Shelf-life Of Fresh-cut Lettuce Research Articles

PH-driven formation of soy protein isolate-thymol nanoparticles for improved the shelf life of fresh-cut lettuce

Plant essential oils as natural preservatives are attracting attention for their non-toxic and antibacterial properties, and are gradually being used in food preservation. In this study, thymol was encapsulated in Soy protein isolate (SPI) via pH-driven method to construct a convenient, efficient and safe thymol delivery system without the need of adding other substances. The loading efficiency of thymol in complexes formed in 10 mg/mL SPI and 6 mg/mL thymol was 37.3 %, and the particles were spherical with a z-average diameter less than 120 nm. Results of antibacterial activity showed that SPI-thymol nanoparticles effectively inhibited growth of Escherichia coli and Bacillus subtilis. Applying on fresh-cut lettuce, the nanoparticles also reduced weight loss, retain ascorbic acid and chlorophyll contents during shelf-life. Additionally, SPI-thymol nanoparticles effectively inhibited growth of bacteria, mold, and yeast during storage. The sensory evaluation results indicated that the nanoparticles had a satisfactory impact on the sensory characteristics of lettuce. These results illustrated that SPI-thymol nanoparticles are a simple and promising composite transportation system and have the potential to be applied to the preservation of postharvest fruits and vegetables.

Postharvest shelf life simulation for lettuce (Lactuca sativa L.) based on coupling dynamic models of respiration, gas exchange, and Pseudomonas fluorescens growth

Shelf life simulation of fresh-cut lettuce was established when packed in two commercial packaging materials with four levels of O2 transmission rate (OTR) from 5 to 3875 cm3/m2/d/0.1 MPa. This study has established mathematic models coupling respiration of fresh-cut lettuce and Pseudomonas fluorescens, O2 and CO2 exchange, and microbial growth. The coupling models succeeded in predicting the dynamic change of O2 and CO2 in the headspace of biaxially oriented polyamide/low-density polyethylene (BOPA/LDPE) and polyethylene (PE) films. The coupling model contained Baranyi function showed the best fitting performance when predicting P. fluorescens growth. Quality attributes of lettuce showed that the BOPA/LDPE film with the lowest OTR significantly inhibited the P. fluorescens growth, extensively maintained color and texture, and extended the shelf life of fresh-cut lettuce. The established coupling models could be further utilized for evaluating the microbial safety and shelf life of other types of leaf vegetables where pseudomonads are dominant for spoilage.

Combination of vaporized ethyl pyruvate and non-thermal atmospheric pressure plasma for the inactivation of bacteria on lettuce surfaces

The effect of vaporized ethyl pyruvate (EP) and atmospheric pressure plasma (APP) treatments on the inactivation of total viable counts of bacteria on fresh lettuce leaves samples after treatment and during storage (1 and 3 days) at 6 and 25 °C was studied. For this purpose, freshly grown B. cereus and Escherichia coli were inoculated on the lettuce leaves prior to treatments. Combination of EP (at a concentration of around 10 μL dm−3) with APP was more effective on inactivation of bacteria when compared to EP and APP treatments separately, reducing the total viable counts nearly 5 CFU cm−2 compared to control. The use of EP and APP together led to around 2.5 more log (CFU cm−2) reductions when compared to the sole use of EP and APP separately. B. cereus cells were almost three times more susceptible to APP treatment than E. coli. Growth inhibition increased after storing the treated samples at 25 °C by around 2.5 and 1.5 logs for E. coli and B. cereus, respectively, compared to 6 °C. APP treatment time (30 and 60 s) and storage time (1 and 3 days) did not significantly affect the inactivation levels. E. coli was more effectively inactivated after EP + O2 treatment followed by storage at 25 °C. The highest level of inactivation was noted as nearly 5 log reductions. Slight differences in the peak intensities of FTIR spectra of treated lettuce samples were observed compared to control, indicating slight modifications on the chemical structure on the lettuce leaves. Industrial relevanceThe microbial load influences the quality, safety, and shelf-life of fresh produce such as lettuce. Current decontamination techniques may cause some unwanted effects such as odor, discoloration, and decreased nutritional value. This study shows that the use of the APP-EP hurdle represents a promising strategy to improve the decontamination efficiency and hence, enhance the shelf-life of freshly cut vegetables. The data obtained contribute to a better understanding of APP-EP-induced effects on the quality and shelf-life of fresh-cut lettuce and provide a scientific basis for industrial implementation.

Identification of romaine lettuce (Lactuca sativa var. longifolia) Cultivars with reduced browning discoloration for fresh-cut processing

Discoloration (browning) represents a major challenge that limits the quality and shelf life of fresh-cut lettuce. In this study, we aimed to find romaine lettuce (Lactuca sativa var. longifolia) accessions with low browning potential. Midribs of 14 accessions (11 cultivars, two breeding lines, and a single plant introduction) were shredded and packaged in perforated bags for five days. Images of processed samples were captured daily and analyzed with computer vision technology to quantify browning intensity via L*a*b* color values and browning index (BI). Enzymatic activity[phenylalanine lyase (PAL), peroxidase (POD), and polyphenol oxidase (PPO)] and total phenolic content (TPC) were measured daily. After five days in storage, the accessions in the Tall Guzmaine and Parris Island Cos pedigree groups exhibited the greatest and least browning, respectively. In addition, while the PAL, POD, and TPC increased substantially over time, the PPO of twelve accessions fluctuated with only minor increases. For all accessions, the temporal increase of PAL, POD, and TPC showed significant, positive correlation to browning progression. Comparing between accessions, those that had greater amounts of accumulated PAL and smaller amounts of POD tended to have a greater amount of browning after five days of storage, despite relatively low correlation coefficients. However, the accumulation of TPC and PPO was not correlated to browning severity after five days of storage. This systematic study provides lettuce growers and breeders with guidance for selecting accessions with limited browning, and it supplies researchers in plant physiology and genetics with more information on the roles of enzymes in the lettuce browning process.

Potential of Ozonated Water at Different Temperatures to Improve Safety and Shelf-Life of Fresh Cut Lettuce

ABSTRACTThe present study was carried out to determine the effect of ozonated water (2 mg L−1) at different temperatures (4 °C and 15 °C) on the microbiological, color and sensory properties of lettuce. Cold ozone treatment (4 °C) significantly reduced the natural background microflora of lettuce. Salmonella Typhimurium and Escherichia coli inoculated on lettuce samples were insignificantly influenced by the temperature of water. During storage period at +4 °C for 14 days, the highest quality was observed from the samples treated with cold ozonated water. Ozone treatments did not affect the color properties and sensory quality of lettuce samples.

Untargeted metabolomics approach using UPLC-ESI-QTOF-MS to explore the metabolome of fresh-cut iceberg lettuce

The shelf-life of fresh-cut lettuce after storage is limited by several factors that affect its quality and lead to consumer rejection. Different metabolic events occur after cutting as an abiotic stress response. This study aims to explore the metabolome of iceberg lettuce and to understand the changes related to storage time and genetics applying an untargeted metabolomics approach. Two cultivars with different browning susceptibility, fast-browning (FB) and slow-browning (SB), were analyzed by UPLC-ESI-QTOF-MS just after cutting (d0) and after five days of storage (d5). Extraction, metabolic profiling, and data-pretreatment procedures were optimized to obtain a robust and reliable data set. Preliminary principal component analysis and hierarchical cluster analysis of the full dataset [around 8551 extracted, aligned and filtered molecular features (MFs)] showed a clear separation between the different samples (FB-d0, FB-d5, SB-d0, and SB-d5), highlighting a clear storage time-dependent effect. After statistical analysis applying Student’s t test, 536 MFs were detected as significantly different between d0 and d5 of storage in FB and 633 in SB. Some of them (221) were common to both cultivars. Out of these significant compounds, 22 were tentatively identified by matching their molecular formulae with those previously reported in the literature. Five families of metabolites were detected: amino acids, phenolic compounds, sesquiterpene lactones, fatty acids, and lysophospholipids. All compounds showed a clear trend to decrease at d5 except phenolic compounds that increased after storage. The untargeted metabolomics analysis is a powerful tool for characterizing the changes on lettuce metabolome associated with cultivar and especially with storage time. Some families of compounds affected by storage time were reported to be closely related to quality loss.

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).

Allicin Inhibits Microbial Growth and Oxidative Browning of Fresh-Cut Lettuce (Lactuca sativa) During Refrigerated Storage

Fresh-cut lettuce has a short shelf life since it is very perishable and susceptible to enzymatic browning. The aim of this study was to examine the effectiveness of allicin treatment in prolonging the shelf life of fresh-cut lettuce (Lactuca sativa L. var. angustana Irish). Fresh-cut lettuce slices were treated with water (control), 0.2 and 1 % of allicin solutions, respectively, and stored at 4 °C, >90 % relative humidity. Sensory parameters, microbiological indicators, and physiological indices were determined at 0, 2, 4, and 6 days of storage. The sensory analyses revealed that allicin inhibited the color change and maintained the visual quality of lettuce slice without impairing flavor. Allicin treatment delayed microbial growth at cold storage, as evidenced by the lowered total viable counts (decreased by 2.52 log cfu/g) and yeast and mold counts (decreased by 1.59 log cfu/g) after 6 days in 1 % allicin-treated samples compared to control samples. In addition, differences between lettuce treated with 1 % allicin and control slices in objective color (total color change, chrome, and hue angle), total phenolic compounds and quinones content, activities of browning-related enzymes, and antioxidative enzymes suggested that allicin had antioxidative properties. Conclusively, it was demonstrated for the first time that allicin effectively protected fresh-cut lettuce from tissue browning and microbiological spoilage. These findings indicate that allicin has great potential as a natural additive to extend the shelf life of fresh-cut lettuce.

PRE-HARVEST LIGHT INTENSITY AFFECTS SHELF-LIFE OF FRESH-CUT LETTUCE

The industry of fresh-cut produce is continuously growing due to increasing demand for fresh, healthy and convenient foods. However, processing of vegetables accelerates quality deterioration due to structural, physiological and biochemical changes. Therefore, the value of the produce to the consumer is decreased by negative changes in appearance, texture, flavor and nutritional value. Cultivation practices, such as nitrogen application, light and temperature regimes and, the choice of varieties with a higher resistance to processing might greatly influence the postharvest characteristics of lettuce. In this study, the effect of light intensity during growth on shelf-life of fresh-cut lettuce was examined in different varieties. Plants were grown under controlled environmental conditions with day/night temperature 20°C/15°C relative humidity of 70% and high (250 μmol m -2 s -1 ) or moderate (120 μmol m -2 s -1 ) photosynthetically active radiation (PAR) provided by white fluorescent tubes, with a 12h photoperiod. The shelf-life of plants grown under high light was two-fold that of the plants grown under moderate light. The level of leaf chlorophyll differed between light treatments and varieties. The variety with highest pre-harvest chlorophyll content had the shortest shelf life under both light conditions. The shelf life data are supported by chlorophyll fluorescence images indicating that the latter technique may be used as a quality evaluation tool.

EFFECTS OF SALINITY AND PLANT DENSITY ON QUALITY OF LETTUCE GROWN IN FLOATING SYSTEM FOR FRESH-CUT

Quality of fresh-cut lettuce depends strongly on the raw material characteristics. Floating system allows to enhance quality as well hygienic characteristics of raw material. Different researches investigated the effect of nutrient solution EC and plant density on yield and quality of leafy vegetables, while scarce attention was addressed to influence on quality parameters during fresh-cut storage. For this purpose a trial was carried out to evaluate the influence of different EC of nutrient solution and plant density on production, quality and shelf-life of fresh-cut lettuce. Plants of Lactuca sativa var. longifolia 'Xanadu' were grown in floating system adopting three nutrient solutions with different electrical conductivity (2.8, 3.8 and 4.8 mS cm -1 ) and two plant densities (366 and 750 plant m -2 ). At harvest (35 days after sowing) plants (5-6 leaves) were weighed, processed as fresh-cut product and stored at 5°C. Some parameters (respiration rate, dry matter percentage, firmness, colour, chlorophyll and nitrate content) to evaluate the shelf life were determined after 1, 4 and 9 days of storage. Salinity decreased yield and leaf nitrate content and these effects were more evident in the highest plant density. In relation to storage, our results showed the better suitability to fresh-cut processing in product obtained with 3.8 mS cm -1 EC treatment. Despite the highest yield obtained, the fresh-cut product of plants grown at highest plant density showed large variation of some parameters considered, probably in relation to higher respiration rate.

Effect of Preharvest Application of a Second-generation Harpin Protein on Microbial Quality, Antioxidants, and Shelf Life of Fresh-cut Lettuce

The effect of preharvest application of a newly developed second-generation harpin product (2G-Harpin) on shelf life of fresh-cut lettuce (Lactuca sativa) was investigated. The lettuce plants were grown in three locations in the United States: Watsonville, CA, Cedarville, NJ, and Yuma, AZ, and treated 5 days before harvest at 140, 280, and 420 g·ha−1 (30, 60, and 90 mg·L−1). Lettuce processed and bagged were stored at 1 to 3 °C and evaluated for quality for 20 days. Lettuce from California treated with 2G-Harpin at 280 to 420 g·ha−1 consistently showed better visual quality and lower microbial population than the control. Overall results in New Jersey showed no major differences among treatments. In Arizona, microbial population was lower and visual quality was higher in lettuce treated at 280 and 420 g·ha−1 during part of the storage period. In further experimentation, we examined the phenolic content of lettuce harvested 1 and 7 days after treatment with 2G-Harpin. The results showed that phenolic content was higher in all treated lettuce than in the control lettuce after 24 h. Six days later, the levels fell back to the initial stage. Antioxidants capacity increased by 40% in head leaves when plants were treated with 280 and 420 g·ha−1 2G-Harpin, but no change was observed in outer leaves. Overall, it was revealed that a field application of 2G-Harpin can improve quality of fresh-cut lettuce under environmental conditions that need to be determined. Our results with phenolic content and antioxidant activity suggested that improvement in quality is probably the result of alteration of metabolites' composition and demonstrated that increased phenolics do not correlate with lower quality of fresh-cut products.

Ozonated water extends the shelf life of fresh-cut lettuce.

The use of ozonated water as a sanitizer to extend the shelf life of fresh-cut lettuce and the effect on the antioxidant constituents (polyphenols and vitamin C) were investigated. Fresh-cut iceberg lettuce (Lactuca sativa L.) was washed at 4 degrees C using three different ozonated water dips [10, 20, and 10 activated by ultraviolet C (UV-C) light mg L(-1) min total ozone dose], and the dips were compared with water and chlorine rinses. Treated lettuce was packaged in air or active modified atmosphere packaging (MAP) (4 kPa of O2 + 12 kPa of CO2 balanced with N2) and stored for 13 days at 4 degrees C. Despite its strong oxidizing activity, ozonated water did not stimulate the respiratory activity of fresh-cut lettuce. Moreover, ozonated water maintained the initial visual appearance of fresh-cut lettuce and controlled browning during storage in air. Initially, ozonated water and chlorine reduced the total mesophilic population by 1.6 and 2.1 log, respectively, when compared with water. Active MAP was effective in controlling total microbial growth, achieving 2.0 log reduction in relation to samples stored in air at the end of storage. On the other hand, active MAP caused a 2.0-3.5 reduction of coliforms on sanitized samples compared with water-washed samples. The most efficient treatments were ozone 20 and ozone 10 activated by UV-C, which were as effective as chlorine. Changes in individual phenolic compounds were independent of the washing treatments. In air, chlorogenic and isochlorogenic acid contents increased noticeably after 13 days while monocaffeoyltartaric and dicaffeoyltartaric acids remained unchanged. MAP effectively suppressed accumulation of caffeoylquinic derivatives, whereas caffeoyltartaric derivatives decreased during MAP storage to reach similar levels. The content of vitamin C (ascorbic acid and dehydroascorbic acid) decreased during storage, particularly under MAP. Ozonated water could be an alternative sanitizer to chlorine for fresh-cut lettuce due to good retention of sensorial quality and browning control with no detrimental reduction in the antioxidant constituents.

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.

932 PB 530 PAL INDUCTION AND FRESH-CUT LETTUCE QUALITY

Phenylalanine ammonia-lyase (PAL) activity in iceberg lettuce (Lactuca sativa L.) is increased in response to several kinds of stress, including wounding, exposure to ethylene, and fungal infection. Ethylene-induced PAL activity is correlated with the discoloration and shelf-life of fresh cut lettuce (Couture et al. 1993. HortScience 28:723). The objective of this research was to further characterize the kinetics of wound-induced PAL in fresh cut lettuce. Leaves of different cvs were cut into salad pieces (1.5 × 3 cm), rinsed in chlorinated water, centrifuged manually, and placed into containers at 5 or 15C through which humidified air flowed. Samples were evaluated for overall visual quality and specific types of discoloration. Midrib tissue was also finely cut (1 × 0.5 cm) for enhanced wound-induction of PAL, which was assayed spectrophotometrically. The kinetics of PAL in midrib tissue of fine cut and salad cut lettuce were similar, with maximum activities obtained within 12-16 h at 15C and within 40-60 h at 5C. Maximum PAL levels in the fine cut lettuce were 1.5-2.0 times those observed in the salad cut pieces, and similar to those induced by ethylene. The usefulness of PAL as a predictor of the storage life of fresh cut lettuce depends on simplifying and expediting the PAL assay.