Evaluation of Nebraska hybrid hazelnuts: Nut/kernel characteristics, kernel proximate composition, and oil and protein properties

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Abstract

Recently, hybrid hazelnuts have emerged as a potential oilseed crop in Nebraska for food and value-added industrial applications. The quality of 20 hybrid hazelnuts genotypes harvested in 2007 and 2008 years were investigated, in terms of physical properties of nuts/kernels, kernels proximate composition, oil properties and amino acid profiles of the meal. Nebraska hybrid hazelnuts appeared to be smaller in size and lighter in weight compared to Turkish hazelnuts. Oil was the predominate component in the kernel with an overall average oil content of 58.2%, followed by 21.7% carbohydrate, and 17.1% protein. Genotype 10-50 was superior to the other genotypes and should be selected for further study, when combining large size and weight, kernel percentage, stable physical properties and oil contents over years. Oleic and linoleic acids were the major fatty acids in the oils and comprised more than 90% of the fatty acids. Oils had an average saponification number of 174.1 mg KOH/g oil, iodine value of 89.8 g I2/100 g oil and free fatty acid content of 0.45 mg KOH/g oil. Sixteen amino acids were identified. Seven essential amino acids were detected, and accounted for approximately 27% of the of total amino acid contents. The effect of harvest year on the quality of nuts was significant (p < 0.05). The average size and weight of the hazelnuts harvested in 2008 were significantly (p < 0.05) smaller and lighter than their counterparts in 2007. Nuts harvested in 2007 had marginally higher oil contents, palmitic, stearic, oleic and linolenic acids, saponification value, free fatty acid content, and lower protein, ash and carbohydrate contents than those harvested in 2008.

Introduction

Hazelnuts (Corylus spp.), also known as filberts, are an important commercial crop in many countries. Turkey is the leading producer of hazelnuts, accounting for approximately 74% of world production. Italy is the second and represents about 16% of worldwide production, followed by the US (∼4%) and Spain (∼3%) (Seyhan et al., 2007). In the USA, commercial hazelnut production is largely in the Willamette Valley in Oregon (Mehlenbacher, 2003). An average 25,000 metric tons are produced each year (Chase and Anagnostakis, 2003). Currently, all commercial hazelnut cultivars have been selected directly from wide European species (Corylus avellana). The European species produce nuts of higher quality and larger size with thinner shells. Unfortunately, they cannot tolerate the harsh winters of the Upper Midwest of the USA, nor are they resistant to Eastern filbert blight (a native disease of hazelnuts in the eastern US that is uniformly fatal to the European hazelnut). On the other hand, American native species are cold-tolerant and disease resistant, but the nuts produced are small and of little commercial value. Therefore, since the early 1900s, attempts have been made to develop commercial-quality hybrid hazelnut shrub cultivars, which combine the superior qualities of the European hazel with disease resistance and cold hardiness of the American species, through interspecific crosses between the European hazelnut C. avellana, and the North American natives Corylus americana and C. colurna L. (Weschcke, 1954, Slate, 1961; as cited by Molnar et al., 2004).

A 9 ac hybrid hazelnut planting at Arbor Day Farm in Nebraska City, NE was established in 1996, and currently is one of the largest plantings of hybrid hazelnuts east of the Rocky Mountains. There are 5200 genetically distinct hybrid hazelnut shrubs which were grown from open-pollinated seedlings derived from a breeding program at Badgersett Research Corporation, Canton, MN. Recent research conducted with the Arbor Day Farm hybrids indicates that the four-year average of the highest yielding selections produced an equivalent of more than 4 tons/ha of husked nuts (Hammond, 2006). Those plants are not cultivated intensively and were not fertilized or irrigated. Under more intensive cultivation, yields are expected to be higher. Further, initial tests at Rutgers University indicate that 60% of the top 10 cultivars do not show symptoms of Eastern Filbert Blight one year after intensive exposure to the disease.

Preliminary evaluations of the hazelnut oil showed that the average oil content was 60% of the dry weight of the kernel. Oxidative stabilities of the hazelnut oils were higher than that of soybean oil, while the cloud points of hazelnut oils were lower than that of soybean oil (Xu et al., 2007). Those initial analyses suggested that hazelnut oil was a potential feedstock for oleochemicals. In addition, there is a growing interest in evaluating the role of hazelnut in human nutrition and health (Alasalvar et al., 2006, Amaral et al., 2006). This is related to their special fatty acid composition, which consists of more than 90% oleic and linoleic acids and small amounts of palmitic and stearic acids, and health-promoting components including tocopherols, phytosterols, polynenols and squalene (Alasalvar et al., 2006, Xu et al., 2007). Further, the defatted meal could be used for food and feed purposes. The objective of this research was to determine the physical–chemical characteristics in terms of nut and kernel quality traits, proximate analyses, oil properties and amino acid profiles of 20 hybrid hazelnut genotypes grown in Nebraska.

Section snippets

Materials

Hybrid hazelnuts, selected from high yielding shrubs, were hand harvested in the Fall of 2007 and 2008 from Arbor Day Farm, Nebraska City, NE. Husks (or the involucre) were removed mechanically and nuts were size sorted and cracked mechanically. Samples of 10 nuts were selected randomly from each of 20 shrubs (top 20 producers of a total of 5199 hybrid hazelnuts planted from 99 different material lines) to measure physical characteristics of nuts and kernels. Hexane, boron trifluoride/methanol

Physical characteristics of nuts and kernels

Physical characteristics, in terms of width, length, and weight of 1 nut/kernel, and kernel weight percentage of 20 hazelnut genotypes harvested in two consecutive years (2007–2008), are presented with descending order of kernel percentage in Table 1. The range, overall means and means of harvest years of the nuts’ physical properties are summarized in Table 2. The nuts had overall average widths and lengths of 17.0 mm and 16.6 mm, respectively, while there was a mean weight of 1.68 g. After

Conclusions

In general, Nebraska hybrid hazelnuts appeared to be smaller in size and lighter in weight compared to report on Turkish ones. Nebraska hybrid hazelnuts had high oil contents with an overall average value of 58.2%, an average carbohydrate content of 21.7%, and an average protein content of 17.1%. Of the 20 genotypes, genotype 10-50 was superior to the other genotypes and should be selected for further study, owing to its large size and weight, kernel percentage, stable physical properties and

Acknowledgements

The authors are grateful to Dr. Susan L. Cuppett, Food Science & Technology Department, for the use of her GC and for her guidance in GC operation and chromatogram analyses, and to Dr. Phillip Miller in the Animal Science Department, for the use of his HPLC and to Ms. Ruth Diedrichsen for her assistance with the measurement of amino acid. We also thank Dr. Scott Josiah in the Nebraska Forest Service for providing hazelnuts and Hui Gao for his assistance in preparing and analyzing the samples.

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