Keywords

These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Dietary fiber has long been recommended as part of a healthy diet based on the observations made by Burkitt and Trowell (1975). Since then, epidemiological evidence has consistently shown that populations consuming higher levels of foods containing fiber have decreased risk of a variety of chronic health disorders such as cardiovascular disease, type II diabetes, and certain cancers. Average fiber intake in the United States is approximately 13 g/day for women and 18 g/day for men (National Academy of Sciences, 2006). The FDA recommends a minimum of 20–35 g/day for a healthy adult depending on calorific intake. In many EU countries including France, Germany and the UK (see Figure 9.1 ), fiber intakes are much lower than authorities recommend for men and women (Buttriss and Stokes, 2008; Gray, 2006). Thus, there is a need to increase fiber consumption and many newly isolated or developed fibers can easily be added to beverages and processed foods. The reasons for such low compliance is somewhat complex, however the most basic rationale for not consuming fiber-rich foods is perceived bad taste and mouthfeel and the availability of conventional food items containing fiber.

Figure 9.1
figure 1_9

Daily intake of fibers.

Full size image

Dietary fibers confer a wide range of health effects, from alleviation of constipation to reduction of cholesterol (Buttriss and Stokes, 2008). The physiological effects of dietary fibers in humans depend on the physico-chemical properties of fiber (viscosity, fermentability, bulking properties) and on the human gastro-intestinal (GI) tract (gut microbiotia, GI transit time). A specific subset of dietary fibers, so called prebiotics, convey health benefits by selectively stimulating the growth and/or activity of one or a limited number of bacteria like bifidobacteria and lactobacilli in the colon (Gibson and Roberfroid, 1995).

There is considerable industry and public interest in the capacity of foods and food components to promote health and lower risk of non-infectious diseases related to diet and lifestyle. Industry is thus challenged to develop fibers that can overcome the problems with stability under manufacturing conditions, functionality in various food systems, and taste in order to give the consumer more options when it comes to getting fiber in their diet. Newly derived starch fibers meet these requirements. In this chapter, prebiotic properties of newly derived fibers from maize and other starches will be reviewed with a specific focus on PROMITOR™ fibers, which were designed for optimal taste and texture and have prebiotic properties. The PROMITOR™ line includes a Soluble Gluco Fiber (PROMITOR™ Soluble Corn Fiber in US) and an insoluble Resistant Starch that are classified as food ingredients.

16.1 9.1 Introduction

The human gut microbiota constitutes a dynamic and ecologically diverse environment. The large intestine is by far the most heavily colonized region of the digestive tract, with up to 1012 bacteria for every gram of gut contents containing more than 400 different species of bacteria. The number of bacteria in the colon outnumber (10-fold) the number of human cells making it a very powerful target for nutritional interventions. Through the process of fermentation, colonic bacteria are able to produce a wide range of compounds that have both positive and negative effects on the gut physiology as well as other systemic influences. For instance, certain microbial populations present in the gut provide an efficient barrier to invading pathogens (Macfarlane, 2008). Competition for nutrients and ecological niches, production of antimicrobial compounds, lowering of intestinal pH through production of short chain fatty acids and stimulation of the immune system play a role in limiting the ability of pathogens to colonize the gut and potentially cause disease. Many of these microbiota-associated activities have a direct impact on host health. While prebiotics are selectively interacting with the intestinal microbiota, they are being fermented by the bacteria into many different metabolites. As the composition of the microbiota is modified, the types of fermentation metabolites into which prebiotic substrates are converted are also modified. Some of these metabolites are utilized by the cells lining the intestine, while others are absorbed into the blood of the host and pass the blood barrier to enter the systemic body space, where they interact with many physiological processes in all vital organs and peripheral tissues of the host (Lenoir-Wijnkoop et al., 2007).

16.2 9.2 Resistant Starches

Resistant starches are defined as the sum of starch and products of starch degradation not absorbed in the small intestine of healthy individuals (Asp, 1997). There are four main groups of resistant starches: RS1, RS2, RS3 and RS4. RS1 is physically inaccessible starch (i.e., starch in whole grains), RS2 is granular starch i.e., starch in green bananas), RS3 is retrograded starch (i.e., starch in cooked and cooled potatoes) and RS4 is a chemically-modified starch (i.e., an esterified starch). PROMITOR™ Resistant Starch is classified as a type 3 resistant starch.

16.2.1 9.2.1 Introduction to a Type 3 Resistant Starch

16.2.1.1 9.2.1.1 Regulatory Status

Resistant starches occur naturally in many foods and thus have been safely consumed across the globe for years. PROMITOR™ Resistant Starch is a food ingredient in the US and EU and can be labeled as “Resistant Starch,” “Starch,” “Maize Starch” or “Corn starch.” It is a non genetically-modified source of dietary fiber which enables, where relevant regulatory conditions are met; the use of fiber nutrient content claims (contains fiber, source of fiber, high fiber).

The European definition of dietary fiber published in Directive 2008/100/EC recognizes as dietary fiber, carbohydrate polymers with three or more monomeric units, which are neither digested nor absorbed in the human small intestine and belong to the following categories:

  • edible carbohydrate polymers naturally occurring in the food as consumed

  • edible carbohydrate polymers which have been obtained from food raw material by physical, enzymatic or chemical means and which have a beneficial physiological effect demonstrated by generally accepted scientific evidence

  • edible synthetic carbohydrate polymers which have a beneficial physiological effect demonstrated by generally accepted scientific evidence

RS meets the European definition and can be incorporated into food products to meet the Regulation (EC) 1924/2006 that requires at least 3 g of fiber per 100 g or at least 1.5 g per 100 kcal for the nutrition claim “source of fiber”; and at least 6 g of fiber per 100 g or at least 3 g per 100 kcal for the nutrition claim “high in fiber.” Levels necessary for nutrient content claims in the US are 2.5 g fiber/serving for a “good source” claim and 5.0 g fiber/ serving for an “excellent source” claim.

16.2.1.2 9.2.1.2 Dietary Fiber Content

PROMITOR™ Resistant Starch has an analysis of approximately 60–75% total dietary fiber per AOAC method 991.43. This AOAC method works well for fibers that are insoluble or nearly insoluble.

16.2.1.3 9.2.1.3 Calorific Value

RS has a calorific value of 1.70 kcal/g, as calculated using standard practices of subtracting the percent fiber content as analyzed by AOAC 991.43 from total carbohydrates. This is the calorific declaration used on specification sheets in the US, as specified by US regulations for insoluble fibers. EU calorific value will be 2 kcal/g as per Commission Directive 2008/100/EC.

The true metabolizable energy (TME) content was also determined in an in vivo avian model at the University of Illinois (Knapp et al., 2008). The model is a more precise model for calorific determination than in vitro models and collection of urine and feces is easier and often more precise than in humans. This method, using bomb calorimetry, determined the calorific value of RS to be in the range of 1.7–2.0 kcal. This suggests that either a small portion of the RS is digested, or that fermentation products generated in the colon adds a small fraction of calories. Fermentation is a more likely hypothesis based on human glycemic response data. The glycemic response for RS is approximately 10% that of a maltodextrin control (Kendall et al., 2008). Since maltodextrin and RS are both glucose polymers, a glycemic response of 10% suggests that the remaining 90% of RS remains undigested and enters the colon. Thus, it is likely the majority of the calories from RS may actually come from fermentation metabolites.

16.2.1.4 9.2.1.4 Digestive Tolerance

Type 3 RS was shown to be well tolerated up to doses as high as 45 g/d (Bouhnik et al., 2004). Stewart et al. (2008, 2009) conducted a study in which subjects (n = 20, 10 men, 10 women) consumed 12 g fiber/d for 14 consecutive days. Subjects were asked to report gastrointestinal symptoms (cramping, bloating, stomach noise, flatulence) on a 10 point scale (1 = minimal symptoms, 10 = severe symptoms). RS was shown to be well tolerated (Stewart et al., 2009). In a dose-response study, tolerance was assessed in 22 healthy volunteers consuming three different doses of RS (5 g, 15 g, 25 g) in acute conditions after an overnight fast (Kendall et al., 2009). Subjects were asked to report gastrointestinal symptoms (belching, bloating, flatulence, nausea and diarrhoea) on a 100 mm VAS scale at 0, 15, 30, 45, 60, 90 and 120 min after consumption. RS was shown to be well tolerated in these conditions.

16.2.1.5 9.2.1.5 Applications

RS acts as an insoluble fiber that can be added to baked products, cereal products or snacks, providing them with higher fiber levels as well as other health benefits. It is one of the most stable resistant starches on the market (unpublished data) and so can be used in extruded or sheared and baked products with less loss of fiber during processing. As a result the final product has a high fiber content while offering a range of health benefits. With only 1.70 kcal/g, it can also be used in low calorie products reducing both calories and carbohydrates when replacing flour or other cereal-based ingredients.

Applications for RS include puffed or sheeted snacks, chips, extruded breakfast cereals, pasta, muffins, cookies and biscuits, crackers, frozen dough, breads.

It can be used as a partial replacement for flour in bakery products that exhibit characteristics comparable to those achieved using conventional wheat flour (e.g., cookie spread, golden brown color, pleasant aroma, surface cracking). Thanks to its low water holding property, it also does not affect height and spread management of biscuits, cookies or other baked goods.

RS enhances crispiness of cookies and crackers as well as the surface of baked sheeted crackers and extruded products. Furthermore, the induced reduction of water activity and moisture content, enhance sensory characteristics as well as the shelf life of goods. Notably, it tends to decrease bulk density, improving expansion in extruded cereals and snacks. In fried snacks, fat uptake may be reduced by up to 25% when RS is used, helping to meet “high/rich in fiber” claims.

Moreover, with a thermal stability as high as 150°C, it will retain more fiber content and structure than other resistant starches, which start to break down below 120°C.

16.2.2 9.2.2 Prebiotic Properties of Various Resistant Starch Products (RS2 and RS3)

16.2.2.1 9.2.2.1 Effect on Microbiota Modulation

The ability of RS to favor growth of bifidobacteria and lactobacilli within the gut flora has been assessed in vitro, in animal models and in humans.

In a study Le Blay et al. (2003) showed the prebiotic properties of RS2. Eighteen rats were fed a low-fiber diet (Basal) or the same diet containing raw potato starch (RS2) (9%) or short-chain FOS (9%) for 14 days. Changes in wet-content weights, bacterial populations and metabolites were investigated in the caecum, proximal, distal colon and feces. Both substrates exerted a prebiotic effect compared with the Basal diet. All bacteriological analysis were performed within 2 h after sampling. Samples were diluted and dilution were applied on plates using both unselective and selective media. After incubation, single colonies were counted. FOS increased lactic acid-producing bacteria throughout the caecocolon and in feces, whereas the effect of RS2 was limited to the caecum and proximal colon. As compared with RS2, FOS doubled the pool of caecal fermentation products, while the situation was just the opposite distally. This difference was mainly because of the anatomical distribution of lactate, which accumulated in the caecum with FOS and in the distal colon with RS2. Feces reflected these impacts only partly, showing the prebiotic effect of FOS and the metabolite increase induced by RS2. In conclusion, this study demonstrates that FOS and RS2 exert complementary effects and combined ingestion could be beneficial by providing health-promoting effects throughout the colon.

Brown et al. (1997) also observed prebiotic effects in 12 young male pigs fed with high amylose cornstarch diet (RS2). Starch provided 50% of total daily energy either as a low amylose cornstarch or as a high amylose (amylomaize) cornstarch. Fecal output, fecal concentrations and excretion of total SCFA (notably propionate and butyrate), fecal culture-based bifidobacteria counts (expressed per gram of wet feces) and their daily fecal excretion were higher when pigs were fed the high amylose cornstarch.

Similar prebiotic effects have been reported for retrograded RS (RS3) in several animal models. Dongowski et al. (2005) and Jacobasch et al. (2006) have shown in rats fed with RS3 that the growth of bifidobacteria and the production of SCFA were increased throughout the digestive tract, favoring thus a decrease of the pH in the caecum, colon and feces.

Using another model of human flora-inoculated gnotobiotic rats (HFA), colonized with microbiotas from UK or Italian donors, Silvi et al. (1999) looked at the prebiotic effects of a RS3. Consumption of this RS3 (15 g/100 g diet) resulted in significant changes in both the UK and Italian flora-associated rats: numbers of lactobacilli and bifidobacteria were increased 10–100-fold, and there was a concomitant decrease in enterobacteria when compared with sucrose-fed rats (control). The induced changes in caecal microbiota of both HFA rat groups were reflected in changes in bacterial enzyme activities and caecal ammonia concentration. This RS3 markedly increased the proportion of n-butyric acid in both rat groups, lowered caecal ammonia concentration, caecal pH and beta-glucuronidase activity.

The prebiotic properties of RS3 have also been demonstrated in humans (Bouhnik et al., 2004). First, this study determined the bifidogenic properties of a RS3 at 10 g/d; Second, the dose-response relationship of the bifidogenic effects of this RS3 at doses ranging from 2.5 to 10 g/d in comparison with a placebo were assessed. Faecal samples were diluted and dilutions were applied on plate using different selective media. RS3 was shown to be bifidogenic at a dose of 10 g/d. However, bacteria counts increased at doses of 5 and 7.5 g/d, but decreased at doses of 2.5 and 10 g/d. Thus, no firm conclusions could be drawn from this study on bifidogenic properties of RS3 in humans, however the authors observed that only a low baseline bifidobacteria count was significantly associated with a bifidogenic response to treatment. This observation was recently corroborated by Roberfroid who highlighted that the baseline level of bifidobacteria together with the time of exposure to a prebiotic are more determinant factors than the amount of prebiotics consumed to assess the potential prebiotic properties of a fiber (Roberfroid, 2007). The lack of bifidogenic effect of RS3 in this study at 2.5 and 10 g/d in phase 2 might be primarily linked to an elevated baseline bifidobacteria count in the groups of volunteers.

In this respect, a recent in vitro study also showed that the RS3 crystalline polymorphism can impact the RS fermentability by human gut microbiota as well as the short chain fatty acids production. Human fecal pH-controlled batch cultures showed that RS induces an ecological shift in the colonic microbiota, with polymorph B being much more efficient in inducing Bifidobacterium spp. growth than polymorphism A. Interestingly, polymorph B also induced higher butyrate production to levels of 0.79 mM (Lesmes et al., 2008). Type-A crystalline polymorph is found in typical cereal starch granules while the type-B polymorph is found in potato and high amylose cereal starch granules. The A polymorph has a much lower water content in the crystal lattice compared to the B polymorph.

PROMITOR™ Resistant Starch has shown to be a potential prebiotic in in vitro studies at TNO (Maathuis et al., 2008). The aim of the study was to investigate the effect of newly developed maize-based fibers on the activity and composition of the microbiota in the colon. The tested fibers were glucose-based and have variable structures including two resistant starch preparations. The fibers were pre-digested, mono- and di-saccharides were removed, and the residual polymer was used to assess the production of microbial metabolites and changes in composition of the microbiota using a dynamic, validated, in vitro model of the large intestine (TIM-2). Microbial metabolite analysis showed an increase in health-promoting metabolites (short-chain fatty acids) and a reduction in toxic metabolites from protein fermentation compared to the poorly-fermentable control (cellulose). The lactate production was also relatively low, indicating that it is slowly fermented. This may contribute to its excellent tolerance and extend its health benefits throughout the entire large intestine. Using microarray technology to compare multiple species and groups of colonic microbiota, RS was found to promote the growth of beneficial bacteria such as bifidobacteria and lactobacilli (Figure 9.2 ). Further studies are underway to determine if these in vitro effects are also seen in vivo.

Figure 9.2
figure 2_9

Use of the microarray technology to evaluate the effects of PROMITOR™ fibers on multiple species and groups of colonic microbito.

Full size image

Based on the above-mentioned studies, it can be reasonably concluded that RS2 and RS3 have prebiotic activity. The mechanisms involved in promotion of bifidobacteria/lactobacilli growth may be different than those observed for the other prebiotics (e.g., FOS or inulin). A study with FOS and high amylose starch (RS2) in pigs fed a diet based on human foods showed that both raised fecal bifidobacteria numbers by approximately equal amounts when fed separately. When fed together there was an increase that exceeded the individual increases, suggesting that they operate by different mechanisms (Brown et al., 1997). If FOS acts as a metabolic substrate for bifidobacteria and lactobacilli, RS2 seems to function differently. Indeed, in vitro studies showed on one hand that pure bifidobacteria strains have limited capacity to use RS2 as a substrate (Topping et al., 2003); on the other hand, they also showed physical adhesion of several bifidobacteria species to RS2 (Topping et al., 2003), suggesting thus that the prebiotic properties of RS2 may be linked to its ability to confer physical protection on the bifidobacteria/lactobacilli throughout the upper digestive tract. The same reasoning may apply to RS3, as Brouns et al. (2007) have shown that breast-fed babies’ microbiota, mainly composed of bifidobacteria was unable to use RS3 as a substrate, though several animal and human studies have shown prebiotic effects of RS3.

Nevertheless, it seems that a limited number of bifidobacteria strains has the ability to use RS2 as a substrate as shown in the study of Crittenden et al. (2001). In this study, 40 Bifidobacterium strains were examined to complement RS in a synbiotic yogurt. Only B. lactis Lafti B94 possessed all of the required characteristics. This isolate was the only one able to hydrolyze Hi-maize (RS2), to survive well in conditions simulating passage through the gastrointestinal tract and to possess technological properties suitable for yogurt manufacture. Bifidobacterium lactis Lafti B94 survived without substantial loss of viability in synbiotic yogurt containing Hi-maize during storage at 4°C for 6 weeks. In this study, RS2 was seen as a good complementary prebiotic ingredient for new synbiotic functional food products.

16.2.2.2 9.2.2.2 Health Benefits Associated with Prebiotic Properties of Resistant Starch

Several health benefits have been linked to prebiotics, notably to FOS, GOS and inulin. One of these benefits is enhancement of the body’s natural immune defenses (Schley and Field, 2002; Vos et al., 2007). This effect is primarily localized to immune defenses in the gut, such as the gut-associated lymphoid tissue, however some studies have shown systemic effects. The precise mechanisms by which prebiotics exert their immune effects are unclear; whether it is through changes in the microbial population, through fermentation metabolites (i.e., SCFA) or through direct interaction of the prebiotics with mucosal membrane receptors. There have been very few investigations into the immune-modulating effects of resistant starch. Preliminary data from a recent study including PROMITOR™ Resistant Starch demonstrates a potential immune-modulating response in an animal model of inflammatory bowel disease. Animals supplemented with Resistant Starch had fewer macroscopic lesions in the gut and a reduction in the size of mesenteric lymph nodes (unpublished data) as compared to animals without Resistant Starch in the diet.

Another benefit seen with fermentable and prebiotic dietary fibers is enhancement of mineral absorption and/or increase in bone mineralization and bone density. There are numerous hypothesized mechanisms by which fermentable fibers may alter mineral absorption and impact bone density, a few of which include increased solubility of minerals, increased gastrointestinal surface area for absorption (by means of SCFA production), and alteration of the microbial population (Scholz-Ahrens et al., 2007). Many of the studies surrounding mineral absorption and bone formation have included prebiotics, such as inulin and FOS. However, RS has also been reported to enhance the ileal absorption of a number of minerals in rats and humans. Lopez et al. (2001) and Younes et al. (2001) reported an increased absorption of calcium, magnesium, zinc, iron, and copper in rats fed RS2-rich diets. Similar preliminary results have been seen in an animal study investigating PROMITOR™ Resistant Starch where it was shown to increase femur calcium concentration after 12 weeks of supplementation (Martin et al., 2009).

16.2.2.3 9.2.2.3 Gut Health Biomarkers

It has been shown that RS has health-promoting actions on the colonic microbiota beyond the prebiotic effect. For instance, studies in children with cholera-induced diarrhoea having consumed RS (high-amylose starch) plus the rehydration therapy have shown major reduction in fluid loss and a halving of time to recovery (Ramakrishna et al., 2000, 2008). This study has been replicated in babies with other forms of infectious diarrhoea where it was shown that both RS (as green bananas) and non-starch polysaccharides (NSP) facilitated recovery and improved intestinal permeability (Rabbani et al., 2001). Accelerated recovery from infectious diarrhoea has also been shown in animals. A specific micro-organism, Brachyspira hyodysenteriae, causes substantial economic losses in the commercial pig breeding industry through morbidity and mortality in the weaning period. The effect is expressed as diarrhoeal disease on the introduction of solid food. Feeding with cooked rice, an established source of RS (Marsono et al., 1993), lowers the incidence and severity of disease with a consequent reduction in mortality (Hampson et al., 2000). Part of the benefit seems to be due to increased fluid absorption through greater SCFA production, as these acids stimulate the uptake of water and cations (Na+, K+, and Ca2+), particularly in the proximal colon. Several studies in humans (Table 9.1 ) as well as in animals (Table 9.2 ) have shown the ability of RS to enhance production of SCFA in the ceacum and throughout the colon. This outcome is an obvious mechanism for reversing diarrhoea-induced fluid loss. SCFA also appear to modulate the muscular activity of the large bowel and to promote the flow of blood through the viscera; both these actions could assist in lowering the severity of diarrhoea. In addition to these well-documented effects, it is possible that RS could limit the viability of the cholera organism in the gut. It may be hypothesized that the bacteria could adhere to the starch granules, very much in the same way as bifidobacteria, and thus be removed from the site of action (Topping et al., 2003). The production of SCFA (Cummings et al., 1996; Heijnen et al., 1998; Jenkins et al., 1998; Muir et al., 2004), the reduction of colonic pH (Birkett et al., 1996; Heijnen et al., 1998; Phillips et al., 1995) together with a beneficial change in microbiota metabolism pattern induced by RS intake (Tables 9.1 and 9.2 ) are further means of biocontrol for pathogens and potential pathogens.

Table 9.1 Human studies investigating the effects of RS intake on gut health biomarkers
Full size table
Table 9.2 Animal studies investigating the effects of RS intake on luminal and epithelial colorectal cancer biomarkers
Full size table

Diet and its interaction with the gut microbiota, and reduced protection from the microbiota with age are likely contributory factors to colorectal cancer (CRC). Genotoxic or carcinogenic metabolites produced or activated by the gut microbiota provide a diversity of environmental insults, which play a role in the initial stages of cancer (Tuohy et al., 2005). There is considerable interest in using microbiota-modulating tools such as prebiotics (Burns and Rowland, 2000) or RS (Cassidy et al., 1994) to protect against colonic tumor development or to maintain a good colonic physiology.

To date, several human studies have examined the effect of RS on human colonic function (Table 9.1 ). These intervention studies have evaluated different types of RS, in combinations or alone, at different amounts. Some studies have mimicked human diets in that they have used a range of food-based sources, whereas others have used single manufactured forms.

In most of the studies, RS intake (17 g/d up to 50 g/d) was shown to increase fecal output, to increase fecal SCFA and to decrease fecal pH (Birkett et al., 1996; Cummings et al., 1996; Heijnen et al., 1998; Hylla et al., 1998; Jenkins et al., 1998; Maki et al., 2009; Muir et al., 2004; Phillips et al., 1995; van Munster et al., 1994).

The effect of RS consumption on fecal output is dose-dependent and increasing doses are associated with increasing recoverable starch in stools (Phillips et al., 1995). An increased fecal output is generally seen as being beneficial to gut health as it helps dilute the carcinogenic compounds and reduce thus their time contact with the epithelium.

The reduction of the fecal pH reflects an acidification of the colonic lumen due to the production of SCFA, notably butyrate linked to the fermentation of RS by the microbiota. The fact that RS favours butyrate production has been largely demonstrated in vitro (Brouns et al., 2007; Fassler et al., 2006, 2007) and in animal studies (Cassand et al., 1997; Dongowski et al., 2005; Jacobasch et al., 2006; Le Leu et al., 2005; Perrin et al., 2001; Sakamoto et al., 1996; Silvi et al., 1999; Toden et al., 2005). Butyrate plays a critical role in mucosal physiology and metabolism, by providing 50% of the daily energy requirements of the colonic mucosa, while also being implicated in cellular differentiation and proliferation. It has been seen in vitro that butyrate could be involved in cancer prevention through hyperacetylation of histone proteins in the cell nucleus (Tran et al., 1998) and selectively induce apoptosis in colon cancer cells but not in healthy colonocytes (Ruemmele et al., 2003).

The fermentation of RS induces changes in the microbiota metabolism pattern reducing either the numbers and/or activities of putrefactive bacteria in the colon, leading to a reduction in enzyme activities involved in carcinogenic pathways (e.g., β-glucuronidase) as well as toxic metabolites such as amines, indoles, p-cresol (Birkett et al., 1996; Heijnen and Beynen, 1997; Hylla et al., 1998). The use of protein fermentation products as a source of nitrogen for the microbiota to grow favours a reduction of fecal ammonia and phenols (Birkett et al., 1996; Muir et al., 2004). As protein fermentation products seem likely to be carcinogenic, this might be an additional mechanism by which RS might be protective. A low colonic pH is also associated with a decreased conversion rate of primary to secondary bile acids, which are thought together with other toxic metabolites like ammonia, phenol, amines, etc, to impact fecal water cytoxicity. In this respect, some human studies have shown that RS intake, due to its fermentation in the colon, can help reduce the production of secondary bile acids (Grubben et al., 2001; Hylla et al., 1998; van Munster et al., 1994). Seeing the fact that RS intake helps in reducing the amount of several toxic compounds in the colon lumen via several mechanisms, a reduction of the fecal water cytoxicity is expected and this has been observed in a human study (van Munster et al., 1994) as well as in in vitro studies (Fassler et al., 2007).

One study in humans did consistently not show any effect (Grubben et al., 2001). That study was conducted in subjects with recently removed colonic adenomas, and the RS was administered in capsule form. They also failed to observe any changes in fecal fermentation, which suggests that the capsules did not effectively release the RS.

Generally speaking, similar effects as in humans have been observed in animals for luminal biomarkers of gut health. That is to say that in all animal studies, RS intake has favored butyrate production, increased fecal output, decreased pH, enzyme activity, ammonia, p-cresol and other toxic metabolites (Dongowski et al., 2005; Ferguson et al., 2003; Jacobasch et al., 2006; Maziere et al., 1998; Perrin et al., 2001; Sakamoto et al., 1996; Silvi et al., 1999; Toden et al., 2005; Young et al., 1996).

In rats, challenged with 1,2-dimethylhydrazine or azoxymethane or again in genetically modified mice models (min mice), the effects of RS intake on colorectal neoplasia and on epithelial markers of colorectal cancer have also been investigated (Table 9.2 ). However, depending on the type of animal model, on the nature and the amount of carcinogenic compounds used to induce colorectal cancer in rats, on the feeding time period, the effects of RS intake on aberrant crypt foci (ACF), cell proliferation, DNA damages, tumor incidence are highly variable. It is therefore very difficult to draw any conclusions on RS intake on markers of colorectal-cancers in animal studies. However, whether these particular animal models are relevant to investigate nutritional benefits of RS on gut health is a question mark as they induce drastic effects that do not reflect what occurs in physiological conditions and may wipe out any potential bioactive-associated preventive effects.

Toden et al. (2005) in this respect used a more appropriate rat model, which consisted in feeding rats with a western type diet enriched in proteins. They demonstrated that RS fermentation in the colon is beneficial to health in the sense that it helps counteract the deleterious effect induced by a high protein intake. The high protein diet resulted in a twofold increase in damage to colonocyte DNA compared to a low-protein diet. This was associated with thinning of the colonic mucosa barrier and increased level of p-cresol. The addition of RS (high amylose starch) to the diet increased SCFA and attenuated DNA damages, suggesting protection against genotoxic agent and lesser genotoxocity of the fecal water.

These observations have been corroborated by a recent study that investigated the effects of in vitro fermentation products of in-vitro-digested or in-vivo-digested RS2 and RS3 on Caco-2 cells (Fassler et al., 2007). Compared to control, the cytotoxicity, anti-genotoxicity against hydrogen peroxide (comet assay) and the effect on barrier function measured by trans-epithelial electrical resistance of fermented samples of RS were determined. Batch fermentation of RS resulted in an anti-genotoxic activity ranging from 9–30% decrease in DNA damage for all the samples. Additionally, in vitro batch fermentation of RS caused an improvement in integrity across the intestinal barrier by approximately 22% for all the samples.

16.3 9.3 Other Starch-Derived Fibers with Potential Prebiotic Effects

Many new starch-derived prebiotic candidates are now available (e.g., Nutriose®, Fibersol-2® and PROMITOR™ Soluble Gluco Fiber).

Made from starch, Nutriose® can be described as a resistant dextrin. During the process of dextrinisation, the starch undergoes a degree of hydrolysis followed by repolymerization. It is this repolymerization step that makes starch become indigestible, due to many α 1,6, α 1,2 and α 1,3 linkages. According to the AOAC method 2001–2003, Nutriose® contains 85% fiber (Lefranc-Millot, 2008). The calorific value of Nutriose® has been reported to be 1.7 kcal/g (Lefranc-Millot, 2008) and is claimed to be consistent with clinical determination in healthy young men (Vermorel et al., 2004) and to be in agreement with the consensual calorific value of soluble dietary fibers (Livesey, 1992). Only 15% is enzymatically digested in the small intestine, while 75% reaches the colon where it is slowly fermented and 10% is excreted in fecal matters (van den Heuvel et al., 2005).

Fibersol-2® is a spray-dried powder produced by a pyrolysis and a controlled enzymatic hydrolysis of cornstarch. It was estimated that most of Fibersol-2 escapes digestion in the upper gastrointestinal tract and that 90% reaches the colon, where half of this fraction is fermented by the microbiota (Flickinger et al., 2000).

16.3.1 9.3.1 Introduction to PROMITOR™ Soluble Gluco Fiber (SGF)

16.3.1.1 9.3.1.1 Regulatory Status

PROMITOR™ Soluble Gluco Fiber is a regular food ingredient in the EU and can be labeled as “Soluble Gluco Fiber,” “Glucose Syrup” or “Dried Glucose Syrup.” The name “Soluble Gluco Fiber” is consistent with EU Directive 2000/13/EU as amended on labeling, presentation and advertising of foodstuffs as it indicates both the precise nature of the food in that it is a glucose type of food and distinguishes the fiber content of the glucose syrup. SGF is a non-genetically modified source of dietary fiber, which enables the use of fiber nutrient content claims (contains fiber, source of fiber, high fiber) where relevant regulatory conditions are met.

In the US, PROMITOR™ Soluble Corn Fiber (SGF in EU) is GRAS and can be labeled as “Soluble Corn Fiber,” “Corn Syrup,” or “Corn Syrup Solids.”

16.3.1.2 9.3.1.2 Dietary Fiber Content

SGF is obtained from a partially hydrolyzed starch-made glucose syrup, using an existing production process that yields approximately 70–85% fiber with exceptional color, clarity and flavor (Figure 9.3 ).

Figure 9.3
figure 3_9

Production process of PROMITOR™ Soluble Gluco Fiber.

Full size image

SGF has a typical analysis of approximately 72% total dietary fiber per AOAC method 2001.03. Highly water soluble fibers such as SGF and some resistant maltodextrins contain digestion-resistant material that is not precipitated by the addition of ethanol as prescribed in the 991.43 method.

In three different human trials SGF has demonstrated a consistent glycemic response, approximately 30% that of rapidly digestible carbohydrates (i.e., glucose, maltodextrin) (Kendall et al., 2009). This correlates well to the amount of digestible carbohydrate (∼70% fiber, ∼30% digestible carbohydrate) based on the AOAC 2001.03 method.

16.3.1.3 9.3.1.3 Calorific Value

SGF, has a calorific content of 2 kcal/g (Fastinger et al., 2007). True metabolizable energy content, was determined in an in vivo avian model which utilizes bomb calorimetry of the food prior to consumption by the animal and subsequent bomb calorimetry of the collected waste (urine and feces) after consumption. Additionally, glycemic response studies in humans support this calorific value (Kendall et al., 2007, 2008). Using the calculation (4 kcal/g × 30% digestible), SGF would have 1.2 kcal/g. However, energy yield from fermentation cannot be estimated by the blood glucose response and likely yields a small amount of additional kcals (<1 kcal). In vitro analysis has also shown it to be approximately 25% digestible, 50% fermented and 25% unchanged. Using a fermentation value of 2 kcal/g, as suggested by (Oku and Nakamura, 2002), the following calculations yield a calorific value for Soluble Gluco Fiber of 2 kcal/g.

$$\eqalign{ {\rm{Soluble\ Gluco\ Fiber\ kcal/g}} & = ({\rm{4\ kcal/g}}) \times ({\rm{25\%\ digestible)}} \cr &+ ({\rm{2\ kcal/g}}) \times ({\rm{50\%\ fermentable}}) \cr & + ({\rm{0\ kcal/g}}) \times ({\rm{25\%\ unchanged}}) \cr & = 2\ {\rm{kcal}}/{\rm{g}}}$$

16.3.1.4 9.3.1.4 Digestive Tolerance

The gastrointestinal tolerance has been assessed in human trials and was shown to be well tolerated up to doses as high as 25 g/d. Stewart et al conducted a study in which subjects (n = 20, 10 men, 10 women) consumed 12 g fiber/d SGF for 14 consecutive days (Stewart et al., 2008, 2009). Subjects were asked to report gastrointestinal symptoms (cramping, bloating, stomach noise, flatulence) on a 10 point scale (1 = minimal symptoms, 10 = severe symptoms). SGF was shown to be well tolerated (Kendall et al., 2009; Sanders et al., 2008). In an acute dose-response study (Kendall et al., 2009), tolerance was assessed in 22 healthy volunteers consuming three different doses (5 g, 15 g, 25 g) in acute conditions after an overnight fast. Subjects were asked to report gastrointestinal symptoms (belching, bloating, flatulence, nausea and diarrhoea) on a 100 mm VAS scale at 0, 15, 30, 45, 60, 90 and 120 min after consumption. It was also shown to be well tolerated in these conditions up to 25 g.

16.3.1.5 9.3.1.5 Applications

SGF is an easy-to-formulate fiber which functions like glucose syrup in most systems. It can be used as a partial or total replacement for regular glucose syrup, other sweeteners, or low calorie bulking agents such as polyols, whilst maintaining texture and mouthfeel.

With 2 kcal/g, it also reduces calories when replacing sugar/glucose syrups (4 kcal/g). It has little to no sweetness and so can be used in combination with high intensity sweeteners to balance sweetness to the level of the standard product (in accordance with the EU legislation on sweeteners use in foodstuffs – Directive EU 94/35). As a result of its high solubility and stability in acidic conditions it is suitable for high solids low pH food matrices such as fruit filling. Its low impact on flavor and viscosity – similar to glucose syrup (Figure 9.4 ) – allows to reduce sugar and calories significantly, while adding fiber which does not affect the food product’s organoleptic quality.

Figure 9.4
figure 4_9

Viscosity of PROMITOR™ Soluble Gluco Fiber at 20°C.

Full size image

Main applications include cereals bars and breakfast cereals, cookies and biscuits, snacks, beverages, yogurts, ice creams, desserts, fruit fillings, sauces, confections and processed meats.

16.3.1.5.1 Beverages

SGF is a 100% water soluble, fiber source which does not cause any sedimentation or dramatically increase viscosity as some hydrocolloids do. These negative effects can occur with other ingredients before or after heat treatment, dependent on the force and the type of shear applied. It also does not create cloudiness or turbidity. As a result, replacing sugar, either partially or totally, has no significant impact on the total “dry matter” or viscosity of the beverage, maintaining the original body and mouthfeel and avoiding the creation of a long or slimy structure.

As the energy is 2 kcal/g, it can help to deliver a significant sugar reduction. The sweetness is about 20% of the sweetness of sucrose, so adding a high intensity sweetener will create the desired taste. As a practical and simple example, replacing 4.5 g of sucrose per 100 mL in flavored and sweetened water with SGF will reduce energy load from 17.2 kcal/100 ml to less than 10 kcal/100 mL whilst adding 3 g fiber/100 mL. It can also be added to an existing beverage formulation and will then enhance its mouthfeel whilst simultaneously improving taste.

SGF is a maize starch derivative with a very bland flavor and does not contain any compounds responsible for off flavors sometimes caused during extraction and other processing stages. Its impact on the flavor of energy reduced drinks is not normally noticeable, with a smooth and non-grainy or powdery perception.

During beverage processing, pasteurization or flash pasteurization is often used to obtain microbiological stability. The combination of a heat treatment together with a low pH (as most beverages are) can damage some ingredients leading to breakdown before and during storage. SGF, however is stable throughout all normal processes in the beverage industry, which means there is no need to “overdose” it in formulations.

16.3.1.5.2 Bakery

Cereals bars are mainly composed of glucose syrups which work as a binder to maintain the cohesive structure of the particles of cereal and fruit. It is therefore particularly effective to replace glucose syrups with SGF, which can work as the sole binder thanks to its cohesive properties. Any reduction in sweetness can be compensated by ingredients such as fructose, although in many cases the dried part of the bar provides enough sweetness already. In addition SGF permits to achieve a fiber content of up to 35 g/100 g, corresponding to approximately 10 g/serving.

In moist matrices such as muffins, it decreases the water activity of the system and helps to maintain the stability of the product. In some cases a humectant (e.g., glycerol, sorbitol) can help to maintain the same water activity, ensuring that the product is preserved.

In biscuit-like and soft dough products, the low sweetness and the textural role of sugar, mean that the percentage of SGF incorporated does not generally exceed 50% of the total sugar.

Combining SGF and RS is a simple way to increase fiber content to reach the fiber amount necessary to make a “high fiber” claim, without affecting sensory characteristics of biscuits or muffin-like cakes whose regular flour based equivalents in the market have less than 1.5 g fiber/100 g.

16.3.1.5.3 Dairy

Because SGF behaves in a similar way to glucose syrup, it can effectively replace sugar while adding fiber in dairy products. At the same time it can contribute to a richer texture and a similar mouthfeel in low fat or non fat dairy products compared to full fat references.

Dairy processing typically includes heat treatment and homogenization steps which are synonymous to high shear, high temperature conditions. The stability in these harsh conditions makes it ideal for such dairy products.

Completely soluble at acidic and neutral pH, SGF adds texture and fibers with a smooth non sandy or powdery mouthfeel. For instance, it will compensate for the lack of body of a low fat and/or low sugar dairy dessert mousse, while increasing fiber and enhancing sensory characteristics.

It is also suitable for formulating fermented products due to its survivability during fermentation and can be added at the beginning of the process with no loss of fibers. (Figure 9.5 ).

Figure 9.5
figure 5_9

Stability of PROMITOR™ Soluble Gluco Fiber under Yogurt processing.

Full size image

In fruit preparations, it can replace the sweetener (either partly or totally) without impacting texture, while maintaining the pleasant mouthfeel stemming from its glucose syrup-like viscosity.

As SGF demonstrates high stability at low pH (pH < 4), it is particularly suitable for fruit preparations – where typical pH is around 3.8 to ensure good microbial stability during shelf-life – offering shelf-life stability with no loss of fiber content. Any sweetness loss is usually compensated by a high intensity sweetener such as sucralose.

In desserts and ice creams, SGF will add texture while replacing sweeteners (sugar or glucose syrup) and/or some fat, and will improve the nutritional profile of the end product. For instance, it is possible to achieve 30% fat and 60% sugar reductions in ice creams. In such formulations, it will help to keep a creamy taste and a mouthfeel similar to the full fat and sugar alternative.

16.3.2 9.3.2 Growing and Preliminary Evidence on Prebiotic Properties of New Starch-Derived Fibers

Fifteen grams per day Nutriose® intake over 2 weeks has been reported to decrease fecal pH and to reduce significantly Clostridium perfringens in humans (Lefranc-Millot, 2008).

Fibersol-2® has been shown to increase both bowel regularity, fecal volume and to favor growth of bifidobacteria in 20 healthy volunteers with a fecal frequency lower than three times a week (Satouchi et al., 1993). In this study, it has been observed that consumption of 3.75 g/d of Fibersol-2® for 5 days increased weekly fecal frequency from 2.6 times to 4.0 times and doubled fecal output. Bifidobacteria counts were also significantly increased. The prebiotic properties of Fibersol-2® have also been demonstrated in dogs (Flickinger et al., 2000). Though, a recent study, during which 38 healthy volunteers consumed 7.5 and 15 g Fibersol-2® over 3 weeks showed that resistant maltodextrin supplementation altered (p < 0.05) bacterial populations from baseline to treatment and increased butyrate production, but failed showing a significant effect (p = 0.12) on fecal Bifidobacterium populations during the treatment period (Fastinger et al., 2008).

SGF has been shown to be a potential prebiotic in in vitro studies at TNO (Maathuis et al., 2008). As described previously, the aim of the study was to investigate the effect of five newly developed maize-based fibers on the activity and composition of the microbiota in the colon. The fibers were pre-digested, mono- and di-saccharides were removed, and the residual polymer was used to assess the production of microbial metabolites and changes in composition of the microbiota using a dynamic, validated, in vitro model of the large intestine (TIM-2). Microbial metabolites analysis showed an increase in health-promoting metabolites (short-chain fatty acids) and a reduction in toxic metabolites from protein fermentation compared to the poorly-fermentable control (cellulose). Using microarray technology to compare multiple species and groups of colonic microbiota, it was found to promote the growth of beneficial bacteria such as bifidobacteria (Figure 9.2 ).

Human studies are ongoing to confirm the prebiotic properties of SGF.

16.4 9.4 Conclusion

The prebiotic effects of RS are promising. Existing data suggest that RS would be able to positively impact immune response, modulate inflammation, improve mineral absorption and help maintain a good colic function. Preliminary data on PROMITOR™ Resistant Starch suggest similar properties as those that have been reported so far for RS2 and RS3.

New soluble non-viscous fibers like PROMITOR™ Soluble Gluco Fiber are easy to integrate into new or existing formulations without compromising flavor or texture. Very well tolerated and clean tasting, the new generation of fibers can help develop new health-plus versions of products in a wide range of food categories. In particular their low calorific value (0–2 kcal/g), makes them preferable alternatives to high calorific ingredient (sugar 4 kcal/g, fat 9 kcal/g). The fact that they can compensate for a lack of body and texture in many low calorie – sugar or fat reduced – products means that they are frequently used in the dairy and bakery sectors in particular. They have also shown high process and acid stability allowing manufacturers to formulate and guarantee fiber content (and other associated benefits) throughout the entire shelf life of products.