The utilisation of high amylose maize starch in animal and human nutrition.

Abstract

42 The utilisation of high amylose maize starch in animal and human nutrition I.L. Brown and K.J. McNaught Starch Australasia Limited, Lane Cove NSW 2066, Australia Summary Starch is the main storage carbohydrate in many higher plants. Due to its ready availability, multiple functionality and relatively low cost, starch and starch derivatives have been widely used in food and industrial applications for many years. However in recent times the versatility and importance of starch based materials have been highlighted as research has endeavoured to learn of its impact on our health. Some starches have been identified as being resistant to digestion and they appear to have important physiological effects in the gastrointestinal tract. coarsely milled grains, cereals, legumes or other starch containing materials where the size or composition of the food particles prevent or delay the action of the digestive enzymes. Secondly there are native starch granules with a coformation which are resistant to digestion. The granules obtained from a number of plant species, including potato, banana, legumes and high amylose (HA) maize, demonstrate this natural resistance. Thirdly, retrograded starch polymers are produced when starch is cooled after gelatinisation (Englyst et al. 1992); the dispersed molecules of arnylose and amylopectin re-associate spontaneously and can form crystallites that resist enzymatic hydrolysis (Sievert and Pomeranz, 1989). Apart from these types of resistant starch it has been suggested that some chemically modified starches also resist enzymatic hydrolysis and that these starches merit separate classification (Brown et al. 1995). Modifications such as esterification and etherification are used commercially to improve the functionality of the starch in conditions associated with food processing, transportation, storage and consumption. The ubiquitous distribution of such modified starches in processed foods suggests that they might be an important dietary source of resistant starch. Small quantities of resistant starch are present in many of the starchy foods that we consume, such as bread, breakfast cereals, biscuits and pasta (Crawford, 1987). In the European Union Dysseler and Hoffem (1994) estimated that the daily intake of resistant starch was between 3.22 g/day to 5.74 g/day. In Australia, Baghurst et al. (1996) estimated that people typically consume approximately 5 to 6 grams of resistant starch per day. It has been suggested that beneficial physiological responses may be obtained by the consumption of higher levels of resistant starch, possibly in the range 15 to 20 g/day (Baghurst et al. 1996). Introduction Starch is quantitatively the most important dietary carbohydrate. In economically developed countries it contributes between 20 and 40 percent of the energy intake (Asp et al. 1986). Research in recent years has observed that starch may be contributing more to our physiological well-being than originally thought. Cassidy et al. (1994) reported that in countries that consumed greater amounts of starch, such as India and China, there was a lower incidence of colorectal cancers than in countries which consume less starch, such as the USA and Australia. No trend was observed between the amount of non-starch polysaccharide consumed in the countries included in the study and the rate of colorectal cancer rates reported. This apparent protective effect related to starch intake may be based on the observation made in the 1980's that starch was the major complex carbohydrate found in the caecal contents of people who were the victims of sudden death (Cummings et al. 1990). Resistant starch A number of mechanisms have been proposed to explain the in vitro indigestibility or malabsorption of starch. Firstly in some food particles the starch is physically inaccessible to digestion. This occurs in whole or Recent Advances in Animal Nut&ion in Australia 1997 University of New England, Armidale NSW 2351, Australia The utilisaton of high amylose starch 43 Small intestine The effects of resistant starch entering the small intestine are related to increasing the bulk of foods and the reduction in the amount of glucose released fiom the starch due to the action of amylases, and the associated effects of reduced insulin response. These factors are believed to be important in the prevention and management of non-insulin dependent diabetes mellitus (NIDDM), which is a disease of high prevalence in western countries (Granner and O'Brien, 1992). The type of dietary starch appears to be able to influence the development of NIDDM. Bymes et al. (1995) found that in rats fed a diet containing waxy maize starch (readily digested starch) insulin resistance was detectable after 12 weeks of feeding whereas in rats consuming a HA maize starch (a granular resistant starch) diet, insulin sensitivity was unimpaired (Table 1). The mechanism is at present unclear. Noakes et al. (1996) found that in a diet where 33% of the carbohydrate was in the form of HA maize starch there was a 17% reduction in the concentration of postprandial plasma insulin relative to a control diet which included the readily digested waxy maize starch. Large bowel HA starch granules have been observed in the caecal digesta of test animals, such as pigs (Topping et al. 1997) and human ileostomates (Muir et al. 1995). These granules exhibited the effects of surface erosion by digestive enzymes (Brown et al. 1994b). The inclusion of HA maize starch in the diet leads to significant quantities of starch being detected entering the caecum Table I Incremental Area Under the Plasma Insulin Curves Following Intravenous Glucose Challenge for AAW Rats.(Byrnes ef al. 1995). Table 2 Concentrations (mg/g of digesta) of starch in the caecal digesta of individual pigs with caecal cannula which were fed either conventional starch or a high amylose maize starch (Topping ef al. 1997). Table 3 Total starch fed to subjects and total starch recovered in the effluent from ileostomates fed low and high resistant starch test meals. (Muir et al. 1995) 44 Brown, /.L.and MclVaught, K.J. in pigs (Table 2) or in the effluent collected from human ileostomates (Table 3). Upon reaching the large bowel the resistant starch acts as a fermentable substrate for the native microflora. A large number of bacterial species, including bljidobacteria and some Zactobacilli, has been found to utilise HA maize starch as a fermentation substrate in vitro (Brown et al. 1994a). A primary product of the fermentation in the bowel is short chain fatty acids (SCFA). In the pig, the consumption of HAmaize starch, when compared to waxy maize starch, led to an increase in the total pool of SCFA (Table 4) including acetate, propionate and butyrate. Support for these findings was provided by the clinical study conducted by Phillips et al. (1995) using the same HA maize starch that was used in the animal trials. It was noted that the consumption of 39g of resistant starch per day over a three week period reduced the faecal pH fiom 6.9 to 6.3 and increased the levels of acetate (by 38% mmoYday) and butyrate (by 100% mmol/da). In a separate experiment with hypertriglyceridemic human subjects, Noakes et al. (1996) observed an increase of 34% in the faecal excretion of butyrate after the consumption of a diet which provided 25% of the carbohydrate as HA maize starch. The amounts of SCFA measured in the faeces may underestimate the actual amounts produced in the large bowel, experimental evidence suggesting that absorption of SCFA may be enhanced at low pH (Sellin et al. 1993). Starch appears to be a desirable substrate for microbial fermentation in the bowel because it encourages some microorganisms to produce large quantities of SCFA. In particular, starch is excellent for stimulating the synthesis of butyrate, which appears to be important in regulating gene expression and the cell growth of colonocytes. Butyrate has also shown antineoplastic characteristics (Dexter et al. 1984). Reduction in colonic pH, for example due to the increased production of SCFA has been shown to decrease the solubility of bile acids that are cytotoxic to colonic cells (Lapre and van der Meer, 1992). The lower pH has also been shown to inhibit the bacterial transformation of primary to secondary bile acids. The experiments using the pig indicated that HA maize starch in the diet could cause a decrease in the concentration of the secondary bile acids, lithocholate and deoxycholate (Table 5). Similar effects have been demonstrated when human subjects were consuming foods containing HA maize starch (Noakes et al. 1996). Phillips et al. (1995) found that the consumption of HA maize starch increased faecal bulk fi-om 13 8 to 197 grams wet weight per day. In addition, the number of bowel movements per day and the ease of defecation increased. This observation has since been supported by the studies of Noakes et al. (1996). Use in foods A novel and practical means of increasing the resistant starch content of foods has been undertaken in Australia. It was found through the examination of many natural sources of resistant starch that a conventionally bred high amylose maize variety developed in Australia Table 4 Concentrations of total and individual short chain fatty acids in the faeces of pigs after consuming waxy and high amylose maize starch for 5 days (Topping et al. 1997). Table 5 Concentration of individual bile acids in gall bladder bile of pigs fed waxy maize, high amylose and a combination of waxy and high amylose maize starches.(Topping et a/.1997). The utilisaton of high amylose starch 45 could provide significant levels of resistant starch, analysed mainly as dietary fibre, and contribute to the functionality of foods without interfering with their taste or texture (Brown, 1993). HA maize starch is now incorporated into bread, breakfast cereals, pasta, noodles, cakes, biscuits, snacks and foods for groups with specialist nutritional requirements and pharmaceutical products. In Australia health authorities have recommended that Australians should consume more dietary fibre and increase their intake of cereal products, such as bread, in an effort to improve public health. During the past few decades the level of dietary fibre consumption has increased for both men and women. However starch consumption has not increased. Some segments of the population, particularly children, have been reluctant to change their food preferences in order to obtain more fibre in their diets. In this regard consumer focus groups found that some people refrain from consuming the high fibre multigrain and wholemeal breads because they preferred white bread. Conventional types of dietary fibre, such as wheat bran, have always coloured the bread, changed its texture by making it more fibrous and chewy or decreased the softness and volume of the loaf HA maize allowed the manufacture of a soft high fibre white bread with excellent keeping qualities. Market surveys show more people consuming white bread (8%) with an increase of 1.4% in the total Australian bread market. This was the first time in many years that bread consumption increased in Australia. A similar white bread containing HA maize has been released in New Zealand with similar effects on bread consumption (Brown et al. 1995). Use with probiotic microrganisms One special application of the ability of HA maize starch . to survive digestion and be fermented in the large bowel was the realisation that it could specifically assist some bacteria that could confer a health benefit. Some of these `probiotic' bacteria, including the bifidobacteria, have been assessed in vitro as being able to ferment HA maize starch (Table 6). In addition the ability of bacteria species and individual strains to utilise the HA maize starch is significantly affected by the type and extent of the chemical treatment of the starch. Table 6 Carbohydrate residue remaining after 48 hours of the in v&o fermentation of native and treated high amylose maize starches.(Brown et al. 1994a). Table 7 Faecal concentrations and daily excretion of bifidobacteria of pigs fed either a waxy or a high amylose maize starch with live Bifidobacferium longurn. 46 Brown, 1. L.and McNaught, K. J. It has been demonstrated (Brown et al. 1997) that HA maize starch, compared with a readily digested waxy maize starch, can be included in the diet for pigs together with bacteria, Bifidobacterium longum, and lead to a significant increase in the level of viable bifidobacteria recovered in the pig faeces (Table 7). The increase in bifidobacteria numbers persisted in the faeces of the test animals even after the addition of the probiotic bacteria to the diet had ceased (Brown et al. 1994a). The use of HA maize starch in foods could allow for the more flexible and reliable use of some probiotic microorganisms and help maintain appropriate levels of beneficial bacteria in the large bowel to assist in improving the health of an individual. The resistant starch could be included in foods such as breakfast cereals, or combined with the beneficial bacteria in cultured products such as yoghurt. The role of starch in the diet is now the focus of both Australian and international research. This research has led to the development of resistant starch products that can be included in a wide variety of foods and feeds to assist in improving the health of both animals and people. Crawford, C. (1987). Survey of resistant starch in processed foods. FMBRA Bulletin 2, 59-64. Cummings, J.H., Banwell, J.G and Segal, I. (1990). The amount and composition of large bowel contents in man. Gastroenterology 98, A408. Dexter, D.L., Lev, R., McKendall, GR., Mitchell, P. and Calabres, P. (1984). Sodium butyrate induced alteration of growth properties and glycogen levels in cultured human colon carcinoma cells. Journal of Histochemistvy 16, 137-49. Dysseler, P. and Hoffem, D. (1994). Estimation of resistant starch intake in Europe. In: Proceedings of the concludingplenary meeting of EURESTA (Eds. N.-G Asp, J.M.M. van Amelsvoort and J.GA.J. Hautvast). EURESTA. pp. 84-6. Englyst, H.N., Kingman, S.M. and Cummings, J.H. (1992). Classification and measurement of nutritionally important starch fractions. European Journal of Clinical Nutrition. Supplement 46 (2), S33-S50. Granner, D. and O'Brien, R. (1992). Molecular physiology and genetics of NIDDM. Diabetes Care. 15,369-395. Lapre, J.A. and van der Meer, R. (1992). Diet induced increased in colonic bile acids stimulates lytic activity of faecal water and proliferation of colonic cells. Carcinogenesis 13,4 l-4. Muir, J.G, Birkett, A., Brown, I., Jones, G and O'Dea., K. (1995). Food processing and maize variety affects amounts of starch escaping digestion in the small intestine. American Journal of Clinical Nutrition 61, 792-9. References Asp, N., Bjorck, I., Holm, J., Nyman, M. and Siljestrom, M. (1986). Enzyme resistant starch fractions and dietary fibre. Scandinavian Journal of Gastroenterology. Supplement 129,29-32. Baghurst, P.A., Baghurst. K.I. and Record. S. J. (1996). Dietary fibre, non-starch polysaccharides and resistant starch-a review. Food Australia. Supplement 48 (3) Sl-S35. Brown, IL., Warhurst, M., Arcot, J. and Playne, M. (1997). Faecal numobers of bifidoacteria are higher in pigs fedHigh amylose starch and faecal bifidobacteria in pgis. First Australian symposium on intestinalflora and health, Melbourne. Noakes, M., Clifton, P.M., Nestel, P. J., Leu, R.L. and McIntosh, G (1996). Effect of high-amylose starch and oat bran on metabolic variables and bowel function in subjects with hypertriglyceridemia. American Journal of Clinical Nutrition 64,944.5 1. Phillips, J., Muir, J.G, Birkett, A., Lu, Z.X., Jones, GP. and O'Dea, K. (1995). Effect of resistant starch on faecal bulk and fermentation-dependent events in humans. American Journal of Clinical Nutrition 61, 10. Sellin, J.H., Desoignie, R and Burlingame, S. (1993). Segmental differences in short chain fatty acids transport in rabbit colon: effect of pH and Na. Journal of Membrane Biology 136,342,7. Brown, I.L., McNaught, K.J. and Moloney, E. (1995). HimaizeTM: new directions in starch technology and nutition. Food Australia 47 (6), 272-275. Brown, I.L., McNaught, K.J., Ganly, R.N., Conway, P.L., Evans, A.J., Topping, D.L. and Wang, X. (1994a). Probiotic compositions. PCT International Patent Application PCT/AU95/006 13. Brown, I.L., Murrie, J., Smit, J., Topping, D. and Muir, J. (1994b). Susceptibility of high amylose maize starch to amylolysis in vitro and in vivo. Proceedings of the RACI Cereal Chemistry Conference. pp. 270-74. Bymes, S., Brand-Miller, J. and Denyer, G (1995). Amylopectin starch promotes the development of insulin resistance in the rat. Journal ofNutrition 125, 143091437. Cassidy, A., Bingham, S.A. and Cummings, J.H. (1994). Starch intake and colorectal cancer risk: an international comparison. British Journal of Cancer 69, 119-125. Sievert, D. and Pomeranz, Y. (1989). Enzyme resistant starch. I. Characterisation and evaluation by enzymatic, thermoanalytical and microscopic. Cereal Chemistry 66 (4), 342-47. Topping, D.L., Gooden, J., Brown, I., Biebrick, D.R., McGrath, L., Trimble, R.P., Choct, M. and Illman, R.J. (1997). A high amylose (amylomaize) starch raises proximal large bowel starch and increases colon length in pigs. Journal of Nutrition (in press).