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. 2016:11:184-197.
doi: 10.1007/s11483-016-9429-4. Epub 2016 Apr 23.

Denaturation and in Vitro Gastric Digestion of Heat-Treated Quinoa Protein Isolates Obtained at Various Extraction pH

Geraldine Avila Ruiz  1 , Mauricio Opazo-Navarrete  2 , Marlon Meurs  3 , Marcel Minor  4 , Guido Sala  4 , Martinus van Boekel  3 , Markus Stieger  5 , Anja E M Janssen  2
Affiliations

Denaturation and in Vitro Gastric Digestion of Heat-Treated Quinoa Protein Isolates Obtained at Various Extraction pH

Geraldine Avila Ruiz et al. Food Biophys. 2016.

Abstract

The aim of this study was to determine the influence of heat processing on denaturation and digestibility properties of protein isolates obtained from sweet quinoa (Chenopodium quinoa Willd) at various extraction pH values (8, 9, 10 and 11). Pretreatment of suspensions of protein isolates at 60, 90 and 120 °C for 30 min led to protein denaturation and aggregation, which was enhanced at higher treatment temperatures. The in vitro gastric digestibility measured during 6 h was lower for protein extracts pre-treated at 90 and 120 °C compared to 60 °C. The digestibility decreased with increasing extraction pH, which could be ascribed to protein aggregation. Protein digestibility of the quinoa protein isolates was higher compared to wholemeal quinoa flour. We conclude that an interactive effect of processing temperature and extraction pH on in vitro gastric digestibility of quinoa protein isolates obtained at various extraction pH is observed. This gives a first indication of how the nutritional value of quinoa protein could be influenced by heat processing, protein extraction conditions and other grain components.

Keywords: Denaturation; Digestibility; Extraction pH; Heat processing; Protein; Quinoa.

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Figures

Fig. 1
Fig. 1
Protein yield and protein purity on dry matter basis of the quinoa protein isolates E8, E9, E10 and E11. Error bars represent the standard deviation based on duplicate extraction experiments
Fig. 2
Fig. 2
a Denaturation temperature (Td) and b denaturation enthalpy (ΔH) of 20 % w/w suspensions of QPI E8, E9, E10 and E11 after processing at different temperatures. Data were obtained from DSC measurements
Fig. 3
Fig. 3
SDS-PAGE profile of the unprocessed QPIs E8, E9, E10 and E11. Lane M: molecular weight marker
Fig. 4
Fig. 4
SDS-PAGE profile of the QPIs E8, E9, E10 and E11 heat-treated for 30 min at 60, 90 and 120 °C. Lane M: molecular weight marker. The gel of E10 seems to be overloaded at the bottom. E10 was run on a different gel and is shown in Fig. 13
Fig. 5
Fig. 5
Degree of hydrolysis (DH) of 5 % w/w suspensions of QPI E8, E9, E10 and E11 processed at different temperatures and subsequently digested for different time periods
Fig. 6
Fig. 6
HPLC chromatograms of 5 % w/w suspensions of QPI E9 processed at different temperatures and subsequently digested for different time periods. Size exclusion chromatography is used for separation. This means that larger peptides have a low elution time. See Fig. 14, 15, 16 for the HPLC chromatograms of E8, E10 and E11
Fig. 7
Fig. 7
Degree of hydrolysis (DH) of wholemeal quinoa flour (5 % w/w protein) processed at different temperatures and subsequently digested for different time periods
Fig. 8
Fig. 8
DSC thermograms of untreated 20 % w/w suspensions of QPI E8, E9, E10 and E11
Fig. 9
Fig. 9
DSC thermograms of 20 % w/w suspensions of QPI E8 after processing at different temperatures
Fig. 10
Fig. 10
DSC thermograms of 20 % w/w suspensions of QPI E9 after processing at different temperatures
Fig. 11
Fig. 11
DSC thermograms of 20 % w/w suspensions of QPI E10 after processing at different temperatures
Fig. 12
Fig. 12
DSC thermograms of 20 % w/w suspensions of QPI E11 after processing at different temperatures
Fig. 13
Fig. 13
SDS-PAGE profile of the QPIs E10 heat-treated for 30 min at 60, 90 and 120 °C. Lane M: molecular weight marker
Fig. 14
Fig. 14
HPLC chromatograms of 5 % w/w suspensions of QPI E8 processed at different temperatures and subsequently digested for different time periods. Size exclusion chromatography is used for separation. This means that larger peptides have a low elution time
Fig. 15
Fig. 15
HPLC chromatograms of 5 % w/w suspensions of QPI E10 processed at different temperatures and subsequently digested for different time periods. Size exclusion chromatography is used for separation. This means that larger peptides have a low elution time
Fig. 16
Fig. 16
HPLC chromatograms of 5 % w/w suspensions of QPI E11 processed at different temperatures and subsequently digested for different time periods. Size exclusion chromatography is used for separation. This means that larger peptides have a low elution time
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