassium sorbate, or sodium metabisulfite for preservation of acidified vegetables without a thermal process. PRACTICAL APPLICATION: This study evaluates the potential application of alternative preservatives for the long-term storage of cucumbers in a reduced NaCl cover brine solution and without a thermal process.     

植物乳杆菌和发酵乳杆菌对胡柚汁发酵品质及其抗氧化性的影响

适用于果汁发酵的乳酸菌植物乳杆菌L1（Lactobacillus plantarum L1）和发酵乳杆菌L2（Lactobacillus fermentum L2）分别发酵胡柚汁,研究胡柚汁发酵过程中活菌数、酸度、pH值、VC、有机酸和色泽变化,以及乳酸菌对发酵胡柚汁总酚、总黄酮类化合物和抗氧化性的影响。结果表明,2?种乳酸菌在胡柚汁中生长良好,活菌数突破108?CFU/mL,pH值显著降低,酸度和VC显著提高;色差值变化明显,L*值呈下降趋势,a*值、b*值呈上升趋势;有机酸变化显著,酒石酸、柠檬酸、乙酸和乳酸的含量均显著提高,草酸、苹果酸和琥珀酸显著下降,其中乙酸、乳酸和苹果酸的变化最为明显;与未接种乳酸菌相比,抗氧化性显著提高,1,1-二苯基-2-三硝基苯肼自由基、超氧阴离子自由基和羟自由基的清除能力分别提高了4.3%、15.9%和0.7%以上;总酚和总黄酮含量均提高。两种乳酸菌接种发酵显著改善了胡柚汁的品质和抗氧化特性,研究结果为胡柚汁益生菌发酵加工及益生菌果汁饮料产品开发提供一定的理论依据。