The Effect of Drying Variables on the Microwave–Vacuum-Drying Characteristics of Mulberries (Morus alba L.): Experiments and Multivariate Models

Round 1

Reviewer 1 Report

1. Mention the statistical methods in methodology which you have used for the data analysis.

2. What was the colour of mulberry? 

3. What was the change in colour after drying? 

4. The crispiness measured with the texture analyzer should also be measured with the help of sensory analysis to find the desirable crispiness. 

5. The number of experiments carried out for the optimization needs to be addressed in the methodology.

Minor editing of English language required.

Author Response

Dear Reviewer

We would like to express our sincere gratitude to the reviewer for the constructive and positive comments concerning our manuscript entitled “The Effect of Drying Variables on the Microwave Vacuum Drying Characteristics of Mulberry ( Fructus Mori ): Experiments and Multivariate Models” (agriculture-2572654). The comments are valuable for revising the paper, as well as of important guiding significance to our researches. We have studied comments carefully and have made corresponding correction. Revised portions are made in red in the revised manuscript.

The main corrections in the paper and the responses to the reviewer’s comments are as follows:

Reviewer :

1. Comment:

• Mention the statistical methods in methodology which you have used for the data analysis.

Response 1: Special thanks for the reviewer’s valuable comments. I have added the content related to data analysis in the method. I have added the content of 2.2.6 data analysis in the method of chapter 2 in the manuscript and marked it in red, see lines 212 to 219 of the manuscript:

2. Comment:

• What was the colour of mulberry?

Response 2: Special thanks for the reviewer’s valuable comments. The mulberry variety used in the drying test was medicinal mulberry, its color was purplish black. I have added and marked in red in the manuscript, see lines 124 of the manuscript.

3. Comment:

• What was the change in colour after drying?  

Response 3: Special thanks for the reviewer’s valuable comments. Because the color of mulberries is dark purplish black close to black, the color change of mulberries before and after drying is not obvious.

4. Comment:

• The crispiness measured with the texture analyzer should also be measured with the help of sensory analysis to find the desirable crispiness.  

Response 4: Special thanks for the reviewer’s valuable comments. It is true that our consideration is not comprehensive enough. According to your valuable suggestions, we have added relevant experiments, added sensory evaluation methods and discussion and results analysis of sensory evaluation results in Chapter 2 of the manuscript, and marked them in red. See 2.25 for sensory evaluation methods and 3.5 for sensory evaluation results. See lines 201-211 and 383-402 of the manuscript for details:

5. Comment:

(v)  The number of experiments carried out for the optimization needs to be addressed in the methodology.

Response 5: Special thanks for the reviewer’s valuable comments. The optimization test and verification part of the manuscript were repeated 3 times to take the average value. Added and marked in red in the manuscript, see line 431 to 432.

6. Comment:

(VI)  Minor editing of English language required.

Response 5: Special thanks for the reviewer’s valuable comments. The manuscript has been touched up by a native English-speaking professional, with the following revisions 51-73, 109-121, 124-143, 144-157, 202-210, 384-399 Changes have also been made to some of the words in the manuscript, which have been labeled in the article.

In addition, we have corrected carefully the several minor mistakes and inaccurately expressed, as shown revised portions marked in red.

Special thanks to you for your good comments.

Reviewer 2 Report

The manuscript focuses on the evaluation of drying parameters in the context of microwave vacuum drying applied to mulberry fruit. The study explores several key process variables, including product temperature, microwave power, vacuum degree, and product height. The main criterion for determining optimal drying variables is the crispness of the dried mulberry. The determined optimal parameters for achieving superior mulberry puffing quality are as follows: microwave temperature of 50 ℃, microwave power of 600 W, vacuum degree of 0.08 MPa, and drying height of 0 cm.

However, I have some concerns regarding with the following issues. I would like the authors to address my following points of criticism, which I hope will help them further improving on their work and its presentation.

Line 17: I recommend using the term "product temperature" or "product surface temperature" instead of "microwave temperature" and "microwave power input."

Line 47: "Anthocyanins become inactive and experience color loss at temperatures exceeding 60 °C[3]. Could you elaborate on the process by which anthocyanins lose their activity and the specific effects of color loss? This statement requires further clarification."

Line 49: “Drying parameters determine the drying quality of materials.” Please revise this, it is unfinished sentence.

Line 94-95: “… conducive to understanding the drying of berry fruits and provides a microwave- vacuum drying law applicable to mulberry.” Could you provide an explanation for the term "law" as used in this context? I recommend revising this sentence for clarity.

Line 103: “During harvest, it will be taken care to…” please use correct tense, revise the sentence.

The 'Materials and Methods' section requires revision to provide more comprehensive details about the methods employed and the samples used. The current description lacks clarity in explaining the methods and does not sufficiently elaborate on the devices utilized. I recommend that the authors consider reworking this section, potentially incorporating a schematic diagram to visually present the experimental procedure, helping readers' understanding.

Could you clarify the criteria used to determine the endpoint of the drying process in order to maintain consistency across all experiments? Additionally, kindly specify the brand and origin of all devices employed for microwave vacuum drying in this study.

Line 158, could you provide information about the quantity of the sample used for the crispiness test? Did you perform measurements on a single fruit piece or multiple samples in one assessment? It would be beneficial to elaborate on the crispiness measurement procedure.

Line 159: please provide the brand and specific name of the device along with its origin for clarity.

In the 'Results and Discussion' section, commencing with a figure alone is not advisable. Consider introducing the section with a brief description of the key findings before presenting the figures.

Regarding the figures, it's essential to revise them for accuracy. For instance, the label 'Microwave temperature' might be misleading; you might consider using 'Product Surface Temperature' instead. Similarly, 'Vacuum degree' might be unclear; 'Chamber Vacuum Level' could be more suitable.

It's advisable to express the applied microwave power input in terms of watts per gram (W/g) or watts per kilogram (W/kg) instead of just using watts. This provides context regarding the amount of product being subjected to the applied power, rendering the measurement more meaningful.

The primary focus of this paper is on crispiness; however, I found the presentation of your results and the depiction of crispiness to be unclear. Given the crucial nature of this parameter in your study, I strongly recommend revising its presentation comprehensively. This should encompass not only the figures and their labels but also extend to the corresponding discussion to ensure clarity.

Author Response

Dear Reviewer

We would like to express our sincere gratitude again to the reviewer for the constructive and positive comments concerning our manuscript entitled “The Effect of Drying Variables on the Microwave Vacuum Drying Characteristics of Mulberry ( Fructus Mori ): Experiments and Multivariate Models” (agriculture-2572654). The comments are valuable for revising the paper, as well as of important guiding significance to our researches. We have studied comments carefully and have made corresponding correction. Revised portions are made in red in the revised manuscript.

The main corrections in the paper and the responses to the reviewer’s comments are as follows:

Reviewer :

The manuscript focuses on the evaluation of drying parameters in the context of microwave vacuum drying applied to mulberry fruit. The study explores several key process variables, including product temperature, microwave power, vacuum degree, and product height. The main criterion for determining optimal drying variables is the crispness of the dried mulberry. The determined optimal parameters for achieving superior mulberry puffing quality are as follows: microwave temperature of 50 ℃, microwave power of 600 W, vacuum degree of 0.08 MPa, and drying height of 0 cm. However, I have some concerns regarding with the following issues. I would like the authors to address my following points of criticism, which I hope will help them further improving on their work and its presentation.

1. Comment:

• Line 17: I recommend using the term "product temperature" or "product surface temperature" instead of "microwave temperature" and "microwave power input."

Response 1: Special thanks for the reviewer’s valuable comments. Although the final result of the microwave power setting and microwave temperature setting is the surface temperature of the product, because our purpose is to make a control parameter guidance for industrial production, it is necessary to divide the product surface temperature into two test control parameters "microwave temperature" and "microwave power input", so that enterprises can adjust the drying parameters more easily. To improve the accuracy of the description, we have replaced "microwave temperature" in the manuscript with "product surface temperature" and marked it in red, See manuscript 18-19, 23, 110, 143, 233, 236, 259, 280-285, 289 lines.

2. Comment:

• Line 47: "Anthocyanins become inactive and experience color loss at temperatures exceeding 60 °C[3]. Could you elaborate on the process by which anthocyanins lose their activity and the specific effects of color loss? This statement requires further clarification."

Response 2: Special thanks for the reviewer’s valuable comments. I am very sorry that I did not make it clear. The process of anthocyanin inactivity and the specific effects of color loss are as follows:

Mulberry is rich in anthocyanins, but the poor stability of anthocyanins leads to the fact that they are rarely detected in free form in nature except in specific structures such as 3-deoxyanthocyanins [1]. Anthocyanins have strong antioxidant properties and are a natural pigment. The main reason for the loss of anthocyanin activity is that anthocyanin is more sensitive to pH environment and temperature in food processing [2], and it will not only undergo oxidative degradation reaction, condensation reaction with free amine group, but also undergo acid-catalyzed degradation reaction [3]. In the drying of fruits and vegetables, Wang et al. [4] found that anthocyanins degrade rapidly after enzymatic reaction and thermal effect when the temperature reaches more than 60 ℃. Wang Li[5] et al. found that when the temperature was higher than 60 ℃, the content of phenols and anthocyanins in mulberries decreased significantly. According to the thermodynamic analysis of Fan[6] et al., anthocyanins degrade rapidly and are accompanied by fading at 90℃, but decline slowly at 50℃~70℃. Luki et al. [7] found that the anthocyanin retention effect was best when the temperature was 20-60 ℃. When Laleh et al [8] studied the stability of anthocyanins in blueberry, they found that anthocyanins in blueberry were most stable at 25℃, and their stability became worse when the temperature increased to 60℃. At this time, anthocyanins existed in chalcone structure, and their color gradually tended to be colorless. Liu Yi et al. [9] found a correlation between the chroma value of blueberry fruit and the content of anthocyanin and total phenol, and the chroma value can be used to predict the content of anthocyanin and total phenol. The above studies showed that the thermal stability of anthocyanins was poor, and with the increase of heating temperature, the degradation rate of anthocyanins was accelerated and the color was lost. Since the mulberry variety in this study is medicinal mulberry, the color of mulberry is considered from the color.

References:

[1] Pereira, B.M.; Buttow, R.T.C.; Rodrigues, B.L.L.; Vieira, Q.V.A.; César, S.P.; Ribeiro, B.F.A. Effect of light, food additives and heat on the stability of sorghum 3‐deoxyanthocyanins in model beverages. International Journal of Food Science & Technology. 2021, 56(9):4746-4755.

[2] Chang, Y.; Yang, X.X.; Jiao, Y.; Han, H.; Liu, X.C.; Cong, M.Q. Study on the Modification and Stability of Mulberry Anthocyanin Nanoliposomes. Food Science And Technology. 2020,45(12):251-257.

[3] Xia, X.Y.; Wang, F.J.; Fu, Q.; Zhang, N.; Guo, Q.Q. Thermal stability and degradation kinetic model of proanthocyanidins in blueberry (Vaccinium spp.) juice beverage. Journal of Nanjing Forestry University(Natural Sciences Edition). 2019,43(05):89-95.

[4] Wang, W.D.; Xu, S.Y. Degradation kinetics of anthocyanins in blackberry juice and concentrate. Journal of Food Engineering 2007. 82(2), 271–275.

[5] Wang, L.; Wen, H.C.; Yang, N.W.; Li, H.J. Effect of vacuum freeze drying and hot air drying on dried mulberry fruit quality. PloS one. 2023, 18(6):e0283303-e0283303.

[6] Fan, L.L.; Wang, Y.; Xie, P.J.; Zhang, L.X.; Li, Y.H.; Zhou, J.Z. Copigmentation effects of phenolics on color enhancement and stability of blackberry wine residue anthocyanins: Chromaticity, kinetics and structural simulation. Food Chemistry. 2018, 275:299-308.

[7] Lukić, K.; Brnčić, M.; Ćurko, N.; Tomašević, M.; Valinger, D.; Denoya, G.I.; Barba, F. J.; Ganić, K.K. Effects of high power ultrasound treatments on the phenolic, chromatic and aroma composition of young and aged red wine. Ultrasonics Sonochemistry. 2019, 59:104725.

[8] Laleh, G.H.; Frydoonfar, H.; Heidary, R.; Jameei, R.; Zare, S. The Effect of Light, Temperature, pH and Species on Stability of Anthocyanin Pigments in Four Berberis Species. Pakistan Journal of Nutrition. 2006, 5(1):90.

[9] Liu, Y.; Wang, Z.Y.; Zhang, J.; Lu, B.J. Correlation analysis of blueberry active ingredient content and its chroma value based on chroma analysis principle.China Food Additives.2019,30(12):189-194.

3. Comment:

• Line 49: “Drying parameters determine the drying quality of materials.” Please revise this, it is unfinished sentence.

Response 3: Special thanks for the reviewer’s valuable comments. The drying process is not only beneficial to the storage of food, but also can improve its taste quality and commercial value. And in the text marked in red, see manuscript 51-52 line.

4. Comment:

• Line 94-95: “… conducive to understanding the drying of berry fruits and provides a microwave- vacuum drying law applicable to mulberry.” Could you provide an explanation for the term "law" as used in this context? I recommend revising this sentence for clarity.  

Response 4: Special thanks for the reviewer’s valuable comments. I have revised and marked in red in the manuscript, lines 109 -121 in the manuscript. Change to:

In this study, the microwave vacuum drying process was used to analyse the effects of product surface temperature, microwave power, chamber vacuum level and drying height on the drying characteristics and crispness of mulberry. The models of Henderson and Pabis, Lewis, Page, Two-term, Logarithmic, Two-term exponential, Weibull distribution 7 empirical equations were employed for the drying process. Then, to assess mulberry water loss, we determined the best prediction model. A heat and humidity transfer model under various drying parameters was established to investigate the water migration rule of the mulberry during drying. Experimental tests were conducted to validate the water loss process of mulberry under different drying conditions. The drying process parameters with the best crispness retention were determined to obtain high-quality dried mulberries in the shortest time. This study is helpful in understanding the drying process of berry fruits and in providing references for improving the drying quality of fruits.

5. Comment:

(v)  Line 103: “During harvest, it will be taken care to…” please use correct tense, revise the sentence.

Response 5: Special thanks for the reviewer’s valuable comments. I have revised the sentence tense to the past tense and marked it in red on lines 125 -126 of the manuscript.

6. Comment:

(vi)  The 'Materials and Methods' section requires revision to provide more comprehensive details about the methods employed and the samples used. The current description lacks clarity in explaining the methods and does not sufficiently elaborate on the devices utilized. I recommend that the authors consider reworking this section, potentially incorporating a schematic diagram to visually present the experimental procedure, helping readers' understanding.

Response 6: Thanks in particular to the valuable comments of the reviewers, a schematic diagram has been added to the manuscript and more comprehensive detailed information on the methods and samples used has been provided, marked in red at lines 124 to 162 of the manuscript, and the content is revised as follows:

The therapeutic mulberry cultivar is purple-black and is harvested in Alar, Xinjiang.. The container for harvested mulberries should be neither too large nor too deep to avoid the accumulation and extrusion of mulberries. After the harvest of mulberries, any fruit that is mouldy, deformed, or diseased is promptly removed. The remaining mulberries are then placed in a foam box with an ice pack and transported to the laboratory without delay. Through the use of a vernier calliper (Shanghai Shenhan Measuring Tools Co., LTD. Products) and an electronic name(model: FA1104; Shanghai Anting Electronic Instrument Factory), the test object was measured and determined to be an individual complete with dimensions of longitudinal diameter 33 ± 0.5 mm, transverse diameter 16.5 ± 0.5 mm and single fruit weight 3 ± 0.5 g fresh mulberry.. To prevent damage to mulberry extrusion and improve the storage time of mulberry, the samples were placed in a single layer on a tray covered with spunlaced nonwoven fabric and refrigerated in a freezer at 4 ± 1 ℃. Prior to the test, mulberry samples were allowed to equilibrate at room temperature for a duration of 2 h in order to achieve a similar temperature to that of the surrounding environment. The microwave vacuum drying oven used in the test (model: HTWB-01; Nanjing Huateng Machinery Technology Co., LTD.) is equipped with a temperature control module and temperature sensor to continuously monitor the surface temperature of the material, This ensured that the material remained at a predetermined temperature, preventing excessive heating during the drying process..

Product surface temperature (40, 45, 50 and 50 ℃), chamber vacuum level (0.02, 0.04, 0.06 and 0.08 MPa), microwave power (1.82, 2.73, 3.64, 4.55 and 5.45 W/g) and drying position (0, 4 and 8 cm) were used as study variables. The specific test process is shown in Figure 1.:(1) Before drying, 110 ± 3 g of mulberry sample are spread evenly on the entire tray (tray size: 137 mm × 158 mm, mulberry thickness: 10 mm). (2) The tray was placed in the microwave vacuum oven, and the mulberry sample was dried using the predetermined drying parameters and time interval. (3) Mulberry samples were promptly extracted and their water content was measured. (4) The mulberry was dried to a moisture content of 5% (wet basis) and subsequently analysed using a texture analyzer (model: TMS-Pro; the embrittlement of mulberry samples of Beijing Yingsheng Hengtai Technology Co., LTD., and the sensory evaluation of the samples was carried out by the evaluation team). The analysis samples were averaged using three parallel tests. Using the oven method, the initial moisture content of the mulberry was determined to be 79.7% ± 0.5% [14].

1, PP material drying tray 2, evenly placed 100±3g fresh mulberries 3, into the microwave vacuum drying oven 4, set the microwave vacuum drying parameters 5, after drying mulberries 6, determine the moisture content

Figure 1. Flow chart of microwave vacuum drying test for mulberries

7. Comment:

(vii)  Could you clarify the criteria used to determine the endpoint of the drying process in order to maintain consistency across all experiments? Additionally, kindly specify the brand and origin of all devices employed for microwave vacuum drying in this study.

Response 7: Special thanks to the valuable comments of the reviewers. In the experiment, the drying end point of mulberries under different drying parameters was the same as 5% (wet base moisture content). We took the samples out of the drying box with a fixed drying time (every 20 min) and used an electronic scale (Model: FA1104; Shanghai Anting Electronic Instrument Factory) quickly weigh the sample mass to calculate the wet base moisture content, and then continue to put the sample in the drying oven to repeat the step, drying the sample to the target moisture content of 5%(wet base moisture content) to stop drying.

All equipment used for drying tests in this study are supplemented with relevant brands and sources in the manuscript and marked in red, See lines 129, 130, 131, 139, 153, 190-191 of the manuscript.

8. Comment:

(viii)  Line 158, could you provide information about the quantity of the sample used for the crispiness test? Did you perform measurements on a single fruit piece or multiple samples in one assessment? It would be beneficial to elaborate on the crispiness measurement procedure.

Response 8: Special thanks to the review experts for their valuable advice. The number of tests for brittleness test was 5 times to take the average value, and the number of mulberries in brittleness test was single. Before each test, a new sample was replaced for brittleness test. The relevant changes have been highlighted in red in the manuscript, on lines 196 -197.

9. Comment:

(ix)  Line 159: please provide the brand and specific name of the device along with its origin for clarity.

Response 9: Special thanks to the review experts for their valuable opinions, and the relevant content has been supplemented: The model of the texture meter is (TMS-Pro), the manufacturer is: Beijing Yingsheng Hengtai Technology Co., LTD. The manuscript has been marked in red, on lines 190-191.

10. Comment:

(x)  In the 'Results and Discussion' section, commencing with a figure alone is not advisable. Consider introducing the section with a brief description of the key findings before presenting the figures.

Response 10: Thanks especially to the valuable comments of the reviewers, I have changed the order of pictures and text in the "Results and discussion" section.

11. Comment:

(xi)  Regarding the figures, it's essential to revise them for accuracy. For instance, the label 'Microwave temperature' might be misleading; you might consider using 'Product Surface Temperature' instead. Similarly, 'Vacuum degree' might be unclear; 'Chamber Vacuum Level' could be more suitable.

Response 11: Special thanks to the reviewers for their valuable comments. It is true that our consideration is not rigorous enough and the vocabulary is not accurate. Now "microwave temperature" has been replaced with "product surface temperature" in the manuscript. Replace "vacuum degree" with "Chamber vacuum degree". Marked in red in the manuscript, See lines 18-19, 23-24, 143-144, 221-223, 233-234, 280-285, 289-290, 327-329, 333-365, 462, 464, 469, 471, 490, 494.

12. Comment:

(xii)  It's advisable to express the applied microwave power input in terms of watts per gram (W/g) or watts per kilogram (W/kg) instead of just using watts. This provides context regarding the amount of product being subjected to the applied power, rendering the measurement more meaningful.

Response 12: Thanks especially to the valuable comments of the reviewers. The units of microwave power in the manuscript have been revised and marked in red, see lines 23-24, 224, 255, 293-294, 306, 308, 326, 330, 366, 493 of the manuscript.

13. Comment:

(xiii)  The primary focus of this paper is on crispiness; however, I found the presentation of your results and the depiction of crispiness to be unclear. Given the crucial nature of this parameter in your study, I strongly recommend revising its presentation comprehensively. This should encompass not only the figures and their labels but also extend to the corresponding discussion to ensure clarity.

Response 13: Thanks especially to the valuable comments of the reviewers, I have added relevant descriptions of crispness to the manuscript and marked them in red, see lines 52-68, 70-72, 197-200, 226-228, 201-211, 383-402 of the manuscript.

Special thanks to you for your good comments.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Authors have addressed all the comments successfully. 

Author Response

Dear Reviewer

We would like to express our sincere gratitude to the editor for the constructive and positive comments concerning our manuscript entitled “The Effect of Drying Variables on the Microwave Vacuum Drying Characteristics of Mulberry ( Fructus Mori ): Experiments and Multivariate Models” (agriculture-2572654). The comments are valuable for revising the paper, as well as of important guiding significance to our researches. 

The main corrections in the paper and the responses to the editor’s comments are as follows:

Editor :

1. Thank you for the new version of the manuscript. However, still remains an important correction that needs to be addressed, related to the botanical name of Mulberry. The correct name is "Morus alba L." and not "Fructus Mori". This correction is crucial to maintain accuracy and precision.
   To rectify this, please make the following changes:
   In the title modify it to read:
   The Effect of Drying Variables on the Microwave Vacuum Drying Characteristics of Mulberry (Morus Alba L.): Experiments and Multivariate Models.
   In line 32, please revise as follows:
   Mulberry (Morus alba L.) is rich in multiple nutrients, including vitamins, minerals, aminoacids....

Response 1: Special thanks for the editor’s valuable comments. We have revised The title of the manuscript to “The Effect of Drying Variables on the Microwave Vacuum Drying Characteristics of Mulberry (Morus Alba L.): Experiments and Multivariate Models. ”, and revise line 32 to read : Mulberry (Morus alba L.) is rich in multiple nutrients, including vitamins, minerals, aminoacids.....

The changes made are highlighted in red in the manuscript, see lines 3 and 24.

Special thanks to you for your good comments.

Reviewer 2 Report

The article has been well corrected and prepared, I suggest to accept the submission.

Author Response

Dear Reviewer

We would like to express our sincere gratitude to the editor for the constructive and positive comments concerning our manuscript entitled “The Effect of Drying Variables on the Microwave Vacuum Drying Characteristics of Mulberry ( Fructus Mori ): Experiments and Multivariate Models” (agriculture-2572654). The comments are valuable for revising the paper, as well as of important guiding significance to our researches. 

The main corrections in the paper and the responses to the editor’s comments are as follows:

Editor :

1. Thank you for the new version of the manuscript. However, still remains an important correction that needs to be addressed, related to the botanical name of Mulberry. The correct name is "Morus alba L." and not "Fructus Mori". This correction is crucial to maintain accuracy and precision.
   To rectify this, please make the following changes:
   In the title modify it to read:
   The Effect of Drying Variables on the Microwave Vacuum Drying Characteristics of Mulberry (Morus Alba L.): Experiments and Multivariate Models.
   In line 32, please revise as follows:
   Mulberry (Morus alba L.) is rich in multiple nutrients, including vitamins, minerals, aminoacids....

Response 1: Special thanks for the editor’s valuable comments. We have revised The title of the manuscript to “The Effect of Drying Variables on the Microwave Vacuum Drying Characteristics of Mulberry (Morus Alba L.): Experiments and Multivariate Models. ”, and revise line 32 to read : Mulberry (Morus alba L.) is rich in multiple nutrients, including vitamins, minerals, aminoacids.....

The changes made are highlighted in red in the manuscript, see lines 3 and 24.

Special thanks to you for your good comments.