Stability of starch-proanthocyanidin complexes to in-vitro amylase digestion after hydrothermal processing.

Proanthocyanidins (PA) form poorly digestible complexes with starch. The study examined amylase degradation mechanism and hydrothermal stability of starch-PA complexes. Sorghum-derived PA was complexed with wheat starch, reconstituted into flour (10% gluten added) and processed into crackers and pancakes. In vitro digestion profile of the complexes and products were characterized. The starch-PA complexes retained more (34-84%) fragments with degree of polymerization (DP) > 6,000 after 120 min digestion than controls (0-21%). Debranching further revealed higher retention of DP 11 - 30 chains in the digested starch-PA complexes than controls, suggesting amylopectin complexation contributed to reduced starch digestion. Starch-PA complexes retained reduced digestibility (50-56% higher resistant starch vs controls) in the cracker, but not pancake model. However, removing gluten from the pancake formulation restored the reduced digestibility of the starch-PA complexes. The starch-PA complexes are stable to hydrothermal processing, but can be disrupted by hydrophobic gluten proteins under excess moisture conditions.

Resistant starch formation through intrahelical V-complexes between polymeric proanthocyanidins and amylose.

Reducing starch digestibility can significantly benefit efforts to combat obesity and associated chronic diseases. Polymeric proanthocyanidins (PA) form complexes with starch via unknown mechanisms, resulting in dramatically decreased starch digestibility. We hypothesized that V-type complexes are involved in these interactions. Sorghum derived PA was complexed with amylose, amylopectin, and granular maize starches in regular and deuterated solvents, and structural properties and in vitro digestibility of the complexes investigated. Based on iodine binding, X-ray diffraction patterns, crystallinity, and thermal properties, we demonstrated, for the first time, that type II semi-crystalline V-complexes are formed between amylose and PA. Furthermore, suppression of H-bonding led to amorphous complexes, suggesting extensive H-bonding facilitate and/or stabilize the V-complexes. We speculate that the complexation involves inclusion of B-rings of the PA units into the amylose helical cavity. The V-complex formation significantly increased resistant starch in gelatinized normal starch and pure amylose (by 35-45%), indicating likely physiological benefits.

Qualitative assessment of 'highly digestible' protein mutation in hard endosperm sorghum and its functional properties.

Sorghum mutants with altered protein body structure have improved protein nutritional quality; however, practical methods to accurately track heritability of the trait are lacking. We evaluated suitability of the in vitro pepsin assay, and a new high-resolution field emission electron microscopy (FE-SEM) method to detect the mutation (HD) in hard-endosperm sorghum; and compared the physicochemical properties of experimental HD sorghums to wild type (LD) lines. FE-SEM reliably resolved sorghum protein body structure, allowing for qualitative classification of sorghum as HD or LD. The pepsin assay was less reliable, with significant variations across environments. Nevertheless, HD lines averaged higher protein digestibility (69.4% raw, 57.6% cooked) than LD lines (61.7% raw, 45.6% cooked). The HD lines also had better water solubility and starch pasting profiles than LD lines. FE-SEM, but not pepsin assay, reliably detects HD nutation in sorghum. The HD trait may improve food-use functionality of sorghum.

Polymeric tannins significantly alter properties and in vitro digestibility of partially gelatinized intact starch granule.

Excess calorie intake is a growing global problem. This study investigated effect of complexing partially gelatinized starch with condensed tannins on in vitro starch digestibility. Extracts from tannin and non-tannin sorghum, and cellulose control, were reacted with normal and waxy maize starch in 30% (30E) and 50% ethanol (50E) solutions at 70°C/20min. More tannins complexed with the 30E than 50E starches (mean 6.2 vs 3.5mg/g, respectively). In the 30E treatments, tannins significantly increased crystallinity, pasting temperature, peak viscosity, and slow digesting starch (from 100 to 274mg/g) in normal, but not waxy starch, suggesting intragranular cross-linking with amylose. Tannins doubled resistant starch (RS) to approx. 300mg/g in both starches. In 50E treatments, tannins made both maize starches behave like raw potato starch (>90% RS), suggesting granule surface interactions dominated. Non-tannin treatments generally behaved similar to cellulose. Condensed tannins could be used to favorably alter starch digestion profile.