Dietary fiber from coconut flour: A functional food

Abstract

To determine the effectiveness of dietary fiber present in coconut flour as a functional food, the following studies were conducted: (a) Dietary Fiber Composition and Fermentability of Coconut Flour; (b) The Effect of Coconut Flour on Mineral Availability from Coconut Flour Supplemented Foods; (c) Glycemic Index of Coconut Flour Supplemented Foods in Normal and Diabetic Subjects; and (d) The Cholesterol Lowering Effect of Coconut Flakes in Moderately Raised Cholesterol Levels of Humans. The dietary fiber content of coconut flour was 60.0 ± 1.0 g/100 g sample, 56% insoluble and 4% soluble. Fermentation of coconut flour produced short chain fatty acids with butyrate (1.73 ± 0.07 mmol/g fiber isolate) > acetate (1.40 ± 0.12; (P < 0.05) > propionate (0.47 ± 0.01; P < 0.05). Iron and zinc availability were highest for carrot cake (Fe, 33.3 ± 0.7%; Zn, 12.6 ± 0.1%) supplemented with 20% coconut flour while multigrain loaf supplemented with 10% and macaroons with 25% coconut flour were highest for calcium availability (63.4 ± 8.0% and 38.7 ± 1.1%, respectively). Increasing concentrations of dietary fiber from coconut flour did not affect mineral availability from all test foods. The significantly low glycemic index foods (< 60 mmol × min/l) investigated were: macaroons (45.7 ± 3.0), carrot cake (51.8 ± 3.3) and brownies (60.1 ± 5.4) with 20–25% coconut flour. The test foods containing 15% coconut flour has a glycemic index ranging from 61 to 77 mmol × min/l. Among the test foods, pan de sal (87.2 ± 5.5) and multigrain loaf (85.2 ± 6.8) gave significantly higher glycemic index with 5% and 10% coconut flour. On the other hand, granola bar and cinnamon which contained 5% and 10% coconut flour, respectively gave a glycemic index ranging from 62 to 76 mmol × min/l and did not differ significantly from the test foods containing 15% coconut flour (P < 0.05). A very strong negative correlation (r = − 85, n = 11, P < 0.005) was observed between the glycemic index and dietary fiber content of the test foods supplemented with coconut. There was a significant reduction (%) in serum total and LDL cholesterol for: oat bran flakes, 8.4 ± 1.4 and 8.8 ± 6.7, respectively; 15% coconut flakes, 6.9 ± 1.1 and 11.0 ± 4.0, respectively; and 25% coconut flakes, 10.8 ± 1.3 and 9.2 ± 5.4, respectively (P < 0.05). Serum triglycerides were significantly reduced for all test foods: corn flakes, 14.5 ± 6.3%; oat bran flakes, 22.7 ± 2.9%; 15% coconut flakes, 19.3 ± 5.7%; and 25% coconut flakes, 21.8 ± 6.0% (P < 0.05). Results from the above study can be a basis in the development of coconut flour as a functional food.

Industrial relevance

The functionality of coconut flour in terms of prevention for risk of chronic diseases, e.g. diabetes mellitus, cardiovascular diseases (CVD) and colon cancer, revealed increase production of coconut and coconut flour. The production of coconut flour is very economical because it can be produced in a small or large scale. The raw material is obtained from the by-product (waste) of the coconut milk industry and the process and equipment used in its production is simple and cheap. Coconut flour as a good source of dietary fiber can be added to bakery products, recipes and other food products for good health.

Introduction

The Philippines is the second largest coconut producer in the world and the largest exporter of coconut products. About 85% is processed into copra, 5% into desiccated coconut and 10% is for home use and other manufacturing coconut products. One by-product of the coconut milk industry is the coconut residue taken after extraction of the coconut milk. The coconut residue is made into coconut flour and believed to contain dietary fiber. Dietary fiber has been shown to have important health implications in the prevention for risk of chronic diseases such as cancer, cardiovascular diseases and diabetes mellitus. It comes from the family of carbohydrates, a non-starch polysaccharide, not digested in the small intestine but may be fermented in the colon into short chain fatty acids (SCFA) such as acetate, propionate and butyrate. SCFA contributes 1.5–2.0 kcal/g dietary fiber (Roberfroid, 1997). It enhances water absorption in the colon, thus prevent constipation. Propionate has been shown to inhibit the activity of the enzyme HMG CoA reductase, the limiting enzyme for cholesterol synthesis. Dietary fiber has the ability to bind with bile acids and prevents its re-absorption in the liver thus, inhibit cholesterol synthesis (Dietary Fiber, 1994). Butyrate enhances cell differentiation thus preventing tumor formation in the colon (Jenkins et al., 1982).

Dietary fiber's viscose and fibrous structure can control the release of glucose with time in the blood, thus helping in the proper control and management of diabetes mellitus and obesity (Dietary Fiber, 1994). Glycemic index, a classification of food based on their blood glucose response relative to a starchy food e.g. white bread, or standard glucose solution, has been proposed as a therapeutic principle for diabetes mellitus by slowing carbohydrate absorption (Creutzfeldt, 1983, Jenkins et al., 1987). Low glycemic index food e.g. high dietary fiber food, has been shown to reduce post-prandial blood glucose and insulin responses and improve the overall blood glucose and lipid concentrations in normal subjects (Collier et al., 1988), and patients with diabetes mellitus (Brand et al., 1991, Fontvieille et al., 1988, Wolever et al., 1992, Wolever et al., 1992).

The general objective of this study is to determine the effectiveness of the dietary fiber component of coconut flour, as a functional food, and the specific objectives are as follows: (a) to determine the dietary fiber composition and fermentability characteristics of coconut flour; (b) to determine the effect of coconut flour on mineral availability from coconut flour supplemented products; (c) to determine the glycemic index of coconut flour supplemented products from normal and diabetic subjects; and (d) to determine the cholesterol lowering effect of coconut flakes in moderately raised serum cholesterol levels of humans. The utilization of coconut flour as a functional food will not only solve the problem of chronic diseases now prevailing in almost all countries but also encourage the industry and farmers to produce value-added or healthful products from coconut flour. This will increase the production and promotion of the coconut industry.