Document Type : Research Article
Authors
Department of Food Science and Technology, Zanjan University, Zanjan, Iran.
Abstract
Introduction: In recent years special attention has been paid to the use of natural sources contain healthy bioactive compounds. Fruit and vegetable juices are a good source of many biologically active compounds, particularly vitamins, minerals and phenols. Phenolic compounds are secondary metabolites widely found in fruits, mostly represented by flavonoids and phenolic acids. Phenols are known for their antioxidant, anticancer and cardio-protective properties among bioactive compounds. The health benefits of these phytochemicals are directly linked to a regular intake and their bioavailability. Berries with dark blue or red colors have the highest bioactive compounds and antioxidant capacities among all common fruits and vegetables. Anthocyanins which are one of the largest and most important group of water-soluble pigments in most species in the plant kingdom are largely responsible for diverse pigmentation from orange to red, purple and blue fruits, such as: blackberry, red and black raspberries, blueberries, bilberries. White mahlab (Prunus mahaleb L.) fruits with a dark red color, which known also as English cherry, Rock cherry, St. Lucie cherry, of the Rosaceae family, subfamily Prunoidae, is a deciduous tree with 1–2 m high. Mahaleb cherry tree which grows abundantly in West Asia such as in Iran used just as basic link for cherry trees because of bitter taste of their fruits. In order to reduce the bitterness and improve the taste of mahaleb juice, a debittering process is considered as an effective solution to overcome the commercial application problem. Several debittering techniques have been used to reduce the content of bitter compounds, such as biodegradation by enzymes, addition of bitterness suppressing agents, ultrafiltration.
Material and Methods: All chemicals used were analytical grade and purchased from Merck (Darmstadt, Germany) and Sigma-Aldrich (St. Louis, MO. USA).
Selected microorganisms including Staphylococcus aureus (PTCC: 1112), Escherichia coli (PTCC: 1338), Aspergillus flavus (PTCC: 5004) and Penicillium chrysogenum (PTCC: 5037) were obtained from the Iranian Research Organization for Science and Technology (IROST), Iran.
The ripened fruits of mahaleb were collected from the orchard of Zanjan University, and transported to the laboratory. Harvest involved a random sampling from 5 trees. Stem and leaves were then discarded, and fruits stored at -18 ℃ until further use.
Frozen fruits were removed from the freezer, thawed and pitted. The fruit juice was obtained using a domestic juicer (Moulinex PC302, France). The juice was filtered through a stainless steel sieve (1 mm) to separate pomace from juice. The juice obtained was placed in dark glass bottles until further analysis.
Vitamin C content was determined using spectrophotometric method. Total phenolic content of the fruit juice was determined using Folin–Ciocalteu’s assay. Total flavonoid and anthocyanin contents of the fruit juice were determined according to the colorimetric assay at 510 and 526 nm, respectively. Antioxidant activity was determined using Diphenyl Picrylhydrazyl (DPPH) free radical scavenging and reducing power of H2O2 methods.
Antimicrobial activity of mahaleb juice against E. coli, Staphylococcus aureus, Aspergillus flavus and Penicillium chrysogenum was evaluated using agar well diffusion, and minimum inhibitory concentration and minimum bactericidal concentration was determined using broth microdilution and surface methods.
Results and Discussion: According to the result obtained, vitamin C, total phenolic, total flavonoid, total anthocyanin content was 39.26±0.01 mg/100 mL, 303.00±0.06 mg GAE/100 mL, 17.00±0.01 mg Rutin/mL and 871.63±0.93 mg Cyanidin/100 mL, respectively. Free radical scavenging activity and reducing power of H2O2 was 72.30% and 6.33%, respectively. Based on these results the white mahaleb juice had bioactive compounds such as other fruits with blue and purple color. According to other researchers there was a higher positive correlation between the amounts of carotenoids, total phenolics and anthocyanins and the antioxidant activity. Of course, it should be noted that several factors such as the plant growth region and the harvest period might have an impact on plant growth and metabolite concentration. Some studies also showed that dark red sour cherries contain higher total phenolic and total anthocyanin content compared to sour cherries with lighter red color. Therefore, mahaleb juice which was used in the current research with dark blue color and high total phenolic and anthocyanin content have high antioxidant activity.
The results also revealed that mahaleb juice had no inhibitory effect on Aspergillus flavus and Penicillium chrysogenum whereas the minimum inhibitory concentration on 102 CFU/ml of E. coli and Staphylococcus aureus was obtained at 0.9 and 0.8 % concertation of mahaleb juice. In addition, no minimum bactericidal concentration was observed. So, mahaleb juice likely has no or little antifungal activity compared to antibacterial effects. Previous studies also showed that antimicrobial activity of many extracts related to their phenolic compounds and anthocyanins. Blueberry methanol extract was shown strongly inhibit the pathogenic bacteria, such as E. coli O157:H7. The antimicrobial properties of blueberry morelikely is due to the compounds of monomeric phenolics, anthocyanins and proanthocyanidins. Therefore, mahaleb juice as a source of natural bioactive compounds such as vitamin C, phenols, carotenoids and anthocyanins is recommended as functional food in industry, especially, after debittering.
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