Juan A. Tudela

HPLC-MS Analysis of Proanthocyanidin Oligomers and Other Phenolics in 15 Strawberry Cultivars†

The phenolic compounds of 15 strawberry cultivars grown in Spain were analyzed and quantified: anthocyanins (20.2-47.4 mg/100 g of fw) (cyanidin 3-glucoside and pelargonidin 3-glucoside, 3-rutinoside, and 3-malonyl glucoside), flavonols (1.5-3.4 mg/100 g of fw) (quercetin 3-glucuronide and kaempferol 3-glucoside and 3-p-coumaroyl-glucoside), proanthocyanidins (53.9-163.2 mg/100 g), p-coumaroyl-glucose (0.84-6.70 mg/100 g), ellagitannins (9.67-22.86 mg/100 g) (sanguiin H-6, lambertianin C, and galloyl bis-HHDP-glucose), and ellagic acid glycosides (0.88-2.06 mg/100 g of fw) (two ellagic acid deoxyhexosides). Proanthocyanidins, the main phenolic compounds, were characterized by phloroglucinol degradation. Their mean degree of polymerization ranged from 3.4 for cv. Chiflon to 5.8 for cv. Ventana, the average value being 4.3. The terminal unit of proanthocyanidin oligomers was always (epi)catechin (17.36-29.93%) and (epi)catechin (61.66-75.39%) or (epi)afzelechin (4.50-10.54%) as extension units. Different combinations of (epi)catechin and (epi)afzelechin were detected, and their sequence of linkage was characterized by HPLC-MS-MS. Relative percentages of dimers, trimers, tetramers, and pentamers were evaluated by the extracted ion chromatogram (EIC) analysis.

Thermal postharvest treatments for improving pomegranate quality and shelf life

Sweet pomegranates (Punica granatum L. cv Mollar de Elche) were cold-stored for 90 days. Curing at 33°C and 95% RH for 3 days before continuous storage at 2 or 5°C and 95% RH was tested for reducing chilling injuries. Alternatively, cycles of intermittent warming (IW) of 1 day at 20°C every 6 days at 2 or 5°C were tested. Control fruits were conventionally stored at 2 or 5°C and 95% RH, and a shelf life of 6 days at 15°C and 75% RH was included in the trials. At the end of the storage and shelf life periods, IW fruits showed the highest anthocyanin concentrations and titratable acidity, and the best visual appearance. After shelf life, IW during 2°C storage was the only treatment that resulted in fruit with flavor similar to that at harvest. Main losses were due to decay (Penicillium spp.) in treatments at 5°C, with the least loss being in the IW2°C treatment. Chilling injuries (pitting and husk scald) were strongly reduced by curing at 2°C but only after cold storage. The lowest chilling injuries were found in the IW treatments. Severity of husk scald development was not directly related to low storage temperature. IW during 2°C storage has proved to be the best treatment for minimizing chilling injuries and maintaining pomegranate fruit quality.

Physiological, phytochemical and structural changes of multi-leaf lettuce caused by salt stress

BACKGROUND Environmental stress due to salt has been described to enhance lettuce processability, shelf life and consumer acceptability. Moderate salinity causes altered leaf carotenoid, lignin, phenolic and flavonol levels without noticeable changes in the green colour and morphology of lettuce. The aim of this study was to understand the improvements in processability, due to salt stress, related to textural properties and structural characteristics. RESULTS Physiological, phytochemical and structural changes were observed that were of significant relevance to salt stress (50, 100 and 150 mmol L(-1) NaCl). Fresh weight per plant, fresh weight per leaf, leaf area, water content, colour saturation, chlorophyll a and b and the area of the intercellular spaces decreased when the concentration of salt was increased. Solute concentration, elasticity, total and individual phenolic acids and the areas occupied by the palisade and spongy parenchyma cells increased when the concentration of salt was increased. CONCLUSION These data illustrate that salt stress can have a positive impact on certain structural parameters, especially tissue elasticity, that can be closely linked to a higher number of cells, of lower size and high leaf strength, explaining the postharvest longevity of lettuce. However, leaf growth and visual quality could be negatively affected by salt stress.

Influence of nutrient solutions in an open-field soilless system on the quality characteristics and shelf life of fresh-cut red and green lettuces (Lactuca sativa L.) in different seasons

BACKGROUND Little information is available about the impact of nutrient solution ion concentration on quality characteristics and shelf life of fresh-cut lettuce grown in soilless systems in open field. Three lettuce genotypes, lollo rosso and red oak leaf as red-leafed genotypes and butterhead as green-leafed genotype, were studied. The influence of three nutrient solutions with low, medium and high ion concentrations, which varied in the macroanion (NO₃⁻) and macrocations (K⁺, Ca²⁺ and NH₄⁺), were compared in summer and winter. RESULTS The nutrient solutions evaluated in this study for the production of lettuce in a soilless system did not strongly influence the quality characteristics of the raw material. When the ion concentration of the nutrient solution was increased, fresh weight decreased, although it depended on the genotype and season. Maturity index and dry matter content varied with the season but independently of the nutrient solution. In summer, maturity index was higher and dry matter lower than in winter. Initial texture and visual quality were not influenced by the nutrient solution. Medium ion concentration provided the highest content of vitamin C and phenolic compounds. Our observations pointed out that the genotype had a strong influence on the shelf life of the fresh-cut product with minor differences among nutrient solutions. In general, red-leafed lettuces showed the highest antioxidant content, helping the maintenance of sensory characteristics throughout storage. CONCLUSION The combination of optimal nutrient solution ion concentration and suitable cultivar is considered essential to ensure lettuce post-cutting life.

Disinfection by-products in baby lettuce irrigated with electrolysed water: Disinfection by-products in lettuce

BACKGROUND Irrigation water disinfection reduces the microbial load but it might lead to the formation and accumulation of disinfection by-products (DBPs) in the crop. If DBPs are present in the irrigation water, they can accumulate in the crop, particularly after the regrowth, and be affected by the postharvest handling such as washing and storage. To evaluate the potential accumulation of DBPs, baby lettuce was grown using irrigation water treated with electrolysed water (EW) in a commercial greenhouse over three consecutive harvests and regrowths. The impact of postharvest practices such as washing and storage on DBP content was also assessed. RESULTS Use of EW caused the accumulation of chlorates in irrigation water (0.02-0.14 mg L-1 ), and in the fresh produce (0.05-0.10 mg kg-1 ). On the other hand, the disinfection treatment had minor impact regarding the presence of trihalomethanes (THMs) in water (0.3-8.7 μg L-1 max), and in baby lettuce (0.3-2.9 μg kg-1 max). CONCLUSIONS Disinfection of irrigation water with EW caused the accumulation of chlorates in the crop reaching levels higher than the current maximum residual limit established in the EU legislation for leafy greens.