An improved approach for evaluating the semicrystalline lamellae of starch granules by synchrotron SAXS

A fitting method combined with a linear correlation function was developed as an improved approach for the SAXS analysis of the semicrystalline lamellae of starch granules. Using a power-law function with two Gaussian plus Lorentz functions, the SAXS pattern was resolved into sub-patterns of the net lamellar peak and the power-law scattering plus scattering background (PL + B). The ratio of the net lamellar peak area (A) to the total scattering area (A) was proposed equal to the proportion of the lamellae within the starch granule (P). Along with this fitting method, we obtained a better profile of linear correlation function, with the elimination of the interference of non-lamellar amorphous starch (i.e., amorphous growth rings). Then, we could accurately calculate the lamellar parameters, e.g., P, the thicknesses of semicrystalline (d), crystalline (d) and amorphous (d) lamellae, and the volume fraction (φ) of crystalline lamellae within semicrystalline lamellae. Quantitative analysis revealed that P was positively correlated with the crystallinity (X) of starch. It was confirmed that the distribution of lamellar thickness was more important than the starch botanical origin in affecting the validity of the developed fitting method. We also proposed a criterion to test the validity of the proposed method. Specifically, the total SAXS pattern should be mostly tangent to the profile of PL + B at a high q tail (close to 0.2 Å)

A further understanding of the multi-scale supramolecular structure and digestion rate of waxy starch

This work concerns how the multi-scale supramolecular structure of starch relates to its digestion rate from a view of structural heterogeneity. The untreated granule starch displayed a dual-phase digestion pattern, ascribed to two digestible fractions within the heterogeneous multi-scale structure of starch, which had prominently different digestion rates. Not only amorphous starch but also part of molecular orders (crystallites with flaws) were digested at a same rate k1 at the first phase; densely-assembled starch including orders with fewer flaws was digested at a rather slow rate k2 (ca. 2/5 of k1) at the second phase. When alkali altered the heterogeneous supramolecular structure of starch, the digestion behaviors were also changed. The 0.1% (w/v) alkali solution slightly disrupted the starch multi-scale structure, which reduced the molecular orders, disrupted the lamellae, weakened the molecular organization within growth rings, and enlarged the granule pores. Then, part of resistant starch was transformed into slowly-digestible fraction with a digestion rate close to k2. In contrast, when stronger (0.5% w/v) alkali was used, the starch multi-scale structure was more apparently disrupted, causing even granule swelling. This structural change resulted in a triple-phase digestion with three different digestion rates. Moreover, especially with stronger alkali, along with the structural disruption, some orders with a higher thermal stability emerged and reduced the accessibility of starch molecules to the enzyme. In this case, the digestion rate decreased with the treatment time

Microwave Cooking Enriches the Nanoscale and Short/Long-Range Orders of the Resulting indica Rice Starch Undergoing Storage

The chain reorganization of cooked starch during storage plays an important role in the performance of starchy products such as rice foods. Here, different analytical techniques (such as small-angle X-ray scattering) were used to reveal how microwave cooking influences the chain assembly of cooked indica rice starch undergoing storage for 0, 24, or 48 h. While stored, more short-range double helices, long-range crystallites, and nanoscale orders emerged for the microwave-cooked starch than for its conventionally cooked counterpart. For instance, after storage for 24 h, the microwave-cooked starch contained 46.8% of double helices, while its conventionally cooked counterpart possessed 34.3% of double helices. This could be related to the fact that the microwave field caused high-frequency movements of polar groups such as hydroxyls, which strengthened the interactions between starch chains and water molecules and eventually their assembly into double helices, crystallites, and nanoscale orders. This work provides further insights into the chain reassembly of microwave-cooked starch undergoing storage, which is closely related to the quality attributes of starch-based products

Species in section Peltidea (aphthosa group) of the genus Peltigera remain cryptic after molecular phylogenetic revision

Closely related lichen-forming fungal species circumscribed using phenotypic traits (morphospecies) do not always align well with phylogenetic inferences based on molecular data. Using multilocus data obtained from a worldwide sampling, we inferred phylogenetic relationships among five currently accepted morphospecies of Peltigera section Peltidea (P. aphthosa group). Monophyletic circumscription of all currently recognized morphospecies (P. britannica, P. chionophila, P. frippii and P. malacea) except P. aphthosa, which contained P. britannica, was confirmed with high bootstrap support. Following their re-delimitation using bGMYC and Structurama, BPP validated 14 putative species including nine previously unrecognized potential species (five within P. malacea, five within P. aphthosa, and two within P. britannica). Because none of the undescribed potential species are corroborated morphologically, chemically, geographically or ecologically, we concluded that these monophyletic entities represent intraspecific phylogenetic structure, and, therefore, should not be recognized as new species. Cyanobionts associated with Peltidea mycobionts (51 individuals) represented 22 unique rbcLX haplotypes from five phylogroups in Clade II subclades 2 and 3. With rare exceptions, Nostoc taxa involved in trimembered and bimembered associations are phylogenetically closely related (subclade 2) or identical, suggesting a mostly shared cyanobiont pool with infrequent switches. Based on a broad geographical sampling, we confirm a high specificity of Nostoc subclade 2 with their mycobionts, including a mutualistically exclusive association between phylogroup III and specific lineages of P. malace

Squamarina (lichenised fungi) species described from China belong to at least three unrelated genera

Volume: 66Start Page: 135-15

Species delimitation at a global scale reveals high species richness with complex biogeography and patterns of symbiont association in Peltigera section Peltigera (lichenized Ascomycota: Lecanoromycetes)

This comprehensive phylogenetic revision of sections Peltigera and Retifoveatae of the cyanolichen genus Peltigera is based on DNA sequences from more than 500 specimens from five continents. We amplified five loci (nrITS, β-tubulin and three intergenic spacers part of colinear orthologous regions [COR]) for the mycobiont, and the rbcLX locus for the cyanobacterial partner Nostoc. Phylogenetic inferences (RAxML, BEAST) and species delimitation methods (bGMYC, bPTP, bPP) suggest the presence of 88 species in section Peltigera, including 50 species new to science, hence uncovering a surprisingly high proportion of previously unnoticed biodiversity. The hypervariable region in ITS1 (ITS1-HR) is a powerful marker to identify species within sections Peltigera and Retifoveatae. Most newly delimited species are restricted to a single biogeographic region, however, up to ten species have a nearly cosmopolitan distribution. The specificity of mycobionts in their association with Nostoc cyanobionts ranges from strict specialists (associate with only one Nostoc phylogroup) to broad generalists (up to eight Nostoc phylogroups uncovered), with widespread species recruiting a broader selection of Nostoc phylogroups than species with limited distributions. In contrast, species from the P. didactyla clade characterized by small thalli and asexual vegetative propagules (soredia) associate with fewer Nostoc phylogroups (i.e., are more specialized) despite their broad distributions, and show significantly higher rates of nucleotide substitutions

The importance of spatio-temporal photobiont patterns of association for comprehensive phylogenetic revisions and macroevolutionary studies of lichens: a worldwide case study of the genus Peltigera.

Within the framework of a worldwide revision of Peltigera, several thousand specimens were gath ered to attempt to sequence all main partners (i.e., Peltigera, nrITS, nrLSU, RPB1, EFT2.1, ß-tubulin, COR1b, COR3, COR16; Nostoc, rbcLX; and Coccomyxa, nrITS and rbcL). We succeeded to sequence the fungal and cyanobacterial partners for 1900 and 650 specimens, respectively. The difficulty to identify Peltigera species and to understand the observed phenotypic variation was due to a high number of cryptic species within phenotypically defined species. This study identified 900 unique fungal ITS haplotypes and increased the number of Peltigera species from 90 known species to > 170 species when using various species discovery and validation methods. Sixty Nostoc phylogroups were found in association with Peltigera. Patterns of Peltigera species and Nostoc phylogroup diversity, iogeographical distributions, and specificity towards their respective partners, greatly differ among Peltigera sections. The overarching trend is that nearly 85% of Peltigera species are specialized on one or two Nostoc phylogroups, whereas > 55% of Nostoc phylogroups associates with at least three Peltigera species. The number of species in sections Peltigera (~95 species) and Polydactylon (~55 species) was much higher than expected and Nostoc phylogroups can help delimit and identify Peltigera specie