Quality Of Fresh-cut Iceberg Lettuce Research Articles

Untargeted volatolomic approach for the identification of sensory quality markers of fresh-cut iceberg lettuce stored in modified atmosphere packaging

Fresh-cut iceberg lettuce is appreciated by consumers for its nutritive properties, convenience, and ease of use. Producers are then pushed to preserve the quality of these products by using modified atmosphere packaging (MAP). In this study, the influence of passive MAP (air) or active MAP (1–5 % O2), on several quality attributes of fresh-cut iceberg lettuce samples was evaluated during storage time (from 3 to 14 d) at 4 °C. The respiration rate and the electrolyte leakage values of samples packaged in active MAP were higher than those of fresh-cut iceberg lettuce stored in the air, indicating stressful storage conditions. Inverse trends were observed for O-quinones content and browning index until the end of the storage period. Sensory analysis highlighted that active MAP has preserved the visual quality, limiting the browning of the cut surfaces. On the other hand, active MAP modified the sensory profile after 3 d at 4 °C, and samples scored below the marketability limit for both odor and off-odor. Finally, a volatile organic compound characterization by headspace solid-phase microextraction (HS-SPME) and gas chromatography-mass spectrometry (GC–MS) allowed the identification of target molecules that could signal a decrease in food quality under different conditions. A total of 118 compounds were identified and, among them, ethyl alcohol and acetaldehyde were identified as the best quality markers for passive MAP and active MAP samples, respectively, while ethyl acetate could represent a good compromise to assess the quality of fresh-cut iceberg lettuce, regardless of MAP conditions.

High carbon-di-oxide modified atmospheric packaging on quality of ready-to-eat minimally processed fresh-cut iceberg lettuce

Fresh-cut lettuce is a very well-known salad for today's routines because it obliges minimal preparation to minimize the loss of health beneficial vitamins, minerals, antioxidants and other phytochemicals. It is a prodigious challenge to serve its consumers fresh. Quality of freshly processed lettuce under high CO2 modified atmosphere packaging (MAP) has been investigated as a realistic alternative technique for its preservation. Storage under high CO2 atmospheric treatments exhibited a significant impact in microbial development, electrolyte leakage, volatile metabolites and sensory quality of fresh-cut iceberg lettuce. This storage condition (MAP 1: 5 kPa O2 and 20 kPa CO2 balanced by N2 at 7 °C for 6 days) inhibited the growth of mesophilic bacteria and yeasts; delayed the enzymatic browning (cut-edges and intact surface) of fresh-cut iceberg lettuce and overall visual quality was also in acceptance limit. The development of off-odors was perceived in high CO2 MAP as a consequence of volatiles (ethanol and acetaldehyde) accumulation which was persisted at an inexcusable level during 6 days of storage periods.

Comparison of ultra-high-pressure water jet and conventional rotating blade cutting for the production of fresh-cut iceberg (Lactuca sativa L.) and endive (Cichorium endivia L.)

Sensory, physiological, and microbial quality of fresh-cut iceberg lettuce (Lactuca sativa L.) and endive (Cichorium endivia L.) produced by ultra-high-pressure water jet cutting was compared to that obtained by conventional blade cutting. Two settings of water pressure (2500, 3300 bar) and nozzle size (0.10, 0.12 mm) were investigated at pilot-plant scale to provide insights into the industrial applicability of the water jet cutting technology. During the subsequent 12 days of storage of the fresh-cut products in consumer-sized film bags, headspace gas composition, activities of phenylalanine-ammonia-lyase, peroxidase and polyphenoloxidase, contents of phenolic compounds, and bacterial viable counts were monitored. Furthermore, visual appearance of the products was examined by stereo microscopy and sensory evaluation. When comparing blade cut and water jet cut products, differences in headspace gas composition, enzyme activities, phenolic contents and bacterial viable counts were insignificant for both fresh-cut iceberg lettuce and endive. Although water pressure and nozzle size only exerted a slight effect on sensory quality and the appearance of cut edges, tentatively, a pressure of 2500 bar and nozzle size of 0.10 mm ensured optimum sensory quality of the cut salads. Hence, fully equivalent product quality was achieved by water jet and conventional blade cutting. Despite higher investment, water jet cutting technology may be considered as a valuable alternative to blade cutting systems in the production of fresh-cut products, thus avoiding interruptions of the production chain due to time- and cost-intense sharpening of the knives.

Preharvest and postharvest factors related to off-odours of fresh-cut iceberg lettuce

The influence of different preharvest and postharvest factors affecting off-odour development of fresh-cut iceberg lettuce in low-O2 modified atmospheres (MA) was investigated. Fresh-cut iceberg lettuce developed undesirable off-odours under low O2 and elevated CO2 atmospheres. A strong relationship between CO2 concentration and off-odour development was observed. Significant differences in off-odour development existed among different cultivars in two harvests in consecutive years. The influence of maturity stage was evaluated, comparing fresh-cut product from immature and over-mature heads with commercial ones. Higher CO2 concentrations and higher accumulation of ethanol and acetaldehyde were detected in the headspace of MA-packed lettuce from immature heads. Differences in respiration rate of the fresh-cut product from heads cultivated during the winter–spring seasons were around 30%. Respiration rate of fresh-cut iceberg lettuce increased when medium temperature during cultivation increased. Changes in the product weight generated different CO2 levels which correlated with the production of ethanol and acetaldehyde and other off-odour metabolites related with the lipoxygenase (LOX) pathway such as hexanal, 1-hexanol, and cis-3-hexen-1-ol. Volatile compounds such as cis-3-hexen-1-ol, β-elemene, ethyl acetate and dimethyl sulphide increased their content more than 10 times compared with other volatiles. Moreover, differences in the initial flushed gas-mixture with or without CO2 showed higher CO2 concentrations and the development of stronger off-odours when samples were flushed with an enriched CO2 gas-mixture. In summary, visual quality of fresh-cut iceberg lettuce is important but so are odour and flavour. MAP currently used for fresh-cut lettuce may need some modification to inhibit off-odours and achieve better aroma and flavour qualities for preserving “freshness” of the cut product. Screening for cultivars with low browning potential and fermentation, harvested at optimum maturity stage and with an adequate package design are recommended.

Effect of new sanitizing formulations on quality of fresh-cut iceberg lettuce

In the present study, three recently patented decontamination agents: peroxyacetic acid combined with lactic acid, and two different combinations of hydrogen peroxide with citric acid (with and without propylene glycol), were compared with sodium hypochlorite and tap water washing regarding their effect on equilibrium modified atmosphere packaged (EMAP) fresh-cut iceberg lettuce. Effects of these sanitizers on respiration rate, electrolyte leakage, microbial levels, and sensory quality of the product after decontamination and during storage (3d at 4°C followed by 4d at 7°C) were elucidated. Hydrogen peroxide based sanitizers provoked a significant increase in the respiration rate and the electrolyte leakage of fresh-cut iceberg lettuce compared with tap water washing. Peroxyacetic acid combined with lactic acid resulted in similar results to those of tap water washing for all the parameters analyzed. However, other aspects of the combination of peroxyacetic and lactic acids (e.g. efficacy for cross-contamination avoidance) should be assessed in the future in order to determine its suitability for fresh-cut iceberg lettuce processing.

Phytoncide 처리가 신선편이 양상추의 저장 중 이화학적, 미생물학적 및 관능적 특성에 미치는 영향

본 연구는 솔잎 유래의 phytoncide essential oil을 증류수에 희석한 것(1%, v/v, DP)과 식용 에탄올에 희석한 것(1%, v/v, EP), 증류수(DW) 및 식용 에탄올(EE)을 침지액으로 이용하였다. pH는 DW 처리구에서 가장 높고 EP 처리구에서 가장 낮았으며, 증류수보다는 에탄올 포함 처리구에서, 대조구보다는 phytoncide 성분이 포함된 처리구에서 낮은 pH인 것으로 나타났다. 적정산도는 EP 처리구가 가장 높고, DW 처리구가 가장 낮은 것으로 나타나 pH의 결과와 잘 일치하는 경향이었다. 총 가용성 고형분 함량은 1.60~2.23의 범위로, 에탄올이 포함된 EE 및 EP 처리구에서 유의적으로 높은 함량으로 나타났으며, 포장필름 내 기체조성 분석결과, EP 처리구가 modified atmosphere packaging (MAP)의 원리인 저산소 및 고이산화탄소 조건인 것으로 나타났다. 관능검사 결과, 외관, 색 및 갈변 정도에서 EP 처리구가 유의적으로 높은 점수를 얻었으며, DW 처리구가 가장 낮은 점수를 얻어 갈변 저해에 뛰어난 효과가 있음을 알 수 있었다. 총균수는 저장 중 꾸준히 증가하는 경향이었으며, EP 처리구가 가장 완만한 증가율을 보여 항갈변뿐만 아니라 항균에도 효과가 있음을 확인할 수 있었다. 이러한 결과들로 보아 EP 처리구는 갈변 저해 및 항균에도 효과가 뛰어나 품질 유지에 긍정적인 영향을 미치므로, 고품질 신선편이 양상추의 가공 및 유통에 있어 효과적인 방법으로 이용될 수 있을 것이라 기대된다. The effect of phytoncide solution treatment on the browning and quality of fresh-cut iceberg lettuce during storage was studied. The treatments were applied as four solutions adjusted at <TEX>$10^{\circ}C$</TEX>: distilled water (DW) as the control; edible ethanol (EE); 1% (v/v) phytoncide essential oil from pine needle diluted with distilled water (DP); and 1% (v/v) phytoncide essential oil diluted with edible ethanol (EP). Fresh-cut lettuce was dipped in each solution for 60 sec, was rinsed with distilled water, was packaged with an OPP film bag, and was then stored at <TEX>$4^{\circ}C$</TEX> for 12 days. The EP group had a significantly high level of total soluble solids, titratable acidity, and carbon dioxide, and low total bacteria counts, pH, and oxygen. The sensory score of color in the EP group recorded a high value, but the EE and EP groups recorded low scores in aroma and taste during the storage period. Alcohol and phytoncide were vaporized by opening the package for two hours, and the score of the aroma and taste of EP showed no differences from those of the other groups. Based on the above results, it was determined that the phytoncide essential oil diluted in edible alcohol with 1% solution inhibited the browning of and microbial growth in fresh-cut lettuce, and will be a useful natural compound in maintaining the quality of fresh-cut produce.

Impact of different washing procedures on quality of fresh-cut iceberg lettuce (Lactuca sativa var. capitata L.) and endive (Cichorium endivia L.)

The objective of this study was to determine the effects of alternative washing procedures on fresh-cut iceberg lettuce and endive, applying warm water (45 °C), warm water with CaCl2 (1 g/L), and chlorinated water (4 °C, 120 ppm), respectively. Processing was conducted on pre-industrial scale, and the produce was subsequently stored in consumer-sized bags (4 °C, 10 days). O2 and CO2 levels in the modified atmosphere, and activities of phenylalanine ammonia-lyase (PAL), peroxidase (POD) and polyphenoloxidase (PPO) of the samples were analyzed. Counts of total aerobic bacteria and pseudomonades were determined on the produce and in the process water. In both commodities, wound-induced PAL activities were significantly reduced by warm water treatment. In iceberg lettuce, adding CaCl2 to warm water resulted in a further reduction of PAL activities. Chlorinated water was less effective than warm water in suppressing wound-induced PAL activity in endive, but proved to be most effective in reducing total microbial cell counts by 1.1 and 2.1 log10 cfu/g in iceberg lettuce and endive, respectively. Warm water treatment exhibited reduction rates of similar magnitudes. For process water, chlorine proved to be the most efficient sanitizer. PPO and POD activities were only marginally affected by the different washing procedures. As indicated by respiration of the fresh-cut produce, warm water treatments applied retained the vitality of both plant species. The results suggest that warm water treatments are suitable measures to improve the quality of iceberg lettuce and endive, but were less efficient in sanitizing the process water.

Quality of fresh-cut Iceberg lettuce and spinach irradiated at doses up to 4 kGy

Fresh-cut Iceberg lettuce packaged in modified atmosphere packages and spinach in perforated film bags were irradiated with gamma rays at doses of 0, 1, 2, 3, and 4kGy. After irradiation, the samples were stored for 14 days at 4°C. O2 levels in the packages of fresh-cut Iceberg lettuce decreased and CO2 levels increased with increasing radiation dose, suggesting that irradiation increased respiration rates of lettuce. Tissue browning of irradiated cut lettuce was less severe than that of non-irradiated, probably due to the lower O2 levels in the packages. However, samples irradiated at 3 and 4kGy had lower maximum force and more severe sogginess than the non-irradiated control. In addition, ascorbic acid content of irradiated lettuce was 22–40% lower than the non-irradiated samples after 14 days of storage. The visual appearance of spinach was not affected by irradiation even at a dose of 4kGy. Consumer acceptance suggested that more people would dislike and would not buy spinach that was treated at 3 and 4kGy as compared to the non-irradiated sample. Overall, irradiation at doses of 1 and 2kGy may be employed to enhance microbial safety of fresh-cut Iceberg lettuce and spinach while maintaining quality.

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.

Sensorial and Chemical Quality of Gamma-Irradiated Fresh-Cut Iceberg Lettuce in Modified Atmosphere Packages

A study was conducted to investigate the effects of various doses of irradiation on the quality of fresh-cut iceberg lettuce and to determine a suitable maximum dose. Fresh-cut iceberg lettuce packaged in film bags was exposed to 0, 1, 2, 3, and 4 kGy of gamma radiation and stored at 3°C for 14 days. CO2 levels were higher and O2 levels were lower in packages containing irradiated lettuce than in those containing nonirradiated lettuce for most of the storage period. Comparison with nonirradiated lettuce indicated that total ascorbic acid (ascorbic acid plus dehydroascorbic acid) content and firmness were not significantly influenced by irradiation at 1 or 2 kGy. The overall visual appearance was best for lettuce irradiated at 1 or 2 kGy. This improved quality may be related to the high CO2 and low O2 levels observed for the irradiated samples. Electrolyte leakage for lettuce increased with higher radiation doses and was correlated (R2 = 0.99) with a soggy appearance. The leakage for lettuce irradiated at ≥2 kGy was significantly more extensive than that for nonirradiated lettuce. The irradiation of fresh-cut lettuce in modified atmosphere packages at doses of 1 kGy and perhaps 2 kGy for safety enhancement and quality improvement is feasible.

Consumer Acceptance of Fresh-Cut Iceberg Lettuce Treated with 2% Hydrogen Peroxide and Mild Heat

An antibacterial treatment consisting of 2% hydrogen peroxide at 50°C for 60 s was evaluated for its effects on the sensory quality of fresh-cut iceberg lettuce. Treated lettuce was packaged in polyethylene film by a protocol used in the fresh-cut produce industry and then stored along with untreated controls for 3, 10, and 15 days at 5°C. Gas chromatographic analysis confirmed that the desired initial volume (~6 liters) and oxygen gas content (~10%) were maintained during storage. Consumers from the local community who were the primary shoppers for their households and who purchased and ate lettuce regularly evaluated the appearance, color, aroma, flavor, and texture of the lettuce and their overall liking of the lettuce. Forty consumers were recruited to evaluate processing replication 1 on 26 April, and another 40 were chosen to evaluate processing replication 2 on 3 May. Because replication differences were observed in instrumental color measurements and in mean sensory ratings, replications were not pooled for the two test dates. Lettuce purchased for processing replication 2 was considerably greener than that used in replication 1. Overall, the antibacterial treatment was more effective than the control treatment in maintaining sensory quality over 15 days of storage, provided that the lettuce was initially intensely green. Three-fourths of the participants indicated that they would be willing to buy precut packaged lettuce that had already been treated at the packinghouse or processing plant with an antibacterial solution, and of these participants, 62.5% indicated that they would be willing to pay 5 to 10 cents more per bag.

Changes in appearance and natural microflora on iceberg lettuce treated in warm, chlorinated water and then stored at refrigeration temperature

The objective of this study was to determine the effect of warm, chlorinated water on the survival and subsequent growth of naturally occurring microorganisms and visual quality of fresh-cut iceberg lettuce. After dipping cut lettuce leaves in water containing 20 mg l−1free chlorine for 90 s at 50°C, samples were stored at 5 or 15°C for up to 18 or 7 days, respectively. Populations of aerobic mesophiles, psychrotrophs, Enterobacteriaceae, lactic acid bacteria, and yeasts and molds were determined. The visual appearance and development of brown discoloration were monitored. Treatment of lettuce in warm (50°C) chlorinated water delayed browning of lettuce. Shelf life of lettuce stored at 5°C, as determined by subjective evaluation of color and general appearance, was about 5 days longer than that of lettuce stored at 15°C. Treatment in warm (50°) water, with or without 20 mg l−1chlorine, and in chlorinated water at 20°C significantly (α= 0·05) reduced the initial population of mesophilic aerobic microflora by 1·73–1·96 log10cfu g−1. Populations increased, regardless of treatment, as storage time at 5°C and 15°C increased. The same trends were observed in populations of psychrotrophs and Enterobacteriaceae. Yeast populations increased slightly in lettuce stored at 5°C but were consistently about 3 logs lower than mesophilic aerobes. Populations of molds and lactic acid bacteria were less than 2 log10cfu g−1throughout storage at 5 or 15°C. Results suggest that heat (50°C) treatment may have delayed browning and reduced initial populations of some groups of micro-organisms naturally occurring on iceberg lettuce, but enhanced microbial growth during subsequent storage.