Research And Application On Quality Characteristics Of Lotus Seed In Different Maturity

Lotus seeds with great nutritional value are the unique economic resources and widely applied in commercial production in China. However, the maturity has great impact on the quality of the lotus seeds and the processing quality, as well as the ultimate commercial value of the product. This paper focused on the characteristics of the fresh lotus seeds in different maturity (milk stage, waxy ripe stage, completed ripe stage, withered ripe stage), the starch quality and the textural characteristics of canned lotus seeds. This study provided the theoretical foundations for the further application of lotus seeds in industry processing.(1) Study on the appearance quality of fresh lotus seeds in different maturityThe results showed that the longitudinal diameter and horizontal diameter of lotus seeds in different maturity were different, but the aspect ratio was similarly located between 1.25 to 1.37. The aspect ratio and the shape of lotus seeds had mainly been formed in completed ripe stage. The shape of the fresh lotus became round in completed ripe stage and withered ripe stage, while in milk stage and waxy ripe stage it tended to be elliptical. Therefore, it is good for commercial processing with fresh lotus seed in completed ripe stage because of the fully growth and the best quality.(2) Study on the nutritional quality of fresh lotus seeds in different maturityNutrients and mineral element contents (except for water and sodium element content) of fresh lotus seeds in four different maturity were significantly different, and both were increased with maturity period increased. There are varieties of amino acids with different amounts in fresh lotus seeds, and methionine is the mainly limiting amino acid. With the increasing of maturity level, the glycemic index of fresh lotus seeds decreased, but was still higher than 70. Fresh lotus seeds is a high glycemic index food. The extraction of fresh lotus seeds were proved to have certain antioxidant capacity:with the extension of maturity level, the total antioxidant capacity (T-AOC) of fresh lotus seeds decreased after an increasing; the hydroxyl radical (·OH) scavenging ability was gradually reduced; the superoxide anion (O2-) scavenging ability increased obviously and the DPPH radical scavenging ability was comparable to the four different maturity.(3) Study on the processing quality of fresh lotus seeds in different maturityTotal phenols contents in fresh lotus seeds in four different maturity levels were quite different. The total phenols content decreased with increasing of maturity levels. Generally the polyphenol oxidase (PPO) activity was firstly increased then decreased during the whole maturity process, and the highest activity of PPO was observed in the completed ripe stage. The peroxidase (POD) activity increased with maturity level increased.(4) Study on the starch quality of lotus seeds in different maturityResearch showed that the size and shape of starch granules in lotus seeds from different maturity were different. The shape of starch granules in milk stage was more irregular, while others were much more oval at high mature level. The maturity level is positively correlated with amylose content, molar mass and gelatinization enthalpy, while is negatively correlated with the degree of crystallinity. Amylose content in lotus seeds at different maturity ranged from 21.96 to 39.94%. X-ray diffraction results showed that the lotus seeds starch belonged to C type with the crystallinity from 57.31 to 63.96%. Infrared spectroscopy showed that the functional groups in lotus seeds starch remained the same but only physical properties changed in different maturity levels. The molar mass of lotus seeds starch is greater than 107g/mol. The root mean square value as well as molar mass increases with the increasing of maturity level. Rheological properties of starch paste demonstrated that it is the typical shear-thinning pseudoplastic fluid. The starch paste thixotropic area, the degree of shear thinning, the gel strength were increased significantly with the increasing of maturity level.(5) Study on the maturity effect on the textural properties of canned lotus seeds during storageThe hardness of the canned lotus seeds increased rapidly then increased slowly and finally reached a stable level during the first 30 d at different maturity levels. The hardness level of lotus seeds was arranged in the descending order of completed ripe stage> waxy ripe stage> milk stage. The adhesion firstly declined rapidly then flattened on the 30th day, the adhesion changes was arranged in the descending order of milk stage>waxy ripe stage> completed ripe stage. The elasticity changes were small due to the less impact of the maturity level on the elasticity. Chewiness increased gradually then stabilized on the 30th day. The highest chewiness was observed in completed ripe stage, while the lowest chewiness was determined in the milk stage.In summary, different qualities of lotus seeds were obtained in different maturity levels. Amylose contents and PPO activities were less at lower maturity level but better flavor was obtained for eating or processing. Except for drying process, it is better to choose lotus seeds in the late waxy ripe stage and early completed ripe stage for further processing according to the actual situation.