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During the past two decades probiotic micro-organisms have been widely applied in different types of products either as pharmaceuticals, nutritional supplements or foods. Among the latter group fermented dairy products such as probiotic yoghurt are becoming popular in the market and the range of such products continues to expand commercially (Manojlovi , Nedovi , Kailasapathy & Zuidam, 2010). An increasing demand for probiotic functional foods is mainly due to the plenty of evidence that exists on the positive effects of probiotics on human health. Together with prebiotics, probiotics are often showed to be effective for the treatment or control of several diseases while the enhancement of the immune system and prevention of diarrhea are the main promising health benefits (Roberfroid, 2000).
In developing functional dairy products with probiotics several aspects must be taken into consideration. The main issue is the functional characteristics of probiotics. In order to exert their proposed health effects probiotic bacteria should be present at a certain level in the products therefore; manufacturers must ensure their viability and survival under industrial conditions, during storage and into the final food products. Moreover probiotic bacteria must survive intestinal bile acids and withstand gastric pH of the gastrointestinal tract (Saarela, Mogensen, Fonden, Mättö & Mattila-Sandholm, 2000). A number of so-called probiotic yoghurt products are sold however studies have shown that very few meet the FAO/WHO guidelines and their viability is not guaranteed thus several microencapsulation techniques have been developed in order to retain the presence of these organisms into yoghurt matrix and the GI tract. Among these methods, spray coating and gel-particle technologies are more often used (Champagne & Fustier, 2007). Furthermore, a new technology called co-encapsulation which refers to encapsulation of both probiotic bacteria and prebiotics together has also shown to have potential in improving viability of probiotics in yoghurt. The overall objective of this presentation is to look at some of the common microencapsulation techniques that are used in production of probiotic yoghurt and to address some challenges in this high-tech method.
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As defined by FAO and WHO Probiotics are: "live micro-organisms which when administered in adequate amounts confer a health benefit on the host" (World Health Organization, 2001). This definition shows two significant characteristics of a probiotic product .The first one is that these products should contain live microorganisms and secondly the live microorganisms must be in an accurate amount to exert their health benefits (Yildez, 2009).
Micro-organisms must have a number of characteristics before they can be considered as probiotics. These include the ability to survive the gastric acid and bile salts of the gastrointestinal tract, colonising in the intestinal mucosa, lack of pathogenicity and the capacity to exert a health improvement on the host. It is unlikely that any one probiotic strain possesses all of these characteristics however, some beneficial effect on human health must have been demonstrated (Tamime, 2005).
Élie Metchnikoff was the first person who reported a correlation between the long life of the Bulgarian peasants and the consumption of fermented dairy products, he mainly related to lactic acid bacteria. Nowadays, the probiotic bacteria used in functional dairy products mainly belong to Lactobacillus and Bifidobacteria genera (Heller, 2001). These bacteria have the ability to improve the microbial balance of the human gut, they antagonize pathogens by making antibacterial compounds and compete for pathogen binding. Their other functions are changing gut pH, simulating immunomodulatory cells and producing lactase (Kopp-Hoolihan, 2001).
2.1. Health Benefits of Probiotics:
Probiotics have been at the forefront of the development of functional dairy products due to a wide range of desirable health benefits that they promote. Some of these health claims have been supported by research such as improving intestinal tract health, enhancing the immune system, synthesizing and enhancing the bioavailability of nutrients, reducing symptoms of lactose intolerance, decreasing the prevalence of allergy in susceptible individuals, and reducing risk of certain cancers (Kopp-Hoolihan, 2001; Virender & Gill, 2009). Most of the current studies mainly focus on the following areas; inflammatory diseases such as inflammatory bowel diseases (IBS and IBD), allergy and diarrhea.
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Table 1: Health benefits of probiotics established in human studies (Apajalahti, Bech Hansen, Friedrich, Schlothauer, Schmid & Staudt, 2005)
Improvement of the immune system
K Arunachalam et al.(2000), BL Chiang et.al. (2000)
Prevention of allergies
L Pelto et al. (1998),E.Isolauri et.al. (2000), M Kalliomaki et.al.(2001), M Kalliomaki et.al.(2003)
Promotion of lactose digestion
ME Sanders (2000) , P Marteau (2002) , M de Vrese et al. (2001)
Regulation of gut mobility(constipation and irritable bowel syndrome)
P Marteau et al.(2002), JA Madden et al. (2002) , AS Naidu et al.(1999) , C Koebnick et al. (2001) , T Ogata et al. (1997), M Seki et al.(1978)
Protection against gastrointestinal and respiratory tract infections
M de Vrese (2002) , K Hatakka (2001)
Inflammatory Bowel Diseases (IBS and IBD)
P Marteau et al.(2002), JA Madden et al. (2002) ,Nobaek et al.(2000),McFarland et al. 2006, McFarland & Dublin 2008, Nikfar et al. 2008
Prevention and treatment of urogenital tract infections
M de Vrese (2002), T Kontiokari et al. (2003), G Reid (2001),
ME Sanders (2000)
Reduction of high cholesterol levels
ME Sanders (1999), MC Bertolami et al. (1999), B Richelsen et al. (1996), G Kiessling et al. (2002)
Effectiveness against Helicobacter pylori infection
LJ Fooks et al. (2002), P Marteau et al.(2002), ME Sanders (1999), M de Vrese et al. (2002)
Reducing risk of certain cancers
Y Aso et al. (1992,1995) Y Ohashi et al.(2002)
2.2. Probiotics in fermented dairy products:
The consumption of fermented dairy products containing bacterial cultures has long been related to various beneficial health effects, and probiotic cultures have had a long association with these types of products. Yoghurt defined as the product of milk fermentation by Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus, has a long history of beneficial impact on the well-being of humans (Elli et al., 2006) which makes it a suitable carrier of
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probiotic strains. There has been a disagreement in considering classical yoghurt as a probiotic product. This disagreement is raised due to the fact that the starter bacteria of yoghurt do not colonize and live in the gastrointestinal system. These bacteria are called 'transient" which means that they do not remain in the GIT for a sufficient time to show probiotic activities; however, they have some beneficial activities. All Streptococcus thermophilus and most Lactobacillus delbrueckii subsp. bulgaricus have a high Î²-galactosidase activity thus yoghurt consumption improves lactose digestion in people with lactose intolerance disorder; furthermore, yoghurt has high numbers of live starters (Guarner, Perdigon, Corthier, Salminen, Koletzko & Morelli, 2007). For these reasons the National Yoghurt Association (NYA) has published a position statement for probiotics in September 2006 that "Live and active yoghurt that contains Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus is probiotic food as it provides a beneficial effect related to lactose digestion."(NYA, 2006 )
Food industries have been quick to recognize the huge market potential of probiotic bacteria due to the several health benefits provided by them. Adding probiotics as dietary adjuncts to various foods and beverages such as cereal bars, juices, cheese, chocolates and frozen yoghurts is becoming an attractive option for companies that are interested in healthy products (Champagne, Gardner & Roy, 2005b). However, the inclusion of probiotics in fermented dairy products plays a principle role as the best carriers of these microorganisms. This is mainly because of the high consumer acceptance of these foods as being healthy and natural carriers of living bacteria. Currently, dairy products especially yoghurtlike products are the largest part of the probiotic market. Around 30% of the global population buys into the probiotic dairy products regularly.
Fermented dairy products promote the healthy image of probiotics for three reasons:
Fermented dairy products such as yoghurt already have a positive health image.
Consumers are familiar with the fact that fermented products contain viable microorganisms.
The image of yoghurtlike products as healthful foods makes the recommendation of daily consumption of probiotics easier.
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In recent years one of the most popular dairy products for the delivery of probiotics is bio-yoghurts. This product contains species of Bifidobacterium most commonly Bifidobacterium bifidum and Lactobacillus acidophilus, Lactobacillus rhamnosus, and Lactobacillus casei among lactobacilli in addition to classical yoghurt culture (Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus) (Talwalkar & Kailasapathy, 2004).The probiotic bacteria can be added prior to fermentation, simultaneously with the traditional yoghurt cultures, or after fermentation to the cooled product before packaging.
3. Challenges in the development of probiotic yoghurt:
In order to exert their health effects, the Intl. Dairy Federation has recommended that the probiotic bacteria should be at a certain level of at least CFU of live microorganisms per millilitre or gram of product at the time of consumption (Chávarri, Mara ón, Ares, Ibá ez, Marzo & Villarán, 2010; Ding & Shah, 2007; Organization, 2001; Shah & Ravula, 2000; Sultana, Godward, Reynolds, Arumugaswamy, Peiris & Kailasapathy, 2000). However, many studies have shown low viability of probiotics in yoghurt. (Table 3) shows some previous reports on the low viability of probiotics in yoghurt.
Table 2: Various studies on poor viability of probiotics in yoghurt