Abstract
Non-food lignocellulosic crops with both high biomass yields and superior adaptation to marginal lands have significant potential as biofuel feedstocks that can replace fossil fuels. Deployment of dedicated crops into single biofuels, however, has been reduced by conversion technology costs and low petroleum prices. Integrated biorefinery strategies, in which value-added coproducts are generated in conjunction with biofuels, by comparison offer opportunities to overcome this economic disadvantage. The objective of this research was to evaluate succinic acid accumulation across candidate lignocellulosic feedstocks. Feedstock entries included pearl millet x napiergrass hybrids (“PMN”; Pennisetum glaucum [L.] R. Br. × P. purpureum Schumach.), napiergrass (P. purpureum Schumach.), annual sorghum (Sorghum bicolor [L.] Moench), pearl millet (P. glaucum [L.] R. Br.), perennial sorghum (Sorghum spp.), switchgrass (Panicum virgatum L.), sunn hemp (Crotalaria juncea L.), giant miscanthus (Miscanthus × giganteus J. M. Greef & Deuter) and energy cane (Saccharum spp. L.). Replicated field plots, as well as an independent greenhouse trial, were characterized for succinic acid content. The PMN, napiergrass, sunn hemp and energy cane entries had greater (P ≤ 0.05) succinic acid yields, up to 556 kg·ha-1, in field trials. Napiergrass and PMN entries similarly had higher succinic acid yields under greenhouse conditions; however, irrigation treatments did not alter succinic acid accumulation in this study. Napiergrass, PMN, and energy cane thus are promising biorefinery feedstocks.
Highlights
The highest average succinic acid concentration among feedstocks was observed at Beeville in September and November (Table 3); large differences in biomass yields resulted in succinic acid yields being more informative
Sunn hemp succinic acid yield data was missing from Beeville because small ruminant herbivory significantly impacted field plot biomass yields
The greatest succinic acid yields were recovered from pearl millet x napiergrass hybrids (PMN), napiergrass, sunn hemp and energy cane
Summary
Succinic acid is among the Department of Energy’s top value-added chemicals from biomass [1]. It is a four-carbon dicarboxylic acid that can be utilized as a key building block for a broad range of products: biodegradable plastics, cosmetics, food ingredients and pharmaceutical products. Increased synthesis and bioaccumulation of such carboxylic acids have been reported when C4 perennial grasses are subject to abiotic stress such as drought [4]. This finding indicates opportunity for direct isolation of succinic acid as a coproduct from biomass feedstocks without typical lignocellulosic hydrolysis and upgrading from glucose in competition for use with primary biofuels (bioethanol, etc.). In order to investigate this potential, the objectives of this research were to: 1) evaluate succinic acid content and total yield across candidate lignocellulosic feedstocks under field conditions, and 2) characterize the impact of deficit irrigation upon succinic acid bioaccumulation across candidate lignocellulosic feedstocks under greenhouse conditions
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