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What is the Difference Between Bioavailability Bioaccessibility and Bioactivity of Food Components?

By: , Posted on: April 27, 2017

The preparation of foods fortified with functional components requires integration of diverse aspects under evaluation. These include selecting of the appropriate source, detecting the bioactive compounds, applying separation and recovery techniques, performing toxicological assessments and finally making stability, activity and bioaccessibility measurements. At this point, it is important to define carefully the terms “bioavailability”, “bioaccessibility” and “bioactivity” (Figure 1) that are often used indistinctly to express similar functions.

Figure 1.1 (Chapter 1) Definition of bioavailability as a sum of bioaccessibility and bioactivity. Physiochemical events involved on each stage. Adapted from Fernández-García et al. (2009).

Bioavailability includes gastrointestinal (GI) digestion, absorption, metabolism, tissue distribution, and bioactivity.  However, it has several meanings depending on the research area used to. For instance, from a pharmacological point of view, bioavailability is the rate and extent to which the therapeutic moiety is absorbed and becomes available at the drug action site. From the nutritional point of view (that is of particular interest in the current book), bioavailability refers to the fraction of the nutrient that is stored or being available in physiological functions. It is a key term for nutritional effectiveness, as not all the amounts of bioactive compounds are used effectively by the organism. For example, when different foods come in contact with the mouth or digestive tract, various interactions may take place affecting phytochemical bioavailability (e.g. fat enhances quercetine bioavailabilty in meals). Therefore, bioavailability expresses the fraction of ingested nutrient or bioactive compound that reaches the systemic circulation and ultimately utilized.

Before becoming bioavailable, bioactive compounds must be released from the food matrix and modified in the GI tract. Thus, bioavailability includes the term bioaccessibility. Indeed, it is important to analyze whether the digestion process affects bioactive compounds and their stability, before concluding on any potential health effect. Bioaccessibility is defined as the quantity of a compound that is released from its matrix in the gastrointestinal tract, becoming available for absorption (e.g. enters the blood stream). This term includes digestive transformations of foods into material ready for assimilation, the absorption/assimilation into intestinal epithelium cells as well as the presystemic, intestinal and hepatic metabolism. However, beneficial effects of unabsorbed nutrients such as calcium binding of bile salts in the tract are missed by definitions based on absorption. Bioaccessibility is usually evaluated by in vitro digestion procedures, generally simulating gastric and small intestinal digestion, sometimes followed by Caco-2 cells uptake.

Bioactivity is the specific effect upon exposure to a substance. It includes tissue uptake and the consequent physiological response (e.g. antioxidant, anti-inflammatory, etc). It also includes information on how the bioactive compounds are transported and reached the target tissue, how they interact with biomolecules, metabolism and biotransformation characteristics, as well as the biomarkers’ generation and the consequent physiological responses.  Digestibility applies specifically to the fraction of food components that is transformed into potentially accessible matter through all physical andchemical processes that take place in the lumen. On the other hand, assimilation refers to the uptake of bioaccessible material through the epithelium by some mechanism of transepithelial absorption. One example where only bioactivity applies concerns the non-digestible polysaccharides, oligosaccharides and dietary fibre. These compounds produce several health benefits although they are not absorbed.

Bioactivity measurements (in vivo, ex vivo, and in vitro) are based on the events that take place during the time the bioactive component interacts with biomolecules. This interaction generates a metabolite, a signal, or a response that will continue to modulate and amplify until the systemic physiologic response is produced (health benefit). The experimental procedures used to measure bioactivity need to be adjusted to every health benefit claim separately. The scientific support of claims of what a food can do (healthy properties or reduced risk of disease) is based on bioactivity data. Claims of what a food contains (nutritional content or comparison to other foods) are provided by bioaccessibility without the need of performing bioactivity studies.

Bioactive compounds are phytochemicals found in foods, being capable of modulating metabolic processes and resulting in the promotion of better health. They exhibit beneficial effects such as antioxidant activity, inhibition or induction of enzymes, inhibition of receptor activities, and induction and inhibition of gene expression. The bioaccessibility and bioavailability of each bioactive compound differs greatly, and the most abundant compounds in ingested fruit are not necessarily those leading to the highest concentrations of active metabolites in target tissues. Indeed, when studying the role of bioactive compounds in human health, bioavailability is not always well known.

nutraceutical and functional food components

Nutraceutical and Functional Food Components: Effects of Innovative Processing Techniques presents the latest information on the chemistry, biochemistry, toxicology, health effects, and nutrition characteristics of food components and the recent trends and practices that the food industry (e.g. the implementation of non-thermal technologies, nanoencapsulation, new extraction techniques, and new sources, like by-products, etc.) has adopted. This book fills the gap in knowledge by denoting the impact of recent food industry advances in different parameters of food components (e.g. nutritional value, physical and chemical properties, bioavailability and bioaccessibility characteristics) and final products (e.g. applications, shelf-life, sensory characteristics).

Key Features

  • Provides a holistic view of the interactions between novel processing techniques and food components
  • Explains how innovative techniques, such as non-thermal, nano-encapsulation, waste recovery, and novel extraction and processing methods impact the nutritional value of ingredients commonly used in functional food and nutraceutical products
  • Covers food applications, shelf-life, and sensory characteristics

Read more articles from Charis Galanakis, Coordinator of Food Waste Recovery Group


Charis M. Galanakis is an interdisciplinary scientist with a fast-expanding work that balances between food and environment, industry, and academia. His research targets mainly the separation and recovery of functional macro- and micromolecules from different food by-products, as well as their implementation as additives in food and other products. He is the research and innovation director of Galanakis Laboratories (Chania, Greece) and the coordinator of Food Waste Recovery Group of ISEKI Food Association (Vienna, Austria).

He serves as an editorial board member and subject editor of Food and Bioproducts Processing and Food Research International, and he has edited 6 books from Academic Press: Food Waste Recovery: Processing Technologies and Industrial Techniques (2015), Innovation Strategies in the Food Industry: Tools for implementation (2016) and Nutraceutical and Functional Food Components: Effects of Innovative Processing Techniques (2017), Olive Mill Waste: Recent advances for the Sustainable Management (2017), Handbook of Grape Processing By-Products: Sustainable Solutions (2017) and Handbook of Coffee Processing By-Products: Sustainable Applications (2017).

See his full portfolio of books here.

Follow Dr. Galanakis via Twitter – @CharisGalanakisLinkedIn or ResearchGate.

Join the Food Waste Recovery Group on LinkedIn or the Food Waste Recovery Page on Facebook.

Charis’ latest books are available to order on the Elsevier Store. Use discount code STC317 at checkout and save up to 30% on your very own copy!

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Food Science & Nutrition

The field of food science is highly interdisciplinary, spanning areas of chemistry, engineering, biology, and many more. Researchers in these areas achieve fundamental advances in our understanding of agriculture, nutrition, and food-borne illness, and develop new technologies, like food processing methods and packaging material. Against a backdrop of global issues of food supply and regulation, this important work is supported by Elsevier’s catalog of books, eBooks, and journals in food science, considered essential resources for students, instructors, and health professionals worldwide. Learn more about our Food Science and Nutrition books here.

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