Volker Gräf

Potential bioavailability enhancement of bioactive compounds using food-grade engineered nanomaterials: a review of the existing evidence

The development of engineered nanometre sized materials (ENM) produced with food-grade ingredients and designed as delivery systems for organic and inorganic materials has gained increasing interest. The major reason for this trend is the aim to overcome problems associated with the low bioavailability of many bioactive compounds (BC) which are usually claimed to benefit human health. In this review, outcomes of studies investigating the potential bioavailability enhancement of BC using ENM as delivery systems are summarised and discussed. It focuses on in vitro and in vivo studies carried out with ENM produced with food-grade materials and designed for the delivery of vitamins, other secondary plant metabolites and minerals. Furthermore, the physical and physicochemical aspects governing the preparation of the systems, the loading of the BC, the stability of the delivery systems in food applications and finally the release of the BC in the gastrointestinal tract are also considered. The mechanisms leading to an enhanced bioavailability are based on (i) improved solubility of the BC under gastrointestinal conditions, (ii) the protection of the BC from the chemical conditions in the gastrointestinal tract (GIT), (iii) the controlled release within the GIT or (iv) an improved transfer through the intestinal wall. The main outcome of the review is that particle size, surface properties and physical state of the ENM are key parameters to be controlled aiming at an enhanced nutritional value of food materials. Furthermore, the bioavailability classification scheme (BCS) can help to understand the efficacy of different ENM for the delivery of specific BC.

Stability of anthocyanin-rich w/o/w-emulsions designed for intestinal release in gastrointestinal environment.

Anthocyanins belong to the most important hydrophilic plant pigments. Outside their natural environment, these molecules are extremely unstable. Encapsulating them in submicron-sized containers is one possibility to stabilize them for the use in bioactivity studies or functional foods. The containers have to be designed for a target release in the human gastrointestinal system. In this contribution, an anthocyanin-rich bilberry extract was encapsulated in the inner aqueous phase of water-in-oil-in-water-double emulsions. The physical stability as well as the release of free fatty acids and encapsulated, bioactive substances from the emulsions during an in vitro gastrointestinal passage were investigated. The focus was on the influence of emulsion microstructural parameters (for example, inner and outer droplet size, disperse phase content) and required additives (emulsifier systems), respectively. It could be shown that it is possible to stabilize anthocyanins in the inner phase of double emulsions. The release rate of free fatty acids during incubation was independent of the emulsifier used. However, the exterior (O/W)-emulsifier has an impact on the stability of multiple emulsions in gastrointestinal environment and, thus, the location of release. Long-chained emulsifiers like whey proteins are most suitable to transport a maximum amount of bioactive substances to the effective location, being the small intestine for anthocyanins. In addition, it was shown that the dominating release mechanism for entrapped matter was coalescence of the interior W(1) -droplets with the surrounding W(2) -phase.

Ultra high pressure homogenization of almond milk: Physico-chemical and physiological effects

Ultra high pressure homogenization (UHPH) of food is a processing technology to improve food safety and shelf life. However, despite very short treatment duration UHPH may lead to changes in chemical and physico-chemical properties including formation of submicro-/nano-particles. This may affect the physiological or toxicological properties of the treated food. Here, we treated raw almond milk (AMr) with UHPH at 350 MPa and 85 °C (AMuhph), known able to inactivate food relevant microorganisms. UHPH-treatment led to about a threefold increase of the mean particle size. There was a nearly complete loss of antigenicity investigated by ELISA for determination of traces of almond proteins. The content of vitamins B1 and B2 remained unchanged, while free exposed sulfhydryl groups decreased. Despite of observed modifications, UHPH-treatment of almond milk did not cause any changes in cyto- or genotoxic effects and antigenotoxic capability of protecting intestinal cells against iron induced DNA damage in vitro.

Influence of Different Nanomaterials on Growth and Mycotoxin Production of Penicillium verrucosum

Nanoparticles are ubiquitous in the environment. They originate from anthropogenic or natural sources or they are intentionally produced for different purposes. There exist manifold applications of nanoparticles in modern life leading unavoidably to a confrontation and interaction between nanomaterial and living organisms. Based on their wide distribution tending to increase steadily, the influence of particles based on silica and silver, exhibiting nominal sizes between 0.65 nm and 200 nm, on the physiology of the mycotoxigenic filamentous fungus Penicillium verrucosum was analyzed. The applied concentration and time-point, the size and the chemical composition of the particles was shown to have a strong influence on growth and mycotoxin biosynthesis. On microscopic scale it could be shown that silver nanoparticles attach to the mycelial surface. Moreover, silver nanoparticles with 0.65 nm and 5 nm in size were shown to internalize within the cell, form agglomerates in the cytoplasm and associate to cell organelles.

Chapter 11 - Engineered Nanomaterials in the Food Sector

Abstract Potential applications of engineered nanomaterials (ENM) in food have shown great potential benefits and improvements over existing technologies. Many of the applications are still in the research and developmental stage and would require rigorous food safety testing and ultimately consumer acceptance. Within the European Union, which has taken active role in regulating ENM, nano/size-specific provisions have been implemented into several food-related directives and regulations. The lack of standardized methods for the detection and characterization of ENM in foods as well as their potential absorption renders the effective implementation of the legal requirements presently difficult. One favored approach is the combination of field-flow fractionation and ICP-MS for successive quantitative and qualitative nanomaterial analysis. For simultaneous characterization of size and chemical composition of inorganic nanoparticles, single-particle ICP-MS arose as a promising technique.

Effect of Food Constituents on Genotoxicity Induced by Silver Ions, Colloidal Silver and Silver Nanoparticles: SFRBM's 22nd Annual Meeting - Program and Abstracts

by Silver Ions, Colloidal Silver and Silver Nanoparticles. Karlis Briviba, Volker Gräf, Elke Walz, Diana Behsnilian, and Ralf Greiner Max Rubner-Institute, Federal Research Institute of Nutrition and Food, Karlsruhe, Germany Silver nano-particles (AgNPs) are used as antibacterial compounds in food contact materials and there are concerns that AgNPs can migrate into the food. Colloidal silver (colAg) is marketed as a dietary supplement. Silver ions (Ag) and particles have been shown to be genotoxic partly due to induction of oxidative stress. Here, we investigated whether nutritional constituents such as glutathione and phytate with known antioxidant properties can protect the intestinal epithelial Caco-2 cells against DNA-damage induced by silver ions and particles. AgNPs (d50,3 = 9 nm) in water and cell culture medium was characterised by dynamic light scattering and electron microscopy; colAg by UV-Vis spectrometry (surface plasmon resonance) and electron microscopy. Cellular uptake of glutathione and phytate was measured enzymatically and by HPLC, respectively. Ag, colAg and AgNPs induced DNA strand breaks in Caco-2 cells in a dose dependent manner. Ag and colAg showed similar genotoxicity and both were more genotoxic than AgNPs. Both glutathione and phytate protected against genotoxicity induced by either silver ions or colAg or AgNPs. Thus, there are food constituents with antioxidant activity which are able to protect intestinal cells against genotoxic effects caused Ag, colAg and AgNPs.