Influence of twin-screw extrusion on soluble arabinoxylans and corn fiber gum from corn fiber

Comparison of hydrothermolysis and mild-alkaline pretreatment methods on enhancing succinic acid production from hydrolyzed corn fiber

In the present work, mild alkaline pretreatments using either sodium hydroxide (0.05 g/g corn fiber) or calcium hydroxide (lime) (0.05 g/g corn fiber) were optimized and compared with hydrothermolysis pretreatment to enhance bioproduction of succinic acid from hydrolyzed corn fiber. The concentration, yield, and productivity of succinic acid from sodium hydroxide corn fiber hydrolysate (SH-CFH) were 14.0 g/L, 0.63 g/g sugars, and 0.47 g/L*h, respectively, while the concentration, yield, and productivity of succinic acid from hydrothermolysis-pretreated corn fiber hydrolysate (H-CFH) were 30.2 g/L, 0.71 g/g sugars, and 1.01 g/L*h, respectively. Very little succinic acid production (<1 g/L) was observed from lime pretreated corn fiber hydrolysate (L-CFH). When SH-CFH was supplemented only with yeast extract, succinic acid concentration was enhanced to 15.2 g/L with a yield of 0.64 g/g sugars, and productivity of 0.51 g/L*h. In this study, succinic acid concentration and productivity from H-CFH both increased by 8.6% and an succinic acid yield from sugars increased 1.2 times when compared to succinic acid production from H-CFH in a previous study in our lab.

Statistical investigation of the bioprocess conditions of alkali combined twin-screw extrusion pretreatment to enhance fractionation and enzymatic hydrolysis of bulgur bran

BACKGROUND

Bulgur bran (BB) is a potential source for the production of value-added products such as fermentable sugars and xylooligosaccharides (XOs). In this study, alkali combined twin-screw extrusion pretreatment was performed and statistically optimized to enhance fractionation and enzymatic hydrolysis of BB. The pretreatment conditions (barrel temperature, screw speed and alkali impregnation) were optimized by Box-Behnken design (BBD) to obtain the highest hemicellulose separation from BB. The obtained fractions were analyzed for the production of fermentable sugars and XOs.

RESULTS

The results revealed that twin-screw extrusion of BB performed at 67 °C barrel temperature and 250 rpm screw speed after alkali impregnation at 0.02 g alkali g^-1 biomass concentration provided 40.4% higher hemicellulose separation yield compared to the untreated BB. Alkali combined twin-screw extrusion pretreatment increased the enzymatic hydrolysis yield of BB fourfold, whereas a 13-fold increase was achieved after the separation of hemicellulose from pretreated BB. Xylose (X1)-free xylobiose (X2) was the main product after xylanase hydrolysis of hemicellulose fraction. SEM images confirmed the morphological modifications in BB, which were in agreement with the enhanced fractionation performance and the higher enzymatic hydrolysis yield.

CONCLUSION

The results of this study suggested that pretreatment by alkali combined twin-screw extrusion followed by alkali extraction could be a reliable and effective process for fractionation of BB and production of fermentable sugars and XOs. © 2022 Society of Chemical Industry.

Production of cellulosic ethanol and value-added products from corn fiber

Corn fiber, a by-product from the corn processing industry, mainly composed of residual starch, cellulose, and hemicelluloses, is a promising raw material for producing cellulosic ethanol and value-added products due to its abundant reserves and low costs of collection and transportation. Now, several technologies for the production of cellulosic ethanol from corn fiber have been reported, such as the D3MAX process, Cellerate™ process, etc., and part of the technologies have also been used in industrial production in the United States. The ethanol yields range from 64 to 91% of the theoretical maximum, depending on different production processes. Because of the multicomponent of corn fiber and the complex structures highly substituted by a variety of side chains in hemicelluloses of corn fiber, however, there are many challenges in cellulosic ethanol production from corn fiber, such as the low conversion of hemicelluloses to fermentable sugars in enzymatic hydrolysis, high production of inhibitors during pretreatment, etc. Some technologies, including an effective pretreatment process for minimizing inhibitors production and maximizing fermentable sugars recovery, production of enzyme preparations with suitable protein compositions, and the engineering of microorganisms capable of fermenting hexose and pentose in hydrolysates and inhibitors tolerance, etc., need to be further developed. The process integration of cellulosic ethanol and value-added products also needs to be developed to improve the economic benefits of the whole process. This review summarizes the status and progresses of cellulosic ethanol production and potential value-added products from corn fiber and presents some challenges in this field at present.

Process-Induced Changes in the Quantity and Characteristics of Grain Dietary Fiber

Daily use of wholegrain foods is generally recommended due to strong epidemiological evidence of reduced risk of chronic diseases. Cereal grains, especially the bran part, have a high content of dietary fiber (DF). Cereal DF is an umbrella concept of heterogeneous polysaccharides of variable chemical composition and molecular weight, which are combined in a complex network in cereal cell walls. Cereal DF and its distinct components influence food digestion throughout the gastrointestinal tract and influence nutrient absorption and other physiological reactions. After repeated consumption of especially whole grain cereal foods, these effects manifest in well-demonstrated health benefits. As cereal DF is always consumed in the form of processed cereal food, it is important to know the effects of processing on DF to understand, safeguard and maximize these health effects. Endogenous and microbial enzymes, heat and mechanical energy during germination, fermentation, baking and extrusion destructurize the food and DF matrix and affect the quantity and properties of grain DF components: arabinoxylans (AX), beta-glucans, fructans and resistant starch (RS). Depolymerization is the most common change, leading to solubilization and loss of viscosity of DF polymers, which influences postprandial responses to food. Extensive hydrolysis may also remove oligosaccharides and change the colonic fermentability of DF. On the other hand, aggregation may also occur, leading to an increased amount of insoluble DF and the formation of RS. To understand the structure–function relationship of DF and to develop foods with targeted physiological benefits, it is important to invest in thorough characterization of DF present in processed cereal foods. Such understanding also demands collaborative work between food and nutritional sciences.

Integrated extrusion-enzymatic treatment of corn bran for production of functional cake

Corn bran, as one of the high-fructose corn syrup industries' by-products, is a rich source of functional fibers. The major fraction of corn bran is insoluble arabinoxylan having lower functional properties than the minor soluble function. Therefore, the main aim of this research was to increase the soluble fiber content of corn bran and use it for functional cake production. In this regard, milled corn bran with three different sizes was exposed to one factor enzymatic treatment to select the best sieving size (the criterion for selecting the best product in each stage of assay was production of the highest amount of soluble fiber). Then, milled corn bran with the best particle size was exposed to nine different enzymatic treatments to select the best enzymatic treatment condition. Additionally, the extruder feed (corn bran) moisture was adjusted to three levels to select the best level of feed moisture content and use it for performing nine different extruding experiments. Concerning integrated extrusion-enzymatic treatment, nine different extruding pretreatments were conducted on corn bran through selecting the optimum moisture level of extruding. Afterward, the product was milled and sieved to the optimum size for enzymatic treatment, and the nine pretreatments were combined with nine different enzymatic treatments. The product containing the highest soluble fiber was selected and used at various levels for functional cake production. Finally, some organoleptic and physicochemical properties (springiness, gumminess, hardness, cohesiveness, Bostwick number, density) of the produced product were analyzed.

Health-related effects and improving extractability of cereal arabinoxylans

Arabinoxylans (AXs) are major dietary fibers. They are composed of backbone chains of β-(1-4)-linked xylose residues to which α-l-arabinose are linked in the second and/or third carbon positions. Recently, AXs have attracted a great deal of attention because of their biological activities such as their immunomodulatory potential. Extraction of AXs has some difficulties; therefore, various methods have been used to increase the extractability of AXs with varying degrees of success, such as alkaline, enzymatic, mechanical extraction. However, some of these treatments have been reported to be either expensive, such as enzymatic treatments, or produce hazardous wastes and are non-environmentally friendly, such as alkaline treatments. On the other hand, mechanical assisted extraction, especially extrusion cooking, is an innovative pre-treatment that has been used to increase the solubility of AXs. The aim of the current review article is to point out the health-related effects and to discuss the current research on the extraction methods of AXs.

Changes in dietary fiber fractions and gut microbial fermentation properties of wheat bran after extrusion and bread making

The dietary fiber in wheat bran, principally non-starch polysaccharides (NSP), is mostly water-unextractable and is poorly utilized by human gut microbiota. The purpose of this study was to determine the change in water-extractability of NSP in wheat bran upon extrusion and then to determine if extrusion impacts the availability of NSP for fermentation by the fecal microbiota during in vitro fecal fermentation. A secondary objective was to incorporate extruded bran into a product formulation to determine if changes in WE-NSP and NSP fermentation were maintained in a finished product. Bran was extruded using combinations of high or low moisture (15% and 30% wb) and high or low screw speed (120 and 250rpm). All extrusion conditions resulted in increases in WE-NSP and fecal microbiota short chain fatty acid (SCFA) production upon fermentation compared with unextruded bran. Low screw speed and low moisture resulted in the greatest increase in WE-NSP (3-fold) as well as the highest production of SCFA during fermentation (1.4-fold) compared with unextruded bran. Whole wheat breads containing extruded bran did not show increases in either WE-NSP or SCFA production compared with the control. In conclusion, extrusion of wheat bran increased WE-NSP, which enabled greater fermentability by human fecal microbiota. However, once extruded bran was used in a whole wheat bread formulation the changes in fermentation outcomes were no longer evident.

The Effect of Extrusion Conditions on Water-extractable Arabinoxylans from Corn Fiber

The effect of feed moisture contents (30%, 40%, and 50%) and screw speed (200 rpm, 250 rpm, and 300 rpm) on the corn fiber gum (CFG) yield and soluble arabinoxylans (SAX) content of destarched corn fiber was investigated. The CFG yields and SAX contents of extruded, destarched corn fiber were higher than that of destarched corn fiber. In extruded, destarched corn fiber, increased screw speed and decreased feed moisture contents resulted in a higher SAX contents. The maximum yields of CFG obtained from extruded, destarched corn fiber were 79.1±19.0 g/kg (30% feed moisture content) and 82.3±11.30 g/kg (300 rpm screw speed). The highest SAX content was also observed at a screw speed of 300 rpm. The results of the present study show that water extraction and extrusion combined have the potential to increase CFG and SAX yields from corn fiber.