Two-step modification of pullulanase and transglucosidase: A novel way to improve the gel strength and reduce the digestibility of rice starch.

The multiscale structure, gel strength and digestibility of rice starch modified by the two-step modification of pullulanase (PUL) pretreatment and transglucosidase (TG) treatment for 6, 12, 18 and 24 h were investigated. The debranching hydrolysis of PUL produced some linear chains, which rearranged to form stable crystalline structures, reducing the digestible starch content, but weakening the gel strength. TG treatment connected some short chains to longer linear chains via α-1,6-glycosidic bonds, generating the structures of linear chain with fewer branches. The short branches promoted the interaction between starch molecules to form a more compact three-dimensional gel network structure, showing higher hardness and springiness. Moreover, these chains could form more stable crystals, reducing the digestible starch content, and the increase of branching degree inhibited digestive enzyme hydrolysis, reducing the digestion rate. The multiscale structure of starch tended to stabilize after TG treatment for 18 h, which could form a gel with stronger strength and lower digestibility than native starch gel. Therefore, the two-step modification of PUL and TG was an effective way to change the structure of rice starch to improve the gel strength and reduce the digestibility.

Structural, physicochemical and digestive properties of rice starch modified by preheating and pullulanase treatments.

The structural, physicochemical and digestive properties of rice starch modified by the combination of different temperature (60, 70, 80, 90 and 100 °C) preheating and pullulanase (PUL60, PUL70, PUL80, PUL90 and PUL100) treatments were investigated. The PUL60 treatment mainly modified the surface layer of starch granules, which increased the amylose content and damaged some ordered structures, resulting in slight decreases of gel strength and estimated glycemic index (eGI). With the increase of preheating temperature, PUL could act on more enzymatic sites to release a large amount of linear chains, reduce the ordered degree, and transform the A-type crystalline structure into B-type. The low molecule interaction strength between linear chains weakened the gel network structure, and some stable crystal structures formed by longer chains resisted the enzyme digestion. The gel strength and eGI value of PUL70 starch decreased significantly, and the properties of PUL80-100 starches tended to be stable, showing a further significant decrease of gel strength and a slight reduction of eGI value. Therefore, the preheating treatments at 60, 70 and 80 °C were suitable for the PUL modification of rice starch to obtain strong, medium and weak gel strength respectively, and the digestibility decreased with increasing preheating temperature.

Understanding the texture and digestibility attributes of rice noodles supplemented with common vetch starch.

The effects of common vetch starch (CVS) substitution on rice noodle quality were investigated, aiming to improve their texture and reduce starch digestibility. The CVS had larger granule sizes, higher amylose content and more long branch chains compared with rice starch (RS). When the CVS substitution level was 20 %, the rice noodles had the best texture quality, as the mixtures with more total starch and amylose could form denser gel structures. Moreover, the starch chains were easier to rearrange to form double helix ordered structures, resulting in a slower digestion rate. With the further increase of CVS, the noodle structure weakened and the starch digestion rate increased. This was due to the formation of looser gel structures and less ordered structures as RS granules could be easily separated into different parts by large amount of CVS with larger granule sizes, and RS with more short chains tended to be cross-linked with RS during retrogradation. With increasing CVS substitution level, the estimated glycemic index (eGI) of rice noodles decreased and then tended to be stable. Therefore, appropriate CVS substitution could improve the texture quality of rice noodles and reduce the eGI value, and the best substitution level was 20 %.

Effects of damaged starch on glutinous rice flour properties and sweet dumpling qualities.

This study focused on exploring the effects of damaged starch on glutinous rice flour properties and sweet dumpling qualities. Glutinous rice flours with different damaged starch contents (2-8%) and the same particle size were prepared through sifting and blending of semidry-milled and dry-milled rice flour. The increase of damaged starch content led to an increase in elastic modulus (G'), viscous modulus (G″) and agglomeration of starch granules, and a decrease in peak viscosity, breakdown value and enthalpy change (ΔH). Among all the samples, the rice flour batters with damaged starch content 3% and 4% were more stable and structured, and rice flours with damaged starch content 2% and 3% showed better pasting properties. As for the sweet dumpling qualities, compact structure, weak water mobility, less water loss, slight cracking and desirable cooking and texture properties were observed in the sweet dumplings made from rice flour with damaged starch content of less than 5%. All the results demonstrated that glutinous rice flour with damaged starch content of less than 5% had good flour properties and was suitable for the production of sweet dumplings.

Dietary Proteins Alter Fermentation Characteristics of Human Gut Microbiota In Vitro.

The objective of this study was to evaluate the fermentation characteristics of proteins from diverse sources by human gut microbiota. Cereal proteins (rice and oat), red meat proteins (pork and beef), chicken protein and casein were selected as the substrates for simulated gastrointestinal digestion (SGID), and human faecal samples were collected from healthy donors as the inoculum of fermentation. In this study, we further analyzed the correlations of amino acids (AA) compositions, fermentation productions and gut microbiota. As the results, the animal protein groups had higher degree of hydrolysis (DH) after digestion and higher levels of ammonia nitrogen (NH3-N) after fermentation than cereal proteins. The pH value of fermentation liquid declined as proteins were added during fermentation. Cereal protein groups promoted the gut microbiota to produce more short chain fatty acids (SCFAs) with the high proportion of acetate, propionate and butyrate by lowering the pH than red meat proteins. The abundance of Firmicutes at phylum level in cereal protein groups was lower than red meat proteins after fermentation. The cereal protein groups enhanced the growth of Bacteroides spp. and Bifidobacterium spp. while red meat proteins stimulated the growth of Peptoclostridium spp.. Taken together, our research implies that cereal proteins have better fermentation characters than red meat proteins.

Effects of Lactobacillus plantarum Inoculum on the Fermentation Rate and Rice Noodle Quality.

To accelerate the fermentation rate and reduce the adverse effects of undesirable microorganism contamination on rice noodle quality, the pure inoculum fermentation method was used to produce fermented rice noodles. The results indicated that the pure inoculum fermented rice slurry required 10 h to reach a stable pH value. While, the pH value of the natural, pure and natural inoculum fermented rice slurries required 54, 18 and 20 h to stabilize, respectively. Free amino acids and lactic acid concentrations of the pure inoculum fermented rice slurry were higher than those of the natural and natural inoculum fermented rice slurries. The pure inoculum fermentation modified the proximate composition and lowered the pasting viscosities of the rice flour. The texture, cooking and eating qualities of the pure inoculum fermented rice noodles were similar to those of the natural fermented ones. In addition, the pure inoculum fermented rice noodles had higher relative contents of aldehydes than other fermented rice noodles and thus had a better flavor. Therefore, pure inoculum fermentation accelerated the fermentation rate and improved the rice noodle flavor while maintaining the texture, cooking and eating qualities of the rice noodles.

Effects of Lactobacillus combined with semidry flour milling on the quality and flavor of fermented rice noodles.

To shorten the fermentation time and reduce the contamination with heterozygous bacteria during the process of fermenting rice noodles, pure bacterial fermentation combined with semidry flour milling was used to produce fermented rice noodles. The changes in the pH value and microbial community diversity of the rice slurries, the physicochemical properties of the rice flours, and the texture, cooking qualities, sensory qualities and volatile components of the rice noodles prepared with different fermentative methods were investigated. The results showed that the pure bacterial fermentation required 18 h to reach a stable pH value, while the natural fermentation required 54 h. In addition, compared with naturally fermented rice slurry, the bacterial community diversity of the pure bacterial fermented rice slurry was significantly lower, while the fungal community diversity did not differ significantly. Significant differences were observed in the content of the damaged starch, amylose and protein between semidry milled pure bacterial fermented (SP) and wet milled naturally fermented (WN) rice flours (P < .05), while these differences had no significant effect on the texture and cooking qualities of the SP and WN rice noodles (P > .05). In addition, the types of volatile components of the SP noodles were significantly lower than those of other noodles, while the primary volatile component categories of the SP noodles were consistent with that of the WN noodles, and they had a similar flavoring substance.

Wheat Gluten Regulates Cholesterol Metabolism by Modulating Gut Microbiota in Hamsters with Hyperlipidemia.

The objective of this research was to evaluate the effect of wheat gluten on gut microbiota from hamsters and also analyse whether alterations in microbiota could result in wheat gluten's lipid-lowering properties. Four weeks male hamsters were divided into 3 groups (n=10). Two hypercholesterolemic groups were fed for 35 days with hypercholesterolemic diet, containing 20% (w/w) wheat gluten or casein. Wheat gluten significantly reduced serum total cholesterol (TC), low density lipoprotein cholesterol (LDL-C) concentrations, and also decreased the liver total cholesterol (TC), free cholesterol (FC), cholesterol ester (CE), triglycerides (TG) concentrations. Wheat gluten group had a higher fecal lipids, total cholesterol (TC) and bile acids (BA) than that of casein group (p < 0.05). Moreover, wheat gluten significantly increased total short-chain fatty acids (SCFA) concentrations in feces. Sequencing of 16S rRNA gene revealed that intake of wheat gluten decreased the relative abundances of Firmicutes and Erysipelotrichaceae, but to increased the relative abundances of Bateroidetes, Bacteroidales_S24-7_group and Ruminococcaceae. The lipid lowering properties of wheat gluten was associated with the lower ratio of Firmicutes/Bateroidetes, the lower of the bacterial taxa Erysipelotrichaceae and the higher of the bacterial taxa Bacteroidales_S24-7_group and Ruminococcaceae. These results suggest that wheat gluten modulate cholesterol metabolism by altering intestinal microflora.