R. J. Straub

ENZYMIC SACCHARIFICATION OF ALFALFA FIBRE AFTER LIQUID HOT WATER PRETREATMENT

Liquid hot water (LHW) at a high temperature has been advocated as a pretreatment for herbaceous and lignocellulosic materials prior to enzymic saccharification. The focus of our research was the suitability of LHW pretreatment of alfalfa (Medicago saliva) fibre in the presence and absence of mild acid for optimum saccharification using enzymes. Enzymic saccharification was optimised in terms of substrate and enzyme concentrations. The main components of the enzymic hydrolyzates were sucrose, glucose, xylose, arabinose, and low amounts of uronic acid. After LHW pretreatment, both the soluble hemicellulose-rich ‘extract’ fraction and the insoluble residue ‘raffinate’ fraction (which contains predominantly cellulose) of alfalfa were recovered; the yield was 48 and 41%, respectively. Enzymic saccharification released more reducing sugars from pretreated fibre than from untreated fibre. For untreated alfalfa, a commercial pectinase and cellulase mixture caused maximum release of reducing sugars; using 2 and 4% (w/v) enzyme, a maximum of 51 g/l reducing sugars was released from 100 g/l untreated alfalfa. The soluble extract, LHW-pretreated alfalfa, was clarified and saccharified with the same cellulase and pectinase mixture releasing 8.4 g/l reducing sugars from 15.5 g/l solids. Release of reducing sugars from the insoluble raffinate ranged from 59 to 65 g/l from 100 g/l substrate, using 2 and 4% (w/v) cellulase. Addition of 0.07% sulphuric acid to the LHW pretreatment facilitated hemicellulose solubilisation; 9.9 g/l reducing sugars were released from the alfalfa extract by enzymic saccharification. However, pretreatment with sulphuric acid reduced sugar release and decreased fibre degradation of the raffinate.

Ethanol production from alfalfa fiber fractions by saccharification and fermentation.

This work describes ethanol production from alfalfa fiber using separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF) with and without liquid hot water (LHW) pretreatment. Candida shehatae FPL-702 produced 5 and 6.4 g/l ethanol with a yield of 0.25 and 0.16 g ethanol/g sugar respectively by SHF and SSF from alfalfa fiber without pretreatment. With LHW pretreatment using SSF, C. shehatae FPL-702 produced 18.0 g/l ethanol, a yield of 0.45 g ethanol/g sugar from cellulosic solids or ‘raffinate’. Using SHF, it produced 9.6 g/l ethanol, a yield of 0.47 g ethanol/g sugar from raffinate. However, the soluble extract fraction containing hemicelluloses was poorly fermented in both SHF and SSF due to the presence of inhibitors. Addition of dilute acid during LHW pretreatment of alfalfa fiber resulted in fractions that were poorly saccharified and fermented. These results show that unpretreated alfalfa fiber produced a lower ethanol yield. Although LHW pretreatment can increase ethanol production from raffinate fiber fractions, it does not increase production from the hemicellulosic and pectin fractions.

LEACHATE CONDUCTIVITY AS AN INDEX FOR QUANTIFYING LEVEL OF FORAGE CONDITIONING

A method based upon measuring the conductivity of the leachate (LC) from mechanically conditioned forage was evaluated and used as an index for quantifying the extent of mechanical damage caused by various mechanical treatments. Relative to a Surface Area Index (SAI) method previously used, the LC method was simple, fast, and could be completed with readily available laboratory equipment (orbital shaker table, Waring® blender, and conductivity meter). The LC method differentiated various mechanical conditioning treatments more often and with greater sensitivity than the SAI method. The consistency of different Waring blender treatments was assessed to determine if it could be used as a standard treatment for normalizing leachate conductivity values.

An overview of physical treatments of lucerne performed at Madison, Wisconsin, for improving properties

Macerated (shredded) forage has been shown to have two important properties: drying rates several times those of conventional forage and dry matter digestibilities 10–15% higher than conventional forage. A field-drying process was developed which consists of mowing, macerating, pressing the forage into thin cohesive mats, and placing these on the stubble. A small prototype machine was constructed to carry out these processes concurrently. Equipment was also developed to harvest the forage mats either for dry hay or for silage. Ensiled macerated lucerne fermented twice as fast as conventional lucerne. Feeding trials with sheep, goats, and dairy cattle verified the higher digestibility of macerated as compared with unmacerated lucerne. Heat treatment of hay increased the “escape” or “bypass” protein of lucerne, which is expected to improve efficiency of protein utilization by ruminants. The increase in escape protein due to heat treatment was approximately 50% greater for macerated lucerne than for conventional lucerne.

Drying Rates of Macerated Alfalfa Mats

ABSTRACT ALFALFA was macerated and then formed into thin mats which were deposited onto the forage stubble for field drying. Drying rates of mats and control swaths having equal dry matter per unit area were determined. The macerated alfalfa mats dried to 20% (w.b.) moisture content in 6 h or less, while the control swaths did not reach this moisture content during the first day. Mat drying rate is roughly proportional to mat dry matter per unit area. The evaporation rate of water from a standard evaporation pan poorly models the moisture evaporation rate from mats or swaths.

Evaluating Longitudinal Shear as a Forage Maceration Technique

ABSTRACT ALFALFA can be dried rapidly if it is macerated and formed into a mat. Maceration must severely condition the plant for rapid drying and still maintain fiber length to insure mat strength. A maceration method which produces these physical qualities involves repeated shearing of the plant stem along its length. The effects of stem segment, plant maturity and harvest on the longitudinal shear properties of alfalfa were studied. Results indicate that longitudinal shear of alfalfa stems requires less than 1/10 the reported energy to shear alfalfa transversely. Therefore, energy requirements for maceration should be comparable with those of other alfalfa processes.

Alfalfa fiber as a feedstock for ethanol and organic acids

Valuable co-products derived from fractionation of alfalfa herbage give the resulting fibrous fraction an economic advantage as a feed stock for ethanol or other organic products. Alfalfa fiber was saccharified and fermented with or without a liquid hot water (LHW) pretreatment. The LHW pretreatment hydrolyzed approximately 60% of the original fiber, yielding a high cellulose residue and aliquid extract. These yielded predominantly hexoses and pentoses, respectively, after enzymatic saccharification. Yields of ethanol and lactic acid resulting from fermentations are given.

Ammonia Treatment of Large and Small Hay Packages

ABSTRACT ALFALFA bales of 18 to 50% moisture content (w.b.) were injected with anhydrous ammonia. Temperature history, dry matter loss, and presence of mold were used to determine the adequacy of the preservative treatment. Treated, uncovered bales were adequately preserved at moisture contents up to 28% w.b. Treated bales enclosed in plastic bags were adequately preserved at higher moisture contents.

Mechanical and Chemical Treatments to Modify the Digestibility of Alfalfa Stems

ABSTRACT MACERATION, ammoniation, explosion (rapid pressure release), and combinations of these treatments to alfalfa stems caused significant (P<0.05) increases in the in vitro digestibility of neutral detergent fiber (NDF) over untreated controls. Maceration (mechanical shredding) and explosion gave increases in NDF digestion of 39% and 32%, respectively at 12 h and 39% and 17% at 24 h relative to the control. Ammoniation did not show a significant increase relative to the control until 72 h at which time it was 16% higher. For the first 24 h, maceration plus explosion was not different than maceration alone whereas maceration plus ammoniation actually resulted in slower NDF digestion than maceration alone. A combination of all three treatments resulted in increases in NDF digestion of 54%, 49%, and 43% at 12, 24, and 72 h, respectively. The water absorption rates of the macerated materials were almost three times those of the unmacerated materials, indicating that maceration altered the surface charateristics of the original material.

Physical Parameters of Macerated Alfalfa Related to Wet Strength of Forage Mats

ABSTRACT IN order to utilize the fast-drying properties of macerated forage mats, adequate wet mat strength must be produced to allow placing them intact on the forage stubble. Mat strength and drying rate are dependent upon, among other formation factors, adequate maceration. Methods were developed to determine physical parameters of macerated alfalfa, including specific surface area, quantity of long fibers, short particle length and material compliancy. The quantified physical parameters were then related to mat strength. Results indicate that wet mat strength decreases with the severity of the maceration. A surface area index, based on rate of water absorption, was found to be a good measure of severity of maceration, and can be used to predict mat properties and the other physical parameters measured.