Barley cultivar, kernel composition, and processing affect the glycemic index

Insights into Grain Milling and Fractionation Practices for Improved Food Sustainability with Emphasis on Wheat and Peas

Cereal grains and pulses are staple foods worldwide, being the primary supply of energy, protein, and fiber in human diets. The current practice of milling and fractionation yields large quantities of byproducts and waste, which are largely downgraded and end up as animal feeds or fertilizers. This adversely affects food security and the environment, and definitely implies an urgent need for a sustainable grain processing system to rectify the current issues, particularly the management of waste and excessive use of water and energy. The current review intends to discuss the limitations and flaws of the existing practice of grain milling and fractionation, along with potential solutions to make it more sustainable, with an emphasis on wheat and peas as common fractionation crops. This review discusses a proposed sustainable grain processing system for the fractionation of wheat or peas into flour, protein, starch, and value-added components. The proposed system is a hybrid model that combines dry and wet fractionation processes in conjunction with the implementation of three principles, namely, integration, recycling, and upcycling, to improve component separation efficiency and value addition and minimize grain milling waste. The three principles are critical in making grain processing more efficient in terms of the management of waste and resources. Overall, this review provides potential solutions for how to make the grain processing system more sustainable.

Acute Effects of Dietary Fiber in Starchy Foods on Glycemic and Insulinemic Responses: A Systematic Review of Randomized Controlled Crossover Trials

Dietary fiber (DF) consumption has been associated with improved glycemic control in epidemiological and long-term interventional studies. However, its acute effects are not yet clear. This systematic review aims to elucidate the postprandial effects of DF in starchy products on glycemia and insulinemia. An electronic search of databases was conducted, and forty-one records met the inclusion criteria and underwent a risk-of-bias assessment. It was shown that soluble DF does not clearly affect glycemia in individuals with normal weight, while resistant starch may be more effective in flattening glycemic responses. Concerning insulinemia, both soluble DF and resistant starch have mixed results, with either favorable or no effects. Data on insoluble DF and glucose metabolism are scarce. The same mixed results for glycemia can be seen in healthy volunteers with overweight/obesity, while resistant starch seems to improve insulinemic responses. Finally, more studies need to examine the acute effects of DF in starchy foods on glucose metabolism and insulin secretion in individuals facing glucose abnormalities. Additionally, more studies are needed to prove whether ingesting high-fiber carbohydrate-containing products per se can result in blunted glycemic and insulinemic responses and which DF type and amount are more effective.

Effect of processing on the solubility and molecular size of oat β-glucan and consequences for starch digestibility of oat-fortified noodles

White wheat salted noodles containing oats have a slower digestion rate those without oats, with potential health benefits. Oat β-glucan may play an important role in this. Effects of sheeting and shearing during noodle-making and subsequent cooking on β-glucan concentration, solubility, molecular size and starch digestibility were investigated. The levels of β-glucan were reduced by 16% after cooking, due to the loss of β-glucan into the cooking water. Both the noodle-making process and cooking increased the solubility of β-glucan but did not change its average molecular size. Digestion profiles show that β-glucan in wholemeal oat flour did not change starch digestion rates compared with isolated starch, but reduced the starch digestion rate of oat-fortified wheat noodles compared to the control (wheat noodles). Confocal laser scanning microscopy suggests that interaction between β-glucan and protein contributes to the starch-protein matrix and changes noodle microstructure, and thus alters their digestibility.

Whole grain intake, compared to refined grain, improves postprandial glycemia and insulinemia: a systematic review and meta-analysis of randomized controlled trials

Whole grain (WG) intake has been associated with reduced risk of type 2 diabetes (T2D) and may protect against T2D by lowering postprandial glycemia and insulinemia and improving insulin sensitivity. The objective of this systematic review and meta-analysis was to evaluate the effect of WG intake, compared to refined grain (RG) intake, on postprandial glycemia and insulinemia and markers of glycemic control and insulin resistance in randomized controlled trials (RCTs) in adults. A search of PubMed and Scopus yielded 80 relevant RCTs. Compared to RG, WG intake significantly reduced postprandial glycemia (SMD: -0.30; 95% CI: -0.43, -0.18; P < 0.001), insulinemia (SMD: -0.23; 95% CI: -0.35, -0.10; P < 0.001) and glycated hemoglobin (HbA1c) (SMD: -0.21; 95% CI: -0.37, -0.06; P = 0.007). There was no effect of WG on fasting glucose, fasting insulin, or homeostatic model assessment of insulin resistance (HOMA-IR). These results suggest WG foods improve short-term glycemia and insulinemia, which may improve HbA1c, a marker of long-term glycemic control. This may partially explain the inverse association between WG intake and risk of T2D, but further investigations are needed to understand if short-term reductions in glycemia translate to longer term benefits in reducing the risk of T2D.Systematic Review Registration: PROSPERO Registration CRD42020180069.

The effect of oat β-glucan on postprandial blood glucose and insulin responses: a systematic review and meta-analysis

To determine the effect of oat β‑glucan (OBG) on acute glucose and insulin responses and identify significant effect modifiers we searched the MEDLINE, EMBASE, and Cochrane databases through October 27, 2020 for acute, crossover, controlled feeding trials investigating the effect of adding OBG (concentrate or oat-bran) to carbohydrate-containing test-meals compared to comparable or different carbohydrate-matched control-meals in humans regardless of health status. The primary outcome was glucose incremental area-under-the-curve (iAUC). Secondary outcomes were insulin iAUC, and glucose and insulin incremental peak-rise (iPeak). Two reviewers extracted the data and assessed risk-of-bias and certainty-of-evidence (GRADE). Data were pooled using generic inverse-variance with random-effects model and expressed as ratio-of-means with [95% CIs]. We included 103 trial comparisons (N = 538). OBG reduced glucose iAUC and iPeak by 23% (0.77 [0.74, 0.81]) and 28% (0.72 [0.64, 0.76]) and insulin by 22% (0.78 [0.72, 0.85]) and 24% (0.76 [0.65, 0.88]), respectively. Dose, molecular-weight, and comparator were significant effect modifiers of glucose iAUC and iPeak. Significant linear dose-response relationships were observed for all outcomes. OBG molecular-weight >300 kg/mol significantly reduced glucose iAUC and iPeak, whereas molecular-weight <300 kg/mol did not. Reductions in glucose iAUC (27 vs 20%, p = 0.03) and iPeak (39 vs 25%, p < 0.01) were significantly larger with different vs comparable control-meals. Outcomes were similar in participants with and without diabetes. All outcomes had high certainty-of-evidence. In conclusion, current evidence indicates that adding OBG to carbohydrate-containing meals reduces glycaemic and insulinaemic responses. However, the magnitude of glucose reduction depends on OBG dose, molecular-weight, and the comparator.

Glycemic Index Values of Pasta Products: An Overview

Durum wheat pasta is considered a low-glycemic index (GI) food. In recent years, the interest in developing enriched pasta has increased. Since both the formulation and processing technologies may affect the GI, this study aimed to investigate the GI values of pasta products (pp) reported in the literature until 2020. GI values of pp analyzed following the ISO guidelines were included in this survey. A total of 95 pp were identified and, according to their formulation, classified into 10 categories (n, mean GI): category n 1: 100% refined wheat (35, 55); category n 2: 100% whole wheat (6, 52); category n 3: other cereal-based products (8, 52); category n 4: containing egg (5, 52); category n 5: gluten free (11, 60); category n 6: containing legumes (9, 46); category n 7: noodles and vermicelli (9, 56); category n 8: containing vegetable or algae (6, 51); category n 9: containing other ingredients (5, 37); category n 10: stuffed (1, 58). Overall, pasta is confirmed to be a medium–low-GI food, even if a high variability among or within each category emerged. The formulation of enriched pp able to elicit a controlled glycemic response could represent a strategy to improve the nutritional value of pasta.

High β-Glucan Barley Supplementation Improves Glucose Tolerance by Increasing GLP-1 Secretion in Diet-Induced Obesity Mice

The aim of this study was to investigate the underlying mechanism for the improvement of glucose tolerance following intake of high β-glucan barley (HGB) in terms of intestinal metabolism. C57BL/6J male mice were fed a fatty diet supplemented with HGB corresponding to 5% of dietary fiber for 83 days. An oral glucose tolerance test was performed at the end of the experimental period. The concentration of short-chain fatty acids (SCFAs) in the cecum was analyzed by GC–MS (gas chromatography–mass spectrometry). The mRNA expression levels related to L cell function in the ileum were measured by real-time PCR. Glucagon-like peptide-1 (GLP-1) levels in the portal vein and cecal content were assessed by enzyme-linked immunosorbent assay. GLP-1-producing L cells of the ileum were quantified by immunohistochemistry. HGB intake improved glucose tolerance and increased the cecal levels of SCFAs, acetate, and propionate. The number of GLP-1-positive L cells in the HGB group was significantly higher than in the control group. GLP-1 levels in the portal vein and cecal GLP-1 pool size in the HGB group were significantly higher than the control group. In conclusion, we report improved glucose tolerance after HGB intake induced by an increase in L cell number and subsequent rise in GLP-1 secretion.

An Insight into Unani Hypoglycemic Drugs and Their Mechanism of Action

BACKGROUND

Diabetes mellitus type-II is a major health problem characterized by hypoinsulinemia and insulin resistance, leading to hyperglycemia and its complications. In Unani medicine, it is known as ziyābetus. Several drugs are prescribed in Unani medicine as single and compound formulations for this disease. Most of these drugs have been studied on scientific parameters and shown significant activity in reducing the symptoms and complications of diabetes.

OBJECTIVES

Critical evaluation of Unani medicines for treating diabetes patients have been conducted. The aim of the study is to provide complete information on this subject with the action of the mechanism so that proper treatment should be done with prospective research.

METHODS

Unani literature was reviewed extensively via various search engines for the herbs, shrubs used for diabetes treatment. Ten drugs were selected for the present review.

RESULTS AND CONCLUSION

There is convincing evidence to suggest that the selected drugs have promising actions against diabetes and its complications. In addition, none of the studies has reported any adverse effects with the drugs. Also, there is evidence to suggest that the method of usage described in Unani medicine may reduce or eliminate adverse events, if any. Further, there is a great need to do more research on making medicine more effective. Besides, the review article is useful for treating patients effectively by advancing the research.

Consumption of a meal containing refined barley flour bread is associated with a lower postprandial blood glucose concentration after a second meal compared with one containing refined wheat flour bread in healthy Japanese: A randomized control trial

OBJECTIVE

Foods reducing postprandial hyperglycemia could suppress the postprandial blood glucose response after the next meal (a "second-meal" effect). However, the second-meal effect of refined barley flour bread has not been evaluated. The aim of this study is to determine whether consumption of refined barley flour bread reduces postprandial glucose concentrations after this and the subsequent meal.

METHODS

We enrolled 23 healthy young Japanese adults and conducted a randomized, double-blind, placebo-controlled, crossover study. The participants consumed refined barley flour bread containing 2.5 g β-glucan or refined wheat flour bread in a first meal, then consumed three rice balls as a second meal. Their postprandial blood glucose concentrations were measured 0, 15, 30, 45, 60, 90, and 120 min after both meals. Participants with fasting glucose concentrations above the diagnostic threshold for diabetes were excluded.

RESULTS

The blood glucose concentration 30 min after the first meal was significantly lower (P < 0.05) if refined barley flour bread (7.1 ± 1.0 mmol/L) rather than refined wheat flour bread (7.7 ± 1.2 mmol/L) was consumed. Significantly lower glucose concentrations after the second meal measured at 60 (P < 0.05, barley flour bread: 8.7 ± 1.8 mmol/L, wheat flour bread: 9.3 ± 1.7 mmol/L) and 90 min (P < 0.01, barley flour bread: 7.8 ± 1.4 mmol/L, wheat flour bread: 8.8 ± 2.1 mmol/L) were lower in participants who had previously consumed the refined barley flour bread.

CONCLUSIONS

Consumption of bread made with refined barley flour lowers postprandial blood glucose concentration after this and a subsequent meal compared with the consumption of refined wheat flour bread in healthy young Japanese adults.

High-Amylose Wheat Lowers the Postprandial Glycemic Response to Bread in Healthy Adults: A Randomized Controlled Crossover Trial

BACKGROUND

Conventional wheat-based foods contain high concentrations of readily digestible starch that commonly give these foods a high postprandial glycemic response and may contribute to the development of type 2 diabetes and cardiovascular disease.

OBJECTIVES

The aim of this study was to determine if bread made from high-amylose wheat (HAW) and enriched in resistant starch dampens postprandial glycemia compared with bread made from conventional low-amylose wheat (LAW).

METHODS

This single-center, randomized, double-blinded, crossover controlled study involved 7 consecutive weekly visits. On separate mornings, 20 healthy nondiabetic men and women (mean age 30 ± 3 y; body mass index 23 ± 0.7 kg/m2) consumed a glucose beverage or 4 different breads (each 121 g); LAW-R (refined), LAW-W (wholemeal), HAW-R, or HAW-W. The starch contents of the LAW and HAW breads were 24% and 74% amylose, respectively. Venous blood samples were collected at regular intervals before and for 3 h after the breakfast meal to measure plasma glucose, insulin, ghrelin, and incretin hormone concentrations, and the incremental area under the curve (AUC) was calculated (mmol/L × 3 h). Satiety and cravings were also measured at 30-min intervals during the postprandial period.

RESULTS

HAW breads had a glycemic response (AUC) that was 39% less than that achieved with conventional wheat breads (HAW 39 ± 5 mmol/L × 3 h; LAW 64 ± 5 mmol/L × 3 h; P < 0.0001). Insulinemic and incretin responses were 24-30% less for HAW breads than for LAW breads (P < 0.05). Processing of the flour (wholemeal or refined) did not affect the glycemic, insulinemic, or incretin response. The HAW breads did not influence plasma ghrelin, or subjective measures of satiety or cravings during the postprandial period.

CONCLUSIONS

Replacing LAW with HAW flour may be an effective strategy for lowering postprandial glycemic and insulinemic responses to bread in healthy men and women, but further research is warranted. This trial was registered at the Australian and New Zealand Clinical Trials Registry as ACTRN12616001289404.

Effect of processing on phenolic acids composition and radical scavenging capacity of barley pasta

Phenolic acids, total phenolics content and DPPH radical scavenging capacity in raw ingredients, fresh and dried spaghetti, and in uncooked and cooked spaghetti were evaluated and compared with semolina spaghetti as a reference. Ferulic acid was the major phenolic acid found in the free and bound phenolic extracts in all the investigated pasta samples. The addition of barley flour into pasta at incorporation levels of 30, 50 and 100% increased phenolic acids and total phenolics content. Pasta processing did not significantly affect the total phenolics content and free radical scavenging capacity, but a significant reduction in total phenolic acids measured by HPLC was found. Drying process differently affected individual phenolic compounds in the free and bound fractions, and thus, the total phenolic acids content. Free vanillic, caffeic and p-coumaric acids did not significantly change, while p-hydroxybenzoic and ferulic acids of the free extracts showed higher values compared to the corresponding fresh pasta. Cooking did not greatly affect total phenolic acids, more leading to conserving free and bound phenolic compounds.

Phenolics from Whole Grain Oat Products as Modifiers of Starch Digestion and Intestinal Glucose Transport

Four oat varieties and three product forms (porridge, cereal, and snack bar) were assessed to determine the impact of oat phenolics on starch digestibility and intestinal glucose transport. α-Amylase activity was enhanced by 20 GAE μM (gallic acid equivalent) of phenolics extracted from oat (96.7-118%, p < 0.05), while it was modestly inhibited at 500 GAE μM (83.0-95.4%). Maltose hydrolysis was reduced (49.6-82.4%, p < 0.05), albeit with high IC₅₀ values (500-940 GAE μM). Free and bound oat phenolic extracts dose-dependently attenuated transport of d-glucose-1,2,3,4,5,6,6-d₇ by Caco-2 monolayers over 60 min. Oat foods were then subjected to a coupled in vitro digestion/Caco-2 intestinal cell model to determine relevance to whole food systems. Digestive release of glucose was similar among products; however, glucose transport was significantly reduced from digesta of GMI 423 porridge and puffed cereal by 34% ± 12% and 20% ± 10% (p < 0.05) at 60 min. Results suggest phenolics might be a factor modulating glycemic response of oat products.

Wholegrain barley β-glucan fermentation does not improve glucose tolerance in rats fed a high-fat diet

Fermentation of oat and barley β-glucans is believed to mediate in part their metabolic health benefits, but the exact mechanisms remain unclear. In this study, we sought to test the hypothesis that barley β-glucan fermentation raises circulating incretin hormone levels and improves glucose control, independent of other grain components. Male Sprague-Dawley rats (n = 30) were fed a high-fat diet for 6 weeks and then randomly allocated to 1 of 3 dietary treatments for 2 weeks. The low- (LBG, 0% β-glucan) and high- (HBG, 3% β-glucan) β-glucan diets contained 25% wholegrain barley and similar levels of insoluble dietary fiber, available carbohydrate, and energy. A low-fiber diet (basal) was included for comparison. Immediately prior to the dietary intervention, gastric emptying rate (using the (13)C-octanoic breath test) and postprandial glycemic response of each diet were determined. At the end of the study, circulating gut hormone levels were determined; and a glucose tolerance test was performed. The rats were then killed, and indices of cecal fermentation were assessed. Diet did not affect live weight; however, the HBG diet, compared to basal and LBG, reduced food intake, tended to slow gastric emptying, increased cecal digesta mass and individual and total short-chain fatty acid pools, and lowered digesta pH. In contrast, circulating levels of glucose, insulin, gastric-inhibitory peptide, and glucagon-like peptide-1, and glucose tolerance were unaffected by diet. In conclusion, wholegrain barley β-glucan suppressed feed intake and increased cecal fermentation but did not improve postprandial glucose control or insulin sensitivity.

Quantification of amylose, amylopectin, and β-glucan in search for genes controlling the three major quality traits in barley by genome-wide association studies

Genome-wide association studies (GWAS) for amylose, amylopectin and β-glucan concentration in a collection of 254 European spring barley varieties allowed to identify 20, 17, and 21 single nucleotide polymorphic (SNP) markers, respectively, associated with these important grain quality traits. Negative correlations between the content of amylose and β-glucan (R = -0.62, P < 0.01) and amylopectin and β-glucan (R = -0.487, P < 0.01) were found in this large collection of spring barley varieties. Besides HvCslF6, amo1 and AGPL2, sex6, and waxy were identified among the major genes responsible for β-glucan, amylose and amylopectin content, respectively. Several minor genes like HvGSL4, HvGSL3, and HvCesA6, PWD were also detected by GWAS for the first time. Furthermore, the gene encoding β-fructofuranosidase, located on the short arm of chromosome 7H at 1.49 cM, and SRF6, encoding "leucine-rich repeat receptor kinase protein" on chromosome 2 H, are proposed to be new candidate genes for amylopectin formation in barley endosperm. Several of the associated SNPs on chromosome 1, 5, 6, and 7H mapped to overlapping regions containing QTLs and genes controlling the three grain constituents. In particular chromosomes 5 and 7H carry many QTLs controlling barley grain quality. Amylose, amylopectin and β-glucan were interacted among each other through a metabolic network connected by UDP showing pleiotropic effects. Taken together, these results showed that cereal quality traits related each other and regulated through an interaction network, the identified major genes and genetic regions for amylose, amylopectin and β-glucan is a helpful for further research on carbohydrates and barley breeding.

Review of human studies investigating the post-prandial blood-glucose lowering ability of oat and barley food products

Oat and barley foods have been shown to reduce human glycaemic response, compared to similar wheat foods or a glucose control. The strength of the evidence supporting the hypothesis that the soluble fibre, mixed linkage β-glucan, reduces glycaemic response was evaluated. A search of the literature was conducted to find clinical trials with acute glycaemic response as an end point using oat or barley products. Of the 76 human studies identified, 34 met the inclusion and exclusion criteria. Dose response and ratio of β-glucan to available carbohydrate as predictors of glycaemic response were assessed. Meals provided 0.3-12.1 g oat or barley β-glucan, and reduced glycaemic response by an average of 48 ± 33 mmol · min/l compared to a suitable control. Regression analysis on 119 treatments indicated that change in glycaemic response (expressed as incremental area under the post-prandial blood-glucose curve) was greater for intact grains than for processed foods. For processed foods, glycaemic response was more strongly related to the β-glucan dose alone (r(2)=0.48, P<0.0001) than to the ratio of β-glucan to the available carbohydrate (r(2)=0.25, P<0.0001). For processed foods containing 4 g of β-glucan, the linear model predicted a decrease in glycaemic response of 27 ± 3 mmol · min/l, and 76% of treatments significantly reduced glycaemic response. Thus, intact grains as well as a variety of processed oat and barley foods containing at least 4 g of β-glucan and 30-80 g available carbohydrate can significantly reduce post-prandial blood glucose.

The effect of dietary fibre on reducing the glycaemic index of bread

As bread is the most relevant source of available carbohydrates in the diet and as lowering dietary glycaemic index (GI) is considered favourable to health, many studies have been carried out in order to decrease the GI of bread. The most relevant strategy that has been applied so far is the addition of fibre-rich flours or pure dietary fibre. However, the effectiveness of dietary fibre in bread in reducing the GI is controversial. The purpose of the present review was to discuss critically the effects obtained by adding different kinds of fibre to bread in order to modulate its glycaemic response. The studies were selected because they analysed in vivo whether or not dietary fibre, naturally present or added during bread making, could improve the glucose response. The reviewed literature suggests that the presence of intact structures not accessible to human amylases, as well as a reduced pH that may delay gastric emptying or create a barrier to starch digestion, seems to be more effective than dietary fibre per se in improving glucose metabolism, irrespective of the type of cereal. Moreover, the incorporation of technologically extracted cereal fibre fractions, the addition of fractions from legumes or of specifically developed viscous or non-viscous fibres also constitute effective strategies. However, when fibres or wholemeal is included in bread making to affect the glycaemic response, the manufacturing protocol needs to reconsider several technological parameters in order to obtain high-quality and consumer-acceptable breads.