Comparison of gamma and electron beam irradiation for using phyto-sanitary treatment and improving physico-chemical quality of dried apricot and quince

ABSTRACT The present study was conducted to compare the effect of gamma and electron beam irradiation for use a phyto-sanitary treatment and improving the physico-chemical and antioxidant activity of dried apricot and quince irradiated at doses of 1, 2, 3, and 4 kGy. Results of the present study revealed that both gamma and electron beam irradiation were significantly (p ≤ 0.05) effective in maintaining the physico-chemical quality and enhancing the antioxidant potential of dried apricot and quince. The ΔE*ab values indicated that there was no significant (p ≤ 0.05) noticeable difference induced in color of the dried apricot and quince by the two methods of irradiation. Textural parameters (hardness, chewiness, gumminess) recorded decreasing trend with irradiation particularly at doses beyond 2.0 kGy under both the methods of irradiation. Strong inverse correlation (r = –0.85) existed between gamma irradiation and rehydration ratio whereas moderate inverse correlation (r = –0.73) existed between rehydration ratio and electron beam irradiation for both the products. Both gamma and electron beam irradiation at 3.0 and 4.0 kGy proved effective in reducing the number of viable microorganisms to below detection limits in both the products. In dried apricots treated with 4.0 kGy of gamma irradiation, the increase in fructose, glucose, and sucrose content over control was of the order of 10.6% and 25.7% compared to 8.9%, 7.8% and 17.5% for same dose of electron beam irradiation. Dried quince treated with gamma and electron beam irradiation at 4.0 kGy recorded an enhancement in fructose, glucose, and sucrose contents of the order of 14.8%, 15.5%, 30.1% and 11.2%, 14.2%, 27.2%, respectively. The results of the antioxidant activity revealed significant (p ≤ 0.05) decrease in EC50 values and corresponding increase in antioxidant activity of dried apricot and quince due to gamma and electron beam irradiation.


Introduction
Apricot (Prunus armeniaca L.) and quince (Cydonia oblonga M.), both belong to climacteric class of fruits and have gained much consumer attention in the recent years due to their nutritional and health benefits. Both the fruits are rich source of health protecting and functional compounds which are essential for normal growth and development (Jimenez, Martinez-Tome, Ega, Romojaro, & Murcia, 2008;Szychowski, Munera-Picazo, Szumny, Carbonell-Barrachina, & Hernández, 2014;Wei et al., 2014). In addition, both these fruits are potential candidates of phenolic compounds and flavonoids which act as potent antioxidants and immune modulators. Fresh quince and apricot are known to have hypoglycemic, anti-inflammatory, antimicrobial, anticancer, antiallergic, and antiulcer action, thus have great potential for use as raw material for food and pharmaceutical industries (Ibrahim et al., 2015;Légua et al., 2013;Wojdyło, Teleszko, & Oszmian´ski, 2014). However, both the fruits being perishable have short shelf-life and are susceptible to microbial spoilage. Further, due to quarantine regulations arising because of the presence of codling moth (Cydia pomonella) pest in fresh apricots of Ladakh, the fruit is sold locally and mostly used in dried or dehydrated form (Mir, Peerzada, Fouzia, & Rather, 2009). Likewise, quince fruit due to astringency and strong acidity is not much appreciated for its fresh consumption and is mostly eaten after cooking or processed in to dehydrated products (Silva et al., 2005).
The most conventional method of drying of apricot and quince is sun drying where in the fruit is spread on rooftops or on ground. This conventional method is time consuming and fruit is exposed to open environment and gets contaminated with dust⁄dirt, flies, microorganisms, and results in an unhygienic and inferior quality product. The high relative humidity and high temperature encountered during extended period of drying are the favorable conditions for microorganisms to grow, under which dried apricots and quince get easily contaminated and decomposed; thereby raising concerns for the safety of the consumers (Gonzalo, Angel, Domingo, & Antonio, 2009). The importance of microbiological food safety is paramount because of the potential for harmful microorganisms to grow and multiply in food commodities. Entry of possible contaminants such as microbiological agents into food is a threat to the safety of food products. This can result in food poisoning, increase in food borne outbreaks and a decrease in food availability because of discarding the contaminated food products besides acting as barrier for export (Kuo & Chen, 2010). To sanitize the foods, use of conventional chemical preservatives against microbial and insect infestation is being restricted throughout the world. These chemicals besides having adverse environmental issues, pose serious health hazards, and limit the export capabilities of dried fruits (Cetinkaya, Ozyardimci, Denli, & Ic, 2006). Use of steam heat treatment for achieving the sanitization is also limited because it involves additional decontamination step prior to packaging. To overcome these environmental issues and quarantine barriers posed by chemical preservatives, and at the same time address the limitations of other sanitization treatments, alternate processes are needed.
Food irradiation has been recognized as an effective alternative to chemical preservatives for treating fresh and dried food products (Teets, Sundararaman, & Were, 2008). Foods can be irradiated using gamma rays produced from cobalt-60 (1.17 and 1.33 MeV) or cesium-137(0.662 MeV) and electron beams and X-rays generated from machine sources having energies not exceeding 10 MeV and 5 MeV (Cember & Johnson, 2009). Stronger interactions of radiations with matter are known to occur for high energy charged particles emitted from electron beams than for photons of gamma rays and X-rays (Cember & Johnson, 2009;Stewart, 2001). Therefore, the three types of radiations used for treating foods show different penetration and effects with respect to microbiological and physicochemical qualities of foods. Gamma rays from radionuclide source are usually preferred compared to electron beams and X-rays because of their greater penetration. However, rising prices of cobalt-60 and the increased public concerns toward the safety of radioactive materials and the issues related to their safe disposal has put a question mark for their future use. This safety concern of consumers has paved ways for the development of electron beam and X-ray machines based on "on-off" principle. Although electron accelerators are currently in use for sterilization of hospital items and food products, but comparison with gamma irradiation in terms of efficacy for obtaining desired objectives are rarely reported (Arvanitoyannis, 2010). Jung, Seon-Min, Byeong-Geum, Beom-Seok, and Jong-Heum (2016) studied the comparative effect of gamma ray, X-ray, and electron beam irradiation at dose range of 200-1000 Gy on the sensory properties of fresh Fuji apples and Niitaka pears. The authors reported that sugar contents in Fuji apples and Niitaka pears were not changed by the three types of radiations. Based on comparison with gamma and electron beam irradiation, authors identified the applicability of X-ray irradiation as a phytosanitary treatment for Fuji apples and Niitaka pears. Jung et al. (2015) investigated the effect of X-ray, gamma ray, and electron beam irradiation (2-10 kGy) on the hygienic and physic-chemical qualities of red pepper powder. The study revealed that dose of 6.0 kGy (for all radiation sources) reduced the total aerobic microbe population effectively without affecting major quality indicators. The three radiation types did not change the pungency of red pepper powder based on the capsacinoid content. The authors finally concluded that X-ray can be used for the irradiation of dried condiments with the same effects as gamma rays and electron beams. In another study, Jong-il et al. (2009) compared the effect of gamma ray and electron beam irradiation (0.5 and 10 kGy) on extraction yield and morphological properties of polysaccharides from tamarind seed and reported that extraction yield was increased significantly by both methods of irradiation. Morphological studies revealed that tamarind seed polysaccharides treated with gamma ray irradiation had a fibrous structure whereas those treated with electron beam irradiation had particle structure. Keeping in view that very few studies have been conducted so far on comparative basis, the present study was carried out to investigate the immediate effect of gamma and electron beam irradiation on microbiological, physicochemical, and antioxidant quality of dried apricot and quince.

Sample preparation and irradiation
Sun dried apricots of Halman variety were procured from progressive apricot grower of village Karkitchoo, district Kargil of Ladakh region. Based on the inputs of grower, apricots were sun dried under open conditions (25-27 ± 2°C, RH 50-60%) within 15-18 days. The quince fruit slices (2 mm thick) of Oblong variety were dried at 35 ± 2°C, RH 65% using a tray drier for 32 h. The average moisture contents after dying were 15.2 ± 0.25% in apricot samples and 12.2 ± 0.2% in quince slices. The dried samples (250 g) were placed in aluminum foil pouches (20 × 30 cm; thickness: 0.09 mm). The samples were packed to a thickness of 2.0 cm to minimize the variation in penetration depth between the radiation sources. The packed dried apricot and quince samples were irradiated with irradiation doses of 1, 2, 3, and 4 kGy using gamma and electron beam irradiation. Gamma irradiation treatment was given at Food Technology Division, BARC using Co-60 gamma-ray source (GC-5000, BARC, Mumbai). The samples were irradiated at a dose rate of 3 kGy/h. Electron beam irradiation was performed at Electron Beam Centre, BARC, Mumbai using 10 MeV electron accelerator operated at 1 KW beam power, 35 mA beam current and 2857 MHz RF. The electron beam irradiation was carried out at dose rate of 1 kGy/3.5 min. Both the irradiation treatments were carried out at room temperature (25 ± 2°C, RH 75%) under normal light conditions. To ensure uniformity of dose, the samples irradiated with gamma rays were treated by rotating 360°during the irradiation time. The electron beam irradiation was performed by double sided irradiation to minimize the variation in penetration depth among the radiation sources, because electron beam has lower penetration ability than those of gamma rays. To ensure that fruit receives the exact dose, cericcerous, and alanine EPR dosimeters were placed in each fruit box for each treatment at high as well as low dose spots and the actual doses were within 5% of the targeted dose. The After completion of irradiation, samples were evaluated for microbial and physico-chemical quality parameters. Triplicate samples were used for each treatment and parameter.

Determination of color values, instrumental texture, and rehydration ratio
The color of non-irradiated and irradiated dried apricot and quince samples were determined in terms of L*(lightness), a*(redness), and b*(yellowness) values using Hunter color meter (Konica Minolta CM-5, Tokyo, Japan). The color difference (ΔE*ab) was calculated using the equation Texture is a major component of consumer preference for eating quality in fresh as well as dried foods in addition to appearance and flavor (King et al., 2000). Harker, Kupferman, Marin, Gunson, and Triggs (2008) reported that textural parameters have an universal impact on the acceptability and purchase intentions and consumer acceptability increases with increase or retention of texture. Texture measurement of control and gamma irradiated apricot and quince chips was conducted by means of texture analyzer (TA-XT2i of Stable Micro Systems, Godalming, England) as per the method of Velickova, Winkelhausen, and Kuzmanova (2014). All textural measurements were performed at room temperature (8 ± 2°C) using three replicates each consisting of 10 samples of apricot and quince. In case of apricot texture was measured at four different positions (two sides and two edge) while as in dried quince measurements were done at middle and two end positions for each sample and the mean of 40 and 30 readings was reported for apricot and quince, respectively. To determine rehydration ratio, known weight of the dry sample was placed in a beaker and 100 ml of distilled water was added followed by boiling for 5 min on a heating element. Sample was cooled, drained, and weighed.
Rehydration ratio (RR) was calculated using where a is the weight of dehydrated sample and b the weight of rehydrated sample.

Microbial analysis
Total bacterial count (TBC) and yeast and mold count (YMC) were determined by the serial dilution method using pour-plate technique (Aneja, 1996) and expressed as log cfu/g of sample.

Overall acceptability (OAA)
Overall acceptability based on color, texture, and taste was done by a trained panel of seven judges having good experience in sensory analysis of foods on round table basis using a 4-point scale where 4 = excellent, 3 = good, 2 = fair, and 1 = poor. Fifteen grams of sample in triplicates were selected randomly, coded and served to judges for evaluation of color, texture, and taste. The testing was under taken in a place free from extraneous odors and sound. The panel test was carried out under normal light conditions. The temperature of the samples during tasting was the existing normal temperature. The panelists were instructed to evaluate the taste of the samples by chewing the dried samples and rate the acceptability of taste in terms of sweetness. The overall acceptability was reported as the mean of the triplicate values of color, texture, and taste.

Analysis of sugars, total ascorbic acid, and beta carotene
Sugar content (glucose, fructose, and sucrose) was determined by using JASCO, Japan make HPLC system (model, LC-NetII/ADC), fitted with an automatic degassing unit, RI-2031 detector, PU-2080 pump and a HiQ-Sil C18 column (size 4.6 × 250 mm) as per the method of Beitane, Straumite, and Cinkmanis (2013). Total ascorbic acid was calculated as sum of ascorbic and dehydroascorbic acid, which were determined by HPLC method fitted using UV-2070 detector asper the method of Pasternak, Potters, and Caubergs (2005). βcarotene was also determined by HPLC as per the method of Díaz-Mula et al. (2008).

Total phenols and flavonoids
Total phenols were determined by Folin-Ciocalteu assay (Waterhouse, 2002) and total flavonoid content was measured by the aluminum chloride spectrophotometric assay (Chen, Lin, & Hsieh, 2007). Total phenols and flavonoids were determined with the use of an external standard curve of gallic acid and catechin in the concentration range of 0.1-1.0 mg/mL and expressed as mg gallic acid and catechin equivalents per 100 g.
2.7. DPPH radical scavenging activity, ferric reducing ability power (FRAP), and hydroxyl radical scavenging activity (HRSA) DPPH radical scavenging activity of extracts was measured according to the method of Brand-Williams, Cuvelier, and Berset (1995). The reducing power of extracts of dried apricot and quince was determined according to the method of Oyaizu (1986). Hydroxyl radical scavenging assay was carried out according to method of Elizabeth and Rao (1990) with minor modifications. The corresponding EC 50 values for all the three assays were calculated from the graph of concentration versus inhibition percentage. In all the assays used, the antioxidant activity of the control and gamma irradiated apricot and quince samples were compared in terms of EC 50 values against the standard ascorbic and gallic acid.

Statistical analysis
The data were analyzed statistically using completely randomized design experiment (Cochran & Cox, 1992). For each measurement, three replicates of samples were tested per treatment and mean ± standard deviation values were reported. Analysis of variance (ANOVA) of the data was performed using MINITAB statistical analysis software package (Minitab, version 11.12, 32 bit, Minitab, Inc., State College, PA, USA).

Results and discussion
3.1. Evaluation of color, texture parameters, and rehydration ratio To compare the effect of gamma and electron beam irradiation on the color scores of dried apricot and quince, the ΔE* ab values were calculated from Hunter a, b, and L values. According to Young and White (1985), a ΔE* ab value in the range of 0-0.5 indicates an imperceptible difference in color between the samples, 0.5-1.5 indicates a slight difference, 1.5-3.0 indicates a just noticeable difference, 3.0-6.0 a remarkable difference, 6.0-12.0 an extremely remarkable difference in color, and value above 12.0 indicates color of different shade. Effect of radiation treatments on color scores of dried apricot and quince is shown in Table 1. The data analysis indicated that no significant (p ≤ 0.05) difference existed among color parameters between unirradiated and irradiated dried apricot samples irradiated using either gamma or electron beam irradiation. However, in quince samples L and h values were significantly (p ≤ 0.05) higher in 3.0 and 4.0 kGy irradiated samples for both the methods of irradiation used. The ΔE* ab values were in the range of 0.3-1.6 for apricot samples and 1.1-1.9 for dried quince samples for both the methods of irradiation. The ΔE* ab values clearly indicate that there was no significant (p ≤ 0.05) noticeable difference induced in color of the dried apricot by the two methods of irradiation. For dried apricot samples, the ΔE* ab values were same for 1.0, 2.0, and 4.0 kGy doses for both the methods of irradiation. However, in dried quince, a just noticeable difference in color was observed at 3 and 4 kGy of gamma irradiation and 2 and 3 kGy of electron beam irradiation. These results demonstrate that color changes due to radiation exposure did not proceed in a predictable manner. Similar results on color changes during radiation processing of red pepper powder using gamma and electron beam irradiation are reported by Jung et al. (2015). Effect of irradiation type and dose on textural parameters (hardness, gumminess, and chewiness) of dried apricot and quince is shown in Table 1. Data analysis indicated that both dose applied and type of irradiation used had a profound effect on textural parameters of both the fruits. Hardness of dried apricot and quince decreased significantly (p ≤ 0.05) at doses above 2.0 kGy for both the methods of irradiation applied. In case of dried apricots, decrease in hardness was 25.6% and 34.1% at 3.0 and 4.0 kGy of gamma ray irradiation compared to 20.5% and 28.9% for electron beam irradiation. Similarly in dried quince samples, hardness decreased by 16.4% and 23.1% at 3.0 and 4.0 kGy dose of gamma irradiation compared to 13.9% and 20.6% at same dose of electron beam irradiation. Both chewiness and gumminess also recorded a decreasing trend with dose for both methods of irradiation. The decrease in gumminess and chewiness was significantly (p ≤ 0.05) higher at doses above 2.0 kGy. For both the methods of irradiation, gumminess, and chewiness of dried apricots decreased in the range of 9.5-34.5% and 12.0-37.5%, respectively. On the other hand, in quince samples the corresponding decrease in the two parameters was in the range of 5.1-25.6% and 14.0-34.2% for the two methods of irradiation. Further, close comparison of the methods of irradiation applied indicated that decrease in hardness was insignificantly (p ≥ 0.05) higher in samples treated with gamma irradiation compared to electron beam irradiation. Similar trend in textural parameters has been reported in apples and pears irradiated by gamma rays, electron beams, and X-rays (Jung et al., 2016). Numerous studies have reported that loss of textural parameters Table 1. Effect of gamma and electron beam irradiation treatments on physical, microbiological and sensory quality parameters of dried apricot and quince.  in dried as well as fresh fruits induced by irradiation is associated with the degradation of pectic substances which act as cementing materials between the middle lamella of cell walls and depolymerization of cell wall materials like cellulose (Kim & Yook, 2009). Effect of dose and type of irradiation on the rehydration ration of dried apricot and quince samples is depicted in Table 1. Data analysis revealed that gamma as well as electron beam irradiation caused a decrease in rehydration ratio of dried apricots and quince. The decrease in rehydration ratio was statistically nonsignificant (p ≥ 0.05) between control, 1.0 and 2.0 kGy irradiated samples. However, beyond 2.0 kGy dose, decrease in rehydration ration of apricot and quince samples was significantly (p ≤ 0.05) higher for both the methods of irradiation. In case of dried apricots, decrease in rehydration ratio recorded at 3.0 and 4.0 kGy dose was of the order of 9.5% and 14.3% for gamma ray irradiation and 5.9% and 9.5% for electron beam irradiation respectively. The decrease in rehydration ratio of quince samples irradiated at γirradiation doses of 3.0 and 4.0 kGy was 10.3% and 14.8% compared to 8.9% and 11.2% for same dose of electron beam irradiation. Decrease in rehydration ratio has also been reported in other irradiated foods and has been attributed to decrease in water holding capacity as a result of disruption in cellular integrity and pore size during radiation treatment. (Wei et al., 2014).

Microbial load and overall acceptability
Data analysis pertaining to microbial load indicated that gamma as well as electron beam irradiation treatment of dried apricots and quince was significantly (p ≤ 0.05) effective in reducing the number of both yeast and mold and bacterial count in a dosedependent manner (Table1). Before irradiation, dried apricots and quince samples had average yeast and mold count of the order of 4.5 ± 0.2 and 3.5 ± 0.2 log cfu/g sample and average bacterial count of 4.6 ± 0.2 and 3.7 ± 0.2 log cfu/g sample. After gamma irradiation treatment at dose of 1.0 kGy, log reduction of 2.2 and 1.6 was recorded in yeast and mold count of dried apricot and quince. In samples treated with gamma irradiation at doses above 1.0 kGy, no yeast and mold count was detected just after treatment. Also in samples treated with gamma irradiation at doses of 3.0 and 4.0 kGy, no bacterial count was observed after the treatment. In samples treated with electron beam irradiation at dose of 2.0 kGy, log reductions of the order of 1.9, 1.1, 2.2, and 1.5 were recorded in yeast and mold count and bacterial count of dried apricot and quince respectively. Electron beam irradiation at 3.0 and 4.0 kGy also proved effective in reducing the number of viable microorganisms to below detection limits. This desirable and beneficial effect of radiation processing on decreasing the number of viable cells in dried foods is attributed to the direct effect of radiations. When radiations interact with microorganisms, the DNA present in the cells is the point of target. As the radiations hit the DNA molecule, the hydrogen bonds in DNA; which are responsible for double helical structure of DNA are broken. This hydrogen bond breaking favors the breaking of double helical structure of DNA and renders the DNA unable to replicate, thereby causing death of the cell (Egea, Sanchez-Bel, Martinez-Madrid, Flores, & Romojaro, 2007;Swailam, Hammad, Serag, Mansoar, & Abuel-Nour, 2007). Radiation disinfestations of these microbial contaminants has immense importance in national and international trade of dried fruits. Therefore, from public viewpoint, present study revealed that radiation pasteurization of dried apricots and quince at optimized doses of 3.0 and 4.0 kGy of gamma and electron beam irradiation marks a definite advance in the merchandising of these dried products thereby benefiting the growers who are involved in and solely dependent on their cultivation. Overall acceptability data based on color, texture and taste of the dried apricots and quince is depicted in Table 1. Data analysis revealed that there existed no significant (p ≥ 0.05) difference in sensory attributes like color, texture, and taste as well as in OAA between control and irradiated samples treated with either gamma or electron beam irradiation. The OAA of control and irradiated dried apricot and quince samples ranged between 4.5 and 4.8 just after gamma and electron beam irradiation. Similar nonsignificant (p ≥ 0.05) differences were reported in appearance, texture and overall acceptability values among irradiated and control apricot samples immediately after electron beam irradiation in the dose range of 1.0-3.0 kGy (Wei et al., 2014).

Sugar content, total ascorbic acid, and beta carotene
The sugar content of unirradiated and irradiated dried apricots and quince samples is depicted in Table 2. Among the sugars identified, fructose was present in higher concentration than glucose and sucrose in both the dried fruits. In case of dried apricot; fructose, glucose and sucrose were present at an average concentration of 38.4 ± 1.3, 35.1 ± 1.4, and 10.2 ± 1.4 g/ 100 g DW where as in dried quince the concentrations of the three sugars were 31.1 ± 1.3, 25.5 ± 1.2, and 8.2 ± 1.1 g/100 g DW, respectively. After irradiation, sugar content of both the fruits increased with dose for both the methods of irradiation. Fructose content of dried apricots treated with either gamma or electron beam irradiation recorded a significant (p ≤ 0.05) increase at doses above 1.0 kGy while as glucose and sucrose content of dried apricots and quince showed significant increase at doses above 2.0 kGy. In dried apricots treated with 4.0 kGy of gamma irradiation, the increase in fructose, glucose, and sucrose content over control was of the order of 10.6% and 25.7% compared to 8.9%, 7.8%, and 17.5% for same dose of electron beam irradiation. Dried quince treated with gamma and electron beam irradiation at 4.0 kGy recorded an enhancement in fructose, glucose, and sucrose contents of the order of 14.8%, 15.5%, 30.1% and 11.2%, 14.2%, 27.2%, respectively. The significantly (p ≤ 0.05) higher increase in sugar contents in irradiated samples has also been reported by Hussain, Meena, Dar, and Wani (2011). Increase in sugar content upon irradiation is attributed to the degradation of higher polysaccharides such as starch and cellulose in to lower monosaccharides due to the breaking of glycosidic bonds. Further, the increased chain scission during irradiation treatment and the subsequent decrease in interchain hydrogen bonds also contribute to the increase in lower monosaccharides especially sugars (Liu, Ma, Xue, & Shi, 2012). The data pertaining to total ascorbic acid showed no significant (p ≥ 0.05) difference in ascorbic acid content of control and irradiated apricot and quince samples treated with gamma and electron beam irradiation immediately after the treatment; although the contents were marginally lower in irradiated samples compared to unirradiated samples (Table 2). Total ascorbic acid contents in unirradiated apricots and quince were in the range of 21.9 ± 0.22-22.1 ± 0.23 mg/100 g and 24.8 ± 0.24-25.1 ± 0.13 mg/100 g, respectively. On the other hand, gamma and electron beam irradiated apricot and quince samples showed total ascorbic acid content in the range of 20.5 ± 0.24-21.9 ± 0.24 and 23.5 ± 0.21-24.8 ± 0.24 just after irradiation. Among treatments, gamma irradiated samples of apricot and quince showed slightly lower ascorbic acid content compared to electron beam irradiated ones at all the doses applied. The decrease in total ascorbic acid content in 4.0 kGy gamma and electron beam irradiated apricots was 6.4% and 5.4%, respectively; where as in quince samples, decrease of 5.2% was noticed for same dose of irradiation for both the methods of irradiation used. During food irradiation, maximum loss of ascorbic acid occurs via indirect effect of radiations, i.e. through products of water radiolysis especially the OH radicals rather than the direct effect of radiations (Wong & Kitts, 2001). In the present study, no significant difference in ascorbic acid contents between control and irradiated samples was observed just after irradiation; which is attributed to the fact that in dried foods, the formation of products of water radiolysis is limited; hence, net effect on total ascorbic acid loss is also negligible. Murcia et al. (2004) reported that irradiation up to 10 kGy did not have any significant deleterious effect on antioxidant compounds like ascorbic acid of dried foods; which was attributed to the low water content, which limited the possibility of free radicals being formed.
Beta-carotene content was determined in dried apricots only and is shown in Table 2. Average beta carotene content of unirradiated dried apricots was 13.3 ± 0.23 mg/100 g. The data analysis indicated that beta carotene increased with dose in both the methods of irradiation used and revealed the existence of positive correlation (r = 0.89) between irradiation treatment and β-carotene content. The significant (p ≤ 0.05) increase in beta carotene was recorded at doses above 1.0 kGy of gamma irradiation and 2.0 kGy of electron beam irradiation. The beta carotene content of dried apricots irradiated with gamma and electron beam irradiation was in the range of 13.8 ± 0.24-16.7 ± 0.34 mg/100 g. Among the irradiation doses, significantly (p ≤ 0.05) higher beta carotene content was recorded in samples irradiated at 4.0 kGy of gamma irradiation. The data analysis also revealed that beta carotene content of dried apricots irradiated at 3.0 kGy of gamma irradiation and 4.0 kGy electron beam irradiation was same (15.8 mg/100 g). In samples irradiated at 4.0 kGy of gamma irradiation, percentage increase in beta carotene content was 24.6% compared to 19.7% for same dose of electron beam irradiation. Higher β-carotene content of irradiated samples is explained on the basis of the effect of irradiation on increasing the extractability of carotenoids because of the changes in the cellular structure (Hussain et al., 2011). Gamma or electron beam irradiation makes the cell walls more permeable and open which results in increased diffusion of extracting solvent and enhanced swelling of the cells. This enhanced swelling of the cell walls favors the efficient leaching and extraction of the constituents (El-Samahy, Youssef, Askar, & Swailam, 2001). Moreno et al. (2007) also recorded an increase in carotene levels of mango irradiated at low doses (0.5-1.5 kGy) using gamma rays. In another study; Sebastiao, Almeida-Muradian, Romanelli, Koseki, and Villavicencio (2002) reported no change in total betacarotene upon irradiation (0-20 kGy) of dehydrated parsley. Wen, Chung, Chou, Lin, and Hsieh (2006), also reported no change in beta-carotene level upon irradiation (0-14 kGy) of lyceum fruit. Thus, irradiation treatment of dried apricots has proved beneficial in enhancing the release of nutritionally rich and biologically active constituent of apricots rather than causing any significant degradation.

Total phenols and flavonoids
Effect of gamma and electron beam irradiation on total phenolics and flavonoids of dried apricots and quince is shown in Table 2. The data analysis indicated a dosedependent increase in total phenol and flavonoid content of dried apricot and quince in both the methods of irradiation. In dried apricots strong positive correlation (r = 0.95) existed between dose and total phenols and flavonoids, while as moderate positive correlation (r = 0.88) was observed in quince samples between dose and total phenols and flavonoids for both the methods of irradiation. Statistical analysis of the data also indicated that there was no significant (p ≥ 0.05) difference in total phenols and flavonoid content of unirradiated and 1.0 kGy gamma and electron beam irradiated quince samples just after irradiation. Similar trend in total phenols and flavonoids was also observed in quince samples treated with 2.0 and 3.0 kGy of gamma and electron beam irradiation. In irradiated apricot and quince samples, percentage increase in total phenols was in the range of 1.6-7.8% and 0.3-2.0% under gamma irradiation and 2.1-7.8% and 0.6-2.1% under electron beam irradiation respectively. Increase in phenolic contents after irradiation with sanitization doses has also been reported for other plant foods such as Justica Adhatoda, a medicinal plant (Rajurkar, Gaikwad, & Razavi, 2012). A more recent study on black soybean extracts also demonstrated increase in total phenols during irradiation and the increase occurred in a dose-dependent manner (Krishnan et al., 2018). The observed increased total phenol and flavonoid content in irradiated dried apricot and quince could be attributed to the release of phenolic compounds from glycosidic components, degradation of larger phenolic compounds into smaller ones by irradiation, with a concomitant improvement in the extraction yield of the phenolic compounds because of the change in tissue structure by gamma and electron beam irradiation (Harrison & Were, 2007;Stajner, Milosevic, & Popovic, 2007;Variyar, Limaye, & Sharma, 2004).
3.5. DPPH radical scavenging activity, ferric reducing ability power, and hydroxyl radical scavenging activity Effect of gamma and electron beam irradiation treatments on DPPH radical scavenging activity of dried apricot and quince is shown in Figure 1(a-d). It is clear from the figure that DPPH radical scavenging activity of dried apricot and quince increased significantly (p ≤ 0.05) with concentration and dose for both methods of irradiation. However, statistical analysis of data indicated that in dried apricot samples treated with gamma or electron beam irradiation, no significant (p ≥ 0.05) difference in DPPH radical scavenging activity was observed between control and 1.0 kGy samples at concentration of 25 µg/ml. Further, in case of control apricot samples; inhibition in DPPH activity was nonsignificant (p ≥ 0.05) up to concentration of 50 µg/ml and beyond that inhibition in DPPH activity increased linearly with concentration. On the other hand in control quince samples, significant (p ≤ 0.05) differences existed in DPPH radical scavenging activity at all the concentration. Among the treatments, maximum inhibition in DPPH activity was observed in samples irradiated at 4.0 kGy of gamma or electron beam irradiation at concentration of 300 µg/ml. Comparison of the data also showed that dried apricot and quince samples treated with 4.0 kGy of gamma and electron beam irradiation recorded an increase of 36.2%, 35.1%, 42.4%, and 41.4% in DPPH radical scavenging activity over control at concentration of 300 µg/ml, respectively. Krishnan et al. (2018) also reported an increase of 55% in DPPH radical scavenging activity of gamma irradiated black soybean extracts. The reducing power of control and irradiated dried apricot and quince is shown in Figure 2(a-d). The data analysis revealed that reducing power recoded a dose-dependent increase with concentration for both methods of irradiation. It could be seen from the data that ferric reducing power of dried apricot and quince increased nonsignificantly (p ≥ 0.05) with concentration up to 75 µg/ml in the dose range of 1.0-3.0 kGy for both methods of irradiation. Interestingly the ferric reducing power of apricot and quince samples irradiated at 4.0 kGy of gamma and electron beam irradiation was significantly (p ≤ 0.05) higher at all the concentrations compared to other doses and control. Ferric reducing power of dried apricot and quince samples treated with 4.0 kGy of gamma and electron beam irradiation recorded an increase of 39.6%, 34.8%, 40.7%, and 33.4% over control at concentration of 300 µg/ml respectively. Based on the concentration effect, it can also be inferred that up to concentration of 50 µg/ml no significant (p ≥ 0.05) difference was observed in ferric reducing power of control and 1.0 kGy apricot and quince samples irradiated with gamma and electron beam irradiation. Increase in reducing power during irradiation has also been observed in other foods (Hussain, Wani, Meena, & Dar, 2010).
Effect of gamma and electron beam irradiation treatments on hydroxyl radical scavenging activity of dried apricot and quince is shown in Figure 3(a-d). Hydroxyl radical scavenging activity also recorded a significant (p ≤ 0.05) increasing trend with increase in concentration and dose of irradiation under both methods of irradiation. In dried apricot samples treated with gamma irradiation, no significant (p ≥ 0.05) difference in HRSA was observed between control and 1.0 kGy samples at concentration of 25 µg/ml. Similar trend in HRSA was also noted in samples treated with 1.0 and 2.0 kGy gamma irradiation at concentration of 50 µg/ml. In electron beam irradiated apricots, no significant difference (p ≥ 0.05) in HRSA was observed in control, 1.0 and 2.0 kGy samples at concentration of 25 µg/ml and 50 µg/ml respectively. Concentration data also revealed a nonsignificant (p ≥ 0.05) difference in HRSA in control apricot samples up to concentration of 75 µg/ml. On the other hand, in 1.0 kGy gamma and electron beam irradiated apricot samples, similar observation was recorded up to 50 µg/ml concentration. In all other gamma and electron beam irradiated samples, HRSA increased significantly with concentration. HRSA of control and 1.0 kGy gamma and electron beam irradiated quince samples also differed marginally (p ≥ 0.05) with respect to each other at concentration of 25 µg/ml. Concentration data indicated that in control quince samples, HRSA was statistically nonsignificant up to 50 µg/ml concentration. Among the irradiation treatments, 4.0 kGy of gamma and electron beam irradiation resulted in significantly (p ≤ 0.05) higher HRSA of apricot and quince samples at concentration of 300 µg/ml. Dried apricot and quince samples treated with 4.0 kGy of gamma and electron beam irradiation recorded an increase of 32.6%, 36.6%, 42.5%, and 39.4% in HRSA over control at concentration of 300 µg/ml, respectively. The enhancement in antioxidant activities through ionizing radiations has been also reported by many authors. Variyar et al. (2004) reported that gamma irradiation is capable of breaking the glycosidic bonds of polyphenols, thereby releasing soluble phenols of low molecular weight, leading to an increase of antioxidant rich phenolics responsible for higher antioxidant activities. Increased antioxidant activities of irradiated foods have also been attributed to increased enzymatic activity (phenylalanine ammonia-lyase and peroxidase) or to the increased extractability of antioxidant compounds from the tissues (Bhat, Sridhar, & Bhushan, 2007). Positive correlations have been found between antioxidant activity and phenolics, indicating that antioxidant activity is directly related to phenolic profiles. Hussain et al. (2011) andPerez, Calderon, andCroci (2007) also reported a significant correlation coefficient between total phenolics and antioxidant activity in gamma irradiated apricot and rosemary extracts. Another likely explanation for increase in antioxidant activity in irradiated apricot and quince is that irradiation leads to the formation of Maillard reaction products (MRPs) and these MRPs possess antioxidant potential in actual food system (Chawla, Chander, & Sharma, 2007). These MRPs are able to scavenge the hydroxyl radical and superoxide anion radical to the extent of 33% and 58%, respectively.

EC 50 values in antioxidant activities
Antioxidant activity is the main physiological role of functional foods. In biological systems, reactive oxygen species (ROS) and radicals may oxidize nucleic acids, proteins or lipids and result in initiation of number of degenerative diseases. To reduce the incidence of chronic diseases including heart disease and other cancers, the antioxidant activity is the main factor governing the efficacy of the foods. The EC 50 is an important parameter to compare the radical scavenging potential of fruits and vegetables and evaluate the effects of processing methods on the levels of bioactive compounds responsible for health promoting effects. Therefore, to compare the effect of gamma and electron beam irradiation on antioxidant potential of dried apricot and quince, the results obtained from the DPPH radical scavenging, ferric reducing power, and hydroxyl radical scavenging activity were expressed as EC 50 values. The obtained EC 50 values of control and irradiated apricot and quince for different antioxidant assays were compared with standard gallic and ascorbic acid and are presented in Table 3 can be inferred that both gamma and electron beam irradiation have beneficial effect in modifying the nutraceutical potential of dried apricot and quince; however, close comparison of the EC 50 values of the two fruits for the three studied assays with the standard antioxidants such as gallic and ascorbic acid indicated that DPPH radical scavenging activity and FRAP of control and irradiated samples was significantly lower than standard gallic and ascorbic acid. However, for hydroxyl radical scavenging assay, EC 50 values of gamma and electron beam irradiated dried apricot and quince were significantly (p ≤ 0.5) lower; particularly in 3.0 and 4.0 kGy irradiated samples compared to standard gallic and ascorbic acid. Rajurkar et al. (2012) and Perez et al. (2007) also reported significant radiation induced decrease in EC 50 values for various antioxidant assays, thereby confirming that radiation enhances the antioxidant activity of the treated foods. The significantly lower EC 50 values recorded in irradiated samples are attributed to the presence of higher levels of total phenolics and flavonoids.

Economic analysis of food irradiation
The cost of irradiating food is estimated at between1.43 and 28.7 rupees per kilogram of the product. This wide Values are mean ± SD (n = 3); LSD (d × IT) = least significant difference (dose × irradiation type) at p ≤ 0.05; RSA = radical scavenging activity; IP = inhibition percentage; FRAP = ferric reducing ability power; HRSA = hydroxyl radical scavenging activity; OD = optical density; GA = gallic acid; AA = ascorbic acid Values with in treatments with different superscript lowercase letters (a-e) differ significantly (p ≤ 0.05).
range results from the many variables involved in any irradiation operation. Among the factors which affect the cost of irradiation are the dose of radiation employed (which can vary widely depending on the purpose of the treatment), the volume and type of product being irradiated, the type and efficiency of the radiation source, whether the facility handles one or a variety of food products, the cost of transporting food to and from the irradiator, special packaging of the food, and the cost of supplementary processing such as freezing or heating. The approximate cost required for construction of an irradiation plant large enough to permit economic operation is estimated in the range of rupees 10-15 crores excluding the land cost. However, based on the diverse application of technology, processing cost is quite inexpensive compared to other methods of preservation. Approximate costs of irradiation are in the range of rupees 0.50-1.0/kg of the produce for a low-dose application such as sprout inhibition and rupees 3-5/kg for a high dose application such as treatment for microbial decontamination. The processing costs can further be brought down in a multipurpose facility by irradiating a variety of products throughout the year. Extension in shelf life of the produce also offsets the extra cost. Radiation processing can have a stabilizing effect of the market price of the product by reducing storage and distribution losses, improving the hygiene of food and increasing availability of the produce and avoiding market glut. Additional benefit of the processing to overcome quarantine barriers for export will further reduce the processing cost and will help in good market returns. However, comparison on the basis of safety, additional cost involved in the replenishment of the source after few half lives and above all safe disposals of the natural radioactive sources like Co-60 may affect the economic utility of gamma irradiation compared to electron beam irradiation in future.

Conclusion
Based on the results of the present study, it is concluded that both gamma and electron beam irradiation were significantly effective in maintaining the physicochemical quality and enhancing the antioxidant potential of dried apricot and quince. Results of rehydration ratio, inferred that electron beam irradiation could prove beneficial compared to γ-irradiation in preserving the cellular integrity and minimizing the disruption in pore size, thus maintaining higher re-constitutional capacity and textural quality of the irradiated foods. EC 50 data indicated that dried apricot and quince irradiated at 3.0 and 4.0 kGy of gamma or electron beam can act as good quenchers of hydroxyl radicals and may prove helpful in preventing the hydroxyl radical induced damage to important bio-molecules. Further, microbial analysis data demonstrated that electron beam irradiation at doses of 3.0 and 4.0 kGy can be used an equally potential alternative to chemical fumigants as gamma irradiation for use as phyto-sanitary treatment and in overcoming the quarantine barriers for export of dried apricot and quince. Finally, the present study recommends that dose of 3.0-4.0 kGy of gamma or electron beam irradiation can be used as phytosanitary treatments for dried apricot and quince to achieve microbial inactivation and overcome quarantine barriers for export purposes without any deleterious effect on overall acceptability and antioxidant quality of the product.

Disclosure statement
No potential conflict of interest was reported by the authors.