Rice-Shaped Extruded Kernels: Physical, Sensory, and Nutritional Properties

Transcription

1 International Journal of Food Properties ISSN: (Print) (Online) Journal homepage: Rice-Shaped Extruded Kernels: Physical, Sensory, and Nutritional Properties Juhyun Yoo, Sajid Alavi, Koushik Adhikari, Mark D. Haub, Rick A. Aberle & Gordon Huber To cite this article: Juhyun Yoo, Sajid Alavi, Koushik Adhikari, Mark D. Haub, Rick A. Aberle & Gordon Huber (2013) Rice-Shaped Extruded Kernels: Physical, Sensory, and Nutritional Properties, International Journal of Food Properties, 16:2, , DOI: / To link to this article: Copyright Taylor and Francis Group, LLC Accepted author version posted online: 24 Jun Published online: 24 Jun Submit your article to this journal Article views: 265 View related articles Citing articles: 5 View citing articles Full Terms & Conditions of access and use can be found at

2 International Journal of Food Properties, 16: , 2013 Copyright Taylor & Francis Group, LLC ISSN: print / online DOI: / RICE-SHAPED EXTRUDED KERNELS: PHYSICAL, SENSORY, AND NUTRITIONAL PROPERTIES Juhyun Yoo 1, Sajid Alavi 1, Koushik Adhikari 2,MarkD.Haub 2, Rick A. Aberle 3, and Gordon Huber 3 1 Department of Grain Science and Industry, Kansas State University, Manhattan, KS, USA 2 Department of Human Nutrition, Kansas State University, Manhattan, KS, USA 3 XIM Group, LLC, Sabetha, KS, USA Rice-shaped kernels were produced from micronutrient-fortified blends of corn and wheat flours, sorghum and wheat flours, or rice flour alone using a pilot-scale twin screw extruder. The color of extruded kernels from rice flour was similar to that of natural rice grain, but other treatments had significant color differences. Sorghum/wheat kernels had the highest cooking loss (13.4%) and water uptake (137.8%), and were also significantly different from other treatments with regard to instrumental texture profile and descriptive analysis. Vitamin C retention in extruded kernels was the lowest, ranging from 4.3 to 27.6%, whereas iron and folic acid had high stability. Keywords: Synthetic kernels, Rice, Sorghum, Wheat, Corn, Extrusion. INTRODUCTION Despite progress in reducing world hunger in the last several decades, micronutrient deficiency continues to be a widespread problem. Anemia, resulting from iron deficiency, affects an estimated 1.62 billion people that corresponds to 24.8% of the world population, with the highest prevalence in preschool-age children. [1] Vitamin A deficiency affects an estimated 127 million children. [2] Iodine and zinc are also globally recognized as critical micronutrient deficiencies. [3,4] The consequences of micronutrient malnutrition are often unnoticed as it is an insidious hidden hunger, not the overt and obvious hunger of poor people who cannot afford enough to eat, although the two are inextricably linked in a vast majority of cases. Rice can serve as a suitable carrier for micronutrients as it is an important and popular food grain in developing countries, serving as a staple for nearly half the global population. [5] Nutritional problems, including protein-energy malnutrition and micronutrient deficiencies, are common in regions of the world where rice is a staple food. This is not necessarily a result of rice consumption, but a consequence of socio-economic factors and lack of a balanced diet. [5,6] Fortification of rice with micronutrients has been Received 31 December 2009; accepted 16 May Address correspondence to Sajid Alavi, Department of Grain Science and Industry, Kansas State University, 201 Shellenberger Hall, Manhattan, KS 66506, USA. salavi@ksu.edu 301

3 302 YOO ET AL. attempted in several countries, including the Philippines, China, Indonesia, Thailand, Brazil, Costa Rica, USA, and Canada, either voluntarily or mandated by law. [5 7] The primary methods for rice fortification include powder enrichment, blending with a fortified grain premix that employs acidic solutions and/or protective coatings, and blending with synthetic fortified rice grains. [5 10] Although the first two methods are the least expensive, they have some drawbacks including loss of micronutrients during rinsing prior to cooking and/or poor odor and taste. Synthetic rice grains are made from rice flour using extrusion processing and have same size and shape, and similar texture upon cooking as regular rice kernels. Production of extruded rice grains has the advantage of employing a high capacity, continuous process, with the added benefit of being able to utilize rice flour from broken grains, which can comprise as much as 25% or more of a harvest and have a relatively low value. [6,11] There have been several studies focused on processing, shelf stability and sensory quality of fortified synthetic rice, and its efficacy as a micronutrient carrier when blended in ratios of 1:100 to 1:200 with virgin rice. An example is the Ultra Rice TM fortification technology, developed in the late 1980s, which involves a low temperature and shear process similar to pasta extrusion for production of synthetic rice fortified with micronutrients such as iron and vitamin A. Ultra Rice TM has been successfully used in clinical trials, and studies involving market acceptability and stability of micronutrients. [6] Other studies have utilized conventional extrusion, in both hot and cold (relatively low shear and temperature) processes, for production of synthetic rice fortified with iron, having good organoleptic characteristics and appearance. [9,10] Synthetic rice is solely meant for dilution with virgin rice as a fortification strategy. It is not for replacement of rice altogether because of differences in sensory quality and also much higher costs due to the processing involved. As a novel concept, this study explored cheaper ingredients (corn, sorghum, and wheat) to substitute rice flour in the production of synthetic rice-shaped kernels fortified with micronutrients. The fortified rice-shaped kernels were meant for consumption by the target population without dilution, and with much reduced preparation time and energy. The motivation for this study was work by Grains for Hope, a Kansas-based nonprofit organization that annually provides several tons of fortified grain products to villages in Mozambique. Corn, sorghum and wheat are commodities that are 40 60% cheaper than rice and have great potential for addressing caloric deficiencies and as micronutrient carriers in regions where rice is not a staple. Corn and sorghum are dominant crops in Africa, and are important caloric sources for its population. Sorghum especially plays an important role in food security in Africa because of its high tolerance to semi-arid conditions, and 55% of world s sorghum cultivation area is in the continent. However research is lacking in processing and improved utilization of this food grain as a major source of energy and protein. [12] The primary objective of this study was to use extrusion processing for manufacture of rice-shaped synthetic kernels from micronutrient-fortified blends of corn and wheat flours or sorghum and wheat flours. Cooking quality, physical and sensory attributes, and micronutrient retention in these extruded kernels were characterized, and compared with a control treatment comprising of extruded kernels based on rice flour. Effects of micronutrient inclusion level on color, sensory attributes and flavor of the control treatment were also evaluated.

4 RICE-SHAPED EXTRUDED KERNELS 303 MATERIALS AND METHODS Materials Enriched bread flour (11.8% protein; Mennel Milling Company, Fostoria, OH, USA), CCF 602 degermed yellow corn flour (6.3% protein; Bunge Milling Inc., St. Louis, MO, USA), Fontanelle 1000W whole white sorghum flour (7.6% protein; Sorghum Technologies, New Cambria, KS, USA), and RL-100 general purpose long grain rice flour (8.0% protein; Riceland Foods Inc., Stuttgart, AR, USA) were the base ingredients used in this study. All protein contents mentioned above are on 14% moisture basis. Bonus Blend (item ; Caravan Ingredients Inc., Lenexa, KS, USA) micronutrient enrichment premix was used to fortify all products. One serving (250 mg) of this premix provided 100% of the recommended daily intake (RDI) of 10 nutrients (including vitamins A and C, folic acid, and iron) and 25% of the RDI of 4 additional nutrients (including thiamin, riboflavin, and niacin). Other ingredients used were DIMODAN HS K-A distilled monoglycerides (Danisco USA Inc., New Century, KS, USA) and iodized salt (Morton International Inc., Chicago, IL, USA). Extrusion Processing Experimental formulations were based on a 50:50 blend of corn and wheat flours, a 50:50 blend of sorghum and wheat flours, and rice flour alone. All formulations had 1% salt, 0.75% monoglycerides, and 0.12% enrichment premix on a dry blend basis. An additional rice flour-based formulation was prepared with only 0.06% of the enrichment premix. All ingredients were blended for 10 min prior to extrusion using a ribbon blender (Wenger Manufacturing Inc., Sabetha, KS, USA). To ensure uniformity of blending, the minor ingredients were first mixed with a small amount of flour, followed by addition to the larger batch in the ribbon blender. Moisture content of raw blends and extruded rice before and after drying was measured using the AACC approved method 44-15A [13] with some modification, and expressed on wet basis (wb). Extrusion was conducted using a pilot-scale co-rotating twin screw extruder (TX-52; Wenger Manufacturing Inc., Sabetha, KS, USA) equipped with a preconditioning system. The dry feed rate was set at 100 kg/h for all treatments. Steam and water injection in the preconditioning cylinder were adjusted to 5.2 and 23.6 kg/h, respectively, for rice flour blends and 10.5 and 17.9 kg/h, respectively, for corn/wheat and sorghum/wheat flour blends in order to obtain the best product based on visual evaluation of appearance and stickiness. There was no steam and water injection in barrel. The target in-barrel moisture was 30% (wb) for all treatments. The extruder screw diameter was 58 mm and length to diameter ratio (L/D) was 16:1. The screw configuration and barrel temperature profile are shown in Fig. 1. A maximum compression ratio of 2:1 was achieved during the extrusion process. Screw speed was kept constant at 165 rpm for all treatments. The extruded melt was formed and sized into rice-shaped kernels using a special multi-opening die and a multi-bladed flex knife at the end of the barrel. The die consisted of 32 symmetrically distributed slots, each with a width of 1.2 mm and length of 7.4 mm. The knife speed was 810 rpm. Specific mechanical energy (SME) input during the extrusion process was calculated as follows: SME (kj/kg) = ( ) ( ) T N 100 N rated ṁ P rated, (1)

5 304 YOO ET AL. Barrel temperature Room temp. 45 C 90 C 90 C 90 C 105 C Product discharge Element No. 1 3 = SE, 1; 4 = KB, 45; 5 9 = SE, 0.75; 10 = SE, 0.5; 11 = KB, 45; 12 = SE (conical), 0.75 Figure 1 Schematic of pilot-scale twin extruder screw profile and set barrel temperatures. SE = screw element (all double flighted and forward ); KB = forward kneading blocks. Number: 1 = full pitch, 0.75 = 3/4 pitch, 0.5 = 1/2 pitch. Number: angle of blocks. First two elements (1 and 2) of the right screw are single flighted. where T = net motor load percentage, N = screw speed (rpm), N rated = rated screw speed (336 rpm), P rated = rated power (22.38 kw), and ṁ = net mass flow rate. Extruded kernels were pneumatically conveyed to a pilot-scale double-pass drying and single pass-cooling system (Series 4800; Wenger Manufacturing Inc., Sabetha, KS, USA) for drying at 77 C for 64 min followed by cooling at room temperature for 15 min. Differential Scanning Calorimetry Thermal transitions, including gelatinization temperature and enthalpy, for individual flours, raw blends, and extruded kernels were measured using a differential scanning calorimeter (DSC) (Q200; TA Instruments, New Castle, DE, USA). DSC cell constant calibration was carried out using indium as the reference. Extruded kernels were ground before the DSC tests. About 10 mg of sample was placed in an aluminium pan and distilled water was added to ensure a sample to water ratio of 1:2. The pan was then hermetically sealed, placed in the DSC cell, and heated from 10 to 180 C at a heating rate of 10 C/min. The TA Instruments Universal Analysis 2000 software (version 4.3A) was used to analyze the resultant scans or thermograms. Duplicate tests were conducted for each sample. Degree of starch gelatinization (DG) in extruded kernels was calculated according to the following equation: [14] DG (%) = [ 1 H ] ext 100, (2) H blend where H ext = gelatinization enthalpy of extruded kernel and H blend = gelatinization enthalpy of the corresponding raw blend. Color Measurement Color of extruded kernels was measured with a chromameter (CR-210; Konika Minolta Sensing Inc., Japan). The camera was calibrated using a standardized white plate (CR-A44) having CIELAB values of L = 97.83, a = -5.52, and b = The L

6 RICE-SHAPED EXTRUDED KERNELS 305 value represents whiteness of sample, ranging from 0 for black to 100 for perfect white. A negative value of a indicates greenness, whereas a positive value indicates redness. A negative value of b indicates blueness, and a positive value indicates yellowness. Measurements were replicated five times for each treatment. Color of extruded kernels was compared with natural long grain rice kernels, and overall color difference was expressed by the parameter E, which was calculated as follows: E = [ (L 1 L ) 2 ( 2 + a 1 a ) 2 ( 2 + b 1 b ) ] 2 1/2 2, (3) where the subscript 1 represents the color values of the treatments and the subscript 2 represents the color values of natural rice kernels. Cooking Properties: Cooking Loss and Water Uptake The medium water method for cooking rice, as described by Batcher et al., [15] was used with some modification for this test. One hundred grams of extruded kernels were placed in 400 g of boiling water for 2 min accompanied by stirring. Subsequent simmering was not needed as pressing the hydrated grains revealed disappearance of the dry core. Excess water was drained, and subsequently used for cooking loss test adapted from the standard method for pasta (AACC 16 50). [13] The drained water was evaporated in an air oven at 100 C for 20 h, and the mass of the solid residue in grams was equal to the percent cooking loss. Water uptake (increase in kernel weight after hydration as a percentage of the original kernel weight) [16] was determined after correcting for loss of solids as follows: W (%) = M f + M r M o M o 100, (4) where M f and M o are the net masses of the hydrated and original kernels, respectively, and M r is the mass of solid residue in the drained water. Measurements were replicated three times for each treatment. The amount of water used for preparation of the extruded kernels for other tests, including texture profile analysis, sensory analysis, and glycemic index, was standardized based on water uptake results. Instrumental Texture Profile Analysis For preparing the extruded kernels for texture profile analysis (TPA), 125 g of water wasboiledina2qtsauce pan and 100 g of extruded kernels were added at low heat. Kernels were allowed to hydrate for 3 min, removed from the heat, and cooled for 5 min before further testing. A texture analyzer (TA-XT2; Texture Technologies, Scarsdale, NY, USA) with a 25-kg load cell was used for the TPA test. One gram of sample was spread in a single layer on the base platform. A cylindrical test probe of 35 mm diameter was set at 20 mm above the platform and programmed to travel up to 90% strain at a speed of 1 mm/s. A two-cycle compression was performed, and the resultant force (g) versus time (s) curves were used to derive the TPA attributes of hardness (peak height of first compression), adhesiveness (negative work on the first upstroke), cohesiveness (ratio of area under second compression to area under first compression), springiness (ratio of distance traveled by probe on the two curves), gumminess (cohesiveness hardness), and

7 306 YOO ET AL. chewiness (gumminess springiness). [17] Ten replicates measurements were conducted for each treatment. Descriptive Sensory Analysis Six highly trained panelists from the Sensory Analysis Center at Kansas State University (Manhattan, KS, USA) participated in this study. Each panelist had completed more than 120 h of descriptive training, averaged more than 2000 h of testing experience, and had prior experience testing grain products and using the flavor profile method adapted from Caul [18] and Keane. [19] Samples were prepared following the same method used for TPA. In order to prepare the lexicon to be used, panelists reviewed the entire set of samples two times before testing started. They were instructed to review the samples, establish the terminology necessary to describe texture and flavor characteristics of the grain products, and assign definitions and references to each term. The descriptive terms and references are described in Table 1. Data were generated using a modified flavor profile based on a 15-point scale with 0.5-point increments (0 = none; 15 = extremely high). This scale has been used previously to describe a wide variety of products including cheese, [20] green tea, [21] and black walnut syrup. [22] Samples were observed in three replications and data was collected using Compusense five (v SP3, 2003; Compusense, Inc., Guelph, Ontario, Canada), a computerized data collection system. Three days, including one 60-min session and two 90-min sessions, were necessary to complete orientation and testing. Vitamin and Mineral Retention and Recommended Daily Intake (RDI) Concentration of selected micronutrients in the raw blends and extruded kernels were measured by Medallion Labs (Minneapolis, MS, USA) following AOAC (Vitamin A), AOAC (vitamin C), AOAC (iron), and AOAC (folic acid) methods. [23] RDI values based on a 2000 calorie diet for adults and children 4 or older were used as the reference. The equation used for calculating the micronutrient retention during extrusion processing is as follows: Micronutrient retention (%) = m ker nel m blend 100, (5) where m kernel = concentration of micronutrient in the extruded kernel (g/g) and m blend = concentration of micronutrient in the corresponding raw blend (g/g). Glycemic Response A glycemic response study for the extruded kernels was carried out using human subjects. This study was approved by the Institutional Review Board at Kansas State University. Five volunteers visited the laboratory on four different occasions each. Randomization was applied to all the test products and the volunteers consumed a different extruded product (total carbohydrate = 50 g) during each visit and a glucose beverage (GLUC; dose = 198 ml; total carbohydrate = 50 g). Extruded products were prepared for consumption following the same method as TPA.

8 RICE-SHAPED EXTRUDED KERNELS 307 Table 1 Sensory descriptors, definitions, and references for descriptive analysis of extruded rice kernels. Category/ attribute Definition Reference and intensity Texture Adhesiveness Wipe your lips before evaluation. Degree to to lips which product sticks to the upper lip. Firmness The force required to compress (or bite through) cooked sample using the molar teeth. Soft Firm Adhesiveness, Rinse the mouth before evaluation. Degree to grain to which the sample holds together when first grain placed in the mouth and then separates into individual pieces when manipulated with the tongue. Cohesiveness Rinse the mouth before evaluation. The of mass maximum degree to which the mass holds together during mastication. Measured after 7chews. Metallic feel A basic taste factor of which ferrous sulfate in water is typical. After swallowing Residuals Rinse mouth before evaluating. Use 4 pieces of Cheerios. Amount of particles remaining in the mouth after swallowing. Masticate the sample on one side of the mouth, but avoid making an effort to contain the particles in a ball. Toothpacking Degree to which product sticks on/in surfaces of teeth. Rinse mouth before evaluating. Use 4 pieces of Cheerios. Starchy mouthcoating Flavor Grain Degree to which sample mixes with saliva to form a starchy, pasty slurry that coats mouth surfaces. Use 2 pieces of elbow macaroni. A general term used to describe the aromatics associated with grains, such as corn, oats, and wheat. It is an overall grainy impression characterized as sweet, brown, sometimes dusty, and sometimes generic nutty. American Beauty elbow macaroni = 7.0 Kraft Mild Cheddar Cheese = 4.5 Uncle Ben s Long Grain Rice = 6.0 Hershey s Twizzlers = 8.0 Jiffy Cornbread Muffin Mix = 4.0 Fresh Mushroom = 4.0 Kraft Mild Cheddar Cheese = % Ferrous Sulfate = 5.0 General Mills Cheerios = 3.0 General Mills Cheerios = 3.5 American Beauty elbow macaroni = 8.0 American Beauty elbow macaroni = 6.0 Cereal Mix (Dry) = 8.0 (flavor) Corn Grain aromatics characteristic of corn. Quaker Yellow Corn Meal = 5.0 (flavor) Tostitos 100% White Corn Tortilla Chips (Restaurant Style) = 6.5 (flavor) General Mills Corn Chex = 7.5 (flavor) Toasted Corn Doritos = 8.0 (flavor) Fritos Corn Chips = 9. 0 (flavor) Rice A light, slightly baked sweet grain flavor identified as rice. Uncle Ben s Long Grain Rice = 5.0 (flavor) Wheat Oats A brown, musty/dusty, slightly nutty aromatic characteristic of products made from wheat. A slightly brown, dusty aroma characteristic of oats. Gold Medal All-Purpose Flour = 4.5 (flavor) Gold Medal Whole Wheat Flour = 6.0 (flavor) Quaker Quick Oatmeal (Uncooked) = 8.0 (flavor) (Continued)

9 308 YOO ET AL. Table 1 (Continued) Category/ attribute Definition Reference and intensity Barley A light baked barley grain aromatic. Quaker Quick Barley = 6.0 (flavor) Starch Aromatics associated with starch and American Beauty elbow macaroni = 9.0 starch-based ingredients. A clean, flat aromatic reminiscent of distilled water. Musty Aromatics associated with wet grain and damp earth. American Beauty elbow macaroni = 5.0 Fresh mushroom = 10.5 Water-like Aromatics and mouthfeel of the minerals and Tap water (character reference) = 15.0 metallic commonly associated with tap water. This exludes any chlorine aromatics that may be perceived. Overall sweet A sweet impression that may appear in the aroma and/or aromatics and/or taste. Spoon-size Post Shredded Wheat = 1.5 General Mills Wheaties = 3.0 Sweet A fundamental taste factor of which sucrose is 2% Sucrose Solution = 2.0 typical. Salty The fundamental taste sensation of which sodium chloride is typical. 0.15% Sodium Chloride Solution = % Sodium Chloride Solution = 2.5 Bitter The fundamental taste factor of which caffeine or quinine is typical % Caffeine Solution = % Caffeine Solution = % Caffeine Solution = 5.0 Metallic An aromatic associated with iron, copper, and silver. 0.10% Potassium Chloride solution = % Light Salt solution = % Potassium Chloride solution = 4.0 In the morning of each test day, capillary blood from each volunteer was collected by finger pricking to determine fasting blood glucose levels. Ten minutes were allowed for volunteers to consume the test product. Over a 2-h period following the start of each test, finger-pricked capillary blood samples were collected at 30, 60, 90, and 120 min. Blood glucose levels were immediately measured in duplicate using a blood glucose analyzer (YSI 2300, Yellow Springs, OH, USA). Analysis was repeated if the difference between duplicate samples was greater than 0.1 mmol/l. The glycemic index (GI) was defined as the ratio of the iauc (area under curve) value of food relative to that of standard food (GLUC). The iauc was calculated by using the trapezoidal method (NCSS and PASS 2004, Kaysville, UT, USA). The average of two iauc values of the standard drink was used as the reference value, and GI for each volunteer was calculated as follows: GI = iauc product iauc reference 100, (6) where iauc product = average area under the curve for the test product and iauc reference = average area under the curve for the glucose beverage. Experimental Design and Statistical Analyses The experimental design consisted of four treatments. These included the corn/wheat, sorghum/wheat, and rice flour blends, and an additional rice flour blend with

10 RICE-SHAPED EXTRUDED KERNELS 309 only half the level of micronutrient enrichment as other treatments. Fisher s least significant difference (LSD) method was employed for pair-wise comparison of means at p < 0.05 using SAS (version 9.1, SAS Institute, Inc., Cary, NC, USA). Correlation analysis was also conducted for studying the correspondence between texture attributes obtained with TPA and descriptive analysis. RESULTS AND DISCUSSION The process variables and physical characteristics of the two rice-based treatments were very similar. This was expected as the only difference between the two was the enrichment level (0.06 and 0.12%), which would not cause significant differences in the processing or product attributes such as specific mechanical energy, texture, gelatinization, etc. Hence, most of the results described below were based on the three treatments with different formulations but the same enrichment level (0.12%). However, differences in color, sensory, and nutritional attributes were expected as a result of micronutrient level; therefore, all four treatments were compared for those results. Moisture Content Moisture contents of the raw blends were 10.6, 10.0, and 9.2%, respectively, for formulations based on corn/wheat, sorghum/wheat, and rice. For extruded kernels corresponding to the above formulations, moisture contents before drying were 27.0, 29.3, and 25.7, and after drying were 9.3, 7.7, and 9.7%, respectively. Only a small fraction of water in the extrusion melt was lost through evaporation at the die, in accord with the low shear cooking and forming process that was designed to result in dense, unexpanded kernels. The higher pre-drying moisture content of sorghum/wheat kernels meant there was relatively less loss of water vapor upon exit from the die, possibly a consequence of lower specific mechanical energy and melt temperature as compared to other treatments. Specific Mechanical Energy Highest specific mechanical energy (SME) input was observed during processing of the rice flour treatment (104 kj/kg), followed by corn/wheat (61 kj/kg), and then sorghum/wheat (49 kj/kg). These results imply higher viscosity of rice flour dough during extrusion as compared to other formulations, since SME is directly related to viscosity under constant processing conditions. Rice starch viscosity under low and intermediate moisture (16 24%) extrusion conditions has been reported to be lower than that of corn and wheat starches. [24] This apparently contradicts the SME data, however the rheological behavior of flours can be different than starches due to the presence of other components and the changes they undergo given the complex thermo-mechanical history experienced during extrusion. [25] Further investigation is needed on comparative on-line rheology of various flours during extrusion, but this is beyond the scope of this study. Thermal Transitions Typical DSC thermograms of individual flours, raw blends, and extrudates are shown in Fig. 2, and the corresponding peak gelatinization temperature (T G ) and gelatinization enthalpies ( H) are summarized in Table 2. Starch gelatinization in individual flours was

11 310 YOO ET AL. (a) sorghum flour wheat flour wheat/sorghum blend extrudate 1.8 Heat Flow (w/g) Exo Down Temperature ( C) (b) 2.0 wheat/com blend extrudate com flour 1.9 wheat flour 1.8 Universal V4.3A TA Heat Flow (w/g) (c) Universal V4.3A TA Temperature ( C) 2.0 Exo Down 1.9 extrudate rice blend rice flour Heat Flow (w/g) Universal V4.3A TA Temperature ( C) Exo Down Figure 2 Typical differential scanning calorimetry thermograms for individual flours, raw blends, and extruded kernels: (a) sorghum/wheat, (b) corn/wheat, and (c) rice.

12 RICE-SHAPED EXTRUDED KERNELS 311 Table 2 Results from gelatinization experiments using DSC. 1,2 Individual flours Wheat Corn Sorghum Rice T G ( C) 65.4d 74.0c 74.7b 78.4a H (J/g) 7.0b 10.2a 7.8b 10.6a Raw blends Wheat/corn Wheat/sorghum Rice T G ( C) 67.7b/78.7a 67.2b/75.8a 80.4a H (J/g) 9.3a 7.6b 10.3a Extruded kernels Corn/wheat Sorghum/wheat Rice T G ( C) 86.9b 83.6c 88.9a H (J/g) 0.1c 0.9a 0.8b DG (%) 98.5a 88.2c 92.8b 1 T G and H indicate the peak temperature of gelatinization and gelatinization enthalpy, respectively. Raw blends include salt and monoglycerides. 2 Results are expressed as means of two replicates. Samples sharing the same letter within a row are not significantly different (p < 0.05). represented by the first endothermic peak, and T G of corn, sorghum, wheat, and rice flours were 74.0, 74.7, 65.4, and 78.4 C, respectively. The corresponding H were 10.2, 7.8, 7.0, and 10.6 J/g, respectively. A second endothermic transition was observed for all flours at a peak temperature (T p1 ) between C, which represented the reversible dissociation of type I (amorphous) amylose-lipid complexes. Although thermal transitions depend greatly on the flour variety, similar data has been reported previously for corn, [26,27] sorghum, [28,29] wheat, [30 32] and rice [33 36] flours. Thermograms of raw corn/wheat and sorghum/wheat blends showed two overlapping gelatinization peaks. It was obvious that wheat flour contributed the first peak (T G of C), and corn or sorghum flour contributed the second peak (T G of 78.7 and 75.8 C, respectively) in these blends. Biphasic gelatinization behavior of mixtures of different flour and/or starches has been observed previously. [30,37] H of all raw blends reflected the contribution of individual flours. However, T G values in blends were shifted slightly higher ( C) as compared to the individual flours, which could be due to the presence of salt (1%) that competes with starch for water. [31] Peaks for type I amylose-lipid complexes were also observed (T p1 = C) during scanning of each blend. The thermograms of extruded kernels exhibited a residual gelatinization peak (T G of C), implying that a small fraction of ordered starch crystallites did not melt during the extrusion process. The degree of starch gelatinization (DG) of extruded kernels, calculated using gelatinization enthalpies of unextruded blends as reference, was 98.5, 88.2, and 92.8%, respectively, for the corn/wheat, sorghum/wheat, and rice treatments. Thus, the mechanical and thermal energy input during extrusion resulted in kernels that were predominantly pre-cooked, irrespective of their formulation. The lower degree of gelatinization for sorghum/wheat kernels could possibly be due to interference caused by sorghum protein bodies in the hydration and swelling of starch granules. [38] The thermograms of extruded kernels showed a more prominent endothermic peak for type I amylose-lipid complexes (T p1 of C). An additional endothermic

13 312 YOO ET AL. peak (T p2 125 C) was observed which was absent during thermal scanning of raw flours or their blends and was irreversible as confirmed by its disappearance during rescanning (not shown). This represented melting of ordered or crystalline type II amylose-lipid complexes that are formed during heat treatment of flour/starch under limited moisture, including extrusion processing. [33,39] Presence of monoglycerides in the blends might have further favored type II amylose-lipid complex formation. [40 42] Degradation of starch due to shear inside the extruder could also have promoted the formation of both types of complexes. Color Measurement Color results are shown in Table 3. Extruded rice kernels were significantly lighter (L = ) than corn/wheat (67.1) and sorghum/wheat (67.6) kernels, which was expected because of the darker color of the non-rice ingredients. It should also be noted that the corn flour was based on a yellow corn variety, which led to significantly higher yellowness values for corn/wheat extrudates (b = 51.0) as compared to other treatments ( ). The effect of the micronutrient mix on color can be ascertained from the significantly lower yellowness of extruded rice kernels with only half the enrichment level (0.6%). Riboflavin and folic acid in micronutrient blend could be the reason for this effect, [43,44] which was masked in the corn/wheat and sorghum/wheat kernels due to the strong colors of the base ingredients. Color difference ( E) data using natural, long grain, white rice kernels as reference are also shown in Table 3. As expected, corn/wheat kernels had the highest E value (33.2), followed by sorghum/wheat (11.6) and rice ( ). Extruded rice kernels had similar level of lightness (L ) and greenness (a ) as natural rice. The color difference of the former was mainly due to higher yellowness, caused by the micronutrient blend and possibly Maillard reaction during the extrusion process. Cooking Properties Compared with natural rice, which takes 2 min of boiling in a medium amount of water (4:1 w/w) followed by min of simmering, [15] the extruded kernels required boiling in water for 2 min but no simmering in order to prepare them for consumption. This step was required primarily to achieve hydration for softening of the texture, rather than cooking, as the extruded kernels were already 90% precooked. Results from the cooking quality test for extruded kernels are shown in Fig. 3. Water uptake ranged from Table 3 CIELAB color values of extruded kernels. 1 Treatment L a b E 2 Corn/wheat 67.1b 1.1a 51.0a 33.2a Sorghum/wheat 67.6b 1.1a 23.5d 11.6b Rice 79.2a 3.5b 26.2b 6.4c Rice-half enriched 78.8a 3.6b 24.5c 4.6d 1 Results are expressed as means of five replicates. Samples in a column sharing the same letter are not significantly different (p < 0.05). 2 Calculated using natural rice grains as reference (L = 78.4, a = -3.6, and b = 19.9).

14 RICE-SHAPED EXTRUDED KERNELS a Water uptake (%) b 10.9 b 13.4 a 97.1 b 8.0 c Cooking loss (%) Corn/Wheat Sorghum/Wheat Rice Water uptake Cooking loss 0.0 Figure 3 Water uptake and cooking loss for extruded kernels. Results are expressed as means of three replicates. Treatments sharing the same letter are not significantly different (p < 0.05) to 137.8%, which was much lower than the uptake reported for natural rice grains ( %) at optimum cooking time. [16] Substantial degradation of starch granules during the extrusion process led to lower swelling and water uptake of the extruded kernels. Significantly higher water uptake was observed for sorghum/wheat kernels as compared to corn/wheat and rice kernels. Cooking loss ranged from 8.0 to 13.4%, with sorghum/wheat kernels again having the highest loss, followed by corn/wheat and rice kernels. Starch had an important role in binding the kernel matrix in the relatively high temperature extrusion forming process. The interference caused by sorghum protein bodies (kafirins [38] in gelatinization and formation of a continuous starch matrix led to poor binding and, thus, relatively softer and permeable sorghum/wheat kernels. This allowed water to absorb into the kernels more easily than the other two treatments and also more starch to leach out during hydration in boiling water. Corn proteins (zeins) are analogous to sorghum proteins, but their protein bodies were relatively easier to disrupt via the moderate amount of shear applied during extrusion. [45] This factor, in combination with the high DG of corn/wheat kernels, led to intermediate cooking loss and similar water uptake as rice kernels. Instrumental Texture Profile Analysis Typical TPA force-distance curves for extruded kernels from corn/wheat, sorghum/wheat, and rice after hydration are shown in Fig. 4, and the corresponding texture parameters are summarized in Table 4. Most notable differences were again observed in the case of sorghum/wheat kernels. These kernels were significantly lower in hardness (11,882 g) as compared to other treatments (14,986 16,906 g). Sorghum/wheat kernels also had significantly lower cohesiveness (0.28) than the other treatments ( ). This can be related to the poor binding properties of sorghum starch as discussed previously,

15 314 YOO ET AL corn/wheat sorghum/wheat rice Force, g Time, s 5000 Figure 4 Typical TPA curves for extruded kernels. Table 4 Texture profile analysis (TPA) results for extruded kernels after hydration. 1 TPA parameters Corn/wheat Sorghum/wheat Rice Hardness (g) 14, a 11, b 16, a Adhesiveness (g s) 270.2a 710.6b 256.4a Cohesiveness 0.34ab 0.28b 0.38a Springiness 0.43a 0.44a 0.44a Gumminess (g) b c a Chewiness (g) ab b a 1 Results are expressed as means of 10 replicates. Samples in a row sharing the same letter are not significantly different (p < 0.05). leading to a softer, less cohesive matrix on hydration. Sorghum/wheat kernels had significantly higher adhesiveness (711 g s) as well compared to other treatments ( g s). This was due to the greater leaching of amylose molecules from the starch granules on hydration, leading to enhanced stickiness of the matrix to the test probe. This was confirmed by the high cooking loss observed for sorghum/wheat kernels. Springiness ( ) did not differ significantly among the various treatments. Gumminess and chewiness values were derived from other parameters, and followed the same trends as hardness and cohesiveness, with the sorghum/wheat kernels having significantly lower values than other treatments. TPA properties of corn/wheat kernels were intermediate to the other two treatments, although they were not always significantly different from extruded rice kernels. Hardness of extruded rice grains was previously reported to range from 10,600 13,000 g, [10] which compares well with the hardness of rice kernels in this study considering the differences in processing and also preparation method. Adhesiveness, cohesiveness, and springiness data of extruded rice kernels reported in the same study ( , , and g s, respectively) were also comparable to the current treatments. In contrast, hardness of cooked, natural, long grain rice (8950 g) [10] was 25 47% lower than the extruded kernels in the current study. The harder texture of extruded kernels was due to lower water uptake during hydration than that of natural rice during which that was cooked with a water/rice ratio of 2:1. Natural rice had a similar

16 RICE-SHAPED EXTRUDED KERNELS 315 adhesiveness (329 g s), but higher cohesiveness (0.42) and lower springiness (0.16) than the extruded kernels. [10] Descriptive Sensory Analysis Descriptive analysis results for extruded corn/wheat, sorghum/wheat, and rice kernels after hydration are shown in Table 5, along with those for extruded rice kernels with only half the enrichment level (0.06%). Also, correlations of these data with TPA parameters are summarized in Table 6. Extruded sorghum/wheat kernels had significantly higher adherence to the palate (adhesiveness) and also stickiness to each other (grain to grain adherence), as compared to other treatments. These kernels also required significantly lower force for molar compression (firmness) than the extruded corn/wheat and rice kernels. It is clear from these trends that most of the sensory texture attributes mirrored the TPA data closely, as can also be seen by the high correlations between instrumental adhesiveness and the two sensory adhesiveness parameters (ρ = ), and instrumental hardness and sensory firmness (ρ = 0.90). Sensory cohesiveness of mass of extruded rice, however, was an exception and had a negative although statistically insignificant correlation to instrumental cohesiveness (ρ = -0.91). However, a significant correlation (ρ = 1.00) was observed between Table 5 Descriptive analysis results for extruded kernels after hydration. 1 Sensory attributes Corn/wheat Sorghum/wheat Rice Rice-half enriched Texture terms Adhesiveness to lips 6.56c 8.53a 7.06b 6.80bc Firmness 6.64b 5.67c 7.06a 7.03a Adhesiveness, grain to grain 4.20b 10.33a 2.22c 2.39c Cohesiveness of mass 4.80b 11.70a 3.94c 3.92c Metallic feel 0.53c 2.44a 1.11b 1.14b After swallowing terms Residuals 3.80c 4.92a 4.28b 4.17b Toothpacking 2.72b 5.19a 2.61b 2.58b Starchy mouthcoating 6.22c 9.83a 6.89b 6.72b Flavor terms Grain 6.80b 8.23a 6.17c 6.03c Corn 3.41a 0.30b 0.11c 0.00c Rice 2.94b 2.14c 4.22a 4.22a Wheat 1.50c 3.50a 1.83b 1.83b Oats 0.00b 4.20a 0.00b 0.00b Barley 0.05b 1.08a 0.00b 0.00b Starch 6.06c 9.47a 6.58b 6.53b Musty 3.36b 4.86a 3.28b 3.36b Water-like 1.03a 0.50b 1.00a 0.97a Overall-sweet 1.78a 1.78a 1.64a 1.69a Sweet 0.64a 0.50a 0.61a 0.69a Salty 2.22b 2.44a 2.17cb 2.03c Bitter 2.33b 3.61a 2.22b 2.28b Metallic 1.42b 2.33a 1.36b 1.28b 1 Results are expressed as means of three replicates. Samples in a row sharing the same letter are not significantly different (p < 0.05).

17 316 YOO ET AL. Table 6 Correlation coefficients between instrumental and sensory attributes of extuded rice kernels after hydration. Instrumental attributes Sensory attributes Hardness Adhesiveness Cohesiveness Springiness Gumminess Chewiness Adhesiveness to lips Firmness Adhesiveness, grain to grain Cohesiveness of mass Metallic feel Residuals Toothpacking Starchy mouthcoating Significant at p < this attribute and instrumental adhesiveness. This was due to the fact that the descriptive definition of cohesiveness of mass was based on product integrity rather than the resistance offered during repeated biting (Table 1). Good correlations have also been observed for cooked natural rice between instrumental texture attributes, especially hardness, and sensory attributes including overall quality. [17,46] Sorghum/wheat kernels were inferior in post-swallowing sensory attributes, and had significantly higher residuals, toothpacking, and starchy mouthcoating than other treatments. These attributes were highly correlated with instrumental adhesiveness (ρ = 0.89, 1.00, and 0.98, respectively). This also confirmed that the latter was impacted by starch leached during the hydration process, as was discussed earlier. Panelist could detect significantly higher corn and rice flavors in the extruded corn/wheat and rice kernels, respectively. The attribution of significantly higher grain, wheat, oats, and barley flavors to the sorghum/wheat kernels point to lack of recognition of the flavor associated with sorghum within the available cereal-based descriptive terms. This was not unexpected as sorghum is not a mainstream cereal grain in the North American diet. In addition, the sorghum/wheat kernels ranked significantly higher in musty, metallic, and bitter flavors, which is a characteristic perception of sorghum and one of the reasons for its low utilization in food applications in North America. [47,48] It was also interesting to note that the difference in the amount of micronutrient enrichment did not result in significant changes in any of the flavor attributes of extruded rice. Micronutrient Retention and Recommended Daily Intake (RDI) Micronutrient contents in the raw blends and extruded rice are shown in Table 7. Data for the extruded rice treatment with only half the enrichment level (0.06%) are also included. All data were adjusted to 150 g of blend or extruded rice, which corresponds to one serving size. The raw blends with 0.12% enrichment contained IU of vitamin A. These concentrations were 19 30% lower than expected based on the specifications of the micronutrient blend. On the other hand, concentrations of vitamin C ( mg), iron ( mg), and folic acid ( μg) in the raw blends were higher than expected even after taking into account that the wheat flour was already enriched with iron and folic acid. Similar discrepancies were observed for the rice blend with 0.06% enrichment. The variability in micronutrient data for raw blends and their lack of consistency with expected levels could be due to inhomogeneous mixing of the micronutrient premix, which is a possibility considering its low level of inclusion ( %).

18 RICE-SHAPED EXTRUDED KERNELS 317 Table 7 Micronutrient content and recommended daily intake (RDI) based on 150 g of sample. Corn/wheat Sorghum/wheat Rice Rice-half enriched Raw blend Vitamin A IU Vitamin C mg Iron mg Folic acid μg Extruded kernels Vitamin A IU Vitamin C mg Iron mg Folic acid μg RDI % (extruded kernels) Vitamin A % Vitamin C % Iron % Folic acid % % corn/wheat sorghum/wheat rice full vit rice half vit Vit A Vit C Iron Folic Acid Figure 5 Vitamin and mineral retention rate for the treatments. The retention rates of micronutrients in extruded kernels are shown in Fig. 5. The level of enrichment did not appear to have any consistent effect on retention rate, as can be seen by comparing the data from extruded rice kernels with 0.12 and 0.06% micronutrient premix. Micronutrient contents in the extruded kernels were lower than the raw blends in most cases. The only consistent exception was iron, which was 2 11% higher in the extruded kernel. This was well within the variability observed in the raw blends but could also be due to extruder screw wear. [49] On the other hand, in most cases, vitamins had decreased retention due to extrusion processing, as has been shown in other studies. [50] Vitamin C had the poorest retention rate (4 28%) of all micronutrients, with the lowest retention in sorghum/wheat kernels. This was expected, as vitamin C is known to be most sensitive of all vitamins. [51] The vitamin A retention rate was higher and ranged from %, with the lowest retention again observed in sorghum/wheat kernels. Retention of 82% was reported for vitamin A in extruded rice kernels. [21] Folic acid

19 318 YOO ET AL. content had large variability and even exhibited an 8 11% increase in two of the treatments. Retention of vitamins typically has a negative correlation with specific mechanical energy input, [50] however, this was not observed in the current study. For example, the extruded rice kernels were associated with the highest SME but did not have the lowest retention in most cases. In fact, the vitamin C retention rate was highest (20 28%) in the case of extruded rice kernels. RDI % per serving of extruded rice (150 g) is also shown in Table 6. The extruded kernels with 0.12% enrichment level were able to provide 19 54% RDI of vitamin A, % RDI of iron, and % RDI of folic acid, but only 4 30% of vitamin C because of its poor stability during extrusion processing. Glycemic Response of Extruded Kernels The glycemic response of extruded kernels is shown in Fig. 6. The reference glucose beverage elicited a higher postprandial blood glucose level compared to extruded kernels for the first min after intake. The latter, however, had a higher level of blood glucose from 60 to 120 min because glucose from extruded kernels was elicited into the blood gradually, which led to larger iauc than the reference. Glycemic index values were 101.3, 103.2, and for corn/wheat, sorghum/wheat, and rice kernels, respectively. These results point towards another potential benefit of corn/wheat and sorghum/wheat formulations based on their lower glycemic index than rice. Further study is, however, required to confirm these results. CONCLUSIONS This study demonstrated the potential of a novel approach to alleviate caloric and the micronutrient deficiencies through extruded rice-shaped kernels that required very little time and energy for preparation prior to consumption. The use of non-rice formulations for these extruded kernels would make them more cost-effective and also possibly less glycemic intense, without compromising too much on the texture and flavor of the products. This is especially true for the kernels based on corn and wheat flours, which were closer to extruded rice in both instrumental texture and sensory attributes. The non-rice 7 6 Glucose (mmol/l) S/W Rice C/W Glucose Time (min) Figure 6 Glycemic response: postprandial blood glucose level over time for the extruded rice treatments.

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