**3.** *Miscanthus x giganteus* **history and general characteristics**

*Miscanthus x giganteus* is a hybrid plant created in Japan, likely by the combination of *M. sinensis* and *M. sacchariflorus* [8]. Presumably it was then brought to Denmark in the mid 1930's and spread throughout Europe and North America as a horticultural plant [8]. The hybrid is sterile; thus, its propagation is through viable rhizome plantings and spread (**Figure 1A**). In the past it was used as forage for animals and for thatching [11]. However, in recent years, it has been considered as a source of cellulose for fuel to produce heat and electricity [12] via ethanol production [9], as well as construction materials, and absorbents [13].

*M. x giganteus* is a C4 plant relying on the NADP-malic enzyme pathway [14]. This pathway allows for the continuous photosynthesis even at lower temperatures (8°C) [15]. This is an important characteristic that has allowed this plant to be successfully cultivated in colder climates, such as northern Europe and North America. Moreover, this plant efficiently uses nitrogen and water [16, 17] compared to other crops. Thus, while *M. x giganteus* has not been adapted to produce food, it does grow well in marginal soils which are not suitable for cultivation.

Some authors report that the plant once established can remain productive for 5 to 40 years [11, 18, 19] depending on the region in which it is cultivated and cropping pressure (**Figure 1B**). Thus, *M. x giganteus* is considered a perennial crop. In this state it grows quickly and reaches 2 m in height with a close canopy cover which reduces sun light penetration, limiting weed growth, thus eliminating the need for herbicide administration (**Figure 1B**). Although, weed control is necessary before this stage as the plant is getting established [20]. Nutrient use by *M. x giganteus* is very efficient as it translocates nitrogen, phosphorus, and potassium to

*Miscanthus Grass as a Nutritional Fiber Source for Monogastric Animals DOI: http://dx.doi.org/10.5772/intechopen.99951*

#### **Figure 1.**

Miscanthus x giganteus *rhizome (A; from Adams et al. [9]), growth stage approximately 2.5 m (B); dried (C; from Adams et al. [9]); baled (D; from Adams et al. [9]), stored bales (E), and ground (F; from Pontius et al. [10]) with a particle size of 134 ± 93* μ*m and a 5X magnification.*

the rhizomes at the end of the growing season when the aerial portion of the plant begins to senesce (**Figure 1C**) [16]. This senescence starts with a killing frost during fall [21]. Predation by insects is limited [22]. As a result, this plant has been primarily utilized for biomass production; although, there may be more value for this crop than has been identified to date.

In general, fiber rich ingredients have been gaining more attention. In part because obesity in the pet and human population is a substantial issue [23, 24] and fiber is one possible solution to decrease the energy density of food. It may also increase the volume of the digesta in the gastrointestinal tract, and the fermentation of fiber in the colon to short chain fatty acids like butyrate (a preferred fuel source for the colonocyte) may aid in the prevention of cancer and the reduction in intestinal inflammation [25]. Moreover, food fiber through bulking of digesta can help alleviate constipation [26]. Despite these health benefits, fiber-added foods are usually less preferred than "regular" foods [27, 28]. Part of the changes in the flavor and texture attributes of fibers could be related to the composition of various fiber sources. For example, lignin a phenylpropanoid component of some fiber ingredients is known to have a bitter taste [29]. An alteration to texture is likely an effect of the changes that fiber cause in the product during processing that changes the mouthfeel as the food is consumed [30]. However, acceptance of dietary fiber

may be changing as consumers attribute more importance to the health benefits and their palates adjust to the flavor and texture profile of these more fibrous products.

Despite the health benefits and their popularity in some human and pet foods, adding fiber ingredients brings challenges to manufacturing. For example, in extruded expanded products (like breakfast cereals and dry extruded pet foods) fiber ingredient addition decreases product expansion [31] and increases cutting force [32]. However, when considering the diversity of foods in the grocery stores, there are several examples of insoluble and soluble fibers which have been used successfully in select products [33].

### **4. Chemical and physical characterization**

Before detailing the uses and effects of Miscanthus grass as a fiber source for monogastric animals, it is beneficial to gain an understanding regarding how fiber as a nutrient is characterized. While the term "fiber" is commonly used, it relates to a very diverse group of compounds that are not easy to characterize and quantify. To add to the complexity of this food group, differences in raw material composition (plant variety, age at harvest, environmental conditions, and harvest date) and the process in which the plant material was produced can influence the composition and concentration of the fiber nutrient in the final ingredient [26, 34]. Regardless of the challenges to evaluate fiber sources [35], it is important to characterize the fiber content of an ingredient to properly understand its effects on food processing and the possible health benefits it may have.

Different methods are used across industries to quantify the fiber content of ingredients and foods. Historically, the method initially developed was "crude fiber" (Thaer, 1809 and Hennenburg and Stohmann, 1860 and 1864 in [36]). In this method the sample is digested in a strong acid and then in a base with the residue remaining considered as fiber. In this procedure, all the soluble fibers are washed away; thus, underestimating the total fiber content of the sample. However, this is the method required on the pet food labels by state feed control officials as outlined by Model Bill within the Official Publication for the American Association of Feed Control Officials [37]. Other methods have been developed to measure fiber in forages [38–40] and are common for the beef, dairy, swine, and poultry industries. These procedures boil the forage in neutral or acid detergent solutions and measure the resulting residue. Like the crude fiber method, several of the soluble components of the sample are washed away and not accounted in the measure of fiber. In an attempt to recover the soluble fibers, the total dietary fiber method (TDF) [41] was developed to capture all the fibrous fractions. It was revised a few years later to include the analysis for the insoluble and soluble fractions [42]. This procedure is based on an enzymatic digestion to remove the proteins and starches from the sample. This method is commonly used by the human foods and nutrition industry, as some of its results are correlated with some health benefit. Since some fibers are not recovered by the TDF analysis, other methods have been developed to quantify the fiber content of a given sample; however, they are not standardized and variation in the procedures and results are known to occur [35]. **Table 1** provides a summary of the methods and what fiber component is or not recovered by them. For the sake of this review, fiber composition will be classified by its solubility in water (soluble vs. insoluble) and fermentability (fermentable vs. non-fermentable). We have evaluated the composition of Miscanthus grass as an ingredient for pet food production and its composition is shown on **Table 1**. From the values reported, clearly Miscanthus grass is a source rich in insoluble fibers with some meaningful amount of lignin consistent with most forages.


*Miscanthus Grass as a Nutritional Fiber Source for Monogastric Animals DOI: http://dx.doi.org/10.5772/intechopen.99951*

*1 From Food and Agriculture Organization [43].*

*2 From Hossain et al. [44].*

*3 From Curti et al. [45].*

*4 From Babu et al. [46].*

#### **Table 1.**

*Methods commonly used to analyze fiber content of ingredients and values for Miscanthus grass and wheat bran from research referenced in this review.*

On the physical side of fiber analysis, the most common analytical method used to characterize ingredients for the production of animal foods is particle size and its distribution. This is usually done with the standard method described by the American Society of Agriculture and Biological Engineers ([47], method S319.4) which consists of stacked sieves in a shaker tapping device. In the procedure a sample is placed on the top sieve and after 10 min on the shaker the content remaining in each subsequent sieve below is weighed and the geometric mean diameter of the particle is calculated from the sieve hole size and residual weight. This is not a characterization of the ingredient as a whole, but rather the specific batch and grinding equipment, as the grind size can be adjusted as needed (**Figure 1F**). For example, in the work of [1] they used a fine (108.57 ± 66.25 μm) and a coarse particle size (294.10 ± 253.22 μm) Miscanthus grass to evaluate the possible effects of particle size in broiler chicken performance and digestibility. This laboratory group has also reported use of a similar fine particle size Miscanthus grass used in a feeding study with cats. In this experiment the particle size of the Miscanthus grass was 103.46 ± 76.39 μm [5] and had positive effects. Pontius et al. [10] reported the exploration of Miscanthus grass as a potential premix carrier. In this work the average particle size was 134 ± 93 μm. They also evaluated flowability and angle of repose (a measure of resistance to flow) of powdered ingredients considered in a manufacturing setting for their ability to move out of bin-bottoms and through transfer pipes [48]. The angle of repose is estimated after a certain amount of the powdered ingredient has been poured onto a level bench top. The lower the angle, the easier the material will flow. The flowability index (FlowDex) is measured by adding a known amount of the powdered ingredient into a cylindrical hopper with

a fitted disk of known orifice diameter. The minimum diameter for the material to flow freely is determined after 3 successful tests. From the evaluation of [10] they were unable to determine the flowability index of Miscanthus grass since the ingredient did not flow through the biggest diameter disk (34 mm diameter). Additionally, angle of repose for MG was 47.8° which compared unfavorably to all other tested fibers. These characteristics indicate that Miscanthus grass in a simple ground form may have poor flowability. Though that might be modified with alternative processing steps as has been applied to other fiber carriers and excipients from other sources (*e.g.*, cellulose).
