Enhancement of biogas production rate from bioplastics by alkaline pretreatment.

The effect of alkali-based pretreatment on the methanization of bioplastics was investigated. The tested bioplastics included PHB [poly(3-hydroxybutyrate)], PHBH [poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)], PHBV [poly(3-hydroxybutyrate-co-3-hydroxyvalerate], PLA (polylactic acid), and a PLA/PCL [poly(caprolactone)] 80/20 blend. Prior to methanization tests, the powdered polymers (500-1000 µm) at a concentration of 50 g/L were subjected to alkaline pretreatment using NaOH 1 M for PLA and PLA/PCL, and NaOH 2 M for PHB-based materials. Following 7 days of pretreatment, the amount of solubilized carbon for PLA and its blend accounted for 92-98% of the total initial carbon, while lower carbon recoveries were recorded for most PHB-based materials (80-93%), as revealed by dissolved total organic carbon analysis. The pretreated bioplastics were then tested for biogas production by means of mesophilic biochemical methane potential tests. Compared to unpretreated PHBs, methanization rates of pretreated PHBs were accelerated by a factor of 2.7 to 9.1 with comparable (430 NmL CH4/g material feed) or slightly lower (15% in the case of PHBH) methane yields, despite featuring a 1.4-2.3 times longer lag phases. Both materials, PLA and the PLA/PCL blend, were only extensively digested when pretreated, yielding about 360-380 NmL CH4 per gram of material fed. Unpretreated PLA-based materials showed nearly zero methanization under the timeframe and experimental conditions tested. Overall, the results suggested that alkaline pretreatment can help to enhance the methanization kinetics of bioplastics.

Co-cultures of Propionibacterium freudenreichii and Bacillus amyloliquefaciens cooperatively upgrade sunflower seed milk to high levels of vitamin B12 and multiple co-benefits.

BACKGROUND: Sunflower seeds (Helianthus annuus) display an attractive source for the rapidly increasing market of plant-based human nutrition. Of particular interest are press cakes of the seeds, cheap residuals from sunflower oil manufacturing that offer attractive sustainability and economic benefits. Admittedly, sunflower seed milk, derived therefrom, suffers from limited nutritional value, undesired flavor, and the presence of indigestible sugars. Of specific relevance is the absence of vitamin B12. This vitamin is required for development and function of the central nervous system, healthy red blood cell formation, and DNA synthesis, and displays the most important micronutrient for vegans to be aware of. Here we evaluated the power of microbes to enrich sunflower seed milk nutritionally as well as in flavor. RESULTS: Propionibacterium freudenreichii NCC 1177 showed highest vitamin B12 production in sunflower seed milk out of a range of food-grade propionibacteria. Its growth and B12 production capacity, however, were limited by a lack of accessible carbon sources and stimulants of B12 biosynthesis in the plant milk. This was overcome by co-cultivation with Bacillus amyloliquefaciens NCC 156, which supplied lactate, amino acids, and vitamin B7 for growth of NCC 1177 plus vitamins B2 and B3, potentially supporting vitamin B12 production by the Propionibacterium. After several rounds of optimization, co-fermentation of ultra-high-temperature pre-treated sunflower seed milk by the two microbes, enabled the production of 17 µg (100 g)-1 vitamin B12 within four days without any further supplementation. The fermented milk further revealed significantly enriched levels of L-lysine, the most limiting essential amino acid, vitamin B3, vitamin B6, improved protein quality and flavor, and largely eliminated indigestible sugars. CONCLUSION: The fermented sunflower seed milk, obtained by using two food-grade microbes without further supplementation, displays an attractive, clean-label product with a high level of vitamin B12 and multiple co-benefits. The secret of the successfully upgraded plant milk lies in the multifunctional cooperation of the two microbes, which were combined, based on their genetic potential and metabolic signatures found in mono-culture fermentations. This design by knowledge approach appears valuable for future development of plant-based milk products.

Biodegradation of bioplastics under aerobic and anaerobic aqueous conditions: Kinetics, carbon fate and particle size effect.

The biodegradation of PHB, PHBV, PBS, PBAT, PCL, PLA, and a PLA-PCL blend was compared under aerobic and anaerobic aqueous conditions assessing biodegradation kinetics, extent, carbon fate and particle size influence (in the range of 100-1000 µm). Under standard test conditions, PHB and PBHV were biodegraded anaerobically (83.9 ± 1.3% and 81.2 ± 1.7%, respectively) in 77 days or aerobically (83.0 ± 1.6% and 87.4 ± 7.5%) in 117 days, while PCL was only biodegraded (77.6 ± 2.4%) aerobically in 177 days. Apparent biomass growth accounted for 10 to 30.5% of the total initial carbon depending on the bioplastic and condition. Maximum aerobic and anaerobic biodegradation rates were improved up to 331 and 405%, respectively, at the lowest particle size tested (100-250 µm). This study highlights the usefulness of analysing biodegradation kinetics and carbon fate to improve both the development and testing of biodegradable materials, and waste treatments in the context of a circular bioeconomy.

Genome-based selection and application of food-grade microbes for chickpea milk fermentation towards increased L-lysine content, elimination of indigestible sugars, and improved flavour.

BACKGROUND: Plant-based milk alternatives are more popular than ever, and chickpea-based milks are among the most commercially relevant products. Unfortunately, limited nutritional value because of low levels of the essential amino acid L-lysine, low digestibility and unpleasant taste are challenges that must be addressed to improve product quality and meet consumer expectations. RESULTS: Using in-silico screening and food safety classifications, 31 strains were selected as potential L-lysine producers from approximately 2,500 potential candidates. Beneficially, 30% of the isolates significantly accumulated amino acids (up to 1.4 mM) during chickpea milk fermentation, increasing the natural level by up to 43%. The best-performing strains, B. amyloliquefaciens NCC 156 and L. paracasei subsp. paracasei NCC 2511, were tested further. De novo lysine biosynthesis was demonstrated in both strains by 13C metabolic pathway analysis. Spiking small amounts of citrate into the fermentation significantly activated L-lysine biosynthesis in NCC 156 and stimulated growth. Both microbes revealed additional benefits in eliminating indigestible sugars such as stachyose and raffinose and converting off-flavour aldehydes into the corresponding alcohols and acids with fruity and sweet notes. CONCLUSIONS: B. amyloliquefaciens NCC 156 and L. paracasei subsp. paracasei NCC 2511 emerged as multi-benefit microbes for chickpea milk fermentation with strong potential for industrial processing of the plant material. Given the high number of L-lysine-producing isolates identified in silico, this concept appears promising to support strain selection for food fermentation.