Graduate Thesis Or Dissertation
 

Factors influencing storage quality of hazelnut varieties

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  • This thesis research is a series of five studies dealing with various aspects of hazelnut quality: 1. Identification of kernel mold and its incidence among hazelnut varieties. 2. Seasonal development and composition of kernels. 3. Hazelnut oil composition (fatty acids and tocopherols) of seventeen varieties. 4. Hazelnut oil composition compared to 14 other nuts and oilseeds. 5. Storage and roasting effects on lipid oxidation. Barcelona, Daviana, and Ennis varieties of hazelnuts used to study white mold showed that mold incidence was highest in 1986, and much less in 1987 and 1988. Ramularia spp was the only fungus that was identified in all samples with kernel mold and was usually found at high percentages. Temperatures for drying, storage, and numbers of nuts per cluster had no significant effect on percent mold. The second part of this study measured fatty acid and vitamin E concentrations during the growing season. Samples were collected from seven varieties (Barcelona, Daviana, Ennis, Tonda Romana, Tonda Gentile della Langhe, Tombul, and Tombul Ghiaghli). Kernel oil and vitamin E (tocopherol) concentrations increased with time, while moisture decreased. Oleic acid was the major fatty acid (ca.75%) found in hazelnuts, followed by linoleic(ca.20%). Linolenic was high at the beginning of the season but then decreased to about 1% at harvest. Alpha-tocopherol was the major form of vitamin E found, composing almost 95% of total tocopherols. Hazelnuts are a rich source of vitamin E, with about 350 μg/g oil. Fourteen types of nuts, oil seeds, and seventeen varieties of hazelnuts were compared for oil content, fatty acid, and tocopherol composition. Macadamia nuts were the highest in oil content (77%) and chestnuts were the lowest (3%). Oil concentrations in oil seeds ranged from 5% in corn to 50% in sesame seeds. Oil concentration also varied among hazelnut cultivars. Hall's Giant had low concentrations (58%) of oil and Tombul had high concentrations (66%) of oil. Gamma-tocopherol was the dominant form in pistachios, English walnuts, black walnuts, pinenuts, and Brazil nuts. All four tocopherols were found in oil seeds and tocotrienols were found in some. Hazelnut varieties were stable during storage for up to two years with only slight loss in vitamin E.
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