Di Acyl Glycerol s

8/12/2019 Di Acyl Glycerol s

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2Diacylglycerols

Brent D. Flickinger1 and Noburo Matsuo2

1Archer Daniels Midland Company

Decatur, Illinois2Kao Corporation

Tochigi, Japan

1. INTRODUCTION

Diacylglycerols (DAG) are natural components of various edible oils (1, 2). Typi-

cally, the level of DAG in edible oils is below 5% of total oil; however, several

edible oils have levels above 5% (Table 1). Also, DAG have been used as emulsi-

fiers for use in food systems, particularly baked goods, and are approved as such(3). Human consumption of DAG has been estimated at 3 g per day.

The traditional method of producing DAG is interesterification of triacyl-

glycerols (TAG) with glycerol in the presence of a chemical catalyst at elevated

temperatures (4). Preferred catalysts are alkali such as sodium/potassium hydro-

xide, sodium methoxide, or potassium acetate. Formation of monoacylglycerols

(MAG) and DAG can be controlled to a certain degree by the molar ratio of glycerol-

to-TAG in the initial reaction mixture. Nonetheless, the resulting DAG is part of a

mixture of glyceridic components that present difficulties in obtaining a high-purityDAG fraction using standard industrial separation processes (i.e., chromatography,

distillation, or winterization) caused by similar chemical and physical properties of

these components.

DAG oil is prepared through the process of enzymatic esterification. Starting

with a blend of soybean and canola oils, fatty acids are prepared then mixed

Baileys Industrial Oil and Fat Products, Sixth Edition,Six Volume Set.Edited by Fereidoon Shahidi. Copyright# 2005 John Wiley & Sons, Inc.

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with glycerol. This mixture undergoes esterification using a 1,3-specific lipase from

Rhizomucor miehei, which has been immobilized on a resin bed. After several

finishing processes, including deodorization, the resulting edible oil is obtained.

This oil is bland in flavor and light in color making it suitable for use as a bottled

oil or oil ingredient for various food applications. For more information on DAG oilmanufacturing, physical properties, and food application uses, a book containing

chapters solely devoted to these issues of DAG oil has been published (5).

The nutritional characteristics of DAG oil (80%) have been compared with

dietary TAG of similar fatty acid composition. In particular, the 1,3-DAG isoform

appears to have distinct metabolic characteristics that can impact postprandial lipid

metabolism and use of macronutrients for energy compared with TAG.

The rationale for anticipating metabolic differences is a result of the difference

in metabolism of the digestion product of 1,3-DAG. The body digests DAG oil

yielding monoacylglycerols (MAG) and free fatty acids (FFA) just as observed

with TAG oil. As a result of the significant content of 1,3-DAG, 1-monoacylglycer-

ol (1-MAG) is a major digestion product of DAG oil that is not observed in any

significant amount upon TAG oil digestion. The small intestine typically reassem-

bles digested monoacylglycerols and free fatty acids into TAG beginning with

2-MAG. Previous reports in the literature indicate that providing 1-MAG results

in lower amounts of fat-rich particles appearing in serum following consumption.

This difference in fat metabolism with DAG oil is apparent in fewer fat-rich parti-

cles appearing in the blood after a meal containing DAG oil. As a result, fatty acids

not appearing as chylomicron triacylglycerols must be excreted in the feces or used

by the gut or liver for energy or triacylglycerol storage.

The following review focuses on experimental data supporting different meta-

bolic characteristics of 1,3-DAG or DAG oil containing 1,3-DAG (Table 2). Rele-

vant areas of observed differences between 1,3-DAG/DAG oil and TAG/TAG oil

metabolism include postprandial lipid metabolism and use of macronutrient fuels.

Observations from animal and human experimental data are included.

TABLE 1. Glyceride Content of Various Edible Oils.1

% of Total Oil

Oil TAG DAG MAG Others

Cottonseed 87.0 9.5 0.2 3.3

Palm 93.1 5.8 0.0 1.1

Olive 93.3 5.5 0.2 2.3

Corn 95.8 2.8 0.0 1.4

Safflower 96.0 2.1 0.0 1.9

Lard 97.9 1.3 0.0 0.8

Soybean 97.9 1.0 0.0 1.1

Rapeseed 96.8 0.8 0.1 2.3

1

Data sourced from (1) and (2).

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Differences caused by 1,3-DAG/DAG oil in the following discussion are made

under the assumption of being compared with TAG/TAG oil control of similar fatty

acid composition. DAG oil refers to an oil containing 8090% DAG, 1020% TAG,

with the DAG portion containing 70% 1,3-DAG, 30% 1,2-DAG (Figure 1). TAG oil

refers to a conventional edible oil.

2. COMPARISON OF DAG OIL VS. TAG OIL

2.1. Digestion Products

Digestion of 1,3- and 1,2-DAG (70%:30%, respectively, as diolein) results in the

preferential formation of 1(3)-MAG and FFA in rats (6). 1(3)-MAG is 65% of

the monoacylglycerol after 60 minutes of interaction with the small intestine.

This observation has been demonstrated also in mice using labeled fatty acids

incorporated into 1,3-DAG (7). After exposure of labeled 1,3-DAG to the small

intestine in mice, the percentage of 1(3)-MAG from total lipid content increased

to 14.2% compared with 1.5% (p


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with 22.3% (p


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decreased during the initial 1 hour following administration by approximately 50%

(17% in DAG oil vs. 31%) (9).

Two human studies have focused on serum levels of triglycerides after consump-

tion of test emulsions. Using single doses of 10 g, 20 g, or 44 g of DAG oil, signifi-

cant differences (p


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increased also significantly, consistent with increased ACO activity, compared with

a conventional triacylglycerol oil (14). Enhanced beta-oxidation in the small intes-

tine has been reported in mice fed DAG oil compared with triacylglycerol oil (7).

Increased beta-oxidation in the small intestine caused by DAG oil consumption was

associated with increased expression of genes involved in beta-oxidation and lipidmetabolism, including ACO, medium-chain acyl-CoA dehydrogenase (MCAD),

liver-fatty acid binding protein (L-FABP), fatty acid transporter (FAT), and UCP-

2. These changes in beta-oxidation and mRNA expression are not apparently con-

sistent with regard to tissue specificity. In mice, these changes occurred solely in the

small intestine, whereas in rats, these changes occurred solely in the liver.

Indirect calorimetry provides the ability to measure the relative contribution of

macronutrients toward energy use. The measurements of expired carbon dioxide

and consumed oxygen are used to calculate respiratory quotient (RQ). An RQ of1.0 indicates use of carbohydrate solely, an RQ of 0.7 indicates use of fat solely,

whereas an RQ of 0.85 indicates mixed use of macronutrients. Data in rats demon-

strates a significant increase in using fat as an energy substrate following DAG oil

infusion (gastric) as observed by a decreased respiratory quotient value between 3

5 hours post-infusion (15).

In humans, a recently published study reported the influence of DAG oil versus

conventional oil on energy expenditure, energy substrate use, and subjective appe-

tite ratings during a 36-hour stay in a metabolic chamber (16). Using healthywomen (n 12), each subject consumed a defined, eucaloric diet for 3 days prior

to each chamber. During the chamber stay, DAG oil or conventional oil with a simi-

lar fatty acid composition provided 40% of the fat consumed, which was as part of a

defined (55% en from carbohydrate, 15% en from protein, 40% en from fat) euca-

loric diet. For data analysis, differences over the entire 36-hour experimental period

were evaluated. A significant decrease in respiratory quotient (0.006, p


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Serum levels of ketones, as measured by beta-hydroxybutyrate, and free fatty

acids tended to be greater following DAG oil consumption with serum ketone levels

being significantly greater on day 2 (at first draw) after DAG oil consumption

(p


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change in body weight (p


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toward greater fat use. Animal experiments demonstrate a smaller accumulation of

body weight and body fat over extended periods of consumption.

In humans, DAG oil consumption decreases serum triglycerides (postprandial

and fasting) and enables greater degrees of body fat and body weight loss compared

with conventional oil when used as a dietary aid as part of a healthy diet or caloricmanagement plan. Studies in Japanese individuals and overweight adult Americans

show similar apparent changes in body weight and body fat with greater differences

in both measures occurring in groups consuming DAG oil.

Relatively mild losses in body fat and body weight loss have occurred following

consumption of DAG oil over a period of several months with an approximate dif-

ference in daily caloric expenditure or intake between 50 100 calories. The differ-

ence in greater weight loss over six months observed between DAG oil and

conventional oil could be attributed to a daily caloric deficit of approximately 48calories (24). Although the difference in weight loss over 4 months observed

between DAG oil and conventional oil could be attributed to a daily caloric deficit

of approximately 90 calories (23). Correspondingly, the data from the metabolic

chamber study did not indicate a significant change in daily energy expenditure

after DAG oil consumption compared with TAG oil in humans (16). Detecting

an energy expenditure difference of 50100 calories over a 2436-hour period

would be difficult in a metabolic chamber setting under the best of conditions.

These investigators also indicate a significant increase in fat oxidation of approxi-mately 45 g on a daily basis, which corresponds to a shift in using approximately

3545 calories from fat rather than other fuel sources. Apparently, this shift in sub-

strate use may affect overall energy intake (i.e., appetite) to a greater degree than

overall energy expenditure. Interestingly, individuals subjected to acute overfeeding

of 1-MAG did not show any differences with regard to energy intake and appetite

regulation compared with TAG (25, 26), whereas jejunal infusions of free fatty

acids have shown the ability to reduce food intake and body weight in rats (27).

These studies may indicate that the combination of 1-MAG and FFA, potentially

more so the FFA, caused by the digestion of 1,3-DAG results in observed differ-

ences in energy expenditure and appetite regulation.

From a mechanistic viewpoint, fatty acid oxidation as a metabolic control for

energy intake appears to be an important relationship (2830). Products of fatty

acid oxidation have been implicated in playing a role in control of food intake.

Historically, ketones have received considerable attention, whereas glycerol and

free fatty acids have received less attention. Using ketogenic diets (defined as

severe CHO restriction) for weight loss has been long espoused with an underlying

assumption that elevated serum ketone levels provide a certain degree of appetite

suppression. This effect of appetite suppression by elevated serum ketones remains

to be conclusively documented.

Effects of compounds that inhibit enzymes of fat metabolism have been reported

in recent literature. Changes in fatty acid oxidation have been inversely correlated

to changes in food intake using rodent models as well as human subjects. After

administration of compounds that directly inhibit fatty acid oxidation or inhibit

fatty acid synthesis, significant increases or decreases in food intake, respectively,

SUMMARY 45


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as well as changes in body weight over extended durations have been observed (31

36). Etomoxir, a carnitine palmitoyl transferase I inhibitor, causes decreased mito-

chondrial oxidation of long-chain fatty acids and increases insulin resistance in

mice as a result of intramyocellular lipid accumulation over prolonged administra-

tion (37). Limited studies with acute administration of etomoxir in human subjectsshow mixed evidence regarding an increase in food intake (38, 39). C75, a fatty

acid synthase inhibitor, results in decreased fatty acid synthesis and decreased

food intake and body weight in mice through its proposed modulation of hypotha-

lamic neuronal activity and neuropeptide Y levels (40, 41). Studies in human sub-

jects administered C75 have yet to appear in the scientific literature.

Use of fatty acids for energy during the postprandial period after DAG oil con-

sumption has been reported to occur in the liver or small intestine via beta-oxida-

tion based on rodent studies (13, 14, 42). Regulation of hepatic fat oxidation isbelieved to be under the control of hepatic glucose metabolism, rather than dietary

fat intake, which implies that the status of glycogen stores and carbohydrate meta-

bolism may be more important parameters in controlling total energy balance and

fat mass than fat intake (43, 44). This mechanism suggests that increased postpran-

dial fatty acid oxidation may potentially lead to smaller glycogen stores, which

have been observed to correlate with lower body fat stores and decreased effort

to replenish the loss of body fat.

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