| Nanfeng tangerine is one of the most characteristic fruits in Jiangxi Province and is known as the "King of Tangerines".With its golden color,rich aroma,thin skin and tender flesh,it is one of the best fruits.The health benefits of oranges are not only limited to the edible part,but also extend to the inedible part.Its pulp and peel can be used medicinally to relieve cough,phlegm,swelling and pain,and it can also regulate the liver and qi.In addition,tangerines are rich in flavonoids,amino acids,phenolic acids,coumarins,alkaloids and dietary fiber with high nutritional value,which can anti-aging,anti-allergy,lower cholesterol levels and prevent tumor diseases.Therefore,tangerine is a fruit that can be used for both medicine and food.In the book "Nanfeng Folklore and Products",Lu Qiguang of the Qing Dynasty had a high opinion of Nanfeng tangerine: " Tangerines are well-known nationwide.At the end of autumn,its fruits are abundant beside the hedge".The pulp of tangerines can be processed into fresh juice,jelly and other products,while the peel is a by-product of the process that,if not utilized,will eventually become waste and pollute the environment.Citrus peel is recognized as a raw material rich in natural beneficial ingredients that can be used in the nutraceutical,pharmaceutical,and fragrance industries.The accumulation of tangerine components is a dynamic development process.In addition to cultivars,external environment,storage conditions and genotypes,different maturity levels are also important factors affecting the quality of tangerines.In addition,different maturity of tangerines affects the consumers’ enjoyment of it because of its unique aroma,flavor and color.So far,the research on Nanfeng tangerine has mainly focused on the extraction of chemical constituents,aroma substances,and variety differences during the pulp ripening period,but the dynamic changes in the different growth stages and the whole ripening process of tangerine pulp and peel have not been studied.Therefore,we used metabolomics techniques combined with chemometrics to investigate the types,distribution patterns and content trends of chemical constituents in Nanfeng tangerine from the fruiting stage,expansion stage and ripening process.In addition,Nanfeng tangerine can be processed into a new type of orange peel tea,which becomes a fashionable beverage.The research content of this paper is as follows.In the first chapter: introduces the main active compounds of Nanfeng tangerine.The efficacy of terpenoids,flavonoids,phenolic acids and limonoids in reducing blood lipids,anti-oxidation,immune regulation and improving cardiovascular and cerebrovascular diseases was discussed.In addition,the use of chromatographic mass spectrometric methods,chemometric techniques(including principal component analysis and partial least squares discrimination)and metabolomics in the field of tangerine is discussed.In the second chapter: an amino acid analyzer was used to quantify the hydrolyzed amino acid contents of the peel and peel of Nanfeng tangerines throughout the ripening process.The results showed that the content of 17 free amino acids measured fluctuated during the ripening of tangerines,and the total amount of amino acids in the pulp was higher than that in the peel.Among them,aspartic acid(Asp),glutamic acid(Glu)and histidine(His)were the three most abundant amino acids in the pulp and peel.The content of essential amino acids(EAA)in the pulp and peel first tended to decrease during ripening,then increased in the middle of ripening,and finally decreased significantly as the maturity of tangerines increased.In the third chapter: based on headspace solid-phase microextraction(HS-SPME)combined with gas chromatography-mass spectrometry(GC-MS)techniques to separate and identify volatile organic compounds in the pulp and peel of tangerine from the young fruit stage in June to the commercial maturity stage in November,and then to investigate the changes of volatile compounds during the ripening process.The raw data were preprocessed using Mass Hunter software and rigorously screened by NIST 17 database,and finally 62 and 76 volatile compounds were identified in the pulp and peel of tangerines,respectively,and classified into eight categories.Principal component analysis could clearly distinguish the pulp and peel of fruits in different growing months,and one-way ANOVA showed that there were significant differences between tangerine pulp and peel volatiles during ripening.Among them,monoterpenes and sesquiterpenes were the most abundant flavor compounds.The relative concentrations of monoterpenes in the pulp increased with maturity,while the relative sesquiterpene content showed a decreasing trend,and the content of both compounds in the peel showed fluctuations during ripening,with limonene dominating.In addition,the alcohol content was second only to the terpenes,with linalool being the most abundant alcohol.These results help to deepen the understanding of the quality and flavor of tangerine during ripening,elucidate the metabolic changes of volatile compounds in tangerine,and provide a basis for future breeding efforts to improve fruit quality by affecting fruit aroma,thus providing theoretical guidance for citrus applications in food,pharmaceuticals and cosmetics.In the fourth chapter: explores the effects of different growth periods on the non-volatile components of the pulp and peel of Nanfeng tangerines based on non-targeted metabolomics techniques.The samples were determined by ultra-high performance liquid chromatography(UPLC)-time of flight mass spectrometry(QTOF-MS/MS),and the raw data in positive ion mode were filtered using Mass Hunter Profinder software,combined with Metlin database,the non-volatile components of the growth process of tangerine pulp and peel were identified.Principal component analysis and cluster analysis were performed,and significant differences were found in tangerines at different growth periods.The characteristic differentials,mainly amino acids,flavonoids,sugars and limonoids,were found by partial least squares discriminant method.The analysis of the content of the differential metabolites in the pulp and peel showed that the content of various compounds fluctuated with increasing ripeness,and in general the concentration of flavonoids was relatively high near ripeness.This study provides theoretical support for exploring the metabolic mechanisms of the differential compounds during the ripening process of tangerines.In the fifth chapter: high performance liquid chromatography(HPLC)-triple quadrupole mass spectrometry(QQQ-MS)was used to quantify the phenolic acid compounds in the pulp and peel of Nanfeng tangerines in different growing months.Maturity is one of the factors affecting the phenolic content of citrus.However,studies on the changes of phenolic compounds at different growth stages and throughout the ripening process are limited and not in-depth.Previous studies have rarely analyzed the compositional changes in citrus pulp and peel in a comparative manner,often neglecting the insoluble forms of phenolic acid composition and thus underestimating the actual content of phenolic acids in citrus.In this study,we investigated the effects of different growth periods on the antioxidant capacity,total phenol(TPC),total flavonoids(TFC),phenolic acid compounds,phenylalanine and tyrosine contents in the pulp and peel of tangerines.HPLC-QQQ-MS was used to quantify 10 phenolic acids in the pulp and peel of tangerines at six growth stages,respectively.Overall,the TFC,TPC and antioxidant activities of the pulp decreased continuously with the maturation of the tangerine,while the peel showed fluctuations.The content of most free and bound phenolic acids in the pulp and peel,with the exception of sinapic acid,showed a decreasing trend with increasing maturity of tangerines.The phenolic content in the peel was higher than that in the pulp.Ferulic acid was the most abundant phenolic acid in tangerine during ripening.Phenylalanine and tyrosine showed bending behavior at all growth stages.Partial least squares models(PLS-DA)showed significant differences between tangerines of different maturity levels.Correlation studies showed that phenolic compounds were significantly and positively correlated with antioxidant capacity,TPC and TFC.In the sixth chapter: elaborates the processing process of orange peel tea,deepens the understanding of the new tea,and provides technical support and theoretical basis for the further development of tangerine. |
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