Organic Wastes as Feedstocks for Non-Conventional Yeast-Based Bioprocesses

Round 1

Reviewer 1 Report

Generally, I think that the article is interesting and worth publishing. However, it requires a minor revision. 

Firstly, the statement in the Introduction section, lines 39: "..which can simultaneously lead to reduction of operational costs of these processes." is disputable. It depends on the complexity of waste as more complex ones must be pretreated or detoxified prior utilization as a feedstock for yeast. What generates additional costs. A similar statement occurs at the end of the article in lines 565-566: "This approach represents a promising approach towards more cost-effective processes....." This is a rather unjustified statement, because the article neither presents nor discusses the costs of processing wastes through yeast into valuable products. Furthermore, in many cases the waste utilization in bioprocesses is uneconomical, because of  high costs of the waste pretreatment, e.g. the hydrolysis of lignocellulosic biomass.

Besides, also in the Conclusions and prospects section, lines 558-559 the statement: "This review listed numerous waste feedstocks that have already found use in waste valorization processes involving microbes." is too general. It should be underlined that in laboratory scale  bioprocesses involving some non-conventional yeast.

More detailed remarks and comments are listed below.

1) As this is a review article, authors should give more accuracy to citing articles.

line 49: "Recent reviews have already focused on such engineering aspects [4–7]."- Only ref. 6 and 7 are reviews, while ref. 4 and 5 are the original research articles

lines 65-66: "In fact the global market for CA is currently around 2.4 million tonnes per year [8]." - Please provide a more relevant (the original one) reference for CA production than [8]

lines 86-88: "It is used as the starting material for the synthesis of an antitumor drug, an antioxidative agent and enhancer of wound healing [14]." - Please provide more relevant references (the original ones) than [14] to this sentence.

lines 126-127: "...while China produces 5 million tonnes/year [24]." - Please provide a more relevant reference for the used cooking oil production in China than [24].

line 183: "...and applications based on the utilization of raw glycerol as feedstock has been reviewed [38,44]." - The ref. 38 is not a review paper.

line 282-283: "Hemicellulose from plant biomass is one of the most abundant polysaccharides found on earth  [5]." - Not appropriate ref. 5

lines 436-437: "In the EU, 3 million tonnes / year of beet molasse are produced (CEFS Sugar statistic), while China generates 400 million tonnes /year of sugar cane molasse [99]."-Please provide a more relevant reference than 99 (the first source of information).

lines 524-525: "Approximately 1.3 billion tons of food are wasted annually, an amount equivalent to one third of the total annual food production [115]."- Please provide a more relevant reference than 115 (the first source of information)

2) In my opinion  the sentence in lines 114-116 is unclear: "Candida (Yarrowia) lipolytica 1094 grown on corn oil accumulated 0.55 (w/w) of lipids using a pO2 of less than 0.05 of saturation, which decreased to 0.37 (w/w) for pO2 of less than 0.8 of saturation [22]."

3) Minor editorial and language spell check required, e. g.:

 in line 62: "Secretion of organic acids from the TCA cycle in one of the characteristic features of Y. lipolytica." 

in line 97: "Y. lipolytica is known to produced and secrete large amounts of lipases in the.."

in line 134: "...one mutant mutant (YlE1) showed a.."

Author Response

Please see the attachment

Author Response File: Author Response.docx

Reviewer 2 Report

1.      Introduction: please provide the definition of the “non-conventional yeasts” term

2.      Page 1, line 33: What do you mean by “…glucose-rich saccharides…”? Do you refer on glucose based polysaccharides like starch? Pls rephrase

3.      A brief review of the processes that are tested at pilot scale or industrial scale could provide valuable information. You can add such info in each paragraph of different substrates, or be introduced in a separate paragraph and summarized in a table.

4.      The paragraph conclusions and prospects should probably be rewritten since its present context resembles more to an abstract. Some generic conclusions on the production efficiency of non-conventional yeasts, the applicability of the processes at large scale and a brief comparison with the respective processes using conventional yeasts could be include in this paragraph.

Author Response

Please see the attachment

Author Response File: Author Response.docx