Cut Edge Browning Research Articles

Growing season climates affect quality of fresh-cut lettuce

The objective of this study was to investigate if different growing season climates influenced the quality of fresh-cut lettuce. Different cultivars and harvests of iceberg and romaine lettuce grown over 26 months were processed and stored for 11 d in active modified atmosphere (MA) and then transferred to air for 24h at 7°C. Pearson correlation coefficients were established between different climatic factors and subjective and objective parameters related to quality loss. Growing season mean temperature (GST) and growing cycle influenced the quality characteristics of fresh-cut lettuce but the correlations between GST and quality characteristics were always higher than for growing cycle in both types of lettuce, iceberg and romaine. Winter growing season caused low oxygen (O2) and more significantly high carbon dioxide (CO2) that reduced enzymatic browning although it conferred off-odors. Respiration rate was significantly influenced by GST but only in fresh-cut romaine. Interestingly, off-odors and fermentative metabolites such as ethanol and acetaldehyde were significantly reduced in those months of higher GST. However, cut edge browning was significantly promoted, indicated by the reduction in hue angle as GST increased. These results identified that the mean temperature during cultivation was the climate variable that contributed most to quality loss of fresh-cut lettuce. Due to the strong impact of growing season climate, some changes in raw material specifications, packaging design and days of shelf life are recommended in order to assure the quality of fresh-cut lettuce during the whole year.

Modified atmosphere (MA) prevents browning of fresh-cut romaine lettuce through multi-target effects related to phenolic metabolism

Browning of fresh-cut romaine lettuce was inhibited in modified atmosphere (MA) packaging with low O2 and moderate CO2 concentrations during storage. This study explains the control mechanisms of MA causing differences in phenolic substrates and oxidative enzymes related to browning of two cultivars of romaine lettuce. Modified atmosphere decreased PAL and PPO activities and prevented cut edge browning. In MA, the process from latent to fully active PPO decreased particularly in the cultivar more susceptible to browning. The content of vitamin C was maintained or even increased in MA while decreased markedly in air. Caffeic acid derivatives increased through the storage in air whereas in MA this trend was towards a decrease in these phenolics. Chlorogenic acid was the only caffeic acid derivative that showed the same trend as PAL activity with an increase at d2 after cutting and a progressive decrease after that due to browning development and transformation to isochlorogenic acid. By the analysis of the lettuce midribs, it was possible to correlate the control of browning by MA with the suppressing action on oxidative enzymes and the slowing down of the synthesis and accumulation of caffeic acid derivatives. The browning process seems to correlate better with the biosynthesis of caffeoyl quinic derivatives, rather than with that of caffeoyl tartaric derivatives, that are always the main phenolics present in romaine lettuce midribs. A deeper study of the different behaviour of both groups of caffeic acid derivatives is guaranteed.

Effects of pre- and postharvest lighting on quality and shelf life of fresh-cut lettuce

The effects of pre-and postharvest lighting on quality and shelf life of fresh-cut lettuce was investigated. Lettuce was grown under different light intensities (120 and 250 μmol m -2 s -1 PAR from fluorescent tubes) and quality at harvest and subsequent postharvest performance of intact leaves and fresh-cut product was monitored. Cultivation under high light prolonged the shelf life (dark storage) of both intact leaves and fresh-cut product (butterhead and iceberg lettuce). The improved shelf life was reflected in improved chlorophyll fluorescence values. Postharvest lighting of the fresh-cut product, at low intensities (7 and 30 μmol m -2 s -1 PAR from fluorescent tubes) considerably prolonged the shelf life of fresh-cut product (butterhead lettuce) compared to storage in darkness. This was reflected in higher overall visual quality values and delayed cut-edge browning. The applied light levels caused an 8 to 10 times increase in carbohydrate levels (sugars and starch) whereas carbohydrates decreased when the fresh-cut product was stored in the dark. Storage in light caused an increase in dark respiration leading to increasingly negative photosynthetic values. The prolonged shelf life of low light-treated samples is presumably related to the higher levels of sugar, counteracting starvation processes. Currently, it is not clear which processes are responsible for the sugar accumulation in lit samples. We hypothesize that, under low light conditions, sugars may be produced through the processing of chloroplast degradation products in the glyoxysome, subsequent production of malate and oxaloacetate and production of glucose through reversal of the glycolysis pathway (gluconeogenesis).

Chlorophyll Fluorescence Imaging for Monitoring the Effects of Minimal Processing and Warm Water Treatments on Physiological Properties and Quality Attributes of Fresh-Cut Salads

In this study, chlorophyll fluorescence imaging (CFI) was used to monitor plant stress induced by cutting of mini romaine lettuce (Lactuca sativa L. var. longifolia) and by cutting and washing of endive (Cichorium endivia L.) during storage. Regarding the more detailed study of endive fresh-cut salads, we additionally monitored respiratory activity, phenylalanine ammonia lyase (PAL) activity, contents of plant pigments, and cut edge browning. Determination of maximum quantum efficiency Fv/Fm was feasible through sealed consumer-sized film bags, thus, enabling the non-invasive monitoring of both fresh-cut salad types in the corresponding modified atmosphere during storage. Cutting of romaine lettuce provoked a partially reversible drop of Fv/Fm during the first 24 h. Subsequently, Fv/Fm of cut romaine strongly decreased with elapsing shelf life, whereas intact leaves exhibited only a slight decline. Regarding minimally processed endive, warm water washing progressively reduced Fv/Fm with increasing heat exposure, while respiratory activities and the content of accessory pigments remained unaffected. The heat-dependent decrease of Fv/Fm was correlated to the inhibition of the PAL activity. Mildly warm washing (40 °C, 120 s; 45 °C, 60 s) reduced PAL activities, while Fv/Fm remained widely unaffected and visual quality was only partially improved. However, warm water washing at elevated temperatures (45 °C, 120 s; 50 °C, 30–60 s) enabled maximum visual quality retention, accompanied by a significant decrease of Fv/Fm. CFI may represent a useful tool to monitor the stress conditions due to cutting and warm water treatments, hence, allowing the systematic improvement of fresh-cut produce.

Effect of Water Jet Cutting and Moderate Heat Treatment on Quality of Fresh-Cut Red Oak Leaf Lettuce (Lactuca sativa L. var. crispa)

Fresh-cut red oak leaf lettuce was produced by six different processing lines in order to assess the effect of water jet cutting (nozzle diameter 0.1 mm, pressure 2,500 bar) versus blade cutting as well as washing with cold and warm water (4 and 45 °C, 120 s) prior to and after shredding, respectively. Throughout refrigerated storage (4 °C, 12 days), O2 and CO2 levels in the modified atmosphere of the consumer-sized sample bags were monitored, and fresh-cut products and process water were subjected to microbiological analysis. As further quality parameters, phenylalanine ammonia lyase (PAL) activity as well as levels of chlorophyll a and b, β-carotene and cyanidin 3-O-(6”-O-malonyl)-glucoside were determined by HPLC with diode array detection (HPLC-DAD) and HPLC coupled with diode array detection and tandem mass spectrometry (HPLC-DAD-MSn) throughout storage. Additionally, visual appearance and cut edge browning were assessed by sensorial evaluation and stereo microscopy on storage day 8. Microbiological quality throughout commercial shelf life was best retained by warm water washing of shredded lettuce. Furthermore, moderate heat treatment significantly reduced PAL activity and cut edge browning without affecting pigment contents and vitality of the lettuce tissue. Additionally, warm water treatment significantly lowered the microbial load in the process water. Throughout storage, water jet cutting did not affect the microbial, physiological and sensorial fresh-cut lettuce quality compared to blade cutting using a newly sharpened blade, thus indicating a similar degree of wounding due to the cutting techniques applied. The application of a pre-washing step prior to shredding was found to be suitable to reduce the risk of cross-contamination in subsequent process steps.

Optimizing water management to control respiration rate and reduce browning and microbial load of fresh-cut romaine lettuce

We studied the influence of both deficit and excess irrigation on the quality of fresh-cut romaine lettuce, the second most important type of lettuce after iceberg. The influence of different irrigation regimes on respiration rate, browning and microbial quality of fresh-cut romaine lettuce (Lactuca sativa L.) was studied in 6 different harvests during 3 consecutive years. The total amount of water supplied to the crop was calculated taking into account the irrigation water and rainfall. Six different irrigation regimes were established based on a standard irrigation regime (SIR): −35% SIR (<221mm), −15% SIR (221–265mm), SIR (266–320mm), +15% SIR (321–370mm), +35% SIR (371–430mm) and +75% SIR (>430mm). Quality characteristics of romaine heads as raw material for fresh-cut were significantly influenced by irrigation regimes. The lowest fresh weight was obtained when cultivated with the most severe deficit and excess of water. Microbial loads were higher in whole heads subjected to the highest irrigation regime (+75% SIR). These differences were also observed in fresh-cut romaine lettuce after processing (d 0). However, after d 10 of storage, psychrotrophic aerobic bacteria increased around 3 log units without significant differences among irrigation regimes. Despite the high number of Pseudomonas bacteria in fresh-cut romaine lettuce, 6.2logcfug−1 in the deficit irrigated samples (−35% SIR) and 7.8logcfug−1 in the excess one (+75% SIR), no association with quality loss was observed at the end of storage. In fact, visual quality of the fresh-cut romaine lettuce did not differ among irrigation regimes because of the similar headspace gas composition, independently of the irrigation regime. However, when midribs were stored in air, cut edge browning was reduced in the less irrigated midribs despite the accumulation of phenolic compounds. PPO activity increased with the highest irrigation regime. Respiration rate of fresh-cut lettuce was significantly higher when lettuce was cultivated under extreme conditions, which corresponded to deficit irrigation (−35% SIR) or to excess of water (+35% SIR). In conclusion, adequate agricultural irrigation practices are needed to both guarantee the sustainability of the environment but also to assure the quality of the whole and fresh-cut produce. Because differences occur with distinct lettuce type, the optimization of water management is needed for each type of lettuce.

INFLUENCE OF FRUIT MATURATION, MODIFIED ATMOSPHERE PACKAGING AND STORAGE TEMPERATURE ON PHYSICO-CHEMICAL QUALITY ATTRIBUTES OF FRESH-CUT WEST INDIAN LIME (CITRUS AURANTIFOLIA)

ISHS International Conference on Postharvest and Quality Management of Horticultural Products of Interest for Tropical Regions INFLUENCE OF FRUIT MATURATION, MODIFIED ATMOSPHERE PACKAGING AND STORAGE TEMPERATURE ON PHYSICO-CHEMICAL QUALITY ATTRIBUTES OF FRESH-CUT WEST INDIAN LIME (CITRUS AURANTIFOLIA)

Effects of Gamma Irradiation, Modified Atmosphere Packaging, and Delay of Irradiation on Quality of Fresh-cut Iceberg Lettuce

This study was conducted to investigate the effect of modified atmosphere packaging (MAP) and delay of irradiation application on the quality of cut Iceberg lettuce. Overall visual quality and tissue browning of cut lettuce were evaluated using a scale of 9 to 1, whereas texture was analyzed instrumentally during 14 days of storage at 4 °C. Results showed that irradiation (0.5 and 1.0 kGy) of cut lettuce induced tissue browning when stored in air; however, when cut lettuce was stored in MAP, irradiated lettuce had better appearance than the non-irradiated ones as a result of lower O2 levels in the packages of irradiated samples compared with the levels in control packages. In general, irradiation at doses of 0.5 and 1.0 kGy did not affect firmness of the lettuce. After 14 days of MAP storage, overall visual quality of non-irradiated samples had a score of ≈4, a score below the limit of sales appeal, whereas the two irradiated samples had scores of 6.5 to 7.9, indicating the irradiated samples had a fair to good quality. Delaying irradiation by 1 day after preparation of cut lettuce did not significantly (P &gt; 0.05) affect cut edge browning, surface browning, or overall visual quality compared with lettuce irradiated immediately after preparation. Our results suggest that MAP is essential to minimize quality deterioration caused by irradiation.

Apple Cultivar and Temperature at Cutting Affect Quality of Fresh Slices

The response of four apple (Malus ×domestica) cultivars (Gala, Granny Smith, Ambrosia, and Aurora Golden Gala™) to fresh-cut processing at core temperatures of 1, 5, 13, and 20 °C was investigated. Fruit were cut after a 24-h preconditioning at one of the four temperatures and a commercial antibrowning formulation was applied as a 7% (w/v) dip before packaging the slices and storing them for 3 weeks at 5 °C. Fruit firmness generally decreased with increasing core temperature, except for Aurora Golden Gala™, which maintained similar firmness at all temperatures. Firmness varied among cultivars, but all except Granny Smith apples held at 13 and 20 °C, were at or above a minimum processing firmness standard of 14 lbf. Cut-edge browning of slices, in response to processing temperature, varied among the cultivars. In the extreme, ‘Granny Smith’ was the most responsive, showing the largest variance in surface lightness across the temperature range. ‘Ambrosia’ was the least responsive to temperature, showing no significant difference in L-value despite the temperature at which it was processed. ‘Gala’ and Aurora Golden Gala™ were intermediate in response. The visual quality rating for ‘Granny Smith’ at 3 weeks was poor for slices from all processing temperatures. ‘Ambrosia’ slices maintained acceptable quality ratings over the full test temperature range. ‘Gala’ slices had lower quality ratings when processed at warmer temperatures, whereas Aurora Golden Gala™ showed increased quality ratings with warmer processing temperatures. It was concluded that ‘Gala’ were best processed at low core temperatures, ‘Ambrosia’ could be processed at all tested temperatures, and Aurora Golden Gala™ produced better quality slices when fruit were are room temperature (20 °C) before slicing.

Apple Cultivar and Temperature at Cutting Affect Quality of Fresh Slices

The response of four apple (Malus ×domestica) cultivars (Gala, Granny Smith, Ambrosia, and Aurora Golden Gala™) to fresh-cut processing at core temperatures of 1, 5, 13, and 20 °C was investigated. Fruit were cut after a 24-h preconditioning at one of the four temperatures and a commercial antibrowning formulation was applied as a 7% (w/v) dip before packaging the slices and storing them for 3 weeks at 5 °C. Fruit firmness generally decreased with increasing core temperature, except for Aurora Golden Gala™, which maintained similar firmness at all temperatures. Firmness varied among cultivars, but all except Granny Smith apples held at 13 and 20 °C, were at or above a minimum processing firmness standard of 14 lbf. Cut-edge browning of slices, in response to processing temperature, varied among the cultivars. In the extreme, ‘Granny Smith’ was the most responsive, showing the largest variance in surface lightness across the temperature range. ‘Ambrosia’ was the least responsive to temperature, showing no significant difference in L-value despite the temperature at which it was processed. ‘Gala’ and Aurora Golden Gala™ were intermediate in response. The visual quality rating for ‘Granny Smith’ at 3 weeks was poor for slices from all processing temperatures. ‘Ambrosia’ slices maintained acceptable quality ratings over the full test temperature range. ‘Gala’ slices had lower quality ratings when processed at warmer temperatures, whereas Aurora Golden Gala™ showed increased quality ratings with warmer processing temperatures. It was concluded that ‘Gala’ were best processed at low core temperatures, ‘Ambrosia’ could be processed at all tested temperatures, and Aurora Golden Gala™ produced better quality slices when fruit were are room temperature (20 °C) before slicing.

Influence of harvest maturity on cut-edge browning of ‘Granny Smith’ fresh apple slices treated with anti-browning solution after cutting

Over several years, many fresh-cut apple processors have complained about browning of slices made from ‘Granny Smith’ apples during the harvest season, before fruit have been stored for any length of time. ‘Granny Smith’ apples are a late harvest apples and quite often, at higher latitudes, they are harvested to avoid frost injury and may not always be physiologically mature. It was postulated that immature fruit would have greater susceptibility to browning, despite the application of anti-browning solution after cutting. Fruits were harvested from selected trees beginning five weeks before anticipated commercial harvest and continued weekly until two weeks after commercial harvest. The maturity indicators internal ethylene and starch clearing indices were measured. Ten fruits were sliced, dipped in 7 g L −1 NatureSeal ® and then packaged in zip-loc bags and held at 5 °C. Slices made from apples that were harvested two weeks early or earlier than the optimal maturity, as determined by the maturity measures, had significant levels of cut-edge browning despite the post-cutting application of anti-browning dip. These results clearly indicate that ‘Granny Smith’ apples harvested two weeks or earlier before induction of climacteric ethylene production (when starch index is less than 2.5) should be avoided for use in fresh slicing.

APOPLASTIC LEVELS OF HYDROXYL RADICALS IN FOUR DIFFERENT APPLE CULTIVARS ARE ASSOCIATED WITH SEVERITY OF CUT-EDGE BROWNING

Past research has shown that severity of cut-edge browning in apples used to make fresh slices is highly dependent on the cultivar. 'Ambrosia' and 'SPA343' are resistant to browning, while 'Delicious' and 'Spartan' are very susceptible. Prior experiments have shown a relationship of browning severity with superoxide dismutase/peroxidase activity ratios and peroxide contents in the apoplast. However, peroxides themselves are not sufficiently active to cause lipid peroxidation and membrane degradation. Lipid peroxidation and membrane degradation are the processes that lead to the intermingling of phenolics and polyphenol oxidase, thus leading to the initiation of browning reactions. Hydroxyl radicals can directly initiate lipid peroxidation and they are formed in vivo through the interaction of the superoxide anion with hydrogen peroxide. This research used a newly-developed method to measure hydroxyl radicals in vivo to evaluate whether hydroxyl radical accumulation in the apoplast could be associated with severity of cut-edge browning. The results clearly show that apoplastic levels of hydroxyl radical are closely related to the severity of cut-edge browning, whereas peroxide levels, water soluble antioxidants and phenols are not. A model is presented to explain the results.