Dynamic change of mineral elements in hops (Humulus Lupulus L.) in different developmental periods

It is necessary to investigate the characteristics of absorption and accumulation of mineral elements during the growth of hops, and which is also important for scientific farming and fertilizing to get these valuable data or rules. In this study, a total of twenty-two mineral elements (Al, Pb, As, Cd, Ba, Ni, Mn, Cu, Sr, Co, Cr, Zn, Li, V, Fe, Ga, Rb, Cs, K, Ca, Na and Mg) derived from different hops samples were determined by using the methods of inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma atomic emission spectrometry (ICP-OES). The varieties of hops for investigating were Tsingtao Flower, SA-1 and Marco Polo, which are three main hops varieties cultivated in Xinjiang, China; and hops samples were collected from different planting areas in different developmental periods. Results of the methodological evaluation showed that the established method was accurate and reliable, which could meet the requirements for simultaneous determination of multi-element derived from hops. The result of this study indicated that the content of the 22 analyzed elements in hops showed significant variation in the whole developmental periods of hops. And results also indicated that hops may have the characteristics of "areal differentiation" and "period differentiation" in the absorption and accumulation of these mineral elements. Specifically, the content of Sr, Na, Rb, Li, Ba, Ga, Co and V was greatly influenced by planting areas. Furthermore, during the whole developmental periods, all analyzed hops samples did not accumulate or absorb heavy metals such as Cd and Pb. Principal component analysis (PCA) was used to further investigate the relationships between the 22 mineral elements and hops maturity, as well as planting areas. The results of PCA indicated that the first three principal components could explain 84.36% of the total variance, which could be used as the feature vectors. And the elements of Ba, Ni, Mn, Cu, Co, Zn, Li, Fe, Ga, Rb, Cs and Ca showed great contribution on the first principal component; the elements of Li, K, Na and Mg showed great contribution on the second principal component; Al, Pb and V showed important contribution on the third principal component. However, elements of Cd, Sr and Cr showed little contribution on the first three principal components, which indicated that these mineral elements were non-characteristic components in hops samples and there was no significant relationship with the growth stages of hops. The result of sample score showed that the scatter plot made up by PC 1 and PC 2 could be used for distinguishing the hops samples with different planting areas; the scatter plot made up by PC 1 and PC 3 could be used for differentiating the maturity of hops, and the result was affected little by the hops varieties and planting areas. Moreover, the PCA results also indicated that the elements of Mg, K, Li and Na made great contributions on distinguishing the planting areas of hops, and the elements of Al, Pb and V showed significant value on evaluating the maturity of hops. However, the result also showed that it is hard to discriminate the difference of hops varieties only by using the discrepancy of the mineral elements, but which may be further realized by combining with other components. © 2019, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.