Photo-Stimulated Luminescence Approach for Effective Identification of Irradiated Fruit

Round 1

Reviewer 1 Report

I believe this study has scientific merit and it is very useful topic. The subject of the manuscript “Photo-stimulated luminescence approach for effective identifi-2 cation of irradiated fresh and dried fruit” is in good relevance with the scope of Applied Science however, minor revision is needed. After analyzing the manuscript. I have some suggestions for the authors listed below before being considered for publication.

 

 

 

1-      In the Materials and Methods section, I recommend to add an image or general sketch for the setup and samples.

 

2-      In the whole manuscript, I love seeing numbers and it seems there is no quantitative analysis done (how better? How good? Comparison using percentage and number in the result obtained. I think the highlight of the results would be better if it is quantitatively highlight the finding of the current investigation. Please use numbers/percentage. 

Author Response

We are grateful for the useful comments/suggestions for the manuscript. We revised text, tables and figures following your indications, which greatly improved the quality of the work.

Below our reply point by point.

1-      A figure (Figure 1) reporting a description of the stimulated luminescence (1.a) and a sketch of the setup for photo-stimulated luminescence (PSL) measurement (1.b) has been added.

 2-      In Table.3 the total numbers of Negative, Intermediate and Positive responses have been replaced with their percentages and in the Results and discussion section (starting from line 217 ) as well as in the Conclusions (starting from line 287) the following sentence has been inserted:

Kiwi samples gave 50% of intermediate responses at 0.5 kGy and 12.5 % at 1 kGy, orange samples 87.5 % at 0.5 kGy and 93.5 % at 1 kGy. Also irradiated hazelnut and walnut samples provided intermediate responses, not observed by Bortolin et al. (2019) [26], especially at the lowest dose (25 %).

Reviewer 2 Report

 

Emanuela and co-workers reported the title of “Photo-stimulated luminescence approach for effective identification of irradiated fresh and dried fruit”, which the experimental is carefully conducted, and the results have been presented correctly, and the contents fall well into the scope of the journal. I recommend the publication of this paper after minor revision : 1. What is the mechanism of this method (Photo-stimulated luminescence approach)?  2. Please cite the following literature if you can: “Micropor. Mesopor. Mater., 2022, 112098; and “Inorganics, 2022, 10, 202”.

Author Response

We are grateful to the reviewer for the useful comments/suggestions for the manuscript. We revised text, tables and figures following your indications, which greatly improved the quality of the work. Below our reply point by point.

1. To better explain the mechanism of the method:

-           a figure (Figure 1) reporting a description of the stimulated luminescence (1.a) and a sketch of the setup for photo-stimulated luminescence (PSL) measurement (1.b) has been added.

-           in the Introduction and the Materials and Methods sections the text has been changed as follows:

Line 48: the following text has been inserted:

In fact, as shown in Figure 1, the minerals can keep track of irradiation for a long time due to the trapping of the electrons released by ionizing radiation in the crystalline defects (impurities, atom vacancies, etc.). The original arrangement of the charges can be restored by heating the minerals, which gives the electrons the energy necessary to leave the traps coming back to the original sites. When specific sites (the so-called luminescent sites) are involved, these processes are accompanied by light emissions (thermally-stimulated luminescence) which allows detecting irradiation.

Line 131: the following text has been inserted:

During the measurement the minerals in the sample were exposed to 60 pulses of infrared radiation (890 nm) to stimulate the emptying of the traps and restore the original assessment of the crystalline structure. The light emitted during the subsequent re-arrangement processes was converted in electrical charge by the phototube (Figure 1.b).

2. The proposed article does not refer to the field of the research reported in the manuscript which focuses in the use of photo-stimulated luminescence technique (PSL) for the identification of irradiated food.

 

Reviewer 3 Report

This is a rather interesting and good paper that certainly can be recommended for publication, but clarifying and detailing some parts of the text.

1.     For greater visibility and interest to readers, it is proposed to expand the introduction.

2.     Line 59-68.  This part needs few supporting references and better explanation of photostimulated luminescence, which was used to detect different types of ionizing radiation, including x-rays, gamma, neutrons and heavy ions:

Batentschuk, M., Winnacker, A., Schwartz, K., & Trautmann, C. (2007). Storage efficiency of BaFBr: Eu2+ image plates irradiated by swift heavy ions. Journal of luminescence, 125(1-2), 40-44.

Popov, A. I., Zimmermann, J., McIntyre, G. J., & Wilkinson, C. (2016). Photostimulated luminescence properties of neutron image plates. Optical Materials, 59, 83-86.

Kudryavtseva, I., Lushchik, A., Nepomnyashchikh, A.I. et al. Thermo- and photostimulated luminescence in LiF : Mg, Ti single crystals irradiated by ions and VUV light. Phys. Solid State 50, 1667–1670 (2008). https://doi.org/10.1134/S106378340809014X

3.     Can you provide more information about PSL detector (image plate) and wavelength of the stimulating laser light.

4.     Data in Table 1 need error bar.

5.     How optimal is the stimulating laser for PSL analysis of each specific fruit?

6.     It is not clear at all how PSL fading was taking into account.

Author Response

We are grateful for the useful comments/suggestions for the manuscript. We revised text, tables and figures following your indications, which greatly improved the quality of the work. Below our reply point by point.

 1. The Introduction has been modify as follows:

- at line 48 the following text has been inserted:

In fact, as shown in Figure 1, the minerals can keep track of irradiation for a long time due to the trapping of the electrons released by ionizing radiation in the crystalline defects (impurities, atom vacancies, etc.). The original arrangement of the charges can be restored by heating the minerals, which gives the electrons the energy necessary to leave the traps coming back to the original sites. When specific sites (the so-called luminescent sites) are involved, these processes are accompanied by light emissions (thermally-stimulated luminescence) which allows detecting irradiation.

- from line 75 to line 94 (end of the Introduction) the text has been changed as follows:

The method has been validated for herbs and spices but, in principle, it can be applied to all vegetables sufficiently “contaminated”. Regarding fruit, successful studies were carried out on several kind of nuts [20] with the exception of chestnuts that show a rather “clean” peel with mineral contamination and irradiation not detectable by PSL technique [21-22]. On the contrary, the PSL responses obtained from irradiated samples are often non-positive for fresh fruit. This is the case of pomegranates irradiated with doses lower than 3 kGy [23], grapefruits and lemons irradiated with doses lower that 1 kGy and oranges irradiated with doses lower than 2 kGy [24-25]. However, a study by Jo et al. (2016) [26], reported positive PSL results for grapefruits and lemons irradiated with 1 kGy as well as for oranges, mandarins, limes and pineapples irradiated with the same dose. Positive results were also obtained by Jo et al. (2006; 2008) [27, 28] when analyzing kiwi irradiated with doses of 1 and 2 kGy. Given the simplicity and rapidity of the PSL analysis, it seemed convenient to test further the method on this category of food, to verify the feasibility of its use in the official control, as an alternative to other methods, above mentioned, which require expensive equipments and/or long time of analysis. In particular, in this work, funded by the Italian Ministry of Health, 15 fruit types, not irradiated and irradiated (0.5 and 1 kGy), have been examined. The work included preliminary tests to select the matrices that responded to the PSL technique and an inter-laboratory blind test to validate the method. The preliminary tests focused mainly on fresh fruit that yielded inconsistent results in previous studies. In particular, the following products were tested: fresh kiwi, lemon, mango, orange, papaya, pineapple and tangerine, dried date, dried prune and raisin. The inter-comparative blind test involved 4 laboratories of the official control that analyzed 8 matrices: 4 that gave good results in the preliminary tests (kiwi, orange, dried fig, raisin) and 4 types of nuts (hazelnut, peanut, pistachio and walnut) so to confirm previous good PSL responses [20]. In total 384 tests were carried out, 256 on aliquots of irradiated samples and 128 on aliquots of non-irradiated samples.

2. Some sentences have been added to the text (line 48) to improve the explanation of the photo-stimulated luminescence (PSL) as indicated above (first point). Regarding the detection of different types of ionizing radiation, the use of neutrons and heavy ions is not authorized for the food treatment (Directives No. 1999/2/EC e No. 1999/3/EC).

3. The infrared radiation wavewlenght provided by the PSL system used in this work is 890 nm. This information has been reported in the text (2.2 section) as well as in in Figure 1.b.

4. There are not data in Table 1. We added the measurement errors in Table 2.

5. The method CEN EN 13751 standardized for the analyses on irradiated food and followed in this work indicates the use of infrared radiation for the stimulation of the minerals contaminating food. Anyway, as the mineral contaminants are more or less the same in all the fruits we did not expect different effects of a specific type of stimulation among fruits whereas what makes the difference is the quantity of the minerals present in each fruit.

6. As the analysis is qualitative (response: irradiated/not irradiated) and does not require the treatment dose evaluation, it is only important to verify whether the method can detect irradiated food during the shelf life of the products. So, it was important to verify in our work that the PSL response of irradiated fruit was still positive (> T₂ threshold) even several months after irradiation, to guarantee the reliability of the checks at the market stage.

Reviewer 4 Report

Bortolin et al. present a study that discusses the applicability of the CEN EN 13751 method, based on the photo-stimulated luminescence (PSL) technique, for identifying irradiated fruit. However, the title suggests that the photostimulated luminescence approach for effective identification is contrary to the conclusion information. Therefore, the presented results are rather the summary of the preliminary study.

Nevertheless, the topic undertaken by the authors, addressing a comparative study of four laboratories funded by the Italian Ministry of Health, should be made public, with some corrections.

My main objections regarding this manuscript relate to the following:

1.       On what basis were doses selected for irradiation?

2.       Who was responsible for preparing and coding ten matrices of fresh and dried fruit?

3.       In the whole of the studies, there were no withdrawn results, despite the author's claim that the variability is very high for fruit due to the different characteristics of the various parts of the peel used for analysis. Could you explain why?

4.       Have the samples for analysis been standardised, and if how?

 

5.       Why did preliminary tests not consider the fruits analysed in inter-laboratory studies (hazelnuts, walnuts, peanuts, pistachios, dried figs)?

Author Response

We are grateful to the reviewer for the useful comments/suggestions for the manuscript. We revised text, tables and figures following your indications, which greatly improved the quality of the work. Below our reply point by point.

The title has been changed in “Photo-stimulated luminescence approach for effective identification of irradiated fruit”.

1. We selected the lowest doses in the range of application for fruit to verify the reliability of the method under the worst conditions (weak PSL signal).

2. The Materials and Methods (section 2.1) has been changed as follows:

Preliminary tests were conducted by Istituto Superiore di Sanità and Istituto Zooprofilattico Sperimentale del Lazio e della Toscana on 10 types of fresh and dried fruit selected on the basis of the results of previous studies and purchased at the local markets: fresh kiwis, lemons, mangoes, oranges, papayas, pineapples, tangerines, dried dates, dried prunes and raisins. For each matrix, 3 samples were prepared: one non-irradiated, one irradiated at 0.5 kGy and one irradiated at 1 kGy. In the inter-laboratory test, 8 types of fruit were proposed, 2 of fresh fruit, 2 of dried fruit and 4 of nuts: kiwis, oranges, hazelnuts, walnuts, peanuts, pistachios, dried figs and raisins. For each matrix, 3 samples were prepared: one non-irradiated, one irradiated at 0.5 kGy and one irradiated at 1 kGy. In total 24 samples, 8 non-irradiated and 16 irradiated, were coded in order not to disclose the treatment carried out. Four laboratories of the official control who meet the requirements in terms of equipment and skills, participated in the test: ATS-Milano, Istituto Superiore di Sanità, Istituto Zooprofilattico Sperimentale del Lazio e della Toscana, Istituto Zooprofilattico Sperimentale della Puglia e della Basilicata. All the samples of the preliminary tests as well those of the inter-laboratory test were purchased and irradiated by the Istituto Zooprofilattico Sperimentale della Puglia e della Basilicata, and then sent to the participants. The treatment with ionizing radiation was carried out at room temperature by means of a biological X-ray radiator (model RS 2400, RAD SOURCE inc.), at a peak voltage of 150 kV and anode current of 45 mA. The doses were selected in the range used for fruit including a very low value (0.5 kGy) to check the detection limit of the method. Before measurement, the samples were stored inside their packaging in the dark at room conditions.

3. As reported in the text, the total counts may vary between the aliquots of the same sample but what is important for classification is that the responses are in agreement (all negative or all positive). The results suggested the use of certain parts of the fruit to have a better PSL response but this is not always possible.

4. The samples were prepared as described in the Materials and Methods section to simulate the real conditions of analysis during the official controls.

5. For the preliminary test, we preferred to test mainly fresh fruit that did not give coherent results in previous studies in order to select the matrices for the interlaboratory validation. This point has been clarified adding the following text to the last part of the Introduction (from line 89):

The work included preliminary tests to select the matrices that responded to the PSL technique and an inter-laboratory blind test to validate the method. The preliminary tests focused mainly on fresh fruit that yielded inconsistent results in previous studies.

Round 2

Reviewer 3 Report

After the first detailed revision, this manuscript can be recommended for publication.