Study On The Relationship Between Cell Wall Components And Texture Variation Of Different Cultivars Lotus Rhizomes After Thermal Pre-treatment

This paper chose representative lotus rhizome varieties as experimental materials,Namely Lulin Lake lotus rhizome(sample A), Mian City lotus rhizome(sample B) and E’lian No.5 lotus rhizome(sample C). Moisture content, color, hardness, starch properties(microstructure, structural composition, gelatinization properties and crystal type), the content of phenolic compounds, antioxidant capacity of phenolic of lotus rhizomes were measured in the harvest time for June, August, October, December, the following year in February and April. Through the comparison of texture variation among different cultivars lotus rhizomes before and after thermal pre-treatment, cell wall components,microstructure, pectin content and the degree of esterificationwere were analyzed. In order to find out the key factors to effect the texture variation and the formation mechanism of different cultivars lotus rhizomes after thermal pre-treatment, we did analysis on the macro level, micro level and molecular level. The main conclusions were as follows:(1) There was significant difference in hardness after thermal pre-treatment between different cultivars and different harvest times of lotus rhizomes(P < 0.05). Lotus rhizome starch particle were oval shaped under the scanning electron microscope observation,diameter length was 20 μ m to 50 μ m. lotus rhizome starch belongs to the C type crystal through the X ray diffraction analysis. The gelatinization temperature were from60.8 ℃ to 70.7 ℃ though the analysis of differential scanning calorimeter.(2) The optimum conditions for the determination of lotus rhizome phenolics by Folin-ciocalteu method were: 0.5 m L Folin-ciocalteu reagent, 2 m L Na2CO3 solution, in25 ℃ for 2 h. On the basis of single factor experiment, using the response surface design principle and statistical methods to establish the mathematical model, the optimum extraction technology of lotus rhizomes free phenolics were 40% ethanol, 20 min ultrasonic period for 3 times; the optimum extraction technology of lotus rhizomes bound phenolics were 3.1 mol/L Na OH, in 50.5 ℃ for 2.1 h. The minimum of lotus rhizomes total phenolics content was in June, the maximum was in August and October, then decreased from the December to the April of the following year, the trend of totalphenolics content was in conformity with the growth cycle of lotus rhizomes. There was no significant difference of free phenolics content among different cultivars, while the bound phenolics were significantly different among different cultivars lotus rhizomes(P< 0.05).(3) The cotent of pectin fractions, hemicelluloses fractions and residue fractions accounted for the percentage of AIR in dry weight were analyzed in the harvest time for June, August, October, December, the following year in February and April. Compare the ratio of CSF and WSF, sample A was maximum, then sample C, sample B was minimum.The principal component analysis was used to study the infrared spectrum information of three pectin components. The results show that lotus rhizomes WSF pectin clustered into different types in principal component space in a relatively independent space, thus could distinguish between different cultivars of lotus rhizomes.(4) The hardness of lotus rhizomes reduced after thermal pre-treatment, and was lower when vacuum-sealed packing. Sample A maintained a better texture than sample B.WSF content increased while CSF and NSF decreased significantly after thermal pre-treatment(P < 0.05), thus could demonstated that the content of WSF, CSF and NSF were the significant factors to influence the texture of lotus rhizomes after thermal pre-treatment. The content of galacturonic acid increased significantly after thermal pre-treatment(P < 0.05), sample A was the lowest, and this was a reason why sample A remained a better texture after thermal pre-treatment. In addition, the DE value of lotus rhizomes reduced significantly after thermal pre-treatment(P < 0.05), sample A was still the lowest, and this was another reason why sample A remained a better texture after thermal pre-treatment. The microstructure of lotus rhizomes befor and after thermal pre-treatment could be observed through scanning electron microscope, which showed that sample A maintained a relatively higher integrity of cell wall structure, while the cell wall of sample B suffered a serious destruction after thermal pre-treatment.