Susanne Huyskens-Keil

Phytochemicals in Fruit and Vegetables: Health Promotion and Postharvest Elicitors

Inverse associations between fruit and vegetable intake and chronic diseases, such as different types of cancer and cardiovascular disease, have been demonstrated in numerous epidemiological studies. Phytochemicals have been indicated to be responsible for this observed protective effect. Application of postharvest elicitors can trigger distinct changes in the plants secondary metabolism. Thus, targeted postharvest elicitor treatments may be used to obtain fruit and vegetables enriched with phytochemicals for sale as fresh market products or used as raw material for functional foods and supplements, thereby promoting higher consumption of these health-promoting substances. Referee: Professor Charles A. Sims, Chair, Food Science and Human Nutrition POB 110370, University of Florida/IFAS, Gainesville, FL 32611-0370

UV-B-Induced Secondary Plant Metabolites - Potential Benefits for Plant and Human Health

Epidemiological studies have revealed an inverse association between the consumption of fruit, vegetables, and herbs and the risk of both cancer and cardiovascular disease. This protective effect is mostly due to secondary metabolites present in plant tissues. During the last decade, it has become increasingly clear that UV-B radiation is an important regulator of plant secondary metabolism. Low, ecologically-relevant UV-B levels trigger distinct changes in the accumulation of, among others, phenolic compounds, carotenoids and glucosinolates. Fundamental understanding of plant UV-B perception and responses opens up new opportunities for crop manipulation. Thus, targeted low dosage UV-B radiation treatments as emerging technology may be used to generate fruit, vegetables, and herbs enriched with secondary plant metabolites for either fresh consumption or as a source for functional foods and nutraceuticals, resulting in increased ingestion of these health-promoting substances. The UV-B induced accumulation of secondary plant metabolites is likely to have evolved as a plant defense response against harmful UV-B radiation. However, UV-B induced secondary metabolites also alter other trophic interactions, for example by altering plant herbivore resistance. Thus, UV-B driven metabolic changes in the plants secondary metabolism have benefits for both ends of the bio-based food chain, i.e., for plants themselves as well as for humans.

Effect of film packaging and surface coating on primary and secondary plant compounds in fruit and vegetable products

The effect of different postharvest treatments (film wrapping in conventional and biodegradable materials, foodtainer, surface coating) were evaluated in respect to their suitability to prevent quality loss of bioactive compounds in highly perishable fruits and vegetables. In lettuce, film packaging did not show any beneficial effects on pectic substances and pigments. However, in pepino dulce fruits the use of foodtainer maintained the β-carotene and chlorophyll contents, whereas Semperfresh coating led to a desired inhibition of pectin degradation. Starch coating and OPP-Coex-film packaging prevented the loss of soluble pectins in radish, whereas glucosinolates were only maintained by film packaging.

Interaction of drought stress and UV-B radiation - impact on biomass production and flavonoid metabolism in lettuce (Lactuca sativa L.)

The response of plants to stress such as UV-radiation or drought highly depends on the species, cultivar, plant organ, developmental stage, and furthermore, is influenced by ecophysiological interactions. Drought stress as well as UV irradiation are the most adverse factors for plant growth and productivity. In the present study, the interactive effect of UV-B and drought stress on biomass, primary and secondary metabolites, and mediated enzyme activity of phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) was investigated in lettuce (Lactuca sativa L.). It was found that biomass production decreased in response to both stressors, while dry matter, total phenolic contents and the flavonol quercetin were not significantly affected by UV-B and drought stress, neither solely nor in combination. In contrast, anthocyanins and luteolin accumulated only in response to drought stress. However, the precursor amino acid proline as well as the activity of PAL increased under conditions of increased UV-B and water deficit. Thus, the present results deduce that both stressors acted either synergistically or to some extent antagonistically in terms of inducing plant protective mechanisms.

Comparison of Different Greenhouse Systems and Their Impacts on Plant Responses of Tomatoes

A semi-closed greenhouse was used for sustainable tomato production and to investigate the effects of the prevailing climate conditions within this greenhouse on different plant parameters of tomatoes. Compared to conventionally cultivated tomato plants, the leaf area index, the number of trusses and the yield of marketable fruit of tomato plants exposed to the microclimatic conditions in the semi-closed greenhouse were significantly increased by 21, 11 and 31.9 %, respectively. Furthermore, the application of this new technology led to a significant increase in contents of lycopene (by 30 %), ß-carotene (by 40 %), phenolic compounds (25 %), titratable acids (by 8 %) and soluble solids (by 15 %) in tomatoes during the summer period. These results were attributed to higher photosynthetic activities, which predominantly occurred in the greenhouse with the semi-closed operation mode. Furthermore, the new technology can be seen as new horticultural approach to reduce the yield of blossom-end rot fruit by 75.2 %. This quality improvement was caused by higher levels of relative humidity, where this humidity states were also responsible for a reduction in the annual plant transpiration rate by 10 %.ZusammenfassungTomaten wurden in einem semi-geschlossenen Gewächshaus im Vergleich zu einem konventionellen Gewächshaus produziert und die Auswirkungen der vorherrschenden Klimabedingungen in den Gewächshäusern auf verschiedene Pflanzenparameter untersucht. Im Vergleich zu konventionell kultivierten Tomatenpflanzen waren der Blattflächenindex (um 21 %), die Anzahl der Rispen (um 11 %) und der Ertrag der vermarktungsfähigen Früchte (um 31.9 %) der Tomatenpflanzen, die den mikroklimatischen Bedingungen im semi-geschlossenen Gewächshaus ausgesetzt waren, signifikant erhöht. Darüber hinaus führte die Applikation dieser neuen Technologie in den Sommermonaten zu einer signifikanten Erhöhung der Gehalte von Lykopin (um 30 %), ß-Carotin (um 40 %), phenolischen Verbindungen (um 25 %), titrierbaren Säuren (um 8 %) und löslicher Trockensubstanz (um 15 %) in Tomaten. Diese Ergebnisse wurden auf höhere photosynthetische Aktivitäten zurückgeführt, die überwiegend im Gewächshaus mit semi-geschlossenem Betriebsmodus auftraten. Weiterhin kann die neue Technologie als gartenbaulicher Ansatz gesehen werden, um den Ertrag der mit Blütenendfäule befallenden Früchte um 75,2 % zu reduzieren. Diese Qualitätsverbesserung wurde durch das höhere Niveau der relativen Luftfeuchtigkeit hervorgerufen, wobei diese Feuchtezustände auch für die Reduzierung der jährlichen Transpirationsrate um 10 % verantwortlich war.

Blueberry Phenolic Compounds: Fruit Maturation, Ripening and Post-Harvest Effects

Abstract Currently, there is great momentum in research on phytochemicals, such as polyphenols, in fruit and vegetables. In this context, berry crops have drawn much attention. Blueberries score extraordinarily well in rankings among polyphenol-rich berry fruits. For blueberries, research has focused primarily on the phenolic compound profiles and antioxidant activities. However, little is reported on the development of phenolic compounds during the process of fruit maturation and ripening as well as during post-harvest. Maturation and ripening of blueberries are accompanied by characteristic physiological changes, which include color change, tissue softening, increasing maturity index. etc. During the different physiological stages shifting within the phenolic compound profile occurs as follows: anthocyanins increase during successive ripening, meanwhile flavonols and hydroxycinnamic acids decrease from unripe green to ripe blue berries. Depending on the harvest date, this trend continues during post-harvest. However, while earlier-harvested berries continue phenol accumulation, all phenolic compounds are degraded in stored full-ripe berries.

Survey of bioactive metabolites in selected cultivars and varieties of Lactuca sativa L. under water stress

Plants respond to water stress with a variety of physiological and biochemical changes, but their response vary between species, varieties and cultivars. The present study focused on changes of bio-functional phytochemicals (phenolic compounds, chlorophyll, carotenoids, dietary fiber) in commercial cultivars and old, traditional varieties of lettuce under different water regimes (water-deficit, well-watered and water-logged). Results revealed lettuce varieties and cultivars with a different response behavior to water stress. Biomass production under drought conditions was reduced significantly. Carotenoid and chlorophyll contents decreased in both water extremes, while total phenols were accumulated under limited water availability. Dietary fiber content was not influenced by different water regimes. Water stress reduces biomass production and led to a change of phytochemicals in lettuce, however, old and traditional varieties did not show a different water stress adaptation compared to commercial cultivars.

Impact of direct-electric-current on growth and bioactive compounds of African nightshade (Solanum scabrum Mill.) plants

Production of indigenous African leafy vegetables such as African nightshade ( Solanum scabrum Mill.), whose high nutritional and medicinal value is well documented is still limited due to insufficient preharvest techniques. Electric current is known to improve quality in food crops. Therefore, in the present study, the effects of direct-electric-current (DC) on growth and characteristic bioactive and health promoting compounds were evaluated in different morphological sections, i.e., leaves and stems of African nightshade cv. Olevolosi. Six weeks old plants were exposed to different DC applied with a voltage of 8 and 16 V, 10 h/day for 12 days. Non-treated plants served as control. Plant growth, primary and secondary plant compounds were evaluated. Applying DC increased leaf fresh (11.5-14.4%) and dry (12.1-24.2%) weight as well as marketable leaves (29.1-55.3%). Biosynthesis of chlorophylls and carotenoids was enhanced by increased DC. Furthermore, dietary fibre fractions such as hemicellulose was promoted (23.3-45.3%) by DC applications, while cellulose and lignin remained unaffected. Minerals accumulated with increasing DC. Alteration of cell membrane permeability due to DC may enhance physiological processes leading to the improved growth and acceleration of bioactive compounds in African nightshade leaves.

African Nightshade (Solanum scabrum Mill.): Impact of Cultivation and Plant Processing on Its Health Promoting Potential as Determined in a Human Liver Cell Model

Plant cultivation and processing may impact nutrient and phytochemical content of vegetables. The present study aimed at determining the influence of cultivation and processing on the health promoting capacity of African nightshade (Solanum scabrum Mill.) leaves, an indigenous vegetable, rich in nutrients and phytochemicals. Anti-genotoxicity against the human liver carcinogen aflatoxin B1 (AFB1) as determined by the comet assay and radical oxygen species (ROS) scavenging capacity of ethanolic and aqueous extracts were investigated in human derived liver (HepG2) cells. ROS scavenging activity was assessed using electron paramagnetic spin resonance and quantification of ARE/Nrf2 mediated gene expression. The cultivation was done under different environmental conditions. The processing included fermentation and cooking; postharvest ultraviolet irradiation (UV-C) treatment was also investigated. Overall, S. scabrum extracts showed strong health promoting potential, the highest potential was observed with the fermented extract, which showed a 60% reduction of AFB1 induced DNA damage and a 38% reduction in FeSO4 induced oxidative stress. The content of total polyphenols, carotenoids and chlorophylls was indeed affected by cultivation and processing. Based on the present in vitro findings consumption of S. scabrum leaves could be further encouraged, preferentially after cooking or fermentation of the plant.

Loss of African Indigenous Leafy Vegetables along the Supply Chain

ABSTRACT Due to high perishability, African indigenous leafy vegetables (AIVs) tend to suffer heavy postharvest loss. There is a lack of information regarding management of loss of these vegetables. This study sought to identify, and assess, types and causes of AIV loss in the supply chain. The study was done across the AIV producing location of Nakuru, Kisii, and Kakamega, in Kenya, involving 45 AIV farmers from each location. Parameters studied were socio-demographic profiles, harvesting, transportation, and marketing in relation to postharvest loss. The AIV production is primarily by women who were mainly smallholder farmers. Major problems identified were inappropriate harvesting and handling techniques, inadequate postharvest treatment and preservation methods, poor roads, lack of cold storage facilities, unhygienic market conditions, and lack of implementation by regulatory bodies on AIV handling, quality, and safety standards. Values were affected by location and supply chain stage. Yellowing, wilting, presence of foreign bodies, mechanical damage, and insect pest and disease damage were major postharvest problems along the supply chain. On average, farmers experienced loss between 10 and 50% with some experiencing >50%; this varied with location and supply stage. Short AIV shelf-life (1–2 d) is a major concern. Postharvest loss is unique for specific locations and supply chain stage, and attributed to AIV production, harvesting, handling, distribution, and marketing dynamics.