Effect of Selected Drying Methods and Emerging Drying Intensification Technologies on the Quality of Dried Fruit: A Review

Reviewer # 1 Comments

Answers

Judging by the title "Effect of drying on quality of dried fruit: A review", I expected a comprehensive review of drying methods, taking into account their impact on individual characteristics of fruit quality. Unfortunaltelly, the article  evaluation met only some of my expectations.

We would like to thank the Referee #1 for their positive and encouraging comments about our work. To the best of our knowledge, we have tried to respond to all raised concerns. We also hope that you will find our responses satisfactorily.

In my opinion, the title does not fully correspond to the content presented in the article. Maybe the described methods should be revised in the title or added with the "selected drying methods ..."?

We agree with the reviewer that not all the aspects of the manuscript were covered with the title, which is difficult to do anyways due to extensiveness of review topic, therefore we slightly modify the title:

“Effect of selected drying methods and emerging drying intensification technologies on the quality of dried fruit: A review”.

In article authors did not writ why only those methods were seslected and described.

    I have impression that only with some pre-treatment those dryings have sense (but it is not mentioned in the title), and without them drying of fruits is insufficient and worthless. And based on this the end of the article used description of US/PEF etc. I understand that pre-treatment is crucial nowadays, but please write it in article and explain way.

The additional explanation is provided and now it states:

“Fruits are commonly subjected to various chemical and/or physical pretreatments prior to thermal drying to shorten the drying time, reduce the energy consumption and preserve the quality of products. By modifying the properties of fruit tissue, pretreatments could increase the drying rate, inhibit the bio-enzymes, and minimize possible deteriora-tion reactions during drying and subsequent storage [8].” (lines 59-63).

    I would ask you to systematize your knowledge and pass it on according to some key. You can make it on your own way (as is in the article) but with better selection and linkage the topic or

    You can make it like this:

        a) At the beginning it would be worth starting with discussing the quality characteristics of the fruit, because it is influenced by the selected drying method,

        b) then move on to the impact of drying methods on them (briefly - as in the beginning of point 4),

        c) then a description of selected methods drying (because not all of them have been described) and their impact on these discriminants,

        d) and finally, a summary of the whole.

We appreciate reviewer’s concern for the quality of our Manuscript. However, we prepared review article with more than 12,500 words to give a readership recent and relevant findings related to selected drying methods and emerging drying intensification technologies on the quality of dried fruit with all critical issues well explained (conventional drying technologies, quality of dried fruits, comparison of drying methods, the use of unconventional/emerging drying intensification technologies).

As this Review is not the type of “Comprehensive Review”, by giving more additional information it would become a comprehensive review, that would be more appropriate for other types of Journals.

Reviewer # 2 Comments

Answers

General: The review gives an overview of “Effect of drying on the quality of dried fruit”, however, a lot of places lack a comprehensive explanation for the ease or reading.

On behalf of our research team, I would like to thank the Referee #2 for their encouraging comments about our work, for reviewing our manuscript, affirming its clarity and comprehensibility, and for her/his suggestions on how to improve the manuscript.

To the best of our knowledge, we have tried to respond to all raised concerns.

We also hope that you will find our responses satisfactorily.

The technology specifications have not been mentioned and the quantified “significant” differences are important when it comes to comparing two technologies while stating controls in a study.

We appreciate reviewer’s concern for the quality of our Manuscript. However, we prepared review article with more than 12,500 words to give a readership recent and relevant findings related to selected drying methods and emerging drying intensification technologies on the quality of dried fruit with all critical issues well explained (conventional drying technologies, quality of dried fruits, comparison of drying methods, the use of unconventional/emerging drying intensification technologies).

As this Review is not the type of “Comprehensive Review”, by giving more additional information it would become a comprehensive review, that would be more appropriate for other types of Journals.

Specific comments are below: 

Line 22: Please re-write this sentence, “ The final product quality and energy efficiency are the most important 22 parameters in the selection of drying techniques.”

“energy efficiency” and “final product quality” are jargons, not scientific terms.

We reword the sentence and now it states: “Drying process energy efficiency and quality of dried fruits are crucial factors in fruit drying”. (lines 23-24)

Line 23-26: Rewrite this part by breaking down into two sentences, also please check the grammar. “Recently, the use of innovative technologies (e.g. 23 ultrasound, pulsed electric field, high pressure etc.) as pre-treatment or in combination with traditional drying technologies for process intensification, can result in enhanced product quality, im-25 proved efficiency and capacity of the production process with a positive impact on environmental 26 and economic benefits.”

As suggested, we rewrite this sentence and now it states:

“Recently, innovative technologies such as ultrasound, pulsed electric field and high pressure may be used as a pre-treatment or in combination with traditional drying technologies for process intensification. That could result in quality improvements of dried fruits, enhanced efficiency and capacity of the production process with positive impact on environmental and economic benefits.” (lines 24-28)

Line 34: “ storage technologies are required [1].” Please explain which technology is used for storage. It would be better to state storage at refrigerated temperatures and controlled humid conditions are required.

As suggested, we rewrite sentence  and now it states:

“Fresh fruits have high moisture contents, as they are classified as highly perishable commodities therefore storage at refrigerated temperatures and controlled humid conditions are required.” (lines 34-36)

Line 44: “which are being used successfully for different kinds of fruits.” Please add some relevant references to support this statement.

We added some references to support the statement and now it states:

“Numerous disadvantages of these technologies led to the development of new technologies such as oven drying, microwaving, vacuuming, as well as infrared, freeze and different hybrid dryings, which are being used successfully for different kinds of fruits [3-5].” (lines 43-45)

3. Mercer, D.G. An Introduction to the Dehydration

and Drying of Fruits and Vegetables. University of

Guelph: Ontario, Canada, 2014; p 166.

4. Chua, K.J.; Chou, S.K. Low-cost drying methods for

developing countries. Trends Food Sci Tech 2003,14,

519-528, doi:10.1016/j.tifs.2003.07.003.

5. Çoklar, H.; Akbulut, M. Effect of sun, oven and

freeze-drying on anthocyanins, phenolic compounds

and antioxidant activity of black grape (Ekşikara)

(Vitis vinifera L.). South African Journal of Enology

& Viticulture 2017, 38, doi:10.21548/38-2-2127.

Line 45:what are “ required” physical, chemical, nutritional characteristics? Please state the specific characteristics

We rewrite this sentence and now it states:

“Each drying technique depends on various factors, such as required type of product, size, level of ripeness, structure, colour, aroma, chemical composition, nutritional composition, together with expected final quality, availability of a dryer and costs.” (lines 46-48)

Line 46: Needs references and details on how these characteristics affect the process of drying.

As suggested, we included more details and references on how these characteristics affect the process of drying references and details:

“Sette et. al. [6] investigated the application of wet and dry infusion, as a pretreatment to air and freeze-drying on physical properties of raspberries. Freeze-dried pre-treated samples exhibited higher firmness and lower deformability as compared to air-dried ones. Moreover, the highest volume reduction was developed after air-drying while freeze-dried samples showed 11% shrinkage.

Color is a very sensitive parameter in terms of the influence of drying methods. Krokida et al. [7] stated that color parameters L*, a* and b* of dried banana, apple, potato and carrot were significantly affected by convective, vacuum and microwaves drying techniques. On the other side, same samples preserved original color after freeze and osmotic drying.” (lines 49-63)

6. Sette, P.; Salvatori, D.; Schebor, C. Physical and

mechanical properties of raspberries subjected to

osmotic dehydration and further dehydration by air-

and freeze-drying. Food Bioprod Process 2016, 100,

156-171, doi:10.1016/j.fbp.2016.06.018.

7. Krokida, M.K.; Maroulis, Z.B.; Saravacos, G.D.

The effect of the method of drying on the colour of

dehydrated products. Int J Food Sci Tech 2001, 36,

53-59, doi:10.1046/j.1365-2621.2001.00426.x.

Line 69: (fresh 68 samples.)- full stop should be outside the bracket.

Corrected.

Lines- 69-70, “Moreover, degradation of L–ascorbic acid was around 80%, while freeze-drying preserved more than 97% of L–ascorbic acid”- please include the control for comparison- if the degradation was 805 then how did freeze-drying preserve 97%- would require re-writing for clarity.

We rewrite this sentence and now it states:

„Moreover, in comparison to fresh samples, L-ascorbic acid content was significantly reduced during convective drying 0.94-97.93%) whereas the losses observed by freeze-drying was round 2.36%.“ (lines 86-88)

Line 114: “dimensional resonance phenomena”- please change this to a scientific term, this is more of a jargon.

Corrected (line 133).

Lines 131-145: The key difference in the freeze-drying is actually the time it takes while using different settings -hence please include the time of freeze-drying in each study for the right comparison- alternatively, a tabular form would be helpful.

As suggested, we prepared and include Table 1 with all necessary data (lines 161-163, 173).

Line 165- “Although freeze-drying was mentioned as a tender method” the word “tender” is not correctly used, please specific what this sentence means.

As suggested, we rewrite this sentence and now it states:

“Although freeze-drying was mentioned as a gentle dehydration process..” (line 195)

Line 197- PEF treatment- what was the treatment? Field strength, temperature, frequency, pulse width etc needs to be mentioned, this needs to be done every time a technology is mentioned as the settings can differ.

In order to improve clarity, we included additional explanations:

“ For example, PEF treatment with assisted hot air drying at atmospheric pressure reduced drying time of apple up to 12% and carrots up to 8% when 10 kV cm^-1, 50 pulses, air temperature 70 °C and 5 kV cm^-1, 10 pulses, 70 °C were applied, respectively. Specific energy of pulsed electric field treatment was 80 and 8 kJ kg^-1 [75,76].Other authors also reported reductions by 5-28% for parsnips and carrots at 60 °C. Specific energy of pulsed electric field delivered was about 65 kJ kg^-1 for carrots and parsnip. PEF (400 V cm^-1) assisted freeze drying of potatoes expedite freezing, reduced drying by 18% ( 0 °C and 0.04 mbar pressure), lowered residual moisture content, decreased shrinkage, and improved appearance of samples [77].” (lines 227-235)

Line 202- “3.2. Chemical quality”  start a new section in a new line.

Corrected. (line 237)

Line 205- reword is “ could significantly (p<???) reduce the vitamin contents…” Also, specify the Vitamin type mentioned along with reduction value.

We reword it and now it states:

“ Nevertheless, one study concluded that applied solar drying even at lower temperatures (24.5-40.3 °C) could significantly (p<0.05) reduce the vitamin contents in the fruits [79].” (lines 239-241)

Line 220: “The stability of the B vitamins in the FD and RWD samples was heavily dependent on the berry type.” add a reference.

We included the reference:

“The stability of the B vitamins in the FD and RWD samples was heavily dependent on the berry type. In particular, blueberries and cherries showed significantly higher total vita-min B during FD processing than the RWD, whereas for cranberry and strawberry, the RWD displayed a significantly greater total vitamin B retention than the FD samples [81].” (lines 227-235)

Line 233- add “A”… to make it “ A recent study”

Corrected. (line 267)

Line 239: Re word as “The authors reported a decrease….

Corrected. (line 273)

Line 243- 245: “Moreover, increasing the infrared power from 100W to 300W risen an antioxidant activity, total anthocyanin and phenolic contents, consequently authors concluded that the range of 200 245 W-300W is the preferable setting for the processing.” This needs a reference.  It’s understandable that it’s a continuation of the previous reference but seems incomplete without citing Ref again.

We included the reference:

“Moreover, increasing the infrared power from 100W to 300W risen an antioxidant activity, total anthocyanin and phenolic contents, consequently authors concluded that the range of 200 W-300 W is preferable setting for the processing [82].”(lines 277-280)

Line 310: “phenolics” please specific the compounds being addressed here.

We specific the term “phenolics”:

“A reduced drying time positively affected preservation of the total phenols, total flavo-noids and total anthocyanins,…” (lines 342-343)

Line 313- “2-fold higher antioxidant activity from the initial values”- please specific the quantified significant difference.

We specific the quantified significant difference:

“Moreover, dried samples exhibited 2-fold higher antioxidant activity from the initial val-ues (18.32 % vs. 37.64 %).” (lines 346-348)

Line 524: The review talks about high hydrostatic pressure (HHP), cold plasma (CP) or to add satisfactory value after drying. Please add a section on each of the technology to show what has been done so far.

As suggested, we included sections about high hydrostatic pressure (HHP), cold plasma (CP) in the revised Manuscript (lines 586-634).

Line 526:  Please add a section on research gap- this would show the hurdle technologies which could improve the results with drying.

We addressed a research gap currently identified in the literature considering the innovative technologies (lines 460-467, 567-575).

Reviewer #3 Comments

Answers

Manuscript entitled "Effect of drying on quality of dried fruit: A review" presents an overview of methods used to dehydrate plant material, mainly fruits in a food industry. The Authors compare a number of methods in terms of both economic and, above all, an impact of individual methods on the physical, chemical and nutritional properties of dried plant materials. Importantly, the Authors also noted the different impact of the use of different methods for drying different plant materials, e.g. with different water content. The manuscript is comprehensive and interesting.

We would like to thank the Referee #3 for their positive and encouraging comments about our work.

To the best of our knowledge, we have tried to respond to all raised concerns given by Reviewers 1 and 2. We also hope that our responses will be found satisfactorily.