Development of highly digestible animal feed from lignocellulosic biomass Part 2: Oxidative lime pretreatment (OLP) and shock treatment of corn stover1

Abstract

Oxidative lime pretreatment (OLP) increases lignocellulose digestibility by removing lignin and hemicellulose acetyl content. Digestibility is improved further by adding mechanical shock treatment, which subjects aqueous slurry of biomass to an explosive pressure pulse. Shock treatment mechanically disrupts the microscopic structure while maintaining the macroscopic integrity of the biomass particle. This study determined the effectiveness of these pretreatments to enhance the ruminant digestibility of corn stover. In terms of compositional changes, OLP and shock treatment should negatively affect the feed value of corn stover; however, digestibility analysis provides a significantly different conclusion. With corn stover, shock + OLP improved the 48-h neutral detergent fiber digestibility (NDFD) to 79.0 g neutral detergent fiber (NDF) digested/100 g NDF fed, compared to 49.3 for raw corn stover. The 48-h in vitro total digestible nutrients (TDNom, g nutrients digested/100 g OM) was 51.9 (raw), 59.7 (OLP), and 72.6 (shock + OLP). Adding extracted corn stover solubles to shock + OLP increased TDNom to 74.9. When enough solubilized chicken feathers were added to match the protein content of corn grain, TDNom increases to 75.5, which is only 12.6 less than corn grain.

Assessment of shock pretreatment and alkali pretreatment on corn stover using enzymatic hydrolysis

“…This is a contrast to Ca(OH) 2 pretreatment, in which previous studies showed oxygen improves digestibility. 7,20,31,35,40 This low effect of oxygen on NaOH pretreatment was observed with and without the inclusion of hydrolyzed filtrate (Figure 12). These results show that in NaOH pretreatments, pressurized oxygen does not benefit enzymatic digestibility.…”

“…According to Falls et al, shock treatment alone causes a slight increase in cellulose crystallinity and has a negative impact on enzymatic digestibility. 20,25 However, previous studies have shown that combining shock treatment with oxidative lime pretreatment greatly increases biomass digestibility. 20,21,25 Falls et al hypothesized that even though shock slightly increases crystallinity, this negative effect is countered from the disruption of the lignin/hemicellulose matrix surrounding cellulose, providing greater access for enzymes.…”

“…11,19 Alkaline pretreatment with NaOH causes biomass to swell, which increases internal surface area, decreases polymerization, reduces crystallinity, and breaks down lignin structure. 14 Among mechanical pretreatments, shock pretreatment is a novel method that uses a detonation wave to disrupt mechanically the microscopic structure without damaging the macroscopic integrity of the biomass particle 20,21 The final shock pressure is 18 times greater than the initial pressure of explosive gas. 22 It is estimated to cost < $5/ton.…”

“…23 Combining shock and lime pretreatments improves enzymatic digestibility of lignocellulose. 11,20,21,24,25 In previous studies on the MixAlco™ process, alkaline OLP and SLP were neutralized by bubbling carbon dioxide through the liquid slurry. Calcium carbonate has low solubility in water, so an excess amount of calcium carbonate can be added to the fermenter.…”

“…Lignocellulose pretreatment can be used to enhance the digestibility of ruminant feeds. 20 In their daily diets, non-lactating beef cattle require 12 times more calcium than sodium (Table 1). Lactating beef cows require higher amounts of sodium in their diets (probably due to the transfer of sodium to the milk) ranging from 0.1% (Table 1) to 0.22% recommended by the US National Research Council.…”