Changwen Lu

Effect of 1 and 100 kPa O2 atmospheric pretreatments of whole ‘Spartan’ apples on subsequent quality and shelf life of slices stored in modified atmosphere packages☆

Abstract Whole ‘Spartan’ apples were exposed to 1 kPa O2, air (21 kPa O2) and 100 kPa O2 at 1°C for 5, 12 and 19 days. Subsequent to the pretreatment, apples were cored, sliced and 400±5 g of slices were sealed in 40-μm-thick low density polyethylene film bags having a moderate O2 transmission rate (OTR∼2.28 fmol s−1 m m−2 Pa−1 at 23°C) and held for up to 2 weeks at 1°C. Cut surface browning and flesh softening were inhibited for packaged slices by pretreating the whole fruit with 100 and 1 kPa O2 as compared with those from the air pretreatment. However the slices from the 100 kPa O2- and air-pretreated apples contained a much lower content of fermentation products associated with off-flavors compared with the slices from apples pretreated in 1 kPa O2. Packages containing apple slices from the air pretreatment developed a more highly modified atmosphere than packages containing apples slices from the other two pretreatments, suggesting that both 1 and 100 kPa O2 pretreatments suppressed the respiration rate of apple slices. Slices from apples pretreated with 1 kPa O2 developed more cut surface browning and greater tissue solute leakage and enhanced accumulations of acetaldehyde, ethanol and ethyl acetate in apple slice tissue as compared with slices cut from the 100 kPa O2-pretreated apples.

1-Methylcyclopropene plus high CO2 applied after storage reduces ethylene production and enhances shelf life of Gala apples

The effect of a combined treatment comprising a 35% CO2 atmosphere plus 250 nL L-1 1-methylcyclopropene (1-MCP) on shelf life of Gala apples app lied after removal from air or controlled atmosphere (CA) storage was evaluated. Fruit were removed from air storage at 10 and 18 wk and from CA storage at 18 and 22 wk, warmed to 20°C and then treated for 16 h with 1-MCP either in combination with or without 35% CO2. Treated fruit were held at 20°C in air for up to 15 d and assessed every 5 d. Onset of ethylene production was delayed and quality retention was only marginally improved with the 1-MCP treatment. In contrast, both were significantly affected when a 35% CO2 atmosphere was applied in combination with the 1-MCP treatment. Fruit that were treated with 1-MCP in a 35% CO2 atmosphere exhibited the lowest levels of internal ethylene concentration (IEC) and the smallest decline of flesh firmness and titratable acidity (TA) during holding at 20°C. No symptoms of CO2 injury were noted. In the high CO2 atmosphe...

Modulation of wound-induced hydrogen peroxide and its influence on the fate of Escherichia coli O157:H7 in cut lettuce tissues.

Wounding of lettuce tissue has been examined previously by others in regard to browning reactions, and treatments to modulate wounding responses were evaluated for reduction of browning. However, the wounding process also releases oxygen radicals such as hydrogen peroxide. This study focused on the evaluation of two treatments that reduce hydrogen peroxide at cut surfaces (heat treatment and pyruvate addition) and one treatment that enhances its production (infusion with the fungal elicitor harpin). Hydrogen peroxide changes in response to treatment were also associated with resultant survival of Escherichia coli O157:H7, which was inoculated onto the lettuce before cutting. Heat-treated lettuce produced significantly less hydrogen peroxide, and microbial analysis showed that E. coli O157:H7 survival on packaged, heat-treated lettuce was higher than on non-heat-treated controls. Lettuce was also cut under a solution of sodium pyruvate (a well-known hydrogen peroxide quencher), and E. coli O157:H7 survival was found to be enhanced with that treatment. When lettuce was infused with harpin before cutting, hydrogen peroxide production was enhanced, and this was associated with reduced survival of E. coli O157:H7. These results collectively support the hypothesis that modulation of wound-generated hydrogen peroxide can have an influence on E. coli O157:H7 survival on cut and packaged romaine lettuce.

Slicing under Chlorinated Water Improves the Disinfection of Fresh-Cut Romaine Lettuce

The aim of this study was to determine whether the timing or mode of application influences the antimicrobial efficacy of a sodium hypochlorite solution against microorganisms on fresh-cut Romaine lettuce. Lettuce leaves were treated with a solution of sodium hypochlorite containing 70 mg liter(-1) free chlorine prior to slicing (WLS), while submerged in the solution (CWS), or after slicing (PCS), the last being common practice in the fresh-cut industry. Immediate antimicrobial effects were determined from analyses performed directly after treatment, while delayed effects were derived from analysis of packaged samples stored at 4 and 15°C. Experiments were performed with both uninoculated and inoculated whole leaves, using Escherichia coli O157:H7 from a type collection as an inoculum. The CWS treatment provided the greatest initial reductions in aerobic plate counts of E. coli O157:H7 populations, followed by PCS and WLS. The advantage afforded by the CWS approach was maintained over 10 days in storage at 4°C. In addition, it was noted that the visual quality attributes of the fresh-cut lettuce from the CWS approach were better than those from the other two treatments. These results collectively suggest that slicing lettuce under a sanitizer solution could provide better disinfection of fresh-cut Romaine lettuce than the current practice of washing with sanitizer after cutting has taken place.