Study On The Quality Evaluation And Freezing Characteirstics Of Lotus Root

Lotus root is a popular vegetable identifed as food as well as traditional medicine duo toits abundant nutrients. China leads the world in the planting species, scale and productionaccount of lotus root, but its exploitation and comprehensive utilization rate is not high due tothe incomplete quality evaluation system and outdated technology. Therefore, the objective ofthis study is to establish the quality evaluation model aided by nondestructive detectingtechnology for building the quality evaluation system, and to apply the ultrasound-assistedimmersion freezing technology for promoting the development of freezing processing of lotusroot with taking it into account about the material characteristics and processingcharacteristics.Firstly, to improve the convenience of quality detection of lotus root, the quality of lotusroot non-destructively detected by the near-infrared spectroscopy technology was investigated.Three pretreatment methods of spectrum data and the NIR analysis models established usingPLS and SiPLS method were analyzed. The results showed the NIR analysis models of thesoluble solids content of lotus root was un acceptable. The primary NIR spectrum of lotusroot by SiPLS method produced good predictive model for detecting water content. TheSiPLS model of the starch content and texture of lotus root by multiple scattering correction,first derivative and smoothing preprocessing were optimum for the practical application. Thecorrelation coefficient of prediction sets of water, tarch content and texture of lotus root were0.9120,0.9238and0.9047, and the RMSEP of prediction sets were1.1067,1.0506and128.5891. In conclusion, the near-infrared spectroscopy technology was feasible tonon-destructively measure the quality of lotus root.Secondly, the physical and chemical parameters for quality evaluation were measured bythe near-infrared spectroscopy technology aiding to form the basis for quality evaluation oflotus root. The result showed that six components from fourteen quality indexs of lotus rootwere obtained by the principal component analysis; they were starch, WI, maximum diameter,protein, titratable acidity and vitamin C. The quality evaluation result established with thelinear weighted of principal component scores and corresponding weights could be expressedby the following equation: Z=0.358F1+0.165F2+0.130F3+0.087F4+0.069F5+0.065F6。Thirdly, the freezing suitability of lotus root were studied on the basis of qualityevaluation to select appropriate materials for freezing processing. The results suggested thatthe starch content and comprehensive score value were positively related with relativefirmness, and negatively related with the initial freezing temperature and drip loss. Theseresults suggested that depending on the quality maintenance or improvement after thawingmay be achieved through selection of lotus root with high starch content and comprehensivescore value for freezing processing, especallily for ultrasound-assisted immersion freezing.Finally, to further determine the superiority of ultrasound-assisted immersion freezing forfrozen quality improvement, the influence of different freezing methods including air blastfreezing, immersion freezing and ultrasound-assisted immersion freezing on the freezingcharacteristics of lotus roots were investigated. The results showed that the ultrasound-assisted immersion freezing at150W and30s intervals shortened the freezingtime by approx.56.46%and11.63%accordingly when compared with the air blast freezingand the immersion freezing. Furthermore, the sample prepared from ultrasound-assistedimmersion freezing held several advantages over air blast freezing and immersion freezingsamples in terms of the color, protein denaturation, calcium content, firmness and drip loss,except that the color difference between immersion freezing and ultrasound-assistedimmersion freezing samples was not remarkable. Speaking for Vitamin C amount, the air blastfreezing and immersion freezing processing showed no obvious impact on it, while slightvitamin C degradation was observed in the ultrasound-assisted immersion freezing samplesprocessed at high power level. The SEM analysis showed that the microstructure of theultrasound-assisted immersion freezing samples corresponds more to the microstructure of theraw lotus root samples than to the microstructure of the immersion freezing and air blastfreezing samples. It is finally concluded that ultrasound-assisted immersion processing seemsto be the optimal freezing method for lotus root with improved quality and less damagedmicrostructure.