Beyond structural disruption: feedstock-specific physicochemical transformation and digestibility responses to steam explosion

Efficient utilization of crop residues as ruminant feed is constrained by the recalcitrant structure of lignocellulosic biomass, and responses to steam explosion (SE) can vary among feedstocks. This study compared the structural, physicochemical, and nutritional responses of corn stover, rice straw, and cotton stalk subjected to the same nominal SE conditions. Steam explosion decreased pH from 6.56 to 7.40 to 4.64–5.97 and increased acetic acid from undetectable concentrations to 3.23–9.27 g kg⁻¹ DM. Scanning electron microscopy revealed extensive fragmentation, peeling, and surface fractures in all three feedstocks, whereas Fourier-transform infrared spectroscopy and X-ray diffraction demonstrated feedstock-specific changes in lignocellulosic structure and crystalline organization. Corn stover showed substantial decreases in neutral detergent fiber and hemicellulose concentrations, accompanied by increased water-soluble carbohydrates (22.95→88.48 g kg⁻¹ DM), xylose (0.662→8.253 g kg⁻¹ DM), and in vitro dry matter digestibility (37.44→46.52%). Rice straw similarly showed decreased structural carbohydrate concentrations together with increased water-soluble carbohydrates (43.14→61.91 g kg⁻¹ DM) and digestibility (41.96→45.99%). In contrast, cotton stalk exhibited increased neutral detergent fiber, acid detergent fiber, and acid detergent lignin concentrations, reduced water-soluble carbohydrates (58.26→16.74 g kg⁻¹ DM), and lower digestibility (40.05→37.50%) despite visible structural disruption. Principal component analysis further differentiated the steam-exploded feedstocks according to their contrasting physicochemical and nutritional profiles. Although SE modified the structure of all three crop residues, compositional and digestibility responses differed among feedstocks. Increased digestibility in corn stover and rice straw coincided with decreased structural carbohydrate fractions and increased water-soluble carbohydrates, whereas this combined response was absent in cotton stalk under the same nominal SE conditions. These findings indicate that structural disruption alone is insufficient to characterize the nutritional response to SE and that the physicochemical and carbohydrate characteristics of the recovered biomass should also be considered when evaluating SE for ruminant-feed applications. Comparative effects of steam explosion (SE) on the physicochemical characteristics and in vitro dry matter digestibility of corn stover, rice straw, and cotton stalk under the same nominal pretreatment conditions (180 °C, 1.5 MPa, 5 min). SE induced feedstock-specific physicochemical changes, with increased IVDMD in corn stover and rice straw but decreased IVDMD in cotton stalk.