Edge Browning Research Articles

Overview of Witloof Chicory (Cichorium intybus L.) Discolorations and Their Underlying Physiological and Biochemical Causes.

Many fruits and vegetables suffer from unwanted discolorations that reduce product quality, leading to substantial losses along the supply chain. Witloof chicory (Cichorium intybus L. var. foliosum), a specialty crop characterized by its unique bitter taste and crunchiness, is particularly sensitive to various types of red and brown discolorations. The etiolated vegetable suffers from three predominant color disorders, i.e., core browning, internal leaf reddening, and leaf edge browning. Additionally, several less frequently observed color disorders such as hollow pith, external red, and point noir can also negatively affect crop quality. In this article, we bring together fragmented literature and present a comprehensive overview of the different discoloration types in chicory, and discuss their potential underlying physiological causes, including laticifer rupture, calcium deficiency, and a disturbed water distribution. We also describe the role of environmental cues that influence discoloration incidence, including cultivation and postharvest storage conditions such as forcing and storage temperature, root ripeness and the duration of the forcing process. Finally, we zoom in on the underlying biochemical pathways that govern color disorders in witloof chicory, with a strong emphasis on polyphenol oxidase.

Combined Effect of Dipping in Oxalic or in Citric Acid and Low O2 Modified Atmosphere, to Preserve the Quality of Fresh-Cut Lettuce during Storage.

Leaf edge browning is the main factor affecting fresh-cut lettuce marketability. Dipping in organic acids as well as the low O2 modified atmosphere packaging (MAP), can be used as anti-browning technologies. In the present research paper, the proper oxalic acid (OA) concentration, able to reduce respiration rate of fresh-cut iceberg lettuce, and the suitable packaging materials aimed to maintaining a low O2 during storage, were selected. Moreover, the combined effect of dipping (in OA or in citric acid) and packaging in low O2 was investigated during the storage of fresh-cut iceberg lettuce for 14 days. Results showed a significant effect of 5 mM OA on respiration rate delay. In addition, polypropylene/polyamide (PP/PA) was select as the most suitable packaging material to be used in low O2 MAP. Combining OA dipping with low O2 MAP using PP/PA as material, resulted able to reduce leaf edge browning, respiration rate, weight loss and electrolyte leakage, preserving the visual quality of fresh-cut lettuce until 8 days at 8 °C.

Descriptive Sensory Analysis of Pizza Cheese Made from Mozzarella and Semi-Ripened Cheddar Cheese Under Microwave and Conventional Cooking.

The present study used descriptive sensory analysis (DSA) to compare Pizza cheeses prepared from various combinations of fresh Mozzarella and semi-ripened Cheddar cheeses and cooked under conventional and microwave cooking methods. A cheese sensory lexicon was developed, and descriptive sensory profiles of the Pizza cheeses were evaluated using a panel of semi-trained judges (n = 12). The following characteristics, flavor (cheddar, acidic, rancid, bitter, salty, creamy, and moldy), texture (stringiness, stretchability, firmness, and tooth pull), and appearance (meltability, oiliness, edge browning, and surface rupture) of Pizza cheeses were analyzed and compared with control samples. The sensory analysis of Pizza cheeses showed more preference toward a higher level of ripened Cheddar cheese (4 months), which was cooked using the microwave. However, the scores for texture properties were decreased with the addition of the semi-ripened cheese. The scores for stretchability and tooth pull were high in the microwave cooked samples compared with the conventionally cooked samples. The appearance attributes (meltability, oiliness, and edge browning) scores were increased with the increasing of ripened Cheddar cheese content while surface rupture was decreased. Microwave cooked Pizza cheese showed better meltability and oiliness but lower edge browning scores. The results showed that amalgamations of fresh Mozzarella and semi-ripened Cheddar cheese had a significant (p < 0.05) and positive effects on the sensory qualities of Pizza cheeses.

Development of antibrowning and antimicrobial formulations to minimize Listeria monocytogenes contamination and inhibit browning of fresh-cut “Granny Smith” apples

In recent years, there have been a number of Listeria monocytogenes recalls involving fresh-cut apples treated with antibrowning solutions. In the present study, we used response surface methodology to develop and optimize formulations for reducing L. monocytogenes populations in the solutions and for maintaining cutting surface color of apple slices. The following two sets of three chemicals at various levels were combined: citric acid + calcium ascorbate+ N-acetyl-l-cysteine (NAC), and citric acid + ascorbic acid +NAC. The survival of a 4-strain cocktail of L. monocytogenes cells (F2365, serotype: 4b; NRRL 33857, serotype: 1/2a; NRRL 33723, serotype: 1/2a; NRRL 33230, serotype: 4c) in the solutions prepared from the combinations was evaluated, and the changes in cutting surface color parameters (L*, a* and b*) and skin edge browning of “Granny Smith” apple slices dipped in the solutions for 3 min were assessed during 21 d of storage at 4 °C. Results showed that combinations of citric acid, calcium ascorbate and NAC were ineffective in achieving 5 log reduction of L. monocytogenes. However, formulations comprised of 4.0–4.5 % citric acid, 3–4% ascorbic acid and 1.5–2.0% NAC achieved more than 5 log reduction of L. monocytogenes in the solutions, and the cutting surface of apple slices treated with these formulations maintained L* values of > 70, and a* values of < −1.8 during 21 d of storage. Our results suggest that the combinations of citric acid, ascorbate and NAC may be used to enhance microbial safety of fresh-cut apples without compromising product quality.

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.

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.

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.

Intense light pulses decontamination of minimally processed vegetables and their shelf-life

Intense light pulses (ILP) is a new method intended for decontamination of food surfaces by killing microorganisms using short time high frequency pulses of an intense broad spectrum, rich in UV-C light. This work studied in a first step the effect of food components on the killing efficiency of ILP. In a second step, the decontamination of eight minimally processed (MP) vegetables by ILP was evaluated, and thirdly, the effect of this treatment on the shelf-life of MP cabbage and lettuce stored at 7 °C in equilibrium modified atmosphere packages was assessed by monitoring headspace gas concentrations, microbial populations and sensory attributes. Proteins and oil decreased the decontamination effect of ILP, whilst carbohydrates and water showed variable results depending on the microorganism. For this reason, high protein and fat containing food products have little potential to be efficiently treated by ILP. Vegetables, on the other hand, do not contain high concentrations of both compounds and could therefore be suitable for ILP treatment. For the eight tested MP vegetables, log reductions up to 2.04 were achieved on aerobic mesophilic counts. For the shelf-life studies, respiration rates at 3% O 2 and 7 °C were 14.63, 17.89, 9.17 and 16.83 ml O 2/h kg produce for control and treated cabbage, and control and treated lettuce respectively; used packaging configurations prevented anoxic conditions during the storage times. Log reductions of 0.54 and 0.46 for aerobic psychrothrophic count (APC) were achieved after flashing MP cabbage and lettuce respectively. APC of treated cabbage became equal than that from control at day 2, and higher at day 7, when the tolerance limit (8 log) was reached and the panel detected the presence of unacceptable levels of off-odours. Control never reached 8 log in APC and were sensory acceptable until the end of the experiment (9 days). In MP lettuce, APC of controls reached rejectable levels at day 2, whilst that of treated samples did after 3 days. Both samples were sensory unacceptable at day 3, controls because of bad overall visual quality (OVQ), off-odour and leaf edge browning and treated samples due to bad OVQ; browning inhibitors might be proposed to preserve OVQ. Yeasts and lactic acid bacteria counts were low in all the samples. It seems that ILP treatment alone under the conditions used in this work does not increase MP vegetables shelf-life in spite of the reduction in the initial microbial load.

EVALUATION OF QUALITY ATTRIBUTES OF FRESH-CUT LETTUCE (LACTUCA SATIVA L.) STORED IN DIFFERENT CONTROLLED ATMOSPHERES

The market of fresh-cut vegetable products is increasing in Brazil. Mechanic injuries, caused by cutting, increase the respiration rate and biosynthesis of ethylene, stimulating chemical and biochemical reactions responsible by changing sensory characteristics. Therefore, the storage of fresh-cut products is critical in maintaining quality. This paper evaluated the storage of fresh-cut lettuce (Lactuca sativa L.) of cultivar Lorca, a kind of iceberg lettuce grown in Brazil, stored 15 days at 5°C in different controlled atmospheres: 5%O2 + 10%CO2; 3%O2 + 10%CO2; 3%O2 + 12%CO2 and atmosphere air, called control. The samples were chemically and sensory analysed. A panel consisting of eight selected and trained judges evaluated the attributes: green intensity; turgidity; midrib browning; edge browning; cooked appearance; dark spots; overall appearance impression. Midrib browning was the main problem in the storage studied. It must be considered as the principal limiting attribute to extend the shelf life of fresh-cut lettuce. The treatments 3%O2 +10%CO2 and 3%O2 +12%CO2 were found to conserve best the sensory characteristics during the used storage time due their efficiency to retain turgidity and overall appearance, and to retard midrib browning. These conditions induced only minor chemical changes in acidity and chlorophyll levels. Russet Spotting was not a limiting factor for the fresh-cut ‘Lorca’ lettuce quality.

First Report of the Pathogenicity of Colletotrichum gloeosporioides on Invasive Ferns, Lygodium microphyllum and L. japonicum, in Florida.

Lygodium microphyllum (Cav.) R.Br. (Old World climbing fern) and L. japonicum (Thunb.) Sw. (Japanese climbing fern), in the family Schizaeaceae, are among the most invasive weeds in Florida (1). L. microphyllum invades fresh water and moist habitats in south Florida, while L. japonicum has spread in relatively well-drained habitats from Texas to North Carolina and central Florida. Some potted plants of both Lygodium spp. grown in shadehouse as well as in full sunlight developed discolored spots on pinnules (foliage), which coalesced and resulted in browning and dieback of severely infected vines. Symptomatic foliage obtained from these plants was surface-sterilized by immersing in a 15% solution of commercial bleach for 90 s, followed by a series of four rinses with sterile deionized distilled water. Disks (4 mm in diameter) of pinnules were cut from the junction of discolored and healthy tissues and placed on potato dextrose agar (PDA). A fungus, Colletotrichum gloeosporioides (Penz.) Penz. & Sacc. was consistently isolated from these disks. Fungal colonies produced abundant conidia on PDA. Conidia were hyaline, straight, cylindrical, averaging 14.7 μm (range 12.5 to 17.5 μm) × 5.0 μm (range 3.8 to 7.5 μm), and similar to those described for C. gloeosporioides (2). To confirm the pathogenicity of C. gloeosporioides on L. microphyllum and L. japonicum, Koch's postulates were performed. A fungal isolate was grown on PDA for 3 weeks, after which 10 ml of sterile deionized distilled water was added to the culture and agitated to dislodge conidia. The conidial suspension was strained through three layers of cheesecloth to remove hyphal fragments, and its concentration was adjusted to 1.7 × 106 conidia/ml. Foliage of healthy L. microphyllum and L. japonicum plants grown in 500-ml containers was sprayed with the conidial suspension until runoff. Plants were covered with plastic bags whose inner sides were misted with water to maintain high humidity and placed in a growth chamber under 12 h of fluorescent light per day. Temperature and relative humidity in the chamber ranged from 26 to 29°C and 44 to 73%, respectively. Plastic bags were removed after 3 days, and plants were further incubated for 3 weeks in the same growth chamber. Control plants were sprayed with sterile water, covered with plastic bags, and exposed to the same temperature, light, and humidity regime as those of the fungus-inoculated plants. Small, discolored foliar spots appeared 3 days after fungus inoculation. These spots were similar to those observed on pinnules of potted plants that originated from shadehouse and outdoor environments. Within 3 weeks after inoculation, the foliage of L. japonicum developed abundant discolored spots that led to edge browning and wilting of the pinnules. L. microphyllum had similar but more severe symptoms, with plants suffering as much as 50% dieback. C. gloeosporioides was consistently reisolated from the symptomatic tissues of both fern species. No symptoms appeared on the water-inoculated plants. To our knowledge, this is the first record of C. gloeosporioides pathogenicity on L. microphyllum and L. japonicum.

Effect of wash water temperature and chlorination on phenolic metabolism and browning of stored iceberg lettuce photosynthetic and vascular tissues.

Cut tissues from distinct anatomical locations in iceberg lettuce (Lactuca sativa L.) were subjected to washing in cold (4 degrees C) and warm (47 degrees C) water with or without chlorine to assess their propensity to discoloration during storage. Total protein (Bradford method) and phenolic (TPH; Folin-Ciocalteu method) contents and polyphenol oxidase (PPO; spectrophotometric method using catechol as a substrate), peroxidase (POD; guaiacol substrate), and phenylalanine ammonia-lyase (PAL; phenylalanine substrate) activities were determined in photosynthetic and vascular tissue from outer and inner leaves. Unprocessed photosynthetic and inner leaf tissues had significantly higher (P < 0.05) levels of protein and TPH and PPO and POD activities than vascular and outer leaf tissues. PAL activities (on a fresh weight basis) were similar in all tissues. Changes in browning (light reflectance measurement) and phenolic metabolism in all four tissue types were observed during aerobic storage at 5 degrees C over 10 days. PAL activity increased in all tissues after 1-2 days of storage and then gradually decreased. POD activity also increased steadily for the storage duration. Protein content and PPO activity remained constant. Edge browning (measured with a Minolta Chroma Meter) and TPH increased in all tissues, especially in outer vascular tissue. Cut photosynthetic and vascular tissues washed at 4 and 47 degrees C with and without 100 microg mL(-1) chlorine for 3 min were analyzed during 7 days in storage at 5 degrees C. Enzyme activities and accumulation of phenolics in all tissues washed at 47 degrees C were significantly (P < 0.05) lower compared to controls or tissues washed at 4 degrees C. Chlorine had no additional effect at 47 degrees C but significantly (P < 0.05) reduced browning and accumulation of phenolics in lettuce washed at 4 degrees C. These results showed that inherent differences between tissues affect phenolic metabolism and browning in stored, fresh-cut lettuce.

Wound-induced phenylalanine ammonia lyase activity: factors affecting its induction and correlation with the quality of minimally processed lettuces

Abstract One of the major causes of quality loss in minimally processed lettuce (Lactuca sativa L.) is the browning of the cut pieces. Phenylalanine ammonia lyase (PAL, EC 4.3.1.5) is a key enzyme in phenolic synthesis. PAL activity increased in lettuce midrib tissue with wounding and storage in the presence or absence of ethylene. PAL activity increased 2.5 and 3-fold at 5 and 15 °C, respectively, by reducing midrib size from 2.5 × 15 to 0.5 × 1 cm. Wounding usually induced maximum levels of enzyme activity within 3 days at 5 °C and 1 day at 15 °C. Pre and postharvest factors affected the kinetics of wound-induced PAL (WI-PAL) activity and of subsequent changes in the quality of minimally processed lettuce. The rate at which WI-PAL activity increased and the maximum level attained were influenced by the duration of storage before processing. These parameters were also affected by the cultivar and type of lettuce used. Butterhead and iceberg types had the highest and lowest levels, respectively, of WI-PAL activity; romaine, green leaf and red leaf had intermediate levels. The activity of PAL 1–2 days after processing, and the slope of the induction curve between days 0 and 2, were the enzyme measurements that gave the highest correlations with processed lettuce quality attributes, including overall visual quality, leaf edge browning, and leaf surface browning.

The visual quality of minimally processed lettuces stored in air or controlled atmosphere with emphasis on romaine and iceberg types

Five different types of lettuce (iceberg, romaine, butter, green leaf, and red leaf) were prepared as salad pieces and stored for 16 days at 5°C in air or in a controlled atmosphere (CA) (3% O2 + 10% CO?). Samples were evaluated for overall visual quality, surface and edge browning, and russet spotting. After 8 days, differences in overall visual quality between air and CA-stored samples were observed; after 12 days, air-stored samples were below the limit of salability, whereas visual quality was maintained in CA-stored pieces from all lettuce types except butter lettuce. Transferring lettuce to air for 12 h at 15°C accentuated the differences between storage atmospheres. An analysis of the various components of overall visual quality showed that surface and edge browning were the defects which most contributed to a decrease in quality. Among the lettuce types studied, the CA benefit for overall visual quality was highest for iceberg lettuce, and some differences between cultivars were observed. There was no CA benefit for butter lettuce, but CA induced surface discoloration and tissue softening. Pre-processing storage of lettuce heads at 5°C for 7 and 14 days negatively affected overall visual quality and leaf edge browning of the prepared salad pieces; this intact head storage effect was more evident on romaine than iceberg pieces.