This study was designed to investigate the effects of dietary starch structure on muscle protein synthesis and gastrointestinal amino acid (AA) transport and metabolism of goats. Twenty-seven Xiangdong black female goats (average body weight = 9·00 ± 1·12 kg) were randomly assigned to three treatments, i.e., fed a T1 (normal maize 100 %, high amylose maize 0 %), T2 (normal maize 50 %, high amylose maize 50 %) and T3 (normal maize 0 %, high amylose maize 100 %) diet for 35 d. All AA in the ileal mucosa were decreased linearly as amylose:amylopectin increased in diets (P < 0·05). The plasma valine (linear, P = 0·03), leucine (linear, P = 0·04) and total AA content (linear, P = 0·03) increased linearly with the increase in the ratio of amylose in the diet. The relative mRNA levels of solute carrier family 38 member 1 (linear, P = 0·01), solute carrier family 3 member 2 (linear, P = 0·02) and solute carrier family 38 member 9 (linear, P = 0·02) in the ileum increased linearly with the increase in the ratio of amylose in the diet. With the increase in the ratio of amylose:amylopectin in the diet, the mRNA levels of acetyl-CoA dehydrogenase B (linear, P = 0·04), branched-chain amino acid transferase 1 (linear, P = 0·02) and branched-chain α-keto acid dehydrogenase complex B (linear, P = 0·01) in the ileum decreased linearly. Our results revealed that the protein abundances of phosphorylated mammalian target of rapamycin (p-mTOR) (P < 0·001), phosphorylated 4E-binding protein 1 (P < 0·001) and phosphorylated ribosomal protein S6 kinases 1 (P < 0·001) of T2 and T3 were significantly higher than that of T1. In general, a diet with a high amylose ratio could reduce the consumption of AA in the intestine, allowing more AA to enter the blood to maintain higher muscle protein synthesis through the mTOR pathway.

Aquafeeds for carnivorous species face a nutritional–technological conundrum: containing sufficient starch to meet specific manufacturing requirements for binding, extrusion and expansion, but ideally containing as little starch as possible owing to their limited ability to utilise carbohydrates. The present study evaluated the effects of dietary starch with different amylose to amylopectin ratios and resistant starch contents on growth performance, hepatic glycogen accumulation and glucose metabolism of an important cultured carnivorous finfish, largemouth bass (Micropterus salmoides). A common starch source (α-cassava starch (CS)) was tested as is or after being enzymatically de-branched at three different inclusion levels in diets for largemouth bass. Results showed that the increased dietary starch levels compromised performance and high dietary α-CS content led to obvious liver damage. However, the growth performances of fish fed the diets with de-branched starch (DS) were improved, and no manifest liver damages were observed even at the higher inclusion level. The increasing dietary starch contents significantly increased hepatic glycogen accumulation, but not when DS was used. High dietary starch content, without regard to starch sources, had no effect on the expression of glucose metabolism-related genes, except for down-regulation of insulin receptor expression. However, the use of dietary DS promoted the expression of genes involved in the insulin pathway and glycolysis. In conclusion, this study showed that the use of starch sources with a high amylose to amylopectin ratio and resistant starch in the feed for cultured carnivorous finfish could alleviate the hepatic glycogen deposition through regulating the insulin pathway and glycolysis.

Amylose-free (waxy) maize has been a vegetable (cooked ears) and staple food in Southeast Asia for centuries, resulting in hundreds of landraces (LRs) across the region. The recessive waxy allele induces soft grains with preferred cooking and flavour properties. We hypothesized that eating preferences resulted in the additional selection for different starch properties, reflected in altered starch granule morphology or amylopectin structure. A total of 41 LRs were available as starting material that had been used by different ethnic groups in Vietnam and Thailand. Unluckily, some LR were not pure waxy, but we successfully regained the original pure waxy status for most. Twenty LR were chosen for analysis of starch traits according to their purity. Four different waxy mutations were identified, including two unknown alleles. This is a strong proof for parallel independent selection of waxy maize in the region. Starch granule morphology and size were similar among all LRs. Gelatinization properties differed only between waxy and wild-type LR, and all waxy LR were comparable to a commercial waxy hybrid. The fine structure of waxy amylopectin had fewer short chains compared with that in wild-type. So far, the differences observed in starch properties are likely associated exclusively with the waxy trait. Despite the strong selection for amylose-free starch, there was no evidence for additional region wide selection for other special starch properties in our collection. In conclusion, all analyses did not encourage further targeted research on allelic variation of other starch metabolism genes for future use in the food and feed industry.

The aim of the present study was to determine if the consumption of barley tortillas varying in fibre and/or starch composition affected postprandial glucose, insulin, glucagon-like peptide-1 (GLP-1) or peptide YY concentrations. A double-blind, randomised, controlled trial was performed with twelve healthy adults. They each consumed one of five barley tortillas or a glucose drink on six individual visits separated by at least 1 week. Tortillas were made from 100 % barley flour blends using five different milling fractions to achieve the desired compositions. All treatments provided 50 g of available carbohydrate and were designed to make the following comparisons: (1) low-starch amylose (0 %) v. high-starch amylose (42 %) with similar β-glucan and insoluble fibre content; (2) low β-glucan (4·5 g) v. medium β-glucan (7·8 g) v. high β-glucan (11·6 g) with similar starch amylose and insoluble fibre content; and (3) low insoluble fibre (7·4 g) v. high insoluble fibre (19·6 g) with similar starch amylose and β-glucan content. Blood was collected at fasting and at multiple intervals until 180 min after the first bite/sip of the test product. Amylose and insoluble fibre content did not alter postprandial glucose and insulin, but high-β-glucan tortillas elicited a lower glucose and insulin response as compared to the low-β-glucan tortillas. The tortillas with high insoluble fibre had a higher AUC for GLP-1 as compared to the tortillas with low insoluble fibre, whereas amylose and β-glucan content had no effect. Results show that processing methods can be used to optimise barley foods to reduce postprandial blood glucose responses and factors that may influence satiety.

Starch is globally important as a source of food and, in addition, has a wide range of industrial applications. Much of this agriculturally produced starch is synthesized in developing seeds, where its biological function is to provide energy for seedling establishment. Storage starch in developing seeds is synthesized in heterotrophic plastids called amyloplasts and is distinct from the transient synthesis of starch in chloroplasts. This article reviews our current understanding of storage starch biosynthesis occurring in these organelles and discusses recent advances in research in this field. The review discusses starch structure and granule initiation, emerging ideas on the evolution of the pathway, the enzymes of starch synthesis, and the post-translational modification and regulation of key enzymes of amylopectin biosynthesis.

Postprandial glycaemic control is important in the prevention and therapy of type 2 diabetes and related diseases. Agents that may reduce postprandial glycaemia and/or insulinaemia, such as consumption of high-amylose foods, are considered beneficial; however, little is known about the dose–response relationship and the effects of cooking. The aim of the present study was to define the dose–response curve for postprandial glycaemic and insulinaemic excursions following meals of different amylose content and to compare the dose–response curves for meals containing cooked and uncooked starches. Following an overnight fast, rats ingested a test meal and blood was sampled over 2 h. The meal was given at 1.0 g carbohydrate/kg body weight, with an amylose content of 0, 270, 600 or 850 g/kg total starch. The area under the glucose curve did not differ under any condition investigated. For the uncooked-starch diets, area under the insulin curve was higher for the 0 g amylose/kg total starch meal than all other meals (P = 0·0001). For the cooked-starch diets, area under the insulin curve was higher in the O than the 600 and 850 g amylose/kg total starch groups (P < 0·01), but did not differ from the 270 amylose/kg total starch group. These results suggest that even a relatively small proportion of uncooked amylose (270 g/kg total starch) is sufficient to achieve a maximal attenuating effect on postprandial insulin concentrations as compared with 0 g amylose/kg total starch. Following cooking, however, a much higher proportion of amylose (≥ 600 g/kg total starch) is needed to achieve a similar effect.