| Starch is the second most abundant polymer carbohydrates found in nature, next to cellulose. However, unmodified native starches have very limited use in the food industry because of some inadequacies, such as insolubility, easy retrogradation and instability during storage. Therefore, investigation of proper modification processing of starch to fulfill the industrial requirements has been a prevalent urgent realm of the current starch researches. Among various physical modification methods, ultra high pressure (UHP) is a non-thermal and physical processing. It provides a new method for starch modification and has a good application prospect. Lotus seed starch was chosen as raw material in this paper. The starch particle structure and physicochemical properties influenced by different pressure, pressure holding time and starch concentration were investigated. In addition, the proliferation effects of lotus seeds starch on Bifidobacterium as well as the quality of canning lotus seed treated by UHP were studied. The results were concluded as follows:The degrees of change in the granule morphology, polarization cross, particle size distribution and crystal structure of lotus seed starch after ultra high pressure treatment were different. The particle characteristics of lotus seed starch exhibited significant change when treated at500MPa for60min or600MPa at30min. The UHP-treated lotus seed starch granules at600MPa showed a complete loss of birefringence and the ordered crystallite structural disrupted. X-ray diffraction analyses revealed that UHP treatment converted native starch (C-type) to a B-type pattern. The UHP treatments altered the shape of starch granules and the starch granules presented irreversible loss of the particle structure and showed viscous gel-like appearance. The diameters and particle size distribution of lotus seed starch granules were maximum after UHP treatment at600MPa. However, UHP treatment had no significant effect on the particle characteristics of lotus seed starch with different starch concentration.The Fourier transform infrared spectra (FTIR) analysis of lotus seed starch showed that UHP is a physical modification processing because no new groups formed and changed. The13C CP/MAS NMR results showed that native lotus seed starch showed multiplicity in the resonance peak of the Cl site, which exhibited A-type crystal structure. However, starch subjected to600MPa displayed a typical B-type crystal structure and the relative crystallinity and intensity in the crystalline state gradually decreased with increasing pressure or pressure holding time. Analysis of SEC-MALLS-RI suggested that the Mw, Mn and Mw/Mn were1.433×107Da,1.118×107Da and1.282respectively. UHP treatment resulted in broadening the molecular weight distribution of lotus seed starch, indicating damage of the internal structure of starch molecule.Light transmittance of lotus seed starch decreased after UHP treatment. The treatment of starch suspension with UHP resulted in a significant decrease of swelling power and solubility at85℃and95℃, but opposite trends were found at55℃,65℃and75℃. Compared with the native starch, the freeze-thaw stability and retrogradation of lotus seed starch were improved under the suitable UHP treatment conditions (100～500MPa for30min or500MPa for10～50min). However, the retrogradation and syneresis rate of lotus seed starch improved significantly with the increasing pressure or pressure holding time. UHP treatment changed the textural properties of lotus seed starch. The gumminess, hardness, cohesiveness, chewiness and stickiness of lotus seed starch decreased significantly after UHP treatment. There was no significant change of the springiness.The RVA viscograms revealed that UHP-treated lotus seed starch revealed an increase in paste viscosity, peak time, and pasting temperatures and a reduction in breakdown and setback viscosity compared to native starch. However, starch treated at600MPa exhibited the lowest PV, PT, BD and SB values. The peak time and pasting temperatures increased under suitable pressure or pressure holding time. The DSC results showed a obvious reduction in gelatinization temperatures and gelatinization enthalpy with increasing UHP treatment pressure or pressure holding time. There were no thermal parameters detected in starch pressurized at600MPa, indicating a total loss of the native crystalline structure and molecular order. During storage, UHP-treated starch gels had higher Avrami exponent values and lower recrystallization rates compared with native starch, which suggested a lower retrogradation tendency.The static rheological properties investigation demonstrated that the native and UHP-treated lotus seed starch pastes were non-Newtonian flow with pseudoplastic flow behaviour. Based on the results determined from static flow curves, the Herschel-Bulkley model can be used to fit well on the flow behavior of starch pastes. Under the same processing conditions, the apparent viscosity of lotus-seed starch pastes decreased with the increasing treatment time. The lotus seed starch pastes displayed shear-thinning pseudoplastic behavior after UHP treatment, with significant thixotropy. The determination of dynamic rheological properties indicated that their storage modulus (G’) and loss modulus(G") increased first and then decreased with the increasing treatment pressure or pressure holding time. The in-shear structural recovery test revealed that it is difficult for the UHP-treated starch pastes to recover their original structure under low-high-low shear conditions.Lotus seed starches treated by UHP were used as carbon source to cultivate Bifidobacterium. The proliferation effect of UHP-treated lotus seed starch on the Bifidobacterium in vitro and its influence on the acid, bile salts and simulated gastrointestinal fluid tolerance of Bifidobacterium were studied. The results showed that UHP-treated starch could significantly promote the proliferation of Bifidobacterium than the control group (native lotus seed starch and glucose). Compared with other substrates, lotus seed starch treated at600MPa for30min could significantly enhance the acid, bile salts and simulated gastrointestinal fluid tolerance of Bifidobacterium.The effective UHP treatment conditions for delaying lotus seed starch retrogradation was selected to apply in the complex system of whole lotus seed, combining with the processing technology of canning lotus seed. The effect of UHP treatment on the quality of canning lotus seed during storage was investigated. The results showed that the content of RS, hardness of canning lotus seed decreased significantly during storage. In addition, the back to raw taste appeared later than control group, indicating good anti-retrogradation effect. The experiment that canning lotus seed storage under room temperature for300days showed that the back to raw taste didn’t appear when lotus seed treated at600MPa for30min. The technology of UHP pre-treatment has great commercial application value in the processing of canning lotus seed. |
PDF Full Text Request