Corn cob

Fig. 7 Stabilization effect of various xylan types isolated from beech wood (GXl and GX2), corn cobs (AGXl), rye bran (AXRl and AXR3), and corn hulls (AXCl and AXC2) on the protein (BSA) foam against thermal disruption foam volume before (V1) and after (V2) heating at 95 °C for 3 min [128]...

The aim of this chapter is to summarize some of the research findings on xylan, a natural polymer extracted from corn cobs, which presents a promising application in the development of colon-specific drug carriers. Physicochemical characterization of the polymer regarding particle size and morphology, composition, rheology, thermal behavior, and crystallinity will be provided. Additionally, research data on its extraction and the development of microparticles based on xylan and prepared by different methods will also be presented and discussed. 

Additionally, corn cobs correspond to an abundant and low-cost renewable material in several coimtries worldwide and their recycling plays a very important role in the reduction of waste products. Consequently, such approach would lead to a relevant increase in the sustainability of agriculture around the world. 

The most common method to extract xylan is the alkaline extraction. Several pretreatment methods can be used in association in order to break the covalent bonds that exist between xylan and other carbohydrates during the extraction (Wang Zhang, 2006). A number of articles studied the use of ultrasound on the xylan extraction. Hromadkova and coworkers reported that 36.1% of xylan was extracted from corn cobs with 5% NaOH solution at 60°C for 10 min of ultrasonication in comparison with 31.5% of xylan in the classical extraction. Both extractive methods yielded xylan with immunogenic properties (Hromadkova et al., 1999). 

Wang and Zhang also investigated the effects on the xylan extracted from corn cobs enhanced by ultrasound at various lab-scale conditions. Results showed that the optimization conditions of xylan extraction should be carried out using (i) 1.8 M NaOH, (ii) corn cobs to NaOH solution ratio of 1 25 (w/w), (iii) sonication at 200 W ultrasound power for 30 min at 5 min intervals, and (iv) 60 °C (Wang Zhang, 2006). 

The efficiency of extraction was observed to be inversely proportional to the corn cob particle size. This was expected because the size reduction corresponds to an increase in total particle surface area. An increase in the time of the alkaline extraction and in the NaOH concentration also improves the efficiency of xylan extraction. This happened because when the NaOH concentration was lower, the xylan present in corn cobs could not be fully dissolved in the solution. Thus, it resulted in lower efficiency of xylan extraction. However, when the NaOH concentration was higher than 2 M, the yields decreased with continuously increasing of the NaOH concentration. This is probably due to the alkaline degradation of xylan chains, proceeding at the higher NaOH concentration, which indicated that the ideal NaOH concentration in the extraction was between 1.5 and 1.8 M (Unpublished data). 

Fig. 2. SEM image of xylan powder after extraction from corn cobs (Oliveira et al., 2010).

Table 1. Rheological properties of xylan powder extracted from corn cobs...

Regarding the characterization of corn cob xylan by Fourier-transform infrared (FT-IR) spectroscopy, two main absorption bands at 3405 cm-i and 1160 cm-i are revealed. They can... 

Fig. 5. Solid-state i C nuclear magnetic resonance spectrum of corn cob xylan.

Fig. 6. X-ray diffraction pattern for corn cob xylan (Unpublished data).

In order to assess the effect of the corn cob xylan on the cell viability and proliferation rate, xylan solutions at concentrations of 0.1, 0.25, 0.50, 0.75, and 1 mg/ml were placed in contact with human cervical adenocarcinoma cells (HeLa cells) for 24 and 72 h. Finally, the cell viability was determined by the MTT assay. It was observed that regardless of the xylan concentration, the samples tested did not affect the viability of HeLa cells after incubation for 24 h (Figure 13) (Unpublished data). 

Large amounts of agricultural waste products, such as corn cobs, are continuously provided in several developing countries. Xylan is considered to be a green polymer that may play an essential role in the renewability of waste products due to its biodegradable and biocompatible nature. Furthermore, as shown in this chapter, xylan presents particular properties that allow a wide range of applications. 

Hromadkova, Z., Kovacikova, J. Ebringerova, A. (1999). Study of the classical and ultrasound-assisted extraction of the corn cob xylan. Industrial Crops and Products, Vol. 9, 2, (Januar 1999), pp. (101-109), ISSN 0926-6690... 

Another excipient used in feed additive premixes is a diluent used to dilute or standardize activity. Diluents are similar in composition to grain carriers, except the particle size is generally smaller. No attempt is made to absorb the active drug to the individual particles of the diluents. If a liquid is used it is mainly for dust control. A diluent is considered for use when the level of the active ingredient components in the premix approaches or exceeds 50% of the product or when two or more active components vary greatly from one another in density [13]. Examples of diluent materials are ground limestone, sodium sulfate, kaolin, corn cob flour, and ground oyster shells. 

Absorbents are another class of excipient material used in feed additive premixes. They are used when the drug substance is a liquid or is readily soluble in water, oil, or some other solvent. The liquid is sprayed onto the absorbent in a mixer as the mixer is running. Examples of absorbents are vermiculite, Fullers earth, corn cob fractions, and clay. 

Xylan occurs in practically all land plants and is said to be present in some marine algae.6 In both wide botanical distribution and abundance in nature it closely follows cellulose and starch. It is most abundant in annual crops, particularly in agricultural residues such as corn cobs, corn stalks, grain hulls and stems. Here it occurs in amounts ranging from 15 to 30%. Hard woods contain 20 to 25% xylan while soft woods contain 7 to 12 %. Spring wood has more pentosan than summer wood. 7 Low strength vegetable fibers of commerce such as jute, sisal, Manila... 

Aqueous alkaline extraction of wood was employed by Poumarede and Figuier48 in 1846 for the removal of a substance called wood gum. Similar very crude xylan or hemicellulose preparations were made by other workers of the early period. Extractions were made not only from wood sawdust, but from annual plant materials such as wheat straw, corn cob, etc.49-66... 

Fig. 1.—Yield of hemicellulose-A and -B and residue obtained by alkali extraction of raw corn cob. O Residue, A-fraction, 3 B-fraction.

Prior to xylan removal it is possible to extract from the plant material those hemicelluloses soluble in dilute alkali. Soluble hemicelluloses of this type are the principal impurities extracted with xylan and consist for the most part of low molecular weight polysaccharides and polyuronides. Corn cob holocellulose may be freed of these compounds (called hemicellulose-B fraction, see Figure 2) by extraction with potas-... 

Relatively pure xylan isolated from the holocellulose of aspen (Populus) wood is said to contain 85% of xylose residues.78 One of the characteristic properties of xylan is its ease of hydrolysis. Because it hydrolyzes much more readily than cellulose, mild acid treatment may be employed to bring about preferential hydrolysis of xylan from plant material. Xylose is ordinarily prepared in the laboratory by direct sulfuric acid hydrolysis of the native xylan in ground corn cobs.74 Hydrolysis in hydrochloric acid proceeds rapidly, but decomposition to furfural also occurs to some extent.76 A commercial method for the production of D-xylose from cottonseed hulls76 and straw77 and from corn cobs17 78 has been described. 

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