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Tomato (Solanum lycopersicum L.) fruit contain several health beneficial antioxidants [1]. Their contents can be greatly influenced by abiotic factors such as light, temperature, or the nutritional status [2]. The macronutrient potassium (K) is essential for several physiological functions in plants, e. g. translocation of assimilates, activation of enzymes, maintenance of turgescence, and stomata regulation. The aim of the study was to investigate the impact of increasing K fertilization on the antioxidants ascorbic acid, phenolic compounds, carotenoids, and tocopherols in tomatoes. Three cocktail tomato cultivars (Primavera, Resi, and Yellow Submarine) raised in an outdoor pot experiment were treated with five rising K doses in the first study year 2014. In 2015, Primavera and Resi were selected for a subsequent experiment using the lowest and highest K doses. In this experiment, the lipophilic antioxidants were additionally measured in three different tomato ripening stages. Increasing levels of K fertilization distinctly affected the contents of antioxidants in cocktail tomatoes (Table 1). However, most of the effects were not consistent across all three cultivars and the two study years. In 2014, K fertilization level positively correlated (p≤0.05 or 0.01) with ascorbic acid and γ-tocopherol in Resi and with p-coumaric acid in Primavera, while significant negative correlations were observed for narigenin and ß-carotene in Primavera and for β-tocopherol and δ-tocopherol in Yellow Submarine. In contrast, significant positive correlations between K fertilization level and ascorbic acid, p-coumaric acid and caffeic acid were demonstrated for both, Primavera and Resi, in 2015. As opposed to 2014, the tocopherols in Resi and Primavera negatively correlated with increasing K fertilization. The only antioxidant that consistently showed positive correlations with increasing K doses across cultivars and study years was p-coumaric acid. In summary, the content of plant antioxidants in cocktail tomatoes cultivated outdoors can be positively or negatively affected by K fertilization. However, other abiotic factors, such as variation in light and temperature may impact or even inverse those effects [3,4]. [ABSTRACT FROM AUTHOR]

Tomato is the most popular vegetable in Germany (BLE, 2015) and one of the most consumed horticultural crops in the world [1]. Tomatoes have a high nutritional value, as they are rich in vitamins and antioxidants [2]. In recent times, consumers have complained about the poor flavor of tomatoes [3,4]. Conventional breeding programs generally focus on yield, firmness, and long shelf life [3,4], which may have caused a decrease in flavor acceptance. Besides, postharvest handling affects the flavor of the tomato fruit [5]. The goal of the PETRAq+n project (participatory development of quality tomatoes for sustainable regional production) is to create a scientific basis to breed tomato cultivars with improved quality and optimal adaption for sustainable regional and urban production. The flavor of a tomato is a complex interaction of taste and aroma [6]. Major contributors are sugars and acids [7]. Other important non-volatile contributors to the flavor include fatty acids and pigments [8]. Over 400 volatiles have been identified in tomatoes so far[9], but only around 16 - 20 contribute to the characteristic tomato flavor [9,10]. It has been shown that refrigeration changes the aroma volatile profile and has a negative effect on the flavor [11,12]. However, the time from harvest to retail is shorter than in earlier decades and it is important to evaluate the whole postharvest handling. The influence of the entire postharvest handling chain has not been considered yet. The studied crossbred offspring are combinations of parental cultivars with high yield and good quality parameters. They were grown in a low-input production system, and the entire transportation route of tomatoes from harvest to retail to the consumer was evaluated. Two methods of household storage were considered, storing at room temperature (20°C) and storing in a refrigerator (7°C). Important non-volatile compounds of tomato fruits were analyzed, comparing fresh fruits with fruits stored in two different temperature regimes, while the fruits were handled in the same manner beforehand and were harvested ripe. Earlier studies raised the issue that many laboratory studies are not comparative to commercial practices and thus it should be assumed that the handling steps at different levels are not isolated [13]. The aroma compounds of the fruits were collected using headspace solid phase microextraction (HSSPME), identified by GC-MS and semi-quantified by GC-FID. We observed an increase in the content of total soluble solids (TSS) after postharvest handling in both storage regimes and only a slight decrease in titratable acidity (TA), while the storage temperature did not show any effect. [ABSTRACT FROM AUTHOR]

Aroma of fruit is a key indicator to depict the quality of fruit flavor and is likely to play an important role in determining the perception and acceptability of products by consumers [1,2]. Flavor has obviously been targeted as a secondary breeding goal in recent decades [3]. Studies reveal that tomatoes grown under organic conditions positively increase the consumer preference [4]. Therefore, it is necessary for plant breeders who are developing cultivars for organic production to select also for better flavor characteristics. Sixty indeterminate cultivars which differ mainly in terms of fruit weight, year of cultivar release and fruit color were grown in an outdoor organic low-input system in a temperate climate. The diversity of volatile organic compounds (VOCs), taste-related primary metabolites, and sensory properties of ripe tomatoes consisting of 27 cocktail and 33 salad tomato cultivars released between 1880 and 2015 from conventional, organic or unknown breeding programs, were investigated at two different harvest dates in 2015. The volatile compounds of tomato fruits were semi-quantified by GC-FID and tentatively identified by GC-MS. Isolation of volatiles were performed through automated headspace solid-phase microextraction (HS-SPME). A non-targeted data analysis (pattern recognition) was used. The evaluation of the cultivars from the two harvest dates exhibited a wide range of variation for all studied traits, with the exception of a few VOCs. Cultivar × harvest date interaction had no significant effect on TA (titratable acidity), TSS (total soluble solid), or overall acceptability but influenced most of the studied VOCs. Further examination was focused on total of 25 VOCs: 7 aldehydes, 5 ketones, 7 alcohols, 4 aliphatic acids, 1 ester and 1 sulfur-containing compound. The main compounds with the highest value in relative concentration in the headspace of tomato fruits include hexanal, 6-me-5-heptene-2-one, (E)-2-hexenal, octanal, 1- hexanol, etc., of which aldehydes are the most abundant volatile group. Variation in all studied traits like fruit type, harvest time, or fruit color was observed, and the discriminative variables characterizing the fruit types were revealed. Principal component analysis differentiated cocktail and salad types with a higher contribution of taste related-primary metabolites (TSS and TA), sensory attributes (sweetness, tomato typical-aroma, and sourness) and phenyl ethyl alcohol, the latter is a discriminative key compound to distinguish cocktail from the salad type. The observed correlations among the metabolites give cues for their biosynthesis pathway. The presence of VOCs such as (Z)-3-hexen-1-ol, phenyl ethyl alcohol, and benzyl alcohol had effect on the perception of ‘sweetness' and ‘tomato typical-aroma'. Therefore, the present findings should provide a preliminary knowledge for cultivar selection in breeding programs that perform better in flavor and are suitable for organic low-input production systems. [ABSTRACT FROM AUTHOR]

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There is evidence that potassium (K) fertilization enhances the yield of medium and large-sized tomato cultivars. Many authors observed positive effects of K fertilization on fruit color, texture, total soluble solids (TSS) and titratable acids (TA) [3, 6]. The market for small-sized cocktail tomatoes is currently growing due to their preferable taste [5] which is positively related to increasing levels of TSS and TA [1, 2, 4]. We hypothesize, that K improves yield and quality of cocktail tomatoes. In order to test our assumption, we carried out pot experiments in two consecutive years. In a pot (6 L) experiment, three cocktail tomato cultivars (Primavera, Resi and Yellow Submarine) were fertilized with five K levels (3.1, 6.3, 9.4, 12.5 and 18.7 g K/pot applied in total over 19 weeks) to find out ideal dosages for well and deficient fertilized plants. Interestingly, the K effect on yield and most quality parameters was highly cultivar specific: while Primavera and Yellow Submarine reached a yield increase of more than 100% from the lowest to the highest K dose, no response of Resi was observed. In contrast to Primavera and Yellow Submarine, Resi showed only weak K fertilization effects on fruit quality aspects. Therefore, in a second experiment we grew the cultivars Primavera and Resi with two K doses (deficient and well-fertilized). In a third treatment, we interrupted K fertilization in order to induce a response in the cv. Resi to a sudden shortage of K. In contrast to Primavera, Resi showed no yield response to K fertilization like in the first experiment. The low yielding cv. Resi seemed to be more K efficient compared to Primavera. We conclude that the effect of K on yield and quality of cocktail tomatoes depends on the cultivar. [ABSTRACT FROM AUTHOR]