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Journal of Clinical Nutrition and Health (JCNH)

Quality Attributes of Black Mulberry (Morus Nigara L.) with Ultraviolet Radiation Open Access Juice Treated

Review Article


Kenan TUNÇ

Sakarya University, Arts and Science Faculty, Department of Biology, 54087 Serdivan, Sakarya, Turkey

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Corresponding Authors

Kenan TUNÇ,

Received : January 01, 2021
Published : July 05, 2021


After exposing the black mulberry juice to ultraviolet light with the intensity of 5, 10 and 20 kJ/m2, their quality analysis have been performed for 4 days at +4 °C and +25 °C. Within the current study the antioxidant activity, Total Phenolic Content (TPC), microbial charges and pH values of the samples have also been investigated. In the UV light exposed samples there existed no meaningful difference in the % DPPH radical scavenging activity level, a small amount of decrease has been detected in the TPC creation process. While the storage time worsens the DPPH activity, it affects the TPC positively. Microbial studies showed reduction in total mesophile aerobic microorganisms, yeasts and mould counts about by 1-log cycle on UV treatments. This is the first report on the effects of UV radiation on black mulberry.

Materıal and Methods

Black mulberry samples (5 kg) were collected from the Serdivan Bahçelievler neighborhood in June. Black berries of 2.5-4 cm in size and similar maturity were crushed by a domestic juicer (Arzum). Juice was immediately filtered on a double layer cheese cloth to remove seeds and pulp from it.


The genus of mulberry (Morus spp.), belonging to the Moraceae family, is tropical and subtropical species. East, West and South East Asia, South Europe, South of North America, Northwest of South America and some parts of Africa are areas of distribution of this species [1]. The mulberry production in Turkey is important and exhibit significant diversity of wild species in Anatolia [2]. Today, mulberry fruit is frequently used as fresh and processed and has a high nutritional value.

UV radiation is a small part of the electromagnetic spectrum, which comprises radio waves, microwaves, infrared, visible, X-rays and gamma rays [3]. Ultraviolet-C is known as germicidal against the microorganisms such as bacteria, viruses, protozoa, yeast, mold and most. The most pronounce effect has been detected at the wavelengths of 250 to 270 nm. Therefore, the wavelength of 254 nm is generally selected to disinfect the surfaces, water and fruit juices [4,5].

UV light treatment is promising in that it is low cost, non-thermal and newly developing technology and frequently used in microbial security of fruit juices and in protection of the food properties [6-9].

There are several studies in the literature on the elongating the shelf life of the fruit juices treated with UV light. In the current study it is aimed to find out the elongation effect of shelf life by the application uf UV light for the black mulberry juice. Throughout the process it is also aimed to evaluate the microbial charge pH value, DPPH scavenging activity and total phenolic content of the samples being researched.

Solvents and Reagents

All the solvents used in the present study were procured from Sigma Aldrich (Laborchemikalien GmbH, 30926, Seelze, Germany) and R&M Chemicals (Essex, UK). Peptone water (buffer), Nutrient Agar (NA), Potato Dextrose Agar (PDA) and Folin-Ciocalteu, Gallic Acid, 2,2-diphenyl-1-picrylhydrazyl (DPPH) and Sodium Carbonate, Ascorbic Acid were procured from MERCK (Darmstadt, Germany).

UV Treatment

As UV-C light source 4 units of low pressured mercury lamps Puritec HNS 8W G5 (Osram, Germany) have been employed. Light intensity (Eo) is defined to be the ratio of the optical power of light source (Q) to the area (S) of applicatlion and has the unit of W/m2 .

Eo = Q/S

The light intensities of the lamps have been measured to be 25 W/ m2 using PRC-Krochmann radiometer and PRC-Krochmann radiometer header 121116-3 at the distance of 5 cm. Optical dose (Ho), which is the absorbed energy amount of UV light in unit area, is calculated by the formula:

Ho = ∫ Eo.t dt

and has the unit of J/m2. These dose calculations have been fulfilled where each lamp was placed 5 cm apart to the centre of petri and being on top of the setup (Figure 1).

After transferring the 10 mL of preparet fruit juice samples into the sterile petri containers (15x 90 mm) they are exposed to UV light in a laminar flow. During the process to eliminate the heat produced a fan is added to the system. Average values of optical doses of 5, 10 and 20 kJ/ m2 have been applied for all experiment groups.


Total Phenolic Content (TPC)

The total phenolic content was determined by Folin-Ciocalteu procedure as described with minor modifications [10]. The 100 μL of Fresh juice sample diluted 1/10 with 50% ethanol was mixed with 200 μL of Folin-Ciocalteu (50%) and was kept waiting for 2 mins. Then, 1 mL of 2% sodium carbonate solution was added and shaken well. The mixture was kept in a dark place for 1 hour. The absorbance of the mixture was measured at 760 nm by using a spectrophotometer (Shimadzu UV mini-1240). The total phenolic content values were determined from a calibration curve prepared with a series of gallic acid standards (50, 100, 200, 300, 400 mg/L). The results were expressed as mg of GAE/100 g.

Antioxidant Activity (DPPH assay)

The modified Blois method was used for the antioxidant activity determination [11]. In short, 1 ml of 0.004% solution of DPPH radical in ethanol was mixed with 1 mL Fresh juice sample diluted 1/100 with 50% ethanol. These solutions were kept in dark place for 30 mins and the optical density was then measured at 517 nm using a spectrophotometer and 50% ethanol was used for the blank. The following equation was employed to evaluate the % DPPH radical scavenging activity: % DPPH radical scavenging = (control absorbance- extract absorbance) / control absorbance) x 100.


Microbial Analysis (aerobic plate count, yeast and mould counts)

UV treated and non-treated juice were analysed for the status of total mesophile aerobic microorganisms, yeast and mould counts. A series of decimal dilutions (10−1 -10−5) was prepared with 0.1% (w/v) peptone water. Further, one millilitre of decimal dilution of the sample was pipetted into Petri dish and the total plate counts were enumerated using the pour plate method. The plates (NA) were incubated at 37 ± 1 °C for 48 h.

The total yeast and moulds were enumerated by pour plate method using potato dextrose agar (PDA) media. To inhibit the growth of others microbes, 10% tartaric acid was added into PDA agar (final pH 3.5-3.7). The plates were incubated at 25 °C for 5-7 days in the incubator. The results were expressed as log colony-forming units (cfus) per millilitre of juice (n=5).

Statictial Analysis

Data were analyzed using SPPS software. Values were expressed as means ± standart deviations.

Results and Dıscussıon (NEED TO ADD TEXT)

PH and acidity is known to be the most reliable indicator to evaluate the general properties of the product and can have the effect to elongate the shelf life during the production process of the fruit juices. pH variation of black mulberry juice with repect to the UV dose and the temperature for 5 days is given in Table 1. The control groups exposed to UV dose and the fruit juices exposed to 5, 10 and 20 kJ/m2 doses have shown no any difference. The storage temperature is seen to be effective on pH values and it has been found that the pH value decreases for both temperatures while the storage time increases.



Consumers think that the acidic fruits or fruit juices are microbiologically safe since they have lower pH values. However the current reports states that presence of the patogens like Alicyclobacillus acidoterrestris, Bacillus spp., Escherichia coli O157: H7, Staphylococcus aureus ve Salmonella spp. within the foods causes several diseases. The acidic pH can also grow very rapidly in mold and yeast. Black mulberry has an acidic pH value such as various fruits (approximately 3.5) and the mold and yeast is responsible for the microbial decomposition/deterioration in the fruits ( Ercişli and Orhan, 2007). The first day total live and yeastmold value for the UV exposed/treated samples is given in Figure 2.



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