Effects of hydrothermal treatment and low-temperature storage of whole wheat grains on in vitro starch hydrolysis and flour properties.

This study evaluated the effect of hydrothermal treatment of whole wheat grains at 100 °C followed by cold-storage (4 °C/ 7 days) on the resulting grains, flakes, and flour characteristics. The extent of starch hydrolysis after oral-gastro-small intestinal digestion in vitro was significantly lower (p < 0.05) in intact grains, flakes, and flours from the cold-stored grains, 35.73 ± 0.34%, 49.92 ± 0.18% and, 89.04 ± 1.51%, than their non-cold-stored counterparts, 44.86 ± 0.24%, 58.73 ± 0.90% and, 95.96 ± 0.43%, respectively. Scanning electron micrographs, pasting properties, water retention capacities and relative crystallinity of the resulting flours revealed enhanced degree of gelatinisation with the treatment temperature; however, cold-storage of treated grains resulted in change in these properties due to the retrogradation of the starch. This study indicates that hydrothermal pre-treatment of grains followed by low-temperature storage for prolonged periods might help to reduce starch digestibility of wheat grains and their resulting products, and could be an effective strategy in developing reduced glycaemic impact grain products.

Effects of Xanthan Gum, Lambda-Carrageenan and Psyllium Husk on the Physical Characteristics and Glycaemic Potency of White Bread.

White bread contains a high proportion of easily digestible starch, which contributes to an undesirable rapid increase in blood glucose concentration. This study investigated the effects of nonstarch polysaccharides (NSP) -xanthan gum, lambda-carrageenan and psyllium husk on the physical functionality and glycaemic potency of white bread. The amount of water for each formulation was adjusted based on DoughLab set at a target torque value of ~500 FU for sufficient dough development. Adding NSP generally resulted in significantly increased loaf volumes and decreased hardness. The glycaemic potency (glycaemic glucose equivalents (GGE) g) of bread was found to be reduced with the addition of NSP at all levels (1, 3 and 5% w/w based on flour weight). Increasing the concentration of xanthan gum and lambda-carrageenan did not show any further decrease in the glycaemic potency. Notably, adding 5% w/w psyllium husk significantly reduced the glycaemic potency from ~49 GGE/100 g in the reference bread to 32 GGE/100 g. The reduction in the glycaemic potency was attributed to viscosity effects (for xanthan) and starch-NSP interactions (for psyllium husk). Overall, the 5% w/w psyllium husk bread sample was most promising in terms of both physical characteristics and its effect on in vitro glucose release.

Glycaemic potency reduction by coarse grain structure in breads is largely eliminated during normal ingestion.

The hypothesis that coarse grain particles in breads reduce glycaemic response only if the particles remain intact during ingestion was tested. Three breads were formulated: (1) White bread (WB - reference), (2) 75 % of kibbled purple wheat in 25 % white bread matrix (PB) and (3) a 1:1 mixture of 37·5 % kibbled soya beans and 37·5 % of kibble purple wheat in 25 % white bread matrix (SPB). Each bread was ingested in three forms: unchewed (U), as customarily consumed (C) and homogenised (H). Twelve participants ingested 40 g available carbohydrate portions of each bread in each form, with post-prandial blood glucose measured over 120 min. Glycaemic responses to WB were the same regardless of its form when ingested. Unchewed PB had significantly less glycaemic effect than WB, whereas the C and H forms were similar to WB. Based on a glycaemic index (GI) of 70 for WB, the GI values for the C, U and H breads, respectively, were WB: 70·0, 70 and 70, PB: 75, 42 and 61, SPB: 57, 48 and 55 (%) (Least significant difference = 17·43, P < 0·05, bold numbers significantly different from WB). The similar glycaemic response to the H and C forms of the breads, and their difference from the U form, showed that the glycaemia-moderating effect of grain structure on starch digestion was lost during customary ingestion of bread. We conclude that the kibbled-grain structure may not effectively retard starch digestion in breads as normally consumed because it is largely eliminated by ingestive processes including chewing.

Meat analogs: Protein restructuring during thermomechanical processing.

Increasing awareness of inefficient meat production and its future impact on global food security has led the food industry to look for a sustainable approach. Meat products have superior sensorial perception, because of their molecular composition and fibrous structure. Current understanding in the science of food structuring has enabled the utilization of alternative or nonmeat protein ingredients to create novel structured matrices that could resemble the textural functionality of real meat. The physicochemical and structural changes that occur in concentrated protein systems during thermomechanical processing lead to the creation of a fibrous or layered meat-like texture. Phase transitions in concentrated protein systems during protein-protein, protein-polysaccharide, protein-lipid, and protein-water interactions significantly influence the texture and the overall sensory quality of meat analogs. This review summarizes the roles of raw materials (moisture, protein type and concentration, lipids, polysaccharides, and air) and processing parameters (temperature, pH, and shear) in modulating the behavior of the protein phase during the restructuring process (structure-function-process relationship). The big challenge for the food industry is to manufacture concept-based (such as beef-like, chicken-like, etc.) meat analogs with controlled structural attributes. This information will be useful in developing superior meat analogs that fulfill consumer expectations when replacing meat in their diet.

Effects of Maillard-reacted beef bone hydrolysate on the physicochemical properties of extruded meat alternatives.

Meat analogues are made from plant proteins using high-moisture extrusion processing, to have the same textural and structural properties as meat. However, meat analogues exhibit very weak aroma and are almost tasteless, which has resulted in limited market success. Maillard-reacted beef bone hydrolysate (MRP) provides important sensory aspects of heat-treated food products, by contributing to their appearance, texture, flavor, and aroma. Therefore, MRP added at different concentrations with the plant proteins before extrusion may produce meat alternatives with high aroma and taste quality while maintaining fibrous structure. This study investigated the effects of MRP at different concentrations (0%, 10%, 20%, 30%, and 40% wet weight) with plant proteins on the physicochemical properties of extruded meat alternatives. The textural, microstructural, chemical, and sensory properties of meat alternatives were studied, where meat alternatives consisting of 40% MRP showed the lowest degree of texturization and observed with multiple segmented layers accompanied with some fibrous microstructure. Results from protein solubility analysis suggested that a large proportion of aggregated proteins was associated with hydrogen bonds. Although the key force in the formation of fibrous structure in meat alternatives was disulphide bonds. Meat alternatives containing 20% MRP obtained highest sensory scores for appearance, meaty aroma, meaty taste, and overall acceptability. Overall results showed that the addition of MRP to produce meat alternatives changed the textural, structural, and sensory properties significantly. PRACTICAL APPLICATION: Maillard-reacted beef bone hydrolysate added into meat analogues to form meat alternatives with high aroma and taste quality while maintaining fibrous structure. The work demonstrated an opportunity for greater returns to the meat industry and the potential of hybrid products with less meat content.

Changes in the physicochemical properties and flavour compounds of beef bone hydrolysates after Maillard reaction.

This study investigated the changes in physicochemical properties and volatile compounds of beef bone hydrolysates during heat treatment as a result of the Maillard reaction (MR). Five beef bone hydrolysates obtained from single (P-Protamex®, B-bromelain, and F-Flavourzyme®) and simultaneous (P + F and B + F) enzymatic hydrolysis treatments were combined with ribose in aqueous solutions and heated at 113 °C to produce Maillard reaction products (MRPs). Total free amino acids decreased after heat treatment indicating the occurrence of the MR. MRPs showed a decrease in pH and an increase in browning intensity as the degree of hydrolysis of hydrolysates increased. The volatiles compounds generated during heat treatment were evaluated using gas chromatography-mass spectrometry (GC-MS) with headspace solid phase microextraction (SPME) sampling. A total of 40 volatile compounds were identified in all MRPs and their concentration were found to increase with increasing degree of hydrolysis. Pyrazines were the most abundant class of compounds produced as a result of the MR. F-MRP showed the highest peak area intensity for 17 volatile compounds in single hydrolysis treatment followed by heat treatment. There was also no significant difference in those major volatile compounds between F-MRP and P + F-MRP or B + F-MRP from simultaneous hydrolysis treatment after heating. Hence, the use of Flavourzyme® alone to increase the flavour intensity of beef bone extract is recommended. Overall results indicated that enzymatic hydrolysis and MR could be used to modify the flavour characters of beef bone extract.

The interactions between wheat starch and Mesona chinensis polysaccharide: A study using solid-state NMR.

The interaction between wheat starch and Mesona chinensis polysaccharide (MCP) was found to change the molecular mobility of the water and carbohydrate populations in starch-MCP gels, when measured using proton and carbon nuclear magnetic resonance relaxation methods. The starch and MCP mobilities appeared similar at a micron scale. However, at a distance of less than 5 nm could they be detected as having separate mobility states, indicating close interaction between the starch and MCP. The carbon-6 of the starch glucan monomer was observed to have the largest mobility change in the presence of MCP. Two mobility populations of carbon-6 were observed, possibly corresponding to the carbon-6 in the linear chains of both amylose and amylopectin, and another to the carbon-6 involved in the branching of amylopectin. The change in the mobility of one of the carbon-6 populations indicates an increase in molecular freedom of movement in the presence of MCP.

The effect of gel structure on the in vitro digestibility of wheat starch-Mesona chinensis polysaccharide gels.

The digestibility of wheat starch gels in the presence of Mesona chinensis polysaccharide (MCP) was studied. MCP was found to be the most effective polysaccharide in reducing wheat starch digestion in comparison to starch gels of similar hardness containing xanthan, guar, locust bean gum (LBG) and agar. A 33% reduction in the digestibility of intact starch gels containing 5% w/w MCP (after 120 minutes of digestion) was observed and this was attributed to the strengthening of the gels in the presence of high concentration of the polysaccharide. In contrast, despite a reduction in the firmness of the gel when 2% w/w MCP was present, there was a 7% reduction in starch digestibility and hence, firmness was deduced to be not solely responsible for the digestibility of the gels. When these gels were macerated, starch digestibility was reduced regardless of the MCP concentration. Starch digestion in the macerated samples seemed to cease after 10 minutes with about 30% more starch remaining when 5% w/w MCP was present, suggesting that the amount of starch available for digestion was reduced in the presence of MCP. The reduced availability of starch for digestion was hypothesised to be due to starch-MCP interactions, which formed amylose-MCP complexes that are likely to be resistant to enzymatic digestion. Overall, this work shows the potential for MCP to be utilized as an ingredient to reduce the glycaemic index.

Predicting the viscosity of digesta from the physical characteristics of particle suspensions using existing rheological models.

The measurement of the viscosity of digesta is complicated by settling and compositional changes that accompany digestion. The current work determined whether the apparent and relative viscosities (ηa and ηr) of digesta could be accurately determined from the actual and maximum solid volume fractions (ϕ and ϕmax, respectively) using the Maron-Pierce equation. The rheological properties of digesta from the small intestine of six pigs were determined at a shear rate of 1 s-1 at 37°C. A series of suspensions of plant fibre in a Newtonian liquid (70% aqueous fructose) were made at viscosities similar to pig digesta by adjusting ϕ The relationships between the apparent and relative viscosities (ηa and ηr) and the plant fibre properties; aspect ratio (AR) and ϕ and ϕmax were then determined for digesta and the suspensions. The ARs for the digesta and plant fibre particles were determined using image analysis of scanning electron micrographs and ηa from rheometric flow curves at 37°C, ϕ from image analysis and gas pycnometry, and ϕmax from AR and suspension viscosity. The ηr of pig digesta and the test suspensions calculated using the Maron-Pierce equation were, with the exception of two outliers, in proportion with ηa determined using a rheometer, indicating that ηr could be successfully predicted from the Maron-Pierce equation.

Does viscosity or structure govern the rate at which starch granules are digested?

The rates of in vitro digestion of incompletely or fully gelatinised potato and corn starch were measured at 37 °C over 20 min in a rheometer fitted with cup and vane geometry at shear rates of 0.1, 1 and 10 s(-1). Shear rate did not influence the rate of starch digestion provided it was close to physiological levels. However, rates of digestion were significantly reduced when shear rates were below the physiological range (0.1 s(-1)) or when gelatinisation was incomplete. At physiological shear rates the relationship between starch digestion and viscosity was sigmoid in form and following a short initial slow phase a rapid decline in viscosity occurred as starch was digested and the structural integrity of the granules was lost. Conversely, when shear rate was reduced below physiological levels or gelatinisation was incomplete, digestion was hindered, granule integrity was maintained and the relationship between starch and viscosity became linear.

The effect of fibre and gelatinised starch type on amylolysis and apparent viscosity during in vitro digestion at a physiological shear rate.

An in vitro system was used to determine if the addition of insoluble or soluble fibre to aqueous suspensions of gelatinised starch affected the rate at which the starch was digested. Pre-gelatinised potato or corn starch suspensions were digested with porcine pancreatic amylase in the presence of either finely milled insoluble fibres from various sources or with guar gum. In vitro digestion was conducted at 37°C in a rheometer at a low and constant shear rate of 10s(-1) and the quantity of glucose released measured. The rates of starch digestion and suspension viscosity declined asymptotically and were unaffected by the addition of wheat fibre, but were considerably reduced by the addition of wood and AllBran(®) fibre and to a much greater extent (60%) by the addition of guar. The latter effect may be due to inhibition of amylase activity by non starch polysaccharide sequences.

The partitioning of water in aggregates of undigested and digested dietary particles.

The hydration of fibre particles derived from wheat and wood was quantified, before and after in vitro digestion, and compared with fibre particles from the colonic digesta of pigs and from human faeces. Total water and the extra- and intra-particulate water components were determined using a combination of centrifugation, drying, gas pycnometry and image analysis. The water of saturation (WS) of wood particles and AllBran® measured after in vitro digestion was up to double that of wheat fibres after in vitro digestion, and increased with particle size and loss of soluble material, but was not associated with the chemical composition of the fibres. Fibre that had undergone in vitro gastric digestion and that had been recovered from the colon or faeces, sequestered about 3% of the Ws into intra-particulate spaces, the remainder occupying extra-particulate spaces. The authors speculate that large quantities of fibre must be eaten to sequester toxins that locate into the intra-particulate space.

Carbohydrate composition, viscosity, solubility, and sensory acceptance of sweetpotato- and maize-based complementary foods.

BACKGROUND: Cereal-based complementary foods from non-malted ingredients form a relatively high viscous porridge. Therefore, excessive dilution, usually with water, is required to reduce the viscosity to be appropriate for infant feeding. The dilution invariably leads to energy and nutrient thinning, that is, the reduction of energy and nutrient densities. Carbohydrate is the major constituent of food that significantly influences viscosity when heated in water. OBJECTIVES: To compare the sweetpotato-based complementary foods (extrusion-cooked ComFa, roller-dried ComFa, and oven-toasted ComFa) and enriched Weanimix (maize-based formulation) regarding their 1) carbohydrate composition, 2) viscosity and water solubility index (WSI), and 3) sensory acceptance evaluated by sub-Sahara African women as model caregivers. METHODS: The level of simple sugars/carbohydrates was analysed by spectrophotometry, total dietary fibre by enzymatic-gravimetric method, and total carbohydrate and starch levels estimated by calculation. A Rapid Visco™ Analyser was used to measure viscosity. WSI was determined gravimetrically. A consumer sensory evaluation was used to evaluate the product acceptance of the roller-dried ComFa, oven-toasted ComFa, and enriched Weanimix. RESULTS: The sweetpotato-based complementary foods were, on average, significantly higher in maltose, sucrose, free glucose and fructose, and total dietary fibre, but they were markedly lower in starch content compared with the levels in the enriched Weanimix. Consequently, the sweetpotato-based complementary foods had relatively low apparent viscosity, and high WSI, than that of enriched Weanimix. The scores of sensory liking given by the caregivers were highest for the roller-dried ComFa, followed by the oven-toasted ComFa, and, finally, the enriched Weanimix. CONCLUSION: The sweetpotato-based formulations have significant advantages as complementary food due to the high level of endogenous sugars and low starch content that reduce the viscosity, increase the solubility, impart desirable sensory characteristics, and potentially avoid excessive energy and nutrient thinning.

The Development of Expanded Snack Product Made from Pumpkin Flour-Corn Grits: Effect of Extrusion Conditions and Formulations on Physical Characteristics and Microstructure.

Pumpkin products confer natural sweetness, desirable flavours and ß-carotene, a vitamin A precursor when added as ingredients to extruded snacks. Therefore, a potential use for dried pumpkin flour is as an ingredient in ready-to-eat (RTE) snack foods. Growth in this market has driven food manufacturers to produce a variety of new high value snack foods incorporating diverse ingredients to enhance the appearance and nutritional properties of these foods. Ready-to-eat snacks were made by extruding corn grits with 5%, 10%, 15% and 20% of pumpkin flour. Snacks made from 100% corn grits were used as control products for this work. The effect of formulation and screw speeds of 250 rpm and 350 rpm on torque and specific mechanical energy (SME, kWh/kg), physical characteristics (expansion ratio, bulk density, true density and hardness) and the microstructure of the snacks were studied. Increasing the screw speed resulted in a decrease of torque for all formulations. When pumpkin flour was added the specific mechanical energy (SME) decreased by approximately 45%. Increasing the percentage of pumpkin flour at the higher screw speed resulted in a harder texture for the extruded products. X-ray tomography of pumpkin flour-corn grit snacks showed that increased levels of pumpkin flour decreased both the bubble area and bubble size. However, no significant differences (p > 0.05) in bubble wall thickness were measured. By understanding the conditions during extrusion, desirable nutritional characteristics can be incorporated while maximizing expansion to make a product with low bulk density, a fine bubble structure and acceptable organoleptic properties.

Sweet potato-based complementary food for infants in low-income countries.

BACKGROUND: In low-income countries, most infants are given cereal-based complementary foods prepared at the household level. Such foods are high in phytate, which limits the bioavailability of nutrients, including iron, calcium, zinc, and in some cases proteins, which are crucial to the development of infants. OBJECTIVE: To compare the levels of macronutrients (protein, fat, and carbohydrate), gross energy, and fructose in sweet potato-based (denoted ComFa) formulations and enriched Weanimix (dehulled maize-dehulled soybean-groundnut blend with fish powder and sugar incorporated). The phytate level was also compared. METHODS: A composite flour of sweet potato and soybeans containing fish powder was processed by oven toasting as a home-based complementary food. Another blend containing skim milk powder was processed by extrusion cooking or roller drying as industrial-based prototypes. The macronutrient composition and the levels of fructose and phytate were determined in the ComFa formulations and enriched Weanimix. RESULTS: The ComFa formulations and the enriched Weanimix met the stipulated values in the Codex Alimentarius Commission standard for energy (400 kcal/100 g), protein (15 g/100 g), and fat (10 to 25 g/100 g) for complementary food, with the exception of the industrial-based ComFa formulations, which satisfied 83% of the protein requirement (15 g/100 g). The ComFa formulations had a quarter of the phytate level of enriched Weanimix. The fructose level in the sweet potato-based complementary foods was more than five times that in enriched Weanimix. CONCLUSIONS: The sweet potato-based formulations were superior to enriched Weanimix as complementary foods for infants in low-income countries, based on the fructose (which makes the porridge naturally sweet) and phytate levels.

Sweetpotato-based complementary food would be less inhibitory on mineral absorption than a maize-based infant food assessed by compositional analysis.

The availability of micronutrients from sweetpotato-based complementary foods (CFs): oven-toasted and roller-dried ComFa, and from a maize-based infant food, enriched Weanimix, was compared using phytate/mineral molar ratios, polyphenols and ß-carotene levels. The phytate/calcium, iron and zinc molar ratios of approximately 0.17, 1 and 15 predict better absorption of calcium, iron and zinc respectively. Generally, the sweetpotato-based CFs had at least half the phytate/mineral ratios of enriched Weanimix. The phytate/iron ratio in both the sweetpotato- and the maize-based CFs was greater than 1. Only the ComFa formulations had phytate/zinc ratio lower than 15. The level of polyphenol (iron inhibitor) was similar for the formulations. Only the sweetpotato-based CFs contained measurable levels of ß-carotene, a possible iron enhancer. The lower phytate/mineral ratios and the ß-carotene level of the sweetpotato-based CFs suggest that calcium, iron and zinc absorption could be better from them than from the maize-based infant food.

A household-level sweet potato-based infant food to complement vitamin A supplementation initiatives.

Vitamin A deficiency (VAD) prevalence in Sub-Saharan Africa is high in spite of vitamin A supplementation programmes among children in most countries. Plant-based complementary foods remain the key source of nutrients in addition to breast milk for infants in lower income countries. Cereal-legume blends are superior in protein and energy densities compared with maize, millet or sorghum-only porridge. However, unfortified cereal-legume and cereal-only porridges are low in vitamin A. A household-level sweet potato-based infant food, rich in vitamin A, has been developed to complement vitamin A supplementation initiatives in Sub-Saharan Africa. A composite flour containing sweet potato, soybean, soybean oil and fishmeal was processed as complementary food by oven toasting (denoted oven-toasted ComFa). The oven-toasted ComFa and enriched Weanimix (processed from dehulled maize, dehulled soybean, groundnut and fishmeal) were assessed for suitability as complementary food based on the nutrient composition using specifications in the Codex Standard (CS) as a reference. The sweet potato-based formulation and enriched Weanimix met the energy, protein, fructose and fat specifications but barely met the amino acid score as indicated in the CS. However, only the oven-toasted ComFa met the calcium and almost half the vitamin A levels as specified in the CS. Oven-toasted ComFa was slightly lower in energy, protein and fat by a difference not greater than 4.0% but was higher by more than 100% in fructose and vitamin A levels. Therefore, the sweet potato-based complementary food is likely to support vitamin A supplementation initiatives in low-income countries better than the cereal-based formulation.

Lycopene bioaccessibility and starch digestibility for extruded snacks enriched with tomato derivatives.

To improve the nutritional value of energy-dense extruded snacks, corn grits were replaced with tomato paste and/or tomato skin powder at ratios of 5, 10, and 20% and extruded to make expanded snack foodlike products. Using a model digestion system, lycopene bioaccessibility and uptake from the snacks into Caco-2 cells were determined. The digestibility of the starch, the main nutrient component of the snacks, was also investigated. While extrusion cooking reduced the lycopene content of the snacks, the proportion of bioaccessible lycopene increased. Lycopene uptake by the Caco-2 cells from the extruded snacks exceeded that of the control in which the lycopene was not extruded, by 5% (p < 0.05). The digestibility of starch in the snacks varied depending on the type of tomato derivative and its concentration. Optimization of the extrusion cooking process and the ingredients can yield functional extruded snack products that contain bioavailable lycopene.

Use of quantitative real-time PCR to estimate maize endogenous DNA degradation after cooking and extrusion or in food products.

Polymerase chain reaction (PCR) is being used increasingly to detect DNA sequences for food quality testing for GM content, microbial contamination, and ingredient content. However, food processing often results in DNA degradation and therefore may affect the suitability of PCR or even DNA sequence detection for food quality assurance. This paper describes a novel approach using quantitative real-time PCR (qPCR) to estimate the extent of DNA degradation. With use of two maize endogenous nuclear sequences, sets of four qPCR assays were developed to amplify target sequences ranging from<100 bp to approximately 1000 bp. The maize nuclear sequences used encode chloroplastic glyceraldehyde-3-phosphate dehydrogenase and cell wall invertase. The utility of the qPCR approach for quantifying the effective concentration of maize DNA that is needed to amplify variable length DNA sequences was demonstrated using samples of maize cornmeal cooked in water for variable times, extrusion products developed using different barrel temperature and torque settings, and a range of food products from supermarket shelves. Results showed that maize DNA was substantially degraded by a number of processing procedures, including cooking for 5 min or more, extrusion at high temperatures and/or high torque settings, and in most processed foods from supermarket shelves. Processing also reduced the effective concentration of DNA sequences capable of directing amplification of the <100 bp assays as well, particularly after popping of popping corn or extrusion at a combination of high temperature and torque settings. The approach for quantifying DNA degradation described in this paper may also be of use in disciplines where understanding the extent of DNA degradation is important, such as in environmental, forensic, or historical samples.