Boosting the value of insoluble dietary fiber to increase gut fermentability through food processing.

Insoluble dietary fibers are typically known to be poorly fermented in the large intestine. However, their value may be high as evidence shows that important butyrogenic bacteria preferentially utilize insoluble substrates to support their energy needs. The objective of this study was to increase fermentability of an insoluble bran fiber (pearl millet) while keeping it mostly insoluble to promote bacteria in the community that rely on fermentable insoluble dietary fibers. Following pretests with different processing methods, a combination of microwave and enzymatic treatments were applied to isolated pearl millet fiber to increase its accessibility of gut bacteria. In vitro human fecal fermentation was conducted and analyses were made for short chain fatty acids and microbiota changes. Combined microwave and enzymatic processing increased the amount of insoluble fiber fermented in vitro from 36 to 59% of total dietary fiber, with a minor increase in soluble fiber (8%). Microwave/enzymatic processing doubled butyrate production and almost tripled acetate production at 6 h fermentation compared to the native millet fiber. 16S rRNA gene sequencing showed that the processing promoted a significant increase in Firmicutes/Bacteroidetes ratio compared to the native fiber with relative abundance increases in Blautia and Copprococcus genera and a decrease in Bacteroidetes. Overall, these data show that processing techniques can be used to increase the value of insoluble fiber, presumably by increasing accessibility of the fiber to degrading bacteria, and to support Firmicutes that preferentially compete on insoluble fibers.

Physicochemical properties and starch digestibility of whole grain sorghums, millet, quinoa and amaranth flours, as affected by starch and non-starch constituents.

Minor grains such as sorghum, millet, quinoa and amaranth can be alternatives to wheat and corn as ingredients for whole grain and gluten-free products. In this study, influences of starch structures and other grain constituents on physicochemical properties and starch digestibility of whole flours made from these grains were investigated. Starches were classified into two groups according to their amylopectin branch chain-length: (i) quinoa, amaranth, wheat (shorter chains); and (ii) sorghum, millet, corn (longer chains). Such amylopectin features and amylose content contributed to the differences in thermal and pasting properties as well as starch digestibility of the flours. Non-starch constituents had additional impacts; proteins delayed starch gelatinization and pasting, especially in sorghum flours, and high levels of soluble fibre retarded starch retrogradation in wheat, quinoa and amaranth flours. Enzymatic hydrolysis of starch was restricted by the presence of associated protein matrix and enzyme inhibitors, but accelerated by endogenous amylolytic enzymes.

Whole grain in manufactured foods: Current use, challenges and the way forward.

Some countries now incorporate recommendations for increased consumption of whole grain (WG) into local dietary guidelines. Cereal and pseudo-cereal grains are good sources of complex carbohydrates, dietary fiber, proteins, phytochemicals, vitamins and minerals. However, research shows that the large majority of consumers are still falling short of WG consumption goals. To address this, we are actively involved in research to help increase the WG content of processed foods without compromising on taste and texture. In order to ensure consumer trust, the advancement of process technologies in incorporating WG to produce tasty food has to go hand in hand with well designed clinical trials that confirm the health benefits resulting from diets rich in WG.

Dosage effect of high-amylose modifier gene(s) on the starch structure of maize amylose-extender mutant.

The objective of this study was to investigate how dosages of high-amylose modifier (HAM) gene(s) affected the structure of maize amylose extender (ae) mutant starch. GEMS-0067 (G), a homozygous mutant of ae and the HAM gene(s), and H99ae (H), an ae single mutant, were self-pollinated or inter-crossed to produce maize endosperms of G/G, G/H, H/G, and H/H with 3, 2, 1, and 0 doses of HAM gene(s), respectively. Endosperm starch was fractionated into amylopectin, amylose, and intermediate component (IC) of large and small molecular weights using 1-butanol precipitation of amylose followed by gel-permeation chromatography. Increases in the dosage of HAM gene(s) from 0 to 3 decreased the amylopectin content. The HAM-gene dosage significantly changed the branch chain-length of small-molecular-weight IC, but had little effect on the branch chain-length distributions of amylopectin and large-molecular-weight IC and the molecular structure of amylose.

Quinoa (Chenopodium quinoa W.) and amaranth (Amaranthus caudatus L.) provide dietary fibres high in pectic substances and xyloglucans.

Dietary fibre of quinoa and amaranth was analysed for its insoluble and soluble fibre content, composition, and structure. Total dietary fibre content was 10% for quinoa and 11% for amaranth. For both pseudocereals, 78% of its dietary fibre was insoluble. Insoluble fibre (IDF) from quinoa and amaranth was mainly composed of galacturonic acid, arabinose, galactose, xylose and glucose. Linkage analysis indicated that IDF was composed of homogalacturonans and rhamnogalacturonan-I with arabinan side-chains (∼55-60%), as well as highly branched xyloglucans (∼30%) and cellulose. For both pseudocereals, 22% of total dietary fibre was soluble; a higher proportion than that found in wheat and maize (∼15%). The soluble fibre (SDF) was composed of glucose, galacturonic acid and arabinose; for amaranth, xylose was also a major constituent. Xyloglucans made up ∼40-60% of the SDF and arabinose-rich pectic polysaccharides represented ∼34-55%.

Selection of stress-tolerant yeasts for simultaneous saccharification and fermentation (SSF) of very high gravity (VHG) potato mash to ethanol.

Highly concentrated bioethanol production requires less volume in fermentation tanks and conserves distillery energy. We screened osmotolerant yeasts from a collection of 1699 yeast strains at our institute and found that three strains, NFRI3062, NFRI3213, and NFRI3225, were candidates for use in bioethanol production. All of these strains belonged to Saccharomyces cerevisiae. NFRI3062 produced 15.0% (w/v) of ethanol from YPD medium containing 35% glucose cultivated at 30 degrees C for 60 h, while S. cerevisiae NBRC0224, which has previously been reported suitable for ethanol production, only produced 13.0% (w/v). The thermotolerances of NFRI3213 and NFRI3225 were also superior to those of NBRC0224 and NFRI3062. We also demonstrated the simultaneous saccharification and fermentation (SSF) of very high gravity (VHG) potato mash and sweet-potato mash. NFRI3225 produced ethanol from potato mash at the fastest rate and in the highest volume (13.7% (w/v)) among the tested strains. The maximum productivity and ethanol yields were 9.1g/L/h and 92.3%, respectively. Although the potato mash was not sterilized, bacterial contamination was not observed. This may have been due to the growth inhibition of bacteria by the rapid glucose consumption and ethanol production of NFRI3225 during the VHG-SSF process.

Bioconversion of L-arabinose and other carbohydrates from plant cell walls to alpha-glucan by a soil bacterium, Sporosarcina sp. N52.

A Gram-positive bacterium, N52, that produces intracellular glucan from l-arabinose, was isolated from soil and identified as Sporosarcina sp. according to rRNA gene sequence analysis and physiological/biochemical characterizations. Glucan production by N52 increased significantly in the exponential phase of aerobic liquid culture and was maintained at the highest level during the stationary phase, reaching 37.0% of the cell dry weight. The glucan was also produced from other tested sugars originating from plant cell walls and was composed exclusively of alpha-1,4- and alpha-1,6-glucosidic linkages. When distillery waste was treated with N52 for 72 h, the total organic carbon (TOC), chemical oxygen demand and biochemical oxygen demand were reduced by 42.6%, 45.9% and 82.5%, respectively. Bacterial cells accumulated 31.9% of glucan per cell dry weight, fixing 16.0% of the TOC in the soluble fraction. Thus, this strain could provide us with a new process for waste management, including the bioconversion of organic materials to the valuable byproduct, alpha-glucan.

Variations in starch physicochemical properties from a generation-means analysis study using amylomaize V and VII parents.

GEMS-0067 (PI 643420) maize line is a homozygous mutant of the recessive amylose-extender (ae) allele and an unknown number of high-amylose modifier (HAM) gene(s). GEMS-0067 produces starch with a approximately 25% higher resistant-starch (RS) content than maize ae single-mutant starches. The objective of this study was to understand how the HAM gene(s) affected the RS content and other properties of ae-background starches. Nine maize samples, including G/G, G/F1, G/H, F1/G, F1/F1, F1/H, H/G, H/F1, and H/H with HAM gene-dosages of 100, 83.3, 66.7, 66.7, 50, 33.3, 33.3, 16.7, and 0%, respectively, were produced from self- and intercrosses of GEMS-0067 (G), H99ae (H), and GEMS-0067xH99ae (F1) in a generation-means analysis (GMA) study. RS contents of examined starches were 35.0, 29.5, 28.1, 32.0, 28.2, 29.4, 12.9, 18.4, and 15.7%, respectively, which were significantly correlated with HAM gene-dosage (r = 0.81, p < 0.01). Amylose content, number of elongated starch granules, and conclusion gelatinization temperature increased with the increase in HAM gene-dosage. X-ray diffraction study showed that the relative crystallinity (%) of starch granules decreased with the increase in HAM gene-dosage. The results suggested that the HAM gene-dosage was responsible for changes in starch molecular structure and organization of starch granules and, in turn, the RS formation in the maize ae mutant starch.

Efficient recovery of glucose and fructose via enzymatic saccharification of rice straw with soft carbohydrates.

Soft carbohydrates, defined as readily-recoverable carbohydrates via mere extraction from the biomass or brief enzymatic saccharification, were found in significant amounts in rice straw as forms of free glucose, free fructose, sucrose, starch, and beta-1,3-1,4-glucan. In this study, we investigated their amounts in rice straw (defined as culm and leaf sheath), and developed an easy method for glucose and fructose recovery from them with heat-pretreatment and subsequent 4-h enzymatic saccharification with an enzyme cocktail of cellulase and amyloglucosidase. The recovery of glucose and fructose exhibited good correlation with the amounts of soft carbohydrates. The maximum yields of glucose and fructose in the rice straw per dry weight at the heading stage and the mature stage were 43.5% in cv. Habataki and 34.1% in cv. Leafstar. Thus, rice straw with soft carbohydrates can be regarded as a novel feedstock for economically feasible production of readily-fermentable glucose and fructose for bioethanol.

Kernel composition, starch structure, and enzyme digestibility of opaque-2 maize and quality protein maize.

Objectives of this study were to understand how opaque-2 (o2) mutation and quality protein maize (QPM) affect maize kernel composition and starch structure, property, and enzyme digestibility. Kernels of o2 maize contained less protein (9.6-12.5%) than those of the wild-type (WT) counterparts (12.7-13.3%). Kernels of a severe o2 mutant B46o2 also contained less starch (66.9%) than those of B46wt (73.0%). B46o2 and QPM starches contained less amylose (28.0 and 26.0%, respectively) than others (31.9-33.7%). The B46o2 starch also consisted of amylopectin with the fewest branch chains of DP 13-24. Thus, the B46o2 starch was the most susceptible to porcine pancreatic alpha-amylase (PPA) hydrolysis. Starches of the dry-ground o2 maize and QPM were hydrolyzed faster than that of the dry-ground WT maize, resulting from the reduced protein content of the o2-maize kernels and the reduced amylose content of the B46o2 and QPM starch. Starch in the dry-ground maize sample was hydrolyzed faster by PPA (85-91%) than was the isolated starch (62-71%), which could be attributed to the presence of mechanically damaged starch granules and endogenous amylases in the dry-ground maize samples. These results showed that o2 maize and QPM had highly digestible starch and could be desirable for feed and ethanol production.

Structure of lintnerized starch is related to X-ray diffraction pattern and susceptibility to acid and enzyme hydrolysis of starch granules.

Acid-resistant residues (lintnerized starches, Ls) were prepared from starches showing A-, B- and C- X-ray diffraction patterns. Ls retained the same X-ray crystalline type as their native counterparts with an improvement in diffraction intensity. Fluorophore-assisted capillary electrophoresis (FACE) study indicated that structural characteristics of Ls were associated with X-ray diffraction patterns. Double helices originated from linear chains with an approximate average degree of polymerisation (DP) 14, 16, and 15 would span the entire length of crystalline lamellae of A-, B-, and C-type starches, respectively. The proportion of singly branched materials (SB) with DP 25 protected in Ls was higher for A-type Ls (10-17%) than for B-type Ls (4-6%) and C-type Ls (8%). The structures of SB were similar in which branched chain (DP 13-15) was longer than main chain (DP 10-12). The structural characteristics of Ls are discussed in relation to acid and enzymatic degradations of starch granules.