| Jerusalem artichoke (JA) is grown extensively in temperate zones for its tuber, which is used to prepare salad or pickle. The tuber of JA contains proteins, minerals, inulin, polyphenols and so on, which has several health benefits. Nevertheless, limited information is available on the characteristic properties and the potential applications of JA tubers. This restricts the further processing and comprehensive utilization of JA.In this thesis, the extraction method for JA polyphenol and its functional activity, polyphenoloxidase (PPO) characterization, and the application of JA were studied. The aim was to explore the comprehensive properties, and improved the processing techniques and the utilization of JA. The main research contents and results were as follows:(1) Polyphenols were extracted using microwave-assisted extraction (MAE) method and the bioactive properties of the extracts were determined using the following parameters:total polyphenol content (TPC), total flavonoid content (TFC), scavenging ability of 2,2’-diphenyl-l-picrylhydrazyl (DPPH) and ferric reducing antioxidant power (FRAP). The optimal-conditions for polyphenols extraction obtained by the Design-Expert-software were as follows:Temp of 79.18℃, TE (extraction time) of 11.96 minutes and MP (microwave power) of 13.49 W. Under the optimized condition, the TPC, TFC,% DPPH and FRAP of the extraction could reach 4483.33 mg GAE/kg,2731.59 mg RE/kg,82.69% and 2.65 mmol/L respectively. The predicted general-desirability value was 0.82. The extraction yield and the antioxidant activity of the JA extract recorded were higher than the conventional extraction methods. The purified extracts from the tubers were subjected to high performance liquid chromatography electrospray ionization mass spectrometry (HPLC-ESI-MS) analysis where the presence of seven phenolic-compounds, namely:4-hydroxybenzoic acid, chlorogenic acid, caffeic acid,7-hydroxy-6-methoxycumarin, p-coumaric acid, ferulic acid and sinapic acid, were identified.(2) The bioactivity (anti-tumor, anti-bacterial and digestion inhibition) of the extracts were studied further. The results indicated that, the cancer-inhibitory effect of the JA extract in HT-29 colon cancer cells was dose dependent. At a concentration of 250 μg/mL inhibition of cell proliferation increased to about 78.05±3.9%. Late apoptotic-induction in HT-29 colon-cancer cells was observed by Annexin V assay, which exhibited a dose-dependent DNA fragmentation. The JA extract (JAE) was able to cause cell-cycle arrest in HT-29 cells at a G1-phase in a concentration dependent pattern.The results presented demonstrated that, the JA extract inhibited the proliferation of HT-29 colon cancer cell, which lead to programmed cell-death. Besides, the extracts can inhibit digestive enzymes, such as α-amylase, and lipase, and was demonstrated to be a potential antibacterial agent.(3) Jerusalem artichoke polyphenoloxidase (JA PPO) was extracted, purified, characterized and its activation studied. The molecular weight of PPO present in JA was estimated to be 65 KDa by SDS-PAGE. Characterization studies showed that, the enzyme showed optimum activity for temperature at 50.0℃ and pH at 5.2 for caffeic acid while catechol recorded temperature of 40℃ and pH of 7.0. The Km of caffeic acid was 1.19 mM having strong affinity for JA PPO. As chemical inhibitor, Thiourea (Ki=0.005mM) was the most effective inhibitor of JA PPO. A significant decrease in JA PPO residual activity from 100% to 19.4% was observed at 180 W,30 min when microwave was employed, while the residual activity of JA PPO reduced from 100% to 32.6%, at 4.0 Tesla 45 pulses using PMF. Microwave exposure and Pulsed Magnetic Field (PMF) was not significantly affected by storage time at 4 ℃. Weibull and Hulsheger models were able to describe the relative activity of the JA PPO and the magnetic strength. PMF treatments potentially inhibited JA PPO activity with an inhibition value of 70.9% and maintained its whiteness index.(4) Physicochemical and functional characterization to the two types of Jerusalem artichoke powder [freeze-dried powder (FDP) and oven-dried powder (ODP)], and their potential application in emulsion-type sausages were evaluated in this research. Component analysis showed that FDP contained lower moisture content, higher total carbohydrate, inulin content and total phenolic content compared with ODP. Oil-binding and water-holding capacities of FDP were higher than those of ODP. Furthermore, FDP and ODP were separately added at 3%,6% and 9% to the emulsion-type sausage, and the resulting formulations were compared with corn starch (CS)-minced sausage, as control. The addition of FDP (9%) and ODP (9%) was promising as compared to that of the percentual additions of 3% and 6%. This could be attributed to the inulin contents in the Jerusalem artichoke powder as well as increased addition of ODP or FDP, which enhanced the content of other component besides the inulin. Replacement of the CS by FDP or ODP reduced cooking-loss and expressible-water, increased the moisture content, oxidative-stability and anti-microbial properties of the sausages. Scanning electron microscopy showed that the addition of FDP or ODP in sausage formation leads to a significant difference between the sausages. This may result from the percentual powder. |
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