Influence of germination on the nutritional value and lipid profile of Vigna unguiculata seeds

Introduction and objectives: Legumes have high levels of protein and fiber and despite their low fat content, their lipid fraction is of high nutritional quality, contributing to a balanced diet. Moreover, when supplemented with cereals, they can be good animal protein substitutes. Objective: In this work, seeds of Vigna unguiculata in different stages – germinated, green (in natura) and dried – were compared regarding their nutritional composition and lipid profile (fatty acids and vitamin E). Materials and Methods: The content of ash, protein, fat, fiber (total and insoluble) were analysed by AOAC methods. The moisture content was determined using an infrared moisture analyser. The content of carbohydrates and soluble fiber was obtained indirectly by calculation. The fatty acid (FA) and vitamin E (tocopherols and tocotrienols) profiles were determined by chromatographic techniques (GC-FID and HPLC-DAD-FLD, respectively). Results: In a dry weight (dw) basis, no significant differences were found between protein and carbohydrate contents of the different types of seeds. However, significantly higher levels of ash (4.97%) and insoluble fiber (24.69%) were found in germinated seeds. In turn, green ones presented significantly higher levels of fat (1.58%) and soluble fiber (8.45%). Regarding vitamin E, total contents ranged from 5.2 to 10.3 mg/100 g dw. δ-Tocopherol (4.2-6.7 mg/100 g dw) was the major compound found, followed by γ-tocopherol (0.6-3.3 mg/100 g dw). Both vitamers were present in significantly higher contents in dried seeds, while α-tocopherol contents were significantly higher in germinated ones. In what concerns to the lipid profile, C16:0 (21.5-24.6%), C18:2n6 (33.5-34.7%), and C18:3n3 (22.1-26.1%) were the major FA. Some differences were noticed between the FA profiles of the different samples, being germinated seeds slightly richer in saturated FA, while dried seeds presented higher relative percentages of polyunsaturated ones. Conclusion: In general, with germination, there was a significant increase in the ash and insoluble fiber contents of the seeds, as well as modifications in the vitamin E and FA profiles. Nevertheless, the nutritional richness of the Vigna unguiculata seeds was demonstrated independently of the seed stage.

The authors thank the financial support to the project Operação NORTE-01-0145-FEDER-000011 – denominada Qualidade e Segurança Alimentar – uma abordagem (nano)tecnológica. This work was also supported by the project UID/QUI/50006/2013 – POCI/01/0145/FEDER/007265 with financial support from FCT/MEC through national funds and co-financed by FEDER. S. Bessada and M. Nunes thank their PhD grants to FCT (SFRH/BD/122754/2016 and SFRH/BD/130131/2017, respectively).

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