Steve W. Cui

Slowly Digestible Starch—A Review

The link between carbohydrate intake and health is becoming increasingly important for consumers, particularly in the areas of glycemic index (GI) and extended energy-releasing starches. From a physiological point of view, slowly digestible starch (SDS) delivers a slow and sustained release of blood glucose along with the benefits resulting from low glycemic and insulinemic response. SDS has been implicated in several health problems, including diabetes, obesity, and cardiovascular diseases (metabolic syndromes). It may also have commercial potential as a novel functional ingredient in a variety of fields, such as nutrition, medicine, and agriculture. The present review assesses this form of digestion by analyzing methods to prepare and evaluate SDS, and factors affecting its transformation, its health benefits, and its applications.

Interaction of wheat and rice starches with yellow mustard mucilage

The effect of yellow mustard mucilage (YMM) on gelatinization and retrogradation of wheat and rice starches were studied. Considerable interactions were observed between YMM and wheat and rice starches which were accompanied by a marked increase in viscosity. DSC studies showed that the presence of YMM did not affect peak gelatinization temperature (Tp) of wheat and rice starches, but slightly increased melting enthalpy (ΔH) and the phase transition temperature range (Tc−T0). Addition of YMM markedly changed wheat and rice starch gel textures by increasing hardness, adhesiveness, chewiness and springiness. The addition of YMM–locust bean gum (LBG) mixture (9:1) similarly increased the viscosity of wheat and rice starches but decreased gel hardness. The swelling power as well as solubilized starch and amylose were decreased for both starches in the presence of YMM. Syneresis in wheat and rice starches was also decreased by the presence of YMM.

Characterization of the Surface-Active Components of Sugar Beet Pectin and the Hydrodynamic Thickness of the Adsorbed Pectin Layer

The fraction of sugar beet pectin (SBP) adsorbed onto limonene oil droplets during emulsification has been isolated, and its chemical and physicochemical characteristics have been determined. While the SBP sample itself was found to contain 2.67 and 1.06% protein and ferulic acid, respectively, the adsorbed fraction contained 11.10% protein and 2.16% ferulic acid. The adsorbed fraction was also found to have a higher degree of acetylation, notably at the C2 position on the galacturonic acid residues, and was also found to contain a higher proportion of neutral sugars, which are present in the ramified side chains of the pectin molecules. The thickness of the layer of SBP adsorbed onto polystyrene latex particles was studied by dynamic light scattering and was found to increase with increasing surface coverage. It was found to have a value of approximately 140 nm at plateau coverage, which closely corresponded to the hydrodynamic diameter of the pectin chains. The adsorbed layer thickness was found to be sensitive to pH and the presence of electrolyte. The thickness at a surface coverage of approximately 20 mg/m(2) in the absence of electrolyte at pH approximately 4 was 107 nm and at pH 8.8 was 70 nm, while at pH approximately 4 in the presence of 10 mM NaCl the thickness was found to be 70 nm. It was concluded that the SBP molecules form multilayers at the surface due to electrostatic interaction between the positively charged protein moieties and the galacturonic acid residues. The removal of calcium from the SBP had no effect on the adsorbed layer thickness; hence, multilayer formation due to calcium ion cross-linking was considered unlikely.

Effects of oat β-glucan on endurance exercise and its anti-fatigue properties in trained rats.

Oat β-glucan was purified from oat bran and its effects on running performance and related biochemical parameters were investigated. Four-week-old male Sparsgue-Dawley rats, fed with/without oat β-glucan (312.5 mg kg(-1) d(-1)) for 7 weeks, were subjected to run on a treadmill system to make them exhausted. All rats were immediately sacrificed after prolonged exercise, and the major metabolic substrates were measured in serum and liver. The results showed feeding dietary oat β-glucan to rats could significantly reduce the body weight and increase the maximum running time compared with normal control (P<0.05). Furthermore, dietary oat β-glucan decreased the levels of blood urea nitrogen, lactate acid, and creatine kinase activity in serum, and increased the levels of non-esterified fatty acids, lactic dehydrogenase activity in serum, and the content of liver glycogen. Therefore, the present study demonstrated that dietary oat β-glucan can enhance the endurance capacity of rats while facilitating their recovery from fatigue.

Gelling property of soy protein–gum mixtures

Abstract Gelling properties of soy protein–gum mixtures were determined by small deformation oscillation measurement and the experimental data were analyzed with blending laws of polymers. Gel strength of soy protein–carrageenan mixture was found to follow either upper or lower bounds depending on the concentration of the constituents, suggesting the occurring of phase shift. G ′ of soy protein–xanthan mixed gel always followed the upper bound, indicating that soy protein was the continuous phase regardless variations of the gum concentration. Combination of soy protein with propylene glycol alginate (PGA) produced a mixed gel with high gel strength and stayed above the upper bound at all gum concentrations examined. Covalent bonds between PGA and soy protein was suggested to contribute to the rigidity. Storage modulus of the mixture of soy protein–locust bean gum (LBG) was below the lower bound at low gum concentrations due to the limited demixing process of LBG. G ′ values of the mixture of soy protein and LBG–xanthan followed the lower bound but approached upper bound on reducing protein concentration, suggesting that the presence of soy protein might inhibit LBG–xanthan mixture from forming continuous networks.

Fractionation, partial characterization and bioactivity of water-soluble polysaccharides and polysaccharide–protein complexes from Pleurotus geesteranus

Fractionation and purification of mushroom polysaccharides is a critical process for mushroom clinical application. After a hot-water treatment, the crude Pleurotus geesteranus (PG) was further fractionated into four fractions (PG-1, -2, -3, -4) using gradient precipitation with water and ammonia sulphate. By controlling the initial polymer concentration and ratio of solvents, this process produced PG fractions with high chemical uniformity and narrow Mw distribution without free proteins. Structurally, PG-1 and PG-2 are pure homopolysaccharide mainly composed of glucose; and PG-3 and PG-4 are heteropolysaccharide-protein complexes. PG-2, a high M(w) fraction mainly composed of glucose presented significant cytotoxicity at the concentration of 200 and 100 μg/ml to human breast cancer cells. Here, we report a new mushroom polysaccharides extraction and fractionation method, with which we produced four fractions of PG with PG-2 appearing effective anti-tumour activity.

Physicochemical characterization of a high molecular weight bioactive β-d-glucan from the fruiting bodies of Ganoderma lucidum

A purified polysaccharide coded as GLP20 was obtained by precipitating a hot-water extract from Ganoderma lucidum fruiting bodies with 20% (V/V) ethanol. Its total carbohydrate content was 95.9%. Structural analysis showed that GLP20 was a β-(1→3)-linked d-glucan with a (1→6)-β-d-glucopyranosyl side-branching unit on every third residue. Cell culture study revealed that GLP20 can significantly increase NO production of RAW264.7 macrophages. The analysis of light scattering and high performance size exclusion chromatography (HPSEC) showed that the molecular weight and polydispersity of GLP20 was 3.75 × 10(6)Da and 1.36, respectively. GLP20 had a rigid chain conformation in aqueous solution. A conformation transition occurred in the alkaline solution with NaOH concentration larger than 0.15M. The transition from ordered structure to single chain happened when GLP20 was heated above 135°C in water solution and was irreversible as demonstrated by differential scanning calorimetry (DSC). GLP20 existed as random coils in DMSO.

Study on Dendrobium officinale O-acetyl-glucomannan (Dendronan®): part II. Fine structures of O-acetylated residues.

Main objective of this study was to investigate the detailed structural information about O-acetylated sugar residues in Dendronan(®). A water solution (2%, w/w) of Dendronan(®) was treated with endo-β-mannanase to produce oligosaccharides rich in O-acetylated sugar residues. The oligosaccharides were partly recovered by ethanol precipitation (70%, w/w). The recovered sample (designated Hydrolyzed Dendrobium officinale Polysaccharide, HDOP) had a yield of 24.7% based on the dry weight of Dendronan(®) and was highly O-acetylated. A D2O solution of HDOP (6%, w/w) generated strong signals in (1)H, (13)C, 2D (1)H-(1)H COSY, 2D (1)H-(1)H TOCSY, 2D (1)H-(1)H NOESY, 2D (1)H-(13)C HMQC, and 2D (1)H-(13)C HMBC NMR spectra. Results of NMR analyses showed that the majority of O-acetylated mannoses were mono-substituted with acetyl groups at O-2 or O-3 position. There were small amounts of mannose residues with di-O-acetyl substitution at both O-2 and O-3 positions. Minor levels of mannoses with 6-O-acetyl, 2,6-di-O-acetyl, and 3,6-di-O-acetyl substitutions were also identified. Much information about sugar residue sequence was extracted from 2D (1)H-(13)C HMBC and 2D (1)H-(1)H NOESY spectra. (1)J(C-H) coupling constants of major sugar residues were obtained. Evidences for the existence of branches or O-acetylated glucoses in HDOP were not found. The major structure of Dendronan(®) is shown as follows: [Formula: see text] M: β-D-mannopyranose; G: β-D-glucopyranose; a: O-acetyl group.

Milk concentration of the mammalian lignan enterolactone, milk production, milk fatty acid profile, and digestibility in dairy cows fed diets containing whole flaxseed or flaxseed meal.

A total of 24 lactating Holstein cows averaging 620 (SE=29) kg of body weight were allotted at week 17 of lactation to eight groups of three cows blocked for similar days in milk to determine the effects of feeding two sources of the plant lignan precursor secoisolariciresinol diglucoside, whole flaxseed and flaxseed meal, on concentrations of the mammalian lignans (enterodiol and enterolactone) in milk. Feed intake, digestion, milk production and milk composition were also determined to compare the use of whole flaxseed and flaxseed meal for milk production. Cows within each block were assigned to one of the three isonitrogenous and isoenergetic total mixed diets: no flaxseed product; 10% flaxseed meal; or 10% whole flaxseed in the dry matter. The experiment was carried out from week 17 to week 21 of lactation and diets were fed at ad-libitum intake. The mammalian lignan, enterodiol, was not detected in the milk of cows. Cows fed whole flaxseed and flaxseed meal had greater concentrations of enterolactone in milk than those fed the control diet. Feed intake, milk production and milk composition were also similar for all diets, indicating that both flaxseed meal and whole flaxseed are suitable feed ingredients for milk production of cows in mid lactation. The results provide new information on the conversion of plant secoisolariciresinol diglucoside from two flaxseed products into mammalian lignans in dairy cows.

Structural characterization of a low-molecular-weight heteropolysaccharide (glucomannan) isolated from Artemisia sphaerocephala Krasch.

Using 60% (w/v) ammonium sulfate precipitation, a heteropolysaccharide (designated 60S), with relatively low molecular weight (38.7kDa), was isolated from the seeds of Artemisiasphaerocephala Krasch. The structural properties of 60S were elucidated by partial acid hydrolysis, methylation analysis, 1D and 2D NMR spectroscopy, and MALDI-TOF-MS. The results of the partial acid hydrolysis and methylation analysis indicated that the main chain of 60S consisted of (1→4)-linked d-Manp and (1→4)-linked d-Glcp in a molar ratio of 1:1.3. Over half of the glucosyl residues in the main chain were branched at the O-6 position. The terminal sugar residues were mainly composed of T-Araf, T-Arap, T-Galp, T-GlcpA, and T-Glcp. Besides, 3-Araf and 2-Galp were also observed in comparable amounts. Based on all the aforementioned results and the data obtained by 1D and 2D NMR spectroscopy as well as MALDI-TOF-MS, a structure of 60S is proposed as follows: R could be one or some of -(3-α-Araf)(n)-(A), T-α-Galp(B), T-α-Glcp(C), T-Araf(H) or T-Arap.