Bacteriocinogenic Lactobacillus plantarum ST16Pa isolated from papaya (Carica papaya) — From isolation to application: Characterization of a bacteriocin

Strain ST16PA, isolated from papaya was identified as Lactobacillus plantarum based on biochemical tests, PCR with species-specific primers and 16S rDNA sequencing. L. plantarum ST16PA produces a 6.5 kDa bacteriocin, active against different species from genera Enterobacter, Enterococcus, Lactobacillus, Pseudomonas, Streptococcus and Staphylococcus and different serotypes of Listeria spp. The peptide is inactivated by proteolytic enzymes, but not when treated with ??-amylase, catalase, lipase, Triton X-100, SDS, Tween 20, Tween 80, urea, NaCl and EDTA. However, presence of 1% Triton X-114 deactivates the bacteriocin. No change in activity was recorded after 2 h at pH values between 2.0 and 12.0, and after treatment at 100 °C for 120 min or 121 °C for 20 min. The mode of activity against Lactobacillus sakei ATCC 15521, Enterococcus faecalis ATCC 19443 and Listeria innocua 2030C was bactericidal, resulting in cell lysis and enzyme-leakage. No significant differences in cell growth and bacteriocin production were observed when strain ST16Pa was cultured in MRS broth at 26 °C and 30 °C for 24 h (25 600 AU/ml). However, even though strain ST16PA grows well in MRS broth at 15 °C and 37 °C, a reduction of bacteriocin production was observed (400 AU/ml and 1600 AU/ml, respectively). In addition, effect of MRS medium components, different initial pH and additions of glycerol or vitamins to the media on bacteriocin ST16Pa production was studied.Peptide ST16PA adsorbs (400 AU/ml) to producer cells. However, bacteriocin ST16Pa was adsorbed at 50% to cells of L. innocua 2030C and at 75% to L. sakei ATCC 15521 and E. faecalis ATCC 19433 when experiments were conducted at 30 °C and pH 6.5. Adsorption of bacteriocin ST16Pa to target cells at different temperatures, pH and in presence of potassium sorbate, sodium nitrate, sodium chloride, ascorbic acid, Tween 80 and Tween 20 were also studied. To the best of our knowledge, this is the first report on detection of L. plantarum in papaya.     

Methyl jasmonate enhances biocontrol efficacy of Rhodotorula glutinis to postharvest blue mold decay of pears

The effect of Rhodotorula glutinis treatment alone or in combination with methyl jasmonate (MeJA) in controlling blue mold decay, the natural fungal decay of pears and the postharvest quality parameters including fruit firmness, total soluble solids, titratable acidity, and ascorbic acid were investigated. The combination of methyl jasmonate (200 μM) and R. glutinis (1 × 10⁸ CFU/ml) was a more effective approach to reduce the disease incidence and lesion diameter of blue mold decay of pears than the application of MeJA or R. glutinis alone after incubation for 7 d at 20 °C. The natural fungal decay of pears treated with the application of R. glutinis combined with MeJA resulted in reduced average decay incidence of 10.42% or 4.16%, respectively, compared with 27.17% or 20.83% in the control fruits following storage at 20 °C for 15 d or 4 °C for 60 d followed by 20 °C for 15 d. The combined treatment did not impair quality parameters of fruits under both conditions.     

Influences of preharvest spraying Cryptococcus laurentii combined with postharvest chitosan coating on postharvest diseases and quality of table grapes in storage

The effects of preharvest spray with Cryptococcus laurentii combined with chitosan coating after harvest on decay and quality of table grapes during storage periods were evaluated in the present study. Preharvest spray with C. laurentii (PreA) significantly decreased decay index (DI), and postharvest chitosan coating (PCC) enhanced the effectiveness of the pre-harvest spray when fruits were stored at 0 °C. PreA combination with PCC increased the activities of polyphenol oxidase (PPO) and phenylalanine ammonia-lyase (PAL) of fruit in storage. PreA + PCC treatment was effective in reducing weight loss of fruits by 85% at 17 d storage and 38% at 42 d storage as compared to PreA alone at the same stage. In addition, PreA enhanced the ratio of soluble solids content (SSC) to titratable acid (TA) by 12% at harvest time, 7% at 17 d storage and 25% at 42 d storage, mainly by increasing SSC and decreasing TA in fruit stored at 0 °C. These results suggested that integration of preharvest spray with C. laurentii and postharvest chitosan coating treatment may be a promising management strategy for decay control and quality maintenance of table grapes.     

Salicylic acid enhances biocontrol efficacy of Rhodotorula glutinis against postharvest Rhizopus rot of strawberries and the possible mechanisms involved

The potential of using Rhodotorula glutinis alone or in combination with salicylic acid (SA) for the control of postharvest Rhizopus rot of strawberries, and their effects on enzyme activities of fruits were investigated. The combination of R. glutinis (1 × 10⁸ CFU ml⁻¹) with SA (100 μg ml⁻¹) resulted in a significant reduction in the disease incidence and lesion diameter of Rhizopus rot on the strawberry fruits at 20 °C and 4 °C, and more so than with SA or yeast alone. SA at the concentration of 100–1000 μg ml⁻¹ significantly inhibited spore germination of Rhizopus stolonifer. About 100 μg ml⁻¹ of SA did not inhibit the growth of the antagonistic yeast, and could significantly increase the population growth of R. glutinis in strawberry wounds at 20 °C. SA, combined with R. glutinis, increased the activity of strawberry host defence enzymes (POD) and cell wall lytic enzymes (β-1,3-glucanase).     

Heat resistance of Listeria species to liquid whole egg ultrapasteurization treatment

The lethality of ultrapasteurization treatments (70 °C/1.5 min.) applied at constant temperature (isothermal condition) and at a constantly raising temperature of 2 °C/min (non-isothermal condition) in liquid whole egg (LWE) against two strains of Listeria monocytogenes (STCC 5672 and 4032) and one of Listeria innocua has been investigated. Isothermal survival curves up to 71 °C were obtained, which followed first-order inactivation kinetics. The obtained D_t values indicated that L. innocua was significantly (p < 0.05) more heat resistant than L. monocytogenes strains. Non-significant (p > 0.05) differences were observed among z values (12.4 ± 0.4 °C, 13.1 ± 0.4 °C and 12.2 ± 0.7 °C for L. innocua and L. monocytogenes 5672 and 4032, respectively). Based on obtained D_t and z values, isothermal ultrapasteurization treatment (70 °C/1.5 min.) would provide 3.5-, 5.0-, and 6.5-Log₁₀ cycles of L. innocua and L. monocytogenes 5672 and 4032, respectively. Non-isothermal heating lag phase increased the thermotolerance of Listeria species in LWE. The simulated industrial pasteurization treatment for LWE (heating-up phase from 25 to 70 °C followed by 1.5 min. at 70 °C) would attain 5-Log₁₀ reductions of L. monocytogenes 5672 and 4032, and 3.7-Log₁₀ reductions of L. innocua. Therefore, the safety level of industrial ultrapasteurization concerning L. monocytogenes could be lower than that estimated with data obtained under isothermal conditions.     

Changes in anthocyanins in arils of chitosan-coated pomegranate (Punica granatum L. cv. Rabbab-e-Neyriz) fruit during cold storage

Edible coatings as chitosan treatments (0%, 1% and 2%) were applied to ‘Rabbab-e-Neyriz’ pomegranate (Punica granatum L.). The effect of chitosan coating on individual anthocyanins and colour parameters of the juice during storage at 2 °C or 5 °C was examined. Six predominant anthocyanins were identified in the juice, with up to 935 mg/L total anthocyanins at the time of harvest. Cyanidin 3,5-diglucoside (402 mg/L) was the major pigment. The total anthocyanin content and chroma decreased with storage time in all applied treatments, although lightness and hue angle increased. These changes were reduced with chitosan treatments and at lower storage temperature (2 °C as compared to 5 °C). Based on the obtained results, the diglucoside anthocyanins were more stable than the monoglucosides. Chitosan coating followed by cold storage delayed anthocyanin degradation and prevented colour deterioration in the pomegranate arils.     

Effect of the application of intermittent drying on Ilex paraguariensis quality and drying kinetics

The aim of this work was to study the effects of the application of tempering periods on the drying kinetics of yerba maté branches and on the resultant quality parameters of the finished product. Experiments were carried out in a convective pilot plant drier. Air temperature (60, 80 and 100 °C) and tempering time (0, 15 and 30 min) influenced the drying kinetics and the product quality (color parameters L and b, and the sugar and caffeine contents of an infusion prepared with the material). The influence of tempering time was higher at 60 °C than at the other temperatures. There were no differences between tempering times of 15 and 30 min. The Page model yielded a good fit to the experimental data, where the model parameter k varied with drying temperature.     

Effect of polythene film activated with enterocin EJ97 in combination with EDTA against Bacillus coagulans

Polythene films coated with the enterococcal bacteriocin enterocin EJ97 alone or in combination with EDTA were tested against Bacillus coagulans CECT 12. Bacteriocin activity was clearly enhanced by EDTA, as shown by viable staining and epifluorescence microscopy observation of treated cells. Activated films were tested in liquids from canned corn and canned peas inoculated with B. coagulans cell suspensions and stored at 4 °C and 20 °C for 24 h. The bacteriocin alone showed highest activity in samples stored at 4 °C, while the maximum performance of EDTA was observed at 20 °C. Films activated with a combination of both antimicrobials showed highest bactericidal activity at 4 °C. In liquid from canned corn and peas stored at 4 °C, the combined treatment reduced the concentrations of viable cells progressively over incubation time. Viable staining revealed an increase in the percentage of dead cells at 20 °C, avoiding proliferation of the bacilli. The bactericidal effect of the combined antimicrobial agents was higher in the liquid of canned peas than that of canned corn. The combined use of viable staining and classical viable cell counts allowed a better estimation of cell damage caused by the antimicrobial treatments.     

Nonthermal inactivation and sublethal injury of Lactobacillus plantarum in apple cider by a pilot plant scale continuous supercritical carbon dioxide system

The objective of this study was to evaluate the efficacy of supercritical carbon dioxide (SCCO₂) for inactivating Lactobacillus plantarum in apple cider using a continuous system with a gas-liquid metal contactor. Pasteurized apple cider without preservatives was inoculated with L. plantarum and processed using a SCCO₂ system at a CO₂ concentration range of 0-12% (g CO₂/100 g product), outlet temperatures of 34, 38, and 42 °C, a system pressure of 7.6 MPa, and a flow rate of 1 L/min. Processing with SCCO₂ significantly (P < 0.05) enhanced inactivation of L. plantarum in apple cider, resulting in a 5 log reduction with 8% CO₂ at 42 °C. The response surface model indicated that both CO₂ concentration and temperature contributed to the microbial inactivation. The extent of sublethal injury in surviving cells in processed apple cider increased as CO₂ concentration and processing temperature increased, however the percent injury dramatically decreased during SCCO₂ processing at 42 °C. Structural damage in cell membranes after SCCO₂ processing was observed by SEM. Refrigeration (4 °C) after SCCO₂ processing effectively inhibited the re-growth of surviving L. plantarum during storage for 28 days. Thus this study suggests that SCCO₂ processing is effective in eliminating L. plantarum and could be applicable for nonthermal pasteurization of apple cider.     

Fate of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella on fresh-cut celery

Illnesses from Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella have been associated with the consumption of numerous produce items. Little is known about the effect of consumer handling practices on the fate of these pathogens on celery. The objective of this study was to determine pathogen behavior at different temperatures under different storage conditions. Commercial fresh-cut celery was inoculated at ca. 3 log CFU/g onto either freshly cut or outer uncut surfaces and stored in either sealed polyethylene bags or closed containers. Samples were enumerated following storage for 0, 1, 3, 5, and 7 days when held at 4 °C or 12 °C, and after 0, 8, and 17 h, and 1, and 2 days when held at 22 °C. At 4 °C, all populations declined by 0.5–1.0 log CFU/g over 7 days. At 12 °C, E. coli O157:H7 and Salmonella populations did not change, while L. monocytogenes populations increased by ca. 0.5 log CFU/g over 7 days. At 22 °C, E. coli O157:H7, Salmonella, and L. monocytogenes populations increased by ca. 1, 2, or 0.3 log CFU/g, respectively, with the majority of growth occurring during the first 17 h. On occasion, populations on cut surfaces were significantly higher than those on uncut surfaces. Results indicate that populations are reduced under refrigeration, but survive and may grow at elevated temperatures.     

A brief study on the degradation kinetics of seven organophosphorus pesticides in skimmed milk cultured with Lactobacillus spp. at 42 °C

Seven organophosphorus pesticides (OPPs) including dimethoate, fenthion, malathion, methyl parathion, monocrotophos, phorate and trichlorphon were added to skimmed milk. The milk was inoculated with one strain of Lactobacillus spp. including L. bulgaricus, L. paracasei and L. plantarum, and cultured at 42 °C for 24 h to investigate their impacts on degradation kinetics of the OPPs. The residual OPPs in the milk were extracted by an extraction solvent and quantified in a gas chromatography after purification. Degradation rate constant and half live periods of the OPPs were calculated from a first-order reaction kinetics model. The result shows that the selected Lactobacillus spp. exhibited some acceleration on OPPs degradation totally. Dimethoate and methyl parathion were more stable but malathion was the most labile. Both L. bulgaricus and L. plantarum had stronger acceleration on the degradation of the OPPs studied.     

Evaluation and characterisation of Citrullus colocynthis (L.) Schrad seed oil: Comparison with Helianthus annuus (sunflower) seed oil

The physicochemical properties, fatty acid, tocopherol, thermal properties, ¹H NMR, FTIR and profiles of non-conventional oil extracted from Citrullus colocynthis (L.) Schrad seeds were evaluated and compared with conventional sunflower seed oil. In addition, the antioxidant properties of C. colocynthis seed oil were also evaluated. The oil content of the C. colocynthis seeds was 23.16%. The main fatty acids in the oil were linoleic acid (66.73%) followed by oleic acid (14.78%), palmitic acid (9.74%), and stearic acid (7.37%). The tocopherol content was 121.85 mg/100 g with γ-tocopherol as the major one (95.49%). The thermogravimetric analysis showed that the oil was thermally stable up to 286.57 °C, and then began to decompose in four stages namely at 377.4 °C, 408.4 °C, 434.9 °C and 559.2 °C. The present study showed that this non-conventional C. colocynthis seed oil can be used for food and non-food applications to supplement or replace some of the conventional oils.     

The effects of the combination of Pichia membranefaciens and BTH on controlling of blue mould decay caused by Penicillium expansum in peach fruit

The feasibility of 0.2 g l⁻¹ benzo-thiadiazole-7-carbothioic acid S-methyl ester (BTH) to improve the efficacy of Pichia membranefaciens in controlling postharvest blue mould decay in peach fruit was investigated. Our results showed that biocontrol activity of P. membranefaciens against blue mould caused by Penicillium expansum in peach fruit could be enhanced by addition of 0.2 g l⁻¹ BTH. The combination of P. membranefaciens and BTH resulted in a more effective control of blue mould than individual treatment of P. membranefaciens or BTH alone. The combined treatment had a synergistic effect on the induction of superoxide dismutase, catalase, ascorbate peroxidase, chitinase and β-1,3-glucanase activities, which induced stronger disease resistance in fruit than BTH or yeast alone, and resulted in a lower lesion diameter and disease incidence of blue mould decay in peaches. Furthermore, the combined treatment did not impair the quality parameters including fruit firmness and contents of total soluble solids, titratable acidity and vitamin C of peach fruit after 6 days of storage at 20 °C. These results suggested that the use of BTH may be an effective method to improve the biological activity of P. membranefaciens.     

Probiotic beverage from cashew apple juice fermented with Lactobacillus casei

This study optimized the conditions of Lactobacillus casei NRRL B-442 cultivation in cashew apple juice, as well as, determined the proper inoculum amount and fermentation time. Moreover, it was investigated the survivability ability of L. casei in cashew apple juice during refrigerated storage (4 °C) for 42 days. The optimum conditions for probiotic cashew apple juice production were initial pH 6.4, fermentation temperature of 30 °C, inoculation level of 7.48 Log CFU/mL (L. casei) and 16 h of fermentation process. It was observed that the L. casei grew during the refrigerated storage. Viable cell counts were higher than 8.00 Log CFU/mL throughout the storage period (42 days). The values of lightness, yellowness and total color change increased and the values of redness reduced along the fermentation and refrigerated storage periods. The fermented juice with L. casei is a good and healthy alternative functional food containing probiotics. Cashew apple juice showed to be as efficient as dairy products for L. casei growth.     

Phenolics, betacyanins and antioxidant activity in Opuntia joconostle fruits

Sour prickly pears (xoconostles) are fruits from Opuntia joconostle cactus, which are cultivated in the central Mexico area. Phenolic and pigment content in various parts of O. joconostle fruits were analyzed. The antioxidant activity of a methanolic extraction and different semi-purified fractions were also evaluated by the DPPH⁺ method. Xoconostle fruits were obtained from a commercial orchard in Mexico State. Fruits were analyzed as whole fruit and each fruit part including pericarp, mesocarp and endocarp. Samples were homogenized and kept at 4 °C until sample preparation. Total phenolic content and total flavonoid content varied among the different parts of the fruit. The highest amount of phenolic compounds and total flavonoids content were found in pericarp 2.07 mg gallic acid equivalents (GAE)/g fresh weight (FW) and 0.46 mg(+)-catechin equivalents (CE)/g FW respectively. Seven phenolics were identified as protocatechuic, 4-hydroxybenzoic, caffeic, vanillic and syringic acids, rutin, and quercetin. The color of the fruit parts was mainly due to the presence of betacyanins. The betacyanin concentration was higher in the endocarp (23.03 mg betanin equivalents/100 g fresh weight) than in the pericarp and mesocarp. Betacyanins were identified by HPLC-PDA-MS as betanin, isobetanin, betanidin, isobetanidin, and phyllocactin. Methanolic extracts and semi-purified fractions A (phenolics and flavonols) and B (betacyanins) of xoconostle showed high antioxidant activity mainly in the pericarp. These results suggest that xoconostle is a rich source of antioxidant compounds such as phenolic compounds and betacyanins.     

Antioxidant action of ganghwayakssuk (Artemisia princeps Pamp.) in combination with ascorbic acid to increase the shelf life in raw and deep fried chicken nuggets

Raw and deep fried chicken nuggets containing various levels of ganghwayakssuk ethanolic extract (GE) in combination with ascorbic acid (Aa) were evaluated for shelf-life during refrigerated storage (4 °C). The pH and color (lightness, redness, and yellowness) values of raw and deep fried samples were significantly affected by the addition of GE (P < 0.05). All antioxidant combinations except for Aa + GE 0.01 were effective at delaying lipid oxidation (CD, POV, and TBARS) when compared to the control or Aa. Raw samples with GE 0.2 and Aa + GE 0.1 exhibited lower bacterial populations during storage. The sensory characteristics (color, juiciness, flavor, tenderness, and overall acceptability) did not differ significantly in all deep fried chicken nugget samples, except color, whereas storage time had a significant effect (P < 0.05). The results suggest the possibility of utilizing raw and deep fried chicken nuggets with a mixture of ganghwayakssuk and ascorbic acid for the increase of shelf-life and quality.     

Survival of human derived Lactobacillus plantarum in fermented cereal extracts during refrigerated storage

The aim of this study was to investigate the survival of a potentially probiotic Lactobacillus plantarum strain in barley, wheat and barley malt extracts. The extracts were produced from three flour/water suspensions, i.e., 5%, 20%, 30% w/w. After inoculation, the cultures were incubated for 24 h at 37 °C, and were subsequently stored at 4 °C for up to seventy days. The lactic acid and reducing sugar concentrations at the beginning of storage were significantly different between the fermented media, ranging from 0.5 g/L to 17 g/L and from 0.8 g/L to 6.5 g/L respectively, while the pH ranged between 2.9 and 3.4. It was observed that the cells survived much better in the malt extracts compared to barley and wheat extracts during refrigerated storage. Based on the results from a study using model media and supplemented cereal extracts it was derived that this was most likely due to their higher sugar concentration and the presence of protective unidentified compounds, albeit the fact that the malt extracts contained higher amounts of lactic acid.     

Evaluation of culture media for enumeration of Lactobacillus acidophilus, Lactobacillus casei and Bifidobacterium animalis in the presence of Lactobacillus delbrueckii subsp bulgaricus and Streptococcus thermophilus

The study compared the growth capability of probiotic (Lactobacillus acidophilus La05, Lactobacillus casei Lc01 and Bifidobacterium animalis Bb12) and non-probiotic (Lactobacillus delbrueckii subsp bulgaricus and Streptococcus thermophilus) cultures on twenty-one culture media grouped according to selectivity: non-selective agars, selective agars without antibiotics and MRS agars containing different combinations of lithium chloride, cystein, bile salts and antibiotics. Four of these media were selected for quantitative enumeration of L. acidophilus La05, L. casei Lc01, and B. animalis Bb12. The best culture media and incubation conditions for enumeration of the probiotic cultures were: B. animalis: MRS agar with dicloxacillin, 37 °C or 42 °C, anaerobiosis; L. acidophilus: MRS agar with bile salts, 37 °C or 42 °C, aerobiosis; L. casei: MRS agar with lithium chloride and sodium propionate, 37 °C or 42 °C, aerobiosis or anaerobiosis. Plating on MRS with glucose replaced by maltose, 37 °C or 42 °C, anaerobiosis, will distinguish probiotic from non-probiotic cultures. For enumeration of each probiotic in a mixed culture, the following media and incubation conditions were recommended: B. animalis: 4ABC-MRS, 42 °C, anaerobiosis, L. acidophilus: LC medium, 42 °C, aerobiosis or anaerobiosis and L. casei: LP-MRS, 42 °C, aerobiosis or anaerobiosis. In all experiments, differences in counts using pour plating or surface plating were not significant (P ≤ 0.05).     

Thermal inactivation of Salmonella spp. during conching

Although chocolate is a microbiologically stable product it has been described as a vehicle for Salmonella spp. Because of the low water activity (a_w) and the high fat content of chocolate Salmonella spp. shows an increased heat resistance, even during the thermal process of chocolate making. The aim of this study was to evaluate the thermal inactivation of Salmonella spp. during conching in various masses of chocolate and cocoa butter at different temperatures (50-90 °C). The effect of thermal treatment on Salmonella spp. was determined with the MPN (Most-Probable-Number) method. Results of thermal treatment showed approximate D-values for cocoa butter from D_50°C = 245 min to D_60°C = 306 min, for cocoa liquor from D_50°C = 999 min to D_90°C = 26 min and for dark chocolate of D_50°C = 1574 min. z-values were found to be z = 20 °C in cocoa liquor and z = 14 °C in dark chocolate. This study demonstrates that the conching process alone does not ensure the inactivation of Salmonella spp. in different chocolate masses and that an additional decontamination step at the beginning of the process as well as an HACCP concept is necessary during chocolate production to guarantee the absence of Salmonella spp. in chocolates and related products.     

Characterization of polyphenol oxidase from butter lettuce (Lactuca sativa var. capitata L.)

Polyphenol oxidase (PPO) was isolated from butter lettuce (Lactuca sativa var. capitata L.) grown in Poland and its biochemical characteristic were studied. PPO from butter lettuce showed a higher affinity to 4-methylcatechol than to catechol. The K_M and V_max values were: 3.20 ± 0.01 mM and 4081 ± 8 U/ml min⁻¹ for catechol and 1.00 ± 0.09 mM and 5405 ± 3 U/ml min⁻¹ for 4-methylcatechol. The optimum pHs of the enzyme were found to be 5.5 using catechol and 6.8 using 4-methylcatechol as substrate. The enzyme had a temperature optimum of 35 °C. The enzyme was relatively stable at 30 °C and 40 °C. The times required for 50% inactivation of activity at 50 °C, 60 °C and 70 °C were found to be about 30, 20 and 5 min, respectively. Inhibitors used for investigation in this study were placed in relative order of inhibition: p-hydroxybenzoic acid > glutathione ≈ ascorbic acid > l-cysteine > EDTA > citric acid. The enzyme eluted in the chromatographic separations was analyzed electrophoretically under denaturating conditions. The analysis revealed a single band on the SDS–PAGE which corresponded to a molecular weight of 60 kDa.