Total Carotenoid, Flavonoid and Phenolic Compounds Concentration in Willowleaf Cotoneaster (Cotoneaster Salicifolius Franch.) Fruits

Willofleaf cotoneaster (Cotoneaster salicifolius Franch.) is a low, prostrate shrub, grown in Romania as an ornamental plant. Its fruits are small, ovoid pomes. Fruit tissues were analyzed for total carotenoid content (through acetone extraction and spectrophotometry), flavonoid content (methanol extraction and spectrophotometry) and total concentration of phenolic and polyphenolic compounds (methanol extraction and spectrophotometric Folin-Ciocâlteu method). C. salicifolius fruits analyzed contained an average of 311.50 mg/kg DW carotenoids (heat-dried fruits – only 100.25 mg/kg). Average flavonoid concentration was 9,777.62 mg/kg in fresh frozen fruits and 4,574 mg/kg in dried ones. 25,056.09 mg/kg GAE was the average concentration of total phenolics in fresh fruits, while dry fruit powder contained 5,271 mg/kg GAE. These concentrations of bioactive compounds are comparable, or even have a higher than in pomes belonging to related species, including domestic cultivars of rowanberry (Sorbus sp.), wild Sorbus species, firethorns (Pyracantha sp.), or other studied cotoneasters. This shows a significant potential for these pomes, requiring further investigation. However, heat-drying was found to be an unsuitable processing method for these fruits, since it led to a 53.22-78.94% decrease in bioactive compounds concentrations.


Introduction
Cotoneaster salicifolius Franch. (common name: willowleaf cotoneaster or cranberry cotoneaster), belongs to the Rosaceae family, Amygdaloideae subfamily, Maleae tribe and is a common ornamental shrub.
An evergreen, or (rarely) semi-evergreen small to medium size low shrub, with extensively spreading branches, reddish to gray brown branchlets, elliptic to lanceolate glossy leaves (4-8.5 cm long), with entire margins and acute apex. White flowers are grouped in dense corymbs. Fruits are scarlet, subglobose to ovoid pomes, with 2-3 pyrenes each, ripening in September-October.
It is native to mountain areas, open slopes and mixed forests in Southern China, but grown worldwide as an ornamental plant (groundcover). It tolerates a wide variety of soils (except for those with water excess), while it is susceptible to some bacterial diseases and insect attack. With proper maintenance, it is able to thrive in urban habitats (Lu & Brach, 2003). In Romania, it is grown in parks and gardens, 'Parkteppich' and 'Repens' being the most popular cultivars (Fig. 1). There are no known other uses for C. salicifolius, however other related species are used in Asian traditional medicine, for treating bronchitis, gastritis, various infections and vascular illnesses (Liu et al., 2018).
The purpose of this research was to determine the concentration of some key phytochemical classes in fresh and heat-dried fruits of C. salicifolius.
Carotenoids (carotenes, lycopene, lutein, zeaxanthin among others) are common pigments in plant leaves, flowers and fruits. They represent the basis for melanin and retinol synthesis, being important for skin and eye health. Some have antitumoral properties (Eldahshan & Singab, 2013).
There are various types of phenolic and polyphenolic compounds, with protective function against pathogens and insects (Kivrak & Kivrak, 2014). Among them are flavonoids, phenolic acids, tannins, with radical scavenging, reducing and lipid oxidation inhibiting activity, thus potent antioxidants (Zymonė et al., 2018).

Material and Methods
Pomes were collected from several C. salicifolius individuals in public gardens from Constanța, Romania, in November 2018. All individuals found belonged to the 'Repens' cultivar.
Fruit pyrenes (kernels) were extracted and the fruit pulp was ground using an electrical grinder. Part of the pulp was frozen at -20°C, prior to analysis, while the rest was oven-dried at 80°C (over 72 hours).
Both fresh frozen tissue and dry one were analyzed for determining carotenoid, flavonoid and phenolic compounds concentrations (triplicate samples each).
For flavonoids, 1 g fruit pulp was ground with 5 mL methanol and filtered. 0.5 mL of the extract was mixed with 4 mL distilled water and 8 mL methanol. Spectrophotometric absorbance was determined at 340 nm, and concentration calculated according to Szabo et al., 2012. Total concentration of phenolic compounds was determined via a spectrophotometric Folin-Ciocâlteu method. 0.1 g pulp was ground with 10 mL methanol. 1 mL of extract was mixed with 5 mL 10% Folin-Ciocâlteu reagent and 4 mL 7.5% sodium bicarbonate. After 30 minutes, absorbance was read at 765 nm (Siddiqui et al., 2017;Stanković, 2011).
Concentrations were expressed as mg/kg DW, respectively mg/kg gallic acid equivalent DW (GAE; for phenolics, after proper calibration).  While literature offers few data on carotenoid content in Cotoneaster fruits, useful comparison can be drawn with related Pyracantha species, with over 65 mg/kg total carotenoids in P. angustifolia (Zechmeister & Schroeder, 1942), and over 22 mg/kg in P. crenulata (a valuable medicinal species growing in the Himalayas; Pal et al., 2013).

Results and Discussions
Sorbus is another related genus (it includes rowans and service-trees), in the Maleae tribe, subject of a detailed that found a total carotenoid concentration of 39-2,659 mg/kg, in various domestic varieties (Zymonė et al., 2018).   Heat-drying of C. salicifolius fruits led to a 67.81% decrease in carotenoids, 53.22% decrease in flavonoids and a 78.94% loss of total phenolics. Thus, the decrease in biocative compounds concentration was a signficant one, higher than the one normal occuring in freeze-drying of various fruits (10-50% for phenolics; Shofian et al., 2011).

Conclusion
Having an average concentration of 311.50 mg/kg total carotenoids, 9,777.62 mg/kg flavonoids and 25,029.09 mg/kg total phenolic snd polyphenolic compounds in their pulp tissues, C. salicifolius fruits are comparable, or even have a higher content of bioactive compounds, than pomes belonging to related species, including domestic cultivars of rowanberry (Sorbus sp.), wild Sorbus species, firethorns (including the medicinal plant Pyracantha crenulata), or other studied cotoneasters.
This show a significant potential for these pomes, requiring further investigation.
However, heat-drying was found to be an unsuitable processing method for these fruits, since it led to a 53.22-78.94% decrease in bioactive compounds concentrations.