Application of flow cytometric DNA measurements in the detection of irradiated onions

Nuclei from meristem tissue cells of onion bulbs γ-irradiated (60–90 Gy) for sprout inhibition and non-irrádiated control bulbs were isolated periodically during ambient (27–32°C) storage, stained with the fluorochrome 4′,6-diamidino-2-phenylindole and their DNA distribution histograms measured by flow cytometry (FCM). Nuclei from irradiated onions showed a broader DNA distribution profile appearing as a wide (high) coefficient of variation (CV, 4–78%) of the G₀/G₁ peak as compared with non-irradiated samples (CV, 2.39%). The DNA index (DI) of the diploid cells in control onions was 1 as against 0.74 in irradiated samples which indicated the presence of G₀/G₁ cells with abnormal DNA content in the meristem tissue cells of irradiated onions. The results indicate the potential application of quantitating changes in DNA content using FCM by determining CV of the G₀/G₁ peak as well as DI for differentiating irradiated from non-irradiated onion bulbs.     

Role of precursors on greening in crushed garlic (Allium sativum) bulbs, and its control with freeze-dried onion powder

BACKGROUND: Lachrymatory factor (LF) synthase in onion bulbs reacts with S‐1‐propenyl‐L ‐cysteine sulfoxide (1‐PeCSO), a key compound in garlic greening. In this study, freeze‐dried onion powder containing LF synthase was used in treatments to control garlic greening. Prior to the use of freeze‐dried onion powder to treat greening garlic bulbs, model reactions were conducted to confirm the reactivity of 1‐PeCSO in onion bulbs to garlic greening. RESULTS: While pink pigments were generated from 1‐PeCSO, green pigments were produced from the combination of 1‐PeCSO and S‐2‐propenyl‐L ‐cysteine sulfoxide (2‐PeCSO). However, pigments were formed in the systems containing 1‐PeCSO, amino acid and alliinase. Even non‐greening garlic bulbs stored at 20 °C turned green with the reaction of 200 g L^?1 1‐PeCSO; therefore 1‐PeCSO isolated from onion bulbs had the same role as 1‐PeCSO in garlic bulbs in terms of greening. Onion bulbs turned green after the addition of 600 g L^?1 2‐PeCSO. The addition of freeze‐dried onion powder inhibited garlic greening, and treatment with 15 g kg^?1 onion powder gave the best storage stability of crushed garlic bulbs. CONCLUSION: The addition of freeze‐dried onion powder inhibited the greening in crushed garlic bulbs, and treatment with 15 g kg^?1 onion powder gave the best storage stability of crushed garlic bulbs. Copyright © 2011 Society of Chemical Industry     

Effect of radiation and other processing methods on protein quality of sunflower meal

The effects of gamma irradiation from a ⁶⁰Co source (10 and 20 kGy), dry heating (121 °C for 10, 20 and 30 min), autoclaving (121 °C at 103.5 kPa for 10, 20 and 30 min) and their combination on chlorogenic acid, soluble protein, available lysine and in-vitro protein digestibility of sunflower meal were studied. The moisture content of the raw sample was 78 g kg⁻¹ as is and on a dry matter basis. The meal contained 26.7 g kg⁻¹ chlorogenic acid, 330 g kg⁻¹ crude protein, 78.5% soluble protein and 2.63 g 16 g N⁻¹ available lysine. Digestibility of raw meal was 81.5%. Chlorogenic acid, soluble protein and available lysine of raw meal decreased during dry heating, autoclaving and radiation processing. The digestibility was significantly affected by processing method (P < 0.05), as well as by the time of dry heating and autoclaving. The influence of combination methods revealed that irradiation alone had a little effect on chlorogenic acid and in-vitro protein digestibility. Autoclaving plus irradiation up to 20 kGy markedly improved the digestibility (90%). Therefore, the results suggested that the combination of autoclaving for 10 min plus irradiation up to 20 kGy has a beneficial effect on the protein quality of sunflower meal with little effect on its content of soluble protein, available lysine and markedly reduced chlorogenic acid by 87%, more than other processing methods. © 1999 Society of Chemical Industry     

Modified Atmosphere Packaging of Fresh Beansprouts

Freshly harvested beansprouts displayed a respiration rate of about 1 mmol O₂ kg⁻¹ h⁻¹ at 10°C which was strongly dependent on temperature, a 10-fold increase being observed every 16·5°C (z=16·5°C, ie Q₁₀=4·4). This commodity is also characterised by a high initial microbial load (about 10⁷ cells g⁻¹). During storage at various temperatures from 1 to 20°C, oxygen uptake rates dramatically increased with time and this phenomenon was well correlated with the development of aerobic microorganisms which reached 10⁹ cells g⁻¹ after 2 days at 20°C or 9 days at 1°C. Beansprouts were packaged in films, with permeabilities ranging from 950 to 200000 ml O₂ m⁻² day⁻¹ atm⁻¹, and stored at 8°C. Due to plant and microbial metabolism, oxygen concentrations decreased steadily within all packs until the onset of plant tissue decay. The latter occurred after 5–6 days with the least permeable films but did not occur within when the film permeability was over 100000 ml O₂ m⁻² day⁻¹ atm⁻¹. However, such films favoured brown discolouration, exudation texture and breakdown. The orientated polypropylene film (OPP) induced anoxic condition within 2 days and favoured anaerobic metabolism and necrosis of the sprouts. In all packages there was a rapid development of aerobic microorganisms and lactic acid bacteria that resulted in the accumulation of acetate and lactate and a decrease in pH. Thus, it clearly appeared that tissue decay was enhanced by microbial activity. At 8°C, 0·24 m² of film per kg of sprouts provided the optimal atmosphere composition (ie 5% oxygen and 15% carbon dioxide) when a film permeability of 50000 ml O₂ m⁻² day⁻¹ atm⁻¹ was used. These conditions allowed a shelf-life of 4–5 days.     

Gamma irradiation as a means to eliminate Listeria monocytogenes from frozen chicken meat

Cells of Listeria monocytogenes ATCC 35152 were sensitive to gamma irradiation in phosphate buffer, pH 7.00 (D₁₀, dose required for 10% survival—0.15 kGy) at 0–5°C. The cells showed higher radiation survival when irradiated under frozen condition, with a D₁₀ of 0.3 kGy. The protection offered by shrimp/chicken/kheema homogenates (100 g litre^?1) was evidenced by even higher D₁₀ values (0.5 kGy) at both 0–5°C and cryogenic temperature. Boneless chicken meat samples were artificially inoculated with L monocytogenes ATCC 35152 cells at low (5 × 10³) colony-forming unit (cfu) g^?1 and high (5 × 10⁶ cfu g^?1) concentrations and irradiated at 1, 3, 4, 6 kGy doses under cryogenic conditions. The efficacy of the radiation process was evaluated by detecting L monocytogenes during storage at 2–4°C in the irradiated samples. These studies, when repeated with three other serotypes of L monocytogenes, clearly suggested the need for a dose of 3 kGy for elimination of 10³ cfu cells of L monocytogenes g^?1 from air-packed frozen chicken meat.     

Physicochemical and microbiological changes in postmortem crayfish (Procambarus clarkii) stored at 4 °C and 25 °C

The physicochemical and microbiological parameters of postmortem crayfish stored at 4 °C and 25 °C were evaluated in order to reduce safety risks of crayfish from temperature abuse during transportation and storage. Results showed that hepatopancreas of postmortem crayfish had significantly higher contents of total volatile basic nitrogen, biogenic amines (BAs) and higher microbial loads than tail meat, regardless of storage temperature. Enterobacteriaceae and Pseudomonas counts reached log 6.41 log₁₀ CFU g⁻¹ and 6.31 log₁₀ CFU g⁻¹ in hepatopancreas of crayfish at 25 ℃ for 6 h. Putrescine and cadaverine were the main BAs in tail meat with levels of 28.18 ± 0.73 mg kg⁻¹ and 187.32 ± 3.57 mg kg⁻¹, respectively, whilst cadaverine, spermidine and spermine were the major BAs in hepatopancreas, reaching 283.45 ± 3.95 mg kg⁻¹, 62.87 ± 9.02 mg kg⁻¹ and 155.31 ± 4.55 mg kg⁻¹, respectively, after postmortem storage at 25 °C for 12 h. With time increasing, Acinetobacter, Flavobacterium, Aeromonas and Chryseobacterium at 25 °C and Acinetobacter, Flavobacterium, Psychrobacter at 4 °C in tail meat as well as Bacteroides and Muribaculaceae at 25 °C, and Acinetobacter, Psychrobacter at 4 °C in hepatopancreas, gradually became the major genus at the end of storage. Based on the results of spoilage microorganisms and biogenic amines, crayfish stored at 4 °C and 25 °C could be edible within 24 h and 6 h, respectively.     

Effects of temperature on the physicochemical properties of starches extracted from microtubers grown from different potato cultivars

Twelve potato cultivars were grown as microtubers in constant environment chambers at two temperatures in total darkness for 28 days. For starch extracted from microtubers grown at 12 or 22 °C, the amylose content ranged from 25.0 to 29.0% (average 27.3 ± 1.4%) or 29.5 to 32.7% (average 30.9 ± 1.4%), the amylose/amylopectin ratio from 1:2.5 to 1:3.0 (average 1:2.7) or 1:2.1 to 1:2.4 (average 1:2.2) and the phosphorus content from 0.41 to 0.93 g kg⁻¹ (average 0.72 g kg⁻¹) or 0.38 to 1.67 g kg⁻¹ (average 0.97 g kg⁻¹) respectively. Two major fractions (F1 and F2) were obtained for isoamylase‐debranched starch (amylopectin), with the chain length (CL) averaging 56 ± 3 or 55 ± 1 for F1 and 20 ± 1 or 21 ± 1 for F2 from 12 or 22 °C growth temperature respectively. Peak gelatinisation temperature (T_p) and enthalpy (ΔH) were influenced strongly by growth temperature, with T_p ranging from 60.8 to 64.5 °C (average 62.1 ± 1.0 °C) or 66.9 to 69.6 °C (average 68.2 ± 0.9 °C) and ΔH from 13.3 to 16.9 J g⁻¹ (average 14.8 ± 1.0 J g⁻¹) or 11.3 to 19.5 J g⁻¹ (average 16.3 ± 2.4 J g⁻¹) from 12 or 22 °C growth temperature respectively. The collective data generated at 12 °C were generally more comparable to data published elsewhere (but discussed in the text) for the same potato cultivars grown in field plots (Perthshire). However, there were cultivar specific responses to field or constant environment chambers which make direct comparisons between starches produced from the two systems subject to some variation. Copyright © 2004 Society of Chemical Industry     

Influence of gamma irradiation on growth and survival of Escherichia coli O157:H7 and quality of cig kofte, a traditional raw meat product

Cig kofte is a traditional Turkish food containing raw ground meat. Samples inoculated with Escherichia coli O157:H7 were irradiated at 0.5–6 kGy with a ⁶⁰Co source and stored at 4 and 25 °C. Total aerobic mesophilic count decreased with increasing irradiation doses, D₁₀ value was 0.83 kGy. Escherichia coli O157:H7 count decreased from 5.1 log₁₀ CFU g^?1 to an undetectable level (<1 log₁₀ CFU g^?1) after 1‐day storage at 4 °C following irradiation at 2 kGy, D₁₀‐value was 0.29 kGy. Irradiation doses up to 2 kGy did not affect sensory quality after 1 day. There was colour loss in samples irradiated at 2 kGy or above and stored for longer periods. Storage of the irradiated products at abused temperature must be avoided for safety assurance. Irradiation at 2 kGy has a great potential for extending the shelf‐life of cig kofte and assuring safety by decreasing the number of E. coli O157:H7 and other bacteria, but further studies with suitable package designs are needed to decrease quality degradation during extended storage.     

Properties of polyphenol oxidase in mango (Mangifera indica) kernel

Polyphenol oxidase (PPO) activity of filtered extract of ground mango kernel suspension (400 g litre⁻¹) was studied spectrophotometrically at 420 nm using catechol as substrate. The enzyme was most active at pH 6·0 and 25°C. Activity was reduced by 50% at pH values of 5·0 and 7·1, and also at temperatures of 14°C and 30°C. The calculated activation energy and the Michaelis constant (K_m) were 21·4 kcal mol⁻¹ °C⁻¹ and 24·6 mM , respectively. The V_max value was 2·14 units g⁻¹ mango kernel. The time to heat inactivate PPO decreased rapidly to < 10 min with increasing temperature of ⩾ 70°C at 50% activity. © 1998 SCI.     

Effect of irradiation on Salmonella survival and quality of 2 varieties of whole green onions

Abstract: Two varieties of green onions, Banner and Baja Verde, were inoculated with a cocktail of 3 Salmonella strains using dip and spot inoculation and irradiated at 0, 0.3, 0.6, 0.9, and 1.2 kGy using electron beam. Salmonella survivors were enumerated using a XLD underlay/TSAYE overlay plating method. The D values were in the range of 0.26 to 0.32 kGy depending on variety but not on the method of inoculation. This indicated that a 5‐log reduction of Salmonella can be achieved at a dose of 1.6 kGy. For the quality study, both varieties of green onions were irradiated at 0, 1.5, 2.0, and 2.5 kGy and evaluated for changes in microbial counts, color, texture, and visual quality during storage at 4 °C. Irradiation reduced total plate counts and psychrotrophs by 3 logs. Although the counts increased during storage, they did not exceed the initial counts of control. No significant difference was observed in color and texture between irradiated samples and control. The control maintained good visual quality for about 13 d as compared to 15 d for 1.5 and 2.5 kGy samples. The 2.0 kGy samples maintained good visual quality for 17 d suggesting that irradiation can increase shelf life by reducing spoilage microorganisms but higher doses can be detrimental to quality. At the dose levels required to achieve a 5‐log reduction in Salmonella, the shelf life of whole green onion can be extended. This study shows that irradiation can be used to enhance safety without adverse effects on quality.     

Modelling the effect of superatmospheric oxygen concentrations on in vitro mushroom PPO activity

The kinetics of polyphenol oxidase (PPO, EC 1.14.18.1) with respect to oxygen concentrations from 5 to 100% using chlorogenic acid (CGA) as substrate was examined. In vitro mushroom PPO activity was determined by measuring the consumption of oxygen during the oxidation reaction. A differential Michaelis–Menten model was fitted to the obtained total depletion curves. The product concentration as well as the concentration of oxygen had a clear inhibitory effect on the reaction rate. However, the inhibitory effect of oxygen was more evident at low product concentration. A linear mixed inhibition model that considered both the product (oxidised CGA) and oxygen as inhibitors was developed. A model with the product as a competitive inhibitor and oxygen as an uncompetitive inhibitor was the most appropriate to explain the reaction kinetics. The values of the inhibition constants calculated from the model were 0.0032 mmol L⁻¹ for K_m (Michaelis–Menten constant related to oxygen), 0.023 mmol L⁻¹ for K_mc (constant for competitive inhibition due to the product), 1.630 mmol L⁻¹ for K_mu (constant for uncompetitive inhibition due to oxygen) and 1.77 × 10⁻⁴ mmol L⁻¹ s⁻¹ for V_max (maximum reaction rate). The results indicate that superatmospheric oxygen concentrations could be effective in preventing enzymatic browning by PPO. Copyright © 2006 Society of Chemical Industry     

Gamma Ray Processing to Destroy Staphylococcus aureus in Mechanically Deboned Chicken Meat

Gamma radiation doses of 0.26 kGy and 0.36 kGy, administered in vacuo at 0°C, destroyed 90% of log-phase and stationary-phase colony forming units (CFU) of Staphylococcus aureus ATCC 13565 (FDA 196E), respectively, in mechanically deboned chicken meat (MDCM). Samples inoculated with 10^3.9 CFU/g of S. aureus were treated with gamma radiation in vacuo at 0°C and then held for 20 hr at 35°C (abusive storage). Viable CFU were found in samples irradiated to 0.75 kGy but not in those irradiated to 1.50 kGy either before or after storage. Enterotoxin was not detected in irradiated MDCM. A predictive equation was developed for the response of S. aureus in MDCM to radiation dose and irradiation temperature.     

Effect of black tea, garlic and onion on corn oil stability and fatty acid composition under accelerated oxidation

Fresh black tea, garlic bulbs and onion skin were macerated in refined corn oil to evaluate their antioxidant properties and the effect of heat on oil stability and fatty acid composition in accelerated oxidation experiments at 55 ° and 140 °C. At the lowest temperature control and onion treatments showed an induction time of 3 days with maximum peroxide values of 62 and 45 meq kg^?1, respectively. Addition of black tea and garlic increased oil stability with peroxide values of 5 meq kg^?1, without appreciable changes in the fatty acid composition. Heating at 140 °C for 48 h produced an accelerated deterioration of corn oil in all treatments. A reduction of polyunsaturated fatty acids of about 40% was observed, with high concentrations of non‐eluted materials which contained thermo‐oxidized substances. It was found that natural extract of black tea and garlic were effective to preserve corn oil under accelerated oxidation at 55 °C which simulates oil behaviour during storage, but cannot reduce the rate of oxidation at frying temperatures.     

Modelling the respiration rate of minimally processed broccoli (Brassica rapa var. sylvestris) for modified atmosphere package design

In this work, the effect of temperature, oxygen and carbon dioxide on the respiration rate of minimally processed broccoli was studied to develop suitable modified atmosphere packaging. Respiration rate was measured at 3, 5, 7, 10, 15 and 20 °C under different gas compositions of O₂ and CO₂ (1%, 5%, 10%, 15% and 21% of O₂ with the balance N₂, a mixture of 10% and 20% of carbon dioxide with the balance air and a mixture at 3% of O₂ and 15% of CO₂ with the balance N₂). As expected, temperature was the most influential factor on respiration rate, for all atmospheres tested: increasing the temperature from 3 to 20 °C resulted, for air‐stored samples, in a 84% change in oxygen respiration rate, whereas at constant temperature, the respiration rate decreased by 35% with lowering the O₂ concentration from 21% to 1% and by 44% with increasing the CO₂ concentration from 0% to 20%. The Michaelis and Menten competitive model with maximum respiration rate varying against temperature with an Arrhenius equation accurately described the influence of gas composition and temperature on the respiration rate of minimally processed broccoli, and it was used to design a suitable package.     

Modeling Respiration Rate of Strawberry (cv. San Andreas) for Modified Atmosphere Packaging Design

A model for strawberry (Fragaria × ananassa cv. San Andreas) respiration rate was determined as a function of O₂ and CO₂ concentrations and temperature. Strawberries were enclosed in containers under different gaseous compositions (0–24% O₂ and 0–15% CO₂) and temperatures (10, 19, 23°C). Respiration rate was determined as O₂ consumption and CO₂ production. Respiration rate data was fitted to Michaelis-Menten models, with temperature dependence according to Arrhenius type equation. Non–linear regression was applied to calculate model parameters. No CO₂ inhibition was verified, so a simple Michaelis–Menten model was selected (R² = 0.91).     

Aflatoxin production in three selected samples of triticale,wheat and rye grown in Argentina

Little is known about mycotoxin contamination of triticale, a hybrid resulting from crossing wheat and rye. The purpose of the present work was to evaluate triticale as a substrate for aflatoxin accumulation in comparison with its parents. Aflatoxin (B₁, B₂, G₁ and G₂) accumulation curves were obtained for the three substrates inoculated with Aspergillus parasiticus NRRL 2999 and incubated at 25 °C and water activity 0.925 for 10 weeks. Wheat and triticale were poor substrates for aflatoxin production. Rye was more prone than the other substrates to fast colonisation by A parasiticus and accumulated larger aflatoxin quantities over the whole incubation period. The maximum aflatoxin concentration in rye (11 840 µg kg⁻¹) was significantly larger (p < 0.05) than those obtained in wheat (2150 µg kg⁻¹) and triticale (2850 µg kg⁻¹). © 2000 Society of Chemical Industry     

Insecticidal efficacy of spinetoram against Sitophilus zeamais: Influence of dose,exposure interval and temperature

The efficacy of spinetoram against Sitophilus zeamais adults was investigated using nine dose rates, 0.01, 0.10, 0.25, 0.50, 0.75, 1.00, 2.00, 5.00 and 10.00 mg kg⁻¹ at 20, 25 and 30 ^°C (55% r.h) in the laboratory. Mortality was assessed 1, 2, 3, 7, 14, 21, and 28 d after exposure, and progeny production was recorded 65 d after the final count. Dose rates and exposure periods affected adult mortality, while temperature did not in most of the exposure period-dose combinations. At low doses of ≤0.50 mg kg-¹, mortality rates did not reach 50%, despite increasing exposure periods. Complete mortality was achieved at ≥ 2 mg kg⁻¹ at 30 ^°C, and at ≥ 5 mg kg⁻¹ at 20 and 25 ^°C after 28 d exposures. Generally, significant increase in mortality were observed at ≥ 7 d exposures. However, at 30 ^°C the mortality rate reached 51% after 2 d exposure to 10 mg kg⁻¹. Increasing the temperature to 30 ^°C had a significant effect in decreasing the dose rates for insect mortality. Significant reductions in progeny development were obtained at ≥ 2 mg kg⁻¹ at 20 and 25 ^°C, and at ≥ 1 mg kg⁻¹ at 30 ^°C. The difference in temperature, with the exception of 1 and 2 mg kg⁻¹ dosages, had no effect on reducing the progeny. In light of the mortality and progeny data, we can conclude that spinetoram can successfully control S. zeamais and suppress its population growth by decreasing progeny production.     

Effect of essential oils of cinnamon,clove, lemon grass,oregano and palmarosa on growth of and fumonisin B1 production by Fusarium verticillioides in maize

The ability of cinnamon, clove, lemon grass, oregano and palmarosa essential oils to prevent growth of and fumonisin B₁ (FB₁) production by Fusarium verticillioides at different water activity (0.95 and 0.995 a_w) and temperature (20 and 30 °C) levels in irradiated maize grain was evaluated. All the essential oils inhibited growth of F verticillioides isolates under all conditions tested, but FB₁ production was only inhibited at 30 °C and 0.995 a_w. Moreover, stimulation of toxin production was found under certain environmental conditions. None of the essential oils showed a significantly greater ability to inhibit FB₁ production when compared with the others. At 1000 mg essential oil kg^?1 maize the essential oils showed a greater inhibitory effect on growth of F verticillioides than at 500 mg kg^?1, but there was no difference in FB₁ production between the two levels of essential oil. Copyright © 2004 Society of Chemical Industry