| Hops is a soul raw material for brewing,which plays an irreplaceable role for forming flavor and aroma of beer.China is the biggest hops plantation in Asia,but domestic hops products show a weak influence in the international market.Especially in recent years,some undesirable phenomenons emerge form time to time,for example companion planting of different quality hops,and adulteration,which seriously shake the consumer market confidence for domestic hops products.Intra-industry has already developed standards for evaluation of hops,these standards however,could not satisfy the requirements of brewing industry to obtain the authenticity of hops.Hence,it's crucial to make a comprehensive system study focused on the variety and quality features of domestic hops.In view of the prominent issues of domestic hops industry,and also the deficiencies of current evaluation methods of hops,this paper aims at analyzing different kinds of important functional components derived from hops,and employing chemometrics to establish hops fingerprints,which was used to understand the variety and quality features,as well as the brewing performance of domestic hops;on the other hand,the above work could be used for studying the construction method of quality evaluation system of hops,and establishing evaluation models based on different purposes.The whole work could provide technical support for optimizing industry and improving market supervision systems of domestic hops,and also offer reference for the construction of evaluation systems in other fields.The main research contents and results of this paper were listed as following:1.A method of headspace solid-phase micro-extraction gas chromatography-mass spectrometry(HS-SPME-GC-MS)was established to analyze volatile components derived hops.Totally 50 compounds were identified as characteristic components,and the flavor characteristics of SA-1 hops were confirmed as fruity,floral,herbaceous,woody and spicy.Hierarchical cluster analysis(HCA)and principal component analysis(PCA)were used to establish the flavor fingerprint of SA-1 hops,and totally 23 components were selected as the key indicators for building fingerprint.Six components were identified as mutagenic factors by using factor weight analysis,which would influence the consistency of flavor features among different SA-1 hops samples.Compared with some world-famous aroma varieties of hops,SA-1 hops showed excellent aroma characteristics,and the overall aroma style was similar to Saaz hops.2.Method for distinguishing the freshness of hops based on volatile components was established.Thirty volatiles were determined as common components in different freshness of SA-1 hops,and 25 compounds showed significant difference(p <0.05);among them,the content of terpene compounds significantly decreased after storage,while the content of oxygenated compounds increased,which indicated that oxidation during storage is the important factor for influencing the flavor characteristics of hops.HCA and PCA were used to establish volatiles fingerprint of different freshness of hops,which showed that there was obvious clustering difference and volatiles fingerprint differentiation between different freshness of hops,and the first principal component was the key vector.Deterioration characteristic of SA-1 hops was that the fruity flavor was covered up by the herbaceous/woody flavor.(Orthogonal)partial least squares-discriminant analysis((O)PLS-DA)was used to establish the discrimination model of different freshness of hops,which showed a discrimination ability,and ?-caryophyllene,?-myrcene,?-farnesene,?-humulene,methyl 4-decenoate,and methyl geranate were determined as the key differentiated components.3.Method for distinguishing the varieties and adulteration of hops based on volatile components was established.By analyzing volatile components derived from three Chinese main varieties of hops,totally eighty-four compounds were identified,and the flavor characteristics of the three varieties of hops were also determined.Among these compounds,28 volatiles were common compounds in the three varieties of hops,and the differentiated components were mainly esters and alcohols.Similarity analysis was used to explain the variety difference of hops,which could be used for distinguishing the varieties,but not for distinguishing adulteration.HCA and PCA were used to establish volatiles fingerprint of different varieties of hops,which indicated that there was obvious clustering difference and volatiles fingerprint differentiation between different varieties of hops,and nineteen components were determined as key indicators for building fingerprint.(O)PLS-DA was used to establish discrimination model for discriminating hops varieties and adulteration,which showed a good power in varieties discrimination and samples prediction.Discrimination factors and flavors of different varieties of hops were also determined.4.Method for distinguishing the geographical origins and varieties of hops based on mineral elements was established.Results of analyzing twenty-two mineral elements derived from hops showed that different varieties and origins of hops showed great difference in the overall distribution features of mineral elements.HCA and PCA were used to establish mineral elements fingerprint of different hops,which showed that there were obvious clustering difference and mineral elements fingerprint differentiation between different varieties and origins of hops,the accuracy of fingerprint in predicting varieties and origin was up to 100%,and 6 components were determined as key indicators for building fingerprint.(O)PLS-DA was used for establishing supervised discrimination model for distinguishing the varieties and origins of hops,which showed a good discrimination power,and the discrimination factors were also determined.In addition,the results also suggested that there were obvious correlations of the accumulation among mineral elements,and also between mineral elements and functional components.The relationships between mineral elements and quality characteristics of hops were clarified preliminarily.5.Method for evaluating growth features of hops based on mineral elements and bitter acids was established.Twenty-two mineral elements derived from hops in different developmental periods were tracked and measured.The result showed that the variation trend of 22 mineral elements derived from hops in the developmental periods was obvious,among them,the absorption of Sr,Na,Rb,Li,Ba,Ga,Co and V was greatly influenced by the hops planting fields.PCA result showed that there were strong relationships between the accumulation of 22 mineral elements and hops maturity,as well as planting areas.The accumulation of Mg,K,Li and Na had origins features,while elements of Al,Pb and V were helpful in evaluating the maturity of hops.The optimum harvest time and bitter taste quality of hops were determined by analyzing the accumulation rules of series of bitter acids in hops,and the proportion of co-humulone and co-lupulone in ?-acids and ?-acids hold constant of hops developmental periods.The correlation analysis results showed that elements of Al and V were helpful in the synthesis of bitter acids.6.Method for evaluating brewing performance of hops based on the conversion of terpene alcohol isomers was established.The results indicated that different hopsvarieties showed differences in stereoisomeric distribution of terpene alcohols,especially,R-form of linalool,geraniol,and R-?-citronellol existed in all hops samples,and linalool showed a single configuration.The rules of thermal conversion behaviors of terpene alcohols were determined by using a simulated brewing experiment,the results showed that S-linalool and nerol were common flavor components in all boiling systems,but S-?-citronellol and(2E,6E)-farnesol had no flavor contribution to all systems.In addition,the results also indicated that boiling time and the varieties of hops were important for regulating flavor characteristics of systems.The results of HCA and PCA further clarified the influence of boiling process on hops flavor characteristics,and geraniol,R-?-citronellol,(2Z,6E)-and(2E,6E)-farnesols were differential components for distinguishing the boiling systems between different categories of hops;nerol,R-and S-linalools were key indicators for distinguishing the flavor variation during boiling. |
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