Chemistry Reference
In-Depth Information
from such materials can be considered logical sources of natural RS that may serve
as the basis of viable prebiotic ingredients.
Resistant starch has been classified principally on a structural basis and most
(with the exception of RS4) could be considered a natural source of RS. The four
classes are simply referred to as RS1, RS2, RS3, and RS4. RS1 is starch trapped in or
by a food material (e.g., whole grains). RS2 is found in native or physically processed
starch granules. High-amylose cornstarches (HACS) including Hi Maize
®
260 are
considered primarily RS2. Resistant starch 3 is formed when starch-containing
foods are cooked and cooled such as in bread, cooked-and-chilled potatoes, or ret-
rograded high-amylose corn. The resistant structure that is formed can be degraded
by microbial fermentation, but is not hydrolyzed by human alimentary enzymes.
Novelose
®
330 starch is a retrograded RS3 generated from annealed, enzyme-treated
HACS (approximately 56 percent RS3). Resistant starch 4 refers to chemically modi-
fied starches using standard starch chemical modification techniques, such as cross-
linking, substitution, or a combination of the various chemistries (Finocchiaro et al.,
2008).
The colon harbors significant populations of butyrate-producing bacteria, such
as
Clostridium, Eubacterium,
and
Fusobacterium
(Pryde et al., 2002). Fermentation
of a commercially available Hi maize RS2 was dominant in the proximal colon, but
degradation of hydrothermally treated HACS was more dominant in the distal colon
(Bird et al., 2007). Fecal output and large bowel digesta mass and concentrations and
pools of individual and total short-chain fatty acids (SCFAs) were higher (by about
two- to threefold; all
P
< 0.05) and digesta pH lower (by about 1 unit, all
P
< 0.001)
in pigs fed either HACS or hydrothermally treated HACS compared to the controls.
In ruminants, SCFAs provide a high proportion of the total energy gained from
the diet. In humans, the overall contribution of SCFAs toward the energy require-
ment is far lower, but they do play an important role in colonic health (Pryde et al.,
2002). Butyrate and propionate are preferred energy sources for the colonic mucosa
as these SCFAs are preferential substrates for the aerobic ATP formation of colono-
cytes. Thus, HACS may play a role in protection against colitis and colorectal cancer
(Jacobasch et al., 1999). Acetate may support these mechanisms by activating capil-
lary blood circulation. High-amylose cornstarch is a suitable substrate for most intes-
tinal bacteria producing glucose and SCFAs. High-amylose cornstarch and other
RSs are considered butyrogenic, as more reduced substrates tend to promote butyrate
formation (Brouns et al., 2002). In a pig study, the intake of HACS increased fecal
butyrate and SCFA concentrations more than did the low HACS diet whether pigs
were supplemented with probiotic bacteria or not (Brown et al., 1997).
Cummings et al. (1996) reported that RS increased stool wet weight by 1.6 g/
day per gram RS fed for potato, 1.7 for banana, 2.5 for wheat, and 2.7 for maize,
but this was significantly less than bran nonstarch polysaccharides (NSP) at 4.9 g/g.
Resistant starch 2 and RS3 are broken down in the human gut, probably in the colon,
although in 26 percent of cases this breakdown was impaired (Cummings et al.,
1996). Resistant starch decreased NSP breakdown and RS2 tended to prolong transit
time. All forms of RS increased fecal total SCFA excretion.
