Effect of different thawing methods on the efficiency and quality attributes of frozen red radish.

BACKGROUND: The thawing process is regarded as an essential step before the consumption of frozen foods. This study aimed to evaluate the possibility of ultrasound thawing of frozen red radish and to explore the characteristics of ultrasound thawing. The influence of low-frequency ultrasound (LFU) on the thawing efficiency of frozen red radish cylinders in air and water mediums was investigated. The effects of different ways of thawing, including air thawing (AT), water thawing (WT), refrigeration thawing (RT), ultrasound-assisted water thawing (UWT), and microwave thawing (MT) on the thawing time and quality of radish samples was studied. RESULTS: The results showed that thawing time decreased remarkably in air and water mediums assisted by LFU. As the LFU power level increased, the thawing time decreased and the value of the drip loss increased. The firmness of thawed radish samples also decreased significantly compared with the fresh samples. Microwave thawing had the highest thawing rate, but the microstructure of MT radish samples was damaged severely, resulting in the highest drip loss, and the lowest firmness, and vitamin C content. In comparison with the AT, WT, and RT, a significant reduction in thawing time could be achieved for UWT (P < 0.05). Ultrasound-assisted water thawing exhibited the highest retention of color and vitamin C, and a lower destructive effect on the microstructure. CONCLUSION: The results showed that LFU could be used as an efficient method to facilitate the thawing process of frozen red radishes, and better preserve the color, vitamin C, and microstructure of the final product. © 2020 Society of Chemical Industry.

Radiosensitization of Salmonella spp. and Listeria spp. in ready-to-eat baby spinach leaves.

The FDA recently approved irradiation treatment of leafy greens such as spinach up to 1 kGy; however, it is important to reduce the dose required to decontaminate the produce while maintaining its quality. Thus, the objectives of this study were: (1) to assess the radiation sensitivities of Salmonella spp. and Listeria spp. inoculated in ready-to-eat baby spinach leaves under modified atmosphere packaging (MAP) and irradiated using a 1.35-MeV Van de Graff accelerator (the leaves were irradiated both at room temperature and at -5 °C); and (2) to understand and optimize the synergistic effect of MAP and irradiation by studying the radiolysis of ozone formation under different temperatures, the effect of dose rate on its formation, and its decomposition. Results showed that increased concentrations of oxygen in the packaging significantly increased the radiation sensitivity of the test organisms, ranging from 7% up to 25% reduction in D(10)-values. In particular, radiosensitization could be effected (P < 0.05) by production of ozone, which increases with increasing dose-rate and oxygen concentration, and reducing temperatures. Radiosensitization was demonstrated for both microorganisms with irradiation of either fresh or frozen (-5 °C) baby spinach. These results suggest that low-dose (below 1 kGy) e-beam radiation under modified atmosphere packaging (100% O(2) and N(2):O(2)[1:1]) may be a viable tool for reducing microbial populations or eliminating Salmonella spp. and Listeria spp. from baby spinach. A suggested treatment to achieve a 5-log reduction of the test organisms would be irradiation at room temperature under 100% O(2) atmosphere at a dose level of 0.7 kGy. Practical Application: Decontamination of minimally processed fruits and vegetables from food-borne pathogens presents technical and economical challenges to the produce industry. Internalized microorganisms cannot be eliminated by the current procedure (water-washed or treated with 200-ppm chlorine). The only technology available commercially is ionizing radiation; however, the actual radiation dose required to inactivate pathogens is too high to be tolerated by the product without unwanted changes. This study shows a new approach in using MAP with 100% O(2), which is converted to ozone to radiosensitize pathogens while improving the shelf life of minimally processed fruits and vegetables. The process results in a high level of microorganism inactivation using lower doses than the conventional irradiation treatments.

Radiation inactivation of foodborne pathogens on frozen seafood products.

Foodborne illness due to consumption of contaminated seafood is, unfortunately, a regular occurrence in the United States. Ionizing (gamma) radiation can effectively inactivate microorganisms and extend the shelf life of seafood. In this study, the ability of gamma irradiation to inactivate foodborne pathogens surface inoculated onto frozen seafood (scallops, lobster meat, blue crab, swordfish, octopus, and squid) was investigated. The radiation D(10)-values (the radiation dose needed to inactivate 1 log unit of a microorganism) for Listeria monocytogenes, Staphylococcus aureus, and Salmonella inoculated onto seafood samples that were then frozen and irradiated in the frozen state (-20°C) were 0.43 to 0.66, 0.48 to 0.71, and 0.47 to 0.70 kGy, respectively. In contrast, the radiation D(10)-value for the same pathogens suspended on frozen pork were 1.26, 0.98, and 1.18 kGy for L. monocytogenes, S. aureus, and Salmonella, respectively. The radiation dose needed to inactivate these foodborne pathogens on frozen seafood is significantly lower than that for frozen meat or frozen vegetables.

Radiation D10-values on thawed and frozen catfish and tilapia for finfish isolates of Listeria monocytogenes.

With the popularity of catfish and tilapia in the healthy diet, the consumption and harvesting of farm-raised finfish have increased. Since 1987 the pathogenic bacterium Listeria monocytogenes has been isolated from seafood, particularly farm-raised catfish in the United States. Seafood isolates of L. monocytogenes are now available. In order to maintain the raw finfish product, nonthermal interventions to remove bacterial pathogens need to be evaluated using these isolates. A nonthermal intervention process, irradiation, was used to determine the destruct values of the L. monocytogenes seafood isolates along with a nonpathogenic Listeria strain and an L. monocytogenes strain previously studied. The irradiation destruct values were obtained for each individual isolate inoculated on raw and frozen catfish or tilapia irradiated at 4 or -10 degrees C. The Dradiation values obtained for L. monocytogenes inoculated on raw or frozen catfish did not differ (P > 0.05) from the values obtained for strains inoculated on the raw or frozen tilapia. The Dradiation-values ranged from 0.48 to 0.85 kGy, with an average of 0.62 +/- 0.09 kGy, which is typical for Listeria. The data obtained have identified a multi-isolate cocktail that can be used for future radiation inactivation studies for L. monocytogenes inoculated on finfish.

Effects of ionizing radiation on sensorial, chemical, and microbiological quality of frozen corn and peas.

The effects of irradiation (0, 1.8, and 4.5 kGy) on the quality of frozen corn and peas were investigated during a 12month period of postirradiation storage at -18 degrees C. Irradiation of frozen corn and peas caused a reduction in ascorbic acid content of both vegetables and a loss of texture in peas but had no significant effects on instrumental color parameters (L*, a*, and b*), carotenoid and chlorophyll content, or antioxidant capacity of corn and peas. Irradiation reduced microbial loads of frozen peas and increased display life at 23 degrees C of thawed peas by preserving the green color, apparently because of slower increases in the population of acid-producing microorganisms in the irradiated samples. Overall, irradiation significantly reduced the microbial load and increased the display life of peas and had minimal detrimental effects on the quality of frozen corn and peas.

Irradiation of diets fed to captive exotic felids: microbial destruction, consumption, and fecal consistency.

Two frozen, raw horse meat-based diets fed to captive exotic felids at Brookfield Zoo were irradiated to determine the extent of microbial destruction and whether radiation treatment would affect consumption and/or fecal consistency in exotic cats. Fifteen cats, two African lions (Panthera leo), two Amur tigers (Panthera tigris altaica), one Amur leopard (Panthera pardus orientalis), two clouded leopards (Neofelis nebulosa), two caracals (Felis caracal), one bobcat (Felis rufus), and five fishing cats (Felis viverrinus), housed at Brookfield Zoo were fed nonirradiated and irradiated raw diets containing horse meat with cereal products and fortified with nutrients: Nebraska Brand Feline and/or Canine Diet (Animal Spectrum, North Platte, Nebraska 69103, USA). Baseline data were obtained during a 2-wk control period (nonirradiated diets), which was followed by a 4-wk period of feeding comparable irradiated diets. Feed intake and fecal consistency data were collected. An estimated radiation dose range of 0.5-3.9 kilograys reduced most microbial populations, depending on specific diet and microbe type. Irradiation had no overall effect on either feed consumption or fecal consistency in captive exotic cats, regardless of species, age, sex, or body mass. Data indicate that irradiation of frozen horse meat-based diets (packaged in 2.2-kg portions) result in microbial destruction in these products but that product storage time between irradiation and sampling may also affect microbial reduction. However, irradiation would be an appropriate method for reducing potentially pathologic bacteria in raw meat fed to exotic cats.

Irradiation as a method for decontaminating food. A review.

Despite substantial efforts in avoidance of contamination, an upward trend in the number of outbreaks of foodborne illnesses caused by nonsporeforming pathogenic bacteria are reported in many countries. Good hygienic practices can reduce the level of contamination but the most important pathogens cannot presently be eliminated from most farms nor is it possible to eliminate them by primary processing, particularly from those foods which are sold raw. Several decontamination methods exist but the most versatile treatment among them is the processing with ionizing radiation. Decontamination of food by ionizing radiation is a safe, efficient, environmentally clean and energy efficient process. Irradiation is particularly valuable as an endproduct decontamination procedure. Radiation treatment at doses of 2-7 kGy--depending on condition of irradiation and the food--can effectively eliminate potentially pathogenic nonsporeforming bacteria including both long-time recognized pathogens such as Salmonella and Staphylococcus aureus as well as emerging or "new" pathogens such as Campylobacter, Listeria monocytogenes or Escherichia coli O157:H7 from suspected food products without affecting sensory, nutritional and technical qualities. Candidates of radiation decontamination are mainly poultry and red meat, egg products, and fishery products. It is a unique feature of radiation decontamination that it can also be performed when the food is in a frozen state. With today's demand for high-quality convenience foods, irradiation in combination with other processes holds a promise for enhancing the safety of many minimally processed foods. Radiation decontamination of dry ingredients, herbs and enzyme preparations with doses of 3-10 kGy proved to be a viable alternative to fumigation with microbicidal gases. Radiation treatment at doses of 0.15-0.7 kGy under specific conditions appears to be feasible also for control of many foodborne parasites, thereby making infested foods safe for human consumption. Microorganisms surviving low- and medium-dose radiation treatment are more sensitive to environmental stresses or subsequent food processing treatments than the microflora of unirradiated products. Radiation treatment is an emerging technology in an increasing number of countries and more-and-more clearances on radiation decontaminated foods are issued or expected to be granted in the near future.