Development and comparison of processes for the extraction of dietary protein from yellow peas

Annoh-Quarshie, Julia (2018-12)

Thesis (MEng)--Stellenbosch University, 2018.

Thesis

ENGLISH ABSTRACT: The food industry is constantly on the lookout for healthier and more affordable options in place of animal-derived proteins, soy (which has taken a lead role in the replacement of animal-based proteins) and proteins that contain gluten. Pea proteins offer equal, if not superior properties to soy and thus show great promise in being used as a replacement. This is because they are non-allergenic, not genetically modified, highly nutritious and gluten-free. Yellow pea is a legume that has a high protein quantity (21 % -33%) contains a good amount of essential amino acids and is marked by its low fat content (1.5% - 2.0%), although more attention has been given to using it for animal feed rather than for human consumption. It has however been discovered that processing of the yellow pea into protein isolates improves its nutritional, functional and economic values. The yellow pea protein used in diets in South Africa is mostly imported from France and Canada, and therefore there is a huge opportunity to further explore the value of South African –grown yellow peas. This study aimed at process optimization to maximize the concentration and yield of protein isolates from yellow peas followed by techno-economic analysis to assess the economic viability of extracting dietary protein from this crop, using two extraction strategies. Screening was conducted to obtain the most suitable cultivar for follow-up optimization using a pH of 8 using, a solid to liquid ratio of 1/5, a temperature of 35 °C, for 120 minutes. Two aqueous protein extraction methods, namely water extraction and alkaline extraction, were explored where three different cultivars, namely Slovan, Salamanca and Astranoute were screened. The screening was followed by bench-scale optimization of the preferred cultivar, selected based on protein content and extraction yield. Slovan recorded the highest protein content of 51.1% and 63.3% for water and alkaline extractions respectively , whereas values of 47.2% and 58.4% were obtained for protein yield for water and alkaline extractions respectively. Slovan, proving to be the best among the three cultivars was chosen and used in the subsequent bench-scale optimization stage of the project. Optimization was carried out with the aid of response surface methodology (RSM) where a quadratic mathematical model was developed to determine the effects of temperature, time, pH and solid loading on protein content and protein yield of extracted isolates for both extraction methods. The highest protein content and protein yield were 88.4% and 73.4% respectively and were obtained for alkaline extractions while the highest values for water extractions were protein content of 83.3% and a protein yield of 56.2%. Desirability profiling conducted on experimental values revealed optimal values of 40℃, 60 minutes and 6.7% for temperature, time and solid loadings for water extractions. At these optimum values, the predicted values of protein content and protein yield were 83.2% and 58.2% respectively. Optimum values for pH, temperature, time and solid loadings for alkaline extractions were 10, 20 ℃, 100 minutes and 5.2% respectively with a resulting protein content and a protein yield of 88.1%and 75.7% respectively. The protein isolates that performed best for both methods were then assessed for protein solubility, water absorption capacity and fat absorption capacity as well as amino acid profiling. Alkaline- extracted isolates had higher values for these properties as well. A process simulation and economic model were developed using Aspen plus V8.8 software by using the experimental data from this work as input. The Aspen model generated mass and energy balances that were used to specify equipment for costing. The costing then helped evaluate the economic viability of extraction dietary protein from yellow peas. A response surface methodology (RSM) was used to determine the effects of operating parameters (pH, temperature, time and solids) on IRR. Data from this evaluation showed that alkaline extractions and lower solid loadings recording IRR values of 1.2% to 41.2% were more profitable as compared to water extractions and higher solids (4.2% to 34.7%). The most profitable method (scenario) was alkaline extraction with a solid loading of 6.7%, recording an IRR of 41.5% and an NPV of R852 255 939.

AFRIKAANSE OPSOMMING: Die voedselindustrie is alewig op die uitkyk vir gesonder en meer bekostigbare opsies in plaas van dierproteïene, soja (wat ’n hoofrol geneem het in die vervanging van diergebaseerde proteïene) en proteïene wat gluten bevat. Ertjieproteïene bied gelyke, indien nie superieure, eienskappe teenoor soja en lyk dus belowend om as plaasvervanger te dien. Dit is omdat dit nie-allergies is, nie geneties aangepas is nie, hoogs voedsaam en glutenvry is. Geelertjie is ’n peulgewas wat ’n hoë proteïenkwantiteit (21% - 33%) het, bevat ’n goeie hoeveelheid essensiële aminosure en word gekenmerk deur sy lae vetinhoud (1.5% - 2.0%). Daar word egter meer aandag gegee aan die gebruik daarvan in dierevoer, eerder as vir menslike gebruik. Die geelertjieproteïen wat in Suid-Afrikaanse diëte gebruik word, word meestal uit Frankryk en Kanada ingevoer. Daarom is daar ’n groot geleentheid om die waarde van geelertjies gegroei in Suid-Afrika, verder te ondersoek. Hierdie studie was gerig op prosesoptimalisering om die konsentrasie en opbrengs van proteïenisolate van geelertjies te maksimeer, gevolg deur tegnoëkonomiese analises om die ekonomiese lewensvatbaarheid te assesseer as die voedselproteïen uit hierdie gewas geëkstraheer word. Twee wateragtige proteïen-ekstraksie metodes, water-ekstraksie en alkaliese ekstraksie, is ondersoek waar drie verskillende kultivars, genaamd Slovan, Salamanca en Astranoute, gekeur is. Die keuring is gevolg deur proefskaal optimalisering van die gekose kultivar, gekies gebaseer op proteïeninhoud en ekstraksie-opbrengs. Slovan het die hoogste proteïeninhoud aangeteken – 51.1% en 63.3% vir water- en alkaliese ekstraksies onderskeidelik, terwyl waardes van 47.2% en 58.4% verkry is vir proteïenopbrengs vir water- en alkaliese ekstraksies onderskeidelik. Slovan, wat bewys is as die beste van die drie kultivars, is gekies en gebruik in die daaropvolgende proefskaal optimalisering-fase van die projek. Optimalisering is uitgevoer met behulp van respons oppervlak metodologie (ROM) waar ’n kwadratiese wiskundige model ontwikkel is om die effek van temperatuur, tyd, pH, en soliede lading op proteïeninhoud en proteïenopbrengs van geëkstraheerde isolate vir beide ekstraksie metodes, te bepaal. Die hoogste proteïeninhoud en proteïenopbrengs was 88.4% en 73.4% onderskeidelik, en is verkry vir alkaliese ekstraksie, terwyl die hoogste waardes vir water-ekstraksie 88.3% vir proteïeninhoud en 56.2% vir proteïenopbrengs was. Wenslikheid profilering uitgevoer op eksperimentele waardes, het optimale waardes van 40 ℃, 60 minute en 6.7% vir temperatuur, tyd en soliede lading vir water-ekstraksie bekendgemaak. By hierdie optimale waardes, was die voorspelde waardes van proteïeninhoud en proteïenopbrengs 83.2% en 58.2% onderskeidelik. Optimale waardes vir pH, temperatuur, tyd en soliede vrag vir alkaliese ekstraksies was 10, 20 °C, 100 minute en 5.2% onderskeidelik met ’n resulterende proteïeninhoud en proteïenopbrengs van 88.1% en 75.7% onderskeidelik. Die proteïenisolate wat die beste presteer het met beide metodes is toe geassesseer vir proteïenoplosbaarheid, waterabsorpsiekapasiteit en vetabsorpsiekapasiteit, sowel as aminosuur profilering. Alkalies geëkstraheerde isolate het ook hoër waardes vir hierdie eienskappe gehad. ’n Proses simulasie en ekonomiese model is ontwikkel deur eksperimentele data van hierdie werk as inset in Aspen plus V8.8 sagteware te gebruik. Die Aspen-model het massa- en energiebalanse gegenereer wat gebruik is om toerusting vir kosteberekening te spesifiseer. Die kosteberekening het toe gehelp om die ekonomiese lewensvatbaarheid van voedselproteïene uit geelertjies te evalueer. ’n Response oppervlak metodologie (ROM) is gebruik om die effek van bedryfsparameters (pH, temperatuur, tyd en soliede lading) op interne opbrengskoers te bepaal. Data vanuit hierdie evaluasie het gewys dat alkaliese ekstraksies en laer soliede ladings interne opbrengskoerswaardes van 1.2% tot 41.2% aangeteken het, meer winsgewend in vergelyking met water-ekstraksies en hoër soliede ladings (4.2% tot 34.7%). Die mees winsgewende metode (scenario) was alkaliese ekstraksie met ’n soliede lading van 6.7%, wat ’n interne opbrengskoers van 41.5% en ’n netto huidige waarde van R852 225 593 aangeteken het.

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