Digestible Protein

Digestible proteins are mainly used when the intent is to develop such delivery systems that can be degraded by the protease activity within the stomach.

From: Nutrient Delivery , 2017

Determining the functional properties of food components in the gastrointestinal tract

M. Champ , in Technology of Functional Cereal Products, 2008

7.7.2 Proteins

The protein digestibility of an ingredient or a food can be evaluated using animal models. For example, calculation of the protein-digestibility-corrected amino-acid score (PDCAAS) is carried out using young rats (recommended animal model) (Darragh & Hodgkinson, 2000). This model is, however, controversial in some cases, such as foods (or ingredients – especially those containing anti-nutritional factors) specifically intended for the elderly (Gilani et al., 2005). Nevertheless the PDCAAS is now widely used as a routine assay for protein quality evaluation, replacing the more traditional biological methods (e.g. measurement of the protein efficiency ratio (PER) in rats) (Schaafsma, 2005).

The determination of the PDCAAS requires the determination of the digestibility of the protein(s) across the entire digestive tract. This faecal digestibility value is subsequently corrected for endogenous contributions of protein using a metabolic nitrogen value determined by feeding rats a proteinfree diet. However, the limitations inherent with this method are well recognized and determining the digestibility of a dietary protein to the end of the small intestine is the preferred alternative. Unlike the faecal digestibility assay, which uses only one basic methodology, ileal digestibility values can be determined in a number of ways (Darragh & Hodgkinson, 2000).

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PROTEIN | Quality

G.S. Gilani , N Lee , in Encyclopedia of Food Sciences and Nutrition (Second Edition), 2003

Recommended method for regulatory purposes

The PDCAAS is the most appropriate routine method for properly processed food where protein digestibility is a good approximation of bioavailability of the amino acids and where there is known to be no or only low levels of antinutrient factors. Where these conditions do not apply, a biological method should be used, whether this is PER, RNPR, or relative nitrogen utilization (RNU). Probably the least expensive and yet still valid and reliable method, and one that gives results that are proportional across a range of protein qualities, is the RNU method. The RNU method gives essentially the same values as the better known RNPR rat assay for routine protein-quality assessment of foods except that, as described in the section Rat Assays, it replaces measurement of protein needed for maintenance with a factor for maintenance. The elimination of the need for feeding a 'zero' protein diet to a group of rats makes the RNU method less costly than the RNPR method.

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Grain Structure, Quality, and Nutrition

C.V. Ratnavathi , in Breeding Sorghum for Diverse End Uses, 2019

4.5 Protein Digestibility

The in vitro protein digestibility is a very important biochemical parameter to assess the nutritional quality of a genotype. It is well accepted that sorghum has lower protein digestibility compared with other cereal grains (MacLean et al., 1981; Hamaker et al., 1987). The low protein digestibility characteristic is more prominent in cooked than uncooked sorghum (Axtell et al., 1981; Hamaker et al., 1987). Although protein digestibility of uncooked sorghum is only slightly lower than corn, it is still considered to affect its feed grain value especially for nonruminant animals. The main cause of the low protein digestibility is that the sorghum kafirins are resistant to peptidase due to the formation of intramolecular disulfide bonds (Belton et al., 2006). In tannin-rich varieties, the complexation of the kafirins with tannins reduces the protein digestibility up to 50% (Taylor et al., 2007). Furthermore, other exogenous factors (interaction of the proteins with nonprotein components such as starch, NSPs, phytic acid, and lipids) and endogenous factors (nature and organization of proteins inside the grain) contribute to the low digestibility (Belton et al., 2006; Ezeogu et al., 2008; Cardoso et al., 2017). Processing such as fermentation and germination may increase the digestibility up to two times (Afify et al., 2012). Wide variability was observed for protein digestibility among the 250 diverse Indian genotypes evaluated, which ranged from 22% to 73%(Ratnavathi and Elangovan, 2009). Further studies on protein digestibility hold promise for promotion of sorghum in feed industry.

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Protein: Quality and Sources

A.V. Kurpad , in Encyclopedia of Human Nutrition (Third Edition), 2013

Calculations and Examples

The EAA composition and protein digestibility of the food or mixed diet being tested are determined. Then the percentage or fractional value of the most limiting EAA (noncorrected amino acid score) is multiplied by the percentage or fractional value of 'true' protein digestibility to obtain the corrected score, which is equivalent to protein quality. This value can be used as such or it can be expressed in relation to the corrected amino acid score of a reference protein or food, usually casein or an animal food (milk, egg, or beef).

Proteins that have no limiting amino acids are assigned an amino acid score of 100% (or 1.00) that must be only corrected for digestibility. Similarly, if the clinical or experimental assessment of 'true' protein digestibility gives a value greater that 100% (generally due to experimental variability), a digestibility correction factor of 100% (or 1.00) is applied to the amino acid score. Table 6 shows examples of calculations for a single food as protein source. The same procedure can be used for food mixtures using a weighted average procedure based on the protein content, amino acid composition, and digestibility of the individual components. Table 7 shows an example of those calculations. For simplicity, the example uses only the four EAAs that are most often limiting.

Table 6. Calculation of amino acids scores of single protein sources corrected for digestibility and in relation to the protein quality to cow's milk

Food Most limiting amino acid Noncorrected amino acid score True protein digestibility Corrected amino acid score Protein quality relative to milk
Cow's milk None >100→100% ×95% =95% –
Polished rice Lysine 36   mg per g protein (36/58)×100=62% ×88% =55% (55/95)×100=58%
Egg white None >100→100% ×97% =97% (97/95)×100=102%

Table 7. Calculation of protein quality of a mixed diet based on whole wheat, polished rice, and chicken breast

Raw ingredients Data from analysis of literature Quantities calculated for the mixed diet
Weight (g) Protein (g per 100   g) Lys SAA Th Trp True digestibility (%) Total protein (g) H=A×B/100 Lys (mg) I=H×C SAA (mg) J=H×D Thr (mg) K=H×E Trp (mg) L=H×F
(mg per g protein)
A B C D E F G
Whole wheat 300 11 28 37 29 11 86 33 924 1221 957 363
Polished rice 200 7 36 38 33 13 88 14 504 532 462 182
Chicken breast 150 19 83 38 40 12 95 28.5 2366 1083 1140 342
Total 75.5 3794 2836 2559 887
M Weighed mean digestibility of the mixed diet (sum of (G×H) for each food component divided by total protein, H) 0.90
N mg amino acid per g protein (total for I, J, K, or L divided by total H) 50 38 34 12
P Amino acid scoring pattern, mg amino acid per g protein 58 25 34 11
Q Score for each amino acid in the mixed diet (N/P) 0.86 1.52 1.00 1.09
R Amino acid score adjusted for digestibility (Q of the limiting amino acid multiplied by M) 0.86×0.90=0.77 (or 77%)

Lys, lysine; SAA, sulfur-containing amino acids; Thr, threonine; Trp, tryptophan.

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Sorghum Grain Quality

C.V. Ratnavathi , V.V. Komala , in Sorghum Biochemistry, 2016

1.1.9 Determination of Protein Digestibility

The samples are estimated for protein digestibility by turbidity assay method (Hamaker and Bugusu, 2003). Digestion of proteins present in sorghum flour was carried out by pepsin followed by extraction and removal of digested protein with phosphate buffer (pH 7, 0.1   M). Undigested protein present in the sample was extracted using borate buffer (pH 10, 0.0125   M) containing 1% SDS and 2% mercaptoethanol for 1   h. Reaction of trichloro acetic acid (72%) with extracted undigested protein results in turbidity; the turbidity of the sample was measured at 562   nm. Corresponding absorbance indirectly gives the percentage of digested protein present in the sample.

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Milk proteins: a cornucopia for developing functional foods

Paul J. Moughan , in Milk Proteins, 2008

Specialized nutritionals

Early in vivo determinations of protein digestibility were based on fecal measurement, which is now known to be flawed given the significant degree of colonic microbial metabolism known to occur and that amino acids either are not absorbed as such from the large intestine or are absorbed to only a very limited extent (Moughan, 2003). The preferred accurate method for determining amino acid digestibility is to determine unabsorbed amino acids at the end of the small bowel (terminal ileum). This can be achieved in humans using naso-intestinal intubation or through the co-operation of ileostomates. Alternatively, animal models can be used with rat and pig ileal digestibility assays, both being suitable (Moughan et al., 1994).

Where a protein has undergone structural alteration due to processing or storage (especially at high temperatures), conventional digestibility measures are inappropriate for some amino acids and in particular the often first-limiting amino acid, lysine. A new lysine bioavailability assay (based on the collection of ileal digesta and application of the guanidination reaction) has been developed; it can usefully be applied to damaged proteins (Moughan, 2003). When digestibility determinations are based on the sampling of ileal digesta, it is important to recognize that digesta contain copious quantities of endogenous (of body origin) protein in addition to undigested protein. This endogenous protein component needs to be taken into account (Moughan et al., 1998), to yield "true" rather than "apparent" estimates of digestibility.

There are very few published data on true ileal protein digestibility as determined using human subjects. A comprehensive set of studies in humans (Gaudichon et al., 1994, 1995, 1996; Mahé et al., 1995, 1996) demonstrated a high true ileal digestibility of protein in milk proteins of around 95%. Comparable values, using the same methodology, for soy and pea proteins were 91 and 89% respectively. Sandstrom et al. (1986) gave soy- and meat-based diets to ileostomates and reported true ileal digestibility coefficients for total nitrogen in the range 80–85%. The naso-intestinal intubation method with normal volunteers has also been used to determine digestibility coefficients for individual amino acids (Gaudichon et al., 2002).

For cow's milk, true ileal digestibility ranged from 92% for glycine to 99% for tyrosine, whereas, for soy bean, digestibility ranged from 89% for threonine to 97% for tyrosine. In our own laboratory, true ileal amino acid digestibility determined using ileostomates ranged from 98% for aspartate to 100% for cysteine in sodium caseinate; from 93% for threonine to 99% for cysteine in whey protein concentrate; from 95% for glycine to 99% for arginine in soy protein isolate; and from 91% for cysteine to 100% for arginine in soy protein concentrate (Moughan et al., 2005a).

There are more comprehensive data on the true ileal digestibility of amino acids in various milk proteins, which have been obtained using animal models for digestion in humans (Rutherfurd and Moughan, 1997). Table 17.1 shows ileal digestibility data obtained using the laboratory rat for selected amino acids in soy protein concentrate, soy protein isolate, lactic casein, sodium caseinate, whey protein concentrate, α-lactalbumin and milk protein concentrate. These data confirm the very high digestibility of milk-derived proteins to the end of the ileum in simple-stomached mammals. The dietary amino acids are virtually completely digested.

Table 17.1. Mean true ileal digestibility of selected amino acids in a range of soy and dairy products

Amino acid Soy protein concentrate Soy protein isolate Lactic casein Sodium caseinate Whey protein concentrate α-Lactalbumin Milk protein concentrate
Lysine 97.3 98.5 98.8 98.0 98.2 94.7 98.3
Methionine 95.3 100.0 100.0 99.6 100.0 99.2 100.0
Cysteine 86.9 95.3 99.2 93.0 99.6 96.1 97.8
Isoleucine 96.4 96.8 94.8 90.6 98.1 95.4 94.9
Leucine 95.7 95.3 99.1 97.6 99.1 96.1 98.9

Source: Adapted from Rutherfurd and Moughan (1997), with permission of the publisher

Almost all dairy proteins have been subjected to some type of processing during their manufacture and, given that milk products often contain the reducing sugar lactose, they are susceptible to damage to the amino acid lysine. A specific assay designed to allow an accurate determination of lysine bioavailability in processed foods (Moughan and Rutherfurd, 1996) has recently been applied to a range of commercially available milk-protein-based products (Table 17.2), once again underscoring the high bioavailability of milk proteins and the limited amount of lysine damage incurred by proteins with modern controlled processing. In contrast, when the same bioassay was applied to grain-based processed foods, including cereals for children, substantial amounts of lysine damage were found (Table 17.3). Milk and milk-based products have an important role in complementing cereal foods and in supplying available lysine.

Table 17.2. True ileal reactive lysine digestibility (bioavailability, %) and digestible total and reactive lysine contents (g/kg air-dry) for 12 dairy protein sources

Product Digestibility Digestible lysine
Total Reactive a
Whole milk protein 98.3 26.2 24.0
Infant formula A 91.0 8.3 8.6
Infant formula B 92.3 9.1 9.2
Infant formula C 93.1 11.1 11.7
Whey protein concentrate 98.5 79.9 77.5
UHT milk 100.0 31.7 31.4
Evaporated milk 96.7 23.4 20.5
Weight-gain formula 99.0 24.4 24.1
Sports formula 98.0 20.4 19.1
Elderly formula 97.1 11.7 11.8
Hydrolyzed lactose milk powder 98.6 27.2 25.1
High-protein supplement 99.9 14.3 14.3

Source: Adapted from Rutherfurd and Moughan (2005), with permission of the publisher

a
Bioavailable lysine; minimal difference between total lysine and reactive lysine denotes minimal Maillard damage

Table 17.3. True ileal digestible total and reactive lysine contents (g/kg air-dry) in selected cereal-based foods

Cereal product Digestible lysine
Total Reactive a
Wheat-based (shredded) 1.3 0.8
Corn-based (flaked) 0.4 0.2
Rice-based (puffed) 1.1 0.6
Mixed cereal (rolled) 3.2 1.9

Source: Adapted from Rutherfurd et al. (2006), with permission of the publisher

a
Bioavailable lysine; a difference between total lysine and reactive lysine denotes Maillard damage

Figure 17.1 highlights the substantial differences that exist in the amounts of digestible amino acids supplied by plant proteins (e.g. soy) and milk proteins (e.g. α-lactalbumin). The often first-limiting amino acids (lysine and methionine plus cysteine) are found in much higher concentrations in the milk proteins, making them excellent sources of amino acids and very important dietary constituents to afford a balanced dietary protein intake.

Figure 17.1. Digestible (true ileal) amino acid contents of a plant protein and a milk protein (adapted from Rutherfurd and Moughan, 1997, with permission of the publisher).

Because of their relatively high levels of nutritionally important amino acids, milk proteins are utilized efficiently by humans, when given as a sole protein source. Tomé and Bos (2000) reported net post-prandial protein utilization values of 80% and 72% for milk protein and soy protein respectively, measured over 8   h after the ingestion of standard meals by healthy human subjects.

Given the high bioavailability of amino acids in milk proteins and their abundant supply, it is hardly surprising that milk proteins are commonly used for the manufacture of so-called nutritionals, i.e. foods designed for a specific nutritional purpose (e.g. infant, sports, elderly formulas).

In the future, with increasing human population growth and greater pressure on food supplies, it is likely that milk proteins will play an ever more important role as protein "balancers" in plant-based processed foods.

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Nutrition and Dietary Recommendations for Bodybuilders

Philip E. Apong , in Nutrition and Enhanced Sports Performance (Second Edition), 2019

Casein

Whey protein is considered a fast-digestible protein, whereas casein is noted in the literature as a slow-digestible protein [30]. This is because on ingestion, the casein protein coagulates in the acidic environment of the stomach, possibly delaying gastric emptying and/or hindering easy accessibility of the amino acid residues to hydrolytic digestion [30,43]. In their archetypical study, Boirie et al. [30] investigated the effects of speed of protein digestion on postprandial protein accretion in resting healthy, physically active male subjects and showed that in young healthy men at rest, casein administration induced a prolonged plateau of moderate hyperaminoacidemia. Moreover, whole-body protein breakdown was inhibited after casein ingestion, but not after whey protein ingestion. Interestingly, even though whey protein administration caused a greater increase in postprandial protein synthesis than did casein administration, the net leucine balance over the 7   h after the test meal (i.e., casein protein or whey protein) was more positive with casein than with whey. So it seems that slow-digestible protein such as casein may have an anticatabolic effect that can lead to better overall net whole-body leucine balance, at rest, in healthy, physically active young men [30]. Therefore quickly digestible protein such as whey can stimulate rapid aminoacidemia and acute activation of protein synthetic machinery, whereas more slow-digestible protein promotes anticatabolic effects and better net leucine balance at the whole-body level [30–32]. Casein's inhibitory effect on protein breakdown can allow for muscle preservation as well as preservation of net protein the splanchnic region [44,45] at least in young individuals. This paradigm seems true for the younger generation of subjects studied, but contradictory results in experiments in elderly subjects with respect to whole-body protein metabolism suggest that the ingestion of a fast-digestible protein is associated with a greater whole-body leucine balance [31,39]. Ultimately, for young bodybuilders, supplementing with casein-based protein may be a good way to stave off catabolism, whereas whey protein can promote acute increases in anabolic activity. Because milk comprises both fast and slow protein components, it is worthwhile asking if milk protein can deliver benefits from each of its constituent parts.

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Seaweed proteins

J. Fleurence , ... J. Dumay , in Proteins in Food Processing (Second Edition), 2018

9.3.2.2 Fermentation processes

The effects of fermentation treatment on improving protein digestibility were studied. For example, the action of Rhizopus macroscopus var. chinensis, Aspergillus oryzae, and Trichoderma pseudokoningii was tested on Palmaria palmata. The fermentation processes significantly increased the in vitro digestibility of P. palmata proteins (Fig. 9.2). The best result was recorded for Trichoderma pseudokoningii which gave a relative digestibility rate close to 73% of that for casein digestibility compared to 50% after treatment by Aspergillus oryzae or Rhizopus macroscopus. The presence of xylanases in T. pseudokoningii probably explains the greater efficiency of this microorganism on Palmaria palmata (Marrion et al., 2003).

Fig. 9.2. Fermentation effects on Palmaria palmata digestibility (pepsin and pancreatin activity).

 From Marrion and Villaume, unpublished data.

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COFFEE | Physiological Effects

R. Viani , in Encyclopedia of Food Sciences and Nutrition (Second Edition), 2003

Nutritional Value of Coffee/Effects on Availability of Nutrients in Diet

The coffee brew is naturally poor in digestible proteins, fats, carbohydrates, and sodium, and is considered a nonnutritive dietary component, drunk for sensory pleasure and for its mild stimulatory effects. Its use as a vehicle for nutritious additives such as milk and sugar, and its contribution to the total water intake must, however, not be neglected.

Among the micronutrients found in coffee, niacin (nicotinic acid), formed from trigonelline during roasting, present at levels of 1–3   mg per cup, which corresponds to 5–20% of the recommended daily intake, has been shown to play a role in preventing pellagra in populations with a marginal diet. Animal studies have indicated that trigonelline itself can be transformed into nicotinic acid. (See NIACIN | Physiology.)

Amounts of soluble dietary fiber (sum of the indigestible carbohydrates and of carbohydrate-like components formed at roasting) of the order of 10–25% of the total coffee solids present in the brew may explain, on one hand, the protective role of coffee against colorectal cancer, and, on the other, together with chlorogenic acids, the reduction in absorption of nonheme iron when coffee is consumed with or just after a meal. (See CANCER | Diet in Cancer Prevention; DIETARY FIBER | Physiological Effects.)

The hypothesis that the phytate content of coffee (1–20   mg per cup) significantly lowers the gastrointestinal absorption of zinc needs verification. (See PHYTIC ACID | Nutritional Impact; ZINC | Physiology.)

Potassium, present at levels of 80–160   mg per cup, may contribute up to 10% of the daily intake for an adult. (See POTASSIUM | Properties and Determination.)

The intake of magnesium and of manganese from coffee is significant. (See MAGNESIUM.)

The importance of coffee in the calcium balance of the bone is still unclear. (See CALCIUM | Properties and Determination.)

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Green Tea and Protein Availability

Joanna Bajerska , ... Jan Jeszka , in Tea in Health and Disease Prevention, 2013

Effects of Green Tea Polyphenols on Protein Availability

The influence of green tea compounds on protein digestibility might be attributable not only to their effects on enzyme activity, but also to their formation of water-insoluble complexes with proteins, resulting in the lower bioavailability of the affected proteins. It is known that polyphenols are able to bind some kinds of nutrients, such as proteins and some minerals (Zhu et al. 1997). In the case of proteins, polyphenols can form ionic and hydrogen bonds with their amino, hydroxyl, and carboxyl groups (Fickel et al., 1999). In fact, in the food industry, polyphenols such as tannic acid, gallotannin, catechin, and proanthocyanidin may play an important role in the formation of sediments and haze, due to their ability to form various complexes with food proteins (Siebert et al., 1996a, b). This may lead to low quality in beverages such as fruit and vegetable juices. The same reactions occur in the lumen of the gastrointestinal tract, causing a decreased absorption of proteins, and thereby modulating their digestibility (Naz et al., 2011).

The bonding and precipitating ability of tea polyphenols has been investigated by He et al. (2006) using a common protein, gelatin. They found that the strength of bonding increased with the concentration of both reagents. It is the phenolic group which binds to protein, and lower-molecular-weight phenols may bind without necessarily causing precipitation from aqueous solutions (Zhu et al., 1997). Such an interaction between human serum albumin and catechins was investigated kinetically by Minoda et al. (2010), who showed that green tea extract catechins have different capacities for protein binding. The authors indicated that the galloyl moiety is the factor that plays the most important role in this effect. As in the case of enzyme inhibition, the ester bond-containing catechins (ECG and EGCG) showed much greater affinity for human serum albumin – about 100 times stronger than that of EC or EGC (the catechins without a galloyl moiety). The authors suggest that the differences are associated with hydrophobicity, which increases drastically with the addition of the galloyl moiety that stabilizes the complex. Treating the green tea product enzymatically with tannase leads to hydrolysis of EGCG and ECG to EGC and EC, and thus to a relatively low ability to form protein-catechins aggregations (Minoda et al., 2010). Moreover, the polyphenols, especially EGCG, have a preference for proteins with a high level of the amino acid proline, such as caseins and the alpha-lactalbumin and beta-lactoglobulin in dairy products (Hursel and Westerterp-Platenga, 2009).

The interactions described above were assayed in vitro, but in the opinion of the investigators, the results should also apply in the human body. The influence of green tea polyphenols was also investigated in in vivo studies on animals. In an experiment conducted by Bajerska et al. (2011), the effect of ingesting 1.1% and 2.0% green tea aqueous extract (GTAE) on the apparent digestion of macronutrients, including protein, in rats fed with a high-fat (HF) diet was evaluated. Doses of 1.1% and 2.0% GTAE added to the diet correspond to an intake in humans of 5 and 8 cups (200 ml/cup) of green tea per day, respectively. A significant reduction in the apparent digestion of protein in the group of rats fed HF diets enriched with GTAE by 11.2% and 9.0% was found, relative to a control group (Figure 40.2). This finding agrees with the results obtained by Unno et al. (2009) and Onishi, Iga and Kiriyama (2005). The first of these studies demonstrated that the apparent rate of digestion of protein was 95.8% for the control and 89.3% for rats receiving a diet with 1.0% extract rich in tea catechins (ERTC), mostly gallate forms (Figure 40.3). In the second study, even doses of green tea polyphenols as low as 0.2% and 0.4% (three times smaller than those used in study conducted by Bajerska et al. (2011)) decreased protein digestion in the small intestine, but had no effect on nitrogen balance. This effect is explained by the phenolic group of catechins binding to proteins through hydrophobic hydrogen bonds, creating catechin-protein complexes, which thereby limit the access of proteolytic enzymes (mainly pepsin and trypsin) to the substrate. Still, there is no evidence to determine whether tea catechins affect the secretion of endogenous proteins or the degradation and reabsorption of endogenously secreted proteins. Pooled results from animal studies on the effect of green tea extracts on apparent protein digestibility are presented in Table 40.2.

FIGURE 40.2. Comparison of Apparent Digestion of Protein and Fat in Treatment (GTAE) and Control Groups.

GTAE: green tea aqueous extract.

Values are the means ± SD for 6 rats per group.

Means with different superscripts are significantly different (P < 0.05).

 (This figure was created on the basis of data from Bajerska et al., 2011.)

FIGURE 40.3. Comparison of Apparent Digestion of Protein and Fat in Treatment (ERTC) and Control Groups.

ERTC: extract rich in tea catechins.

Values are the means ± SD for 7 rats per group.

Means with different superscripts are significantly different (P < 0.05).

 (This figure was created on the basis of data from Unno et al., 2009.)

TABLE 40.2. Pooled Results from Animal Studies on the Effect of Green Tea Extracts on Protein Apparent Digestibility

Animals Fllow-Up Experimental Diet Green Tea Extract Dose Equivalent Number of Cups of Green Tea4 Reported Effects on Apparent Digestibility of Protein5 References
11-week-old male Wistar rats (n = 6/group) 8 weeks High-fat (~50% energy from fat) GTAE1 1.1%
2.0%		 5
8		 Reduction by
11.2%
9.0%		 Bajerska et al., 2011
4-week-old male Wistar rats (n = 7/group) 20 days Diet consist of 20% caseining, 10% corn oil, 50% corn starch, 10% sucrose, 5% cellulose ERTC2 1% 7 Reduction by 6.5% Unno et al., 2009
3-week-old male SD rats (n = 6/group) 15 days High-amylose cornstarch fat (~30% of starch in diet) GTP3 0.2%
0.4%		 1.5
3		 Reduction by
1.8%
2.6%		 Onishi et al., 2005

1 GTAE: green tea aqueous extract – EGCG, 7.0%; EGC, 4.1%; and ECG, 1.8% of dry matter.

2 ERTC: extract rich in tea catechins (aqueous and freeze-dried) – EGCG (22.2%), GCG (27.5%), ECG (6%), CG (5%), EGC (0.4%), GC (0.3%), EC (0.5%), C (0.4%) (given as percentages of dry matter).

3 GTP: green tea polyphenols (total polyphenol content 50%) – EGCG (25%), EGC (7%), C (6%), GC (6%), ECG (5%), and EC (1%).

4 Based on data described by Bose et al. (2008), the level of green tea extract used in the studies corresponds to 5–8, 7 and 1.5–3 cups (200 ml) of green tea, inBajerska et al. (2011), Unno et al. (2009) and Onishi et al. (2005), respectively.

5 Apparent protein digestion was calculated as follows: [(N of the ingested food – N of the feces)/(N of the ingested food)] ×100.

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