Properties of Amaranth Flour With Functional Oat Products

Amaranth flour (Salvia hispanica L.), gluten free and rich in essential amino acids, was composited with oat functional products containing β-glucan known for lowering blood cholesterol and preventing heart disease. The objective of this research was to study the pasting and rheological properties of amaranth flour interacted with functional oat products using Rapid Visco Analyzer followed by an advanced rheometer. The initial peak viscosities of amaranth-Nutrim (oat bran hydrocolloids) and amaranth-OBC (oat bran concentrate) composites were increased with higher Nutrim and OBC contents. The final pasting viscosities of amaranth-OBC composites were increased significantly with higher OBC contents while amaranth-Nutrim composites showed colloidal gel properties similar to Nutrim. On other hand, amaranth interacted with oat bran concentrate displayed the highest rheological solid properties as elastic gels. Shear thinning properties were observed for all the interactions between amaranth flour and functional oat products. The improved water holding capacities were found for interacted compositions with Nutrim and oat bran concentrate compared to amaranth flour. These amaranth flour and oat products compositions demonstrated improved nutritional value and texture qualities for functional food applications.


Introduction
Amaranth (Salvia hispanica L.) is a plant that has been cultivated for about 8,000 years.Amaranth grains contain about thirty percent more protein than cereals like rice, sorghum and rye (Macvean & Pöll, 1997).Cooked amaranth grains contain a source of thiamine, niacin, riboflavin, and folate, and dietary minerals including calcium, iron, magnesium, phosphorus, zinc, copper, and manganese that are comparable to common grains such as wheat germ, oats and others (USDA Nutrient Database, 2014).Amaranth flour has an unusually rich source of the essential amino acid lysine that is low in other grains (Myers & Putnam, 1998).It also contains vitamin E in similar amounts to olive oil (USDA Nutrient Database, 2014).Amaranth also contains a promising source of protein for those who are gluten sensitive because its protein does not contain gluten unlike the protein found in grains such as wheat and rye (USDA Nutrient Database, 2014).Amaranth has a valuable nutrient content for gluten-free diets compared to buckwheat, corn, millet, wild rice, oats and quinoa (Gallagher et al., 2004).The interest in grain amaranth was revived in the 1970s since it has gluten-free palatability.In addition, amaranth seed oil may be of benefit for those with hypertension and cardiovascular disease.Moreover, regular consumption reduces blood pressure and cholesterol levels while improving antioxidant status and some immune parameters (Czerwiński et al., 2004;Martirosyan et al., 2007) via its content of plant stanols and squalene (Alegbejo, 2013).
Amaranth flour has been evaluated as an additive to wheat flour.The different levels of amaranth flour were mixed with the wheat flour and baking ingredients that were fermented, molded, pan-proved and baked.The loaf volume decreased with increasing amount of amaranth grain flour.There were significant differences in the use of 15% amaranth flour in evaluated sensory qualities (Ayo, 2001).
Oat products such as whole oat flour (WOF) and oat bran concentrate (OBC) contain β-glucan that has beneficial health effects on coronary heart disease prevention by reducing serum cholesterol and postprandial serum glucose levels (Klopfenstein, 1988).Oat products have the beneficial effect on gut health since oat grain fibre contributes to an increase in faecal bulk.Therefore, several oat hydrocolloids, including Nutrim, were developed from OBC using mechanical shearing and steam jet-cooking to increase the β-glucan content in oat products (Inglett, 2000;Inglett, 2011).In addition to β-glucans, oat phenolic and other antioxidant compounds also provide health benefits as demonstrated for oat and barley (Madhujith & Shahidi, 2007;Inglett et al., 2011;Inglett & Chen, 2012).Oat hydrocolloid products containing -glucan have numerous functional food applications to reduce fat content and calories in a variety of foods (Lee et al., 2004); control the rheology and texture of food products (Rosell et al., 2001); modify starch gelatinization and retrogradation (Rojas et al., 1999;Lee et al., 2005); and also provide freezing/thawing stability (Lee et al., 2002).It was reported that a 5% dispersion of Nutrim had the same consistency as coconut cream when used in several Thai desserts (Maneepun et al., 1998).In addition, fat in muffins and frozen desserts could be replaced with Nutrim, and the effect on their flavor and texture was evaluated (Warner & Inglett, 2006).A recent study showed that shortening in cakes could be substituted up to 40% of Nutrim without loss of cake quality (Lee et al., 2004).Rheological and physical evaluation of jet-cooked oat bran has been studied in low calorie cookies by replacing 20% of the shortening with oat β-glucan hydrocolloids (Lee & Inglett, 2006).The cookies containing C-Trim20, another oat hydrocolloid, exhibited reduced spreading characteristics and increased elastic properties compared with the control.The study suggested that the replacement should be limited to less than 50% of the substitute for butter and coconut cream in bakery products (Inglett et al., 2000).
Amaranth flour and oat products complement each other since amaranth grains are limited in some essential amino acids, such as leucine and threonine (Bressani et al., 1989;Kaufmann et al., 1990) that are abundant in oats (Pisarikova et al., 2006;University of Wisconsin & University of Minnesota, 2011).Also, the oat components appear to be helpful in improving physical properties such as water holding capacity and viscosity (Inglett et al., 2014) since its viscosity and cohesion are fairly low for food applications.Thus, Nutrim, OBC, and WOF were used in this study to produce unique composites containing -glucan in combination with amaranth's distinctive protein profile along with its gluten free properties.The objectives of this study were to provide useful information on the pasting and rheological properties of amaranth-oat composites for potential new functional food products with desirable texture and health benefits.

Preparation of Amaranth-Oat Composites
Organic Gluten free amaranth flour certified by international certification services Inc. was purchased from Dakota Prairie Organic Flour Co. Harvey, ND, USA.Oat bran concentrate (OBC) was supplied by Quaker Oats, Chicago, IL, USA (Lot 18608408).Nutrim (Lot 35503475N170) was provided by VDF FutureCeuticals (Momence, IL, USA).Nutrim was prepared by steam jet-cooking OBC, sieving, and drum-drying (Inglett, 2000).Organic whole oat flour colloidal fine (WOF) was provided by Grain Millers (Eugene, OR, USA).
Amaranth flour was mixed with corresponding oat product by a KitchenAid mixer (St Joseph, MI, USA) for 2 min.The mixtures were passed a 20 mesh sieve followed by additional mixing in a mixer for 1 min to obtain the desired composites.

Measurement of Water-Holding Capacity
The water-holding capacities (WHC) of the oat-amaranth samples were determined according to a previous procedure with minor modifications (Ade-Omowaye et al., 2003).Each sample (2 g) was mixed with 25 g of distilled water and vigorously mixed using a vortex for 1 min for a homogenous suspension and then held for 2 h, followed by centrifugation at 1,590 g for 10 min.Each treatment was replicated twice.Water-holding capacity was calculated by the difference of water added and decanted water of sample on dry basis.

Pasting Property Measurement
The pasting properties of samples were evaluated using a Rapid Visco Analyzer (RVA-4, Perten Scientific, Springfield, IL, USA).Each sample (2.24 g d.b.) was made up to a total weight of 28 g with distilled water in a RVA canister (80 g kg -1 solids, w/w).The viscosity of the suspensions was monitored during the following heating and cooling stages.Suspensions were equilibrated at 50 °C for 1 min, heated to 95 °C at a rate of 6.0 °C/min, maintained at 95 °C for 5 min, and cooled to 50 °C at rate of 6.0 °C/min, and held at 50 °C for 2 min.For all test measurements, a constant paddle rotating speed (160 rpm) was maintained throughout the entire analysis except for 920 rpm in the first 10 s to disperse sample.Each sample was analyzed in duplicate.The results were expressed in Rapid Visco Analyser units (RVU, 1 RVU = 12 centipoises).

Rheological Measurements
After samples from the RVA were cooled to 25 C and equilibrated, they were loaded on a rheometer (AR 2000, TA Instruments, New Castle, DE, USA) with a 4 cm diameter parallel stainless plate with 1 mm gap to the surface.The outer edge of the plate was sealed with a thin layer of mineral oil (Sigma Chemical Co., St Louis, MO, USA) to prevent dehydration during the test.All rheological measurements were carried out at 25 °C using a water circulation system within ± 0.1 C.A strain sweep experiment was conducted initially to determine the limits of linear viscoelasticity; then a frequency sweep test was carried out to obtain storage modulus (G') and loss modulus (G") at frequencies ranging from 0.1 to 10 rad s -1 .A strain of 0.5%, which was within the linear viscoelastic range, was used for the dynamic experiments.The steady shear viscosity of the paste was measured as a function of shear rates from 1 to 100 s -1 .The steady shear measurements apply varying steady shear deformation on sample material, with magnitude of each deformation depending on user-specified shear rates.All rheological measurements for samples were performed in duplicate.

Statistical Analysis
Data from replicated samples were analyzed by SAS software using analysis of variance with Duncan's multiple comparison adjustment to determine significant differences (P < 0.05) between treatments (SAS Institute, 1999).

Comparison of Amaranth Nutrition Contents With Oat, Wheat, Rice, and Corn
Amaranth is higher in minerals (calcium, iron, phosphorus, potassium), vitamins (riboflavin, niacin, folate, vitamin A, vitamin E), and total polyunsaturated fatty acid than oat, wheat, rice, and corn.It is notable that amaranth is the only one that contains vitamin C among the products in table 1.Also, Amaranth contains more protein (13.56 g /100 g) than any other gluten-free grain (USDA data base, 2014).This small ancient seed has endured the ages, as an important food source for early civilizations to its current resurgence as a highly nutritious gluten-free grain.The replacement of flour by 25% amaranth flour in gluten-free recipes could improve the nutritional value, the taste and texture of gluten free baked goods.On other hand, oat contains the highest protein, magnesium, zinc, thiamin, vitamin K, and total monounsaturated fatty acid among products in Table 1.Especially, vitamin K was not found in amaranth and rice.Vitamin K is a fat-soluble vitamin that the body stores in fat tissue and the liver.It is best known for its role in helping blood clot and bone health (University of Maryland Medical Center, 2013).Therefore, amaranth and oat will complement each other as a nutritious gluten free diet.

Water-Holding Capacity
The water-holding capacities (WHC) of the starting materials and their composites are shown in Table 2. Nutrim had the highest water-holding capacity (5993 g kg -1 ) among all the samples tested.Nutrim was produced by jet-cooking technology using thermal-shearing forces to promote molecular breakdown that probably contributed to increased water absorption (Inglett, 2000;Lee & Inglett, 2006).Overall, the WHC of amaranth-Nutrim composites (1470 g kg -1 , 2450 g kg -1 , 4493 g kg -1 ) were higher than that of amaranth-OBC (1672 g kg -1 , 1939 g kg -1 , 2545 g kg -1 ) and amaranth-WOF composites (1314 g kg -1 , 1329 g kg -1 , 1476 g kg -1 ) at the corresponding levels with the exclusion of amaranth-OBC 3:1.The WHC of amaranth composites with Nutrim and OBC were increased significantly with the increasing amount of the oat component (Table 2).
The -glucan contents for WOF, OBC, and Nutrim were 40 g kg -1 , 120 g kg -1 and 150 g kg -1 , respectively.The trend of WOF, OBC, and Nutrim water-holding capacity (Table 2, 1574 g kg -1 , 3559 g kg -1 , 5993 g kg -1 ) appeared to be related to their -glucan contents, suggesting -glucan may be an important factor for WHC.The WHC for all three composites were higher than amaranth flour alone with exceptions of amaranth-WOF 3:1 and 1:1.WHC for Amaranth-Nutrim 1:1 (2450 g kg -1 ) was almost doubled while WHC for amaranth-Nutrim 1:3(4493 g kg -1 ) was almost tripled compared with the amaranth flour alone (1360 g kg -1 ).Amaranth-oat composites could be widely used in different applications in the food industry because of their ability to retain water compared to amaranth flour alone, also notable for their thickening and gelling properties, syneresis control, and emulsion stabilization.

RVA Pasting Properties
The pasting curves of the amaranth, oat products and their composites were obtained by RVA expressed as RVU (Rapid viscosity units, 1 RVU equal 12 centipoises).As shown in the Figure 1, the pasting curves of all samples had dissimilar patterns.In Fig. 1a, the Nutrim pasting viscosity exhibited a sharply increased (23 RVU/min) and significantly high (250 RVU) peak during the initial 11 min heating period at 90 C followed by a rapid decrease in viscosity to ( 25 RVU) during continued heating, and a slight increase during cooling (final viscosity 58 RVU).It is known that the viscosity of a completely gelatinized starch slurry decreases during heating (Guha et al., 1998).These characteristics are common for pregelatinized flour (Lai & Cheng, 2004) and typical for Nutrim since it had undergone jet-cooking during preparation where starch gelatinization occurred.The viscosity of OBC increased gradually (7 RUV/min) to the initial peak (100 RVU) after temperature reached 95 C, remained almost constant viscosity during heating, and then increased sharply (10 RVU/min) during cooling resulting in a considerably high final viscosity (210 RVU).The viscosity of OBC increased during the heating and shearing possibly due to starch gelatinization and interaction with β-glucan in OBC resulted in an entanglement of molecules during cooling indicating the formation a matrix with greater stability under heat and shear.WOF had a lower viscosity peak ( 50 RVU) than Nutrim and OBC at 95C, showing a small breakdown, and then slowly increased to a final viscosity (85 RVU) that was lower than OBC but higher than the rest of the starting materials.The viscosity of amaranth showed the initial peak (50 RVU) at 95C, and then the viscosity are kept constant until reached a final viscosity (57 RVU) similar to Nutrim (60 RVU).
Amaranth-Nutrim-1:3, 1:1 and 3:1 had similar viscosity curve patterns to Nutrim (Figure 1b) showing initial peaks before reaching 95 C.However the initial peak viscosities of Amaranth-Nutrim-3:1 (50 RVU), 1:1(72 RVU) and 1:3(110 RVU) were lower than Nutrim probably because of a lower viscosity attributed by amaranth (Figure 1b).Furthermore, the initial peak viscosities of Amaranth-Nutrim-3:1, 1:1 and 1:3 were evidently increased with the increasing amount of Nutrim.On the other hand, all the amaranth-Nutrim composites displayed similar final viscosities compared with Nutrim and amaranth flour.It suggested that Amaranth -Nutrim composites would have similar viscosity properties to Nutrim after shearing and cooking Similar viscosity patterns were observed for amaranth-OBC composites showing increased viscosities with the increased OBC contents in composites (Figure 1c).Over all, amaranth-OBC composites had higher final viscosities than amaranth-Nutrim (Figure 1b) and amaranth-WOF composites (Figure 1c) since the highest final viscosities during cooling were found for the OBC compared to Nutrim and WOF.It indicated that amaranth-OBC composites could be suitable for the products receiving heat and shear treatment.The initial and final peak viscosities of amaranth-WOF composites were low since both amaranth and WOF had low initial and final peak viscosities (Figure 1d).Amaranth-WOF 1:3 had the highest final viscosity (72 RVU), whereas WOF-amaranth 3:1 had the lowest final viscosity (54 RVU).Also, the initial viscosity peaks of amaranth-WOF composites were slightly delayed to 12 min compared to amaranth flour at 11min.
Improvement in the textural properties of food using oat β-glucan hydrocolloids has been reported so that the RVA data could provide useful information for food processing and product development (Lee et al., 2009).
Composites having low viscosity may be suitable for products such as nutritional bars.Composites with high initial paste viscosity suggest their uses in food formulations such as beverages.For high viscosities of composites, they could be used for products such as breads, muffin, and cookies for improved the texture quality and health benefits.The appar products, processing s

Table 1 .
Comparisons of amaranth with oat, wheat, rice and corn* *Data were selected from USDA Nutrient Database.

Table 2 .
Water holding capacity of amaranth, oat products, and oat-amaranth composites