Brief Summary of Minutes of Annual Meeting

OBJECTIVE 1. Assess the presence and physiological significance of nutrients and other functional components of fresh-cut vegetables and fruits as affected by storage and handling. Preharvest Effects The composition of fresh peeled garlic in relation to nitrogen fertilization and irrigation regimes was evaluated (CA). On sandy soils; alliin content increased with increased N and irrigation but on clay-loam soils it was increased only by increasing N. Alliin content in garlic from 85 accessions of the USDA germplasm collection varied from ~0 to >25 mg/g dry weight. Broccoli floret composition in relation to nitrogen fertilization was a 4-year project to be completed in Dec 2003. Changes in sugars, chlorophyll, carotenoids, ascorbic acid were determined as well as glucosinolates and sulfurophane in response to five levels of N fertilization (CA). Apple phenolic phytochemicals have chemopreventive activities on colon and liver cancer cells and that apple phenolics also showed strong beneficial effects on dysfunctional gap-junction intercellular communication induced by oxidative stress (NY). Effects of phenolic phytochemicals in apples against oxidative cell death in cultured rat pheochromocytoma neuronal (PC-12) are being studied and the preliminary results showed that apple phenolics protected PC-12 cells from H2O2induced oxidative toxicity in vitro in a dose-dependent manner. Therefore apple phenolics contribute significantly to total antioxidant, antitumor, and antineurodegenerative activities in vitro studies, and hence one apple a day that will provide a significant amount of daily nutraceutical compounds and other possible health benefits. Postharvest Treatments Chitosan coating of tomato (Lycopersicon esculentum Mill cv. VFNT cherry) significantly suppressed polygalacturonase (PG isozymes I & II and total ) and ²-D-galactosidase cell - wall enzyme activities, water- soluble pectin content and maintained cellular integrity longer (AL). Proline accumulation was also enhanced. Effects of chitosan application were attributed to directly to modification of fruit internal atmosphere. Antioxidants, carotenoids, pectin, and flavor volatiles were analyzed during handling and storage of tropical fruits (ARS-FL). This data will be inserted into a database for future reference by researchers, regulators and industry. The potential for postharvest treatments to increase concentrations of bioactive compounds in fresh, fresh-cut, or processed mango is ongoing (FL). The effects of ozone rinse treatments on nutritional components of various fresh-cut fruits and vegetables including tomatoes, cantaloupes, apples and oranges are being evaluated (TN). Ascorbic acid was reduced by 50-90% with ozone washing in tomatoes, while lycopene was unaffected under the same processing conditions. Through a phenomenon known as intramolecular copigmentation, anthocyanins were shown to associate with various metal ions and polyphenolic cofactors such as flavonoid glycosides, hydroxycinnamates, and other anthocyanins to inhibit lipoxygenase (LOX) in fresh-cut carrots. Various combinations of anthocyanins and cofactors resulted in enhanced pigment color, antioxidant capacity, and LOX inhibition (in vitro and in vivo). It was found that 15-50 ppm of four anthocyanin sources were needed to achieve 50% inhibition of LOX using a purified enzyme extract. However, considerably higher concentrations were needed to equivalently inhibit LOX in crude enzyme isolates from carrots (FL). The effect of ionizing radiation on antioxidant capacity, phenolic content and tissue browning of three vegetables was studied (PA). Midrib and non-midrib leaf tissues of Romaine and Iceberg lettuce and endive were irradiated with gamma rays at 0, 0.5, 1, and 2 kGy, and then stored at 7-8 °C for 8 days. Antioxidant capacity and phenolic content of tissues, as well as tissue browning were analyzed at 1, 4 and 8 days of storage. In general, irradiation increased the phenolic content and antioxidant capacity of both tissue types of all vegetables at day 4 and day 8. The rates of the increase were higher in midrib tissues than in non-midribs, and increased with storage time. Irradiation, however, increased tissue browning of midrib tissues of Romaine and Iceberg lettuce. These results suggest that irradiation increased nutritional quality of leafy vegetables, but some adverse visual quality changes were encountered. Storage Effects Changes in amino acid and fermentative volatiles concentrations were studied in broccoli florets stored at 10°C in air, low O2, high CO2 and atmospheres with a combination of high CO2 and low O2. This is the last of a series of studies on broccoli composition in relation to extreme atmospheres with the main objective to provide some reference points for the degree of change expected under a range of extreme modified atmospheres (CA). Compositional changes and important components in garlic bulbs and cloves that were stored under controlled atmospheres (fructan, alliin, thiosulfinates) were evaluated (CA). Determined if spinach could respond well to modified storage atmosphere (CA). Spinach was found to generate substantial concentrations of ammonia when held under atmospheres with relatively high concentrations of carbon dioxide. This offers a good explanation as to why spinach cannot be held in modified atmosphere packaging. The effect of storage temperature on retention of folate, carotenoids, and other quality characteristics in commercially packaged fresh spinach were determined (PA). Based on visual color and appearance, spinach was unacceptable after 8 d, 6 d, and 4 d at 4 °C, 10 °C, and 20 °C, respectively. Color differences (_E), chlorophyll degradation, fresh weight loss, and microbial populations increased at all storage temperatures and occurred more rapidly at higher temperatures. Peroxidase activity increased but was not significantly (P > 0.05) affected by storage temperature. Lipoxygenase activity was unaffected by storage time or temperature. Substantial losses of nutrients occurred at each storage temperature. Only 53% of folate in packaged spinach was retained after 8 d, 6 d, and 4 d at 4 °C, 10 °C, and 20 °C, respectively. Carotenoid losses increased with temperature with only 54%, 61%, and 44%, respectively, of initial detected levels remaining. Vitamin and quality changes were unaffected by presence or absence of packaging. The influences of processing and storage on the postcutting life and nutritional quality of fresh-cut fruits were evaluated and compared with freshly-prepared slices made from fruits that were stored for similar durations (CA). Fresh-cut pineapples, mangoes, cantaloupes, watermelons, strawberries and kiwifruits and whole fruits were stored for up to 9 days in air at 5 ºC. Changes in quality attributes, total ascorbic acid (reduced ascorbic acid and dehydroascorbic acid), carotenoids and phenolics were determined. Fresh-cut processing reduced postcutting life to 6 days for fresh-cut kiwifruit and less than 9 days for fresh-cut pineapple, cantaloupe and strawberry. On the other hand, the shelf-life of fresh-cut watermelon and mango extended beyond 9 days at 5ºC. Changes in total ascorbic acid (vitamin C), total carotenoids, and total phenolics were small and mostly not significant within the 6 to 9 days of optimal post-cutting-life. Processing of whole fruit was found to induce similar variation of nutrient content compared to fresh-cut and resulted in no major changes after storage. Light exposure promoted browning in pineapple wedges and decreased total ascorbate content in kiwifruit slices. In addition, the content of total carotenoids in cantaloupe cubes and kiwifruit slices decreased under light while it increased in mango and watermelon cubes. There was no effect of light exposure on the total phenolics content. In general, fresh-cut fruits visually spoil before any significant nutrient loss occurs. OBJECTIVE 2. Develop and evaluate novel approaches for assuring the quality and safety of fresh-cut vegetables and fruits. Improved tools, methods, facilities or equipment A new ozone generator was obtained for use in evaluating other fruit and vegetable products including tomatoes and cantaloupes (TN). Methods of pretreating whole fruit for improvement of fresh-cut quality and shelf life were developed. Whole apples were pretreated with 1-MCP, heat and ethanol for effect on the sliced product. Heat and ethanol pretreatments resulted in extended shelf life for cut apple, and ethanol treatment enhanced appearance and reduced decay in mango, although some off flavor was associated with the higher level ethanol treatments. (ARS-FL) An improved sanitation system was developed for cut mangoes (ARS-FL). Sanitizing the whole fruit prior to cutting with peroxyacetic acid resulted in less cross-contamination of cut slices than when sodium hypochlorite was used on whole fruit. Methods developed in the laboratory to inactivate attached bacteria on produce must be verified in a safe and controlled manner with commercial-like equipment housed within a secondary containment chamber in the BSL-2 pilot plant (PA). Preliminary results indicate that large-scale produce decontamination trials with pathogenic E. coli bacteria might be conducted safely in the BSL-2 containment system at ERRC. A new process has been developed to produce electrolyzed oxidized (EO) water with enhanced stability (GA). Benefits of the new stable EO water include, long shelf life, no corrosive effect on most food processing and service equipment, and same efficacy for bacteria inactivation as regular EO water. An objective way to determine tissue damage of fresh-cut vegetables was developed and it is based on image processing technology (MD). Similar work is also being conducted in correlating total sensory (appearance, texture, flavor, odor), compositional, and microbiological quality changes in fresh-cut zucchini in MAP with machine vision and electronic nose measurements (FL). The goal of this second project is to develop and train a neural network, using these nondestructive, objective readings as inputs, and shelf life as outputs, in order to predict the shelf life of the product. A PCR (polymerase chain reaction) methods for detecting Salmonella montevideo, Escherichia coli O157:H7, Listeria monocytogenes and other Salmonella strains (GA, MD, PA). In case, the work is focusing on multiple simultaneous tests (MD). The efficacy of cultural methods for detection of Salmonella in alfalfa seeds and fresh produce were tested (PA). Five agar media commonly used for detection of Salmonella in food samples exhibited different degrees of sensitivity. The semi-solid Rappaport-Vassiliadis (SRV) medium was 100-fold more sensitive than the other four media. Fewer than 10 Salmonella cells in a sample containing more than one million native bacteria can be detected on SRV. Micro-perforated films were found to provide significantly better quality retention in broccoli florets than solid films (MI). The micro-perforated films generated high CO2 and high O2 atmospheres, whereas the solid films led to low O2 and high CO2 atmospheres. Development of edible coatings to prolong shelf life of fresh and fresh-cut fruits and vegetables. Improving microbial safety and shelf-life of fresh produce with antimicrobial films to determine the anti-bacterial activities of selected bacteriocins and phenolics incorporated into hydrophilic/hydrophobic edible films/coatings against selected foodborne pathogens on selected fresh and fresh-cut fruits and vegetables (AR). Used model systems of selected hydrophilic or hydrophobic protein films containing nisin and/or pediocin and/or natural phenolics at varying pH, and citric acid/EDTA levels. Optimal anti-pathogen films tested for their ability to conserve the physicochemical quality and sensory attributes of fresh-cut fruits and vegetables. Coatings on apple, peaches and mango showed some promising results for inhibition of browning and maintenance of flavor volatiles (mango) that warrant further research (ARS-FL, FL, MD, GA). CMC-based edible film coatings on fresh-cut peach for maintenance of cut surface moistness and retention of aroma volatiles were tested (ARS-FL, FL). Cut apple slices were treated with various coatings and surface antioxidants (ARS-FL). Coatings reduced water loss, and antioxidant treatments reduced browning. There were various effects on flavor compounds. Cut mango was also treated with various antioxidants, acidulants and coatings. Some polysaccharide coatings resulted in a more hydrated surface, thus improving appearance. Work will continue in this area combined with aroma and sensory analyses. OBJECTIVE 3. Develop a better understanding of the physiology of fresh-cut vegetables and fruits in response to processing and during storage and handling. Chilling injury An ethylene biosynthesis inhibitor (AVG), ethylene pretreatments, ethylene absorbent pads in containers, and containers without and with 1 or 6 perforations were used to help simulate different rates of ethylene production and/or ethylene accumulation levels in the headspace above fresh-cut tomato slices stored in MA containers at 5°C. Ethylene levels were related to the development of chilling injury during storage (MD). Storage of tomatoes for >2 days at any temperature <20°C results in reduced sensory aroma and flavor as well as reduced aroma volatile levels as measured by both GC and electronic nose analyses (FL). These findings have important quality implications for fresh-cut tomatoes and other fresh-cut products, especially products made from chilling sensitive species that are handled at temperatures below the chilling threshold of the intact product Determined if spinach could respond well to modified storage atmosphere (CA). Spinach was found to generate substantial concentrations of ammonia when held under atmospheres with relatively high concentrations of carbon dioxide. This offers a good explanation as to why spinach cannot be held in modified atmosphere packaging. Phenomenon associated with quality changes A phenomenon termed secondary browning has been identified as a major shelf life problem in apple slices (BC). The cause of browning in slices appears to be associated with microbes that have pectolytic activity. The microbial associated discoloration appears to become a predominant problem as the apples are stored for longer periods in storage. Fresh-cut kernels can be stored about 10 days at 1°C or 7 days at 5°C, with shelf life limited by flavor loss and after-cooking browning. The latter increases with advanced maturity and higher storage temperature. The group in FL is examining the browning products to determine if Maillard reaction or phenolic autooxidation may be involved. Ethylene responses in strawberries and different tomato tissues during fruit development were investigated (FL). Exposure of strawberry tissues to C2H4 induces ACC oxidase (ACO) but not ACC synthase activity at all ripening stages, leading to a short-term increase in C2H4 production followed by a sharp reduction to the control level along with a marked reduction in ACC levels. A transition from autoinhibition to autocatalysis of ethylene production occurs in tomato fruit during development, but CO2 production, ACO activity, red color development, tissue liquefaction, and seed germination are stimulated by C2H4 in tissue exhibiting either autoinhibition or autocatalysis. This research relates to the potential for applying or excluding ethylene from packages of fresh-cut fruit. Tomato responsiveness (ripening inhibition) as affected by1-MCP concentration, frequency of application, and stage of development was studied (MI). 1-MCP reduced the rate of red color development in fruit of all maturity classes; however, the effect was more discernable in greener fruit. A single application of 1-MCP delayed the color development by approximately 6 d. While a second application of 1-MCP at 10 days after first treatment delayed color development by another 8-10 d for mature green tomatoes, it did not markedly influence the color change in all other classes of ripeness. Continuous application inhibited color development of turning and half-ripe fruits for the duration (34 d) of application. Firmness loss was reduced by 1-MCP application in all cases, but the effect was not as marked as the effect on color. When fruit at 50% color development were treated with 1-MCP, gel color tended to lag behind the external fruit color compared to non-treated fruit. Some aroma volatiles were affected by 1-MCP. In general, volatiles affected by harvest at a less mature stage were also altered by 1-MCP. Collectively, the data indicate 1-MCP caused minor shifts in the quality attributes of locule color aroma, and firmness relative to external color, which may reduce the value of this treatment, but benefits accrued by slowed firmness loss and color development may afford compensation. Chlorophyll fluorescence changes were found to be closely associated with the accumulation of fermentation products in broccoli tissue (BC). Fermentation product does not easily dissipate when product is removed to air storage conditions. Chlorophyll fluorescence measurements can rapidly (within a few seconds) indicate this problem. The advantage of chlorophyll fluorescence is that it is rapid, non-destructive and tests can be performed while the product is still enclosed in its package. Watersoaking of fresh-cut tomato is a consequence of wounding, not chilling injury (FL). When whole and fresh-cut tomatoes are stored at 5 °C, only fresh-cut slices develop watersoaking. Watersoaking development is also dependant on temperature: watersoaking was much worse in slices prepared at 5 °C then held at 10 °C or prepared at 28 °C then held at 5 °C compared with slices prepared and held at 5 °C. Ethylene may also play a role in watersoaking because treatment of light red tomatoes with 1-MCP (1 uL L-1) for 24 hours at 5 or 20 °C before slicing reduced watersoaking at 5 °C, more so than treatment of red tomatoes. Our current efforts are targeted toward changes in membrane permeability and enzymes involved in membrane deterioration and cell wall hydrolysis in relation to watersoaking of fresh-cut tomato tissue. Reduced O2 plus elevated CO2 (2% O2 + 10% CO2) was very beneficial in maintaining the visual quality of fresh-cut sweetcorn kernels and reduced sugar and flavor losses during 10 days storage at 5 °C compared to storage in air (FL). The main benefit of using controlled atmosphere (CA) storage is preventing after-cooking browning. Preliminary results indicate that after-cooking browning is not associated with a Maillard reaction since 5-hydroxymethylfurfural (HMF), the characteristic intermediate compound produced during the Maillard reaction, is not present in cooked sweetcorn kernels exhibiting browning. There were no significant changes in the total soluble phenolics content during storage in air or CA, but the soluble phenolic levels decreased with cooking, which suggests that the after-cooking brown color may be due to as yet unidentified insoluble phenolic-protein complexes in the cooked sweetcorn tissue. The total aerobic microbe count increased with storage and the increase was significantly greater in air. Several microbial isolates from stored fresh-cut kernels were inoculated onto fresh-cut sweetcorn kernels and it was observed that microbe counts increased earlier and after-cooking browning occurred earlier in storage for the spiked samples. This suggests that the browning could be a response of the sweetcorn tissue to the microorganisms, or it may be associated with some product of microbial enzyme activity. The physiological responses to heat treatment were examined in relation to the effects that the treatment has on quality (CA). Structural changes were induced in broccoli peroxidase following thermal treatments and these changes could potentially be reversed. Low temperature blanching of diced tomatoes improves firmness potentially through the effect of heat on pectin methylesterase. Vacuum infusion of exogenous enzymes (esp. pectinmethylesterase) with CaCl2 to increase cell wall strength of cut fruits and vegetables is currently under investigation (GA).