Date of Award

12-2017

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Food Science and Human Nutrition

Committee Member

Dr. Feng Chen, Committee Chair

Committee Member

Dr. Felix Barron

Committee Member

Dr. Elliot Jesch

Committee Member

Dr. Dilrukshi Thavarajah

Abstract

Jujube (Ziziphus jujuba Mill.) is a desirable fruit that is widely grown in China. Also, it has been used as an herbal medicine and a functional food simultaneously for a very long time. In this study, 15 cultivars of jujube that were collected from a same farm in Shanxi Province, China, were analyzed in terms of their non-volatile components, including reducing sugars, organic acids, fatty acids, amino acids, minerals and antioxidants, and volatile compounds, in an effort to investigate their nutritional values, and the similarity between the cultivars so as to classify the cultivars based on their chemical composition. The results showed that, in generally speaking, there were significant differences in the chemical compositions among the cultivars (p<0.05). The content of glucose varied from 85.87 to 1004.95 mg/100g FW; malic acid and citric acid were main organic acids, of which the contents ranged from 120.15–508.67 mg/100g FW and 29.40–180.69 mg/100g FW, respectively. Jujube fruits contained a variety of polyunsaturated fatty acids, including linoleic acid, linolenic acid, eicosapentaenoic acid, arachidonic acid, and docosahexaenoic acid. In addition, the fruits were rich of lauric acid (967.20–4035.78 μg/kg DW), palmitic acid (685.68–1936.91 μg/kg DW), myristoleic acid (1718.96–5862.64 μg/kg DW), oleic acid (427.87–2864.98 μg/kg DW), linoleic acid (533.34–7330.05 μg/kg DW). Besides, iron (52.72–125.16 mg/kg DW), calcium (162.29–287.53 mg/kg DW) and magnesium (511.77–699.77 mg/kg DW) were also determined as the main minerals in the fruit. By using the hierarchical cluster analysis and principal component analysis, the 15 cultivars, based on the contents of reducing sugars, were classified into 6 groups, including group A (PZ and DB), group B (NP and LZ), group C (YZ, LB, XZ, HP, BJ and JB), group D (YL, JS, JD), group E (BZ) and group F (PB). Except the group E and group F, the other groups can be differientated from each other. Antioxidants including cAMP, ascorbic acid, triterpenes, and the total phenolic content, total flavonoid content, as well as the antioxidant capacity (i.e., FRAP, DPPH, ABTS, HRSA) were also analyzed in this study. According to the results, the content of cAMP was in a range of 66.33 to 2716.88 μg/100g FW; the content of ascorbic acid ranged from 317.9 to 679.6 mg/100g FW. In addition, jujube contained a low content of triterpenes (6.66 to 18.19 mg/100g FW). The total phenolic content was determined in a range from 330.74 to 571.44 mg gallic acid /100g FW, while the total flavonoids content varied from 43.14 to 154.09 mg rutin/100g FW. The range of antioxidant capacity such as DPPH, ABTS, FRAP and HRSA were determined to range from 0.603 to 1.842 mmol Trolox/100g FW, 2.276 to 2.786 mmol Trolox/100g FW, 1.228 to 3.823 mmol Trolox/100g FW, and 1.353 to 3.560 mmol Trolox/100g FW, respectively. All the 15 cultivars were classified into five clusters based on hierarchical cluster analysis. As a result, the cultivars of NP, JS, YZ were categorized in the same cluster, which contained relatively high contents of antioxidant components and strong antioxidant capacity. Solid phase micro extraction method (SPME) was used to extract the volatile compounds of jujube, which were further identified by GC–MS. The identified volatiles included aldehydes, alcohols, acids, ketones and esters. Among them, hexanal (276.5 to 1314 μg/100g FW), (E)-2-hexanal (145.1 to 1876 μg/100g FW), nonanal (188.2 to 1047 μg/100g FW), and n-decanoic acid (58.42 to 1268 μg/100g FW) were found to be the main volatile compounds in fresh jujube. Based on the contents of the volatile components, the jujube fruits were classified into five clusters, including cluster 1 (LB, HP, LZ, NP, JS, PZ, and YL), cluster 2 (BJ, DB), cluster 3 (PB, BZ, JD and XZ), cluster 4 (JB) and cluster 5 (YZ). Cluster 1, cluster 2 and cluster 3 were found to be crossed over together in the two-dimension plot, which means they could not be discriminated from each other based on contents of volatile compounds. However, the cluster 4 and cluster 5 could be separated very well from each other and from the other clusters. Moreover, two extraction methods, SDE and SPME, were compared in regards of their efficiency of extracting volatile compounds from the dried jujube fruits. (E)-2-Hexenal and hexanal were found to be the major aldehyde compounds in the SDE extract, while nonanal and benzaldehyde were major aldehyde compounds extracted by the SPME method.

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