Download phenolic composition of dark coloured fruits and their

PHENOLIC COMPOSITION OF DARK
COLOURED FRUITS AND THEIR IMPACT
ON SENSORIAL PROPERTIES
Fernanda Cosme (1)*, Berta Gonçalves (2), Eunice Areal (2), António Inês (1), António M.
Jordão (3), Alice Vilela (1)
(1) CQ-VR, Chemistry Research Centre, Universidade de Trás-os-Montes e Alto Douro,
School of Life Sciences and Environment, Department of Biology and Environment, Edifício
de Enologia, 5000-801 Vila Real, Portugal. * [email protected]
(2) CITAB, Centre for the Research and Technology of Agro-Environmental and Biological
Sciences, Universidade de Trás-os-Montes e Alto Douro, School of Life Sciences and
Environment, Department of Biology and Environment, 5000-801 Vila Real, Portugal.
(3) Polytechnic Institute of Viseu (CI&DETS), Agrarian Higher School, Estrada de Nelas,
Quinta da Alagoa, Ranhados, 3500-606 Viseu, Portugal.
Abstract
Phenolic compounds are secondary metabolites widely distributed in the plant kingdom
and abundant in our diet. In addition, phenols are today among the most important classes
of phytochemicals. They are decisive to plants life, because they can provide defences
against microbiological attacks and make food unpalatable to predators and other
herbivores. For humans, phenolic compounds may affect positively or negatively the
sensory characteristics of food with important impacts on colour, flavour and astringency,
modifying food palatability. In last decade, much work has been presented by the scientific
community, which focuses on the levels and chemical structures of phenols from different
plant materials. Some fruits with high content of phenolic compounds are grapes, sweet
cherries and blueberries. Grapevine (Vitis vinifera L.) is the most important Mediterranean
fruit crop, used to produce wine, table grapes and raisins. Grapes are one of the most
important fruit commodities. This red fruits contain a large amount of different phenolic
compounds in skins, pulps, seeds and stems, which are responsible for physicochemical and
sensory characteristics of fresh grapes and wines, such as colour and astringency.
Polyphenolic compounds form complexes with salivary proteins, playing a role in the
sensation of astringency, due to delubrication of oral surfaces. For astringency, the tannin
molecular weight seems to be important for its perception and the interactions of tannins
with salivary proteins results on its perception. This polyphenol-salivary protein interaction
may form a layer that acts as a water barrier and produces a mouth-drying sensation.
Flavour and colour are also important factors for the selection of fruit by consumers.
Sweetness and bitterness are mutually suppressed in mixtures but, astringency and
bitterness tend to be perceived as negative attributes. Polyphenols' sensory properties are
related to molecules specific structures, including pigments (yellow, orange, red and blue)
correlated to fruits colour, and volatile polyphenols such as vanillin and eugenol (strong
flavourings). The phenolic compounds in grapes include two classes of phenolic
compounds: non-flavonoids and flavonoids. The major C6-C3-C6 flavonoids in grapes
include conjugates of flavonols, quercetin and myricetin; flavan-3-ols (+)-catechin and (-)epicatechin; and malvidin-3-O-glucoside and other anthocyanins. Non-flavonoids include
C6-C1 hydroxy-benzoic acids, and gallic acid, C6-C3 hydroxycinnmatescaffeic, caftaric, and pcoumaric acids; and C6-C3-C6 stilbenes trans-resveratrol, cis-resveratrol, and trans-resveratrol
glucoside. Also, sweet cherry (Prunus avium L.) is one of the most popular temperate table
fruits. Cherries are an excellent source of phenolic compounds which are currently widely
studied due to its beneficial health effects. Sweet cherries contain flavonoids, flavan-3-ols,
and flavonols in addition to non-flavonoid compounds such as hydroxycinnamic and
hydroxybenzoic acids, which are concentrated in the epicarp and mesocarp of the fruit. The
most abundant phenolic compounds are anthocyanins such as the 3-O-glucoside and 3-Orutinoside of cyanidin, peonidin-3-O-rutinoside and glucoside, as well as pelargonidin-3-Orutinoside. Sweet cherry contains phenolic acids such as hydroxycinnamic acid derivatives
(neochlorogenic acid, p-coumaroylquinic acid and chlorogenic acid) and flavonols and
flavan-3-ols such as (+)-catechin, (-)-epicatechin, quercetin 3-O-glucoside, quercetin 3-Orutinoside, and kaempferol 3-O-rutinoside. Anthocyanin and flavonol compounds
contribute to the sensorial qualities of fruits. Moreover, almost all phenolic compounds in
sweet cherry show strong antioxidant activity. An adequate consumption of phenolic
compounds may offer health benefits that include inhibition of tumour cells growth,
inhibition of inflammation and protection against neurodegenerative diseases. In fact, recent
research indicates that a phenolic-rich extract derived from sweet cherries could be an
attractive candidate to formulate an agent for the prevention of oxidative stress-induced
disorders such as intestinal inflammation disorders or with an appropriated delivery system
for neurodegenerative diseases. On the other hand, blueberries are emerging as a crop with
high international economic value. In recent years the production and fresh marketing of
these fruits have increased rapidly in Europe, as results of the recognition of their high
nutritive value, characteristic taste and flavour but also due to their known health
promoting properties such as source of bioactive compounds. Berries are regarded as high
in phenolic compounds including flavonols, flavones, anthocyanins, and phenolic acids, but
also in vitamins and minerals. Among phenolics, chlorogenic acid, peonidin 3-Ogalactoside, peonidin 3-O-arabinoside, cyanidin 3-O-galactoside and cyanidin 3-Oarabinoside are the most important antioxidants in blueberry. This richness in nutrients is
directly related with the positive effects on human health. The major health benefits include
a reduced risk for cardiovascular and neurodegenerative diseases. However, the quality
attributes of the dark-coloured fruits, including the phenolic composition, depends on
cultivar, maturity, growing environment, cultural practices, postharvest conditions and
processing procedures. After the consumption of fruits, the colon is the main site of
microbial fermentation, where phenolic compounds are transformed into phenolic acids or
lactone structures by intestinal microbiota. Thus, the microbial metabolism of most of the
phenolic classes such as flavonoids, isoflavonoids, lignans, phenolic acids and tannins may
produce metabolites with biological activity, presenting increased antioxidant activity, with
evidence on health benefits for consumers. Therefore, considering the importance of darkcoloured fruits phenolic composition, the purpose of this chapter is to make a review of the
most recently publications about the dark-coloured fruit phenolic composition and their
impact in sensorial properties of the most consumed small dark-coloured fruits, such as
grapes, sweet cherries and blueberries, as well as the effect of microorganisms on fruit
phenolic compounds.
The following topics will be covered:
1. Phenolic composition of dark-coloured fruits
1.1
Phenolic composition of wine grapes and table grapes
1.2
Phenolic composition of sweet cherry
1.3
Phenolic composition of blueberries
2. Impact of fruit phenolic compounds on sensorial characteristics
3. Effect of microorganisms on fruit phenolic compounds
Keywords: phenolic compounds, grapes, table grapes, sweet cherries, blueberries, sensorial
characteristics