Abstract
Quinoa, amaranth, and buckwheat are the most important pseudocereals. Despite pseudocereals resemble in function and composition of those of the true cereals, the seeds overcome cereal properties in some aspects. Recently, the pseudocereals have attracted attention because of the proteins with high nutritive value, and their storage proteins are not toxic for celiac patients. Moreover, the seeds are an important source of dietary fiber and phenols, which are associated with health benefits. Studies have shown the pseudocereal flour suitability as cereal flour replacer in diverse food products (functional and gluten-free). At present, the food application of pseudocereals in bakery products, fermented beverages, and extruded products, among others, has shown successful. Therefore, the pseudocereals have a great potential to popularize in several countries not yet achieved, by introducing crops in human’s food diet and providing new products of high quality (technological, nutritional, and sensorial). For these reasons, this chapter describes some relevant and actual information about worldwide pseudocereal crop production, nutritional and functional composition, use of pseudocereal flours in food product development, and consumer perception.
References
Schoenlechner R, Siebenhandl S, Berghofer E (2008) Pseudocereals. In: Arendt EK, Bello FD (eds) Gluten-free cereal products and beverages. Elsevier, Massachusetts, EUA, p 149–VI
Alvarez-Jubete L, Arendt K, Gallagher E (2010) Nutritive value of pseudocereals and their increasing use as functional gluten- free ingredients. Trends Food Sci Technol 21:106–113. https://doi.org/10.1016/j.tifs.2009.10.014
Ogrodowska D, Zadernowski R, Czaplick S et al (2014) Amaranth seeds and products – the source of bioactive compounds. Pol J Food Nutr Sci 64:165–170. https://doi.org/10.2478/v10222-012-0095-z
Srichuwong S, Curti D, Austin S et al (2017) Physicochemical properties and starch digestibility of whole grain sorghums, millet, quinoa and amaranth flours, as affected by starch and non-starch constituents. Food Chem 233:1–10. https://doi.org/10.1016/j.foodchem.2017.04.019
Nowak V, Du J, Charrondière U (2016) Assessment of the nutritional composition of quinoa (Chenopodium quinoa Willd). Food Chem 193:47–54. https://doi.org/10.1016/j.foodchem.2015.02.111
Pihlanto A, Mattila P, Mäkinen S, Pajari AM (2017) Function bioactivities of alternative protein sources and their potential health benefits. Food Funct 8:3443–3458. https://doi.org/10.1039/c7fo00302a
Matos ME, Rosell CM (2015) Understanding gluten-free dough for reaching breads with physical quality and nutritional balance. J Sci Food Agric Food Agric 95:653–661. https://doi.org/10.1002/jsfa.6732
Kahlon TS, Avena-Bustillos RJ, Chiu MM (2017) Sensory evaluation of gluten-free quinoa whole grain snacks. Heliyon 3:1–12. https://doi.org/10.1016/j.heliyon.2016.e00213
Peksa A, Kita A, Carbonell-Barrachina AA et al (2016) Sensory attributes and physicochemical features of corn snacks as affected by different flour types and extrusion conditions. LWT – Food Sci Technol 72:26–36. https://doi.org/10.1016/j.lwt.2016.04.034
Wang S, Opassathavorn A, Zhu F (2015) Influence of quinoa flour on quality characteristics of cookie, bread and Chinese steamed bread. J Texture Stud 46:281–292. https://doi.org/10.1111/jtxs.12128
Houben A, Hochstotter A, Becker T (2012) Possibilities to increase the quality in gluten-free bread production: an overview. Eur Food Res Technol 235:195–208. https://doi.org/10.1007/s00217-012-1720-0
Collar C, Jiménez T, Conte P, Fadda C (2014) Impact of ancient cereals, pseudocereals and legumes on starch hydrolysis and antiradical activity of technologically viable blended breads. Carbohydr Polym 113:149–158. https://doi.org/10.1016/j.carbpol.2014.07.020
Lorusso A, Verni M, Montemurro M et al (2017) Use of fermented quinoa flour for pasta making and evaluation of the technological and nutritional features. LWT – Food Sci Technol 78:215–221. https://doi.org/10.1016/j.lwt.2016.12.046
Kerpes R, Fischer S, Becker T (2017) The production of gluten-free beer: degradation of hordeins during malting and brewing and the application of modern process technology focusing on endogenous malt peptidases. Trends Food Sci Technol 67:129–138. https://doi.org/10.1016/j.tifs.2017.07.004
Matejčeková Z, Liptáková D, Valík L (2017) Functional probiotic products based on fermented buckwheat with Lactobacillus rhamnosus. LWT – Food Sci Technol 81:35–41. https://doi.org/10.1016/j.lwt.2017.03.018
Kocková M, Dilongová M, Hybenová E, Valík L (2013) Evaluation of cereals and pseudocereals suitability for the development of new probiotic foods. J Chem 2013:1–8
FAO (2017) The future of food and agriculture: trends and challenges. Food & Agriculture Organization of the United Nations, Rome
FAOSTAT (2014) Crops. In: Rome food and agriculture organization of the United Nations. http://www.fao.org/statistics/en/. Accessed 20 Oct 2017
de Morais EC, Alencar NMM (2015) Health benefits and food sources studies on gluten-free diets. In: Langdon RT (ed) Gluten-free diets. Nova Publishers, New York, pp 153–166
Ruiz KB, Biondi S, Oses R et al (2014) Quinoa biodiversity and sustainability for food security under climate change. A review. Agron Sustain Dev 34:349–359. https://doi.org/10.1007/s13593-013-0195-0
Drzewiecki J, Delgado-Licon E, Haruenkit R et al (2003) Identification and differences of total proteins and their soluble fractions in some pseudocereals based on electrophoretic patterns. J Agric Food Chem 51:7798–7804. https://doi.org/10.1021/jf030322x
Deutsch H, Poms R, Heeres H, Kamp J (2008) Labeling and regulatory issues. In: Arendt EK, Bello FD (eds) Gluten-free cereal products and beverages. Academic/Elsevier, Massachusetts, EUA, pp 149–190
Di Fabio A, Parraga G (2016) Origin, production and utilization of pseudocereals. In: Claudia Monika Haros RS (ed) Pseudocereals: chemistry and technology, 1st edn. Willey, Chichester, pp 1–27
Fletcher RJ (2016) Pseudocereals: overview, 2nd edn. Encyclopedia of food grains. Massachusetts, EUA. https://doi.org/10.1016/B978-0-08-100596-5.00039-1
Bressani R (2003) Amaranth. In: Caballero B (ed) Encyclopedia of food sciences and nutrition, 10th edn. Academic, Oxford, pp 166–173
Campbell CG (1997) Buckwheat: Fagopyrum esculentum Moench. Promoting the conservation and use of underutilized and neglected crops. International Plant Genetic Resorces Institute, Rome
Repo-Carrasco-Valencia RA, Serna LA (2011) Quinoa (Chenopodium quinoa, Willd.) as a source of dietary fiber and other functional components. Ciência e Tecnol Aliment 31:225–230. https://doi.org/10.1590/S0101-20612011000100035
Alvarez-Jubete L, Arendt EK, Gallagher E (2009) Nutritive value and chemical composition of pseudocereals as gluten-free ingredients. Int J Food Sci Nutr 60:240–257. https://doi.org/10.1080/09637480902950597
Alencar NMM, Oliveira LC (2015) Technological functions of gluten and implications for celiac disease. In: Rivera H (ed) Gluten food sources, properties and health implications, 1st edn. Nova Publishers, New York, pp 1–345
Malalgoda M, Simsek S (2017) Celiac disease and cereal proteins. Food Hydrocoll 68:108–113. https://doi.org/10.1016/j.foodhyd.2016.09.024
Rastogi A, Shukla S (2013) Amaranth : a new millennium crop of nutraceutical values. Crit Rev Food Sci Nutr 52:109–125. https://doi.org/10.1080/10408398.2010.517876
Gorinstein S, Pawelzik E, Delgado-licon E et al (2002) Characterisation of pseudocereal and cereal proteins by protein and amino acid analyses. J Sci Food Agric 891:886–891. https://doi.org/10.1002/jsfa.1120
Mujica-Sanchez A, Jacobsen S, Izquierdo J (2001) Quinua (Chenopodium quinoa Willd.): ancestral cultivo andino, alimento del presente y del futuro. FAO/RLC, Santiago
Alves LF, Rocha MS, Gomes CCF (2008) Avaliação da qualidade protéica da Quinua Real (Chenopodium quinoa Willd) através de métodos biológicos. e-Scientia 1(1):1–16
Filho AMM, Pirozi MR, Borges JTDS et al (2017) Quinoa: nutritional, functional, and antinutritional aspects. Crit Rev Food Sci Nutr 57:1618–1630. https://doi.org/10.1080/10408398.2014.1001811
Wijngaard HH, Arendt EK (2006) Buckwheat. Cereal Chem 83:391–401
Janssen F, Pauly A, Rombouts I et al (2016) Proteins of Amaranth (Amaranthus spp.), buckwheat (Fagopyrum spp.), and Quinoa (Chenopodium spp.): a food science and technology perspective. Compr Rev Food Sci Food Saf 16:39–58. https://doi.org/10.1111/1541-4337.12240
Gewehr MF, Danelli D, de Melo LM et al (2012) Chemical analysis of quinoa flakes: characterization for use in food products. Braz J Food Technol 15:280–287
Steffolani ME, León AE, Pérez GT (2013) Study of the physicochemical and functional characterization of quinoa and kañiwa starches. Starch – Stärke 65:976–983. https://doi.org/10.1002/star.201200286
Li G, Wang S, Zhu F (2016) Physicochemical properties of quinoa starch. Carbohydr Polym 137:328–338. https://doi.org/10.1016/j.carbpol.2015.10.064
Zhu F (2016) Buckwheat starch: structures, properties, and applications. Trends Food Sci Technol 49:121–135. https://doi.org/10.1016/j.tifs.2015.12.002
Nascimento AC, Motaa C, Coelho I et al (2014) Characterisation of nutrient profile of quinoa (Chenopodium quinoa), amaranth (Amaranthus caudatus), and purple corn (Zea mays L.) consumed in the North of Argentina: proximates, minerals and trace elements. Food Chem 148:420–426. https://doi.org/10.1016/j.foodchem.2013.09.155
Ogungbenle HN (2003) Nutritional evaluation and functional properties of quinoa (Chenopodium quinoa) flour. Int J Food Sci Nutr 54:153–158. https://doi.org/10.1080/0963748031000084106
Valcárcel-Yamani B, Lannes SCDS (2012) Applications of Quinoa (Chenopodium quinoa Willd.) and Amaranth (Amaranthus Spp.) and their influence in the nutritional value of cereal based foods. Food Public Health 2:265–275. https://doi.org/10.5923/j.fph.20120206.12
Hemalatha P, Bomzan DP, Sathyendra Rao BV, Sreerama YN (2016) Distribution of phenolic antioxidants in whole and milled fractions of quinoa and their inhibitory effects on α-amylase and α-glucosidase activities. Food Chem 199:330–338. https://doi.org/10.1016/j.foodchem.2015.12.025
Alvarez-Jubete L, Wijngaard H, Arendt EK, Gallagher E (2010) Polyphenol composition and in vitro antioxidant activity of amaranth, quinoa buckwheat and wheat as affected by sprouting and baking. Food Chem 119:770–778. https://doi.org/10.1016/j.foodchem.2009.07.032
Gómez-Caravaca AM, Iafelice G, Verardo V et al (2014) Influence of pearling process on phenolic and saponin content in quinoa (Chenopodium quinoa Willd). Food Chem 157:174–178. https://doi.org/10.1016/j.foodchem.2014.02.023
Jung K, Richter J, Kabrodt K, Luecke IM, Schellenberg I, Herrling T (2006) The antioxidative power AP – a new quantitative time dependent (2D) parameter for the determination of the antioxidant capacity and reactivity of different plants. Spectrochim Acta Part A Mol Biomol Spectrosc 63:846–850. https://doi.org/10.1016/J.SAA.2005.10.014
Bunzel M, Ralph J, Steinhart H (2005) Association of non-starch polysaccharides and ferulic acid in grain amaranth (Amaranthus caudatus L.) dietary fiber. Mol Nutr Food Res 49:551–559. https://doi.org/10.1002/mnfr.200500030
Yawadio Nsimba R, Kikuzaki H, Konishi Y (2008) Antioxidant activity of various extracts and fractions of Chenopodium quinoa and Amaranthus spp. seeds. Food Chem 106:760–766. https://doi.org/10.1016/j.foodchem.2007.06.004
Taylor JRN, Awika JM (2017) Future research needs for the ancient grains. In: Gluten-free ancient grains. Elsevier Ltd, p 0
Schoenlechner R, Siebenhandl S, Berghofer E (2008) 7 – Pseudocereals. In: Gluten-free cereal products and beverages. Massachusetts, EUA, p 149–VI
de Meo B, Freeman G, Marconi O, Booer C, Perretti G, Fantozzi, P (2011) Behaviour of malted cereals and pseudo-cereals for gluten-free beer production. J Inst Brew 117:541–546. https://doi.org/10.1002/j.2050-0416.2011.tb00502.x
Zhu F (2017) Structures, physicochemical properties, and applications of amaranth starch. Crit Rev Food Sci Nutr 57:313–325. https://doi.org/10.1080/10408398.2013.862784
Venskutonis PR, Kraujalis P (2013) Nutritional components of amaranth seeds and vegetables: a review on composition, properties, and uses. Compr Rev Food Sci Food Saf 12:381–412. https://doi.org/10.1111/1541-4337.12021
Konishi Y, Hirano S, Tsuboi H, Wada M (2004) Distribution of minerals in quinoa (Chenopodium quinoa Willd.) seeds. Biosci Biotechnol Biochem 68:231–234. https://doi.org/10.1271/bbb.68.231
Islas-rubio AR, De Calderon MA et al (2014) Effect of semolina replacement with a raw: popped amaranth flour blend on cooking quality and texture of pasta. LWT – Food Sci Technol 57:217–222. https://doi.org/10.1016/j.lwt.2014.01.014
Bastos GM, Júnior MSS, Caliari M et al (2016) Physical and sensory quality of gluten-free spaghetti processed from amaranth flour and potato pulp. LWT – Food Sci Technol 65:128–136. https://doi.org/10.1016/j.lwt.2015.07.067
Alencar NMM, Steel CJ, Alvim ID et al (2015) Addition of quinoa and amaranth flour in gluten-free breads: temporal profile and instrumental analysis. LWT – Food Sci Technol 62:1011–1018. https://doi.org/10.1016/j.lwt.2015.02.029
Naqash F, Gani A, Gani A, Masoodi FA (2017) Gluten-free baking: combating the challenges – a review. Trends Food Sci Technol 66:98–107. https://doi.org/10.1016/j.tifs.2017.06.004
Deželak M, Zarnkow M, Becker T, Košir IJ (2014) Processing of bottom-fermented gluten-free beer-like beverages based on buckwheat and quinoa malt with chemical and sensory characterization. J Inst Brew 120:360–370. https://doi.org/10.1002/jib.166
Urquizo FEL, Torres SMG, Tolonen T et al (2017) Development of a fermented quinoa-based beverage. Food Sci Nutr 5:602–608. https://doi.org/10.1002/fsn3.436
Chandla NK, Saxena DC, Singh S (2017) Processing and evaluation of heat moisture treated (HMT) amaranth starch noodles; an inclusive comparison with corn starch noodles. J Cereal Sci 75:306–313. https://doi.org/10.1016/j.jcs.2017.05.003
Li M, Zhu K, Sun Q et al (2016) Quality characteristics, structural changes, and storage stability of semi-dried noodles induced by moderate dehydration: understanding the quality changes in semi-dried noodles. Food Chem 194:797–804. https://doi.org/10.1016/j.foodchem.2015.08.079
Suzuki T, Kim S, Mukasa Y et al (2010) Effects of lipase, lipoxygenase, peroxidase and free fatty acids on volatile compound found in boiled buckwheat noodles. J Sci Food Agric 90:1232–1237. https://doi.org/10.1002/jsfa.3958
Han L, Lu Z, Hao X et al (2012) Impact of calcium hydroxide on the textural properties of buckwheat noodles. J Texture Stud 43:227–234. https://doi.org/10.1111/j.1745-4603.2011.00331.x
Condes MC, Anon MC, Dufresne A, Mauri AN (2018) Food hydrocolloids composite and nanocomposite films based on amaranth biopolymers. Food Hydrocoll 74:159–167. https://doi.org/10.1016/j.foodhyd.2017.07.013
Tapia-Blacido D, Sobral PJ, Menegalli FC (2005) Development and characterization of biofilms based on amaranth flour (Amaranthus caudatus). J Food Eng 67:215–223. https://doi.org/10.1016/j.jfoodeng.2004.05.054
Martirosyan DM, Miroshnichenko LA, Kulakova SN et al (2007) Hypertension. Lipids Health Dis 12:1–12. https://doi.org/10.1186/1476-511X-6-1
Diogo A, Vieira S, Bedani R et al (2017) The impact of fruit and soybean by-products and amaranth on the growth of probiotic and starter microorganisms. Food Res Int 97:356–363. https://doi.org/10.1016/j.foodres.2017.04.026
FAO (2011) Quinoa: an ancient crop to contribute to word food security. Reg Off Lat Am Caribb. https://doi.org/10.1016/j.ecoser.2014.09.013
Ávila BP, Braganca GCM, Rockenbach R et al (2017) Physical and sensory characteristics of cake prepared with six whole-grain flours. J Food Meas Charact 11:1486–1492. https://doi.org/10.1007/s11694-017-9527-0
Rizzello CG, Lorusso A, Montemurro M, Gobbetti M (2016) Use of sourdough made with quinoa (Chenopodium quinoa) flour and autochthonous selected lactic acid bacteria for enhancing the nutritional, textural and sensory features of white bread. Food Microbiol 56:1–13. https://doi.org/10.1016/j.fm.2015.11.018
O’Shea N, Arendt E, Gallagher E (2014) State of the art in gluten-free research. J Food Sci 79:1067–1076. https://doi.org/10.1111/1750-3841.12479
Mišana A, Petelin A, Stubelj M et al (2017) Buckwheat – enriched instant porridge improves lipid profile and reduces inflammation in participants with mild to moderate hypercholesterolemia. J Funct Foods 36:186–194. https://doi.org/10.1016/j.jff.2017.06.056
Qin L, Sui X, Zeng H, Xu Z (2014) Fortification of the health benefit of buckwheat (Fagopyrum tataricum) tea. J Food Process Preserv 38:1882–1889. https://doi.org/10.1111/jfpp.12160
Pellegrini N, Agostoni C (2015) Nutritional aspects of gluten-free products. J Sci Food Agric 95:2380–2385. https://doi.org/10.1002/jsfa.7101
Jnawali P, Kumar V, Tanwar B (2016) Celiac disease: overview and considerations for development of gluten-free foods. Food Sci Hum Wellness 5:169–176. https://doi.org/10.1016/j.fshw.2016.09.003
Gao Y, Janes ME, Chaiya B et al (2017) Gluten-free bakery and pasta products: prevalence and quality improvement. Int J Food Sci Technol (in press): 1–14. https://doi.org/10.1111/ijfs.13505
Alencar NMM, de Carvalho Oliveira L (2017) Trends in bread consumption: non-wheat cereals, technological challenges and sensory quality. In: Lewis H (ed) Bread consumption, cultural significance and health effects. Nova Publishers, New York, p 276
Alvarez-Jubete L, Auty M, Arendt EK, Gallagher E (2010) Baking properties and microstructure of pseudocereal flours in gluten-free bread formulations. Eur Food Res Technol 230:437–445. https://doi.org/10.1007/s00217-009-1184-z
Marti A, Bottega G, Franzetti L et al (2015) From wheat sourdough to gluten-free sourdough: a non- conventional process for producing gluten-free bread. Int J Food Microbiol 50:1268–1274. https://doi.org/10.1111/ijfs.12757
Gallagher E, Gormley TR, Arendt EK (2004) Recent advances in the formulation of gluten-free cereal-based products. Trends Food Sci Technol 15:143–152. https://doi.org/10.1016/j.tifs.2003.09.012
Chauhan A, Saxena DC, Singh S (2016) Physical, textural, and sensory characteristics of wheat and amaranth flour blend cookies. Cogent Food Agric 2:1125773. https://doi.org/10.1080/23311932.2015.1125773
Rothschild J, Rosentrater KA, Onwulata C et al (2015) Influence of quinoa roasting on sensory and physicochemical properties of allergen-free, gluten-free cakes. Int J Food Sci Technol 50:1873–1881. https://doi.org/10.1111/ijfs.12837
Chillo S, Laverse J, Falcone PM, Del Nobile MA (2008) Quality of spaghetti in base amaranthus wholemeal flour added with quinoa, broad bean and chick pea. J Food Eng 84:101–107. https://doi.org/10.1016/J.JFOODENG.2007.04.022
Wang S, Zhu F (2016) Formulation and quality attributes of quinoa food products. Food Bioprocess Technol 9:49–68. https://doi.org/10.1007/s11947-015-1584-y
Fiorda FA, Soares MS, da Silva FA et al (2013) Microstructure, texture and colour of gluten-free pasta made with amaranth flour, cassava starch and cassava bagasse. LWT – Food Sci Technol 54:132–138. https://doi.org/10.1016/J.LWT.2013.04.020
Hidalgo MJ, Sgroppo SC, Camiña JM et al (2015) Trace element concentrations in commercial gluten-free amaranth bars. J Food Meas Charact 9:426–434. https://doi.org/10.1007/s11694-015-9250-7
Cárdenas-Hernández A, Beta T, Loarca-Piña G et al (2016) Improved functional properties of pasta: enrichment with amaranth seed flour and dried amaranth leaves. J Cereal Sci 72:84–90. https://doi.org/10.1016/J.JCS.2016.09.014
Kowalski RJ, Medina-Meza IG, Thapa BB et al (2016) Extrusion processing characteristics of quinoa (Chenopodium quinoa Willd.) var. cherry vanilla. J Cereal Sci 70:91–98. https://doi.org/10.1016/J.JCS.2016.05.024
Rozin P (2001) Food preference. In: International encyclopedia of social & behavioral sciences. pp 5719–5722
Raz C (2008) From sensory marketing to sensory design: how to drive formulation using consumers’ input? Food Qual Prefer 19:719–726
Favalli S, Skov T, Byrne DV (2013) Sensory perception and understanding of food uniqueness: From the traditional to the novel. Food Res Int 50:176–188. https://doi.org/10.1016/j.foodres.2012.10.007
American Society for testing and materials standards sensory-evaluation. In: http://www.astm.org/Standards/sensoryevaluation-Stand
Stone H, Sidel JL (2004) Sensory evaluation practices, 3rd edn. Elsevier
Lavini A, Pulvento C, D’Andria R et al (2014) Quinoa’s potential in the Mediterranean region. J Agron Crop Sci 200:344–360. https://doi.org/10.1111/jac.12069
Gimenez-Batista JA, Piskula M, Zielinski H (2015) Recent advances in development of gluten-free buckwheat products. Food Sci Technol 44:58–65. https://doi.org/10.1016/j.tifs.2015.02.013
Diaz JMR, Suuronen J-P, Deegan KC et al (2015) Physical and sensory characteristics of corn-based extruded snacks containing amaranth, quinoa and kaniwa flour. LWT – Food Sci Technol 64:1047–1056. https://doi.org/10.1016/j.lwt.2015.07.011
Alencar NMM, de Morais EC, Steel CJ et al (2017) Sensory characterisation of gluten-free bread with addition of quinoa, amaranth flour and sweeteners as an alternative for coeliac patients. Int J Food Sci Technol 52:872–879. https://doi.org/10.1111/ijfs.13349
Akande OA, Nakimbugwe D, Mukisa IM (2017) Optimization of extrusion conditions for the production of instant grain amaranth-based porridge flour. Food Sci Nutr 5:1–10. https://doi.org/10.1002/fsn3.513
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Alencar, N.M.M., de Carvalho Oliveira, L. (2018). Advances in Pseudocereals: Crop Cultivation, Food Application, and Consumer Perception. In: Mérillon, JM., Ramawat, K. (eds) Bioactive Molecules in Food. Reference Series in Phytochemistry. Springer, Cham. https://doi.org/10.1007/978-3-319-54528-8_63-1
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