In this study, polysaccharides from the whole seed, cotyledon and hull of cowpea were extracted, isolated and purified, and their structural characteristics and antioxidant activities were compared. The results indicated that the basic chemical composition, monosaccharide composition and molecular mass distribution of the polysaccharides from different parts of cowpea, exhibited both similarities and differences. Structural characteristics of the polysaccharides from the whole seed (VUP) and cotyledon (VUCP) of Vigna unguiculata were similar. The polysaccharide from the hull (VUHP) was mainly composed of pectin, whose molecular mass distribution was more uniform. The antioxidant activity of VUHP was significantly stronger than that of VUP and VUCP, and the scavenging capacity of VUHP against 1,1-dipheny1-2-picryl-hydrazyl (DPPH) radical and 2,2’-azino-bis-(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) cation radical was almost equal to that of vitamin C (VC). In summary, more attention should be paid to seed coat polysaccharides in the research and product development of polysaccharides from cowpea.

In this work, starches were extracted from four species of minor legume widely planted in China: cowpea, lentil, pea, and red kidney bean by wet milling, and their structural characteristics and physicochemical properties were analyzed and compared. The infrared spectra of all the samples presented the typical structural characteristics of starch. The starch granules had complete kidney-like or oval shape with a smooth surface. The average hydrodynamic radii of the four starches were in the following decreasing order of cowpea starch > pea starch > lentils starch > red kidney bean starch. The crystal type of pea starch was C_C-type, while the crystal type of cowpea starch, lentils starch and red kidney bean starch was C_A-type. The relative crystallinity of these starches was significantly different, ranging between 27.6% and 38.5%. The gelatinization characteristics varied greatly among them, all of which had high gelatinization temperature (75.3-82.8 ℃), being difficult to gelatinize. Cowpea starch was not prone to retrogradation with the lowest amylose content (26.3%), and the thermal stability of cowpea paste was best. Red kidney bean starch had the highest amylose content (31.5%) and retrogradation value, which was most prone to retrogradation. In conclusion, the four legume starches had similar granular morphology and all exhibited a C-type crystal structure, and they were similar in their retrogradation characteristics but distinct in their molecular structure and gelatinization characteristics.

In this study, a method for the simultaneous detection of 5-hydroxymethyl-2-furfural (HMF), 5-methyl furfural (MF) and furfural (FF) was established by ultra-high performance liquid chromatography (UPLC) after enrichment of furfurals in the acid hydrolysate of dextran by solid phase extraction (SPE) using a hydrophilic-lipophilic balance (HLB) column. The effect of different degrees of acid hydrolysis of dextran on the production of HMF, MF and FF was analyzed. The results showed that the proposed UPLC method was rapid, accurate and sensitive. Under incomplete acid hydrolysis conditions (0.5 mol/L H₂SO₄, 60 ℃), the recovery of monosaccharides from dextran was low and the three furfural compounds were undetectable in the hydrolysate. Under the optimal hydrolysis conditions (2 mol/L H₂SO₄, 100 ℃), the content of monosaccharides in dextran hydrolysate increased, the formation rate and content of HMF increased significantly, and FF was detected; however, the formation rate and content of FF were lower than those of HMF. Under excessive hydrolysis conditions (4 mol/L H₂SO₄, 120 ℃), the recovery of monosaccharides was lower than that under the optimal hydrolysis conditions. Meanwhile, the contents of HMF and FF were higher, and MF was not detected during the whole hydrolysis process. The above results show that during the hydrolysis of dextran, the yield of furfural compounds is closely related to the monosaccharide content in the hydrolysate. In addition, more vigorous acid hydrolysis conditions will promote the formation of HMF and FF in dextran hydrolysate, HMF being the easiest to form, followed by FF. The formation of MF requires more vigorous catalytic conditions.

In this study, chickpea starch was treated with atmospheric pressure steaming, atmospheric pressure boiling, high pressure steaming or high pressure boiling for 20 min. The effects of the four common heat treatment methods on the ordered crystal structure, particle structure and physicochemical properties of chickpea starch were investigated through the determination of physicochemical parameters, X-ray diffraction spectroscopy, infrared spectroscopy and microstructure observation. Results showed that the granular structure of chickpea starch was completely preserved after steaming treatment. It exhibited birefringence under polarized light and its crystal structure was still type C_A. After boiling at atmospheric and high pressure, the relative crystallinity decreased from 31.4% to 25.5% and 20.4%, respectively. Moreover, the peak viscosity, though viscosity, final viscosity, breakdown value and setback value decreased. The degree of retrogradation of chickpea starch after heat treatments was as follows in decreasing order: high pressure steaming > atmospheric pressure steaming > native starch. The granular structure and crystal structure of chickpea starch were damaged seriously after boiling treatment. The relative crystallinity was 5.9% and 3.6% after boiling at atmospheric and high pressure, respectively, and the viscosity decreased. The treatment starch showed no obvious retrogradation after gelatinization. In addition, the crystal structure of chickpea starch was damaged more seriously after high pressure treatment, while there was no significant difference in granular morphology, birefringence or functional groups between the samples treated by atmospheric and high pressure. The results of this research can provide a theoretical basis and guidance for the development and utilization of chickpea starch and are of significance for enriching the basic theory of chickpea starch.

In order to clarify the effect of vitamin C (VC) on physicochemical properties and digestibility of lotus seed starch (LSS) during freeze-thaw cycles, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and differential scanning calorimetry (DSC) were used to characterize the multi-scale structure of the starch, and its rheological properties and in vitro digestibility were determined. The results showed that the pore size of starch gels became lager and the syneresis decreased with increasing freeze-thaw cycles. VC addition promoted the formation of tighter gels during freeze-thaw cycles, resulting in lower syneresis and improved freeze-thaw stability. Overall, the degree of starch recrystallization increased with increasing freeze-thaw cycles. The addition of VC decreased the digestibility of frozen-thawed LSS. One potential reason may be that the addition of VC enhanced short-range ordered structure, double helix structure and relative crystallinity of LSS. In conclusion, VC can improve freeze-thaw stability of LSS and reduce the digestibility of frozen-thawed LSS.