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Int.J.Curr.Microbiol.App.Sci (2017) 6(3): 419-427 International Journal of Current Microbiology and Applied Sciences ISSN: 2319-7706 Volume 6 Number 3 (2017) pp. 419-427 Journal homepage: http://www.ijcmas.com Original Research Article https://doi.org/10.20546/ijcmas.2017.603.048 Rheological Behavior of Honey-Cereal Extrudates as a Function of Extrusion Processing Parameters Hanuman Bobade*, Savita Sharma and Baljit Singh Department of Food Science and Technology, Punjab Agricultural University, Ludhiana, Punjab, India *Corresponding author ABSTRACT Keywords Honey, Cereals, Extrusion, Rheology, Rapid visco analyzer. Article Info Accepted: 10 February 2017 Available Online: 10 March 2017 Rheological characteristics of honey-whole grain cereal extrudates as influenced by varying extrusion processing conditions were studied. Honey, blended at various level with the cereal flours at 14 and 17% feed moisture, was subjected to extrusion processing at different extrusion temperatures. The rheological properties of the resultant extrudates were measured by rapid visco analyzer. It was observed that all the processing conditions significantly affected the rheological properties of the extrudates. Increased extrusion temperature resulted in decreased viscosity of the extrudates. Highest values of rheological characteristics were recorded at lowest extrusion temperature. Honey addition positively influenced the viscosity of extrudates. Addition of honey in the feed resulted in increased rheological characteristics of resultant extrudates. Amongst the rheological characteristics, peak viscosity and final viscosity was found mostly affected by the extrusion parameters. Introduction Refined cereal flours are chiefly utilized in preparation extruded snacks owing to high expansion capability of these cereal flours. However, such refined cereal flours being rich in mere carbohydrate and proteins lack nutritional quality. Hence, in order to provide consumers nutritionally superior extruded snacks, these days, whole grain cereal flours are being increasingly used. Contrary to the refined cereal flours, the whole grain cereal flours produces snacks with decreased expansion and unattractive physical appearance due to high fiber content. Extrusion cooking as an attractive process for continuous food production has been extensively developed in recent years. The high temperature–short time extrusion cooking is used in the food industry to produce direct expanded products such as snack foods, breakfast cereals and pet foods (Miller, 1990; Moore, 1994; Rokey, 1994). Extrusion of food material results in starch gelatinization, denaturation of protein, microbial reduction, enzyme activation or inactivation, color and other changes. The extents of these changes are dependent on the conditions of the extrusion. Those changes at the constituents’ level modify the rheological behavior of flour batters (Hagenimana et al., 2006). This is mainly due to altered rheological behavior of whole cereal flour extrudates. In order to increase the nutritional quality of 419 Int.J.Curr.Microbiol.App.Sci (2017) 6(3): 419-427 extruded snacks, the cereal flours are also being supplemented with other ingredients such as fruits and vegetables, legumes, milk solids and others. Moreover, there is growing interest of consumers in more differentiated food products in recent years (Stolzenbach et al., 2013). In this context, usage of honey as a source of bioactive and nutritionally rich ingredient in formulation of extruded products will be prolific. Honey level, as seen through experimental trials, was also significantly affecting the extrudate properties. The extrusion was carried out by varying the levels of three independent variables (feed moisture, extrusion temperature and honey level in the feed). The feed moisture was varied at two levels (14 & 17%), extrusion temperature was varied at 5 levels (100, 120, 140, 180 & 2000C) while honey level was varied at 5 different levels (1, 5, 10, 15 & 20%). Three types of cereals (wheat, rice, maize) singly and in combination (3:4:3 proportion, which was decided after preliminary trials) were mixed with the honey and extruded at varying feed moisture and extrusion temperature. The levels of independent variables were established based on observations of preliminary trials and literature survey. Rheological changes during extrusion of refined cereal flour with conventional ingredients are reasonably predictable and modestly established. Nevertheless, rheological behavior of whole grain cereal flour is relatively complex. Hence, understanding of rheological changes of whole grain cereal flour with such ingredient as honey is important. Keeping in view this perspective, the study comprising of effect of extrusion processing on rheological properties of honey-whole grain cereals extrudates was undertaken. Extrusion Extrusion of honey-cereals was performed with the help of twin screw co-rotating intermeshing extruder (BC 21, Clextral, Firminy, France) having a screw length of 400 mm and diameter 25 mm. The extruder was powered by an 8.5 kW motor with speeds variable from 0 to 682 rpm. Over entire experiment, the screw speed of the extruder was kept constant (500 rpm). Raw materials were metered into the extruder with a single screw volumetric feeder (D S and M, Modena, Italy). The feed rate was kept at 10kg/hr rate for optimum filling in accordance with the screw speed. A variable speed die face cutter with four bladed knives was used to cut the extrudates. The die plate had one circular hole with 6 mm diameter. Materials and Methods Wheat (var. HD 2967), paddy (var. PR 121), maize (var. PMH 1) was supplied by Directorate Seeds, Punjab Agricultural University, Ludhiana, Punjab, India. Brown rice was obtained by dehulling the paddy in laboratory dehuller (Satake, Japan). Wheat, brown rice and maize after cleaning were grinded in Torrento Flour Mill (Tech Electric Enterprise, Ahmedabad, India) to obtain the whole grain flours (250µ). Honey (sunflower cultivar) was supplied by Department of Entomology, Punjab Agricultural University, Ludhiana, India. Rheological properties Experimental design The extrudates were grinded to particle size less than 200 µm. Pasting properties (peak, trough, breakdown, final and setback viscosity) of samples extruded under different Feed moisture and extrusion temperature were observed from literature as most critical factors affecting extrudate characteristics. 420 Int.J.Curr.Microbiol.App.Sci (2017) 6(3): 419-427 conditions were determined using a rapid visco-analyzer, RVA (Model StarchMaster2; Newport Scientific Inc., Warriewood, Australia). For each analysis, 3.0±0.05 g samples (14% wb) were mixed with 25 mL of distilled water. The profile for analysis was Standard Method 1 according to AACC (2000) Approved Method 76-21. may be associated with a high proportion of un-gelatinized starch, whereas the lowest values of viscosity might reflect greater degradation that is attributed to depolymerization and molecular entanglement resulting from the processing conditions (Hagenimana et al., 2006). At high temperature, the extruded mass becomes plastic and less viscous allowing the molecules to become more susceptible to compression during extrusion. Thus greater thermal and mechanical action was produced, resulting in degradation of the starch granules and subsequently, lower viscosity value was obtained. Similar observations were recorded by Hernandez-Nava et al., (2011). Statistical analysis The analysis of variance was performed with the help of Statistical Package for the Social Sciences (SPSS, [PASW version 18.0] Inc., USA). Tukey’s test (p<0.05) was used to detect differences among treatment means. The final viscosity which depends upon changes in the starch granule structure during extrusion processing varied from 110-302 cP for extrudates prepared at 14 per cent feed moisture and from 88-412 cP for extrudates prepared at 17 per cent moisture and various levels of temperature and honey. Within 17 per cent feed moisture, the highest value of final viscosity was observed at 1000C barrel temperature and 10 per cent honey level while the lowest final viscosity was noted at 2000C barrel temperature and 10 per cent honey. Similar results were seen with respect to the final viscosity of extrudates prepared at 14percent feed moisture. The final lower viscosity of extrusion processed extrudates was the result of starch liquification during processing at higher temperature. These observations are in corroboration with results of Zeng et al., 2011. Results and Discussion Rheological properties Rheological properties of honey-whole grain flours were significantly affected by extrusion processing parameters as well as the level of honey. Influence of extrusion processing parameters and level of honey on rheological properties of various cereal-honey extrudates is discussed in following sections. Honey-wheat extrudates The pasting properties of honey-wheat extrudates were measured by rapid visco analyzer and are presented in table 1. Significant (p<0.05) differences were observed in the pasting properties of honeywheat extrudates. The highest peak viscosity was observed at lower extrusion temperature and lowest peak viscosity was observed at higher extrusion temperature for both feed moistures (14 and 17%). The peak viscosity occurs at equilibrium point between swelling and polymer leaching which causes an increase in viscosity. It also indicates the water binding capacity of starch or mixture. The highest values of viscosity in the product Breakdown viscosity of wheat-honey extrudates also decreased significantly with increase in extrusion temperature. The rate of breakdown depends on the temperature and degree of mixing or shear stress applied to the mixture and the nature of material itself. Increased addition of honey in feed had positive effect on the breakdown viscosity of 421 Int.J.Curr.Microbiol.App.Sci (2017) 6(3): 419-427 extrudates. This could be due to the resistance offered by viscous honey against the degradation of starch during extrusion processing. The high rate of breakdown as a result of increased extrusion temperature might be attributed to excessive dextrinization of starch during extrusion. The setback viscosity of extrudates also lowered upon increase in extrusion temperature. Honey addition increased the setback viscosity of honey-wheat extrudates. During setback, cooling occurs and re-association between starch molecules, especially amylose resulted in formation of a gel structure and therefore viscosity increases during this phase. Setback viscosity is generally related to the retrogradation and reordering of starch granules. is attributable to varying of degrees of depolymerization and molecular entanglement resulting from the processing conditions. Similar observation has been reported earlier (Barres et al., 1990; McPherson et al., 2000) Maximum value of final viscosity was observed at lowest extrusion temperature while the minimum final viscosity of extrudates was observed at highest extrusion temperature. At constant feed moisture and honey level, increasing the barrel temperature resulted in decreased final viscosity of the extrudates while at constant feed moisture and barrel temperature, increased honey level in feed boosted up the final viscosity of extrudates. The results of this study thus indicate that the extrudates successively lose the ability to form a paste or gel after cooking and cooling when extrusion temperature is increased. Honey-brown rice extrudates The pasting properties of honey-brown rice extrudates as determined using RVA are shown in table 2. The pasting temperature of the samples was not detected, indicating that the extrudates were fully cooked during extrusion processing. The peak viscosity of the extrudates varied significantly (p<0.05). Decrease in peak viscosity of extrudates with increase in extrusion temperature was observed. The peak viscosity of extrudates prepared at 17 per cent moisture, 1000C barrel temperature and 10 per cent honey levels was 385 cP which decreased to 86 cP when barrel temperature was increased to 2000C. This suggests that the barrel temperature has profound negative effect on the peak viscosity of extrudates. Conversely, the honey level in feed facilitated the increase in viscosity. This could be due to full gelatinization and degradation of starch at elevated extrusion temperature. The highest values for peak viscosity of extrudates were associated with a high proportion of un-gelatinized starch, whereas the lowest values of peak viscosity indicate a proportion of gelatinized starch that The breakdown viscosity of extrudates, which measures the ability of material to withstand the heating and shear stress, differed significantly (p<0.05). Rapid decrease in breakdown and setback viscosity was noticed when the temperature of extrusion cooking was increased. The effect of honey level on the breakdown and setback viscosity was found exact opposite to the effect of extrusion temperature. However, the increase in these viscosities by increased honey level in feed was apprehensive. The results specify that reassociation or re-ordering of leached amyloseamylopectin molecules is hindered by increased extrusion temperature whereas honey aided in re-association of amylose and amylopectin molecules in the extrudates. The extensive gelatinization that the cereal flours undergo when subjected to severe extrusion intensity could promote the viscosity decrease during the heating-cooling cycle, as it was observed by Hagenimana et al., (2006) and Sharma et al., (2013). Moreover, the reduction observed in the final viscosity and 422 Int.J.Curr.Microbiol.App.Sci (2017) 6(3): 419-427 setback (difference between the minimum viscosity during heating and the final viscosity after cooling) in flour subjected to harsh extrusion, indicated the extension of the effect on the amylose chains, which might lose the ability to retrograde during cooling owing to their fragmentation during extrusion. Table.1 Rheological properties of honey-wheat extrudates Treatments Rheological properties Moisture Temperature Honey (%) (0C) (%) Peak Hold Final Breakdown Setback viscosity viscosity viscosity viscosity viscosity (cP) (cP) (cP) (cP) (cP) 14 17 120 5 336a 71b 289b 265a 218a 180 5 152b 21c 110d 131c 89c 120 15 354c 86a 302a 268a 216a 180 15 187d 27c 144c 160b 117b 100 10 412a 95a 361a 317a 266a 200 10 88e 15d 80e 73e 65e 150 1 239d 38c 195d 201d 157d 150 20 297b 59b 272b 238b 213b 150 10 268c 51b 242c 217c 191c Means followed by different superscript letter in the column differ significantly (p<0.05) for a given feed moisture. Table.2 Rheological properties of honey-brown rice extrudates Treatments Rheological properties Moisture Temperature Honey (%) (0C) (%) Peak Hold Final Breakdown Setback viscosity viscosity viscosity viscosity viscosity (cP) (cP) (cP) (cP) (cP) 14 17 120 5 298b 62b 268b 236b 206a 180 5 142d 16c 91d 126d 75c 120 15 331a 74a 288a 257a 214a 180 15 174c 19c 128c 155c 109b 100 10 385a 86a 308a 299a 222a 200 10 86e 12d 68e 74e 56d 150 1 219d 31c 192d 188d 161c 150 20 283b 46b 247b 237b 201b 150 10 248c 39bc 232c 209c 193b Column wise, means followed by superscript letter within moisture differs significantly (P<0.05). 423 Int.J.Curr.Microbiol.App.Sci (2017) 6(3): 419-427 Table.3 Rheological properties of honey-maize extrudates Treatments Rheological properties Moisture Temperature Honey (%) (0C) (%) Peak Hold Final Breakdown Setback viscosity viscosity viscosity viscosity viscosity (cP) (cP) (cP) (cP) (cP) 14 17 120 5 368b 81a 322b 287a 241b 180 5 162d 25b 124d 137c 99d 120 15 385a 86a 340a 299a 254a 180 15 197c 28b 153c 169b 125c 100 10 431a 107a 387a 324a 280a 200 10 94e 17d 85e 77d 68e 150 1 251d 43c 216d 208c 173d 150 20 309b 67b 284b 242b 217b 150 10 279c 58b 251c 221c 193c Means followed by different superscript letter in the column differ significantly (p<0.05) for a given feed moisture Table.4 Rheological properties of honey-cereals in combination extrudates Treatments Rheological properties Moisture Temperature Honey (%) (0C) (%) Peak Hold Final Breakdown Setback viscosity viscosity viscosity viscosity viscosity (cP) (cP) (cP) (cP) (cP) 14 17 120 5 342b 76a 311a 266b 235a 180 5 150d 20b 106c 130d 86c 120 15 364a 83a 318a 281a 235a 180 15 172c 23b 140b 149c 117b 100 10 418a 102a 373a 316a 271a 200 10 90e 14d 81e 76d 67e 150 1 242d 41c 201d 201c 160d 150 20 286b 57b 268b 229b 211b 150 10 264c 53b 241c 211c 188c Column wise, means followed by superscript letter within moisture differs significantly (P<0.05). and setback viscosity of the extrudates prepared from maize and honey at varying level and processing conditions differed significantly (p<0.05). It was observed that at Honey-maize extrudates The pasting characteristics such as peak viscosity, final viscosity, breakdown viscosity 424 Int.J.Curr.Microbiol.App.Sci (2017) 6(3): 419-427 both the feed moisture and at all the honey levels, the maximum values of pasting characteristics were observed at lower extrusion temperature whereas the minimum values were found at higher extrusion temperature. The extrusion temperature at 17 per cent feed moisture and 10 per cent honey level also adversely affected the pasting characteristics. The effect of extrusion temperature on pasting characteristics was such drastic that the reduction in viscosity by increasing temperature from 120 to 1800C was more than half. Xie et al., (2009) reported that the apparent viscosity of corn starch generally decreased with increasing temperature from 110 to 1400C. The abrupt decrease in the viscosity of extrudates by increased extrusion temperature could be attributable to excessive polymer leaching and disorganization of ordered granular structure of starch, amylose and amylopectin molecules. increase in the final viscosity of mixture. As honey, due to its sticky character could resist the shear stress, may have enhanced the breakdown viscosity. The increase in setback viscosity on increased addition of honey in feed designate that it could hinder the reassociation and re-ordering of starch molecules in the mixture. The results of the present investigation with respect to pasting characteristics of extrudates are in agreement with the study of Martinez et al., (2014). Honey-cereals in combination extrudates The data pertaining to the pasting properties of combined cereals (wheat, rice and maize) and honey extrudates is reflected in table 4. Rapid Visco Analyzer did indicate the pasting temperature for none of the sample. This suggests that most of the starch present in the feed already underwent the gelatinization and cooking. It could be observed from the table 4 that peak viscosity, final viscosity, breakdown viscosity and setback viscosity reduced with increase in extrusion temperature. However, level of honey in feed was found to have positive effect on these pasting characteristics. The peak viscosity was found in the range of 90-418 cP, highest peak viscosity being observed at lowest temperature and vice versa. At intermediate extrusion temperature (1500C) the peak viscosity observed was 264 cP. Increased honey level also found to affect the peak viscosity of extrudates, however, the effect was constructive. Increasing the honey level from 1 to 20 per cent increased the peak viscosity of extrudates from 242 to 286 cP. It is evident from table 3 that quantity of honey added in the feed has marked influence on the pasting characteristics of extrudates. At all the levels, honey produced statistically (p<0.05) significant difference in peak viscosity, final viscosity, breakdown viscosity and setback viscosity. Similarly, at constant feed moisture of 14 per cent and extrusion temperature of 1200C, the increase in honey level from 5 to 15 per cent resulted in increase in peak viscosity from 368 to 385 cP, final viscosity from 322 to 340 cP, breakdown viscosity from 287 to 299 cP and setback viscosity from 241 to 254 cP. Similar increase in all pasting characteristics was examined when honey level in feed was increased at other feed moisture (14 and 17%) and extrusion temperatures (180 and 1500C). The peak viscosity, which is indication of viscous load likely to be encountered during mixing, may have increased owing to natural viscous nature of honey. Honey might contribute in the formation of viscous paste and thereby Table 4 indicates that the final viscosity of extrudates decreased with increase in the extrusion temperature and increased with increase in honey level in the feed. At 17 per cent feed moisture and 10 per cent honey level in the feed, the final viscosity of extrudates decreased from 373 to 81 cP when 425 Int.J.Curr.Microbiol.App.Sci (2017) 6(3): 419-427 temperature of extrusion was increased from 100 to 2000C. This could be due to the intensive molecular breakdown at the elevated extrusion temperature since the viscosity of a paste depends on the degree of gelatinization and molecular breakdown (El-Dash et al., 1983). Contrary to the effect of extrusion temperature an increase in final viscosity from 201 to 268 cP was observed when the honey level in feed was varied from 1 to 20 per cent. All the treatments differed significantly (p<0.05) from each other at various processing conditions. This indicates that the effect of extrusion temperature and honey level in feed was not equal in magnitude. increase in the viscosity of wheat-corn blend extrudates upon addition of sugar. In conclusion, this study revealed that the rheological parameters of extrudates are significantly getting affected as a function of extrusion processing. Non-detection of pasting temperature indicated that the samples were undergone sufficient cooking on extrusion. Reduction in the rheological characteristics was attributed due to depolymerization of feed material as a function of increased extrusion temperature. Incremental addition of honey in the cereal flours lead to slight increase in the viscosity of extrudates. Hence honey addition in whole cereal flour is likely to enhance the textural characteristics of honey. The results of this study will help in modeling and optimizing the extrusion conditions for processing of whole grain cereal flour and liquid ingredient like honey in preparation of extruded snacks. Extrusion temperature and honey level in feed affected the breakdown viscosity and setback viscosity of extrudates quite similar to the peak and final viscosities. At 14 per cent feed moisture and 5 and 15 per cent honey level, increasing the extrusion temperature from 120 to 1800C almost halved the breakdown viscosity of extrudates. However such effect was not noticed when the honey level was increased from 5 to 15 per cent at both, 120 as well as 1800C extrusion temperature. This again verifies that the extrusion temperature was the dominant factor in governing the pasting properties of extrudates, over honey level. The highest setback viscosity was obtained at lower extrusion temperature while the lowest setback viscosity was observed at higher extrusion temperature. 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