ABSTRACT
Title
Influence of food matrix on polyphenol bio-accessibility from almond skins during digestion
Authors
M. Martorana1, T. Arcoraci1, G. Mandalari1,2, C. Bisignano1, A. Tomaino1
1Farmaco-Biologico Dept, Faculty of Pharmacy, University of Messina, Italy
2Institute of Food Research, Norwich, UK
1Farmaco-Biologico Dept, Faculty of Pharmacy, University of Messina, Italy
2Institute of Food Research, Norwich, UK
Abstract
Almond skins (Prunus dulcis [Mill.] D. A Webb.)are low grade by-products of the almond-processing industry. They represent about 7% of the nut weight and are currently mainly used in cattle feed(Grasser et al., 1995). However, they represent a good source of potentially high-value components, such as dietary fibers and flavonoids(Manach et al., 2004). In this study we describe the release of polyphenols from both blanched almond skins (BS) and natural almond skins (NS) during simulated gastrointestinal (GI) digestion and the effect of different food matrices on their bio-accessibility.
NS were prepared by a freeze–thaw method using liquid nitrogen and then milled in a powder with an analytical mill.BS were industrially prepared by hot water blanching (Mandalari et al., 2010) and both supplied by Almond Board of California .
A dynamic gastric model (DGM) of digestion, developed at the Institute of Food Research (UK), that simulates the physic-chemical processing of the stomach and accurately mimics both the transit time and the luminal content of the upper human gut, was used to digest almond skins and food containing almond skins (crisp bread, biscuits and milk). Gastric digesta were then incubated under duodenal conditions in the presence of pancreatic enzymes, hepatic and bile secretion. Determination of phenols in gastric and duodenal digestion samples was performed by HPLC-DAD-RF analysis.
The major flavonoids identified both in NS and in BS almond skins were (+)-catechin (155.69 ± 9.98; 50.57 ± 3.82 for NS and BS, respectively), (-)-epicatechin (109.56 ± 6.54; 15.89 ± 0.86 for NS and BS, respectively), kaempferol (229.49 ± 10.50; 40.76 ± 2.81 for NS and BS, respectively)and isorhamnetin (549.01 ± 3.10; 53.80 ± 3.56 for NS and BS, respectively) (as 3-O-rutinoside and 3-O-glucoside). For all foods tested during simulated gastric digestion the bio-accessibility of these flavonoids was significant (crisp bread: NS= 45.26±3.92%, BS= 41.35±3.88%; biscuit: NS=40.0±3.75%, BS=45.78±4.08%; milk: NS=43.76±4.21%, BS=45.13±3.87%), and at a slightly higher degree during the gastric plus duodenal digestion (crisp bread: NS= 20.51±1.82%; BS= 18.66±1.65%; biscuit: NS= 19.45±1.34%, BS= 11.17±1.01%; milk: 16.85±1.56%; BS= 13.17±1.25%). Higher percentages of polyphenols were released from NS compared to BS during in vitro digestion. Food matrix does not significantly affect polyphenols release during digestion. The presence of milk in the gastric environment does not influence polyphenol release from digested almond skins. However, milk components (for example, proteins) can partially sequester polyphenols released from almond skins, because only a lower polyphenol amount is recovered free in the aqueous medium.
The results of the present study indicate that polyphenols from almond skins are bio-accessible in the upper GI tract and therefore potentially available for absorption during human digestion, so suggesting that almond skins can be potentially used as added value food supplement.
This work has been funded by the Almond Board of California.
Grasser et al., 1995. Journal of Dairy Science 78:962–971.
Manach et al., 2004. Am J Clin Nutr 79:727-747.
Mandalari et al., 2010. Food Chemistry 122:1083–1088.
NS were prepared by a freeze–thaw method using liquid nitrogen and then milled in a powder with an analytical mill.BS were industrially prepared by hot water blanching (Mandalari et al., 2010) and both supplied by Almond Board of California .
A dynamic gastric model (DGM) of digestion, developed at the Institute of Food Research (UK), that simulates the physic-chemical processing of the stomach and accurately mimics both the transit time and the luminal content of the upper human gut, was used to digest almond skins and food containing almond skins (crisp bread, biscuits and milk). Gastric digesta were then incubated under duodenal conditions in the presence of pancreatic enzymes, hepatic and bile secretion. Determination of phenols in gastric and duodenal digestion samples was performed by HPLC-DAD-RF analysis.
The major flavonoids identified both in NS and in BS almond skins were (+)-catechin (155.69 ± 9.98; 50.57 ± 3.82 for NS and BS, respectively), (-)-epicatechin (109.56 ± 6.54; 15.89 ± 0.86 for NS and BS, respectively), kaempferol (229.49 ± 10.50; 40.76 ± 2.81 for NS and BS, respectively)and isorhamnetin (549.01 ± 3.10; 53.80 ± 3.56 for NS and BS, respectively) (as 3-O-rutinoside and 3-O-glucoside). For all foods tested during simulated gastric digestion the bio-accessibility of these flavonoids was significant (crisp bread: NS= 45.26±3.92%, BS= 41.35±3.88%; biscuit: NS=40.0±3.75%, BS=45.78±4.08%; milk: NS=43.76±4.21%, BS=45.13±3.87%), and at a slightly higher degree during the gastric plus duodenal digestion (crisp bread: NS= 20.51±1.82%; BS= 18.66±1.65%; biscuit: NS= 19.45±1.34%, BS= 11.17±1.01%; milk: 16.85±1.56%; BS= 13.17±1.25%). Higher percentages of polyphenols were released from NS compared to BS during in vitro digestion. Food matrix does not significantly affect polyphenols release during digestion. The presence of milk in the gastric environment does not influence polyphenol release from digested almond skins. However, milk components (for example, proteins) can partially sequester polyphenols released from almond skins, because only a lower polyphenol amount is recovered free in the aqueous medium.
The results of the present study indicate that polyphenols from almond skins are bio-accessible in the upper GI tract and therefore potentially available for absorption during human digestion, so suggesting that almond skins can be potentially used as added value food supplement.
This work has been funded by the Almond Board of California.
Grasser et al., 1995. Journal of Dairy Science 78:962–971.
Manach et al., 2004. Am J Clin Nutr 79:727-747.
Mandalari et al., 2010. Food Chemistry 122:1083–1088.