Extraction, quantification and degree of polymerization of yacon (Smallanthus sonchifolia) fructans

Yacon tubers have been a distinguished alternative of fructans, drawing the attention of researchers and food industries. Since fructans are carbohydrate reserves storage can reduce their contents. Additionally, the type of extraction used can provide a higher yield of fructans. Therefore, it was necessary to study yacon storage and its influence on the extraction and quantification of fructans. Thus, the objective of this study was to evaluate three fructan extractions (water 75°C, water 95°C, ethanol 90°C) in yacon with 3 sizes (large, medium, small), stored for 20 days, at room temperature as well as to compare two quantification techniques. The three extractions can be used when fructans are quantified by high performance liquid chromatography (HPLC). For quantification by spectrometry, the best extraction method was ethanol at 90°C. Medium and small-sized tubers presented the highest contents of fructans that large tubers, and storage negatively influenced these contents. Fructan quantification by HPLC was higher than the spectrophotometric technique. All treatments showed a degree of polymerization in the range from 3 to 7, allowing numerous technological applications for fructans present in yacon.Key words: Fructooligosaccharides, storage, tuber size

Spatial Guilds in the Serengeti Food Web Revealed by a Bayesian Group Model

Food webs, networks of feeding relationships among organisms, provide fundamental insights into mechanisms that determine ecosystem stability and persistence. Despite long-standing interest in the compartmental structure of food webs, past network analyses of food webs have been constrained by a standard definition of compartments, or modules, that requires many links within compartments and few links between them. Empirical analyses have been further limited by low-resolution data for primary producers. In this paper, we present a Bayesian computational method for identifying group structure in food webs using a flexible definition of a group that can describe both functional roles and standard compartments. The Serengeti ecosystem provides an opportunity to examine structure in a newly compiled food web that includes species-level resolution among plants, allowing us to address whether groups in the food web correspond to tightly-connected compartments or functional groups, and whether network structure reflects spatial or trophic organization, or a combination of the two. We have compiled the major mammalian and plant components of the Serengeti food web from published literature, and we infer its group structure using our method. We find that network structure corresponds to spatially distinct plant groups coupled at higher trophic levels by groups of herbivores, which are in turn coupled by carnivore groups. Thus the group structure of the Serengeti web represents a mixture of trophic guild structure and spatial patterns, in contrast to the standard compartments typically identified in ecological networks. From data consisting only of nodes and links, the group structure that emerges supports recent ideas on spatial coupling and energy channels in ecosystems that have been proposed as important for persistence.Comment: 28 pages, 6 figures (+ 3 supporting), 2 tables (+ 4 supporting