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

Effect of home-refrigerator storage temperature on tomato quality

Postharvest storage, handling and distribution of fruit at low temperatures is the most common and manageable approach to control ripening and subsequent deterioration and to maximize product shelf-life. However, tomatoes, as many other subtropical fruits, are susceptible to develop symptoms of chilling injury, a physiological disorder caused by the exposure to low temperature above the freezing point. Development of chilling injury depends on temperature, time, ripening stage and tomato type/cultivar. We studied the effect of home-refrigerator storage temperature on the quality of two types of tomato: cocktail tomato (cultivars ‘Amoroso’ and ‘Brioso’) and truss tomato (cultivars ‘Capricia’ and ‘Roterno’). Fully ripe tomatoes were stored for 10 days at two temperatures: 4°C as simulation of home-refrigerator storage and 15°C as an optimal storage temperature. We evaluated several quality parameters: weight loss, firmness, soluble solid content, titratable acidity, carbohydrates, titratable acidity and citrate content. Although we did not observe any apparent symptom of chilling injury, we found that 4°C temperature stimulates firmness decay in both cocktail tomato cultivars, increasing fruit susceptibility to mechanical injury. Moreover, already after 5 days of 4°C storage, tomatoes generally showed decreased sugar and increased acid content (especially in cocktail tomatoes) compared to 15°C stored fruit, indicating a loss of sensoric quality at 4°C

Factors affecting the postharvest performance of fresh-cut lettuce

The quality of fresh-cut fruits and vegetables is often offset by a rapid deterioration, due to severe physical stress, such as peeling, cutting, slicing, shredding, and trimming. Due to this wounding, the already short shelf-life of these harvested products is even more reduced in the market place. In addition, consumers have become more critical on the use of synthetic and chemical additives to preserve quality attributes of fresh-cut produce. Developing new, effective, non-invasive and non-chemical techniques for improving and maintaining quality in fresh-cut produce are the timely questions of the industry. The work reported in this thesis adds to the increasing knowledge and understanding on how pre- and postharvest factors affect the storability of fresh-cut leafy vegetables. This work focused in particular on factors that up to date have not been systematically investigated such as (i) environment and genetic dependent antioxidant levels, (ii) plant age at harvest, (iii) light during post-processing storage and (iv) duration and conditions of storage prior to processing. The factors under investigation are discussed in the light of their effects on the shelf-life of fresh-cut tissue as related to a number of physiological processes associated with tissue browning and senescence. We found that plant age at harvest and storage of the harvested crop prior to processing are important determinants of fresh-cut performance: the younger the plant and the shorter the storage period prior to processing, the longer the shelf life of the fresh-cut product. In addition, the application of low levels of light during storage and display of the fresh-cut product greatly prolonged the shelf-life. The physiological and biochemical background of these phenomena was investigated.</p

Comparison of methods for determining the fatty acid composition of photosynthetic tissues

The fatty acid (FA) composition of photosynthetic tissue differs from that in other plant or animal tissues. In leaves, the lipid fraction constitutes less than 10% of the dry weight and is mostly located in the chloroplasts. An extraction solvent should dissolve polar lipids readily, but should also overcome interactions between the lipids and the tissue matrix. A mixture of chloroform/methanol (C/M) is commonly used. However, less toxic alternative methods such as hexane/isopropanol (H/I) and ethanol (E) have been suggested. In this preliminary study we compared the effectiveness of these three methods which are used as standard extraction protocols for FA analysis of plant material at three different European Universities. C/M extraction gave the highest total FA content and H/I the lowest, suggesting that C/M is indeed the best general-purpose lipid extraction solvent. Significant differences were also observed for FA composition including the ratio of saturated to unsaturated FA indicating selectivity of the various solvents in extracting different individual FA. Further and more detailed investigations are required to confirm this hypothesi

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)

Plant Age Affects Wound-Induced Senescense in Lactuca Sativa L

In the present study we investigated the performance of dark-stored wounded leaf discs and pieces (to some extent mimicking fresh-cut product) of Lactuca sativa L. in relation to the physiological maturity at harvest. We used two related genotypes, i.e. a green (cv. Troubadour) and a red butterhead (cv. Teodore) differing in their pigment levels. For both genotypes, senescence of the wounded (fresh-cut) tissue prepared from leaves of younger plants was significantly delayed compared to wounded tissue prepared from the more mature plants. Shelf-life (time to unacceptable quality) of fresh-cut was doubled when plants were harvested one week before the commercial harvesting date. To explain differences in shelf-life between fresh-cut products prepared from plants harvested at different age, a number of physiological and nutritional parameters were determined at harvest. The red lettuce contained about two times more chlorophyll, carotenoids, and polyphenolic antioxidants than the green lettuce, but the shelf-life of both genotypes was about similar. Increasing the amount of pigments and polyphenols through application of LED light (with high percentage blue) during cultivation did not affect the shelf life of the wounded leaf tissue. The content of chlorophyll, carotenoids, phenolic compounds, as well as total antioxidant capacity was not affected by age of the plants for either genotype. The content of ascorbic acid decreased with maturation in the green lettuce but it was not affected by maturity in the red lettuce. This shows that there are no obvious signs of leaf senescence with age and the differences in pigments and antioxidants show no relation to the fresh-cut shelf life and thus cannot explain the effect of plant age on senescence of the wounded tissue. The net photosynthesis rate and carbohydrate reserves in the red lettuce were about half of that in the green lettuce but the shelf-life of both genotypes was similar. The net photosynthesis rate was not influenced by plant maturity in the green lettuce, whereas it decreased with maturation in the red lettuce. A decrease in sucrose and starch, and therefore the total content of carbohydrates with aging was observed in both genotypes. This effect was more pronounced in the red than in the green lettuce. There was no apparent relationship between the absolute levels of the total carbohydrates and the shelf-life of the fresh-cut product showing that carbohydrate reserves in itself cannot explain the effect of plant age on senescence of the wounded tissue. The leaves from older plants apparently have a reduced capability to cope with the stress from wounding. No simple one to one relationship emerged between any of the measured nutritional parameters, their change during maturation and the eventual shelf-life of the fresh-cut produce

Storage of intact heads prior to processing limits the shelf-life of fresh-cut Lactuca sativa L.

Harvested lettuce heads are usually transported and stored for some period of time under a variety of conditions prior to processing. During storage, especially under suboptimal conditions, nutritional composition of the harvested produce continues to change. The possible impact of prior storage of the heads on the performance of the fresh-cut product has not been quantified, and was the aim of this study. The experiments were performed with three related genotypes of Lactuca sativa L. (butterhead lettuce): two green varieties and one red variety. The effect of prior storage on quality parameters in the stored whole heads and on subsequent fresh-cut quality performance was investigated. In addition, the effect of prior storage of heads with and without their root system and the application of light during storage were investigated. The changes in visual quality, the levels of energy reserves, and some selected senescence markers, i.e. chlorophyll content and electrolyte leakage were evaluated. Despite the relatively high storage temperature of 12 °C, the intact heads still looked fresh even after 17 days of storage. However, a decline in the soluble sugars, a decrease in chlorophyll, and an increase in electrolyte leakage were observed with advancing storage duration. Prior storage of intact heads greatly decreased the shelf-life of the fresh-cut product prepared from these heads. Storage of rooted heads and the continuous application of light (above the light compensation point) did not alter the effect of prior storage of the heads on the quality of the fresh-cut produc

Effects of post-harvest treatments on concentrations and profile of fatty acids in fresh perennial ryegrass (Lolium perenne L.)

Plant lipids are complex, polar and highly unsaturated constituents of membranes. During collection and/or handling of a plant sample, the membrane integrity gets lost due to plant injury and losses of fatty acids (FA) can occur as a result of oxidative or enzymatic processes. Quantitative and qualitative effects of various post-harvest treatments on the concentrations and proportions of FA in herbage are not well known. In this study, effects of various post-harvest treatments regarding conditions following sample collection of perennial ryegrass were examined. The handling of the samples, before applying all pre-treatments, was uniform, i.e., all samples were put in a cooling box at 4 °C and transported to the lab for approximately 30 min. The moment when the samples arrived to the lab was considered ¿time zero¿, and the applications of treatments started. We studied effects of two ways of sample handling (dry ice vs. no dry ice), two frozen storage temperatures (-80 °C vs. -18 °C) and two durations of frozen storage (1 day vs. 2 weeks) on concentrations and proportions of FA in cut herbage. The effects of the treatments appeared to be small and inconsistent, with exception of prolonged storage, which decreased FA concentrations, and increased the proportion of alpha-linolenic acid (C18:3). Contrary to expectation, using dry ice (rapid freezing) did not differ from slow freezing (without dry ice). Also, there were no effects of storage temperature (-80 or -18 °C). Future research questions are discusse

Effects of Nitrogen fertilisation and regrowth period on fatty acid concentrations in perennial ryegrass (Lolium perenne L.)

Information on lipids in forages is scarce, and effects of nitrogen (N) application level and regrowth period on the fatty acid (FA) concentration and composition of perennial ryegrass (Lolium perenne L.) were studied. N was applied at 0, 45 and 100 kg ha1, and swards were cut after various regrowth periods, resulting in six treatments designed as randomised blocks with three replicates. The stages of development ranged from vegetative to elongating swards, with herbage yield levels from 1.9 to 4.2 t dry matter (DM) ha1. Concentrations of individual FA were determined by gas chromatography, and canopy characteristics and herbage quality were assessed. The treatments resulted in canopies with contrasting DM yields and protein concentrations. Five FAs, representing 98% of total FAs, were studied in detail. On an average, the concentration of these major FAs in fresh grass was 15.1 g kg1 DM, and 69% of the major FAs consisted of C18:3. Regrowth period affected (P <0.05) the total FA concentration, and significantly (P <0.01) lower concentrations of C18:3 and C16:1 were found after a longer period of regrowth. N application resulted in higher (P <0.001) concentrations of all FAs. The FA composition was not affected by N application, but a longer regrowth period significantly (P <0.001) decreased the proportion of C18:3 and increased those of C18:2 and C16:0. A strong, positive overall linear relation was found between the concentrations of total FAs and C18:3 with the crude protein concentration in the herbage. These studies demonstrate opportunities to affect the FA concentration and composition of FA in herbage through management strategies, which could affect milk FA composition