Steam pressure induced changes in carbohydrate molecular structures, chemical profile and in vitro fermentation characteristics of seeds from new Brassica carinata lines

Abstract

Recently, new lines of Brassica carinata with high oil and erucic acid contents in their seeds have been developed for bio-fuel industry. The co-product after oil extraction, carinata meal, is high in crude protein (CP) and low in neutral detergent fiber (NDF) content, and can be used as feed ingredient in ruminant rations after processing such as steam pressure heating. However, the effects of steam pressure on the molecular structures, nutritional and metabolic characteristics of carinata meal produced from newly developed Brassica carinata lines has not been investigated. The objectives of this study were to investigate effects of steam pressure heating, autoclaving, at 121 °C for 0, 30, 60 and 90 min on changes in carbohydrate chemical profile, the Cornell Net Carbohydrate and Protein System (CNCPS) carbohydrate subfractions, ruminal fermentation characteristics and gas production (GP; in vitro) in relation to changes in carbohydrate molecular structure, of the newly develop Brassica carinata seeds. Except total carbohydrates, steam pressure heating altered (P < 0.05) all measured carbohydrate chemical components and CNCPS subfractions. The contents of neutral detergent fiber (aNDF), acid detergent fiber (ADF), acid detergent lignin (ADL), cellulose and soluble fiber (subfraction CB2) increased (P < 0.01) with increasing duration of steam pressure heating from 0 to 90 min in linear fashions. Whereas, the contents of sugar (fraction CA4), non-fibrous carbohydrate (NFC) and digestible fiber (fraction CB3) decreased (P < 0.05) linearly. Compared to raw seeds, the indigestible fiber subfraction increased (P = 0.001) with steam pressure heating (30−90 min). On average, the heated seeds had lower (P < 0.05) values of theoretically maximum GP (44 vs. 56.5 mL), dry matter digestibility (644 vs 559 g/ kg), and crude protein digestibility (886 vs 645 g/kg) after 48 h fermentation. The largest decrease in theoretically maximum GP (31 %), dry matter digestibility (57 %) and crude protein digestibility (35 %) after 48 h incubation was recorded for the 60 min steam pressure heating. As compared to raw seeds, the heated seeds produced higher (P = 0.01) content of acetate and lower (P ≤ 0.01) content of ammonia, isobutyrate and valerate after 24 h of fermentation. These heat-induced changes in chemical profile and ruminal fermentation characteristics were strongly correlated with the changes in inherent molecular structures of carbohydrates, particularly, with peak areas of structural carbohydrates and cellulosic compounds.