title: Evaluating the freezing impact on the proximate composition of immature cowpea (Vigna unguiculata L.) pods: classical versus spectroscopic approaches.
abstract: BACKGROUND
  Freezing represents a common conservation practice regarding vegetal foodstuffs. Since compositional features need to be monitored during storage, the development of rapid monitoring tools suitable for assessing nutritional characteristics arises as a pertinent issue. In this study, cowpea (Vigna unguiculata L.) pods, both fresh and after 6 and 9 months of freezing at -18 °C, were evaluated by high-performance liquid chromatography for their content of protein as well as of essential and nonessential amino acids, while their Fourier transform infrared spectra in the mid infrared (MIR) and near infrared (NIR) ranges were concomitantly registered to assess the feasibility of this approach for the traceability of these frozen matrices.
  
  
  RESULTS
  For the NIR interval, the application of the 1st derivative to the spectral data retrieved the best results, while for lower concentrations the application of the Savitzky-Golay algorithm was indispensable to achieve quantification models for the amino acids. MIR is also suitable for this purpose, though being unable to quantify amino acids with concentrations below 0.07 mmol g-1dry weight, irrespective of the data treatment used.
  
  
  CONCLUSIONS
  The spectroscopic approach constitutes a methodology suitable for monitoring the impact of freezing on the nutritional properties of cowpea pods, allowing accurate quantification of the protein and amino acid contents, while NIR displayed better performance. © 2017 Society of Chemical Industry.
authors.affiliation: Centre for the Research and Technology of Agro-Environmental and Biological Sciences, University of Trás-os-Montes and Alto Douro (UTAD-CITAB), Vila Real, Portugal.
authors.forename: Nelson
authors.initials: N
authors.lastname: Machado
authors.affiliation: Centre for the Research and Technology of Agro-Environmental and Biological Sciences, University of Trás-os-Montes and Alto Douro (UTAD-CITAB), Vila Real, Portugal.
authors.forename: David
authors.initials: D
authors.lastname: Oppolzer
authors.affiliation: Centre for the Research and Technology of Agro-Environmental and Biological Sciences, University of Trás-os-Montes and Alto Douro (UTAD-CITAB), Vila Real, Portugal.
authors.forename: Ana
authors.initials: A
authors.lastname: Ramos
authors.affiliation: The Animal and Veterinary Research Centre, University of Trás-os-Montes and Alto Douro (UTAD-CECAV), Department of Veterinary Sciences, Vila Real, Portugal.
authors.forename: Luis
authors.initials: L
authors.lastname: Ferreira
authors.affiliation: Centre for the Research and Technology of Agro-Environmental and Biological Sciences, University of Trás-os-Montes and Alto Douro (UTAD-CITAB), Vila Real, Portugal.
authors.forename: Eduardo As
authors.initials: EA
authors.lastname: Rosa
authors.affiliation: The Animal and Veterinary Research Centre, University of Trás-os-Montes and Alto Douro (UTAD-CECAV), Department of Veterinary Sciences, Vila Real, Portugal.
authors.forename: Miguel
authors.initials: M
authors.lastname: Rodrigues
authors.affiliation: Centre for the Research and Technology of Agro-Environmental and Biological Sciences, University of Trás-os-Montes and Alto Douro (UTAD-CITAB), Vila Real, Portugal.
authors.forename: Raúl
authors.initials: R
authors.lastname: Domínguez-Perles
authors.affiliation: Centre for the Research and Technology of Agro-Environmental and Biological Sciences, University of Trás-os-Montes and Alto Douro (UTAD-CITAB), Vila Real, Portugal.
authors.forename: Ana Irna
authors.initials: AI
authors.lastname: Barros
mesh_terms: D000596:Amino Acids / Q000032:analysis; D002851:Chromatography, High Pressure Liquid; D005519:Food Preservation / Q000379:methods*; D061353:Food Storage; D005615:Freezing; D064209:Phytochemicals / Q000032:analysis; D010940:Plant Proteins / Q000032:analysis; D012639:Seeds / Q000737:chemistry* / Q000254:growth & development; D017550:Spectroscopy, Fourier Transform Infrared; D000070658:Vigna / Q000737:chemistry* / Q000254:growth & development
chemical_list: D000596:Amino Acids; D064209:Phytochemicals; D010940:Plant Proteins
keywords: FTIR spectroscopy; amino acids; chromatography; cowpea pods; multivariate analysis; protein content