Nanotechnology and Functional Foods E-Book

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Serie: Institute of Food Technologists Series
• Sprache: Englisch

Seitenzahl: 1079

Veröffentlichungsjahr: 2015

Beschreibung

The continued advancement in the sciences of functional foods and nutraceuticals has clearly established a strong correlation between consumption of bioactives and improved human health and performance. However, the efficacy and bioavailability of these bioactive ingredients (e.g., omega-3 oils, carotenoid antioxidants, vitamins, and probiotic bacteria) in foods often remains a challenge, due to their instability in food products and gastrointestinal tract, as well as their limited bioavailability. In some cases, these bioactive ingredients may impart an undesirable organoleptic characteristic to the final product, which hinders acceptance by consumers. In addressing these challenges, development of effective delivery systems is critical to meet the consumer needs for effective bioactives. The scientific knowledge behind developing effective delivery of bioactive components into modern and wide-ranging food products will be essential to reap their health-promoting benefits and to support the sustained growth of the functional foods market. Nanotechnology and Functional Foods: Effective Delivery of Bioactive Ingredients explores the current data on all aspects of nanoscale packing, carrying and delivery mechanisms of bioactives ingredients to functional foods. The book presents various delivery systems (including nano-emulsions, solid lipid nanoparticles, and polymeric nano-particles), their properties and interactions with other food components, and fate in the human body. Later chapters emphasize the importance of consumers attitude towards nano-delivery for the success of the technology and investigate the challenges faced by regulatory agencies to control risks and harmonize approaches worldwide. The wide applicability of bioactive delivery systems with the purpose of improving food quality, food safety and human health will make this book a worthy reference for a diverse range of readers in industry, research and academia.

Leseprobe

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IFT Press Advisory Group

Nicolas BordenaveYiFang ChuJ. Peter ClarkChristopher J. DoonaJung Hoon HanFlorence FeeherryChris FindlayThomas J. MontvilleKaren NachayMartin OkosDavid S. ReidSam SaguyFereidoon ShahidiCindy StewartHerbert StoneHilary ThesmarYael VodovotzRon Wrolstad

 Bob Swientek (IFT)Melanie Bartelme (IFT)David McDade (Wiley)

Nanotechnology and Functional Foods

Effective Delivery of Bioactive Ingredients

Edited by

Cristina M. Sabliov

Louisiana State University and LSU Agricultural Center, Baton Rouge, LA, USA

Hongda Chen

United States Department of Agriculture, Washington, DC, USA

Rickey Y. Yada

University of British Columbia, Vancouver, British Columbia, Canada

This edition first published 2015 © 2015 by John Wiley & Sons, Ltd. and the Institute of Food Technologists, 525 W. Van Buren St., Suite 1000, Chicago, IL 60607

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Library of Congress Cataloging-in-Publication Data

Nanotechnology and functional foods : effective delivery of bioactive ingredients / edited by Cristina M. Sabliov, Hongda Chen, Rickey Y. Yada.  pages cm. – (Institute of food technologists series) Includes bibliographical references and index.

ISBN 978-1-118-46220-1 (hardback)1.  Food–Biotechnology. 2.  Bioactive compounds–Biotechnology. 3.  Functional foods. I.  Sabliov, Cristina M., editor. II.  Chen, Hongda, editor. III.  Yada, R. Y. (Rickey Yoshio), 1954- editor.  TP248.65.F66N35 2015 664–dc23

          2015000039

A catalogue record for this book is available from the British Library.

Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic books.

Cover image: © Thanida Chuacharoen, PhD candidate, LSU

Titles in the IFT Press series

Accelerating New Food Product Design and Development

(Jacqueline H. Beckley, Elizabeth J. Topp, M. Michele Foley, J.C. Huang, and Witoon Prinyawiwatkul)

Advances in Dairy Ingredients

(Geoffrey W. Smithers and Mary Ann Augustin)

Anti-Ageing Nutrients: Evidence-based Prevention of Age-Related Diseases

(Delminda Neves)

Bioactive Compounds from Marine Foods: Plant and Animal Sources

(Blanca Hernández-Ledesma and Miguel Herrero)

Bioactive Proteins and Peptides as Functional Foods and Nutraceuticals

(Yoshinori Mine, Eunice Li-Chan, and Bo Jiang)

Biofilms in the Food Environment

(Hans P. Blaschek, Hua H. Wang, and Meredith E. Agle)

Calorimetry in Food Processing: Analysis and Design of Food Systems

(Gönül Kaletunç)

Coffee: Emerging Health Effects and Disease Prevention

(YiFang Chu)

Food Carbohydrate Chemistry

(Ronald E. Wrolstad)

Food Industry Design, Technology and Innovation

(Helmut Traitler, Birgit Coleman, and Karen Hofmann)

Food Ingredients for the Global Market

(Yao-Wen Huang and Claire L. Kruger)

Food Irradiation Research and Technology, second edition

(Christoper H. Sommers and Xuetong Fan)

Foodborne Pathogens in the Food Processing Environment: Sources, Detection and Control

(Sadhana Ravishankar, Vijay K. Juneja, and Divya Jaroni)

Food Oligosaccharides: Production, Analysis and Bioactivity

(F. Javier Moreno and Maria Luz Sanz)

Food Texture Design and Optimization

(Yadunandan Lal Dar and Joseph M. Light)

High Pressure Processing of Foods

(Christopher J. Doona and Florence E. Feeherry)

Hydrocolloids in Food Processing

(Thomas R. Laaman)

Improving Import Food Safety

(Wayne C. Ellefson, Lorna Zach, and Darryl Sullivan)

Innovative Food Processing Technologies: Advances in Multiphysics Simulation

(Kai Knoerzer, Pablo Juliano, Peter Roupas, and Cornelis Versteeg)

Mathematical and Statistical Methods in Food Science and Technology

(Daniel Granato and Gastón Ares)

Membrane Processes for Dairy Ingredient Separation

(Kang Hu, James Dickson)

Microbial Safety of Fresh Produce

(Xuetong Fan, Brendan A. Niemira, Christopher J. Doona, Florence E. Feeherry, and Robert B. Gravani)

Microbiology and Technology of Fermented Foods

(Robert W. Hutkins)

Multiphysics Simulation of Emerging Food Processing Technologies

(Kai Knoerzer, Pablo Juliano, Peter Roupas and Cornelis Versteeg)

Multivariate and Probabilistic Analyses of Sensory Science Problems

(Jean-François Meullenet, Rui Xiong, and Christopher J. Findlay)

Nanoscience and Nanotechnology in Food Systems

(Hongda Chen)

Nanotechnology and Functional Foods: Effective Delivery of Bioactive Ingredients

(Cristina M. Sabliov, Hongda Chen, and Rickey Y. Yada)

Natural Food Flavors and Colorants

(Mathew Attokaran)

Nondestructive Testing of Food Quality

(Joseph Irudayaraj and Christoph Reh)

Nondigestible Carbohydrates and Digestive Health

(Teresa M. Paeschke and William R. Aimutis)

Nonthermal Processing Technologies for Food

(Howard Q. Zhang, Gustavo V. Barbosa-Cánovas, V.M. Balasubramaniam, C. Patrick Dunne, Daniel F. Farkas, and James T.C. Yuan)

Nutraceuticals, Glycemic Health and Type 2 Diabetes

(Vijai K. Pasupuleti and James W. Anderson)

Organic Meat Production and Processing

(Steven C. Ricke, Ellen J. Van Loo, Michael G. Johnson, and Corliss A. O’Bryan)

Packaging for Nonthermal Processing of Food

(Jung H. Han)

Practical Ethics for the Food Professional: Ethics in Research, Education and the Workplace

(J. Peter Clark and Christopher Ritson)

Preharvest and Postharvest Food Safety: Contemporary Issues and Future Directions

(Ross C. Beier, Suresh D. Pillai, and Timothy D. Phillips, Editors; Richard L. Ziprin, Associate Editor)

Processing and Nutrition of Fats and Oils

(Ernesto M. Hernandez and Afaf Kamal-Eldin)

Processing Organic Foods for the Global Market

(Gwendolyn V. Wyard, Anne Plotto, Jessica Walden, and Kathryn Schuett)

Regulation of Functional Foods and Nutraceuticals: A Global Perspective

(Clare M. Hasler)

Resistant Starch: Sources, Applications and Health Benefits

(Yong-Cheng Shi and Clodualdo Maningat)

Sensory and Consumer Research in Food Product Design and Development

(Howard R. Moskowitz, Jacqueline H. Beckley, and Anna V.A. Resurreccion)

Sustainability in the Food Industry

(Cheryl J. Baldwin)

Thermal Processing of Foods: Control and Automation

(K.P. Sandeep)

Trait-Modified Oils in Foods

(Frank T. Orthoefer and Gary R. List)

Water Activity in Foods: Fundamentals and Applications

(Gustavo V. Barbosa-Cánovas, Anthony J. Fontana Jr., Shelly J. Schmidt, and Theodore P. Labuza)

Whey Processing, Functionality and Health Benefits

(Charles I. Onwulata and Peter J. Huth)

Contributors

Carlos E. AsteteDepartment of Biological and Agricultural EngineeringLouisiana State University and LSU Agricultural CenterBaton Rouge, LouisianaUSADeepak BhopatkarWhistler Center for Carbohydrate ResearchDepartment of Food SciencePurdue UniversityWest Lafayette, IndianaUSAJeffrey B. BlumbergAntioxidants Research LaboratoryJean Mayer USDA Human Nutrition Research Center on AgingTufts UniversityBoston, MassachusettsUSAToni BorelDepartment of Biological and Agricultural EngineeringLouisiana State University and LSU Agricultural CenterBaton Rouge, LouisianaUSADiana BowmanDepartment of Health Management and Policy and Risk Science CenterUniversity of MichiganAnn Arbor, MichiganUSAOsvaldo H. CampanellaWhistler Center for Carbohydrate ResearchDepartment of Food SciencePurdue UniversityWest Lafayette, IndianaUSALaurence CastleThe Food and Environment Research AgencySand Hutton York, UKQasim ChaudhryThe Food and Environment Research AgencySand Hutton York, UKC-Y. Oliver ChenAntioxidants Research LaboratoryJean Mayer USDA Human Nutrition Research Center on AgingTufts UniversityBoston, MassachusettsUSAHongda ChenUSDA-National Institute of Food and AgricultureWashington, District of ColumbiaUSAHuaiqiong ChenDepartment of Food Science and TechnologyUniversity of TennesseeKnoxville, TennesseeUSAOana CraciunescuDepartment of Cellular BiologyNational Institute R and D for Biological SciencesBucharestRomaniaEric Andrew DeckerDepartment of Food ScienceUniversity of MassachusettsAmherst, MassachusettsUSAStephanie R. DunganDepartment of Food Science and TechnologyDepartment of Chemical Engineering and Materials ScienceUniversity of CaliforniaDavis, CaliforniaUSAAnna GergelySteptoe & Johnson LLPBrusselsBelgiumMaria Fernanda San Martin-GonzalezFood Science DepartmentPurdue UniversityWest Lafayette, IndianaUSARenuka GuptaDepartment of Chemistry and BiologyRyerson UniversityToronto, OntarioCanadaWilliam K. HallmanDepartment of Human EcologyRutgers UniversityNew Brunswick, New JerseyUSABruce R. HamakerWhistler Center for Carbohydrate ResearchDepartment of Food SciencePurdue UniversityWest Lafayette, IndianaUSAQingrong HuangDepartment of Food ScienceRutgers UniversityNew Brunswick, New JerseyUSAElizabeth J. JohnsonAntioxidants Research LaboratoryJean Mayer USDA Human Nutrition Research Center on AgingTufts UniversityBoston, MassachusettsUSAAlison KamilAntioxidants Research LaboratoryJean Mayer USDA Human Nutrition Research Center on AgingTufts UniversityBoston, MassachusettsUSAKetinun KittipongpittayaDepartment of Food ScienceUniversity of MassachusettsAmherst, MassachusettsUSADavid D. KittsFood Science, Food, Nutrition and HealthThe University of British ColumbiaVancouver, British ColumbiaCanadaIsao KobayashiAlliance for Research on North Africa (ARENA)University of Tsukuba andFood Engineering DivisionNational Food Research Institute NAROTsukuba, IbarakiJapanYunqi LiDepartment of Food ScienceRutgers UniversityNew Brunswick, New JerseyUSALoong-Tak LimDepartment of Food ScienceUniversity of GuelphGuelph, OntarioCanadaYazheng LiuFood Science, Food, Nutrition and HealthThe University of British ColumbiaVancouver, British ColumbiaCanadaDavid Julian McClementsDepartment of Food ScienceUniversity of MassachusettsAmherst, MassachusettsUSAEmily S. MohnAntioxidants Research LaboratoryJean Mayer USDA Human Nutrition Research Center on AgingTufts UniversityBoston, MassachusettsUSADorel MoldovanDepartment of Mechanical and Industrial Engineering, andCenter for Computation and TechnologyLouisiana State UniversityBaton Rouge, LouisianaUSAMitsutoshi NakajimaAlliance for Research on North Africa (ARENA)andFaculty of Life and Environmental SciencesUniversity of TsukubaandFood Engineering Division, National Food Research Institute, NAROTsukuba, IbarakiJapanMarcos A. NevesAlliance for Research on North Africa (ARENA)andFaculty of Life and Environmental SciencesUniversity of TsukubaandFood Engineering Division, National Food Research Institute, NAROTsukuba, IbarakiJapanBrian NovakDepartment of Mechanical and Industrial Engineering, andCenter for Computation and TechnologyLouisiana State UniversityBaton Rouge, LouisianaUSAMary L. NucciDepartment of Human EcologyRutgers UniversityNew Brunswick, New JerseyUSAGraciela PaduaDepartment of Food Science and Human NutritionUniversity of IllinoisUrbana, IllinoisUSAKang PanDepartment of Food Science and TechnologyUniversity of TennesseeKnoxville, TennesseeUSAMoumita RayDepartment of Chemistry and BiologyRyerson UniversityToronto, OntarioCanadaDérick RousseauDepartment of Chemistry and BiologyRyerson UniversityToronto, OntarioCanadaCristina M. SabliovDepartment of Biological and Agricultural EngineeringLouisiana State University and LSU Agricultural CenterBaton Rouge, LouisianaUSALorena SalcedoDepartment of Food ScienceUniversity of MassachusettsAmherst, Massachusetts,USAPaul B. ThompsonDepartments of Philosophy, Community Sustainability and Agricultural, Food and Resource EconomicsMichigan State UniversityEast Lansing, MichiganUSARohan V. TikekarDepartment of Nutrition and Food ScienceUniversity of MarylandCollege Park, MarylandUSAMihaela TrifInstitute of Biochemistry of the Romanian AcademyBucharestRomaniaWan WangDepartment of Food Science and TechnologyUniversity of TennesseeKnoxville, TennesseeUSAZheng WangAlliance for Research on North Africa (ARENA)University of TsukubaandFood Engineering DivisionNational Food Research Institute, NAROTsukuba, IbarakiJapanMeocha WhaleyDepartment of Biological and Agricultural EngineeringLouisiana State University and LSU Agricultural CenterBaton Rouge, LouisianaUSARickey Y. YadaFaculty of Land and Food SystemsDepartment of Food ScienceUniversity of British ColumbiaVancouver, British ColumbiaCanadaGenyi ZhangWhistler Center for Carbohydrate ResearchDepartment of Food SciencePurdue UniversityWest Lafayette, IndianaUSAYue ZhangDepartment of Food Science and TechnologyUniversity of TennesseeKnoxville, TennesseeUSAQixin ZhongDepartment of Food Science and TechnologyUniversity of TennesseeKnoxville, TennesseeUSA

1Introduction

Cristina M. Sabliov,1 Hongda Chen,2 and Rickey Y. Yada3

1 Department of Biological and Agricultural Engineering, Louisiana State University and LSU Agricultural Center, Baton Rouge, Louisiana, USA

2 USDA-National Institute of Food and Agriculture, Washington, District of Columbia, USA

3 Department of Food Science, University of British Columbia, Vancouver, British Columbia, Canada

Antioxidants, polyunsaturated fatty acids, and proteins are common bioactives that can be added to food to improve its nutritional value and to prevent diseases such as cancer and heart disease for an improved overall health of the consumer. Bioactive stability, poor solubility in water, and low bioavailability are some of the challenges faced by the functional food industry interested in achieving optimum activity of the bioactives. It is generally accepted that nanoparticles offer distinct advantages for delivery of bioactives over traditional methods of delivery, such as improved stability, controlled release kinetics, and targeting of the bioactive for enhanced uptake and functionality of the bioactive. Nanodelivery systems, emulsions, solid lipid nanoparticles, polymeric nanoparticles, nanocomplexes, etc., are unique; their individual physical, chemical, and biological properties make them suitable for some specific food applications. No delivery system is superior above all others across the board. While the advantages of nanodelivery systems for food applications are supported by a wealth of data, the interaction of nanoparticles with the human body is complex and not fully understood. Due to their small size, nanoparticles have the potential to translocate to various parts of the body, raising concerns about their safety. The multitude of types of delivery systems and associated properties make safety assessment a challenging task for the researchers and regulatory agencies. Without compelling scientific data supporting safety of nanodelivery systems, their application in functional foods has no future, regardless of their proved beneficial impact on the functionality of the bioactive.

This book attempts to gather and present the latest data on all aspects of nanodelivery of bioactives ingredients to functional foods. It starts by describing the gastrointestinal (GI) tract and its function, with emphasis on uptake of macro- and micronutrients (Chapter 2). Nutrients can be effectively delivered by nanoparticles through two mechanisms: (i) the load is released from the delivery systems in the GI tract and absorbed by established bioactive-specific mechanisms; (ii) particles are absorbed intact and the load carried to the blood stream and cells, where the bioactive is released. Nanoparticle properties, composition, morphology, size, and surface properties among others play a key role in their interaction with biological systems. The effect of nanoparticle–cell interaction on bioactive uptake in the GI tract can be thoroughly understood by performing experimental studies accompanied by molecular dynamic simulations, as highlighted in Chapter 3.

Several methods are available to synthesize nanoparticles of controlled properties out of biocompatible and biodegradable food-grade materials. Interfacial science is at the basis of nanoparticle formation, nanoparticle stability profiles, and release kinetics of the bioactive (Chapter 4). The process of emulsification is a key component of most nanoparticle synthesis methods, hence a thorough understanding of emulsion formations and ways to control emulsion size is provided in Chapter 5.

Various loadings, release properties, and nanoparticle stability profiles can be achieved by carefully selecting a synthesis method and associated parameters from the multitude of available processes (Chapter 6). More often than not, these properties are reported in the literature for newly synthesized nanoparticles. It is now understood that when particles are incorporated into the food or en-route through the GI tract, these properties are changed as a result of nanoparticle interaction with the food components or the media to which it is exposed. In general, methods for the detection of soft, nonmetallic nanoparticles incorporated into complex food matrixes are not readily available. Methods that are available for characterization of the nanoparticle itself or when suspended in a simple food medium include spectroscopic and microscopic technique as described in Chapter 7.

The most significant improvements that can be offered by nano-entrapment include enhanced stability and improved bioavailability of the bioactives. Chapter 8 provides an overview on the stability of bioactives entrapped in emulsions and stabilized emulsions, while Chapter 9 covers the stability of a particular bioactive folic acid, delivered with various polymeric encapsulants. Improved bioavailability of polyphenols delivered with polymeric nanoparticles is discussed in Chapter 10.

Organic, soft, nonmetallic nanodelivery systems designed for food applications are classified into two main groups: liquid (nanoemulsions, nanoliposomes, and nanopolymersomes) and solid (solid lipid nanoparticles, polymeric nanoparticles, nanocrystals, and complexes). A significant portion of the book (Chapters 11–18) is dedicated to different types of particles, emulsions, liposomes, solid lipid nanoparticles, polymeric nanoparticles, nanocomplexes, bi-continuous systems, and nanofibers, with an emphasis on synthesis methods, properties, and applications.

The type of nanoparticle, as well as physical and biological nanoparticle properties determine the route of clearance from the gastrointestinal system and possible toxic effects. Safety concerns stem from the potential of the nanoparticle to translocate to tissues due to their small size and the higher than physiological normal concentrations of the nanodelivered bioactive in this tissue. Involvement of scientists, risk assessors, and the broader public is necessary in addressing possible risks from nanotechnology for bioactive ingredient delivery (Chapter 19). If consumer attitude toward nanodelivery systems in foods is not addressed early, the technology has the risk of failing before reaching its potential. Consumer attitude must therefore be addressed to see the full potential of nano-enabled applications in foods (Chapter 20). In addition, safety assessment is needed to label a certain nanodelivery system safe under conditions of use. It is not surprising that with the wide-variety of nanodelivery systems and application significant roadblocks exist in assessing safety in a broad sense (Chapter 21). Regulatory agencies throughout the world are challenged to effectively regulate the risk of nano-enabled materials to be used as delivery systems for bioactives in functional foods (Chapter 22). The approaches are different in different countries and harmonization of regulations might be attempted in the future. It is hoped that with the evolving science, increasing consumer awareness, and recent developments in the regulatory field, nanotechnology can make a true and significant impact on the functional foods industry in the area of delivery of bioactives for improved consumer health.

2Nutrient absorption in the human gastrointestinal tract

Emily S. Mohn and Elizabeth J. Johnson

Antioxidants Research Laboratory, Jean Mayer USDA Human Nutrition Research Center on Aging, Tufts University, Boston, Massachusetts, USA

2.1 INTRODUCTION

The human body possesses an intricate, but highly organized system for the digestion and absorption of nutrients. Research spanning hundreds of years has shed light on how exactly this process works, with new pieces of information still being discovered. This chapter focuses on the mechanisms by which our bodies isolate and obtain the various nutrients required for optimal health.

2.2 OVERVIEW OF THE GASTROINTESTINAL TRACT

The gastrointestinal (GI) tract is divided into different sections: the mouth, esophagus, stomach, small intestine, large intestine, rectum, and anus. The small intestine is further divided into three sections called the duodenum, jejunum, and ileum. The large intestine is made up of several parts called the ascending, transverse, descending, and sigmoid colon. Some of the sections of the GI tract are separated from one another by rings of muscles that act as valves by contracting and relaxing to control the movement of food between each part of the tract. These rings of muscle are known as sphincters and there are several located in various spots along the GI tract (Byrd-Brenner et al., 2009). The upper esophageal sphincter separates the mouth and esophagus, the lower esophageal sphincter separates the esophagus and stomach, the pyloric sphincter separates the stomach and small intestine, the ileocecal valve separates the small and large intestine, and the internal and external anal sphincters control the defecation reflex of feces from the anus. All of these sphincters are involuntary muscles except for two, the upper esophageal and external anal sphincters, which are under voluntary control. In addition to each section, there are several accessory organs that work in cooperation with the GI tract to aid the digestion and absorption of food. These accessory organs include the liver, gallbladder, and pancreas (Byrd-Brenner et al., 2009).

2.3 THE GASTROINTESTINAL TRACT

The oral cavity is where food first enters the GI tract and it is considered to be the gateway to the digestive tract. The mouth consists of several different parts, including the tongue, teeth, and salivary glands. Each plays a role in either the lubrication or breakdown of food, both mechanically and chemically. Teeth begin to mechanically breakdown food into smaller pieces, which increases its surface area. This increased surface area allows for a greater amount of contact between the food and saliva (Salles et al., 2011). Saliva, produced from the salivary glands, consists of mucus, lysozyme, and salivary amylase. Infants also contain an additional component in saliva called lingual lipase. The amount of saliva produced per day varies among individuals but, on average, the salivary glands can produce about 1 L of saliva in a day (Schipper et al., 2007; Byrd-Brenner et al., 2009). Saliva mixes with particles of food produced from chewing with help from the tongue. As food and saliva mix, lysozyme kills any bacteria and pathogens in the food, while the mucus lubricates food and holds it together. Salivary amylase begins the chemical breakdown of starches by hydrolyzing α 1–4 glycosidic bonds. Due to the limited amount of time food actually spends in the mouth, however, the salivary amylase provides minimal digestion (5%) of these carbohydrates. In infants, lingual lipase begins to chemically digest fats in the mouth. The presence of this enzyme in babies helps them digest fat found in breast milk. However, once more foods are introduced into the diet, the need to digest fat in the mouth lessens and the presence of this enzyme in saliva gradually declines (Gropper et al., 2005; Byrd-Brenner et al., 2009). Saliva is also essential for taste perception. That is, when eating, the food that gets dissolved in saliva is tasted because it is able to dissolve the taste-forming compounds found in foods. As the tongue mixes food and saliva, the food becomes known as bolus (Salles et al., 2011).

The next step in the digestive process is moving the bolus out of the mouth and into the esophagus. This is known as swallowing. Since there are two openings in the back of the throat, the trachea and esophagus, the process requires particular coordination of the mouth and throat to prevent choking. The bolus must be able to enter the esophagus without getting into the trachea, which is the airway to the lungs. The organization of structures in the mouth and throat allows for this process to occur quite easily. When the bolus is ready to be swallowed, the tongue retracts back in the mouth toward the throat and pushes against the epiglottis, a flap of tissue, which then closes over the top of the trachea (larynx), causing breathing to stop (Salles et al., 2011). At the same time, the upper esophageal sphincter relaxes, opening the esophagus and allowing the bolus to enter. Once the bolus has entered the esophagus, the upper esophageal sphincter contracts and the tongue moves back toward the mouth, releasing the epiglottis from the top of the trachea and allowing breathing to resume (Salles et al., 2011).

The esophagus is a 10-inch (~25 cm) muscular tube which moves the bolus from the mouth to the stomach (Byrd-Brenner et al., 2009). This is accomplished by peristalsis. Peristalsis is the coordinated movement of voluntary and involuntary muscle contractions and relaxations that push the bolus down the esophagus. As it is propelled forward, bolus is further lubricated by more mucus secreted from the esophagus. It takes approximately 10 s for the bolus to move from the top to the bottom of this section (Gropper et al., 2005). Once it reaches the end, the lower esophageal sphincter relaxes and the bolus enters the stomach. The sphincter contracts after the bolus passes in order to block acidic gastric secretions from flowing into the esophagus and causing damage (Hershcovici et al., 2011).

The stomach section of the GI tract serves as the main site of storage for partially digested food as well as the beginning of fat and protein digestion. No carbohydrate digestion occurs in the stomach (Whitney and Rolfes, 2011). Bolus from the esophagus enters the stomach corpus (or body), which is the holding area. This space is lined with a series of cells specific to the stomach. Each cell secretes a different substance to aid in the digestion process. Secretions from these cells are stimulated by the hormone gastrin, which is released when the bolus first enters the stomach (Schubert, 2008). The first of the stomach-specific cells are the parietal cells. These cells secrete hydrochloric acid (HCl), which serves several purposes. First, it destroys any remaining pathogens in food that cannot survive in an acidic environment. Second, it destroys the activity of proteins in the bolus and denatures them. Third, it dissolves any dietary minerals that may be present, and last, it activates the stomach enzyme pepsinogen, to its active form, pepsin (Schubert, 2009). Pepsin is a zymogen, which is an enzyme that is synthesized and stored in an inactive form in order to protect the surrounding areas of the body. These zymogens only become activated under certain conditions or are activated by other enzymes. Pepsinogen is secreted by peptic chief cells. Once activated, pepsin digests denatured proteins into smaller peptides by hydrolyzing peptide bonds. In addition to pepsinogen, these cells also secrete gastric lipase, which functions to breakdown dietary fat. Like pepsin, gastric lipase is active in the acidic environment (Gropper et al., 2005). Another important cell type in the stomach is the mucus neck cell. These cells, as their name implies, secrete mucus. Again, this mucus works to lubricate the food; however, it also plays an important role in protecting the cells lining the stomach from the acidic environment created by the hydrochloric acid (Ensign et al., 2012). Another important substance that is secreted in the stomach is intrinsic factor (IF). This protein is secreted by the parietal cells and is very important for the absorption of vitamin B12 (Byrd-Brenner et al., 2009). Upon secretion, it binds to the vitamin and forms a complex that will be described later in the chapter.

Around the stomach body there is a complex network of muscles. This network consists of oblique, circular, and longitudinal muscles that wrap around the stomach in every direction. The coordinated contraction and relaxation of these muscles squeezes and relaxes the stomach body, which causes all of the secretions to mix well with the bolus (Kong and Singh, 2010). This provides enzymes with adequate exposure to the appropriate nutrients to cleave them. This is especially important for gastric lipase, since dietary fat separates out from the rest of the fluids because it is too hydrophobic to dissolve in the acid, and forms a layer that rests on top of the aqueous HCl layer. The contractions of the muscles around the stomach allow for the emulsification of the fat so that gastric lipase can make contact with the fat and hydrolyze bonds (Gropper et al., 2005). Upon further digestion in the stomach, the food is now referred to as chyme.

Flow of chyme from the stomach to the small intestine is controlled by stomach contractions and the pyloric sphincter (Janssen et al., 2011). The alternating relaxation and contraction of the stomach body and sphincter causes chyme to be ejected out of the stomach in small doses. The release of chyme in small doses is carried out in order to allow the small intestine to adequately neutralize the highly acidic chyme so that the small intestine is not damaged (Byrd-Brenner et al., 2009). The speed at which gastric emptying occurs depends on the composition of the meal consumed and caloric content. For example, a high caloric meal containing large amounts of fat will empty out of the stomach more slowly, while less energy dense meals leave the stomach more quickly (Janssen et al., 2011).