Effectiveness of lemon juice in the elimination of Salmonella Typhimurium in stuffed mussels

Street foods are becoming more and more prominent in countries all over the world. There are many reports of disease due to consumption of street foods contaminated by pathogens. With the modern trend toward more natural preservatives, the use of organic acids can achieve a good microbiological safety in food. In the present study, stuffed mussels were inoculated with Salmonella Typhimurium suspension to provide initial populations of approximately 6 and 3 log CFU/g. After inoculation, samples were treated with fresh lemon juice and lemon dressing for 0, 5, and 15 min, and pathogens were enumerated by using direct plating on brilliant green agar. Treatment of stuffed mussels inoculated at high inoculum level, with lemon juice and lemon dressing for different exposure times caused reduction ranging between 0.25 and 0.56 log CFU/g and 0.5 and 0.69 log CFU/g, respectively, whereas in stuffed-mussel samples inoculated at low level, lemon juice and lemon dressing caused 0.08 to 0.25 log CFU/g and 0.22 to 0.78 log CFU/g reductions, respectively. Results of the study showed that both lemon juice and lemon dressing used as flavoring and acidifying agents for stuffed mussels caused slight decrease in Salmonella Typhimurium as an immediate inhibitor, but this effect increased by time. However, treatment of stuffed mussels with the inhibitors until 15 min is not enough to prevent Salmonella Typhimurium outbreaks related to stuffed mussels.     

On the induction of cold acclimation in carrots (Daucus carota L.) and its influence on storage performance

We investigated the role of cold acclimation in carrot plants with respect to its influence on the storage performance of the harvested taproots. The induction of cold acclimation was followed in plants cultivated in a growth chamber under strict climate control and in taproots harvested from two separate field cultivations where the plants had been exposed to the natural variations in climate. Under controlled growth conditions, levels of antifreeze protein (AFP) mRNA were used as a marker for cold acclimation in carrot taproot tissue. Expression of this gene was induced by cold in discs excised from harvested taproots and this induction was clearly affected by the growth temperature of the plants from which the taproots were taken. These in vitro data were consistent with those from field-grown plants. In the cell wall of taproots harvested in year 2000, where the intact plants had frequently been exposed to temperatures below 6 °C, a 36 kDa AFP accumulated to higher levels during storage than in the taproots harvested from plants grown in year 2001, where cultivation temperatures had rarely dropped below 6 °C. The taproots from 2001 exhibited poor storage performance as shown by an earlier increase in relative electrolyte leakage and decrease in dry matter compared to taproots harvested in 2000. The capacity of the AFP to accumulate during storage was consistent with a high storage performance.     

Nitrogen nutrition and flavour compounds of carrots (Daucus carota L) cultivated in Mitscherlich pots

Carrots (Daucus carota L) of the cultivar ‘Nanthya’ F₁ were grown in Mitscherlich pots containing quartz sand with inorganic nitrogen fertilisation (five levels, four replications) and time‐controlled drip irrigation. The effect of different nitrogen uptake on the yield and on the amount and composition of essential oils, sugars and organic acids was investigated. Sucrose, glucose and fructose were extracted and analysed by HPLC; L ‐malic acid and citric acid were measured with an enzymatic test. Medium‐ and higher‐boiling flavour components were isolated as essential oils by simultaneous watersteam distillation and pentane extraction (SDE) and separated gas chromatographically (HRGC–FID). Thirteen essential oil components were identified by mass spectrometry as well as by comparison of retention times and quantified by external standards. The higher the supply of nitrogen, the higher was its uptake and as a consequence the higher were the nitrogen and nitrate contents of the leaves as well as the roots of the carrots. Carrots with lower nitrogen application had higher amounts of sucrose and essential oils but lower amounts of glucose and fructose. Fertilisation with nitrogen affected not only the total content but also the composition of the essential oils. A correlation between nitrogen nutrition and organic acids could not be found. © 2000 Society of Chemical Industry     

Effectiveness of household natural sanitizers in the elimination of Salmonella typhimurium on rocket (Eruca sativa Miller) and spring onion (Allium cepa L.)

Experiments were done with fresh lemon juice, vinegar and their mixture (1:1) to evaluate their efficacy in reducing the numbers of Salmonella typhimurium on fresh salad vegetables. Fresh whole rocket leaves and shredded spring onion samples were inoculated with S. typhimurium suspensions to provide initial populations of approximately 6 and 3 log cfu/g. After inoculation, vegetables were treated with the test solutions for 0, 15, 30 and 60 min, and pathogens were enumerated by using direct plating on Bismuth Sulphite Agar (BSA). Prior to this work, it was shown that BSA was not toxic for acid injured Salmonella cells by statistical analysis applied to enriched and non-enriched samples (P>0.05). Treatment of rocket leaves with fresh lemon juice and vinegar caused a significant reduction ranging between 1.23 and 4.17 log cfu/g and between 1.32 and 3.12 log cfu/g, respectively, while the maximum reduction reached by using lemon juice-vinegar mixture (1:1) for 15 min, which reduced the number of pathogens to an undetectable level. In the spring onion samples, lemon juice, vinegar and their mixture caused 0.87-2.93, 0.66-2.92 and 0.86-3.24 log cfu/g reductions, respectively.     

Optimization of enzymatic process parameters for increased juice yield from carrot (Daucus carota L.) using response surface methodology

The effects of enzyme concentration (50–650 mg/kg grated carrot), pectolytic and cellulolytic enzyme ratio (3:7–7:3), incubation time (30–150 min) and temperature (25–65 °C) on juice recovery and viscosity from grated carrot were studied. A central composite rotatable design (CCRD) was used in designing the treatment combinations of four variables at five levels. The process involved in treating the blanched grated carrot with mixture of crude pectolytic enzyme from Aspergillus foetidus and crude cellulolytic enzyme from Trichoderma ressi, keeping the samples at the desired time, followed by extraction of juice. Enzyme-treated grated carrot sample showed increased juice recovery as compared to control. A second-order response surface model adequately fitted the data. All the variables affected juice recovery and viscosity significantly. Enzyme concentration, pectolytic and cellulolytic enzyme ratio, incubation time and temperature had total and combined effect at linear, square and interactive level on both responses. The optimum condition was enzyme concentration, 210.7 mg/kg of grated carrot; pectolytic and cellulolytic enzyme ratio, 3.84:6.16; incubation time, 130 min and incubation temperature 47 °C. Under the optimal conditions, juice extracted from enzyme-treated grated carrot was 74.3% having juice viscosity 1.07 cP, corresponding to the increase in yield by 13.95% and decrease in viscosity by 0.45 cP.     

Low Frequency Ultrasonics for Texture Measurements in Cooked Carrots (Daucus carota L.)

The use of low frequency ultrasound for texture evaluation of carrots cooked at 100°C for 0 to 15 min was examined. Uniaxial compression, microscopy and analyses of density and dry matter were used to provide comparative results for evaluating relationships between texture and ultrasonic parameters. During the first minutes of cooking the sound velocity (v) decreased and a positive correlation was found between compressive Young's modulus (E_cy) and sound velocity (v). During extended heating, sound velocity (v) increased and attenuation (α) decreased as a result of changes in mechanical properties and air and water content of the tissue.     

Combined effects of coating, modified atmosphere packaging, and gamma irradiation on quality maintenance of ready-to-use carrots (Daucus carota)

The objective of this study was to evaluate the effect of an edible coating combined with modified atmosphere (MA; 60% O2, 30% CO2, and 10% N2) packaging and gamma irradiation on the microbiological stability and physicochemical quality of minimally processed carrots. A coating based on calcium caseinate and whey protein isolates was used. Coated and uncoated peeled minicarrots were packed under the MA or air (78.1% N2, 20.9% O2, and 0.036% CO2), irradiated at 0.5 or 1 kGy, and stored at 4 +/- 1 degrees C for 21 days. Samples were evaluated periodically for aerobic plates counts (APCs) and physicochemical properties (firmness, white discoloration, and whiteness index). Gamma irradiation did not significantly affect the physicochemical properties of the carrots (P > 0.05). Microbiological analysis revealed that for uncoated carrots irradiation at 0.5 and 1 kGy under air and MA reduced the APCs by 3.5 and 4 log CFU/g and by 4 and 4.5 log CFU/g, respectively. For coated carrots, irradiation at 0.5 and 1 kGy under air and MA reduced the APCs by 4 and 4.5 log CFU/g and by 3 and 4.25 log CFU/g, respectively. The coating was able to protect carrots against dehydration during storage under air. Coating and irradiation at 1 kGy were also able to protect carrot firmness during storage under air. MA packaging retarded whitening of uncoated carrots but had a detrimental effect on firmness. The edible coating used in this study did not significantly inhibit (P > 0.05) microbial growth on carrots.     

Combined effects of antimicrobial coating, modified atmosphere packaging, and gamma irradiation on Listeria innocua present in ready-to-use carrots (Daucus carota)

The objective of this study was to evaluate the effect of an edible antimicrobial coating combined with modified atmosphere (MA) packaging (60% O2, 30% CO2, and 10% N2) and gamma irradiation on peeled minicarrots inoculated with Listeria innocua. Carrots were inoculated with L. innocua (10(3) CFU/g) and then coated with an antimicrobial coating based on calcium caseinate containing trans-cinnamaldehyde. The same formulation without trans-cinnamaldehyde was used as an inactive coating. Coated and uncoated carrots were packed under the MA or under air, irradiated at 0.25 or 0.5 kGy, and stored at 4 +/- 1 degrees C for 21 days. Samples were evaluated periodically for enumeration of L. innocua. Unirradiated carrots stored under air had the highest concentrations of L. innocua after 21 days of storage: 2.23 CFU/g in the uncoated samples and 2.26 CFU/ g in samples coated with the inactive coating. These results suggest that the inactive coating did not have any antimicrobial effect against L. innocua. However, the addition of the antimicrobial coating resulted in a 1.29-log reduction in the concentration of L. innocua in carrots packed under air after 21 days of storage and a 1.08-log reduction in carrots packed under MA after 7 days of storage. After 7 days of storage, no L. innocua was detected in samples treated at 0.5 kGy under air or in samples treated at 0.25 kGy under MA. A complete inhibition of L. innocua was also observed during all storage periods in uncoated and coated samples treated at 0.5 kGy under MA. These results indicate that the combination of irradiation and MA conditions play an important role in the radiosensitization of L. innocua.     

Effectiveness of radiation processing in elimination of Salmonella typhimurium and Listeria monocytogenes from sprouts

The effectiveness of radiation treatment in eliminating Salmonella Typhimurium and Listeria monocytogenes on laboratory inoculated ready-to-eat sprouts was studied. Decimal reduction doses (D10-values) for Salmonella Typhimurium and L. monocytogenes in dry seeds of mung (green gram), matki (dew gram), chana (chick pea), and vatana (garden pea) ranged from 0.189 to 0.303 kGy and 0.294 to 0.344 kGy, respectively. In sprouts made from these seeds, the D10-values ranged from 0.192 to 0.208 kGy for Salmonella Typhimurium and from 0.526 to 0.588 kGy for L. monocytogenes. Radiation treatment with a 2-kGy dose resulted in complete elimination of 10(4) CFU/g of Salmonella Typhimurium and 10(3) CFU/g of L. monocytogenes from all the four varieties of sprouts. No recovery of Salmonella Typhimurium and L. monocytogenes was observed in the radiation treated samples stored at 4 and 8 degrees C up to 12 days. Radiation treatment with 1 kGy and 2 kGy resulted in a reduction of aerobic plate counts and coliform counts by 2 and 4 log CFU/g, respectively; the yeast and mold counts and staphylococci counts decreased by 1 and 2 log CFU/g, respectively. However, during postirradiation storage at 4 and 8 degrees C, aerobic plate counts, coliform counts, yeast and mold counts, and staphylococci counts remained constant throughout the incubation period. This study demonstrates that a 2-kGy dose of irradiation could be an effective method of processing to ensure microbial safety of sprouts.     

Influence of antimicrobial compounds and modified atmosphere packaging on radiation sensitivity of Listeria monocytogenes present in ready-to-use carrots (Daucus carota)

Radiosensitization of Listeria monocytogenes was determined in the presence of trans-cinnamaldehyde, Spanish oregano, winter savory, and Chinese cinnamon on peeled minicarrots packed under air or under a modified atmosphere (60% O2, 30% CO2, and 10% N2). Samples were inoculated with L. monocytogenes HPB 2812 serovar 1/2a (106 CFU/g) and were coated separately with each active compound (0.5%, wt/wt) before being packaged under air or the modified atmosphere and irradiated at doses from 0.07 to 2.4 kGy. Results indicated that the bacterium was more resistant to irradiation under air in the absence of active compound. The dose required to reduce L. monocytogenes population by 1 log CFU (D10) was 0.36 kGy for samples packed under air and 0.17 kGy for those packed under the modified atmosphere. The active compounds evaluated in this study had an effect on the radiation sensitivity of L. monocytogenes on carrots. The most efficient compound was trans-cinnamaldehyde, where a mean 3.8-fold increase in relative radiation sensitivity was observed for both atmospheres compared with the control. The addition of winter savory and Chinese cinnamon produced a similar increase in relative radiation sensitivity but only when samples where packed under modified atmosphere conditions.     

Activity,localisation and thermal inactivation of deteriorative enzymes in Australian carrot (Daucus carota L) varieties

Four Australian carrot varieties have been selected for a study of deteriorative enzymes. The varieties included those commonly used for table and also for processing purposes (Red Hot Original, Red Count, Top Pak and Red Hot Carotene 100). The activities of three deteriorative enzymes (peroxidase, catechol oxidase and pectinesterase) have been assayed in juices prepared from whole carrot as well as superficial tissues, core, root tip and stem end. The levels and relative distribution vary for the different enzymes and varieties studied. Thermal inactivation was assessed over a range of temperatures. Catechol oxidase was found to be the least stable and pectinesterase the most stable in each of the varieties. In most cases, effective inactivation was achieved within 2 min at 85 °C. The enzymes of Top Pak variety showed greater thermal stability. In this variety, pectinesterase required treatment at 90 °C to ensure rapid inactivation. It is concluded that pectinesterase should be used as the indicator enzyme in the assessment of blanching sufficiency for processing of carrots. © 1999 Society of Chemical Industry     

Autoclaving effects on the dietary fibre content of carrots (Daucus carota) and turnips (Brassica napus): an evaluation of different methods

Different methods have been used to evaluate variations in the dietary fibre content of carrots and turnips during autoclaving. Autoclaving was carried out at 121°C under pressure for 15 min. The methods used were the gravimetric (neutral and acid detergent fibre) method, the enzymatic-gravimetric method for (insoluble and soluble fibre and the spectrophotometric method for pectic substances. When the methodologies were compared it was observed that in raw carrots and turnips, the neutral detergent fibre and insoluble fibre contents were statistically different (P<0.05). This was not the case for processed samples of the vegetables. The correlation between the different methodologies was studied. A good correlation was found between neutral detergent fibre and insoluble fibre in raw turnips (r = 0.999). Variance analysis indicated that quantitative variations resulting after thermal treatment were statistically significant (P<0.05) for neutral detergent fibre in carrots (raw = 1.97%, processed = 1.68%), and for pectic substances in carrots (raw = 0.54%, processed = 0.47%) and turnips (raw = 0.33%, processed = 0.25%). Optical microscopy has been used to identify different dietary fibre components in raw and processed samples.     

The survival of E. coli O157:H7, S. Typhimurium and L. monocytogenes in black carrot (Daucus carota) juice

In this study the survival and growth patterns of Escherichia coli O157:H7, Salmonella Typhimurium and Listeria monocytogenes in various concentrations of black carrot juice were investigated during incubation period at 4 °C and 37 °C for 7 days. Several parameters, such as juice concentration (%), pH, incubation temperature (°C) and time (days) were found effective on the survival of pathogens tested. Although L. monocytogenes has been found to be the less resistant microorganism to the variable conditions, there were only ca. 1 and 2 log reductions in the number of the cells in the juice samples incubated at 4 °C for 2 and 7 days, respectively. Incubating at low temperature (4 °C) enhanced the survival of test microorganisms.     

Effects of thermosonication and orange by‐products extracts on quality attributes of carrot (Daucus carota) juice during storage

Effect of thermosonication on carrot juice containing peel (CJPL) and pulp (CJPP) extracts from orange at different concentration (0.5, 2.0 and 4.0 mg GAE per g extracts) of total phenolic contents (TPC) was evaluated for quality attributes. Thermosonication of juice was done at 52 °C, 6 min for CJPL and 60 °C, 5 min for CJPP (values based on our preliminary optimisation results of ultrasound process conditions of the juice) at 40 kHz and 110W. Effect of thermosonication and addition of peel and pulp extracts at highest concentration increased the TPC and antioxidant activity of the juice (P < 0.05). Highest inactivation of microorganisms and better sensory attributes was achieved in thermosonicated CJPP for 21 days. Titratable acidity, pH, browning index and viscosity were improved by thermosonication and at highest extract concentration. °Brix and total carotenoid were not significantly affected by treatments. Therefore, thermosonication at 60 °C and 4.0 mg GAE per g extract concentration of peel and pulp may be used in formulation of functional carrot juice with improved health properties.     

大孔树脂分离纯化黑胡萝卜红色素的研究

黑胡萝卜红色素是从黑胡萝卜果实中提取的天然食用色素,其色素属于花青素。采用6种大孔树脂(BM-2、LS-305A、LSA-5B、HP-20、LSA-7,LAS-800)对黑胡萝卜红色素粗提液进行了吸附纯化研究,初步筛选出吸附和解吸性能均较好的BM-2树脂,通过静态吸附和解吸研究黑胡萝卜红色素的吸附等温线和吸附解吸动力学。研究结果表明,树脂吸附的最适宜的料液p H为2.0;BM-2树脂适合Langmuir模型拟合,相关系数为0.9878,属于单分子层吸附机理;拟一阶动力学模型能很好地描述此树脂的吸附过程特征,内外膜扩散是影响吸附的主要因素;最佳解吸条件为65%乙醇水溶液(含0.3%的柠檬酸)。     

Radiation processing to ensure safety of minimally processed carrot (Daucus carota) and cucumber (Cucumis sativus): optimization of dose for the elimination of Salmonella Typhimurium and Listeria monocytogenes

Minimally processed vegetables are in demand, because they offer convenience to consumers. However, these products are often unsafe because of possible contamination with pathogens, such as Salmonella, Escherichia coli O157:H7, and Shigella species. Therefore, this study was carried out to optimize the radiation dose necessary to ensure the safety of precut carrot and cucumber. Decimal reduction doses (D-values) of Salmonella Typhimurium MTCC 98 were ca. 0.164 kGy in carrot samples and 0.178 kGy in cucumber samples. D-values of Listeria monocytogenes were determined to be 0.312 and 0.345 kGy in carrot and cucumber samples, respectively. Studies of inoculated, packaged, minimally processed carrot and cucumber samples showed that treatment with a 1-kGy dose of gamma radiation eliminated up to 4 log CFU/g of Salmonella Typhimurium and 3 log CFU/g of L. monocytogenes. However, treatment with a 2-kGy dose was necessary to eliminate these pathogens by 5 log CFU/g. Storage studies showed that both Salmonella Typhimurium and L. monocytogenes were able to grow at 10 degrees C in inoculated control samples. Neither of these pathogens could be recovered from radiation-processed samples after storage for up to 8 days.     

Effectiveness of radiation processing for elimination of Salmonella Typhimurium from minimally processed pineapple (Ananas comosus Merr.)

ABSTRACT:  The microbiological quality of market samples of minimally processed (MP) pineapple was examined. The effectiveness of radiation treatment in eliminating Salmonella Typhimurium from laboratory inoculated ready-to-eat pineapple slices was also studied. Microbiological quality of minimally processed pineapple samples from Mumbai market was poor; 8.8% of the samples were positive for Salmonella. D₁₀ (the radiation dose required to reduce bacterial population by 90%) value for S. Typhimurium inoculated in pineapple was 0.242 kGy. Inoculated pack studies in minimally processed pineapple showed that the treatment with a 2-kGy dose of gamma radiation could eliminate 5 log CFU/g of S. Typhimurium. The pathogen was not detected from radiation-processed samples up to 12 d during storage at 4 and 10 °C. The processing of market samples with 1 and 2 kGy was effective in improving the microbiological quality of these products.     

Electron microscopic studies in cultivated plants. II. Fresh and stored roots of Daucus carota L

Scanning (SEM) and transmission (TEM) electron microscopic studies in fresh and stored roots (4 months at an average temperature of +8 degrees C) of Daucus carota L. (carrots) were carried out. Chief stress was laid on the analysis of the histological and cytological structure of the secondary phloem parenchyma cell. SEM images show the three-dimensional histological arrangement of the cells. Moreover, the outlines of lipid droplets, mitochondria, starch grains, and carotin pigment crystals are visible within the parietal cytoplasmic layer. In TEM, besides the usual cell organelles (mitochondria, golgi-apparatus, ER, etc.) nuclei with several nuclear bodies can be recognised. The morphological structure of the chromoplasts shows a remarkable diversity. Within stored carrots a strong reduction of lipid droplets and starch grains within the chromoplasts takes place.