Encapsulation Technologies for Active Food Ingredients and Food Processing

Consumers prefer food products that are tasty, healthy and convenient. Encapsulation, a process to entrap active agents into particles, is an important way to meet these demands by delivering food ingredients at the right time and place. For example, this technology may allow taste and aroma differentiation, mask bad tasting or bad smelling components, stabilize food ingredients and/or increase their bioavailability. Encapsulation may also be used to immobilize cells or enzymes in the production of food materials or products, as in fermentation or metabolite production.

This book provides a detailed overview of the technologies used in the preparation and characterization of encapsulates for food active ingredients to be used in food products, processing, or production. This book aims to inform people, with both a limited and an advanced knowledge of the field, who work in the academia or R&D of companies on the delivery of food actives via encapsulation and on food processing using immobilized cells or enzymes.

Encapsulation may be defined as a process to entrap one substance within another substance, thereby producing particles with diameters of a few nm to a few mm. The substance that is encapsulated may be called the core material, the active agent, fill, internal phase, or payload phase. The substance that is encapsulating may be called the coating, membrane, shell, carrier material, wall material, external phase, or matrix. The carrier material of encapsulates used in food products or processes should be food grade and able to form a barrier for the active agent and its surroundings. Please see Chap. 3 for more information on this.

A multitude of substances are known which can be used to entrap, coat, or encapsulate solids, liquids, or gases of different types, origins, and properties. However, only a limited number thereof have been certified for food applications as “generally recognized as safe” (GRAS) materials. It is worth mentioning that the regulations for food additives are much stricter than for pharmaceuticals or cosmetics. Consequently, some compounds, which are widely accepted for drug encapsulation, have not been approved for use in the food industry. Moreover, different regulations can exist for different continents, economies, or countries, a problem which has to be addressed by food producers who wish to export their products or who intend expanding their markets.

Food active ingredients can be encapsulated by different processes, including spray drying, spray cooling, spray chilling, spinning disc and centrifugal co-extrusion, extrusion, fluidized bed coating and coacervation (see Chap. 2 of this book). The purpose of encapsulation is often to stabilize an active ingredient, control its release rate and/or convert a liquid formulation into a solid which is easier to handle. A range of edible materials can be used as shell materials of encapsulates, including polysaccharides, fats, waxes and proteins (see Chap. 3 of this book). Encapsulates for typical industrial applications can vary from several microns to several millimetres in diameter although there is an increasing interest in preparing nano-encapsulates. Encapsulates are basically particles with a core-shell structure, but some of them can have a more complex structure, e.g. in a form of multiple cores embedded in a matrix. Particles have physical, mechanical and structural properties, including particle size, size distribution, morphology, surface charge, wall thickness, mechanical strength, glass transition temperature, degree of crystallinity, flowability and permeability. Information about the properties of encapsulates is very important to understanding their behaviours in different environments, including their manufacturing processes and end-user applications. E.g. encapsulates for most industrial applications should have desirable mechanical strength, which should be strong enough to withstand various mechanical forces generated in manufacturing processes, such as mixing, pumping, extrusion, etc., and may be required to be weak enough in order to release the encapsulated active ingredients by mechanical forces at their end-user applications, such as release rate of flavour by chewing. The mechanical strength of encapsulates and release rate of their food actives are related to their size, morphology, wall thickness, chemical composition, structure etc. Hence, reliable methods which can be used to characterize these properties of encapsulates are vital. In this chapter, the state-of-art of these methods, their principles and applications, and release mechanisms are described as follows.

Flavor is one of the most important characteristics of a food product, since people prefer to eat only food products with an attractive flavor (Voilley and Etiévant 2006). Flavor can be defined as a combination of taste, smell and/or trigeminal stimuli. Taste is divided into five basic ones, i.e. sour, salty, sweet, bitter and umami. Components that trigger the so-called gustatory receptors for these tastes are in general not volatile, in contrast to aroma. Aroma molecules are those that interact with the olfactory receptors in the nose cavity (Firestein 2001). Confusingly, aroma is often referred to as flavor. Trigeminal stimuli cause sensations like cold, touch, and prickling. The current chapter only focuses on the encapsulation of the aroma molecules.

For those fortunate to live near rivers, lakes and the sea, fish has been part of their diet for many centuries, and trade in dried fish has a long history. The important fishing industry developed when fishermen started to fish over wider areas of the seas and when improvements in freezing facilities allowed storage at sea, and subsequent distribution to urban consumers. For many, fresh fish and fried fish are now a part of their standard diet.

The original medicinal use of fish oils began with cod liver oil in the 1780s in England for arthritis and rheumatism. By the 1800s, it was used to prevent rickets. The prevention of rickets also depended on the vitamin D content. Fish oil contains several special types of fatty acids, the so called long-chain polyunsaturated fatty acids (LCPUFA, with more than 20 carbon atoms). The chemical structures of selected long-chain and other PUFAs are shown in Fig. 6.1.

Omega-3 fatty acids are those that have the first double bond at the third carbon-carbon bond from the terminal methyl group of the carbon chain, the omega (chemists normally start counting from the other side, the alpha). In Fig. 6.1, the omega-3 fatty acids are α-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). Omega-6 fatty acids are those which have the first double bond at the sixth place from the end, here linoleic, γ-linoleic, and arachidonic acids. The characteristics of the omega-3 fatty acids are described in more detail below, since most people have a shortage of these (Garg et al. 2006).

Iodine, vitamin A and iron deficiencies are important global public health problems, particularly for preschool children and pregnant women in low-income countries (World Health Organization 2000). These deficiencies are mainly due to monotonous, poor-quality diets that do not meet nutrient requirements. In countries where existing food supplies and/or limited access fail to provide adequate levels of these nutrients in the diet, food fortification is a promising approach. Co-fortification of foods with iron, iodine and vitamin A may be advantageous due to beneficial interactions of these micronutrients in metabolism. Studies in animals and humans have shown that iron deficiency anemia (IDA) impairs thyroid metabolism (Zimmermann et al. 2000a, 2000b; Hess et al. 2002a, 2002b). Vitamin A deficiency may exacerbate anemia through impairment of iron metabolism (Semba and Bloem 2002). Vitamin A, together with iodine, may reduce thyroid hyperstimulation and risk for goiter (Zimmermann et al. 2007). These micronutrient interactions strongly argue for multiple micronutrient fortification. However, food fortification with iron is not straightforward.

Carotenoids are natural pigments, which are synthesized by microorganisms and plants. More than 600 naturally occurring carotenoids have been found in the nature. The main sources of carotenoids are fruits, vegetables, leaves, peppers, and certain types of fishes, sea foods, and birds. Carotenoids may protect cells against photosensitization and work as light-absorbing pigments during photosynthesis. Some carotenoids may inhibit the destructive effect of reactive oxygen species. Due to the antioxidative properties of carotenoids, many investigations regarding their protective effects against cardiovascular diseases and certain types of cancers, as well as other degenerative illnesses, have been carried out in the last years (Briviba et al. 2004; Krinsky et al. 2004; Kirsh et al. 2006). A diet rich in carotenoids may also contribute to photoprotection against UV radiation (Stahl et al. 2006). In vitro studies have shown that carotenoids such as β-cryptoxanthin and lycopene stimulate bone formation and mineralization. The results may be related to prevention of osteoporosis (Kim et al. 2003; Yamaguchi and Uchiyama 2003; 2004; Yamaguchi et al. 2005).

A large part of formulated peptides and proteins, e.g., enzymes used as food ingredients, are formulated in a liquid form. Often, they are dissolved in water to which glycerol or sorbitol is added to reduce the water activity of the liquid, thus reducing the change of microbial growth. Still, there are reasons to formulate them in a solid form. Often, these reasons are stability, since a dry formulation is often much better than liquid formulations, and less transportation cost, since less mass is transported if one gets rid of the liquid; however, most of the times, the reason is that the product is mixed with a solid powder. Here, a liquid addition would lead to lump formation.

Additional issues that play a role when formulating these products in a solid form are, for example, allergenicity, dust reduction, dosing accuracy, and dissolution.

Stability in a solid formulation is often much better than in a liquid formulation, since the water activity is low. Often, stabilizers are added to the solid forms to protect the proteins against denaturation.

The history of the role of probiotics for human health is one century old and several definitions have been derived hitherto. One of them, launched by Huis in’t Veld and Havenaar (1991) defines probiotics as being “mono or mixed cultures of live microorganisms which, when applied to a man or an animal (e.g., as dried cells or as a fermented product), beneficially affect the host by improving the properties of the indigenous microflora”. Probiotics are living microorganisms which survive gastric, bile, and pancreatic secretions, attach to epithelial cells and colonize the human intestine (Del Piano et al. 2006). It is estimated that an adult human intestine contains more than 400 different bacterial species (Finegold et al. 1977) and approximately 10¹⁴ bacterial cells (which is approximately ten times the total number of eukaryotic cells in the human body). The bacterial cells can be classified into three categories, namely, beneficial, neutral or harmful, with respect to human health. Among the beneficial bacteria are Bifidobacterium and Lactobacilli. The proportion of bifidobacteria represents the third most common genus in the gastrointestinal tract, while Bacteroides predominates at 86% of the total flora in the adult gut, followed by Eubacterium. Infant-type bifidobacteria B. bifidum are replaced with adult-type bifidobacteria, B. longum and B. adolescentis. With weaning and aging, the intestinal flora profile changes. Bifidobacteria decrease, while certain kinds of harmful bacteria increase. Changes in the intestinal flora are affected not only by aging but also by extrinsic factors, for example, stress, diet, drugs, bacterial contamination and constipation. Therefore, daily consumption of probiotic products is recommended for good health and longevity. There are numerous claimed beneficial effects and therapeutic applications of probiotic bacteria in humans, such as maintenance of normal intestinal microflora, improvement of constipation, treatment of diarrhea, enhancement of the immune system, reduction of lactose-intolerance, reduction of serum cholesterol levels, anticarcinogenic activity, and improved nutritional value of foods (Kailasapathy and Chin 2000; Lourens-Hattingh and Viljoen 2001; Mattila-Sandholm et al. 2002). The mechanisms by which probiotics exert their effects are largely unknown, but may involve modifying gut pH, antagonizing pathogens through production of antimicrobial and antibacterial compounds, competing for pathogen binding, and receptor cites, as well as for available nutrients and growth factors, stimulating immunomodulatory cells, and producing lactase (Kopp-Hoolihan 2001).

Beer production with immobilised yeast has been the subject of research for approximately 30 years but has so far found limited application in the brewing industry, due to engineering problems, unrealised cost advantages, microbial contaminations and an unbalanced beer flavor (Linko et al. 1998; Brányik et al. 2005; Willaert and Nedović 2006). The ultimate aim of this research is the production of beer of desired quality within 1–3 days. Traditional beer fermentation systems use freely suspended yeast cells to ferment wort in an unstirred batch reactor. The primary fermentation takes approximately 7 days with a subsequent secondary fermentation (maturation) of several weeks. A batch culture system employing immobilization could benefit from an increased rate of fermentation. However, it appears that in terms of increasing productivity, a continuous fermentation system with immobilization would be the best method (Verbelen et al. 2006). An important issue of the research area is whether beer can be produced by immobilised yeast in continuous culture with the same characteristic as the traditional method.

In beer production, as opposed to a process such as bio-ethanol production, the goal is to achieve a particular balance of different secondary metabolites rather than the attainment of high yields of one product. Any alterations of the fermentation procedure can thus have serious implications on the flavor profile. At present, only beer maturation and alcohol-free beer production are obtained by means of commercial-scale immobilised yeast reactors, because in these processes no real yeast growth is required. Immobilised cell physiology control and fine-tuning of the flavor compounds formation during long-term fermentation processes remain the major challenges for successful application of immobilised cell technology on an industrial scale. The key factors for the implementation of this technology on an industrial level are carrier materials, immobilization technology and bioreactor design.

The purpose of this chapter is to summarise and discuss the main cell immobilization methods, process requirements, available carrier materials and bioreactor designs aimed for better yeast physiology control and fine-tuning of the flavor formation during beer fermentation process. Further, it will provide an overview on the latest important breakthroughs, accomplished in understanding of the effects of immobilization on yeast physiology, metabolism and fermentation behaviour.

Wine- or cider-making is highly associated with biotechnology owing to the traditional nature of must fermentation.. Nowadays, there have been considerable developments in wine- or cider-making techniques affecting all phases of wine or cider production, but more importantly, the fermentation process. It is well-known that the transformation of grape must by microbial activity results in the production of wine, and the fermentation of apples (or sometimes pears) in the production of cider. In this process, a variety of compounds affecting the organoleptic profile of wine or cider are synthesized. It is also common sense that in wine- or cider-making, the main objective is to achieve an adequate quality of the product. The technological progress and the improved quality of the wines or ciders have been associated with the control of technical parameters. Herein, cell immobilization offers numerous advantages, such as enhanced fermentation productivity, ability for cell recycling, application of continuous configurations, enhanced cell stability and viability, and improvement of quality (Margaritis and Merchant 1984; Stewart and Russel 1986; Kourkoutas et al. 2004a).

The objective of the present chapter is to analyze and assess data on the impact of immobilization technologies of viable microbial cells on the alcoholic and malolactic fermentation (MLF) of wine and cider. The immobilized biocatalysts are evaluated for their scale-up ability and their potential future impact in industrial application is highlighted and assessed. Handicaps associated with maintenance of cell viability and fermentation efficiency during preservation and storage, constraining the industrial use of immobilized cell systems are discussed.

Historically, we can find fermented products in almost all cultural backgrounds around the world. Notably, there are many different milk or meat-based foods and this chapter will focus on them (Kosikowski 1982; Wood 1998). Cheese, yoghurt, sour cream, kefir, or cultured butter are probably the most common fermented dairy products, but many regional varieties exist (Farnworth 2004). Fermented meats are typically found as dry sausages (Lüke 1998). Yeasts are mostly involved in the manufacture of bread and alcoholic beverages, which are basically cereal- or fruit-based products. In fermented meat and milk, the main microorganisms used are the lactic acid bacteria (LAB). Yeast and molds are rather involved in ripening. Therefore, the LAB will constitute the main focus of this chapter.

The control of production costs in the food industry must be very strict as a result of the relatively low added value of food products. Since a wide variety of enzymes and/or cells are employed in the food industry for starch processing, cheese making, food preservation, lipid hydrolysis and other applications, immobilization of the cells and/or enzymes has been recognized as an attractive approach to improving food processes while minimizing costs. This is due to the fact that biocatalyst immobilization allows for easier separation/purification of the product and reutilization of the biocatalyst. The advantages of the use of immobilized systems are many, and they have a special relevance in the area of food technology, especially because industrial processes using immobilized biosystems are usually characterized by lower capital/energy costs and better logistics. The main applications of immobilization, related to the major processes of food bioconversions and metabolite production, will be described and discussed in this chapter.