Effect of Microwave Irradiation on Pesticides Residues and Physiochemical and Microbial Properties of Dried Apricots during Storage Time

The use of pesticides has increased considerably for crop production in recent years. Despite advantageous properties of pesticides for controlling different pests and preventing diseases, they have many negative effects on humans and environment. Different methods have been proposed to reduce the effects of pesticides on fresh and dried foods, including washing, storage, peeling, heating, boiling, frying and bleaching, canning, freezing, etc, but they don't have enough ability in this regard (Ali Mohammadi and Jihadi 2014). For these reasons, efficient and novel methods such as microwave irradiation have received great attention to decrease residues of pesticides in vegetables and fruits. Reducing their residues can be effective in improving the quality of foods and human health (Guillet et al 2009, Kaushik et al 2016). Iran is the third largest producer of apricot in the world. Dried apricot has many nutritional and health benefits and is considered as healthy choice (Wani et al. 2017). In the present study, effect of microwave irradiation was evaluated on residues of Orthocide (trade name: captan) pesticide and physicochemical properties of dried apricots during storage.

Apricot fruits (Nasiri variety) were provided by agricultural jihad organization of Kermanshah province and were dried (Hussain et al. 2010). Then, Orthocide (trade name: captan) pesticide in three levels of 25, 50 and 75 ppb (μg/ kg) were inoculated to organic dried apricots. In the next stage, inoculated samples were subjected to microwave irradiation (2.5 and 5 min) and pesticide residues were determined after irradiation during two months of storage (Cieslik et al. 2011, Seid Mohammadi et al. 2012). Also, a series of samples without any pesticide inoculation were irradiated with microwave (2.5 and 5 min) and were evaluated in terms of ash content (AOAC 2005, 940.26), moisture content (AOAC 2005, 934.06), total phenolic content (Arabshahi and Urooj 2007), reducing sugar content (AOAC, 2005, 925.36), total microbial count, mold and yeast counts (Rahman et al. 2011), color (parameters of L*, b* and a*) (Basaran and Akhan 2010) and antioxidant activity (Arabshahi and Urooj 2007) in different storage times (0, 30 and 60 days). Obtained data were analyzed by repeated measure design and factorial design using analysis of variance (ANOVA) and least square means in significance level of 0.05 (p < 0.05).

The results showed that microwave irradiation caused a significant decrease in pesticide residues of dried apricot in all levels of pesticide inoculation (5.05-26.07 %) compared to control sample. This reduction can be attributed to existence hot spots and non-thermal effects of microwave (Sajjadi et al. 2016). In addition, increase of storage time had significant effect on reduction of pesticide residues (p < 0.05). Overall, the highest reduction amount in pesticide residues (26.07 %) was related to samples treated with microwave radiation for 5 min at zero time (Table 2). In accordance with our results, residue of cypermethrin pesticide in brinjal reduced after processing with microwave (Walia et al. 2010). Microwave radiation also led to an increase in the content of phenolic compounds and antioxidant activity (Figures 2 and 3) which may be associated with breakdown of covalent bonds between phenolic compounds and other components (such as protein and sugar) by microwave, increasing extraction efficiency of phenolic compounds and therefore antioxidant activity (Hayat et al. 2010a). Similar results have been reported by Igual et al (2010). Moreover, ash and reducing sugar contents of samples increased by microwave but a significant decrease was observed in the moisture content of dried apricot (p < 0.05). Microwave radiation could significantly diminish total microbial count and mold and yeast counts compared to control sample. This can be justified by thermal and non-thermal effects of microwave on microorganisms (Heddleson and doores 1994, Kozempel et al. 1998). The lowest microbial count (2.39 log CFU/g) was related to samples treated with microwave for 5 min at zero time. Similarly, microbial load of saffron samples decreased after microwave irradiation (Hosseini Nejad et al. 2003). Also, irradiation with microwave led to a decrease in L* factor and an increase in a* (redness) and b* (yellowness) factors of samples (p < 0.05). The least color changes were found in samples irradiated with microwave for 2.5 min (Table 5). Color changes can be attributed to the degradation of vitamin C, carotenoids and other pigments due to heating effect of microwave and environmental factors. Also, loss in moisture content may be effective in making these changes. Similar results have been reported by Jogihalli et al (2017) for chickpea.

Microwave irradiation for 5 min resulted in more changes in determined parameters in comparison with 2.5 min of irradiation time and was more effective in reducing pesticide residues of dried apricot. Therefore, microwave irradiation can be considered as appropriate and promising way to decrease pesticides residues in fruits and vegetables.