Xuetong Fan

A role for jasmonates in climacteric fruit ripening

Abstract. Jasmonates are a class of oxylipins that induce a wide variety of higher-plant responses. To determine if jasmonates play a role in the regulation of climacteric fruit ripening, the effects of exogenous jasmonates on ethylene biosynthesis and color, as well as the endogenous concentrations of jasmonates were determined during the onset of ripening of apple (Malus domestica Borkh. cv. Golden Delicious) and tomato (Lycopersicon esculentum Mill. cv. Cobra) fruit. Transient (12u2009h) treatment of pre-climacteric fruit discs with exogenous jasmonates at low concentration (1 or 10u2009μM) promoted ethylene biosynthesis and color change in a concentration-dependent fashion. Activities of both 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase and ACC synthase were stimulated by jasmonate treatments in this concentration range. The endogenous concentration of jasmonates increased transiently prior to the climacteric increase in ethylene biosynthesis during the onset of ripening of both apple and tomato fruit. The onset of tomato fruit ripening was also preceded by an increase in the percentage of the cis-isomer of jasmonic acid. Inhibition of ethylene action by diazocyclopentadiene negated the jasmonate-induced stimulation of ethylene biosynthesis, indicating jasmonates act at least in part via ethylene action. These results suggest jasmonates may play a role together with ethylene in regulating the early steps of climacteric fruit ripening.

Food irradiation research and technology.

List of Contributors. Preface. Chapter 1. Introduction: Food Irradiation Moving On (Joseph Borsa). Chapter 2. Advances in Gamma Ray, Electron Beam, and X-ray Technologies for Food Irradiation (Marshall R. Cleland). Chapter 3. Regulation of Irradiated Foods and Packaging (George H. Pauli). Chapter 4. Toxicological Safety of Irradiated Foods (Christopher H. Sommers, Henry Delincee, J. Scott Smith, and Eric Marchioni). Chapter 5. Consumer Acceptance and Marketing of Irradiated Foods (Ronald F. Eustice and Christine M. Bruhn). Chapter 6. Detection of Irradiated Foods (Eric Marchioni). Chapter 7. Dosimetry for Food Processing and Research Applications (Kishor Mehta and Kevin OHara). Chapter 8. Mechanisms and Prevention of Quality Changes in Meat by Irradiation (Doug U. Ahn and E.J. Lee). Chapter 9. Irradiation as a Phytosanitary Treatment for Fresh Horticultural Commodities: Research and Regulations (Peter A. Follett and Robert L. Griffin). Chapter 10. Low-Dose Irradiation of Fresh and Fresh-Cut Produce: Safety, Sensory, and Shelf Life (Brendan A. Niemira and Xuetong Fan). Chapter 11. Irradiation of Seafood with a Particular Emphasis (on Listeria monocytogenes in Ready-to-Eat Products (Denise M. Foley). Chapter 12. Ionizing Radiation of Eggs (I. Alvarez, B.A. Niemira, X. Fan, and C.H. Sommers). Chapter 13. Irradiation Treatment of Nuts (Akua Kwakwa and Anuradha Prakash). Chapter 14. Irradiated Ground Beef for the National School Lunch Program (Xuetong Fan). Chapter 15. Potential Applications of Ionizing Radiation (Myung-Woo Byun, Cheorun Jo, and Ju-Woon Lee). Chapter 16. A Future Uncertain: Food Irradiation from a Legal Perspective (Denis W. Stearns). Chapter 17. Technical Challenges and Research Directions in Electronic Food Pasteurization (Suresh D. Pillai, Les Braby, and Joe Maxim). Index.

Radiation (Gamma) Resistance and Postirradiation Growth of Listeria monocytogenes Suspended in Beef Bologna Containing Sodium Diacetate and Potassium Lactate

Listeria monocytogenes, a psychrotrophic foodborne pathogen, is a frequent postprocessing contaminant of ready-to-eat (RTE) meat products, including frankfurters and bologna. Ionizing radiation can eliminate L. monocytogenes from RTE meats. When they are incorporated into fine-emulsion sausages, sodium diacetate (SDA) and potassium lactate (PL) mixtures inhibit the growth of L. monocytogenes. The radiation resistance of L. monocytogenes, and its ability to proliferate during long-term refrigerated storage (9 degrees C), when inoculated into beef bologna that contained 0% SDA-0% PL, 0.07% SDA-1% PL, and 0.15% SDA-2% PL, were determined. The radiation doses required to eliminate 90% of the viable L. monocytogenes cells were 0.56 kGy for bologna containing 0% SDA-0% PL, 0.53 kGy for bologna containing 0.07% SDA-1% PL, and 0.46 kGy for bologna containing 0.15% SDA-2% PL. L. monocytogenes was able to proliferate on bologna containing 0% SDA-0% PL during refrigerated storage, but the onset of proliferation was delayed by the addition of the SDA-PL mixtures. An ionizing radiation dose of 3.0 kGy prevented the proliferation of L. monocytogenes and background microflora in bologna containing 0.07% SDA-1% PL and in bologna containing 0.15% SDA-2% PL over 8 weeks of storage at 9 degrees C. Little effect on lipid oxidation and color of the control bologna, or bologna containing SDA-PL mixtures, was observed upon irradiation at either 1.5 or 3.0 kGy.

Delaying establishment of controlled atmosphere or CO2 exposure reduces 'Fuji' apple CO2 injury without excessive fruit quality loss

Abstract Storage of ‘Fuji’ apple fruit in a high CO 2 (3 kPa) and low O 2 (1.5 kPa) controlled atmosphere (CA) reduced firmness and titratable acidity (TA) loss during long term storage. This CA environment also induced development of internal CO 2 -injury (brown-heart) and slowed the disappearance of watercore. The symptoms of internal CO 2 -injury were first detected 15 days after CA establishment and the severity increased during the first 4 months of CA-storage. Delaying establishment of CA conditions for 2–12 weeks significantly reduced the severity of CO 2 -injury. Delaying CO 2 accumulation to 3 kPa for 1–4 months during CA (1.5 kPa O 2 +0.05 kPa CO 2 ) storage also reduced development of CO 2 -injury symptoms. Delaying CA or CO 2 accumulation resulted in lower firmness and TA compared to establishment of CA within 72 h of harvest. However, the delay treatments did result in firmness and TA that were significantly higher compared to values for fruit stored in air. The incidence and severity of senescent injuries (flesh browning and core flush) detected during the late period of storage were greater in air- than CA-stored fruit. The results indicate the susceptibility of ‘Fuji’ apples to CO 2 -injury is highest during the first weeks of storage after harvest. Delaying establishment of CA or exposure to elevated CO 2 after harvest may be a practical strategy to reduce CO 2 -injury while maintaining other important quality attributes at acceptable levels.

Factors affecting thermally induced furan formation.

Furan, a potential carcinogen, can be induced by heat from sugars, ascorbic acid, and fatty acids. The objective of this research was to investigate the effect of pH, phosphate, temperature, and heating time on furan formation. Heat-induced furan formation from free sugars, ascorbic acid, and linoleic acid was profoundly affected by pH and the presence of phosphate. In general, the presence of phosphate increased furan formation in solutions of sugars and ascorbic acid. In a linoleic acid emulsion, phosphate increased the formation of furan at pH 6 but not at pH 3. When an ascorbic acid solution was heated, higher amounts of furan were produced at pH 3 than at pH 6 regardless of phosphates presence. However, in linoleic acid emulsion, more furan was produced at pH 6 than at pH 3. The highest amount of furan was formed from the linoleic acid emulsion at pH 6. In fresh apple cider, a product with free sugars as the major components (besides water) and little fatty acids, ascorbic acid, or phosphate, small or very low amounts of furan was formed by heating at 90-120 degrees C for up to 10 min. The results indicated that free sugars may not lead to significant amounts of furan formation under conditions for pasteurization and sterilization. Importantly, this is the first report demonstrating that phosphate (in addition to pH) plays a significant role in thermally induced furan formation.

Sensorial and Chemical Quality of Gamma-Irradiated Fresh-Cut Iceberg Lettuce in Modified Atmosphere Packages

A study was conducted to investigate the effects of various doses of irradiation on the quality of fresh-cut iceberg lettuce and to determine a suitable maximum dose. Fresh-cut iceberg lettuce packaged in film bags was exposed to 0, 1, 2, 3, and 4 kGy of gamma radiation and stored at 3 degrees C for 14 days. CO2 levels were higher and O2 levels were lower in packages containing irradiated lettuce than in those containing nonirradiated lettuce for most of the storage period. Comparison with nonirradiated lettuce indicated that total ascorbic acid (ascorbic acid plus dehydroascorbic acid) content and firmness were not significantly influenced by irradiation at 1 or 2 kGy. The overall visual appearance was best for lettuce irradiated at 1 or 2 kGy. This improved quality may be related to the high CO2 and low O2 levels observed for the irradiated samples. Electrolyte leakage for lettuce increased with higher radiation doses and was correlated (R2 = 0.99) with a soggy appearance. The leakage for lettuce irradiated at > or = 2 kGy was significantly more extensive than that for nonirradiated lettuce. The irradiation of fresh-cut lettuce in modified atmosphere packages at doses of 1 kGy and perhaps 2 kGy for safety enhancement and quality improvement is feasible.

Microbial safety of fresh produce.

Section I: Microbial Contamination of Fresh Produce. Chapter 1. Enteric human pathogens associated with fresh produce: sources, transport and ecology (Robert E. Mandrell). Chapter 2. The origin and spread of human pathogens in fruit production systems (Susan Bach and Pescal Delaquis). Chapter 3. Internalization of Pathogens in Produce (Elliot T. Ryser, Jianjun Hao, and Zhinong Yan). Section II: Pre-harvest Strategies. Chapter 4. Produce safety in organic vs conventional crops (Francisco Diez-Gonzalez and Avik Mukherjee). Chapter 5. The Role of Good Agricultural Practices in Produce Safety (Robert B. Gravani). Chapter 6. Effective Managing through a Crisis (Will Daniels and Michael P. Doyle). Chapter 7. The Role of Water and Water testing in Produce Safety (Charles P. Gerba ). Chapter 8. Role of manure and compost in produce safety (Xiuping Jiang). Section III: Post-harvest Interventions. Chapter 9. Aqueous antimicrobial treatments to improve fresh and fresh-cut produce safety (Joy Herdt and Hao Feng). Chapter 10. Irradiation enhances quality and microbial safety of fresh and fresh-cut fruits and vegetables (Brendan A. Niemira and Xuetong Fan). Chapter 11. Biological control of human pathogens on produce (John Andrew Hudson, Craig Billington, and Lynn McIntyre). Chapter 12. Extension of Shelf-life and Control of Human Pathogens in Produce by Antimicrobial Edible Films and Coatings (Tara H. McHugh, Roberto J. Avena-Bustillos, and Wen-Xian Du). Chapter 13. Improving Microbial Safety of Fresh Produce Using Thermal Treatment (Xuetong Fan, Lihan Huang, Bassam Annous). Chapter 14. Enhanced Safety and Extended Shelf-life of Fresh Produce for the Military (Peter Setlow, Christopher J. Doona, Florence E. Feeherry, and Kenneth Kustin, Deborah Sisson, and Shubham Chandra). Section IV: Produce Safety during Processing and Handling. Chapter 15. Consumer and Food Service Handling of Fresh Produce (Christine M. Bruhn). Chapter 16. Plant Sanitation and Good Manufacturing Practices for Optimum Food Safety in Fresh-cut Produce (Edith Garrett). Chapter 17. Third party audit programs for the fresh produce industry (Kenneth S. Petersen). Chapter 18. Pathogen Detection in Produce using Applications of Immunomagnetic Beads and Biosensors (Shu-I Tu, Joseph Uknalis, Andrew Gehring, and Peter Irwin). Section V: Public, Legal, and Economic Perspectives. Chapter 19. Public Response to the 2006 Recall of Contaminated Spinach (William K. Hallman, Cara L. Cuite, Jocilyn E. Dellava, Mary L. Nucci, and Sarah C. Condry). Chapter 20. Produce in public: Spinach, safety and public policy (Douglas A. Powell, Casey J. Jacob and Benjamin Chapman). Chapter 21.Contaminated Fresh Produce and Product Liability: A Law-in-Action Perspective (Denis W. Stearns). Chapter 22. The Economics of Food Safety: The 2006 Foodborne Illness Outbreak Linked to Spinach (Linda Calvin, Helen H. Jensen and Jing Liang). Section VI: Research Challenges and Directions. Chapter 23. Research Needs and Future Directions (Brendan A. Niemira, Xuetong Fan, Christopher J. Doona, Florence E. Feeherry, Robert B. Gravani).

Combination of Hot-Water Surface Pasteurization of Whole Fruit and Low-Dose Gamma Irradiation of Fresh-Cut Cantaloupe

Improvements in methods for disinfecting fresh-cut cantaloupe could reduce spoilage losses and reduce the risk of foodborne illness from human pathogen contamination. The objective of this study was to investigate the feasibility of using hot-water treatment in combination with low-dose irradiation to reduce native microbial populations while maintaining the quality of fresh-cut cantaloupe. Whole cantaloupes were washed in tap water at 20 or 76 degrees C for 3 min. Fresh-cut cantaloupe cubes, prepared from the washed fruit, were then packaged in clamshell containers, and half the samples were exposed to 0.5 kGy of gamma radiation. Native microflora populations and sensory qualities were evaluated during the subsequent 7 days of storage at 4 degrees C. The hot-water surface pasteurization reduced the microflora population by 3.3 log on the surface of whole fruits, resulting in a lower microbial load on the fresh-cut cubes compared with cubes cut from fruit treated with cold water. Irradiation of cubes prepared from untreated fruit to an absorbed dose of 0.5 kGy achieved a low microbial load similar to that of cubes prepared from hot-water-treated fruit. The combination of the two treatments was able to further reduce the microflora population. During storage, the headspace atmosphere of the packages was not significantly influenced by any of the treatments. Color, titratable acidity, pH, ascorbic acid, firmness, and drip loss were not consistently affected by treatment with irradiation, hot water, or the combination of the two. Cubes prepared from hot-water-treated whole fruit had slightly lower soluble solids content. The combination of hot-water pasteurization of whole cantaloupe and low-dose irradiation of packaged fresh-cut melon can reduce the population of native microflora while maintaining the quality of this product.

Ionizing Radiation Sensitivity of Listeria monocytogenes ATCC 49594 and Listeria innocua ATCC 51742 Inoculated on Endive (Cichorium endiva)

Ionizing radiation inactivates the pathogenic bacteria that can contaminate leafy green vegetables. Leaf pieces and leaf homogenate of endive (Cichorium endiva) were inoculated with the pathogen Listeria monocytogenes (ATCC 49594) or Listeria innocua (ATCC 51742), a nonpathogenic surrogate bacterium. The radiation sensitivity of the two strains was similar, although L. innocua was more sensitive to the type of suspending leaf preparation. During refrigerated storage after irradiation, the population of L. monocytogenes on inoculated endive was briefly suppressed by 0.42 kilogray (kGy), a dose calibrated to achieve a 99% reduction. However, the pathogen regrew after 5 days until it exceeded the bacterial levels on the control after 19 days in storage. Treatment with 0.84 kGy, equivalent to a 99.99% reduction, suppressed L. monocytogenes throughout refrigerated storage. Doses up to 1.0 kGy had no significant effect on the color of endive leaf material, regardless of whether taken from the leaf edge or the leaf midrib. The texture of leaf edge material was unaffected by doses up to 1.0 kGy, whereas the maximum dose tolerated by leaf midrib material was 0.8 kGy. These results show that endive leaves may be treated with doses sufficient to achieve at least a 99.99% reduction of L. monocytogenes with little or no impact on the products texture or color.

Effect of pH on the survival of Listeria innocua in calcium ascorbate solutions and on quality of fresh-cut apples

Fresh-cut apple slices were dipped in calcium ascorbate (CaA) solution at pH values ranging from 2.5 to 7.0 to inhibit browning. After treatment, the cut apples were stored at 4 and 10 degrees C for up to 21 days. Color and texture of the apples were determined on days 1, 14, and 21. In a separate experiement, the pH of CaA solution was adjusted with acetic acid to six different pH levels, and the solution was inoculated with Listeria innocua. The survival of the bacterium and the stability of CaA were determined at 0, 20, and 96 h. The cut apples maintained fresh quality when the pH of the CaA solution was above 4.5, but slight discoloration of apple slices dipped in pH 4.5 solution was observed after 14 days at 10 degrees C. At pH 5.0, the CaA dip maintained the quality of the apples at both temperatures for at least 21 days. The L. innocua population was reduced by 4 to 5 log CFU/ml at pH 4.5 after 96 h. At pH 5, the bacterial population in the CaA solution was reduced by approximately 2 log CFU/ml during the same period. The CaA solution was stable at pH 5 for at least 96 h. Reduction of the pH to between 4.5 and 5.0 might reduce the risk of foodborne illness due to consumption of fresh-cut apples treated with a CaA solution contaminated with Listeria.