Amaranth and quinoa in extruded corn snacks: Effect of storage temperature on lipid oxidation

Transcription

1 Amaranth and quinoa in extruded corn snacks: Effect of storage temperature on lipid oxidation Jose M. Ramos Diaz and Kirsi Jouppila Department of Food and Environmental Sciences, Agnes Sjöbergin katu 2 P.O. Box 66, FI University of Helsinki, Finland. ABSTRACT Amaranth and quinoa are pseudocereals cultivated in South America that could become attractive food alternatives in Europe due to their status as gluten-free. The aims of this investigation were to prepare corn-based snacks containing amaranth and quinoa using extrusion cooking, and to evaluate lipid stability of snacks exposed to different storage temperatures. Amaranth and quinoa grains were delivered from South America, and precooked cornmeal (polenta) was purchased from a local store. Grains were milled with a pin disc mill (flour particle size <500 μm). A co-rotating twin-screw extruder was used to obtain corn-based extrudates containing various concentrations of amaranth and quinoa flour (tested flours). Samples for analyses (content of tested flours, TF: 20, 35 and 50%) were collected under specific extrusion conditions (water content of mass: 14%; screw speed: 350 and 500 rpm; temperature of die: 140 and 150 C). Analyses included determination of sectional expansion index (SEI), hardness and water content of extrudates (WCE). Formation of hexanal was evaluated from extrudates stored in sealed headspace vials at 20 and 40 C in darkness using headspace gas chromatography at intervals during storage (0, 1, 3 and 5 weeks). Extrudates containing 20% TF presented significantly higher SEI (p<0.05) than those containing 35 and 50% TF. Hardness and WCE was generally higher in extrudates containing 35% TF than in those containing 20 and 50% TF. SEI was above 8 and hardness below 70 N/mm regardless of the TF. In general, extrudates containing quinoa presented lower hexanal production than extrudates containing amaranth in storage. Extrudates containing quinoa and exposed to 20 C presented a stable hexanal production along time in contrast to those containing amaranth. At 40 C, extrudates containing quinoa and amaranth showed a rapid increase in hexanal production after 1 week of storage. This study proved that it is possible to obtain expanded extrudates with relatively low hardness and containing up to 50% amaranth or quinoa. Extrudates containing amaranth appeared more sensitive to oxidation than those containing quinoa. 1 Introduction Amaranth (Amaranthus caudatus) and quinoa (Chenopodium quinoa) have been cultivated in South America for 5000 years and were important sources of protein and fiber before colonial times. Over the last decades, food researchers have become increasingly interested in these pseudocereals due to their potential as gluten-free components, for example, in cereal breakfast (Gallagher et al., 2011; Repo-Carrasco et al., 2011). Different levels of gluten sensitivity are increasingly diagnosed in Western Europe responding to genetic variations (prevalence of HLA genotypes) and cereal protein intake during infancy. The latter may seriously increase the incidence of gluten-related disorders especially among populations with genetic predisposition to celiac disease, which is the case in Sweden, Finland and Denmark (Ascher and Kirstiansson, 1997; Greco 1997). Therefore, insufficient gluten-free alternatives are a matter of growing concern in Northern Europe, this being mainly caused by overreliance on wheat as principal source of carbohydrates. Several studies affirmed that amaranth and quinoa have high quality protein in terms of digestibility, efficiency ratio and nutrition balance, almost equivalent to that of milk protein casein (Ranhotra et al., 1993; Repo-Carrasco et al., 2003). Additionally, these pseudocereals are also rich in polyunsaturated fatty acids (high linolenic:linoleic acid ratio) and bioactive compounds such as γ- and β-tocopherol, polyphenols and flavonoids. Despite the nutritional advantage of pseudocereals compared to wheat, their industrialization has been limited to low cost technological processes such as extrusion with moderate success in developing countries. The nutritional and technological effects of extrusion cooking in relation to these particular ingredients are still a matter of scientific investigation. The aims of the present research are to (1) prepare gluten-free corn-based extrudates containing various concentrations of amaranth and quinoa, and (2) to study their sensitivity to lipid oxidation in storage at different temperatures. InsideFood Symposium, 9-12 April 2013, Leuven, Belgium 1 P a g e

2 2 Material and Methods 2.1 Materials Amaranth and quinoa were delivered from South America as seeds and milled at VTT research centre (tested flours; particle size <500 μm). Precooked corn meal (polenta) was obtained from a local store (bulk flour). 2.2 Extrusion The extrusion was conducted in a twin-screw extruder (Thermo Prism PTW24 Thermo Haake, Polylab System, Germany) that consisted of seven sections with individual temperature control in six of them. The screw had a length of 672 mm and consisted of six conveying screws, six mixing areas and an extrusion screw element. There was a constant feed rate (84 g/min) and fixed temperature profile (90, 95, 95, 100, 110, 140 C). A split-plot experimental design with four independent variables was used: content of tested flours (20, 35 and 50%; TF), temperature of die (140, 150 and 160 C; TEM), screw speed (200, 350 and 500 rpm; SS) and water content of mass (14, 16 and 18%; WCM). From a total of 48 samples per tested flour, the most expanded extrudates were collected under specific extrusion conditions for further analysis (Table 1). Table 1. Processing conditions of most expanded extrudates containing various contents of amaranth and quinoa Content of tested flours, % of solids Temperature of die, C Screw speed, rpm Water content, % Determination of sectional expansion index (SEI), hardness and water content of extrudates (WCE) The diameter of 10 specimens per sample was measured using a vernier caliper. SEI was calculated by dividing the cross sectional area of the extrudate and the area of the die (Ø= 5 mm). Hardness was, on the other hand, measured as the slope of force-distance curve (N/mm) when compression was enforced perpendicularly under three-point bending. A universal testing machine (Instron 4465, Instron Ltd., High Wycombe, UK) was fitted with a flat-shaped aluminium probe (3 mm 29 mm) that moved perpendicularly to the sample holder. The speed of the cross head was 5 mm/min. Before hardness measurement, 10 specimens per sample were vacuum-dried at 54 C for 72 hours. This pre-treatment was done in order to prevent the plasticising effect of water on hardness. WCE was calculated from the weight loss in drying (vacuum-drying at 54 C for 72 hours) 2.4 Hexanal analysis Extrudates were cut into pieces (10-15 mm) before being placed into separate 20-ml headspace vials (0.5 g/vial). Sealed vials were kept at 20 and 40 C for 0, 1, 3 and 5 weeks in darkness. Hexanal was analysed using static headspace gas chromatography (HS-GC). The Autosystem XL gas chromatograph was equipped with an HS40XL head space sampler (Perkin-Elmer, Shelton, CT; column NB-54, Nordion). The column had a length and diameter of 25 m and 32 μm, respectively. Injection and detection temperature was set at 250 C. Flame gases were synthetic air and hydrogen, and carrier gas was helium. Vials were thermostated at 80 C for 18 min prior to injection. The run temperature was 60 C for 10 min (per vial). 2.5 Statistical analysis Data obtained from physical measurements (10 replicates) were statistically analysed by analysis of variance (ANOVA), and by computing Least Significant difference (p<0.05) (v17.0 SPSS Inc., Chicago, Illinois). Headspace analyses were conducted in triplicate and results expressed as means and standard deviation (SD). P a g e 2

3 3 Results 3.1 Sectional expansion, hardness and water content Extrudates containing 20% TF presented SEIs of 11.8 (amaranth) and 11.3 (quinoa) while those containing 35 % TF presented SEIs of 9.70 (amaranth) and 9.73 (quinoa). At 50% TF, SEIs were 9.14 (amaranth) and 9.27 (quinoa). There was significant difference in SEI (p<0.05) between extrudates containing 20% TF and those containing 35 and 50% TF. In terms of expansion, extrudates containing amaranth and quinoa showed very similar behaviour (Figure 1 and 2). Fig. 1 Cross-sectional area of corn-based extrudates containing amaranth and quinoa at various concentrations Extrudates containing 20% amaranth presented the lowest hardness (25.9 N/mm) while those containing 35% amaranth presented the highest (57.6 N/mm). Extrudates containing quinoa maintained a considerable degree of hardness stability around 40 N/mm irrespective of the content of TF. At 50% TF, extrudates containing either amaranth or quinoa showed very similar traits in terms of hardness (~36 N/mm) and SEI (~9.2) (Figure 2). Fig. 2 SEI ( ) and hardness ( ) of corn-based extrudates containing amaranth (A) and quinoa (B). Error bar shows ±1 SD. Extrudates containing 20 and 35% amaranth did not show significant differences (p<0.05) in their water content (7.7 and 7.81%, respectively). However, extrudates containing 50% amaranth showed much lower water content (5.74%). Extrudates containing 20% quinoa presented low water content (6.34%) compared to those containing 35 and 50% quinoa (8.15 and 7.61%, respectively) (Figure 3). 3 P a g e

4 Fig. 3 Water content of extrudates at different concentrations of amaranth ( ) and quinoa ( ) flour. Error bar shows ±1 SD. 3.2 Hexanal formation In general, extrudates containing amaranth presented comparatively higher hexanal production than those containing quinoa. During the first three weeks at 20 C, the hexanal content of extrudates containing quinoa was close to zero, before a slight rise by the end of the fifth week. For extrudates containing amaranth, hexanal production increased gradually before reaching a maximum (plateau for extrudates containing 50% amaranth) in the third week. Extrudates containing different content of TF exhibited quite similar trends of hexanal formation in storage at 20 C (Figure 4). Extrudates containing amaranth presented a faster start-up production of hexanal compared to those containing quinoa in the first week of storage at 40 C (Figure 4). By the third week, hexanal content of extrudates containing quinoa increased considerably while extrudates containing amaranth (20 and 35% TF) seemed to reach a plateau. Between the third and fifth week, extrudates containing 20 and 35% quinoa showed a noticeable degree of stability while those containing 50% quinoa presented a steady increase in hexanal content. On the other hand, extrudates containing 20 and 50% amaranth exhibited a steady production of hexanal, surpassing extrudates containing 20 and 35% quinoa. By the end of the fifth week, extrudates containing 35% amaranth and 50% quinoa presented the highest hexanal content. Fig. 4 Production of hexanal in extrudates containing 20% (Δ), 35% ( ) and 50% ( ) amaranth and quinoa. Error bar shows ±1 SD. InsideFood Symposium, 9-12 April 2013, Leuven, Belgium 4 P a g e

5 4 Discussion 4.1 Effect of tested flours on the physical characteristics of extrudates Content of TF had barely any effect on SEI and hardness if compared to screw speed and water content of mass as calculated using PLS modelling (data not included). However, a closer look to the most expanded extrudates obtained at similar operational conditions (except for samples containing 35% TF) evidenced a statistically significant difference between extrudates containing 20% TF and those containing 35 and 50% TF. According to previous studies (Repo-Carrasco, 2011; Ramos Diaz, 2011), amaranth and quinoa had contents of protein and dietary fiber above 12% and 8% (w/w dry weight), respectively. In that sense, a steady increase in protein and dietary fiber did not seem to affect considerably the physical structure of extrudates. Observable differences in pore size distribution between extrudates containing quinoa were hardly distinguishable while extrudates containing amaranth presented relatively smaller pore sizes as content of TF increased. The results obtained in this study disagreed with those of Coulter and Lorenz (1991). Coulter and Lorenz (1991) observed that as content of quinoa increased from 10 to 30%, corn-based extrudates showed tremendous decrease in expansion. Unlike the present study, Coulter and Lorenz (1991) found that the effect of quinoa was very significant (p<0.001) on expansion. On the other hand, Ilo et al. (1999) used up to 60% amaranth in blend with rice and found that increasing amaranth contents caused an enormous decrease in expansion and increase in hardness (p<0.001). Extrudates containing quinoa exhibited higher WCE at lower content of TF while extrudates containing amaranth presented higher WCE at higher content of TF. Slight variations in the content of fiber, fat and hydrophobicity of proteins might have had some effect on the amount water retained in the extrudates. For extrudates containing 35% TF, lower screw speed (350 rpm) might have led to consistently higher WCE compared to other samples; Kirjoranta et al. (2012) and Ramos (2012) affirmed that WCE increased at lower screw speed while experimenting on barley- and corn-based extrudates, respectively. This study also found that screw speed had a strong negative effect on WCE as calculated using PLS modelling (data not included). 4.2 Effect of storage temperature and tested flours on hexanal formation Content of TF did not seem have a clear effect on hexanal formation at either 20 or 40 C. In fact, extrudates containing different types of tested flour (amaranth or quinoa) showed distinct patterns. Extrudates containing quinoa were slightly more stable than those containing amaranth at lower temperature. Despite their growing trend at higher temperature, extrudates containing quinoa maintained lower hexanal production than those containing amaranth. These results suggested that higher temperature might lead to higher formation of linoleic hydroperoxides and, therefore, hexanal in extrudates. According to previous studies (Ramos Diaz, 2011; Repo-Carrasco 2011), quinoa was particularly rich in γ- and β-tocopherol while amaranth was richer only in β- tocopherol. This might lead to slightly higher antioxidant activity on extrudates containing quinoa than in those containing amaranth. 5 Conclusions This study proved that it was possible to prepare expanded gluten-free corn-based snacks containing up to 50% amaranth or quinoa. Apparently, the increase of fiber and protein had a minor observable effect on the expansion, and almost negligible effect on hardness of extrudates containing quinoa. This not only contradicts previous studies but also introduces alternatives ingredients for the development of edible gluten-free snacks. As expected, hexanal formation as an indicator of rancidity was comparatively low at 20 C compared to 40 C. Extrudates containing amaranth were slightly more sensitive to oxidation than quinoa as evidenced by the curves of hexanal formation. InsideFood Symposium, 9-12 April 2013, Leuven, Belgium 5 P a g e

6 Acknowledgements References We wish to thank Timo Holopainen from University of Helsinki for technical help during extrusion. Ascher, H., Kristiansson, B., The highest incidence of celiac disease in Europe: The Swedish experience. J. Pediatr. Gastroenterol. Nutr. 24, 3 6. Coulter, L.A., Lorenz, K., Extruded corn grits quinoa blends: II. Physical characteristics of extruded products. J. Food Process. Preserv. 15, Gallagher, E., Gormley, T.R., Arendt, E.K., Recent advances in the formulation of gluten-free cereal-based products. Trends Food Sci. Tech. 15, Greco, L., From the Neolithic revolution to gluten intolerance: Benefits and problems associated with the cultivation of wheat. J. Pediatr. Gastroenterol. Nutr. 24, Ilo, S.E., Liu, Y., Extrusion cooking of rice flour and amaranth blends. Lebensm.-Wiss. u-technol. 32, Kirjoranta, S., Solala, K., Suuronen, J.-P., Penttilä, P., Peura, M., Serimaa, R., Tenkanen, M., Jouppila, K., Effects of process variables and addition of polydextrose and whey protein isolate on the properties of barley extrudates. Int. J. Food Sci. Technol. 47, Ramos Diaz, J.M., Use of amaranth, quinoa and kañiwa in extruded corn snacks. Master s thesis. University of Helsinki. Ranhotra, G.S., Gelroth, J.A., Glaser, B.K., Lorenz, K.J., Johnson, D.L., Composition and protein nutritional quality of quinoa. Cereal Chem. 70, Repo-Carrasco, R., Andean indigenous food crops: Nutritional value and bioactive compounds. Doctoral dissertation. University of Turku. Repo-Carrasco, R., Esponiza, C., Jacobsen, S.-E., Nutritional value and use of the Andean crops: quinoa (Chenopodium quinoa) and kañiwa (Chenopodium pallidicaule). Food Rev. Int. 19, P a g e 6