Question 1: This work could be of interest, but in its current
form it is difficult to assess. The text is poorly written, and it is
difficult to understand the meaning of many phrases. Furthermore, the
references are inappropriately placed in the text, which is riddled with
inconsistencies. For example: ”At present, there are few types of
healthy oils and fats on the market, and the quality is uneven.” Are you
sure that there are few healthy oils on the market? Please provide a
reference. ”Compared with TAG, DAG has similar energy value,
digestibility and antiobesity characteristics. Their calorific value is
low, which has a positive effect on lipid metabolism, decreasing total
serum cholesterol, low-density lipoprotein cholesterol, and fat
accumulation, thereby reducing liver and abdominal fat levels.” If you
affirm that TAG and DAG have the same properties, it is not worth
carrying out the study that you have carried out…This is a sample of
the poverty of expression throughout the entire manuscript.
We sincerely thank the reviewers for their careful reading. We have
rewritten lines 49-130 on pages 3-5 of the original manuscript as
follows:
Therefore, it is of great significance to further increase the content
of DAG in human diet for health. The preparation methods of DAGs are
principally chemical and biological enzyme methods. The chemical method
has advantages of high reaction rate and simple operation (Zhong et al.,
2010). However, it increases the cost incurred in removing organic
reagents from the product. The bioenzymatic method using lipase as a
catalyst can effectively avoid contamination with organic reagents. At
present, the main methods for the preparation of DAGs by bioenzymatic
methods are esterification, hydrolysis, glycerolysis, and
transesterification. The esterification method uses lipase as a catalyst
to esterify free fatty acids (FFAs) and glycerol in water to obtain
DAGs. This method requires the use of vacuum, silica gel, molecular
sieves, and nitrogen stream to separate the water produced in the
reaction (Arcos et al., 1998; Weber & Mukherjee, 2004; Lo et al.,
2004). In the hydrolysis method, the fatty acids in TAG are substituted
with alcohol hydroxyl groups in the presence of water and lipase to form
FFAs, DAGs, monoacylglycerols (MAGs), and glycerol. The disadvantage of
this method is that the degree of hydrolysis is difficult to control and
often occurs at the oil-water interface (Li et al., 2018). The DAG
content obtained by a single method is not high, and the product has to
be purified by molecular distillation, solvent crystallization,
supercritical CO2 extraction, and silica column chromatography (Huang et
al., 2023; Li et al., 2018). Combining multiple methods may be an
effective way to prepare samples with high contents of DAG. Li et al.
(2021) partially hydrolyzed soybean oil using Lipase DF “Amano” 15 and
obtained DAG content of 55.2% by molecular distillation. Other products
were combined with PGL AOL-V269 D esterification reaction and molecular
distillation to obtain high purity DAG (99.3%). Liu et al. (2020)
prepared DAGs rich in α-linolenic acid by a two-step enzymatic method.
The combination of Lipase TL100L and Lipase PCL hydrolyzed silkworm
pupae oil to obtain 96.51% FFA, and then silkworm pupae oil diglyceride
oil with a purity of 97.01% was obtained by molecular distillation
after esterification catalyzed by lipase PCL. Based on the above
analysis, it is indeed feasible to prepare a high content of DAG by
coupling two or more methods.