Dimitrios Gerasopoulos

Evolution of watermelon fruit physicochemical and phytochemical composition during ripening as affected by grafting

Flesh reflectance colorimetry, mechanical texture analysis, pH, titratable acidity (TA), and soluble solid (SS), soluble carbohydrate, lycopene and citrulline content of watermelon fruit were assessed throughout ripening (30-50 days post-anthesis; dpa) in grafted and self-rooted plants. Grafting increased firmness, TA, and lycopene content though it delayed its peak. Lycopene content was mostly ripening-dependant, highly correlated and synchronous with changes in pulp chroma (C) and colour a. The sweetness was affected only by ripening. However, total sugars and SS peaked later in fruit of grafted plants than in non-grafted ones, and significant interaction of ripening with grafting was observed. Citrulline content increased with ripening in fruit of grafted plants, reaching a peak at 45 dpa; whereas in non-grafted ones it was unchanged between 30 and 45 dpa and declined at 50 dpa. As ripening overall was retarded by grafting, fruit quality of grafted watermelon may benefit from belated harvest.

Configuration of watermelon fruit quality in response to rootstock-mediated harvest maturity and postharvest storage.

BACKGROUND The configuration of watermelon fruit quality was analysed in a multi-factorial approach accounting for the effects of grafting, harvest maturity and postharvest storage. Diploid, seeded, hybrid cv. Pegasus, cultivated as scion on interspecific hybrid squash rootstock TZ148 and as non-grafted control, was stored at 25 °C following sequential harvests from the onset of ripening to over-maturity. RESULTS Delayed rootstock-mediated climax in pulp lycopene and chroma was observed, while both were heightened by postharvest storage when harvest preceded full maturity. Pulp firmness was increased by 46.5% on TZ148, while postharvest decrease in firmness was non-significant. Non-grafted fruits attained their peak in pulp carbohydrate content earlier during ripening. Monosaccharide content declined and sucrose content increased both preharvest and postharvest; overall sugar content declined by 4.3% during storage. Pulp acidity decreased steadily with ripening but was moderately increased by grafting. Citrulline content increased by 12.5% on TZ148; moreover, it climaxed with ripening and declined with storage only in grafted fruit. CONCLUSION Grafting enhances pulp texture and bioactive composition. Potential suppression of sugar content as a result of grafting is minimized at full commercial maturity. Brief postharvest ambient storage enhances pulp lycopene and chroma, especially in early-picked fruit, notwithstanding the depletion of monosaccharides and citrulline and a limited deterioration of texture.

Effects of Genetic, Pre- and Post-Harvest Factors on Phenolic Content and Antioxidant Capacity of White Asparagus Spears

The effects of genetic, pre-harvest (season of harvest, spear diameter, spear portion and spear tip color) and post-harvest factors (storage and domestic preparation practices, e.g., peeling and cooking) on total phenolic, flavonoid and ascorbic acid content of white asparagus spears and their correlation with antioxidant capacity (DPPH and FRAP) were studied. Results showed that genetic material was important for the total phenolic content but not season of harvest, spear diameter or storage. Violet spear tips and apical spear portions showed the largest amount of total phenolics. Peeling did not affect total phenolics in fresh asparagus, whereas it reduced their content in stored asparagus, while cooking resulted in an increase in both fresh and stored asparagus. However, the soluble extract of total phenolics and flavonoids were minor and the missing significance of phenolics and flavonoids in antioxidant capacity of white asparagus spears depends on these small amounts.

Hypoxic acclimation prevents avocado mesocarp injury caused by subsequent exposure to extreme low oxygen atmospheres

Avocado fruit (Persea americana Mill., cv. Hass), preclimacteric and ripening-initiated, were either hypoxically pretreated (HPT, 3% O2 for 24 h) or exposed directly to 1 and 0.25% O2 for 1–3 days (NHPT) at 20 °C. Low O2 treatments resulted in fruit maintaining higher flesh firmness. Hypoxic acclimation of preclimacteric and ripening-initiated avocado fruit increased their tolerance to subsequent 0.25 and 1% O2 levels, as assessed by visual quality attributes when the fruit returned to air. Hypoxic pre-treatment also produced a stronger expression of the anaerobically induced ADH isoenzymes than in NHPT avocado fruit that were subjected directly to 1 and 0.25% O2 for 1–3 days at 20 °C. Thus, acclimation of avocado fruit to hypoxia resulted in a beneficial increase in tolerance to subsequent ultra-low O2 treatments.

Effect of degree of cutting of leek on physicochemical characteristics of Greek traditional sausages.

Fresh-cut leek is one of the principal ingredients of Greek traditional sausages. In this study the effect of the degree of cutting of leek on the physicochemical traits of Greek traditional sausages was investigated. Leek was cut to three different degrees (coarse, medium and fine), before being mixed with meat, salt and seasonings; the mixture was placed in natural casings and stored for six days at 15-18°C. Sausages lost about 25% of their initial weight by the end of storage. While pH decreased in all treatments, it was significantly more so (to pH 4.1) in sausages with fine-cut leek, from as early as the second day of storage. During storage all sausages showed a decrease in lightness and a change in colour from yellow to red. The internal atmosphere of the sausages with fine-cut leek showed peak CO(2) concentrations of 30% while those with coarse and medium-cut leek showed peak CO(2) concentrations of 20% by day one of storage and equibrated to 5%. Ethylene in the internal atmosphere of sausages with fine and medium-cut leek peaked by day one at 5.5μll(-1) but to only 2μll(-1) for those with coarse-cut leek. Sausage nitrate content and antioxidant capacity did not show major differences between treatments. Fine-cut leek contributed to sausage stability and quality more rapidly than medium or coarse-cut leek.

Biochemical and histological contributions to textural changes in watermelon fruit modulated by grafting

Increased watermelon fruit flesh firmness is systematically incurred with grafting on Cucurbita hybrid rootstocks (heterografting). Possible differences in mesocarp cell wall constitution and histology between heterografted, homeografted (self-grafted) and non-grafted watermelon were examined, as well as their contributions to fruit texture. Firmness correlated positively (r=0.78, p<0.001) with cell density (cellsmm-2) which was higher in heterografts (5.83) than homeografts (4.64) and non-grafted controls (4.69). Mean cell size was smallest in heterografts and correlated negatively (r=-0.75, p<0.001) with firmness. Cell wall material, particularly the water-insoluble pectin fractions associated with firmness, were highest in heterografts. No associations with firmness were found for cell wall neutral sugars and membrane permeability. Higher parenchymatic cell density with higher content of alcohol insoluble residue and more abundant water-insoluble pectin fractions underscore enhanced firmness in heterografts. Possible implication of osmolytes in rootstock-mediated cell pressure regulation warrants further investigation.

Genotype, ultraviolet irradiation, and harvesting time interaction effects on secondary metabolites of whole lettuce and browning of fresh-cut product

ABSTRACT This study evaluated the importance of three factors (genotype, ultraviolet [UV] radiation and harvest time) and their interaction on phenolics, tannins, flavonoids and antioxidant activity of ‘Paris Island’ (romaine type) and ‘Sanguine’ (red leaf type) lettuce plants as well as on the severity of browning of their fresh-cut product. Ten genotypes had significant effect on secondary metabolite accumulation and higher levels were found in ‘Sanguine’, while no interaction effect was found among all the studied factors. Therefore, a new analysis of variance was performed for each genotype separately. The results showed that in ‘Paris Island’ the time of harvest had a significant effect on all measured parameters with higher levels for plants from the night harvest, while UV radiation had little effect on the plants’ biochemistry. On the contrary, in ‘Sanguine’, UV radiation significantly affected the concentration of secondary metabolites and antioxidant capacity, with higher levels for plants grown under UV-open film. Browning evaluation of fresh-cut product derived from the above plants showed that factors affecting secondary metabolite concentration in whole plants at harvest did not have a similar effect. The findings indicate that there are appropriate treatments, for each genotype, that could achieve high production of secondary metabolites and improve their antioxidant properties.

Salt-stressed fresh cut leek accelerates CO2 and C2H4 production and enhances the development of quality characteristics of traditional Greek sausages during storage

Fresh cut leek was mixed with salt for 0.5 (IM) and 5 (LM) min or remained untreated (control) and stored alone or mixed with minced meat and seasonings, cased and stored at 15 °C for 7 days. The fresh cut leek and sausage metabolics and sausage microbiological and physicochemical traits were measured during storage. Sausages with LM leek had significantly higher counts of lactic acid bacteria, faster rates of pH drop and dehydration and increased red color compared with the other treatments. Sausage to fresh cut leek peaks of CO₂ or C₂H₄ production was 5 or 2 fold higher in LM than the other treatments indicating that the sausage flora was the source of both. The use of salt-stressed fresh cut leek before manufacture of sausages enhances microbial activity as well as its stability and shortens the necessary storage time needed for the development of the quality characteristics of Greek traditional sausages.