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Yaguang Luo

Washing is a critical step for maintaining quality and safety of fresh-cut produce during its preparation and is often the only measure taken to reduce microbial populations and remove tissue fluids. However, little is known about the effect of washing method on water quality or its consequence on microbial growth and finished product quality. This study was conducted to evaluate the effect of wash water reuse on changes in water quality and its subsequent effect on microbial growth and product quality of packaged fresh-cut Romaine lettuce (Lactuca sativa L.). Romaine lettuce leaves were sliced and washed in water with chemical oxygen demand levels ranging from 9.8 mg·L−1 (fresh water) to 1860.5 mg·L−1 (reused water) and product-to-water ratios of 1:20 and 1:150. The washed samples were dried and placed into packages prepared from films with an oxygen transmission rate of 8.0 pmol·s−1·m−2·Pa−1 and stored at 5 °C for 14 days. Microbial growth and product quality were monitored at days 0, 4, 8, 11, and 14 during storage. Results indicate that as the quantity of lettuce dipped in 40 L of water increased from 2.0 kg to 18.0 kg, water chemical oxygen demand increased from 124 mg·L−1 to 1721 mg·L−1 and biological oxygen demand increased from 140 mg·L−1 to 526 mg·L−1, whereas free and total chlorine levels declined from 151.5 mg·L−1 to 4.7 mg·L−1 and from 171 mg·L−1 to 31.5 mg·L−1, respectively. Thoroughly washed lettuce in clean water with a small product-to-water ratio had the least off-odor development. Samples without wash treatment and those washed with reused water had 0.8 to 1.6 log cfu·g−1 higher populations of lactic acid bacteria than those washed with clean water at the end of storage.

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Yaguang Luo and Max E Patterson

The control of enzymatic browning of apple slices with papain is presented. Fresh apple slices dipped in a 1% Papain solution for 2 min did not brown for more than 12 hours at room temperature. Papain also gave good browning control of sliced pears. Further study indicated that polyphenoloxidase, a key enzyme involved in browning, was inactivated by this treatment.

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Ji Gang Kim*, Yaguang Luo, Yang Tao and Kenneth C. Gross

The effects of 1-methylcyclopropene (MCP), sanitizer and their combination on ethylene action, microbial growth and storage life of fresh-cut cilantro were studied. Fresh cilantro was treated with 1.5 μL·L-1 MCP for 18 hours at 10 °C. The treated and nontreated cilantro leaves were cut and washed in water, chlorine, and mixed solution of sodium chlorite and citric acid (SANOVA). Samples were dried, packaged with 29.2μmol·kg-1 Pa s oxygen transmission rate films, and stored for 14 days at 5 °C. Results indicated that MCP affected respiration rate of fresh-cut cilantro and the headspace gas composition (O2 and CO2) of sample packages. The combined treatment had lower tissue electrolyte leakage and ethanol concentration, and delayed color changes during storage. SANOVA and the combination of MCP and SANOVA were effective in reducing aerobic microbial population and coliform population. Samples treated with MCP and SANOVA had good quality with high overall quality score at the end of storage.

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Liping Kou, Tianbao Yang, Xianjin Liu and Yaguang Luo

We reported previously that the preharvest treatment of broccoli microgreens with 10 mmol·L−1 calcium chloride (CaCl2) increased the yield and postharvest quality. The objective of this study was to investigate whether other calcium forms have the similar effect, in particular, after postharvest dip in calcium solution. Our results are as follows: 1) Preharvest spray without postharvest dip: Both 20 mmol·L−1 calcium lactate (Ca lactate) and calcium amino acid (Ca AA) chelate significantly improved broccoli microgreens quality and inhibited microbial populations as compared with the water-only control during storage at 5 °C for 21 days. However, they were less effective than 10 mmol·L−1 CaCl2. 2) Postharvest dip without preharvest spray: The microgreens sprayed with water-only control were dipped in 0, 25, 50, or 100 mmol·L−1 Ca lactate solution containing 100 μL·L−1 chlorine immediately after harvest. During storage at 5 °C for 14 days, 50 mmol·L−1 Ca lactate dip showed the highest overall quality and lowest tissue electrolyte leakage. 3) Preharvest spray and postharvest dip: Combined preharvest 10 mmol·L−1 CaCl2 spray and postharvest 50 mmol·L−1 Ca lactate dip resulted in better postharvest quality than individual pre- or postharvest calcium treatments. However, the preharvest 10 mmol·L−1 CaCl2 spray without postharvest dip displayed a best overall visual quality and longest storage life. Our data indicate that pre- and postharvest calcium treatments have positive effect on maintaining the microgreens quality and extending shelf life. However, current postharvest dip/spinning/drying method profoundly reduces the shelf life due to mechanical damages. Technologies to optimize microgreens wash are needed to provide ready-to-eat product. Alternatively, the wash step can be avoided when the microgreens are grown under controlled settings.

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Liping Kou, Yaguang Luo, Wu Ding, Xinghua Liu and William Conway

Alternatives to sulfur dioxide to maintain quality of table grapes, including various combinations of rachis removal, chlorinated wash, hot water treatment, and modified atmosphere packaging, were explored in this study. Grapes were prepared by cutting off the rachis 1 to 2 mm from the fruit or by keeping the clusters intact. After initial preparation, short-stem and cluster grapes were subjected to chlorinated wash and/or hot water (45 °C, 8 min) treatment and packaged in plastic trays sealed with a gas-permeable film. The treated grapes as well as the commercially packed grapes (COM) in their original packages were stored at 5 °C for up to 4 weeks. Hot water treatment resulted in significantly (P < 0.05) higher oxygen retention and lower carbon dioxide accumulation in package headspaces, maintained a firmer texture, higher overall visual quality, lower decay rate, and lower microbial populations than other treatments or COM during the entire storage period. Grapes that were cut from the rachis and treated with hot water and chlorine maintained the highest quality for 4 weeks with the least decay among all treatments. A chlorine prewash treatment significantly (P < 0.05) reduced microbial populations on cluster grapes and maintained better overall quality. Conventional COM grapes developed dark decay and lost turgidity and were of unacceptable quality at 28 days of storage.

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Ryan J. Hayes, Carlos H. Galeano, Yaguang Luo, Rudie Antonise and Ivan Simko

Fresh-cut lettuce (Lactuca sativa) packaged as salad mixes are increasingly popular to consumers but are highly perishable. Cultivars bred with extended shelf life could increase overall production efficiency by reducing the frequency of product replacement in the marketplace. Understanding the inheritance of shelf life is needed to develop efficient breeding strategies for this trait. A population of 95 recombinant inbred lines (RILs) from slow-decaying ‘Salinas 88’ × rapidly decaying ‘La Brillante’ was grown in four field experiments. Cut lettuce was evaluated for decay in modified atmosphere (MA) packages flushed with N2 or air (control). Correlations between field experiments ranged from 0.47 to 0.84 (P < 0.01). Three quantitative trait loci (QTL) for decay of cut lettuce were detected on linkage groups (LGs) 1, 4, and 9 with ‘Salinas 88’ alleles associated with slower decay. The QTL on LG 4 (qSL4) was a major determinant of decay explaining 40% to 74% of the total phenotypic variance of the trait. The greatest effect of this QTL was observed between 29 and 50 days after harvest. QTL × environment interactions contributed less than 14% to the total variation. RILs with the ‘Salinas 88’ allele of qSL4 had slower decay when packaged in air compared with N2, whereas no difference between air and N2 packaging was detected with the ‘La Brillante’ allele. A subset of RILs with either the ‘Salinas 88’ or ‘La Brillante’ allele of qSL4 was grown in two field experiments and evaluated for decay of whole heads. Genetic variation among RILs for whole-head decay was found but could not be attributed to qSL4. Decay of cut lettuce in ‘Salinas 88’ × ‘La Brillante’ is a highly heritable trait conditioned by a few QTL and phenotypic selection is likely to be effective. However, shelf life evaluations are time-consuming, destructive, and require large amounts of field-grown lettuce. Therefore, qSL4 is a good QTL to develop molecular markers for marker-assisted selection. The mechanism of decay controlled by qSL4 is unknown but appears to be specific to cut lettuce and may have allele specific interactions with packaging atmospheric compositions.

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Ji Gang Kim, Yaguang Luo, Robert A. Saftner and Kenneth C. Gross

Fresh-cut tissues are subjected to severe injury during preparation that leads to increased respiratory activity and quality deterioration. Modified atmosphere packaging (MAP) has been used to maintain quality of fresh-cut produce, but O2 depletion and excessive CO2 accumulation can be injurious. This study was conducted to evaluate the effect of delayed packaging and MAP using two different oxygen transmission rate (OTR) films on quality maintenance and shelf stability of fresh-cut romaine lettuce (Lactuca sativa L.). Romaine lettuce leaves were cut, washed, dried, and placed for 0, 4, 8, and 12 hours at 5 °C in ambient air before packaging. Fresh-cut samples were placed into packages prepared from films having OTRs of 8.0 and 16.6 pmol·s-1·m-2·Pa-1, flushed with N2 to reach an initial headspace O2 level of 1.5 kPa O2, and stored at 5 °C for up to 14 days. Delayed packaging affected gas composition, fermentative volatile production, off-odor development, color, CO2 injury, and tissue electrolyte leakage. With increasing delay before packaging, fermentative volatile production, off-odor development, and CO2 injury progressively decreased and discoloration increased. The modified atmospheres obtained with 16.6 OTR film increased discoloration when present, and generally had less off-odor development and CO2 injury compared to MAP with 8.0 OTR film. Delayed packaging affected overall quality of fresh-cut romaine lettuce packaged with both films. A 12-hour delayed packaging into packages prepared from 8.0 OTR film maintained quality by inhibiting CO2 injury, off-odor development, and tissue electrolyte leakage. However, an 8-hour delayed packaging into packages prepared from 16.6 OTR film was better at maintaining the quality of fresh-cut romaine lettuce at 5 °C for 14 days. The results indicated that delayed packaging could be an alternative method to optimize or balance package O2 during suboptimal OTR film packaging conditions.

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Max Patterson, M. Ahmedullah, Frank Younce, Jo Ann Robbins and Yaguang Luo

Blueberries were exposed to a series of atmospheric gas mixtures using an automated, computerized, gas-mixing, monitoring, controlling and recording system. Nitrogen was obtained from a PSA generator, O2 from an in-house air compressor and CO2 from compressed gas cylinders. Precise mixtures were made by introducing source gas streams into electronic gas-mixing valves where they were pre-mixed at desired concentrations and directed to fruit chambers. Gas mixtures giving maximum decay control and retention of harvest quality at 0°C were determined. Mixtures preserving fruit without causing fermentation or toxicity were also determined. Quality was retained in excess of 60 days at optimum gas levels. Increasing the fresh market period of blueberries with CA storage and prolonging shelf life and extending shipping distances with MA packaging appears promising.

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Yaguang Luo, James L. McEvoy, Marian R. Wachtel, Ji Gang Kim and Yun Huang

Experiments were conducted to develop a modified atmosphere packaging system for fresh-cut cilantro (Coriandrum sativum L.) leaves, and to determine the effect of package film oxygen transmission rate (OTR) on package atmosphere and the consequence on quality and microbiology of the product. Package film OTR significantly (P < 0.001) influenced the package atmospheres and the resultant postharvest physiology and quality of fresh-cut cilantro leaves under the tested package configuration (bag size 19 × 22 cm, product fill weight 85 g/bag) and storage condition (0 °C). Oxygen and carbon dioxide levels of the packages prepared with 3500 mL·d-1·m-2 OTR films equilibrated at 1.5 to 2.3 kPa and 3.6 to 4.1 kPa, respectively, on day 3 and maintained this level throughout the storage. The gas compositions of the packages with 6200 mL·d-1·m-2 OTR films showed a similar trend, except they equilibrated at a higher O2 (3.6 to 5.6 kPa) and lower CO2 (2.7 to 3.3 kPa) level. Fresh-cut cilantro leaves in both packages exhibited the highest tissue integrity as evidenced by the lowest tissue electrolyte leakage, with high overall visual quality scores (like moderately to like very much) at the end of 14 days storage. However, atmospheres in 1700 mL·d-1·m-2 OTR film packages displayed a rapid depletion of O2 and accumulation of CO2, with essentially no O2 (≈0.02 kPa) and high CO2 (7.7 to 9.0 kPa) levels inside the packages from day 6 until the end of storage. A rapid increase in tissue electrolyte leakage was observed in cilantro leaves in these packages starting on day 6, increasing 6-fold at the end of the storage period. Products in these packages developed a strong off-odor, accompanied by a rapid loss of typical aroma and overall visual quality, with an unacceptable quality rating at the end of storage (dislike slightly). Samples packaged in perforated bags (without modified atmosphere) lost moisture over time, and small numbers of wilted leaves were seen. There was a slow but significant (P < 0.001) increase in aerobic organisms over time with no significant (P > 0.05) difference among treatments. There was an increase in anaerobic microorganisms on cilantro leaves packaged in 1700 mL·d-1·m-2 OTR film, although only ≈0.5 log cfu/g difference was observed among the treatments and over time.

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John R. Stommel, Mary J. Camp, Judith M. Dumm, Kathleen G. Haynes, Yaguang Luo and Anne Marie Schoevaars

Fresh pepper (Capsicum) fruit that are sliced and/or diced are referred to as fresh-cut products. The current report evaluates the inheritance of postharvest attributes that contribute to pepper fresh-cut quality. Marketable green fruit of large-fruited Capsicum annuum accessions with bell and related pod types (Class 1), C. annuum accessions with jalapeno and serrano pod types (Class 2), and thin-walled “aji”-like tabasco pod types from Capsicum baccatum, Capsicum frutescens, and Capsicum chinense (Class 3) were processed and stored up to 14 days in selective oxygen transmission rate packaging. Fresh-cut attributes were influenced by genotype as well as year. For all pod types, O2 and CO2 partial pressures in storage packages, tissue weight loss, and electrolyte leakage differed among accessions, days of storage, and years of testing. Percent O2 declined and CO2 and electrolyte leakage generally increased during storage. Some accessions in Class 1 and Class 2 maintained acceptable product quality during storage. Changes in fruit weight loss were small with greater weight loss observed in Class 1 accessions relative to weight loss for Class 2 and Class 3. Broad-sense heritability for fresh-cut attributes was moderate to low indicating that it will be difficult to breed for fresh-cut quality.