Evaluating the effect of X ray irradiation in the control of food bacterial pathogens

1 Introduction

Food manufacturing environment may support the growth of pathogenic microorganisms that may cause illnesses and even deaths to humans (Todd, 2014). Human complications are caused by both the ingested microbes through contaminated food and the toxins produced by the microbes present in food.

Natural antimicrobials such as the extracts of different microbial metabolites have been shown to inhibit pathogenic bacteria in food (Lozada et al., 2022; Yassin et al., 2022). The microbial treatment, however, is laborious and cannot easily be used to large amounts of food materials. Nanoparticles of different metals such as silver have been used in food packages to ensure food safety (Carbone et al., 2016). However, serious concern about the accumulation of metal nanoparticles in the environment and humans has raised recently (Rzayev et al., 2022; Siddiqui and Alrumman, 2021) Therefore, interest towards the use of physical control measures such as temperature, UV rays, and X rays has increased (Barkai-Golan and Follett, 2017). The physical methods aim to kill or inhibit the growth of undesirable microbes present in the food or in the food processing environment (Lung et al., 2015). The problem using UV-rays and heating above 150 °C is that they may change the chemical structure, odor, and taste of food (Todd, 2020). The recent advanced commercially available technology is X-ray radiation, of which use is increasing.

X-ray was shown to eliminate bacteria such as E. coli from parsley leaves (Mahmoud, 2012a). Dairy products, meat, seafood, berries, and vegetables have successfully been treated with X ray; the amounts of bacteria have decreased to minor amounts (Mahmoud et al., 2016; Moosekian et al., 2012; Ricciardi et al., 2019).More information on different foods and the possible change in taste and nutritional value is still needed, as reviewed recently (Zehi et al., 2020).

For the X ray treatment, the general assumption is that the effectiveness of the treatment depends only on the quantity of energy deposited in the target food (Gomez-Lopez et al., 2022). However, the ISO standard does not include technical requirements for the minimum energy or dose of the treatment. This is problematic because a wide range of different values can be chosen. Too low values chosen for energy and too few irradiation cycles are not efficient in eliminating bacteria from food. Too high values are unnecessary and may cause changes in the nutritional value and taste of food. Doses between 0.1 kGy and 10 kGy have been reported as efficient in reducing bacteria in different foods in a recent review (Zehi et al., 2020). More detailed information on the optimal treatment is needed and more food materials should be tested. In this study, we evaluated the efficiency of different doses of X-ray irradiation and the treatment cycles needed to control food bacteria using ten different food materials, both liquid and solid. We hypothesize that higher dose eliminates more bacteria. An experiment consisting of a wide range of doses with three irradiation cycles with a subsequent bacterial count was carried out. We also studied whether the irradiation causes chemical changes in the food.

2 Materials and methods

3 Results

Five pathogens namely C. jenjuni, B. abortus, E. coli, B. cerus, and C. perfringes were identified (Table 1).

After the first X ray cycle, the bacterial counts were high (TNTC- Too numerous to count) at the lowest doses (0.1–0.5 kGy/h) (Table 2). Higher doses (1 – 2 kGy/h) gave bacterial counts of 250–100 CFU. The second cycle reduced bacterial counts in all foods remarkably, the bacterial counts varying between 20 and 36 CFU in the two lowest doses (Table 3). The highest dose gave 8 – 15 CFU. After the third cycle, no bacteria were observed at the highest dose 2 kGy/h (Table 4). Low counts (0 – 4 CFU) were observed also with 1.5 kGy/h dose.

The turbidometric analysis of the foods before the treatment gave absorbance values between 1.85 and 8.6 (Table 5). After the treatment (2 kGy/sec) the values varied between 0.01 and 0.3 showing a drastic decrease. No changes were observed for the amounts of sugar, fat, proteins, and vitamin C due to the X ray irradiation (Table 6).

4 Discussion

X-ray technology has been shown efficient in reducing bacterial pathogens in foods as reviewed recently (Zehi et al., 2020). However, the technique needs the clarification of the doses used. Both low and high doses have been used. While a low dose of 0.75 kGy decreased bacterial counts to almost zero in ready-to-eat shrimp (Mahmoud, 2009), a relatively high dose of 3 kGy was needed to eliminate bacteria in raw chicken meat (Song et al., 2018).

This study was conducted in three parts, in first part the food samples were treated with X ray in five different doses (0.1, 0.5, 1.0, 1.5 and 2.0 kGy/sec for 10 min). Here, 40–45 % of reduction observed in last dose (2.0 kGy/sec). In the second treatment there was a slight variation occurred between the last dose of 1st treatment and 1st dose of 2nd treatment. Similarly, last dose of 2nd treatment and 1st dose of 3rd treatment also have 30–35 % of variation. It is because of the influence of X ray on the growth and multiplication of the pathogens (Nohemi et al., 2022). Besides, there is no variation in components and taste of the checked food materials. Inactivation of pathogens isolated from spinach leaves by the application of X ray dose 0.1–2 kGy with no changes in colour or texture, in other hand this irradiation effectively control the pathogenic microbiota while preservation of food (Mahmoud et al., 2010).

Radiation processing of food one of the most valuable methods for the preservation and disinfection of food (Lima et al., 2018; Mahmoud, 2012a; Mahmoud et al., 2016).Irradiation of 2 kGy reduced natural bacteria in chicken meat, shrimps and strawberries (Van Calenberg et al., 1999). Similarly, Salmonella enterica was reduced in chicken meat to acceptable levels (Mahmoud et al., 2015). E.coli was reduced in meat with 0.3 to 0.8 kGy (Cho and Ha, 2019; Curry et al., 2000; Kundu, 2013). (Zehi et al., 2020) reported that by the application of X ray doses between 1 and 5 kGy decreased the bacterial growth in Atlantic oysters (Crassostrea virginica, without causing any changes in colour. Moreover, the count of pathogenic bacteria such as E. coli, Salmonella and Listeria were decreased by the application of X ray dose 0.6 kGy (Mahmoud, 2012b). (Tallentire and Miller, 2015) explained that X rays have high penetration power which have the ability to kill bacteria by damaging its DNA. No human health effects have been shown so far (Zehi et al., 2020). Our study showed that the efficient X ray dose was 1.5 and 2 kGy when the dose was given three times, ten min per cycle. We can report two remarkable observations. The first is that a very high amounts of bacteria, too high to be counted, was reduced to uncountable amounts with this treatment. The second is that the efficiency was shown with ten different foods including solid and liquid materials.

5 Conclusion

The results obtained from the study revealed that the X ray dose 1.5 kGy and 2 kGy have effective power for the inactivation of food pathogens in various solid and liquid foods. The treatment was efficient for ten types of liquid and solid foods opening up an immense possibility for the control of bacteria causing severe infection to humans.