Hazelnut is an important food item in terms of nutrition with the fat, protein, vitamins and minerals it contains. The edible inner part of hazelnuts constitutes approximately 50% of the fruit. The chemical composition of hazelnut kernels is 2-6.5% moisture, 10-24% protein, 50-73% oil, 10-12% CHO, 1-3% cellulose, 1-3.4% ash.

Protein Content of Hazelnuts

The protein content of hazelnut kernels varies between 10-24%, and its digestibility varies between 73-83%, depending on the variety, care conditions and ecological factors. The amount of protein in hazelnuts is higher than eggs and grains, and almost equal to the amount contained in meat and legumes. Protein quality is lower than eggs and meat products.

Carbohydrate Content of Hazelnuts

Hazelnut kernels contain 10-22 % carbohydrates . The total amount of sugar in dry matter is between 2.8-7.9% . A total of 90% is sucrose, 6% is stachyose, 3% is raffinose, and 1% is glucose, fructose and myoinositol. Sucrose provides flavor to hazelnut kernels , and in some varieties it is present in high enough amounts to be felt by tasting.Since the amount of stachyosis and raffinose is very small, they have no effect on the taste of hazelnut kernels. Additionally, starch is found in 1-3.6% of dry matter .

Dietary fiber (pulp) and pectins are found in hazelnuts at a rate of 1-3% . These compounds prevent the toxic effects of chemical compounds in the intestine , colon diseases, constipation and heart diseases , and reduce serum lipid levels and blood sugar. 

Table 1. Hazelnut energy and nutrient amount (mg/100 g),

Moisture g/100 g Moisture	Fat g/100 g Fat	Carbonhydrate g/100 g Carbonhydrate	Protein g/100 g Protein	Diet Fiber g/100 g Diet Fiber	Ash g/100 g Ash	Energy Cal/100 g Energy
5,8 (2–6,5)	62,4 (50–73)	16,7 (10–22)	12,6 (10–24)	3 (1–3)	2,5 (1–3,4)	634

 Table 2. The amount and vitamins found in hazelnuts (mg/100 g), 

Vitamin B₁	Vitamin B₂	Vitamin B₆	Niasin / Niacin	Vitamin E
0,46	0,10	0,24	1,9	35,5

 Table 3. The amount and minerals found in hazelnuts (mg/100 g), 

Fe	K	Cu	Ca	Na	Mn	Zn	Mg	P
3,4	704	1,3	209	2	5,1	2,2	16,2	337

Table 4. Amino acid composition of different foods (mg/100 g fresh weight), 

Amino acid	Hazelnut	Almond	Walnut	Wheat	Chickpea	Egg	Beef
Soleucine	1463	700	717	426	891	778	852
Leucine	1455	1267	1376	871	1505	1091	1435
Lysine	690	454	285	374	1376	863	1573
Methionine	188	518	247	196	209	416	478
Cystine	101	172	–	332	238	301	226
Phenylalanine	833	975	753	589	1151	709	778
Tyrosine	878	593	–	391	589	515	637
Treo	623	492	494	382	756	634	812
Tryptophan	–	–	185	–	–	–	–
Valine	1500	1053	809	577	913	847	886
Arginine	3506	1976	2261	602	1891	754	1118
Histidine	424	450	359	299	531	301	603
Alanine	700	784	–	472	872	733	1033
Aspartic acid	1688	1908	–	644	2332	1190	1590
Glutamic acid	4815	4426	–	3900	3187	1576	2703
Glycine	2040	1056	–	512	807	410	860
Proline	1313	982	–	1298	849	515	668
Serine	2261	710	–	600	1023	946	713

 

  Fat Content of Hazelnuts

     The amount of oil in hazelnuts varies between 50-73 g/100 g depending on the region, climate, soil and variety. In addition to providing energy in the organism, fats have important functions such as maintaining body temperature, protection against external factors and transporting fat-soluble vitamins. In addition, the composition of fats contains fatty acids that have various functions and benefits in the organism . In studies conducted on the composition of hazelnut oil, it was determined that it is similar to olive oil in composition and that the highest amount of oleic fatty acids are found in all varieties, followed by linoleic, palmitic, stearic and linolenic fatty acids, respectively. The high content of oleic acid provides oil resistance. In the scientific research conducted by Istanbul University, TÜBİTAK and Yıldız Technical University, a diet enriched with hazelnuts containing monounsaturated fatty acid (oleic acid) in type 2 diabetics reduced serum total cholesterol level by 26.2%, regulated blood sugar and protected Apoliopoprotein A-11 against heart diseases. It has been determined that it increases blood pressure by 28% and reduces risky Apolipoprotein B by 7.5%, and therefore it has been emphasized that it has a protective effect against cardiovascular diseases. Therefore, 1/3 of the fat composition in the daily diet should be saturated, 1/3 should be monounsaturated, and 1/3 should be polyunsaturated. "Nurses" Health Study, a multi-center, prospective cohort-type study, on the effects of nutrition with hazelnuts and peanut oil, which are hard-shelled fruits, on the development of type 2 DM, which is one of the important risk factors of cardiovascular diseases and is considered to be the equivalent of CHD (Coronary heart disease) today. Published as a heart group analysis of . 83,818 healthy nurses were included in the study and followed for 16 years. It has been shown that the development of type 2 DM decreases with the increase in the amount of hazelnut and peanut oil consumption, and this relationship is independent of people's age, body-mass index, presence of DM in the family, physical activity level, cigarette and alcohol use, daily total calorie intake and diet components. As a result of this study, it was suggested that the increase in daily calorie intake due to high consumption of hazelnuts and peanut oil in the diet could be balanced by reducing the consumption of refined grains and red meat. Recent studies have shown that regular consumption of hazelnuts as part of a healthy diet reduces the risk of CHD development in healthy individuals, as well as heart attacks (acute myocardial infarction) and cardiac deaths due to CHD. In another study, Dr. from Brigham and Womens Hospital in Boston, USA. In the research started by Christina Albert and her colleagues in 1982, the effects of nutritional habits on long-term cardiovascular diseases in 21 thousand healthy male doctors were evaluated. According to the study results, it was observed that those who consumed two or more handfuls of hazelnuts and peanuts per week reduced the risk of sudden cardiac death by 47% and the risk of death due to CHD by 30%. It has been stated that the risk of developing CHD is lower in those who prefer the diet called the Mediterranean diet. Studies have shown that oleic acid prevents the increase of cholesterol levels in the blood, reduces cholesterol by 26.2%, regulates blood sugar, has a protective effect against cardiovascular diseases, increases protective apoprotein A-1 in heart diseases by 28%, and reduces risky apoprotein B by 7.5%.

Table 5. Amount of cholesterol and fatty acids in 100 grams of hazelnut 

Cholesterol	Saturated fatty acids (g)	Unsaturated fatty acids (g)
		Monounsaturated fatty acids	Polyunsaturated fatty acids
0	Total	14:0	16:0	18:0	Total	16:1	18:1	20:1	Total	18:2	18:3
	4,60	0,12	3,12	1,27	49,0	90,21	48,63	0,10	6,00	5,83	0,15

 

Linoleic acid prevents the sedimentation of blood platelets and intravascular narrowing . This feature alone reveals that linolenic fatty acid should be given importance in daily diets in terms of healthy nutrition . It is known that the linoleic and linolenic fatty acids found in hazelnut oil have a lowering effect on the lipid and triglyceride levels in the blood, thus lowering blood pressure , and can synthesize prostaglandins , which have functions to regress cardiovascular diseases . In a study, when a diet rich in linoleic acid was applied to diabetic patients who did not require insulin and those who ate a diet high in fat ,for 10 days, at the end of the period , it was observed that the triglyceride, cholesterol and insulin levels in the blood decreased.

The human body needs 1 g of polyunsaturated fatty acids daily , 7-8 hazelnuts weighing 1.4 g , with an average of 61% fat and 14.9% of this fat being linoleic acid , are sufficient to meet the daily essential fatty acids . At Table 5 the fatty acid distributions of different oils are given.

The antioxidant and phytochemical substances contained in the hazelnut and hazelnut oil have a preventive effect on the development of many chronic diseases such as diabetes (cancer, atherosclerotic heart diseases, cataracts , etc.) by preventing cell damage by free radicals and increasing body resistance . In a study conducted by Alphan et al., at the end of two diets containing the same amount of fiber ; it was found that while there was a 21% increase in fasting insulin level in the diet containing hazelnuts , there was no change in postprandial insulin and there was significant decrease in Hb A ₁ C levels.

Many studies show that dietary fat has an important place in the formation of human and breast cancers . Studies show that dietary fats has stimulant effect in spontane tumors. Dietary fats affect tumor formation , especially in the development and metastasis stages rather than the beginning . Cholesterol is not considered an agent directly causes or promotes cancer. Vegetable oils rich in polyunsaturated fatty acids oils becomes easy oxidized. Elements formed as a result of oxidation cause DNA degradation and increases the risk of cancer by causing immunity cells to wear out .

     Another important feature of hazelnut oil is that it does not contain cholesterol, which is known to play a role in the formation of cardiovascular diseases . In addition, b-sterol, one of the sterols found in hazelnuts , not only prevents cholesterol synthesis , but also has the ability to absorb cholesterol and reduce its absorption in the intestine .As a result of studies on public health in the USA , it has been observed that coronary heart diseases are reduced by 50% in those who consume shell fruit 4 times a day per person . In another study on the subject , decreases in blood sugar and blood pressure were observed in diabetic patients who followed a hazelnut diet due to the oleic acid in hazelnuts , and it was determined that the triglyceride and LDL cholesterol levels in the blood decreased, HDL cholesterol increased , and therefore total cholesterol decreased.

     The fatty acid composition of hazelnut oil contains up to 82 % oleic acid . Oleic acid increases the rate of high- density lipoprotein (HDL) in human blood and reduces blood cholesterol , thus reducing the risk of cardiovascular diseases . People who eat hazelnuts at least once a day have half the risk of cardiovascular disease compared to people who never eat hazelnuts.

As a result of various studies , it has been determined that monounsaturated fatty acids constitute the majority of the fatty acids found in hazelnut oil (79.5%). The amount of polyunsaturated fatty acids constitutes 12.5 % of the total fatty acids found in hazelnut oil. Saturated fatty acids are found in small amounts (8%) in the fatty acids in hazelnut oil. The ratio of these fatty acids varies from variety to variety . The main reasons for the difference between the fatty acid compositions of hazelnut oils are the genetic structure of the hazelnut fruit , the year and place where the hazelnuts grow , environmental conditions and the agricultural method applied . Mono and polyunsaturated fatty acids found in hazelnuts ; oleic (C18:1), linoleic (C18:2), palmitic (C16:2), stearic (C18:1), linolenic (C18:3), arachidonic (C20:0), eicosanoic (C20:1) acid.

As a result of a 6- year study in America , those who eat hazelnuts at least once a day or consume hazelnut oil havereduced  risk of dying from heart attack by half compared to those who never use it.

A study conducted on 15 individuals , they were given 40 g of hazelnuts daily for 4 weeks . As a result of the research, they determined that LDL, VLDL and triglyceride levels decreased and HDL levels increased. As a result, we believe that hazelnuts can be included in an adequate and balanced program to protect against coronary heart diseases , and also due to their high fat content they have high energy content.

Mineral Content of Hazelnuts

Hazelnut is a very rich source of mineral substances and contains between 1-3.4% ash . Considering the mineral composition of 100 g of hazelnut kernels and the daily mineral requirement of an adult , Fe, Mg, Cu, Mn, K, P, Zn, Ca, which are essential for human nutrition , can be easily met. In addition, the salt in hazelnuts is lower than the amount found in normal water ( per liter in spring water according to GMT). 30 mg , maximum 600 mg in drinking water ) . It is also seen that hazelnut consumption will not be a big problem , especially in patients with high blood pressure due to diets low in salt .

Low Na in hazelnuts , and  high Mg, Ca and K levels regulate blood pressure in the body. Hazelnuts, are the most Ca containing fruit after almonds and dairy products ( cheese 250-1200 mg/100 g), molasses (400 mg/100 g), vine leaves (392 mg/100 g) especially in terms of Ca which are necessary for bone and tooth development . Hazelnut is also one of the rich sources of Fe , which is necessary to prevent anemia and disorders of the digestive and respiratory systems . Hazelnuts contain between 3.4-5.8 mg Fe per 100 g . The use of plant-derived iron at lower rates than animal- derived iron despite consuming it with foods containing Vitamin C makes it equivalent to the iron content of meat . Hazelnuts  also contain Mg which is essential in preventing respiratory and digestive system disorders. Cu which prevents anemia, weight loss, reproduction and growth disorders Mn, which is necessary for development, growth and reproductive disorders ,K which is necessary for disorders in the heart, muscle, digestive system, development and hormonal systems disorders and prevents strokes and high blood pressure. Zn, which is necessary to prevent disorders in growth, reproduction and the immune system , hair loss and loss of appetite, and P ions to prevent rickets.

   Vitamin Content of Hazelnuts

Hazelnut contains vitamin B ₁ , which acts as a regulator in carbohydrate, protein and fat metabolism in the body. and vitamin B ₂ Good for vitamin B ₆ In addition to being a very good source of vitamin E, it is one of the best sources after vegetable oils , especially in terms of natural antioxidants and vitamin E. In a screening study conducted by TÜBİTAK with 960 school children across the country , 90% of the children were malnourished for B₂ and 84% were for B₆ in terms of vitamin has been observed. Since B₂ and B₆ vitamins are important for blood production and mental health and consuming hazelnut regularly every day can be considered as a practical solution to the nutritional problem of our country 's children .

Vitamin E found in hazelnuts is of great importance in terms of nutrition as well as providing durability to the product. Hazelnut oil is also very rich in α-tocopherol. A-tocopherol is essential for the normal functions of muscle tissues and reproductive system in the human body. It is also known to have a protective effect against cancer and anemia. Tocopherols are compounds that have antioxidant effects, especially in fats and oils, and are beneficial for human health. It prevents the oxidation of fats and the destruction of the cell by oxygenated compounds. Tocopherols, which have a protective effect against many diseases, including cancer and cardiovascular diseases, relax the heart by reducing lipid oxidation in human blood. When additional vitamin E was given to experimental animals treated with carcinogenic substances, cancer formation decreased in most of the animals. Tocopherols, which are essential for the functioning of muscle tissues and the reproductive system, also have a protective effect against anemia.

Türkiye has an important position in hazelnut production and export. In addition to its economic importance, it is very important in terms of nutrition and health with the fat, protein, vitamins and minerals it contains. In order to protect general health, 25–30% of the total daily energy intake of a healthy individual should be provided by fats (2/3 of which should be hazelnut oil or olive oil, 1/3 of which should be sunflower or corn oil) (25). Therefore, it can be recommended to consume hazelnuts directly every day for a balanced and healthy diet, or projects can be developed to increase hazelnut consumption by adding them to the compositions of various foods to be processed. For example, the development of products enriched with natural foods with high nutritional value, which are popular today, can contribute to both increasing the amount of consumption and making the nutritional content of the developed products richer and healthier by including hazelnuts within the scope of the projects.

Written by;

Levent KIRCA¹, Tuba BAK², Semanur KIRCA³, Turan KARADENİZ⁴