Blueberry Phenolic Compounds

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Blueberry Phenolic Compounds: Fruit Maturation, Ripening and Post-Harvest Effects Ines Eichholz*, Susanne Huyskens-Keil*, Sascha Rohn† *Humboldt-Universität zu Berlin, Division Urban Plant Ecophysiology, Section Quality Dynamics/Postharvest Physiology, Berlin, Germany, †University of Hamburg, Hamburg School of Food Science, Institute of Food Chemistry, Hamburg, Germany

CHAPTER POINTS • B  lueberries are a good source of phytochemicals such as phenolic compounds. • Processes of maturation and ripening influence the phenolic profile. • Fruit maturation and ripening are characterized by a decrease in flavonol and hydroxycinnamic acid contents at early maturation and throughout ripening, while an accumulation of anthocyanins occurs. • Due to the fact that phenolic compounds are mainly present in the berry skin and outer layer of the pulp, the increase of anthocyanin contents during successive harvests is influenced by the diminishing berry weight. • In stored full-ripe berry fruits, all phenolic compounds are degraded. • Berries harvested before the full-ripe stage continue maturation in post-harvest that include an increase of anthocyanins and a decrease of minor complex phenolic compounds (hydroxycinnamic acids, flavonols).

INTRODUCTION In recent years, the research interest has been increasingly directed towards problems of the physiological functionality of food constituents arising from plant secondary metabolism, in particular polyphenols. Phenolic compounds include a wide range of different chemical

Processing and Impact on Active Components in Food http://dx.doi.org/10.1016/B978-0-12-404699-3.00021-4

classes with a high diversity in chemical structures and functions. They play important roles in the interaction of plants with their environment, e.g., protection from UV radiation, as feeding deterrents, pollination attractants, protective compounds against pathogens or various abiotic stresses, antioxidants or signaling molecules (Winkel-Shirley, 2001; Treutter, 2010). Among berry fruits, blueberries are considered to be a rich source of phenolic compounds and are praised for their high antioxidant activity scores (Prior et al., 1998). From the existing research results, it has to be considered that they comprise not only the main blueberries cultivated, i.e., the Northern and Southern highbush blueberries, but also the lowbush (or wild blueberries) and rabbiteye blueberries. Between these blueberry types as well as between different varieties and within other Vaccinium species, there are significant differences in the phenolic content and antioxidant activity (Prior et al., 1998; Taruscio et al., 2004). Due to the increasing health awareness of the consumers and the apparent relationship of phytochemicals in plant foods with the prevention of degenerative diseases (Watzl and Leitzmann 2005), the content of phenolic compounds in blueberries has been studied. As a result, phenolic compound profile and quantitative composition of blueberries is well documented (e.g., Kalt et al., 1999; Howell et al., 2001; Moyer et al., 2002). Even though literature on blueberry issues is vast, expanding from different culture practices to potential health effects of blueberry extracts in animal studies, little is reported on the development of phenolic compounds during the process of fruit maturation and ripening preand post-harvest. It is known that the content of polyphenols in berries is not only affected by genetic differences,

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pre-harvest environmental conditions, but also by physiological processes during maturation, ripening, and postharvest (Zadernowski et al., 2005). During fruit maturation and ripening, as well as after harvest, an array of physiological changes takes place in berry fruits. Therefore, the understanding of these processes and the identification of suitable maturity stages are important pre-requisites for crop exploitation and for the development of appropriate physiological adapted post-harvest technologies.

HOW COMPOSITION IS ALTERED Fruit Maturation and Ripening of Blueberries Fruit development is a dynamic process commencing with pollination and fertilization, followed by intensive cell division and expansion, with concurrent seed development as well as maturation (Vvedenskaya and Vorsa 2004). The growth and development of blueberry fruit during a plant’s annual cycle is presented in Figure 21.1. Many complex biochemical changes occur within the single fruit during this time, including those that result in softening, heightened pigmentation, sweetening, and cell enlargement (Gough, 1993). The development and ripening of blueberry fruits can last from 8 to 16 weeks, depending on cultivar and climatic conditions (Ebert, 2005) and was classified in three stages by Shoemaker (1948): (I) an accelerated growth rate for about 29 days after pollination; (II) a retarded

pericarp growth of 5–56 days (the embryos and seeds develop and mature); and (III) a second period of rapid development that continues to fruit maturity (rapid increase in volume caused by cell enlargement). Maturity may be defined in terms of either physiological maturity or horticultural maturity of plant food crops and is based on the measurement of various qualitative and quantitative parameters (Thompson and Thompson 2003). Physiological maturity of a crop was described by Watada et al. (1984) as “the stage of development when a plant or plant part will continue ontogeny even if detached,” whereas horticultural commercial maturity is defined as “the stage of development when a plant or plant part possesses the prerequisites for the utilization by consumers for a particular purpose.” Maturation of blueberries occurs during the period between stage III of berry growth and ripening (Gough, 1993). Blueberries, growing on the same bush, do not all ripen at the same time and therefore, berries were harvested weekly over a period of three to four weeks. During maturation, blueberry fruits suffer from physiological changes that include softening of the flesh, a decrease in chlorophyll content with a subsequent increase in anthocyanin concentration (i.e., the berry turns from green to blue), and an increase in size (Gough, 1993). Moreover, blueberries are considered climacteric fruits showing two rises in respiration rate during their development, initially with the beginning of coloration in transition from the green–pink to the blue–pink stage, and secondly during the ripe stage towards over-ripening (Ebert, 2005).

FIGURE 21.1  Growth and development of blueberry fruit during a plant’s annual cycle. The figure shows the growth and development of blueberry fruit at three specific maturity stages: IG, Immature Green; BP, Blue Pink; MB, Mature. Adapted with permission from Ebert (2005).

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175 FIGURE 21.2  Physiological and chemical changes during ripening of blueberries. Quality attributes and chemical composition of blueberry cv. Bluecrop during maturation and ripening. Gray lines indicate minor values, dark lines indicate major values. Source: Eichholz et al. (2008).

All biochemical and physiological changes that take place during fruit ripening are driven by a cascade of molecular events starting with the activation of signalling pathways that stimulate the coordinated expression of fruit ripening-related genes (McManus, 2012). These correspond to visually verifiable changes such as fruit growth and color changes, textural changes such as fruit softening resulting from changes in structural carbohydrate pattern, as well as sensory changes including aroma composition and changes in sweetness and acidity (see Figure 21.2).

Phenolic Composition During Blueberry Fruit Maturation and Ripening Color changes during fruit ripening implicate both synthesis and degradation of the plant pigments including chlorophyll, carotenoids, as well as flavonoids. Flavonoids and non-flavonoids are the two major classes of phenolic compounds common to small fruits (Howell et al., 2001). The predominant flavonoids found in berries and red grapes are anthocyanins and flavonols, which are almost exclusively present in their glycosylated forms. Wu and Prior (2005) identified and characterized anthocyanins from 25 different fruits. Anthocyanins were found in 14 fruits ranging from two different anthocyanin structures in peaches (Prunus persica) and nectarines (Prunus persica var. nucipersica) to 31 different anthocyanin structures in grapes (Vitis vinifera). Blueberry cultivars were found to contain 20–27 different anthocyanins. Phenol profiling of blueberries showed that flavonoids (40%) and phenolic acids (59%) are the dominant phenolic compound fractions

(Törrönen et al., 1997). Major flavonoids comprise of several anthocyanins (Moyer et al., 2002); however, they also include flavonols such as quercetin (­ Taruscio et al., 2004). The most common flavonols in fruits and vegetables are quercetin and kaempferol with their corresponding glycosides. Bilyk and Sapers (1986) quantified the quercetin contents of the ripe highbush blueberries ‘Earlible’, ‘Weymouth,’ ‘Coville,’ and ‘Bluetta’ (24–29  mg/kg fresh weight), but neither kaempferol nor myricetin were found. Not to be underestimated is the presence of phenolic acids, which were also found in diverse Vaccinium species (Taruscio et al., 2004), including the phenolic acids caffeic, chlorogenic, p-coumaric, ferulic, as well as p-hydroxybenzoic acid. Among these phenolic compounds, chlorogenic acid is the colorless phenolic compound to be found dominantly in both highbush and lowbush blueberries in concentrations ranging between 5 and 10 mg/kg fresh fruit (Gao and Mazza 1994). The influence of cultivar and maturity on the content of polyphenols and antioxidant activity has been reported for berry fruits such as blackberry (Rubus fructicosus) (Siriwoharn et al., 2004) and strawberry (Fragaria × ananassa) (Kosar et al., 2004). Maturity stage is also an important factor affecting the content of phenolic compounds in blueberries. Mainland and Tucker (2000) reported that the anthocyanin and total phenolic content as well as the antioxidant activity (measured by Oxygen Radical Absorbance Capacity, ORAC) of five blueberry cultivars increased with progressing maturity. Here, the samples were picked from berries almost ripe with a blue color and red around the stem scar, in fully ripe stage with a blue color ready for marketing, and overripe beginning

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FIGURE 21.3  Content of phenolic subclasses of different blueberry cultivars during fruit development at selected maturity stages. The figure shows the mean ± SD of phenolic subclasses of blueberries. The corresponding phenolic compound is equivalent as follows: Anthocyanins = cyanidin-3-glucoside; Hydroxycinnamic acids = chlorogenic acid; Flavonols = rutin; A) Reka, B) Bluecrop, C) Puru, and D) Berkeley. RS1 = Ripening stage 1 = unripe green; RS2 = Ripening stage 2 = unripe purple; RS 3/H1 = Ripening stage 3/Harvest 1 = 50–70% ripe blue; HS2 = Harvest stage 2 = 20–40% ripe blue; HS3 = Harvest stage 3 ≤ 15% ripe blue. With permission from Rodarte-Castrejon et al. (2008).

already to soften. However, Rodarte-­Castrejon et al. (2008) determined different phenolic compound classes and the antioxidant activity [measured by Electronic Paramagnetic Resonance spectroscopy (EPR) and Trolox Equivalent Antioxidant Capacity assay (TEAC) in four blueberry cultivars at five different stages (unripe green, unripe purple, 1.harvest, 2.harvest, and ­3.harvest)]. They reported an increase in anthocyanins during maturation and ripening of berries (Figure 21.3). Here, their antioxidant activity was higher in early maturation and during initial pigmentation than at ripeness. Authors concluded that the latter finding was attributed to the higher concentrations of hydroxycinnamic acids and flavonols found prior to ripening; whereas lower antioxidant activity of mature berries might suggest that anthocyanins have less antioxidant capacities than the other phenolic compound classes. Anthocyanins are not expected to be present in unripe green berries. This was confirmed by Kalt et al. (2003). The synthesis of anthocyanins in fruit tissues, as studied in bilberry (Vaccinium myrtillus) (Jaakola et al., 2002), correlates with the expression of the flavonoid pathway

genes during berry fruit ripening. At the time of harvest, anthocyanins are the second-most prevalent phenolic compounds in blueberry fruits and concentrations are higher in extracts of successive picking dates (RodarteCastrejon et al., 2008). The highest concentration of red pigments in blueberries occurs in the skin and outer layer of the pulp. Moreover, Gao and Mazza (1994) noted the relationship of anthocyanin accumulation with berry size in different blueberry cultivars. The small berries of lowbush blueberry cultivars and hybrids had higher anthocyanin contents in comparison to the larger berries of highbush blueberry cv. Bluecrop. Moyer et al. (2002) found that fruit size highly correlated (r = 0.84) with anthocyanins within V. corymbosum, but did not correlate with anthocyanins across eight other Vaccinium species, or within 27 blackberry hybrids. There was also no relationship between fruit weight and anthocyanin content among 135 lowbush clones and the 80 highbush clones studied by Howell et al. (2001). However, Rodarte-Castrejon et al. (2008) detected anthocyanins only at the ripe stages correlating significantly with fruit weight (r = −0.521,

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p ≥ 0.01). Here, fruit size increased progressively until full ripening and, thereafter, decreased with each successive picking date. Therefore, authors explained the correlation by an anthocyanin increase with successive harvests and, conversely, a fruit weight decrease. The decrease of flavonols during the ripening process occurs not only in blueberries as presented by RodarteCastrejon et al. (2008), but also in other fruits, e.g., strawberries and cranberries (Vaccinium macrocarpon Ait.) (Stöhr and Herrmann, 1975; Celik et al., 2008). Already in 1976, it had been observed that the elevated synthesis of anthocyanins during maturation and ripening was not associated with an accumulation of flavonol glycosides (Starke and Herrmann, 1976). When comparing the total content of flavonols with the total anthocyanins of blackberries, no correlation was found between the accumulation of flavonols and anthocyanins (Bilyk and Sapers, 1986). There is evidence that flavonoid biosynthesis is strongly regulated depending on the developmental stage of the fruit. The enzyme activities are regulated in response to different developmental and environmental cues (Jaakola et al., 2002). In bilberry, a coordinated expression of flavonoid biosynthetic genes in relation to the accumulation of anthocyanins, proanthocyanidins, and flavonols was demonstrated in developing fruits. In strawberry, it was detected that flavonoid biosynthesis has two distinct key flavonoid enzymes activity peaks during fruit ripening at an early and late developmental stage (Halbwirth et al., 2006). If this applies to other berry fruits such as blueberries, Rodarte-Castrejon et al. (2008) hypothesized from their results that during maturation and ripening the first flavonoid biosynthesis peak corresponds to flavonols and hydroxycinnamic acids, while the second peak relates to anthocyanin accumulation. Kalt et al. (2003) also reported an increase of anthocyanin content and a decrease of phenols during fruit ripening. They suggested that during ripening of highbush blueberry there is a shift in the pool of total phenols towards anthocyanin synthesis, and an overall decline in the content of further phenolic compounds.

Post-Harvest Effects on Phenolic Composition of Blueberry at Different Ripening Stages Post-harvest handling comprises all steps from the producer to the consumer including harvesting, handling, post-harvest treatment, packaging, cooling, storing, shipping, wholesaling, and retailing. However, losses in post-harvest from harvest until the product has reached the consumer are comparatively high, specifically for highly perishable fruits that are very susceptible to decay and deterioration (Huyskens-Keil and Schreiner, 2004). Recently, strong emphasis has been placed on the development and improvement of new post-harvest treatments in berry fruits ranging from the improvement

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of new film packaging to the application of post-harvest elicitors accelerating the synthesis of stress compounds in the products, e.g., heat-shock proteins, phenolic compounds, leading to an extended shelf-life and improved product quality (Huyskens-Keil and Schreiner, 2004; Schreiner et al., 2012). Film packaging is widely used for berry fruits in order to prevent mechanical damage and maintain fruit quality. Studies on environmentally friendly film packaging material for berry fruits are still ongoing (e.g., Netzker et al., 2005). For the blueberry cv. Bluecrop, it was found that biodegradable film packaging (based on corn starch) induced an increase in total phenols and antioxidant activity in fruits stored at 2°C for 3 weeks, indicating maturation processes that, however, did not differ to fruits packed in conventional polypropylene packaging material. In conclusion, a substitution of biodegradable film packaging for PVC or PP-packaging material still needs to be investigated more in detail. Temperature is known to affect anthocyanin content in berry fruits, e.g., in blueberries (Kalt et al., 1999) and strawberries (Miszczak et al., 1995) during storage. Storing different types of blueberries at temperatures of 0–2°C induced phenolic synthesis and increased the fruit total antioxidant capacity (Kalt et al., 1999; Netzker et al., 2005). Blueberries harvested before the full-ripe stage continued maturation during storage being associated with an increase of anthocyanins and a decrease of minor complex phenolic compounds (hydroxycinnamic acids, flavonols) (unpublished data). In contrast, for stored full-ripe blueberry fruits it was found that anthocyanins and flavonols decreased while phenolic acids (hydroxycinnamic acids and hydroxybenzoic acids) remained almost constant during storage (Figure 21.4, unpublished data). Controlled atmosphere (CA) storage (2.5  kPa O2 + 15 kPa CO2) for up to 6 weeks increased total phenolic content of blueberry cultivars (‘Centurion’ and ‘Maru’). However, a negative relationship existed between antioxidant activity and phenol content during storage in CA storage compared to regular atmospheric storage conditions at low temperature. It is assumed that prolonged CA storage may lead to the oxidation of the phenolic compounds (Schotsmanns et al., 2007). Zheng et al. (2005) reported that antioxidant capacity is correlated with total phenolic and anthocyanin contents and, thus, high-oxygen treatments may improve the antioxidant capacity of blueberry fruit, however, only to a limited storage period as these effects were found to diminish with prolonged storage duration. Post-harvest strategies that included enriched CO2 atmosphere and/or SO2 fumigation were found to maintain polyphenol content and total antioxidant activity of blueberry fruit, but varying significantly among cultivars. SO2 fumigation followed by controlled atmosphere

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FIGURE 21.4  Change of phenolic sub-

3.5 3.0 2.5 Phenolic subclasses mg g-1 DM

classes profile in blueberry cv. Bluecrop during storage. Contents of phenolic subclasses (mean  ±  SD) in blueberry during 14 days of storage under simulated retail condition (12  h at 20°C and 12  h at 5°C, 80% rH) are shown. The corresponding phenolic compound is equivalent as follows: AY = anthocyanins = cyanidin-3-glucoside; HYZ = hydroxycinnamicacids = chlorogenicacid; HYB = hydrobenzoic acids = gallic acid; FLAV =  flavonols = rutin. Source: Authors’ unpublished data.

2.0 1.5 1.0 0.5 0.0

control/ 0 days

7 days

14 days

2.69

a

a

1.14 1.32

b

b

0.16

2.97

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HYB

1.15 1.05

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FLAV

0.19

AY HYZ

2.60

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1.11 1.22

a ab

ab

0.14

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Storage me

storage (3% O2 + 6 or 12% CO2) is reported to be a promising post-harvest strategy for fresh blueberries to reduce decay, extend market life, and maintain high nutritional value (Cantin et al., 2012). Elicitor applications also comprise the targeted UV-C and UV-B treatment in post-harvest for meeting hygienic requirements on the one hand and for increasing healthpromoting phytochemical compounds of fruits and vegetables on the other hand (Schreiner et al., 2012). Flavonoids have various physiological functions such as antioxidant as well as UV protective effects (Treutter, 2010). Especially anthocyanins and quercetin are known as protective pigments against UV irradiation and thus, increases in fruits upon post-harvest UV-irradiation (Schreiner et al., 2012). Wang et al. (2009) indicated that post-harvest application of UV-C (2.15 and 4.30 kJ/m2) is effective in stimulating the antioxidant capacity and flavonoid content of blueberries, however, differing in dependence on the original flavonoid profile. Timecourse measurements of the effect of UV-C revealed that the strongest responses of fruit to UV-C treatment occurred instantly after the illumination and the effects diminished with storage time. Post-harvest UV-B treatment of ripe black currant (Ribes nigrum) induced the increase of total phenol content and phenolic composition (flavonols, anthocyanins, hydroxycinnamic, and hydroxybenzoic acids) to a large extent (Huyskens-Keil et al., 2007). Anthocyanins were concluded to absorb UV radiation within a short time; meanwhile flavonols and phenolic acids were assumed to have an impact on antioxidant protection of UV-Bmediated tissue damage. Recent studies reported an increase of phenolic compounds and corresponding antioxidant activity in blueberry cv. Bluecrop resulting from an UV-B post-harvest mediated stress response (Eichholz et al., 2010).

OTHER WAYS IN WHICH COMPOSITION IS ALTERED- FURTHER IMPACTS ON PHENOLIC COMPOUNDS IN BLUEBERRY FRUITS It is well accepted that maturity at harvest plays an important role for quality and storability of fruits and vegetables (Shewfelt, 1993). However, various factors in pre- and post-harvest influence the composition and quality of fruits. These include: genetic factors (selection of cultivars and rootstocks), pre-harvest climatic conditions and cultural practices, maturity at harvest and harvesting method, post-harvest handling procedure, post-harvest treatments, and processing methods (Kader, 2002). These factors also affect the phenolic profiles of plant tissues including the flavonoid biosynthesis being tissue specific, developmentally regulated and induced by a variety of environmental factors, e.g., light, UV-radiation, fungal infection, interaction with microorganisms, or wounding (Winkel-Shirley, 2001; HuyskensKeil et al., 2007). Most of these factors imply stress in plants and, thus, result in an accumulation of phenolic compounds as a plant defense response. For example, excessive fertilization as well as a shortage of macroand microelements indicates a change in phenol concentration as a defense reaction in plants. However, here the element boron gains special attention. Due to its structure, boron forms stable phenol–borate complexes and, therefore, high boron availability inactivates soluble phenolic compounds in plants (Brown et al., 2008). In this case, higher but not excessive concentrations of boron in fruits, applied by foliar spraying, led to lower total phenolic contents in blueberries, as it was reported by Eichholz et al. (2011). Moreover, it has been assumed that under boron deficiency, polyphenols concentrate via the stimulation of the enzyme phenylalanine-ammonium

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References

lyase (PAL) (Cakmak et al., 1995), the key enzyme that induces the flavonoid metabolism in plants (WinkelShirley, 2001). Nevertheless, it is noticeable that most of the pre-harvest factors accelerating the synthesis of phenolic compounds also influence other (undesired) metabolic processes, e.g., leading to a pronounced loss of biomass and yield of blueberries (Eichholz, 2008).

ANALYTICAL TECHNIQUES Primarily, when investigating phenolic compounds, total phenolic content (often abbreviated as TPC) is estimated spectrophotometrically in a high variety of different approaches. One of the most cited works in this context is Singleton et al. (1999), who described the use of the Folin–Ciocalteu reagent for an easy-to-use assay for all kinds of plant extracts. Traditionally, as already mentioned for the analysis of the profile of phenolic compounds, high-performance liquid chromatography (HPLC) is used with various detection systems. Detection with UV light is the common one, but also its use over a selected wavelength range (diode array detection), the use of electrochemical detection systems, or mostly preferred coupling to mass spectrometry is highly appreciated. Similarly, as for the estimation of the total phenolic content, also in this case many different operating procedures are applied, differing in the selection of extraction solvents (e.g., 70% methanol versus 80% ethanol), use of solid-phase extraction cartridges (e.g., polyamide versus C18 material), chromatographic conditions, especially solvent gradients, etc. With regard to the analysis in blueberries, from the mid 1990s, the groups of Kalt et al. (1999, 2003), or the US and Scandinavian groups (Heinonen et al., 1998; Prior et al., 1998, 2001; Häkkinen et al., 1999, 2000) presented some approaches that are still the basis for other research groups in this field. At this point, the reader is referred to these and further publications for detailed methodological descriptions.

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Celik, H., Ögen, M., Serce, S., Kaya, C., 2008. Phytochemical accumulation and antioxidant capacity at four maturity stages of cranberry fruit. Sci. Hort. 117, 345–348. Ebert, G., 2005. Anbau von Heidelbeeren und Cranberries. Eugen Ulmer KG, Stuttgart, p.104. Eichholz, I., 2008. Veränderung bioaktiver Inhaltsstoffe in Kulturheidelbeeren (Vaccinium corymbosum L.) in Abhängigkeit von der Mineralstoffverfügbarkeit. Verlag im Internet GmbH, HumboldtUniversität zu Berlin, dissertation.de, p. 174. Eichholz, I., Huyskens-Keil, S., Keller, A., Ulrich, D., Kroh, L.W., Rohn, S., 2010. UV-B-induced changes of volatile metabolites and phenolic compounds in blueberries (Vaccinium corymbosum L.). Food Chem. 126, 60–64. Eichholz, I., Huyskens-Keil, S., Kroh, L.W., Rohn, S., 2011. Phenolic compounds, pectin and antioxidant activity in blueberries (Vaccinium corymbosum L.) influenced by boron and mulch cover. J. Appl. Bot. Food Qual. 84, 26–31. Gao, L., Mazza, G., 1994. Quantitation and distribution of simple and acylated anthocyanins and other phenolics in blueberries. J. Food Sci. 59, 1057–1059. Gough, R.E., 1993. The highbush blueberry and its management. The Haworth Press- Food Products Press, New York, p. 288. Halbwirth, H., Puhl, I., Haas, U., Jezik, K., Treutter, D., Stich, K., 2006. Two-phase flavonoid formation in developing strawberry (Fragaria x ananassa) fruit. J. Agric. Food Chem. 54, 1479–1485. Heinonen, I.M., Meyer, A.S., Frankel, E.N., 1998. Antioxidant activity of berry phenolics on human low-density lipoprotein and liposome oxidation. J. Agric. Food Chem. 46, 4107–4112. Häkkinen, S., Heinonen, M., Karenlampi, S., Mykännen, H., Ruuskanen, J., Törrönen, R., 1999. Screening of selected flavonoids and phenolic acids in 19 berries. Food Res. Int. 32, 345–353. Häkkinen, S.H., Törrönen, A.R., 2000. Content of flavonols and selected phenolic acids in strawberries and Vaccinium species: influence of cultivar, cultivation site and technique. Food Res. Int. 33, 517–524. Howell, A., Kalt, W., Duy, J.C., Forney, C.F., McDonald, J.E., 2001. Horticultural factors affecting antioxidant capacity of blueberries and other small fruit. HortTechnol.11, 523–528. Huyskens-Keil, S., Schreiner, M., 2004. Quality dynamics and quality assurance of fresh fruit and vegetable products in pre- and postharvest. In: Dris, R., Jain, S.M. (Eds.), Production practices and quality assessement of food crops, Vol. 3. Kluwer Academic Publishers, Dordrecht, Boston, London, pp. 401–449. Huyskens-Keil, S., Eichholz, I., Kroh, L.W., Rohn, S., 2007. UV-B induced changes of phenol composition and antioxidant activity in black currant fruit (Ribes nigrum L.). J. Appl. Bot. Food Qual. 81, 140–144. Jaakola, L., Määttä, K., Pirttilä, A.M., Törrönen, R., Kärenlampi, S., Hohtola, A., 2002. Expression of genes involved in anthocyanin biosynthesis in relation to anthocyanin, proanthocyanidin, and flavonol levels during bilberry fruit development. Plant Physiol. 130, 729–739. Kader, A.A., 2002. Fruits in the global market. In: Knee, M. (Ed.), Fruit quality and its biological basis. Sheffield Academic Press, Sheffied, p. 279. Kalt, W., Forney, C.F., Martin, A., Prior, R.L., 1999. Antioxidant capacity, vitamin C, phenolics, and anthocyanins after fresh storage of small fruits. J. Agric. Food Chem. 47, 4638–4644. Kalt, W., Lawand, C., Ryan, D.A.J., McDonald, J.E., Donner, H., Forney, C.F., 2003. Oxygen radical absorbing capacity, anthocyanin and phenolic content of highbush blueberries (Vaccinium corymbosum L.) during ripening and storage. J. Am. Soc. Hort. Sci. 128, 917–923. Kosar, M., Kafkas, E., Paydas, S., Baser, K.H.C., 2004. Phenolic composition of strawberry genotypes at different maturation stages. J. Agric. Food Chem. 52, 1586–1589. Mainland, C.M., Tucker, J.W., 2000. Blueberry health information-some new mostly review. Acta Hort. 574, 39–43. McManus, M.T., 2012. Annual Plant Reviews, The plant hormone ethylene. Wiley-Blackwell. , p. 416.

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2. FRUIT