Evaluating the sustainability of phytochemicals and biopolymer extraction from grain sorghum stubble

Sorghum has emerged as a promising renewable source of natural red biocolorants and biopolymers which could be used to manufacture multiple value-added products like food dyes, bio-composites, pulp, fiber, biofuel and bioenergy. Sorghum is the fifth most widely cultivated cereal crop globally, with an estimated 63.5 million tons of grain biomass produced annually. Notably, 80–90% of sorghum biomass consists of non-grain residues (stalks, leaves, and sheaths), much of which remains underutilized. Traditionally, sorghum residues are grazed by animals or returned to the soil for nutrient recycling, but they hold significant untapped potential as feedstock for biorefineries. Further, sorghum’s resilience—drought tolerance, deep rooting, reduced tillering, and ability to regulate transpiration—makes it particularly well-suited for semi-arid regions. In this study we developed a process for the maximum extraction of biocolorants from grain sorghum stubble using “green solvents”, namely water and acetone. We have shown that speed extraction at 100 C, 10 min hold time, and 100 bar pressure will provide the maximum yield of 29% biocolorants from grain sorghum stubble on a dry weight basis. The luteolinidin concentration was improved from 0.3% to 0.4% (by weight of original biomass) via a facile post acidification process which uses 60% less acid than the current leading method. We then investigated the natural variability of biocolorants in an effort to understand the feasibility of extracting biocolorants from grain sorghum stubble on a commercial scale. Comparing three genotypes  two irrigation treatments showed that biocolorants yield is significantly affected by both factors and that there is a significant interaction between the two (p < 0.001). Henceforth, it will be essential to screen multiple grain sorghum genotypes to select the maximum biocolorant yielding variety and to optimize the irrigation regimen to further increase color saturation. vi Grain sorghum stubble is also a valuable source of extractives and biopolymers and our research showed that only the water-soluble extractives are affected by the irrigation conditions. The lignin and structural polysaccharides content, on the other hand, were not affected by the genotype or genotype  irrigation interaction. This promises a better future for the extraction of value-added extractives and biopolymers from grain sorghum stubble.