| Sunflower(Helianthus annuus L.) is one of the most important oilseed crops cultivated in the world, ranking fourth with respect to oil production. Defatted meal is the main by-product after oil extraction. This meal, containing about 40-45 % protein, may constitute an optimal source of proteins for humans. The techno-functional properties of sunflower proteins are comparable with those of soy and other leguminous proteins. Although lysine deficiency is a major drawback from the nutritional point of view, proteins from sunflower meal are considered a valuable alternative as food ingredients, since they are low in antinutritional compounds and devoid of toxic substances. Sunflower protein hydrolysates can be obtained from sequentially an endo-protease(Alcalase) and an exo-protease(Flavourzyme) and they might be used in food industries with high nutritional value. On the other hand, Maillard reaction technique has been recently used for further improve the physicochemical properties as well as the sensory characteristics of protein hydrolysates. The combination of both enzymatic hydrolysis and Maillard reaction techniques during this research could further increase the added value of sunflower protein and its utilization in food industries.First phase of this research reports on the process optimization of enzymatic production of sunflower protein hydrolysates. The analysis of proximate analysis showed that sunflower meal has 43.66% protein content. Prior to enzymatic hydrolysis, the protein content was improved through preparation of sunflower protein isolates. The protein content in sunflower protein isolates was increased from 43.66% to 72.50%. The optimum condition for production of sunflower protein hydrolysates using a sequential enzymatic hydrolysis with alcalase(endo-peptidase) and flavourzyme(exo-peptidase), results revealed that 2 hours alcalase and 2 h flavourzyme hydrolysis time was adequate to produce non-bitter sunflower protein hydrolysates. Therefore, it was concluded that the optimum processing conditions for hydrolysis sunflower meal proteins were as follow: alcalase [E/S] 0.6%(w/w) at 58 °C, p H 8 for 2h and flavourzyme [E/S] 0.4%(w/w) at 50 °C, p H 6.5 for 2h. The protein content at optimum conditions was improved up to 92.32%.In the next phase of research, the effect of different sugar types on the sensory characteristics of sunflower protein hydrolysates Maillard reaction products(MRPs) were evaluated and compared using(fructose, glucose, galactose, xylose, lactose, maltose). Results showed that the browning intensity, colour development and free and total amino acids of MRPs were highly affected by the sugar types and the sugars reactivity range was; as pentoses > hexoses > disaccharides. PXC were more darker-brown in colour with lower FAA and TAA content compared to the other MRPs. However, peptide-xylose-cysteine(PXC) MRPs showed great mouthfulness and continuity taste with stronger meat-like flavour and umami taste compared to MRPs from the other sugar types. MRPs from hexose except PGa C, showed acceptable mouthfulness and continuity taste while PLC and PMC and PGa C showed higher caramel-like flavour and bitter taste. It was observed that the addition of cysteine accelerated high molecular weight(HMW) peptide degradation while suppressing low molecular weight(LMW) cross-linking and colour formation in all MRPs. Furthermore, pentose sugars(xylose) were great precursor of sulphur containing compounds and all monosaccharides were good source of nitrogen containing compounds than disaccharides. Additionally, disaccharides favored the formation of furans and oxygen containing compounds. It was therefore concluded that sunflower peptides, xylose, cysteine model system can be a good precursor of flavour enhancers with stronger “Kokumi” effect.In the next phase of study, comparative study of sensory characteristics and antioxidant capacity of Maillard reaction products(MRPs) from two substrates namely sunflower free amino acid and peptides MRPs was carried out. Results showed that AXC had greater meat-like flavour and umami taste, while PXC showed great mouthfulness and continuity taste, and AX and PX showed higher caramel-like flavour and bitter taste. The addition of cysteine was found to accelerate high molecular weight peptide degradation while suppressing low molecular weight cross-linking and colour formation in PXC and AXC. Furthermore, it was observed that sensory attributes of MRPs were not significantly affected by the peptides size. Results also showed that caramel-like flavour and bitter taste were significantly and positively correlated with furans and most of the nitrogen-containing compounds while these compounds had significant and negative impact on mouthfulness, continuity and meat-like flavour. Additionally, sulphurcontaining compounds showed significant and positive influence on meat-like flavour, while PXC and PX showed higher antioxidant activities than AXC and AX. It was therefore concluded that sunflower peptides MRPs can be a good precursor of flavour enhancers with high antioxidant activity, while sunflower free amino acid MRPs can be used to produce meat-like flavour enhancers.In the next phase of study, the temperature and cysteine addition effect on sensory characteristics of sunflower Maillard reaction products revealed that MRPs formed at 120 °C with cysteine addition(PXC-120) had greater meat-like flavour, mouthfulness and continuity taste compared to other MRPs. Molecular weight distribution showed that the presence of cysteine inhibited the low molecular weight(LMW) peptide cross-linking but accelerated the high molecular weight(HMW) peptide degradation with increasing temperature. Furthermore, results showed that the peptide above 5 k Da has a significant negative contribution to sensory attributes of PXCs, while the peptide between 1 and 5 k Da showed no significant but positive influence on PX sensory attributes. Sulphur containing compounds showed a significant and positive correlation to sensory attributes of PXCs while nitrogen containing compounds and furan were significantly but negatively correlated to sensory attributes of PXCs.In the next phase of research, a comparative study of sensory attributes and antioxidant capacity of Maillard reaction products(MRPs) from sunflower protein hydrolysate, xylose and L-cysteine model system(PXC) and soybean MRPs(MSP) was evaluated. Results showed that PXC exhibited stronger(p < 0.001) antioxidant effect. The reducing power and DPPH radical scavenging activity were higher compared to MSP(0.689 vs. 0.667 at 3 mg/m L and 95.06% vs. 90.73% at 1 mg/m L, respectively). Furthermore, the sensory attributes showed that PXC had greater mouthfulness and continuity taste compared to MSP due to the higher content in Maillard peptide between 1-5 k Da(18.05% vs. 16.01%), and also an acceptable meat-like flavour from sulphur substituted furan and good overall acceptability. Therefore, sunflower MRPs could potentially be used to produce flavour enhancers with high antioxidant activity as an alternative to soybean MRPs.In the next phase of this study, the contribution of crosslinking products in the flavour enhancer processing was investigated. Sunflower, corn and soybean peptides(SFP, CP, SP) were used to prepare Maillard systems namely PXC, MCP and MSP respectively. All sensory attributes were significant differences. The highest scores for mouthfulness and continuity were registered in MCP with the lowest Maillard peptide content(1-5 k Da). This revealed that the MCP with the lowest Maillard peptide content had the strongest Kokumi effect compared to the other MRPs and demonstrated that “Kokumi effect” of MRPs was contributed by not only the “Maillard peptide” defined by the molecular weight(1-5 k Da). Results on sensory evaluation after fractionation of PXC followed by enzymatic hydrolysis showed no significant differences between PXC, PPXC and their hydrolysates. This observation therefore confirms results on the contributors to “Kokumi” effect. It was deduced that the unhydrolyzed crosslinking products might have contributed to the “Kokumi” effect of MRPs. The structures of four probable crosslinking compounds were proposed and these study findings have provided new insights in the sensory characteristics of xylose, cysteine and sunflower peptide MRPs.Last part of our research was related to the investigation of the application of sunflower as natural anti-oil oxidant in fish and olive oil O/W nanoemulsions under accelerated storage conditions at 40 oC for 4 weeks. Results showed that the antioxidant and antibacterial activity of sunflower protein hydrolysates were improved after Maillard reaction. Results of nanoemulsion characterisation showed that olive oil O/W based nanoemulsion was more stable compared to fish oil O/W based nanoemulsion during 4 storage weeks at 40 °C. The application of sunflower to O/W based nanoemulsions as natural antioxidant showed that 450 mg/ 100 m L PXC concentration was sufficient to inhibit the primary and secondary oxidation of fish and olive oil after 28 days storage time compared to BHT. Therefore, it was concluded that sunflower protein hydrolysates MRPs could be used as a natural antioxidant to inhibit the oils oxidation. |
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