Adel A. Kader

Preharvest and postharvest factors influencing vitamin C content of horticultural crops

Abstract Vitamin C, including ascorbic acid and dehydroascorbic acid, is one of the most important nutritional quality factors in many horticultural crops and has many biological activities in the human body. The content of vitamin C in fruits and vegetables can be influenced by various factors such as genotypic differences, preharvest climatic conditions and cultural practices, maturity and harvesting methods, and postharvest handling procedures. The higher the intensity of light during the growing season, the greater is vitamin C content in plant tissues. Nitrogen fertilizers at high rates tend to decrease the vitamin C content in many fruits and vegetables. Vitamin C content of many crops can be increased with less frequent irrigation. Temperature management after harvest is the most important factor to maintain vitamin C of fruits and vegetables; losses are accelerated at higher temperatures and with longer storage durations. However, some chilling sensitive crops show more losses in vitamin C at lower temperatures. Conditions favorable to water loss after harvest result in a rapid loss of vitamin C especially in leafy vegetables. The retention of vitamin C is lowered by bruising, and other mechanical injuries, and by excessive trimming. Irradiation at low doses (1 kGy or lower) has no significant effects on vitamin C content of fruits and vegetables. The loss of vitamin C after harvest can be reduced by storing fruits and vegetables in reduced O 2 and/or up to 10% CO 2 atmospheres; higher CO 2 levels can accelerate vitamin C loss. Vitamin C of produce is also subject to degradation during processing and cooking. Electromagnetic energy seems to have advantages over conventional heating by reduction of process times, energy, and water usage. Blanching reduces the vitamin C content during processing, but limits further decreases during the frozen-storage of horticultural products.

Quality changes in fresh-cut pear slices as affected by controlled atmospheres and chemical preservatives

Low O2 (0.25 or 0.5 kPa) elevated CO2 (air enriched with 5, 10 or 20 kPa CO2), or superatmospheric O2 (40, 60, or 80 kPa) atmospheres alone did not effectively prevent cut surface browning or softening of fresh-cut pear slices. A post-cutting dip of 2% (w/v) ascorbic acid, 1% (w/v) calcium lactate and 0.5% (w/v) cysteine adjusted to pH 7.0 did significantly extend shelf-life of ‘Bartlett’ pear slices, by inhibiting loss of slice flesh firmness and preventing cut surface browning. Participants in a quality evaluation could not distinguish between pear slices treated with this preservative solution and stored overnight at 0 °C and freshly prepared control pear slices. After 10 days storage in air at 0 °C, 82% of participants judged treated pear slices to be acceptable in appearance and 70% judged flavor to be acceptable.

Effects of superatmospheric oxygen levels on postharvest physiology and quality of fresh fruits and vegetables

Abstract Exposure to superatmospheric O 2 concentration may stimulate, have no effect, or reduce rates of respiration and ethylene production, depending on the commodity, maturity and ripeness stage, O 2 concentration, storage time and temperature, and concentrations of CO 2 and C 2 H 4 present in the atmosphere. In some plant organs, cyanide-resistant respiration is enhanced by elevated O 2 atmospheres. Ripening of mature-green, climacteric fruits was slightly enhanced by exposure to 30–80 kPa O 2 , but levels above 80 kPa retarded their ripening and caused O 2 toxicity disorders on some fruits. High O 2 concentrations enhance some of the effects of ethylene on fresh fruits and vegetables, including ripening, senescence, and ethylene-induced physiological disorders (such as bitterness of carrots and russet spotting on lettuce). While superatmospheric O 2 concentrations inhibit the growth of some bacteria and fungi, they are much more effective if combined with elevated (15–20 kPa) CO 2 , which is a fungistatic gas.

Fruit ripening and quality

The conversion of a tomato fruit from the mature green to fully ripe state involves dramatic changes in colour, composition, aroma, flavour and texture. Ripening used to be thought of simply as the result of a series of degradative processes, probably because some of the more obvious changes require the action of hydrolytic enzymes. However, it is now clear that ripening is dependent on a wide range of separate synthetic as well as degradative reactions. These include alterations in metabolism and gene expression which have a dramatic effect on fruit quality. The changes are highly coordinated; they occur in the majority of the cells of the fruit and involve every subcellular compartment. The various facets of ripening appear to be coordinated and regulated by plant hormones but may be modified by genetic and environmental factors. In this chapter the general features of tomato ripening are outlined first, together with a discussion of the cellular mechanisms regulating the process. This is followed by a consideration of the ways in which genotype, growing conditions, disease, and post-harvest history can influence specific quality attributes.

Plasma Antioxidant Capacity Changes Following a Meal as a Measure of the Ability of a Food to Alter In Vivo Antioxidant Status

Objective: Determine 1) if consumption of a meal of different fruits or berries increases plasma hydrophilic (H-) or lipophilic (L-) antioxidant capacity (AOC) measured as Oxygen Radical Absorbance Capacity (ORACFL); 2) if including macronutrients in the meal alters postprandial changes in AOC; and 3) if preliminary recommendations can be developed for antioxidant intake. Methods: Changes in plasma AOC following consumption of a single meal of berries/fruits (blueberry, dried plum, dried plum juice, grape, cherry, kiwifruit and strawberry) were studied in 5 clinical trials with 6–10 subjects per experiment. In two studies with blueberry or grape, additional macronutrients (carbohydrate, fat, protein) were included in the control and treatment meals. Blood samples collected before and after the meal were analyzed for AOC. Results: Consumption of dried plums or dried plum juice did not alter either the H- or L-AOC area under the curve (AUC). Consumption of blueberry in 2 studies and of mixed grape powder [12.5 (Study #1), 39.9 (Study #4) and 8.6 (Study #5) mmole Trolox Equivalents (TE) AOC, respectively] increased hydrophilic AOC AUC. L-AOC increased following a meal of blueberry containing 12.5 mmole TE AOC (Study #1). Consumption of 280 g of cherries (4.5 mmol TE AOC) increased plasma L-AOC but not H-AOC. The AOC in the control groups in which additional macronutrients (Studies #4 and #5) were added decreased from the postprandial baseline AOC measurement. Conclusion: We have demonstrated that consumption of certain berries and fruits such as blueberries, mixed grape and kiwifruit, was associated with increased plasma AOC in the postprandial state and consumption of an energy source of macronutrients containing no antioxidants was associated with a decline in plasma AOC. However, without further long term clinical studies, one cannot necessarily translate increased plasma AOC into a potential decreased risk of chronic degenerative disease. Preliminary estimates of antioxidant needs based upon energy intake were developed. Consumption of high antioxidant foods with each meal is recommended in order to prevent periods of postprandial oxidative stress.

Effect of controlled-atmosphere storage on the quality and carotenoid content of sliced persimmons and peaches

Abstract Changes in quality, retinol equivalents (RE) and individual provitamin A carotenoids in fresh cut ‘Fay Elberta’ peaches ( Prunus persica (L.) Batsch) held for 7 days and ‘Fuyu’ persimmons ( Diospyros kaki L.) held for 8 days at 5 °C in air or controlled atmospheres were evaluated. Controlled atmospheres of 2% O 2 , 12% CO 2 in air, and 2% O 2 + 12% CO 2 had no effect on quality attributes of sliced peaches over 7 days of storage. Visual quality of persimmon slices was slightly enhanced by the treatments containing 12% CO 2 , which also resulted in significant differences in color. Peach slices stored in air + 12% CO 2 had a lower content of β-carotene and β-cryptoxanthin, resulting in lower RE than the other treatments. The various carotenoids found in persimmon slices responded differently to the tested atmospheres; storage in 2% O 2 or air + 12% CO 2 tended to result in lower RE after 8 days, but the loss was not significant for fruit stored under 2% O 2 + 12% CO 2 . For sliced peaches and persimmons, the limit of shelf life was reached before major losses of carotenoids occurred.

Controlled atmosphere-induced changes in pH and organic acid metabolism may affect color of stored strawberry fruit

Skin and flesh of ‘Selva’ strawberries (Fragaria x ananassa Duch.) stored at 5°C in air or 2 kPa O2 became darker red and accumulated anthocyanin levels, but these changes were reduced in fruit stored in air 20 kPa CO2, 2 kPa O220 kPa CO2, 0.5 kPa O2,, and 0.5 kPa O220 kPa CO2 (balance N2 in all CA treatments). Increasing pH and decreasing titratable acidity in tissues during storage, especially in the internal tissues, were more marked in fruit stored in high CO2 atmospheres. Since pH affects color expression of the anthocyanin pigment, these changes may contribute to the observed changes in color. Combined citric and malic acid concentrations were higher in the external tissues (10.6 mg g 1 ) than internal tissues (5.5 mg g 1 ), and decreases in concentration of both acids were greater in fruit kept in high CO2 atmospheres. Succinic acid in fruit tissues was present in low concentrations, but usually increased in high CO2 atmospheres.

Postharvest life and flavor quality of three strawberry cultivars kept at 5 °C in air or air+20 kPa CO2

The postharvest life and flavor quality of three strawberry (Fragaria x ananassa D.) cultivars (Aromas, Diamante and Selva) kept at 5 8C in air or air� /20 kPa CO2 for up to 15 days were investigated. ‘Diamante’ and ‘Selva’ had better flavor quality than ‘Aromas’ strawberries, as indicated by levels of titratable acidity and total soluble solids, organic acids, sugars and some aroma compounds and by a consumer preference test. Flesh firmness was maintained in ‘Aromas’ and increased in ‘Diamante’ and ‘Selva’ strawberries during storage at 5 8C in both air and air� /20 kPa CO2. Fruit color was not affected by CO2 treatments. The postharvest life based on appearance was 7, 9 and 9 days for ‘Aromas’, ‘Diamante’ and ‘Selva’ fruits stored in air and it was extended by 2, 2 and 4 days, respectively, by the CO2enriched atmosphere. However, the level and proportion of flavor components (sugars, organic acids, aroma compounds) and fermentative metabolites, as well as the results of sensory evaluations, indicated that the flavor life was shorter than postharvest life based on appearance in ‘Aromas’ fruit stored in air (5 vs. 7 days) and in CO2-stored ‘Aromas’ (7 vs. 9 days) and ‘Selva’ (11 vs. 13 days) fruit. ‘Selva’ and ‘Diamante’ strawberries retained their flavor quality during storage at 5 8C in air for 9 days and CO2-stored ‘Diamante’ fruit for 11 days. # 2002 Elsevier Science B.V. All rights reserved.

Effect of down-regulation of ethylene biosynthesis on fruit flavor complex in apple fruit

The role of ethylene in regulating sugar, acid, texture and volatile components of fruit quality was investigated in transgenic apple fruit modified in their capacity to syntheize endogenous ethylene. Fruit obtained from plants silenced for either ACS (ACC synthase; ACC – 1-aminocyclopropane-1-carboxylic acid) or ACO (ACC oxidase), key enzymes responsible for ethylene biosynthesis, expectedly showed reduced autocatalytic ethylene production. Ethylene suppressed fruits were significantly firmer than controls and displayed an increased shelf-life. No significant difference was observed in sugar or acid accumulation suggesting that sugar and acid composition and accumulation is not directly under ethylene control. Interestingly, a significant and dramatic suppression of the synthesis of volatile esters was observed in fruit silenced for ethylene. However, no significant suppression was observed for the aldehyde and alcohol precursors of these esters. Our results indicate that ethylene differentially regulates fruit quality components and the availability of these transgenic apple trees provides a unique resource to define the role of ethylene and other factors that regulate fruit development.

Effect of slicing and controlled-atmosphere storage on the ascorbate content and quality of strawberries and persimmons

Abstract Changes in quality, total ascorbic acid, reduced ascorbic acid and dehydroascorbate in fresh cut ‘Selva’ strawberries ( Fragaria × ananassa Duch.) held for 7 days and ‘Fuyu’ persimmons ( Diospyros kaki L.) held for 8 days at 5 °C in air or controlled atmospheres were evaluated. Various atmospheres had significantly different effects on the color, pH, and titratable acidity of the fruits. The two fruits responded differently to the wounding stress in regards to oxidation of ascorbic acid, but in both cases, the postcutting life based on visual quality ended before significant losses of total ascorbic acid occurred. Controlled atmospheres of 2% O 2 , air + 12% CO 2 , or 2% O 2 + 12% CO 2 had no significant effect on changes in total ascorbate content for either fruit. Washing of intact or sliced strawberries in 100 ppm sodium hypochlorite was found to induce significant oxidation of reduced ascorbic acid, but resulted in no changes in total ascorbic acid.