Effect of inclusion of soluble and insoluble fibres into extruded breakfast cereal products made with reverse screw configuration

Five dietary fibre rich ingredients were used at 5%, 10% and 15% replacement levels in a white flour cereal base to produce an extruded cereal product. The inclusion of the dietary fibres into the flour bases had no significant effect on the expansion ratio of the products. However, the bulk density of the extruded products increased with inulin addition. The pasting properties of the raw flour and fibre base as well as the extruded products were altered with the incorporation of dietary fibre, with guar gum enriched products showing elevated peak and final viscosity readings. This appeared to be related to moisture manipulation and hence the regulation of gelatinisation. In vitro starch hydrolysis of the raw bases and the extruded samples illustrated that the extrusion process significantly increased the availability of carbohydrates for digestion. Additionally, the inclusion of dietary fibres in the raw bases significantly reduced the rate and extent of carbohydrate hydrolysis of the extruded products. As such the addition of dietary fibres to extruded products reduced the amount of readily digestible starch components of breakfast products, and increased the amount of slowly digestible carbohydrates.     

Effects of dietary fibre and soybean oil on the digestion of extruded and roller-dried maize starch

The effects of soybean dietary fibre (SDF), microcrystalline cellulose (MCC), konjac glucomannan (KGM), soluble soybean polysaccharide (SSPS) and soybean oil (SO) on in vitro digestion of extruded maize starch (EMS) and roller-dried maize starch (RDMS) samples were investigated. Adding MCC, particularly in high doses, induced slow digestion in EMS and RDMS samples, but not after adding SDF. KGM and SSPS addition reduced starch hydrolysis of RDMS but did not have a significant effect on EMS, whereas SO addition reduced starch hydrolysis of EMS but had no effect on RDMS. Principal component analysis demonstrated that the addition of MCC, SO, KGM (0.51%), and SSPS (0.51%) to EMS and KGM (0.51%) to RDMS were the best choices to slow the hydrolysis of starch, compared with that of other additives. These findings provide useful information on the selection of exogenous additives in the development of low glycaemic index products for maize starch.     

Impact of Guar and Wheat Bran on the Physical and Nutritional Quality of Extruded Breakfast Cereals

Two non‐starch polysaccharides, guar gum and wheat bran, were used at 15% replacement level in a cereal base to produce an extruded breakfast cereal product from both wholemeal and high‐ratio wheat flour mixes. The inclusion of the non‐starch polysaccharides into the flour bases had no significant effect on the expansion ratio of the products. However, the product density and bulk density of the extruded products increased with guar gum and wheat bran addition. The pasting properties of the raw flour and polysaccharide base as well as the extruded products were altered with the incorporation of polysaccharides, with guar gum‐enriched products showing elevated peak and final viscosity readings. This appeared to be related to moisture manipulation and hence the regulation of gelatinisation. In vitro starch hydrolysis of the raw bases and the extruded samples illustrated that the extrusion process significantly increased the availability of carbohydrates for digestion. Additionally, the inclusion of non‐starch polysaccharides in the raw bases significantly reduced the rate and extent of carbohydrate hydrolysis. This potentially glycaemic reducing action was also evident in the extruded products where the incorporation of guar gum at 15% yielded a reduction of starch hydrolysis of 36% in the wholemeal base and 32% in the high‐ratio white wheat flour base.     

A Study of Native and Chemically Modified Potato Starch. Part I: Analysis and Enzymic Availability in vitro

The availability of native and chemically modified potato starch to α-amylase was studied in vitro (distarch phosphate, acetylated distarch phosphate and hydroxypropyl distarch phosphate). Enzyme availability was also related to results obtained during analysis of starch and dietary fibre, The degree of substitution (DS) was determined by ¹HNMR spectroscopy and the substitution sites were evaluated by gasliquid chromatography and mass spectrometry. Substitution with acetyl- and hydroxypropyl groups reduced the availability of drum-dried starch derivatives to α-amylase. In contrast, the susceptibility of raw starch increased after introduction of hydroxypropyl groups. Cross-linking with phosphate only had but minor effects on enzyme availability. The recovery of starch during analysis depended on (a) degree of hydrolysis to glucose (b) whether or not the substitution groups were removed. The lowest yields were observed when analyzing substituted derivatives after boiling and enzymic hydrolysis (60-70%). Enzymically unavailable starch was not recovered as dietary fibre when using an enzymic gravimetric assay.     

Measurement of Health-Promoting Properties in Fruit Dietary Fibres: Antioxidant Capacity,Fermentability and Glucose Retardation Index

The aim of this work was to compare some in vitro health-promoting properties in fruit dietary fibre (antioxidant activity, fermentability and glucose retardation index), which could be useful to predict their physiological effects better than physico-chemical analyses. These properties were evaluated in mango and lemon peel fibre. Mango fibre was better than lemon fibre because of the highest values of antioxidant activity (67·6%) and glucose retardation index (21·5%). Antioxidant activity is proposed as a new health-promoting property associated to dietary fibre.     

Twin-Screw Extrusion as a Continuous Pretreatment Process for the Enzymatic Hydrolysis of Cassava

Twin-screw extrusion was evaluated as a pretreatment for the enzymatic hydrolysis of cassava starch to glucose. Extrusion temperature and pH affected the key parameters associated with the enzymatic hydrolysis of starch such as the water solubility index, the water absorption index, the apparent viscosity, and the susceptibility of the extruded starch to glucoamylase. The glucose concentration of extruded and enzyme-hydrolyzed cassava starch was approximately 5% greater than that of acid-liquefied and enzyme-hydrolyzed cassava starch.     

螺杆挤压对马铃薯淀粉消化性及血糖指数的影响

目的研究螺杆挤压对马铃薯淀粉消化特性的影响。方法马铃薯淀粉经过螺杆挤压后(过程中淀粉未膨化),采用酶重量法测定挤压后抗性淀粉的含量变化情况,并通过模拟体外消化和动物实验评价挤压后淀粉的消化性能和餐后血糖上升速率。结果螺杆挤压后马铃薯淀粉中抗性淀粉的含量增加了1.08%,酶解时间为0~1.5 h时,马铃薯淀粉快速消化淀粉的含量减少,酶解时间为1.5~6.5 h时,抗性淀粉和慢消化淀粉的含量增加。挤压后的马铃薯淀粉在一定程度上可以降低小鼠的餐后血糖指数。结论螺杆挤压技术可以提高抗性淀粉和慢消化淀粉的含量,减缓餐后血糖上升速率,为马铃薯食品的深度开发提供一定的参考。     

Rheological and Thermal Properties of Extruded Mixtures of Rice Starch and Isolated Soy Protein

Many foods gain new mechanical, thermal and textural properties after being processed due to interactions between carbohydrates and proteins. This effect is characteristic for each foodstuff. The properties of extruded isolated soy protein (ISP) and rice starch were studied considering the following extrusion variables: starch proportion with respect to ISP (0–100%), pH (3–9), moisture content (20–30%) and temperature (140–180ºC). The following characteristics were measured: Water absorption index (WAI), water solubility index (WSI), glass transition temperature (T_g), melting temperature (T_m), viscosity at 90ºC and at 50ºC, storage (G′), loss modulus (G′′) and tan δ. The results indicate that the extruded starch exhibits higher WAI and WSI values than untreated starch. For extruded ISP these values are much lower than for untreated ISP. Extrudates with higher starch proportion had higher T_g and T_m values; pH has a significant effect (p<0.05), at pH 3 higher T_g values were observed, and at pH 9 higher values of T_m. The highest viscosities at 90ºC and 50ºC were observed for extrudates with a higher starch proportion and pH 9. Extruded mixtures showed a more elastic than viscous behavior and an extruded 1:1 blend of starch‐ISP exhibited the behavior of a viscous liquid.     

Impact of dietary fibre‐enriched ready‐to‐eat extruded snacks on the postprandial glycaemic response of non‐diabetic patients

Food intervention is a financially sensible way for prevention and treatment of diabetes. Extruded snack foods are considered high glycaemic products. Our previous research illustrated that postprandial glycaemic responses to snacks are manipulated by altering dietary fibre and starch contents. The current research assessed the effect of psyllium and oat bran on postprandial glycaemia and in vitro digestibility. Addition of psyllium fibre to extruded snack products significantly reduced both the in vitro and in vivo glycaemic responses of products compared to a control snack product recipe. Oat bran inclusion reduced in vitro starch digestibility but not in vivo glycaemic response. The inclusion of oat bran into the snack products appeared to extend the glycaemic response of individuals compared to the control snack, suggesting a possibility of prolonging glucose release and potentially affecting satiety responses. The positive effect in attenuating glucose response means that psyllium fibre could be a target for inclusion by the snack food industry to effectively manipulate postprandial glucose response of individuals.     

Resistant starch from differently processed rice and ragi (finger millet)

 Resistant starch (RS) formed during parboiling, expanding, popping, flaking, roller drying, extrusion cooking, malting and autoclaving of rice and ragi was determined. The processing conditions were chosen to represent the limits that are being used commercially. RS formation was more pronounced in autoclaving and a drastic increase (∼fivefold) in its content was observed during repeated autoclaving (heating and cooling) was observed. Though processed ragi samples contained more nitrogen, protein and dietary fibre, the RS content was very low compared to rice. Hot paste viscosity studies showed the extruded and malted samples to have low peak and set-back viscosities. Determination of the percentage of starch gelatinization revealed that powdered samples showed 100% gelatinization at higher temperatures whereas malted and extruded samples showed the same at low temperatures.     

Structural and functional characteristics of dietary fibre in beans,lentils, peas and chickpeas

To better understand the role that dietary fibre plays in the health benefits of pulses, the cell wall polysaccharides of pulses were characterized. To allow comparison between this data and nutritional studies, cooked chickpeas, lentils, beans and peas were used rather than raw seeds. Insoluble fibre, soluble fibre, resistant starch and oligosaccharide fractions were isolated using digestive enzymes at 37 °C. Prebiotic galacto-oligosaccharides, including raffinose, stachyose and verbascose made up between 3.5 and 6.9% of the cooked pulses (dry weight basis). Pulse fibre is pectin rich, with most being found in the soluble fibre fraction. The soluble fibre fraction is a diverse mixture of polysaccharides of varying sizes and solutions of soluble fibre exhibit a range of viscosities depending on the pulse type. The sugars which make up the insoluble fibre fraction suggest a large cellulose component. Microscopic examination of cooked whole pulses showed that a large fraction of the starch was partially gelatinized and contained within intact cell walls whereas boiled flour pastes had few ungelatinized granules. After simulated upper-gut digestion, some starch remained inaccessible to digestive enzymes. Cell walls of pulses modulate starch gelatinization and reduce enzymatic hydrolysis, which may account for the low glycemic response attributed to pulses.     

In vitro digestibility,pasting, and structural properties of starches from different cereals

Starches isolated from seven different cereals were evaluated for their composition, physicochemical, in vitro digestibility, structural, morphological, and pasting properties. The in vitro starch digestion rate and estimated glycemic index (GI) of cereal starches were evaluated along with the impact of cooking on starch digestion. The cooking of starch slurries increased the rapidly digestible starch content from a range of 34.7–54.4% to a range of 60.5–78.5%. On the basis of hydrolysis index, the GI ranged from 83.6 to 91.8 and after cooking it increased from 95.1 to 98.6 for different cereal starches. Both the swelling power and solubility showed an increasing trend with rising temperature. Paste clarity of starches negatively correlated with fat content. The amylose content of various starches ranged from 17.7 to 24.7% and was negatively correlated to crystalline index (r = -0.975, p ≤ 0.05). XRD pattern revealed A-type pattern of crystalline starch, where crystallinity index ranging between 28.2 to 44.9%. FTIR revealed slight differences among chemical bonding of starches from different cereals. From scanning electron micrograph observations, wheat and barley starch granules proved smoother as compared to other cereal granules. Barley contained the highest (27.5 µm) and rice had the lowest (10.2 µm) size starch granules. The pasting properties were significantly (p ≤ 0.05) different for different cereal starches. Peak, breakdown, and final viscosities were the highest for maize starch (1725, 384, and 2112 mPa.s, respectively), whereas rice and oats exhibited the highest trough and setback viscosities (1420 and 954 mPa.s, respectively).     

The Effect of Extruded Orange Pulp on Enzymatic Hydrolysis of Starch and Glucose Retardation Index

Orange pulp was extruded using a Brabender laboratory single screw extruder (20:1 L/D). The independent variables evaluated were barrel temperature (83, 100, 125, 150, and 167 °C), feed moisture content (22, 25, 30, 35, and 38/100 g), and screw speed (126, 140, 160, 180, and 194 rpm). The apparent density and apparent viscosity values of the extruded orange pulp increased during extrusion, while the oil absorption index decreased, in comparison with the values for raw orange pulp. In vitro studies showed that at the end of the incubation time, 90.68% of the starch was hydrolyzed in the control sample, while only 77.82% and 69.40% pulp of the starch experienced hydrolysis in the presence of raw fiber and extruded orange pulp, respectively. Extruded orange pulp showed a higher glucose retradation index (16.04–25.92%) after 30 min of dialysis and after 60 min (11.66% and 18.33%) than raw orange pulp (8.33%). These results indicated that glucose could be bound with compacted fiber matrices and inhibit alpha-amylase activity. These mechanisms may create a definite benefit by decreasing the rate of glucose absorption and eventually lowering the concentration of postprandial serum glucose. The potential hypoglycemic effects of extruded orange pulp suggest that orange pulp is a good and abundant dietary fiber resource that could be of great benefit in controlling glucose levels in the blood. It could also be added to high-fiber foods as a low-calorie bulk ingredient to reduce the calorie level.     

Utilization of milk proteins and cereal starches to obtain co-extrudates

Extrusion of the cereal mixtures with 25% addition of milk proteins induced several changes in the chemical and physico-chemical properties of starch. Coefficient of expansion was close to the coefficient of natural cereal flours, but the extrudates were characterized by higher water absorption. Starch was only slightly dextrinized, but it contained more nitrogen compounds and mineral salts, and less free lipids. Solubility and swelling power of the extrudates did not change in a way characteristic for cereal starch and flours. Attention should be given to higher content of dietary fibre, pointing to the formation of the starch-lipids and the starch-protein complexes, less susceptible to enzymatic hydrolysis used. Hence, it can be stated that the latter increase was apparent only. It can be said that a mixture of cereal starch and milk proteins can be used to modify quality of the extruded products of increased protein content. More attention should be devoted to biochemical characteristics of the protein added, as this largely determines quality of the extruded starch-protein products.     

Milk lipid in vitro digestibility in wheat,corn and rice starch hydrogels

Starch-based hydrogels or nanoemulsions have been used to regulate lipid digestibility. However, there is a paucity of reports on how starch gels affect milk lipid in vitro digestion. This study compared the pancreatic-lipase-catalysed digestibility of milk lipids in two matrices: milk fat dispersion and milk fat-loaded starch gels. Optical microscopy analysis illustrated that lipid droplets were distributed evenly in starch gels. The peak viscosities of lipid-containing starch gels were higher than those of samples without filled-lipids, whereas final viscosities were reduced with the addition of lipid. Free fatty acid release measurement showed that milk fat embedded in starch gels were two to three times more digestible than dispersed milk fat globules in aqueous phase, as confirmed by a multistep hydrolysis reaction model. This study offers a feasible way to manipulate milk lipid digestibility by stabilisation with starch gels.     

Studies on the properties of citrate derivatives of cassava (Manihot esculenta Crantz) starch synthesized by microwave technique

Cassava starch citrates with degree of substitution (DS) ranging from 0.005 to 0.063 were synthesized by the microwave‐assisted reaction of cassava starch with citric acid. A response surface small composite design was used to study the effect of different reaction conditions, viz. time, temperature and reagent concentration. All these variables significantly affected the substitution level in the modified starches. The DS increased with increase in the time of reaction and temperature. However, reagent concentration had a negative effect on the DS. The modified starches showed higher viscosity with lower breakdown, lower setback and higher final viscosities in comparison to native starch. Differential scanning calorimetry showed that the modified starches exhibited a decrease in gelatinization temperatures, T_o, T_p, T_e, in comparison to native starch. However, the heat of gelatinization was not significantly affected. The citrate derivatives exhibited reduced swelling volume and enhanced water binding capacities. They were found to be less susceptible to enzyme hydrolysis than native starch. Copyright © 2007 Society of Chemical Industry     

Processing and cooking effects on chemical,nutritional and functional properties of pasta obtained from selected emmer genotypes

BACKGROUND: Emmer wheat (T. turgidum ssp. dicoccum Schrank) is an old Mediterranean crop grown for centuries and progressively replaced with durum wheat. Although most of its supposed nutritional properties have not yet been scientifically proven, emmer seems to be appreciated for its content of dietary fibre, resistant starch (RS) and antioxidant compounds. The aim of this work was to evaluate the profiles of dietary fibre, starch and antioxidant compounds in raw materials and in semolina of 13 selected emmer lines and their parents (a durum wheat cultivar and an old T. turgidum dicoccum population). Moreover, the cooking effect on functional properties and total antioxidant capacity (TAC) of pasta derived from emmer lines and the in vivo effect of pasta on postprandial glucose response were determined. RESULTS: Processing and cooking affected the dietary fibre content of pasta: the insoluble dietary fibre content was increased, while a slight loss of soluble dietary fibre was observed. Cooking also resulted in a noteworthy increase in amylose and RS content. The antioxidant compounds (i.e., tocols and carotenoids) as well as TAC decreased dramatically after cooking. Pasta obtained with an emmer line significantly lowered the glycaemic index, strengthening the concept of pasta product as a source of functional components in the habitual diet. CONCLUSIONS: The results showed that emmer semolina is suitable for the preparation of pasta with good organoleptic quality and represents a source of RS and fibre, but processing and cooking negatively affected the amount of antioxidant compounds detected in the wholemeal. Copyright © 2008 Society of Chemical Industry     

SDS-Sulfite Increases Enzymatic Hydrolysis of Native Sorghum Starches

The sodium dodecyl sulfate (SDS) starch isolation procedure is often used to remove efficiently the surrounding and surface protein of starch granules in order to obtain a pure starch sample. In this study the changes in enzymatic hydrolysis of sorghum starch granules due to SDS-sulfite solution treatment were investigated. As SDS-sulfite solution soak time increased, enzymatic hydrolysis rate increased and the Michaelis-Menten pattern of enzymatic reaction did not change. The degree of this effect differed among starches from three sorghum cultivars. The effect of SDS-sulfite solution treatment on enzymatic hydrolysis became negligible after the treated starch samples were partially hydrolyzed. The adsorption of α-amylase onto the starch granules also increased with SDS-sulfite solution treatment and was highly correlated with hydrolysis rate. The different effects of SDS-sulfite solution on enzymatic hydrolysis of the three sorghum starches were related to the properties of the amorphous regions in starch granules.     

Rheological behaviour of β-glucan preparations from oat products

The cereal dietary fibre β-glucan has outstanding functional and nutritional properties, because of its viscosity in aqueous systems and in the intestinal tract. The rheological behaviour of β-glucan (concentrations: 2% and 4%) isolated from extruded and autoclaved oat meal and from oat bran was evaluated using oscillatory and rheological measurements. In frequency sweep, the storage and loss moduli G′ and G″ of β-glucan preparations from extruded meal and from bran increased continuously with increasing frequency, showing a dominantly viscous behaviour. With increasing frequency, the elastic properties improved. β-Glucan from autoclaved meal also showed elastic behaviour. With the exception of β-glucan from autoclaved meal, G′ and G″ were not influenced by deformation in the amplitude sweep. Complex viscosities decreased with frequency (in all samples) and were independent of deformation (in extruded meal and bran). In shear experiments, β-glucan solutions were structurally viscous non-Newtonian solutions with rheostable behaviour. β-Glucan (2%) from bran had the highest and that from autoclaved meal had the lowest apparent and process viscosities. Fluid dynamic parameters may influence the flow, diffusion or transport behaviour of β-glucan during digestion processes in the small intestine, but the influence of the viscous behaviour is limited.     

可溶性膳食纤维对玉米淀粉体外消化的抑制作用

本文通过模拟人体胃肠道消化过程,研究四种可溶性膳食纤维(青稞β-葡聚糖(barley β-glucan,BBG)、黄原胶(xanthan gum,XG)、魔芋胶(konjac glucomannan,KGM)和罗望子胶(tamarind seed polysaccharide,TSP))对玉米淀粉消化的影响,并建立膳食纤维在胃肠道模拟体系下的表观黏度(60 s-1)与预测血糖指数(predicted glycemic index,pGI)之间的关系,探究可溶性膳食纤维降低餐后血糖响应的机理。结果表明,添加0.1%的BBG、XG、KGM和TSP对淀粉水解的抑制率分别达到11.59%、35.90%、30.54%和19.62%,并能将淀粉的pGI值分别降低12.05、45.54、38.90和15.00。并且,随着可溶性膳食纤维在胃肠道体系下的表观黏度的增大,pGI值呈下降趋势,并且当XG、KGM和TSP的表观黏度超过4 mPa·s后,pGI值的下降趋势愈加平缓。因此,可溶性膳食纤维能够抑制玉米淀粉的消化,并且其黏度是降低餐后血糖响应的重要因素。此研究将为可溶性膳食纤维在降血糖功能方面的应用奠定理论基础。