Raisin fiber

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Hi All, The PDF is available for this article on raisin goodies, mainly the

fiber. Fructans is unique to raisins and comes from the sugar of the

grapes, which have none. Doubling the fiber is a substantial increase.

Cheers, Al.

Camire ME, Dougherty MP.

Raisin dietary fiber composition and in vitro bile Acid binding.

J Agric Food Chem. 2003 Jan 29;51(3):834-7.

PMID: 12537466 [PubMed - in process]

Raisins are dried grapes that are popular shelf-stable

snacks. Three commercially important types

of raisins were studied: sun-dried (natural), artificially

dried (dipped), and sulfur dioxide-treated (golden)

raisins. Dietary fiber composition was analyzed by

ACC method 32-25. Polysaccharides were

hydrolyzed, and the resulting sugars were analyzed

by colorimetric and gas chomatographic methods.

Fructans were measured with a colorimetric kit assay.

Total dietary fiber values agreed with published

values, with pectins and neutral polysaccharides of

mannose and glucose residues predominating.

Dipped raisins had over 8% fructans. No fructans

were found in fresh grapes. Raisin types varied in

their ability to bind bile acids in vitro. Coarsely c

hopped raisins bound more bile than did finely chopped

or whole raisins.

KEYWORDS: Raisin; dietary fiber; fructooligosaccharide; bile acid

INTRODUCTION

Many Americans consume inadequate amounts of dietary

fiber and too few servings of fruits (1). Increased consumption

of fiber and fruit is associated with reduced risks for cardio-vascular

disease and perhaps certain cancers. Most Americans

consume far less than the recommended dietary fiber level of

25-38 g/d. Increased awareness of the health benefits of

common foods such as raisins might encourage some individuals

to increase their consumption of these fruits. Although the exact

role of dietary fiber in prevention of these diseases is a

contentious issue, dietary advice to consume fiber-rich foods

still appears to be valid. Blackwood and others (2) have recently

reviewed the physicochemical properties of dietary fiber and

their relationship to health.

Raisins are dried seedless grapes (Vitis Vinifera

In the United States, raisins are produced only in the state

of California. The U.S. per capita annual consumption of raisins

is approximately 3.26 kg (3). The total dietary fiber content of

raisins is 4.36 g/100 g, according to the USDA Nutrient

Database (4). Increased raisin consumption could provide

consumers with dietary fiber and phytochemicals in a portable,

compact, and shelf-stable form. Three types of raisins are

economically important in the United States. Natural raisins are

sun-dried and account for the majority of raisins produced

and consumed. Dipped raisins are dried artificially and have

a higher moisture content than do natural raisins. Golden

raisins are treated with sulfur dioxide to preserve the light golden

color.

Eastwood and Hamilton (5) demonstrated that fibers could

bind bile acids, thereby causing their excretion in the feces.

Kritchevsky (6) reviewed the topic of in vitro bile binding by

fibers. The continual depletion of bile in this manner is thought

to reduce serum cholesterol levels by diverting the cholesterol

for manufacture of bile acids. Other mechanisms may also play

a role in the ability of a fiber-rich diet to protect against heart

disease. Excessive bile in the colon may increase risks for bowel

cancer; thus, moderation should be considered.

Raisins may offer other cardiovascular benefits. Fructans, also

known as fructooligosaccharides (FOS), in raisins may be

fermented to short-chain fatty acids (7), thereby inhibiting

cholesterol synthesis (8). Both the American Association of

Cereal Chemists (AACC) (9) and the Food and Nutrition Board

(10) definitions include fructans as components of dietary fiber.

Compounds in this group, which includes inulin, are soluble in

aqueous ethanol and thus are not recovered in AACC and

Association of Official Analytical Chemists (AOAC) dietary

fiber methods. Fructans in raisins have previously been reported

only by a commercial laboratory.

Raisins may also contribute to cardiovascular health main-tenance

due to their antioxidant content. Raisins should contain

the same phenolic acid and flavonoid antioxidants as those found

in grapes, but losses occur with drying. Golden raisins retain

the highest amount of hydroxycinnamic acids, approximately

112 ppm (11). Raisins are among the richest fruit sources of

the isoflavones daidzein and genistein, with 1840 íg of these

compounds per kilogram wet weight (12). The objectives of

this study were to characterize the dietary fiber composition of

the commercially important raisin types and to evaluate the in

vitro bile acid binding capacity of raisins.........

RESULTS AND DISCUSSION

Soluble fiber accounted for about 30% of total fiber, but

golden raisin has slightly more soluble fiber (Table 1). Total

fiber values agree with USDA fiber levels. No differences were

found in lignin and pectin (as uronic acids) among the types of

raisins (Table 1). Lignin levels were very low. Insoluble

fractions contained more neutral polysaccharides and uronic

acids than did the soluble fractions. Mannose was the primary

sugar identified by gas chromatography in the soluble fiber

fraction. Insoluble fiber contained more glucose than mannose

residues (Table 2). Glucose was reported as the major sugar in

grape pomace fiber, with approximately equal but low levels

of fucose, arabinose, xylose, mannose, and galactose (18).

Sequential dips of NaOH, citric acid, and potassium met-abisulfite

prior to drying solubilized grape pectins and nonstarch

polysaccharides (19); the sulfur dioxide-treated golden raisins

may have undergone a similar transformation.

Inulin and fructans are not absorbed in the small intestine

(20); thus, these compounds could make important contributions

to colonic health. We found fructans in all types of raisins

(Figure 2). Dipped raisins had more fructans than the other

types of raisins. Fresh grapes had no detectable fructans,

suggesting that processing may influence fructan development

from sugars in the grapes. Adding fructans to total fiber values

nearly doubles the fiber content.

As expected, cholestyramine bound a considerable portion

(>75%) of each of the individual bile acids. The three types of

raisins bound comparable percentages of cholic acid, while

wheat bran bound significantly less (Figure 3). Golden raisins

bound only a trace amount of deoxycholic acid. Binding of

glycholic acid, a conjugated acid, followed the same trend as

for cholic acid (Figure 4). In contrast, golden raisins bound a

significantly higher percentage of taurocholic acid compared

to natural raisins and wheat bran. Our findings for cholestyramine

and bran generally agree with those reported using radiolabeled

bile acids (21).

Coarsely chopped natural raisins bound more bile than did

finely chopped or whole raisins (Figure 5). Bile salt binding

decreased as cereal particle size was reduced (22); therefore,

we expected that larger raisin fragments would have higher

binding. The skin of whole raisins may have been a barrier to

bile acid binding. The amount of raisins used in the assay had

no effect on either the percentage bile bound or the amount

bound per gram. Large standard deviations may have obscured

treatment effects.

These findings suggest that raisins can provide more dietary

fiber in the diet than was previously believed. The carbohydrate

and phenolic composition of raisins may have potential benefits

for cardiovascular health.

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