Water-soluble saponins accumulate in drought-stressed switchgrass and may inhibit yeast growth during bioethanol production.

BACKGROUND: Developing economically viable pathways to produce renewable energy has become an important research theme in recent years. Lignocellulosic biomass is a promising feedstock that can be converted into second-generation biofuels and bioproducts. Global warming has adversely affected climate change causing many environmental changes that have impacted earth surface temperature and rainfall patterns. Recent research has shown that environmental growth conditions altered the composition of drought-stressed switchgrass and directly influenced the extent of biomass conversion to fuels by completely inhibiting yeast growth during fermentation. Our goal in this project was to find a way to overcome the microbial inhibition and characterize specific compounds that led to this inhibition. Additionally, we also determined if these microbial inhibitors were plant-generated compounds, by-products of the pretreatment process, or a combination of both. RESULTS: Switchgrass harvested in drought (2012) and non-drought (2010) years were pretreated using Ammonia Fiber Expansion (AFEX). Untreated and AFEX processed samples were then extracted using solvents (i.e., water, ethanol, and ethyl acetate) to selectively remove potential inhibitory compounds and determine whether pretreatment affects the inhibition. High solids loading enzymatic hydrolysis was performed on all samples, followed by fermentation using engineered Saccharomyces cerevisiae. Fermentation rate, cell growth, sugar consumption, and ethanol production were used to evaluate fermentation performance. We found that water extraction of drought-year switchgrass before AFEX pretreatment reduced the inhibition of yeast fermentation. The extracts were analyzed using liquid chromatography-mass spectrometry (LC-MS) to detect compounds enriched in the extracted fractions. Saponins, a class of plant-generated triterpene or steroidal glycosides, were found to be significantly more abundant in the water extracts from drought-year (inhibitory) switchgrass. The inhibitory nature of the saponins in switchgrass hydrolysate was validated by spiking commercially available saponin standard (protodioscin) in non-inhibitory switchgrass hydrolysate harvested in normal year. CONCLUSIONS: Adding a water extraction step prior to AFEX-pretreatment of drought-stressed switchgrass effectively overcame inhibition of yeast growth during bioethanol production. Saponins appear to be generated by the plant as a response to drought as they were significantly more abundant in the drought-stressed switchgrass water extracts and may contribute toward yeast inhibition in drought-stressed switchgrass hydrolysates.

Dietary supplement safety information in magazines popular among older readers.

Dietary supplements are extensively used in the United States, especially by people age 50 and over. Surveys have shown that magazines and other news media are an important source of information about nutrition and dietary supplements for the American public. It is uncertain, however, whether magazines provide their readers with adequate information about the safety aspects of supplement use. This report presents an analysis of supplement safety information in articles published during 1994-1998 in 10 major magazines popular among older readers. This time period was chosen to allow the impact of the 1994 Dietary Supplement Health and Education Act (DSHEA) to be assessed. The evaluation included 254 magazine articles. More than two-thirds of the articles did not include comprehensive information about the safety aspects of the dietary supplements that were discussed. Information about safety issues such as maximum safe doses and drug-supplement interactions was often lacking even in otherwise informative and well-researched articles. A total of 2,983 advertisements for more than 130 different types of supplements were published in the magazines surveyed. The number of advertisements per year increased between 1995 and 1998. Supplements of particular interest to older adults (such as antioxidants, calcium, garlic, ginkgo biloba, joint health products, liquid oral supplements, and multivitamins) were among the most frequently advertised products. Although magazines popular among older readers contain extensive information about dietary supplements, these publications cannot be relied upon to provide readers with all of the information that they need in order to use supplements safely.