The Effect of Solid-State Fermentation on Air-Classified Pea Protein-Enriched Flour to Improve the Digestibility and Functional Properties
Date
2019-06-13
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
0000-0003-3509-2788
Type
Thesis
Degree Level
Masters
Abstract
The overarching goal of this research was to investigate the effect of solid-state fermentation (SSF) on pea protein-enriched flour (PPEF) to improve the digestibility and functional properties. The pea protein is classified as an enriched flour since it has a higher protein content than pea flour (20-30%) however, is less than a concentrate (70%) or isolate (90%) (Singhal et al., 2016; Lam et al., 2018). PPEF was inoculated with Aspergillus oryzae NRRL 5590 or Aspergillus niger NRRL 334 and evaluated at two temperatures (30C and 40C) over 48 h of fermentation to obtain limited protein hydrolysis (0-10%). Limited protein hydrolysis was acquired to enhance functionality properties in addition to the protein digestibility. The surface charge of fermented PPEF increased in negativity over fermentation time for both fungi: from
-16.2 to -18.4 mV for A. oryzae and from -13.5 to -18.6 mV for A. niger. Whereas, surface hydrophobicity decreased from 14.1 to 8.4 a.u. for A. oryzae and 21.6 and 13.9 a.u. for A. niger. Fermented PPEF was analyzed for nitrogen solubility, emulsifying and foaming properties at pH values of 3.0, 5.0 and 7.0. In all samples, functionality (based on solubility, emulsification and foaming) was found to be greatest at pH 3.0 and 7.0 and lowest at pH 5.0 (near the isoelectric point of PPEF). Specifically, fermented PPEF was found to significantly decrease in solubility over fermentation time for both fungi at all pH values tested (p<0.001). Due to the low solubility in all fermented samples, the functional properties (foaming and emulsifying properties) that are dependent upon high solubility were negatively impacted. However, water and oil holding capacities of fermented PPEF increased over the 6-h of fermentation. Water holding capacity increased from 1.5 g/g to 2.0 g/g with A. oryzae fermentation, and oil holding capacity increased from 1.2 g/g to 2.3 g/g with A. niger fermentation.
Fermentation was found to improve protein quality of PPEF. Proteolysis inhibition, i.e., activities of trypsin and chymotrypsin inhibitors, was found to reduce over fermentation (~11-30% and 22-23% in A. oryzae and A.niger, respectively). Whereas, total phenolic content was shown to increase during fermentation (from ~38-44%). In vitro protein digestibility showed an increase over the fermentation time, from 6-8%, and could be attributed to reduced activity levels of enzyme inhibitors. In vitro protein digestibility corrected amino acid score showed a reduction of ~5-15% at 6 h, with limiting amino acids remaining methionine and cysteine. Together, these findings suggest that SSF of PPEF could potentially improve digestibility through the reduction of bioactive properties and overall improvement of protein quality. Since SSF with A. niger and A. oryzae led to poor protein quality, it is not recommended as a means for altering the nutritional value of pea protein enriched flour. Overall, SSF is an efficient method for improving the oil and water holding capacities and protein digestibility in PPEF.
Description
Keywords
Solid-state fermentation, pea protein enriched flour, functionality, degrees of hydrolysis, bioactive compounds, protein quality
Citation
Degree
Master of Science (M.Sc.)
Department
Food and Bioproduct Sciences
Program
Food Science