TY - JOUR
T1 - Quality and chemical stability of long-term stored soy, canola, and sunflower cold-pressed cake lipids before and after thermomechanical processing
T2 - A 1H NMR study
AU - Vidal, Natalia P.
AU - Rahimi, Jamshid
AU - Kroetsch, Benjamin
AU - Martinez, Mario M.
N1 - Funding Information:
Oxidation products were also investigated by the quantification of (Z,E)- and (E,E)-conjugated dienes supported in hydroxy groups, calculated as mmol per mol of acyl groups (AG) + fatty acids (FA) present (mmol/mol AG + FA) using the areas of signals a and b at 6.49 and 6.16 ppm, and the area of signal 6 (A6) due to the protons in alpha position in relation to the carbonyl group of AG + the carbonyl group of FA (Fig. 2) and equations 14 and 15.It is known that during seed milling, triglycerides can degrade to other glyceride forms such as diglycerides and monoglycerides releasing free fatty acids and, ultimately, glycerol and three free fatty acids, by the action of lipases (Bhunia, Sinha, Kaur, Kaur, & Chawla, 2021). This enzymatic degradation can be specially enhanced during storage (Malcolmson, Przybylski, & Daun, 2000; Przybylski & Daun, 2001). Fig. 1 shows the overlapping of native cold-pressed soybean (SN), canola (CN) and sunflower (SFN) spectra of the lipid fractions between 0.2 and 5.6 ppm, together with the enlargement of some of their main signals. Table 1 depicts the assignment of the signals shown in Fig. 1, the type of protons that generate the signal, and their chemical shifts. As can be observed in Fig. 1, all the 1H NMR lipid spectra pertaining to native oilseeds (SN, CN, SFN) showed intense signals between 4.04 and 4.38 ppm (signal 9), corresponding to the protons of the glycerol backbone of the triglycerides. This evidenced that, as expected, most of the acyl groups were supported in these structures. However, the detailed observation of the spectra, shown in the enlarged regions between 3.5 and 5.15 ppm in Figs. 1 and 2, showed the presence of some signals due to partially degraded glyceride structures, diglycerides (DG) and monoglycerides (MG), especially in canola (CN) and sunflower (SFN) spectra. Signal A and B partially overlapped at 3.73 ppm, which together with a multiplet at 5.08 ppm (signal F), were attributed to the protons in the glycerol backbone of 1,2-diglycerides (1,2-DG). Likewise, the presence of 1,3-diglycerides (1,3-DG) between 4.05 and 4.21 ppm (signal D), which partially overlapped with signal 9, and 1-monoglycerides (1-MG) signals at 3.65, 3.94 and 4.18 ppm (signals A, C and E, respectively), were also detected. Finally, signal 6 ranging from 2.26 to 2.38 ppm, which is attributed to the protons of methylenic groups in α-positions in relation to the carbonyl group of acyl groups and to the carboxyl group of fatty acids, slightly shifted to higher chemical shifts showing new peaks (Fig. 1). This is known to occur when the same protons are supported in diglycerides, monoglycerides or are found as free fatty acids, compared to when they are supported in triglycerides (Nieva-Echevarría et al., 2014). The molar percentage of the different glyceride structures, including triglycerides (TG), 1,2-DG, 1,3-DG, 1-MG, and glycerol (G), were calculated as described in section 2.5 and plotted in Fig. 3a. Native soybean (SN) had almost 90% of their acyl groups supported in triglycerides whereas canola (CN) and sunflower (SFN) showed significantly (p < 0.05) lower values (68% and 63%, respectively), evidencing the partial lipolysis that occurred in these two types of oilseeds. The rest consisted of partially degraded glyceride structures corresponding to glycerol (G) (4.0%, 15.9% and 17.6% in SN, CN and SFN, respectively), 1-MG (6.14%, 6.77% and 11.21% in SN, CN and SFN, respectively), and to a lower extent to 1,3- and 1,2-DG structures. Some authors have detected the hydrolytic breakdown of triglycerides in oils during cold-pressing, i.e. hemp, flax or rapeseed, by measuring the acid value as an estimation of the free fatty acids content (Teh & Birch, 2013); however, this value is generally lower than the maximum limit of 4.0 mg KOH/g of oil established by the Codex Alimentarius Commission (Commission, 1999). Therefore, the enzymatic activity of lipases during the storage period between cold-pressing and analysis (prior extrusion) is probably the most plausible reason for the enzymatic degradation of these cakes, although their endogenous enzyme activity seemed different depending on the oilseed type. Lipase activity can also vary depending on the presence of lipase inhibitors. In fact, soybean protein fractions have been demonstrated to have an inhibitory effect of the in vitro lipase activity compared to other oilseeds (Huang & Wang, 1992).In terms of the formation and concentration of oxidation compounds, (Z,E)- and (E,E)-conjugated dienes supported in hydroxy groups were observed in both stored and non-stored samples (Table S2). The concentration of the (E,E)- isomer remained similar whereas there was a significant decrease in the concentration of the (Z,E)- isomer by ∼25% and ∼54% in SN and SFN, respectively. Canola lipids remained with a negligible concentration of these intermediate oxidation compounds. Extruded samples showed a similar behaviour as their native counterparts in these compounds. Nevertheless, a new signal was observed at 6.58 ppm corresponding to the (Z,E)-conjugated dienes supported in hydroperoxides groups (Table 3, Fig. 4) whose concentrations were 3.65 and 3.94 mmol/mol AG + FA in SE and SFE, respectively. In addition, clear new signals, only partially detected in non-stored samples, were observed at 9.75 and 9.80 ppm due to the n-alkanals and n-alkanals with low molecular weight, respectively. Significantly higher concentrations (p < 0.05) of aldehydes were observed in extruded samples compared to non-extruded samples, as it occurred with the hydroperoxides. Thus, native soybean, canola and sunflower had 0.07, 0.04 and 0.05 mmol/mol AG + FA of the sum of n-alkanals whereas up to 4-fold higher content was observed in extruded samples (0.21, 0.18 and 0.20 mmol/mol AG + FA in extruded soybean, canola, and sunflower, respectively). The formation of other type of aldehydes or secondary oxidation compounds, such as alkadienals or oxygenated aldehydes, was not observed, which could indicate absence or concentration being under the limit of detection for such NMR conditions. Thus, their occurrence during the oxidative process of lipids cannot be completely ruled out and further studies with more sensitive chromatographic techniques should be performed. This could be important since their impact on the sensory of oilseed cakes is higher than that of alkanals due to their lower aroma threshold values (Fu et al., 2020). Nevertheless, the formation of the detected secondary oxidation products indicated that the oxidation process evolved in all the oilseed cakes during storage, and in a remarkably higher extent in extruded samples. The initial hydrolysis that potentially occurred after cold-pressing/milling processing could have promoted the lipid oxidation during storage and, although extrusion efficiently inactivates lipases and lipoxygenases, as demonstrated by other authors (Lampi et al., 2015; Meister et al., 1994; Zhu et al., 1996), and did not enhance lipid oxidation, the non-enzymatic oxidation process was significantly promoted resulting in a degradation of polyunsaturated acyl groups and fatty acids and formation of new oxidation compounds of the lipids of long-term stored oilseed cakes. This reduced storage stability of the lipids in extruded cakes could be due to the temperature applied during extrusion processing, to a possible increase of iron levels in the product migrated from the extruder screw-barrel assembly, and/or to the increase of surface exposure of the extrudates to oxygen during expansion.The authors acknowledge the Good Food Institute (GFI), GFI Competitive Grant Program (grant number 054092) and the Barret Family Foundation (grant number 054294) for funding this research. Some of the data was generated through accessing research infrastructure funded by FOODHAY (Food and Health Open Innovation Laboratory, Danish Roadmap for Research Infrastructure). N.P.V. would like to acknowledge the support of the Aarhus University Research Foundation (Aarhus Universitets Forskningsfond, AUFF), project number AUFF-F-2020-7-5, and the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 754513.
Funding Information:
The authors acknowledge the Good Food Institute (GFI) , GFI Competitive Grant Program (grant number 054092 ) and the Barret Family Foundation (grant number 054294 ) for funding this research. Some of the data was generated through accessing research infrastructure funded by FOODHAY (Food and Health Open Innovation Laboratory, Danish Roadmap for Research Infrastructure). N.P.V. would like to acknowledge the support of the Aarhus University Research Foundation (Aarhus Universitets Forskningsfond, AUFF) , project number AUFF-F-2020-7-5 , and the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 754513.
Publisher Copyright:
© 2022 The Authors
PY - 2023/1
Y1 - 2023/1
N2 - Oilseed cakes obtained by cold-pressing are rich in lipids susceptible to degradation, which could challenge their handling and nutritional, safety, and sensory requirements, especially during long-storage. Although extrusion is effective at reducing antinutritional factors, its effect on the lipid stability of oilseed cakes remains unknown. In this work, a comparative 1H-NMR-based investigation of the lipid quality in terms of lipid composition, hydrolysis, and oxidation status, as well as their stability after long-term storage was performed on soybean, canola and sunflower cold-pressed cakes before and after low-moisture extrusion. Soybean cake was rich in linolenic and linoleic groups, whereas canola and sunflower mostly contained linoleic and monounsaturated acyl groups and fatty acids. Extrusion did not modify lipid quality immediately after processing. Nevertheless, lipid stability was significantly reduced after 12 months, especially in cakes subjected to extrusion, evidenced by the degradation of their polyunsaturated acyl groups and fatty acids, and the increase of primary and secondary oxidation products. Since lipid quality was retained immediately after extrusion (no storage), results indicated that any action to avoid the enzymatic lipid degradation must be performed immediately after cold-pressing. Moreover, long-term storage should be carefully considered as the lipid stability/quality of extruded cakes was compromised after extrusion.
AB - Oilseed cakes obtained by cold-pressing are rich in lipids susceptible to degradation, which could challenge their handling and nutritional, safety, and sensory requirements, especially during long-storage. Although extrusion is effective at reducing antinutritional factors, its effect on the lipid stability of oilseed cakes remains unknown. In this work, a comparative 1H-NMR-based investigation of the lipid quality in terms of lipid composition, hydrolysis, and oxidation status, as well as their stability after long-term storage was performed on soybean, canola and sunflower cold-pressed cakes before and after low-moisture extrusion. Soybean cake was rich in linolenic and linoleic groups, whereas canola and sunflower mostly contained linoleic and monounsaturated acyl groups and fatty acids. Extrusion did not modify lipid quality immediately after processing. Nevertheless, lipid stability was significantly reduced after 12 months, especially in cakes subjected to extrusion, evidenced by the degradation of their polyunsaturated acyl groups and fatty acids, and the increase of primary and secondary oxidation products. Since lipid quality was retained immediately after extrusion (no storage), results indicated that any action to avoid the enzymatic lipid degradation must be performed immediately after cold-pressing. Moreover, long-term storage should be carefully considered as the lipid stability/quality of extruded cakes was compromised after extrusion.
KW - Extrusion
KW - Lipid oxidation
KW - Lipid stability
KW - Oilseeds
KW - Shelf-life
UR - http://www.scopus.com/inward/record.url?scp=85145646574&partnerID=8YFLogxK
U2 - 10.1016/j.lwt.2022.114409
DO - 10.1016/j.lwt.2022.114409
M3 - Journal article
AN - SCOPUS:85145646574
SN - 0023-6438
VL - 173
JO - LWT - Food Science and Technology
JF - LWT - Food Science and Technology
M1 - 114409
ER -