Drip loss is the liquid released from frozen strawberries during defrosting. High levels of drip loss make strawberries unsuitable for many applications that require whole fruit. This study is aimed at investigating the relationship between strawberry drip loss and the colour stability of nectars produced from these strawberries. Both solid (remainder after drip removal during defrosting) and liquid fractions (drip loss) were analysed by HPLC for anthocyanin, sugar and acid concentration, as well as total soluble solids and titratable acidity, to compare differences between the fractions. The results showed a strong correlation between strawberry drip loss and the colour stability of the resulting nectars. Strawberries with high levels of drip loss produced nectars with more stable colour. Determining the percentage of drip loss provides a quick and low-cost method for industrial nectar producers to select strawberries suitable for the production of colour-stable nectars. Furthermore, it was demonstrated for the first time that higher levels of solid content, achieved by separating the drip loss of defrosted strawberries before processing into puree, lead to nectars with higher initial consumer acceptance factor (AF) and a higher AF after 12 weeks. As a result, these nectars had a significantly better colour stability.

Strawberry nectar attributes, particularly colour stability, are highly influenced by cultivar, harvest time, and fruit ripeness. Industrial processors, however, often have little control over these parameters, as they must continuously process strawberries of varying origin and maturity throughout the harvest season. This study investigated incoming strawberry batches received by processing facilities in Austria, Poland, and Spain. Prior to processing, strawberries were analysed for length, width, weight, firmness, drip loss, and anthocyanin content. Resulting nectars had their colour quantified using an Acceptance Factor (AF) to monitor degradation over 12 weeks of storage. While considerable variability was observed between batches within each country, Polish strawberries were in general softer with higher anthocyanin content, producing nectars with superior colour stability. Differences were attributed to cultivation practices: in Poland, strawberries are grown specifically for processing and allowed to ripen fully. Conversely, strawberries processed in Spain and Austria are typically fresh-market rejects, harvested at earlier stages. Colour stability was positively correlated with anthocyanin content and drip loss, and negatively with firmness. These findings highlight the strong influence of raw material quality on nectar colour stability and underscore the variability of industrial raw material, and the limited control processors have over strawberry quality.

BACKGROUND:Identifying the best strawberries to produce colour stable nectars is a priority for the juice industry. Although riper strawberries produce nectars with better colour stability, variability between cultivars means that surface colour cannot be used as a single quality attribute to determine stability. Conductivity and bio-impedance measurements can be used to differentiate ripeness of strawberries. The commercially available PEF Control System (ELEA) can measure cell disruption by measuring conductivity at different frequencies. Updated software measured strawberry conductivity at 121 frequencies between 100 Hz and 1 MHz to determine whether conductivity at these frequencies could differentiate ripeness, and be compared with the colour acceptance and stability of nectars produced from these strawberries. RESULTS:A high-low ratio (HLR) was calculated by dividing the conductivity at frequency 1 MHz by conductivity at 1 kHz. HLR could be used to separate five strawberry ripeness stages, with decreasing HLR associated with increasing ripeness. HLR was then compared with the colour of nectars produced from these strawberries. Although there was a good correlation between HLR and an acceptable colour to consumers on initial production (r = -0.823, P < 0.001) and after 12 weeks of storage (-0.759, P < 0.001), cultivars differed greatly in both HLR and colour stability. Additionally, HLR had a strong correlation with firmness. CONCLUSION:The PEF Control System could be used to differentiate ripeness of strawberries by HLR, and therefore was associated with colour stability. However, no additional information on colour stability was gained from conductivity beyond what could already be deduced from differentiating ripeness based on surface colour. © 2024 The Author(s). Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Strawberry nectars have increased colour stability when produced from overripe, darker, and redder strawberries, with a high anthocyanin concentration. The post-harvest storage of strawberries has been shown to develop these properties. Nectars are frequently produced from strawberries rejected for fresh sale due to poor colour, which are insufficiently ripe to produce colour-stable nectars. This study investigated post-harvest anthocyanin development in strawberries to improve the colour and colour stability of nectars, which is the first time these developments were studied for beverage production. Strawberries at five ripeness stages were stored at 20 °C for 1 and 2 days prior to nectar production. The anthocyanin content of nectars was determined by a pH-differential method, and the colour stability was tracked for 12 weeks using a consumer Acceptance Factor, derived from CIELAB colour components. The anthocyanin content and colour stability were highly correlated, and both were dependent on ripening, with larger increases observed in under-ripe strawberries, and small to no improvement in overripe samples. Stored partially coloured strawberries produced nectars with equivalent colour stability to non-stored strawberries of normal ripeness. This allowed strawberries that were previously unsuitable for both fresh sale and nectar production to be used as a feedstock for nectar production, reducing food waste.

The colour stabilities of 169 different samples of strawberry nectars produced on a lab-scale were measured over 12 weeks. To find a prediction for consumer acceptance at set times, and therefore a shelf-life estimation, a Stability Prediction Value (SPV) was calculated using colour components L*, a* and b* on day of production. The SPV is the first easily measurable calculated value that can be used to predict the Acceptance Factor (AF) – a measure of how likely a strawberry nectar's colour is accepted by consumers – after 12 weeks. It also can predict how many days have elapsed for a nectar's colour to become unacceptable, giving a shelf-life prediction. The SPV values were also calculated for 21 samples produced industrially, and SPV was found to also predict AF after 12 and 36 weeks. SPV, for the first time, gives a quick and simple method to screen raw materials for nectar production, and so could be used by producers to make more colour stable nectars, and breeders to guide development of cultivars. Additionally the potential of the colour component L*, and the concentration of anthocyanins to predict colour stability was evaluated.

Secondary metabolites play a major role as quality factors in horticultural products by significantly contributing to plant health, optical attributes, sensory attributes and health beneficial effects for the consumer. Dihydrochalcones, a rare class of secondary metabolites, which is, however present in particularly high amounts in apple (Malus × domestica. In apple, phloridzin (phloretin 2’-O-glucoside) is prevalent representing more than 90% of the soluble phenolic compounds, but small amounts of 3-hydroxyphloretin and 3-hydroxyphloridzin are also constitutively present. For the systematic investigation, sufficiently comprehensive knowledge of the underlying pathway is yet lacking. Two types of enzymes could catalyze the reaction, polyphenol oxidases (PPOs) and/or cytochrome P450 dependent monooxygenases. To test a possible involvement of the F3‘H of apple in the formation of constitutive 3-hydroxydihydrochalcones, cDNA clones of the two types of F3‘Hs present in the apple was isolated and heterologously expressed in yeast. Despite showing high F3‘H enzyme activity with various flavonoid substrates, hydroxylation of dihydrochalcones was not observed at standard conditions, indicating that F3‘H is not part of the dihydrochalcone pathway.

Apples are an important source of polyphenolic and most popular fruits worldwide. Due to their phenolic content, consuming apple in a diet tend to low risk and prevention some chronic diseases. The main enzyme is responsible for quality loss, which are affecting by phenolic degradation, are polyphenol oxidase (PPO) and peroxidase (POX). PPO and POX are correlated to the rate of browning with substrate content and enzyme activity. The objective of this research was to investigate the polyphenol oxidase (PPO) and peroxidase (POX) activity in different apple cultivars. Apples Gravin Goldach, Bay 4152, Sonnen Glanz, Gala Mitslugla apples were obtained from an orchad of Hohere Bundeslehranstalt und das Bundesamt fur Wein und Obstbau in Klosterneuburg, Vienna, Austria, then Apple from each cultivar was cut and separated in two parts, peel with seed (red flesh) and peel without seed (white flesh), then PPO and POX were determined. The results showed that tThe highest PPO activity is presented by red flesh of Bay 4152 cultivar, whereas the lowest detected in red flesh Gala Mitslugla. PPO activity on apple flesh of red Bay 4152, white Sonnen Glanz, red gravin Goldach and red Gala Mitslugla were 5.01E+04, 4.79+04, 3.17+04 and 1.91E+04 ΔE/S/Kg protein, respectively. PPO activity on apple flesh was not affected by white or red colour. The highest POX activity was found in red flesh of Sonnen Glanz cultivar, whereas the lowest value was presented in white flesh of Gravin Goldach cultivar varied from 1.07E+05 to 7.68E+04 ΔE/S/Kg protein. In all different flesh of apple cultivars showed that the high or low POX activity was not resulted by the red or white flesh coloured. POX is much higher than PPO activity of all cultivars. Result will provide to maintain the phenolic related quality loss and to improve new processing method.

The apple tree (Malus sp.) accumulates high amounts of the dihydrochalconephloretin and its derivatives. Whereas p-coumaroyl-CoA is the precursor for the naringeninchalcone and further flavonoid formation, p-dihydrocoumaroyl-CoA is required for the biosynthesis of dihydrochalcones. The formation of p-dihydrocoumaroyl-CoA from p-coumaroyl-CoA in apple has been characterized at the enzymatic level whereas the corresponding gene is not unequivocally found. Potential candidate genes including an enoyl-ACP reductase, acyl-CoA dehydrogenase and three different double bond reductases were cloned and heterologously expressed. Activity of the heterologous proteins was tested but none of the genes could be definitely identified as responsible for their involvement in dihydrochalcone formation. In parallel, during a challenging protein purification procedure we isolated for the first time a candidate enzyme from apple leaves, which exhibits strong double bond reductase activity with p-coumaroyl-CoA to form p-dihydrocoumaroyl-CoA. Additionally, aflavonoid 3'-hydroxylase cDNA clone was isolated from young leaves of apple. Heterologous expression in yeast provided functionally active enzyme, but hydroxylation of phloretin was not observed.

Dihydroflavonol 4-reductase (EC 1.1.1.219, DFR) catalyses the reduction of (2R,3R)-(+)-dihydroflavonols into (2R,3S,4S)-cis-3,4-leucoanthocyanidins. Depending on the plant species, DFR can be unspecific with regard to the B-ring hydroxylation pattern or selective, as in Petunia hybrida in which the DFR does not convert DHK, or in Fragaria species where a pair of DFRs are present that shows contrasting substrate specificity with regard to DHK. DFR substrate specificity has been largely investigated in many plant species. The amino acids determining DFR substrate specificity are not yet completely understood, but previous studies have identified a region of 26 amino acids putatively relevant and in particular, an aspartic acid in position 134, that seems to be responsible for the non-acceptance of DHK as substrates. The recently identified pair of Fragaria DFRs with contrasting substrate specificity was used to study putative regions responsible for the divergent substrate specificity. We demonstrate that neither the versatile C-terminus nor the DFR length nor two of three putative regions are of any relevance. In addition, we analyse previously published DFRs of Malus × domestica, Pyrus communis and Ginkgo biloba and the correlation between their substrate specificity and amino acid sequences. Technical constraints of DFR enzyme assays and potential putative substrate specificity bias is discussed.

Beetroot was grown in an open soilless cultivation system with nutrition supplied by organic and inorganic sources. This low emission system was tested for microgardening high quality red beets with high water use efficiency and less pollutant emission in the environs. For this purpose, a pot experiment was planned according to completely randomized design. For inorganically grown red beets, peat moss was combined with 150, 200 and 250 ppm NH4NO3, whereas for organic red beets, peat moss was amended with compost having nitrogen equivalent to the mentioned NH4NO3 concentrations. Rosette and roots were analysed for fresh and dry biomass. Nitrate content, total soluble solids, titratable acidity, ripening index, ascorbic acid, betacyanins, flavonols and antioxidant capacity were assessed as beetroot quality attributes. Combination of peat moss with NH4NO3 showed comparatively lower fresh plant biomass, fresh and dry biomasses of rosette and root, and root to rosette ratio. However, enhanced antioxidant activity and bioaccumulation of ascorbic acid, total soluble solids, betacyanins, flavonols and reduced titratable acids, resulting in higher ripening index and good quality were observed in peat moss combined NH4NO3 treated beetroots. Overall, combination of peat moss with NH4NO3 led to higher nutritional and antioxidant quality of red beet plants.

BACKGROUND Different yellow pigments can be responsible for the yellow colouration of flowers. This includes the wide-spread carotenoids, but also betalains, quinones, yellow flavonoids and anthochlore pigments (chalcones and aurones). Many popular ornamental plants do not produce yellow varieties or only ivory and pale yellow varieties despite of intensive conventional breeding efforts. World-wide, there are many attempts to use molecular breeding approaches for the creation of yellow varieties of such ornamental plants. Currently, two approaches are performed; one using aureusidine synthase (AUS) from snapdragon, the others chalcone reductase (CHR) present e.g. in soybean for the accumulation of stable 6’-deoxychalcones. However, there are no reports available on the creation of prototypes showing a satisfying yellow flower colour.

In this study the influence of prohexadione-Calcium (Pro-Ca) treatment on peel colour development and polyphenol metabolism of apples during advanced maturity was investigated. Apple trees were treated 3 weeks before technological maturity. Changes in the content of hydroxycinnamic acids, dihydrochalcones, flavonols, flavanols and anthocyanins were monitored six times during the advanced maturation until technological maturity of the fruits. To evaluate the effect of Pro-Ca on the coloration of apples, the changes in the chromaticy values a*, h degrees and the lightness coefficient L* were monitored. The parameters showed a significant difference in the intensity of red coloration between the treated and untreated apples. The application of Pro-Ca led to a decrease in the enzyme activities of the 2-oxo-glutarate dependent dioxygenases flavanone-3-hydroxylase (FHT) and flavonol synthase (FLS), and the flavonoid pathway was negatively affected in general. Concomitantly, the concentrations of flavonols, anthocyanins and dihydrochalcones in the peel of treated apples decreased, whereas the contents of total phenolic compounds and hydroxycinnamic acids increased. Flavanol contents, however, remained unchanged. In apple pulp, slightly higher concentrations of all phenolic compounds were measured in the treated apples compared to the control on the majority of sampling dates. The results indicate that Pro-Ca modulates the polyphenol spectrum resulting in a pronounced decrease of red coloration during advanced maturation of apples. Pro-Ca therefore to some extent exhibits the potential to avoid undesired red coloration of apple fruit.

The dihydrochalcone phloridzin (phloretin 2′-O-glucoside) is the most abundant phenolic compound in apple trees (Malus × domestica) and was also discussed to have an influence on the pathogen defence by shifting the dihydrochalcone profile from the glucosides to the more active aglycones. The final step in the biosynthesis of phloridzin is the glycosylation of phloretin at position 2′. Three cDNA clones from apple encoding glycosyltransferases are available which are able to catalyze the reaction in vitro. We investigated the possible role of glycosyltransferase UGT71A15 in phloridzin biosynthesis. The recombinant enzyme showed broad substrate acceptance but highest activities were observed with flavonols. Specific activities and the kinetic data indicated that phloretin is not the preferred native substrate of the UGT71A15. However, an increase of the molar ratio phloridzin:phloretin was found in transgenic lines, indicating a physiological relevance of UGT71A15 in planta, although a decrease of the total amount of dihydrochalcones in the majority of the samples was found. Unexpectedly, the increase of the phloridzin:phloretin ratio was not reflected by an increase of the total glucosyltransferase activities. In contrast, the majority of transgenic plants showed a reduced glucosylating activity with both phloretin and quercetin as a substrate, but the observed activity changes in a given sample were not similar for the two substrates. An increased susceptibility of M. robusta against the fire blight causing bacterium E. amylovora as a result of UGT71A15 overexpression could not be observed. Overexpression of UGT71A15 in transgenic apple trees also did not lead to morphological changes.

Transgenic apple plants (Malus x domestica cv. 'Holsteiner Cox') overexpressing the Leaf Colour (Lc) gene from maize (Zea mays) exhibit strongly increased production of anthocyanins and flavan-3-ols (catechins, proanthocyanidins). Greenhouse plants investigated in this study exhibit altered phenotypes with regard to growth habit and resistance traits. Lc-transgenic plants show reduced size, transversal gravitropism of lateral shoots, reduced trichome development, and frequently reduced shoot diameter and abnormal leaf development with fused leaves. Such phenotypes seem to be in accordance with a direct or an indirect effect on polar-auxin-transport in the transgenic plants. Furthermore, leaves often develop necrotic lesions resembling hypersensitive response lesions. In tests, higher resistance against fire blight (caused by the bacterium Erwinia amylovora) and against scab (caused by the fungus Venturia inaequalis) is observed. These phenotypes are discussed with respect to the underlying altered physiology of the Lc-transgenic plants. The results are expected to be considered in apple breeding strategies.

The study was performed on apple trees, ‘Golden Delicious' cv., which is a scab-susceptible cultivar. The phenolic content of apple fruit was determined in different parts of the peel. The phenolic compounds were analysed in the scab spot, in the tissue around the spot and in the healthy tissue. We determined the concentration of various phenolic compounds and related enzyme activities. Infection with the Venturia inaequalis fungus enhanced the metabolism of phenolic compounds at the scab spot, around the spot and in healthy peel. Compared with the healthy tissue and the tissue around the spot, the scab spot showed higher enzyme activity for all tested enzymes, except for dihydrochalcone 2′- O -glucosyltransferase, which had lower activity in the scab spot. In comparison to the healthy peel, the scab spot showed up to 3.4 times more hydroxycinnamic acids, up to 1.1 times more dihydrochalcones and up to 1.4 times more flavan-3-ols. In contrast, the healthy peel showed up to 1.6 times more flavonols than the scab spot.