Pulsed Electric Field (PEF) Processing of Chilled and Frozen-Thawed Lamb Meat Cuts: Relationships between Sensory Characteristics and Chemical Composition of Meat

Round 1

Reviewer 1 Report

The impact of pulsed electric field (PEF) on chemical composition and flavour properties of chilled and frozen-thawed lamb

This article is extremely long and very detailed. The main findings and take-home messages are not at all clear to me. What is the overall significance and impact of this research? Do the advantages of PEF on tenderness outweigh the negatives? I can’t really tell. In general, there is way too much information presented. In the results section there is a lot of jumping around between their results and others published work. I suggest the authors reduce the length of the paper and try to be more focussed in their interpretation. There are lots of reference to seemingly low relevance flavour chemistry pathways like L833 “proline has been associated browned flavour…”, L 883 referring to a study on wine flavour. The paper seriously needs more focussed consideration of findings. There is no discussion of how the samples were cooked for the sensory work. The use of 80oC cooking for volatile analysis is a strange choice and needs justification. How does this correspond to typical cooking methods of lamb?

Other more specific comments below.

Title discusses flavour but not sensory. Since sensory (specifically TDS) was such a large part of the study, please refer to it in the title.

In general, the abstract is quite vague. Please summarise succinctly the main outcomes

L21 volatile correlated well with the sensory perception – what attributes exactly? This statement is too vague. Were the correlations significant? Same comment for amino acid and FA content!

Describe very briefly in a sentence what PEF is?

L31 This sentence could be expressed betterà PEF treatment improved tenderness…

L38 The information in this paragraph does not flow logically from previous. Need a linking statement like; “Although PEF has a positive impact on meat tenderisation, undesirable effects on lipid oxidation have been reported.” Although the references provided do not show evidence of oxidation.

L42 Define TBARS.

L47 Subjected to PEF? Please state this.

L48 It is ambiguous – are they saying that both freeze thaw and PEF separately cause oxidation or are they synergistic? Concise accurate statements please.

L68 However, in that study

L69 The sentence does not make logical sense

L72 decrease in fatty acid and amino acids is not physicochemical but just chemical. I think they mean free amino acids… need more clarity about changed in lipids… was it a decrease in unsaturated lipids only? Seems unlikely that overall lipid would decrease!

L76 Need to have “on the one hand” to have “on the other hand” – the authors use this outdated English expression quite a bit. I would recommend not to use it! Use it correctly and infrequently, if at all.

L79 The current study therefore set out (use past tense)

Confusion between aims. TDoS is different to volatile changes and in fact traditional sensory analysis. More justification for choosing to jump into TDoS rather than descriptive analysis is required.

L84 that influence were (number agreement, past tense)

L90 lamb carcasses

Animal ethics approval number?

It is unclear when in the sequence of events the PEF was applied to the frozen samples

L111 what was the time between freezing and sensory/volatile analysis?

L124 It says that the training was over three sessions of 12 hours. Yet each session was 60 mins. Need far more clarity about overall time commitment from each panellist and compensation.

L131 was it a voucher or a gift card? Was it given after every session or at the end of all sessions?

L134 what does hearing have to do with selection criteria? The criteria and expression sound very dodgy. I doubt that the ethics committee would agree to this language or criteria. Please state exactly as stated in the information sheet.

L137 Previously stated that each session was 60 min

Authors need to state why traditional quantitative descriptive analysis was not considered first – why complicate life and go straight to TDS? Doesn’t make immediate sense!

L144 meat or lamb meat?

L157 how can a cube of meat 1 x 1 x 1 have a mass of 5 g? A I cm3 cube of water is 1 g, Meat is mainly water. A 1 g cube is tiny and doesn’t approach what a normal mouthful would be!

There is no description of how these samples were prepared! Were they grilled? On what? What internal temperature?

L164 All the TDS attributes need to be precisely defined. How is “browned” a flavour attribute? It is an appearance attribute. I assumed browned is related to Maillard grilled and roasted flavour – browned seems like a poor choice of descriptor! The authors need to justify their selection of sensory attributes with reference to published work…

L163 The whole description of the TDS procedure is ambiguous and unclear.. was the tenderness rated just once or dynamically?

L198 meat samples

L202 Since the cooking conditions for the sensory testing are not specified, hard to know how relevant the volatile cooking method is. Who cooks lamb at 80 oC for 5 minutes? Was any validation done? I can’t see how this will produce typical Maillard compounds. Need much higher temperatures for MRs to occur. This is a serious experimental flaw; the relevance of the volatile data are therefore highly questionable.

L265 I find it hard to believe you can rate tenderness on a single bite, again not enough description of how or why. Tenderness would require a certain number of chews to ascertain.

It is still ambiguous; was tenderness determined by TDS or another method?

Figure 1 legend too small to read

It is not obvious what the difference between Fig 1 and 2 is?

It would be useful to plot the same attribute on the one graph so the reader can clearly see the impacts of the treatments. Difficult and annoying to try and make comparisons.

218-372 I appreciate there is a lot going on, but in general this section is very long and hard work to read/make sense of. Would recommend just highlighting the main important conclusions and making this more reader friendly.

L404 The fact that “oxidized” is the dominant sensory attribute is concerning – do they meat fatty, typical lamb fat flavour? If I was a lamb farmer or marketer, I would be really concerned that the take home message is that lamb has predominantly oxidized flavour!  

Once again, I’m not really getting a clear overall story regarding the CVA. What is the main finding? Why is this work significant? What are the implications for lamb eaters? Lamb producers?

L541 How can Maillard reaction be favoured when only heated to 80oC?

542 3-methylbutanal

L546 Refer to olfactometry literature that proves these volatiles are odour-active

L572-627 These sections should first clearly describe what the most important significant effects were found in their study. It is not clear most of the time whether they are referring to their or others work. Since the lamb was only heated to 80 oC the relevance of any statements are dubious!

L573 Drastically? Just say significantly and provide p value.

L578 3-methylbutanal (be consistent and correct!)

L583 There is no mention of how or whether they analysed free amino acids. What is the relevance of this?

L630 They need to briefly describe how amino acids and fatty acids were analysed in M&M and refer to their earlier published wok.

L804 Should refer to relevant literature showing the effect of IMF on flavour in meat

L883 why refer to random studies on wine? There is an abundance of literature on meat flavour.

Figure 5 Hard to read plots. I don’t understand the advantage of having separate plots for fatty acids, volatiles, and amino acids? Surely the synergistic effect of all of these potential flavour compounds together is the closest to reality? I would encourage using just one plot with the most significant factors all together.

Table 1. Volatiles are given to 3 decimal places. I’m sure that the method is not that accurate. Additionally, the information is hard to clearly interpret as it is so cluttered. I recommend rounding to 1 or 2 DP. Need to cross reference volatiles with those reported previously in other studies, especially those proven to be odour-active by olfactometry. The name of volatiles is not clear in some cases. Retention indices? Quan ion m/z?

Author Response

Please see attached for our response.

Author Response File: Author Response.docx

Reviewer 2 Report

The aim of this study is to evaluate the effect of PEF and storage period on volatile compounds and flavour profile attributes of different cuts from chilled and frozen-thawed lamb meat. The main concern of this manuscript is the limited number of animals used (n=4) for chilled and frozen-thawed samples, which could affect the statistical power and interpretation of the results. The authors explain in detail results, however, there is overall a lack of discussion of the results.

-In the Introduction, the authors mention several papers showing the effect of PEF to improve tenderness. However, the authors do not discuss their results with any of this papers. Authors are encouraged to discuss and point out reasons for disagreement of results. Also, it is surprising that storage time did not affect tenderness. Why?

-The authors discuss the results from TDS in chilled and frozen-thawed lamb meat samples. However, discussion comparing chilled vs. frozen-thawed lamb meat sample results is missing. Based on the results, is PEF recommended to apply on chilled or frozen-thawed meat samples?

-The authors discuss separately the effect of storage, PEF and cuts on volatiles. However, when discuss the effect of storage and PEF they also mention differences among cuts. Thus, a joint discussion on the effect of PEF on different storage times and cuts is recommended. Also, authors are encouraged to not only indicate differences among storage, PEF and cuts (i.e., showing results) but also discuss possible reasons for those differences.

-The VIP results should be summarized and showed when discussing the correlation biplots in stead of discussing them in different sections.

Specific comments

-This manuscript does not evaluate the effect of PEF on chemical composition (previously evaluated in another manuscript). Hence, chemical composition should be replaced by volatile compounds in the title and throughout the manuscript.

-Line 140: replace ‘meat nutritional quality’ by ‘meat eating quality’.

-Line 42: Define TBARS for the first time used.

-Lines 68-68: This not completely true as the relationship between volatiles and sensory perception was evaluated by means of the PLSR. Please, reword it.

-Line 79: Replace ‘Sensory qualities’ by ‘Sensory quality’.

-Lines 79-85: Please, remove ‘using the temporal Dominance of Sensations (TDS) method’ and ‘using Partial Least Squares Regression (PLSR) analysis’ as those will be indicated in M&M.

-Lines 88-96: So n = 4 for each cut? This is a very limited number of samples that could affect the statistical power and interpretation of the results. Please, consider this limitation when interpreting the results.

-Lines 104-112: If there were cuts from 4 lambs that were chilled and cuts from 4 lambs that were frozen-thawed, how many of those cuts were control and PEF? PEF was applied to muscle and then 6 replicates were used for analyses of sensory and volatile compounds? Please, clarify this.

-Lines 178-180: were not unsalted crackers used?

-Lines 198 and 199: …lamb meat samples were….

-Lines 226: As there is internal standard, should not it be semi-quantitative identification of volatiles?

-Figure 3. Replace by ‘Canonical Variate Analysis Biplot of dominance durations of sensations of PEF and non-PEF treated cooked chilled (a) and frozen-thawed (b) lamb meat of different cuts. Hotelling-Lawley trace MANOVA test showed significant product differences (a: F(135,192) = 29.655; p < 0.001; b: F(135,192) = 12.043; p < 0.001) based on sensory attributes.

-Line 466: …, respectively.

-Line 538: Concentration of hexanal….

-Lines 569-571: …oxidation product (2-pentylfuran) increased….

-Line 573 and 621: Regarding PEF. Regarding chilled….

-Lines 576 and 579: The 3-methyl….

-Line 578: These volatile compounds are ….

-Line 602: …at significantly lower levels…

-Line 607: The 2,3….

-Line 609: The fatty acids are not shown in this manuscript. Please, rewrite it.

-Lines 616, 788 and 792: The 2-….

-Line 623: …significantly higher compared…

-Lines 630-636: Were all cuts considered for the PLSR analysis? Was the PLSR performed only on the PEF samples? Please, clarify.

-Line 630: ‘PLSR analysis is widely…’.

-Line 632: ‘as well as fatty acid and amino acid composition’.

-Lines 646 and 698: Indicate which figures show these results.

-Lines 650 and 659: The results from this study should be compared to those from previous studies, no the other way around. Please, rewrite (e.g. in agreement with XXX, this study found…..).

-Line 726: ‘frozen at -80’.

-Line 766: ‘PLSR correlations’. In 3.4.1. and 3.4.2. indicate the figures showing these results.

-Line 799: ‘fatty acids. Meat…’.

-Line 901: ‘fatty acids. On the other hand…’.

-Lines 900-904: Please, be more specific in the conclusion. Any fatty acid, volatile compound or amino acid in particular?

Author Response

Please see attached for our response.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The authors appear to have implemented most of the requested changes

Author Response

We'd like to thank the reviewer for this

Reviewer 2 Report

Due to the limited number of animals used in the study, the authors are encouraged to highlight in the conclusion that further studies are required to validate the results of this study.

Author Response

We'd like to thank the authors on this, we have added this comment at the last section of the Conclusion which now reads

One of the limitation of this study was the limited number of animals used in the study. Future studies should consider including more animal samples to validate the results of this study.