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Food Chemistry, (2001), 73(2), 185-190.
  Effect of Roasting on Some Nutrients of Hazelnuts (Corylus Avellena L.).Özdemir, M., Açkurt, F., Yıldız, M., Biringen, G., Gürcan, T & Löker, M. ,
Abstract: Changes in total amino acid composition, thiamine and riboflavin contents, peroxide value and free fatty acid contents were determined in roasted Giresun and Akçakoca hazelnuts. The results showed that roasting significantly affected peroxide value, free fatty acids, thiamine, riboflavine and total amino composition of Akçakoca and Giresun hazelnuts. Riboflavin level decreased at most 30% in Akçakoca hazelnuts and 18% in Giresun hazelnuts. Above 120oC, more than 50% of thiamine was lost. Amino acid levels in Akçakoca and Giresun hazelnuts generally decreased as the roasting temperature increased. Lysine was lost only <6% in samples of roasted Giresun hazelnuts. In Akçakoca hazelnuts, higher lysine loss was observed (31%) in the sample roasted at 126oC for 45 min.
CRC Critical Reviews in Food Science and Nutrition,(2001) 41 (2), (95-132).
  A review on grain and nut deterioration and design of dryers for safe storage, with special reference to Turkish hazelnuts. Özilgen. M. & Özdemir, M.
Food Chemistry (200x).
 Analysis of internal browning of roasted hazelnuts, Özdemir, M., Seyhan, F.G., Bakan, A.K., İlter, S., Özay, G. & Devres, O.
Abstract: Formation of internal browning in hazelnuts during roasting and effect of water activity on internal browning were studied. Water activity significantly affected color attributes of roasted hazelnuts. As the water activity increased the internal browning also increased. Over the water activity range of study (0.29-0.83), water activity of 0.29 was found to be the least susceptible to internal browning. Roasted samples, having dark coloured internals contained significantly higher total sugar and sucrose than roasted samples, having light coloured internals. Brown centre contained higher total sugar and sucrose than light coloured outer layer. Inner layer of raw hazelnuts contained about 50% higher total sugar and sucrose than light coloured outer layer. Polyphenoloxidase activity could not detected in the sample roasted at 130oC for 16 min and 30 min. These results indicated that internal browning during roasting was due to localised concentration of reactants and subsequently, higher non-enzymatic browning reaction rate in the centre of hazelnuts.
Drying Technology (200x).
  Adsorption Isotherms of Raw and Roasted Hazelnuts,  Güzey, D., Özdemir, M., Seyhan, F.S., Doğan, H & Devres, O. .
Abstract: Adsorption isotherms of raw and roasted (at 100oC, 120oC, 140oC and 160oC) hazelnuts of Tombul variety were determined at 25oC, and over relative humidities ranging from 11 to 90% using the gravimetric static method. Eleven sorption models (GAB, BET, Modified BET, Halsey, Iglesias-Chirife, Oswin, Chung-Pfost, Smith, Kuhn, Harkins-Jura and Caurie) were evaluated by using the linear regression method. GAB (Guggenheim-Anderson-de Boer) model satisfactorily described adsorption characteristics of the samples over the experimental range of study. Monolayer values at 25oC were estimated from the GAB model as 0.0155 kg water/kg dry solid for raw and 0.0100-0.0163 kg water/kg dry solid for roasted hazelnuts. Caurie security moisture content for raw hazelnuts was also determined from Caurie model as 0.048 kg water/kg dry solid.
Drying Technology, (2000),  18 (6), 1465-1479.
  Effect of initial moisture content on the thin layer drying characteristics of hazelnuts during roasting, Özdemir, M., Seyhan, F.G., Bodur, A.Ö. & Devres, Y.O. 
Abstract: Effect of initial moisture content on the thin layer drying characteristics of hazelnuts during roasting was described for a temperature range of 100-160oC, using several thin layer equations. The effective diffusivity varied from 2.8x10-7 to 21.5x10-7 m2/s over the temperature and moisture range. Temperature dependence of the diffusivity coefficient was described by Arrhenius-type relationship. The activation energy for moisture diffusion was found to be 2703 kJ/kg, 2289 kJ/kg and 2030 kJ/kg for the initial moisture content of 12.3% db, 6.14% db, and 2.41% db, respectively. Two-term equation gave better predictions than Henderson and Pabis and Thompson equations, and satisfactorily described thin layer drying characteristics of hazelnut roasting. A generalised mathematical model with the linear temperature dependence for moistured, non-treated and pre-dried hazelnuts were also developed.
Journal of Food Engineering, (2000), 45, 17-24.
  Analysis of color development during roasting of hazelnuts using response surface methodology. Özdemir, M. & Devres, O.
Abstract:  Hazelnut roasting was analyzed using response surface methodology to find out the effect of process variables on color development during roasting and to establish prediction models. The roasting temperature was found to be the main factor affecting color development. Developed prediction models satisfactorily described color development as a function of roasting temperature and exposure time for L-value, a-value and b-value of whole-kernel, ground-state and cut-kernel measurements. Whole-kernel measurements were significantly lighter in color compared to ground-state and cut-kernel measurements due to internal browning of the hazelnuts during roasting. The results also indicated that the L-value of ground state measurements, which take into account internal browning during roasting, should be used to monitor roasting of hazelnuts.
Journal of Food Engineering, (2000), 44, 31-38
 Kinetics of color changes of hazelnuts during roasting. Özdemir, M. & Devres, O.
Abstract:  Kinetics of color changes during hazelnut roasting was described for a temperature range of 100-160oC for 60 min. The rate of color changes was significantly affected by temperature and time over the experimental conditions. Roasted hazelnut samples produced significantly lower L-value and b-value in ground-state color measurements compared to whole-kernel measurements. The results showed that color changes during hazelnut roasting can be satisfactorily described by a third degree polynomial with an Arrhenius type temperature dependence of the model coefficients. Activation energy for the L-value of color was found to be 62.3 kJ/mole over the temperature range of the study. A generalized model for color changes during roasting of hazelnuts as a function of temperature and time was established.
Journal of Food Engineering, (1999), 42, 225-233.
The thin layer drying characteristics of hazelnut roasting. Özdemir, M. & Devres, O.
Abstract: Thin layer drying characteristics of hazelnuts during roasting were described for a temperature range of 100-160oC, using five semi-theoretical and two empirical thin layer models. The effective diffusivity varied from 2.301x10-7 to 11.759x10-7 m2/s over the temperature range. Temperature dependence of the diffusivity coefficient was described by Arrhenius-type relationship. The activation energy for moisture diffusion was found to be 1891.6 kJ/kg. Thin layer drying characteristics of hazelnut roasting was satisfactorily described by empirical Thompson model with the linear temperature dependence.
Food Review International, (1999), 15 (3), 309-333
Turkish hazelnuts the properties and the effect of microbiological and chemical changes on the quality, Özdemir, M. & Devres, O.
 Abstract: Turkiye is the biggest hazelnut producer and exporter in the world but it has hazelnut surplus of about 100 000 ton per year. Improvement of quality of the hazelnut and its products may extend the market. In the article, current knowledge about properties of Turkish hazelnut, and microbiological and chemical changes during post-harvest treatments and processing are reviewed. Microbial activities bring about significant quality losses due to insufficient/inadequate harvest, drying and storage methods and conditions. Storage, shelling, roasting and packaging conditions and methods may contribute to lipid oxidation and subsequent rancidity that reduces shelf life of the hazelnut and its products. Roasting method and conditions determines color and aroma formed. Improvement of the harvest, post-harvest and processing conditions and methods should improve the quality but the best quality can only be attained if the whole production and processing line is designed and operated for that
Journal of Agriculture Engineering Research, (1999), 72, 212-216.
 Comparison of the quality of hazelnuts shelled with modified conical cracker and stone cracker, Özdemir, M.
 Abstract:Two crackers (a modified conical sheller, widely used in Spain, and a stone sheller, widely used in Turkey) with different sheller characteristics were evaluated in terms of undamaged kernels, damaged kernels, broken kernels, left-in-the-shell kernels, cracked nuts, unbroken nuts and total recyclable nuts. Trials were carried out in a commercial hazelnut processing plant, using the 1996 Akcakoca hazelnut crop, which had a 50% kernel ratio (weight percentage ratio of the kernel to that of the whole hazelnut). The modified conical sheller gave a significantly higher output of undamaged kernels (67.5%) than the stone sheller (61.5%) (P=0.0001). Left-in-the-shell kernels, cracked nuts and total recyclable nuts were significantly lower in the modified conical cracker (about 6%, 4.5% and 30%, respectively) compared with those produced by the stone sheller (about 8%, 7% and 35%, respectively). The two shellers produced similar levels of damaged kernels (about 3%), broken kernels (about 1%), and unbroken nuts (about 20%). Correlation analysis suggested that a better level of quality (a low percentage of damaged kernels and high percentage of undamaged kernels) can be obtained at the expense of increased unbroken nuts and total recyclable nut percentages for both the modified conical sheller and the stone sheller. At smaller diameter ranges, it is also necessary to accept a higher level of left-in-the-shell kernels for the stone sheller to achieve a better quality of shelled hazelnut.
Food Chemistry, (1999) 65 (3), 313-316.
 Effect of geographical origin and variety on the vitamin and mineral composition of Turkish hazelnut varieties, Açkurt, F., Özdemir, M., Löker, M., & Biringen, G.
 Abstract: The effects of variety and geographical origin on vitamin and mineral composition of eight different varieties of hazelnut cultivated in Black Sea Region of Turkey were studied. The mean contents of niacin, vitamin B1, vitamin B2, vitamin B6 and a-tocopherol were 1.81± 0.28 mg/100g, 0.30± 0.07 mg/100g, 0.10± 0.01 mg/100g, 0.240 ± 0.05 mg/100g, and 35.53± 3.82 mg/100g respectively. The mean contents of iron, zinc, copper, magnesium, manganese, calcium, potassium and sodium were 2.32± 0.21 mg/100g, 1.95 ± 0.25 mg/100g, 0.65± 0.29 mg/100g, 143.59± 14.86 mg/100g, 6.09± 4.27 mg/100g, 83.51± 5.14 mg/100g, 637.14± 105.33 mg/100g and 0.70 ± 0.10 mg/100g respectively. Vitamin and mineral composition of the varieties were not significantly different from each other. Geographical region differences did not significantly affect a-tocopherol, iron, manganese and calcium contents of the samples. Zinc, manganese, and sodium levels of Akçakoca samples were higher than for the other regions. The correlation analysis pointed out that, a-tocopherol content correlated strongly with minerals (manganese, sodium, zinc, potassium) and vitamin B6.
Lipid,(1998), 100 (3), 84-86.
  Oil Composition of Pistachio Nuts (Pistacia vera L.) from Turkey. Yıldız, M., Gürcan, T. & Özdemir, M
Abstract: The oil content, some oil parameters, fatty acid and sterol compositions of pistachio nut (Pistacia vera. L.) samples corresponding to five different varieties, all cultivated in Turkey were determined. Mean values were 59.69± 1.80% for fat content; 0.9143± 0.006 for specific gravity of the oil; 1.4693± 0.004 for refractive index; 94.23± 1.510 for iodine value; and 188.2± 3.80 for saponification value. Fatty acids identified in the oil samples were palmitic, palmitoleic, stearic, oleic, and linoleic acids with oleic acid as the dominant fatty acid (68.78± 2.05%). Halebi variety had higher levels of oleic acid among the varieties studied. The sterols isolated from the unsaponifiable fraction were campesterol, stigmasterol, b -sitosterol and D 5 - avenasterol with b -sitosterol as the major constituent (84.95± 2.80%). Higher levels of b - sitosterol were found in Kırmızı variety. The high level of oil, oleic acid and b -sitosterol content was found in the varieties studied. Fat content, iodine value, palmitic acid and oleic acid content significantly differed between varieties.
 Journal of Agriculture Engineering Research, (1997), 67 (3), 219-227
 Comparison of the Quality of Hazelnuts Unshelling with Different Sizing and Cracking Systems, Özdemir, M. & Özilgen, M.

Abstract: The quality of the hazelnuts, sized and cracked by different systems was compared in a commercial processing plant by determining the percentages of the nuts that were damaged, broken, left-in the-shell, cracked, unbroken, recyclable, or undamaged. Hazelnuts larger than 16 mm diameter had different cracking behaviour, as compared with smaller ones. In experiments with a traditional Turkish cylindrical sizer and stone cracker combination, 3.3 % (standard error 2.7 %) damaged nuts were produced when the diameter of the nuts were larger than 16 mm, and 15.9 % (7.5%) damaged nuts were produced when the diameter of the nuts was less than 16 mm. The average of the damaged nuts was around 16% with all the conical cracker combinations. Hidden-damage (apparently good appearance from the outside, but darker colour and oily appearance inside) was 38 % (4.0 %) for the cylindrical sizer/stone cracker combinations, and 41.7 % (5.8 %) for the cylindrical sizer and conical cracker equipped with big head template combination. Quality control charts (p-charts) for damaged and recyclable nuts were constructed for the hazelnuts from the stone cracker for two diameter ranges.

Gıda, (200x) (In press)
 Effect of variety and initial moisture content on color of roasted hazelnuts, Özdemir, M., Devres, O. & Bakan A. K.
Abstract: Effect of variety and initial moisture content on color of hazelnuts after roasting at 130oC for 30 min were studied. The results showed that there was a significant difference between varieties (Tombul, Palaz, Çakıldak, Foşa) for roasted color attributes. There was, however, no significant difference between roasted color attributes of Tombul and Palaz varieties. Initial moisture content of raw hazelnut significantly affected meal color (ground-state measurements) and inside color (cut-kernel measurements) of roasted hazelnuts but not outside color of the roasted hazelnuts (whole-kernel measurements). Among the 4 varieties, Foşa and Çakıldak varieties were found to be more susceptible to internal browning. At initial moisture content (about 5%), generally used in the hazelnut industry, hazelnuts was susceptible to more internal browning. Pre-dried hazelnuts (2.5% moisture content) obtained lower level of internal browning during hazelnut roasting.
Gıda, (200x) (In press)
 Fındık Hasatı ve Hasat Sonrası İşlemleri ile Fındık İşlemesinde Kritik Kontrol Noktaları Tehlike Analizi. Özdemir, M.
Özet: Türkiye için önemli bir tarımsal ihraç ürünü olan fındıkta, kalite kayıplarının nedenlerini ve bozulma mekanizmalarını anlamak, kalitenin yükseltilmesi ve korunması için gerekli önlemlerin alınması açısından önemlidir. Fındıkta yetersiz/uygun olmayan hasat, kurutma ve depolama yöntemleri ve koşulları nedeniyle, özellikle küfler faaliyet göstermekte, fındık ve fındık ürünlerinde önemli kalite kayıplarına neden olmaktadır. İşleme (kırma, kavurma, ve paketleme) ve taşıma hataları nedeniyle fındıklarda yağ oksidasyonuna bağlı acılaşma meydana gelmekte ve raf ömrü önemli ölçüde azalmaktadır. Ayrıca, enzimatik faaliyetler de fındıkta acılaşmaya neden olmaktadır. En iyi kalite fındık ve fındık ürünlerin üretebilmek ancak tüm işlemlerin doğru ve eksiksiz uygulanmasıyla mümkün olabilecektir. Ayrıca, uygulamaların izlenmesi ve kalitenin güvence altına alınması için kalite güvence ve yönetim sistemlerinin etkin kullanılmasıyla gerekmektedir. Bu kalite güvence sistemlerinden biri olan kritik kontrol noktalarında tehlike analizi fındık hasat ve hasat sonrası iţlemleri ile fındık işlemesi için uygulanmıştır.
Abstract: Hazelnut is an important agricultural product for Turkiye. Determining quality losses in hazelnut and preventive measures is important to achieve and maintain high quality products. Microbial activities and chemical/biochemical reactions contribute to the shelf life of the hazelnut and its products. Microbial activities may bring about significant quality losses as a result of insufficient/inadequate harvest, drying and storage methods and conditions. Moreover, cracking, roasting, packaging and transportation may bring about lipid oxidation and subsequent rancidity in hazelnut and its products. The best quality can be achieved only if all operation stages are optimised to obtain premium quality and are monitored through a quality control system to ensure the desired quality
Gıda, (200x) (In press)
 Effect of freezing pre-treatment prior to shelling operation on the quality of roasted hazelnuts, Özdemir, M., Kaplan, M., Yıldız, M., Gürcan, T., Canlı, O., & Öztürk, K.
Abstract: To determine the influence of freezing pre-treatment prior to shelling operation on the roasted hazelnut quality, untreated and frozen hazelnuts were shelled using a stone sheller in a commercial shelling plant. Hazelnut kernels, produced using two shelling methods, were roasted at temperature of 110 oC and 135 oC for 15 min and 30 min, and stored at room conditions (temperature: 20-22oC, relative humidity: 60-70%) for a period of 12 weeks. Every 2 weeks, samples were taken and analysed for moisture content, peroxide value and free fatty acid content. Fatty acid composition was also determined before roasting and at the end of 12 weeks of storage. Generally, moisture content of all of the samples was above BET monolayer value of 1.5% within the 4 weeks of storage. During the storage period, hazelnuts, frozen prior to shelling operation gave, generally, lower peroxide and free fatty acid content than untreated hazelnuts. Linoleic acid degradation was equal to or lower in the hazelnuts, frozen prior to shelling operation than the untreated hazelnuts. Peroxide value was close to quality end point after 2 weeks of storage regardless of shelling method.
Özet: Bu çalışmada Türkiye'deki bazı fabrikalarda uygulanan kırma öncesi dondurma işleminin, kavrulmuş fındık kalitesine etkisi araştırılmıştır. Bu amaçla, ön işlemden geçirilmemiş fındıklarla dondurulmuş fındıklar, taşlı kırıcıda fabrika koşullarında kırılmıştır. Her iki kırma yönteminden alınan örnekler 110oC ve 135 oC'de 15 dak. ve 30 dak. süreyle kavrularak, oda koşullarında (sıcaklık: 20-22 oC, bağıl nem: %60-70) 12 hafta boyunca depolanmışlardır. Depolama süresince 2 her haftada bir örnek alınmış, nem, peroksit değeri ve serbest yağ asiti içeriği ölçülmüştür. Yağ asitleri komposizyonu kavurma öncesi ve depolama sonunda ölçülmüştür. Nem miktarı, 4 hafta içinde tüm örneklerde yaklaşık %1,5 olan BET monolayer değerini aşmıştır. Depolama süresince, dondurularak kırılmış fındıklarda, dondurulmadan kırılmış fındıklara göre, genellikle, daha düşük peroksit değeri ve serbest yağ asiti içeriği saptanmıştır. Dondurularak kırılmış fındıklarda dondurulmadan kırılmış fındıklara göre, çoklu doymamış yağ asiti olan linoleik asit (C18:2) yıkımının eşit yada daha düşük düzeyde olduğu saptanmıştır. Bu çalışmada bulunan sonuçlar, dondurularak kırma yönteminin kavrulmuş fındıkların raf ömrüne olumlu etkisini göstermektedir. Ayrıca, bu çalışma sonuçları, her iki kırma yönteminde de peroksit değeri 2 hafta içinde 6'nın üzerine çıkması, kavrulmuş fındıkların en kısa sürede vakum altında ambalajlanması ve düşük sıcaklıkta depolanmasi gerektiğini göstermektedir.
Gıda, (200x) (In press)
 Effect of artificial drying air temperature on the stability of the major Turkish hazelnut variety, Tombul, Özdemir, M., Yıldız, M. & Gürcan, T.
Abstract: To investigate the effect of artificial drying on the stability of the major Turkish hazelnut variety, Tombul and to determine the optimum drying air temperature, hazelnuts were dried at 35oC, 40oC, 45oC and 50oC. Changes in fat content, fatty acid composition, free fatty acid content, iodine value, degree of unsaturation and rancimat value were investigated. Oil content, linoleic acid (C18:2), palmitic acid (C16:0) and stearic acid (C18:0) content were not significantly effected by the drying air temperatures. Oleic acid (C18:1) content significantly differed between dried samples and undried samples, but not between dried samples. Relative proportion of the linoleic acid, palmitic acid and stearic acid decreased, but that of oleic acid increased as the drying air temperature increased. FFA content was not significantly affected at drying air temperatures of 35oC and 40oC. Rancimat value was highest in the undried samples, followed by the sample dried at 35oC. Rancimat value did not differ between 40oC and 45oC. The results pointed out that drying air temperature below 45oC is necessary not to disturb stability of the major Turkish hazelnut variety, Tombul.
Gıda Teknolojisi, 3 (3), 66-71, 1998.
 ndıkta Raf ömrüne etki eden faktörler, Özdemir, M.
Özet: Türkiye için önemli bir tarımsal ihraç ürünü olan fındıkta, kalite kayıplarının nedenlerini belirmek ve gerekli önlemleri almak, kalitenin yükseltilmesi ve korunmasına açısından önemlidir. Yetersiz/uygun olmayan hasat, kurutma ve depolama yöntemleri ve koşulları nedeniyle, özellikle küfler faaliyet göstermekte, fındık ve ürünlerinde önemli kalite kayıplarına neden olmaktadır. İşleme hataları nedeniyle (depolama, kırma, kavurma, paketleme, taşıma) fındıklarda yağ oksidasyonu bağlı acılaşma meydana gelmekte ve raf ömrü önemli ölçüde azalmaktadır. En iyi kalite fındık ve ürünlerin üretebilmek ancak tüm işlemlerin doğru ve eksiksiz uygulanmasıyla mümkün olabilecektir.
Gıda Teknolojisi, (1997) 2 (11), 56-62.
Quality Control Charts for Hazelnut Unshelling Operation,  Özdemir, M. (Kalite Güvence Çizgelerinin Fındık Kırma İşleminde Kullanılması)

Özet: Kalite güvence çizgelerinden olan p-çizgeleri, fındık kırma işleminde, 3 ayrı boy Akçakoca fındığında, vurgunlu ve geri-dönen özürleri için çizildi. p-Çizgeleri fındık kırma işleminin izlenmesinde, iyileştirme olasılıklarının belirlenmesinde ve gerekli tedbirlerin alınmasında kullanılabilir. Her boy, randıman ve üretim bölgesi için ayrı bir p-çizgesi çizmek gereklidir.
Abstract: The p-charts were constructed for 3 different diameter grades of Akçakoca hazelnuts for damaged and recyclable hazelnut units for hazelnut unshelling operation. The p-charts satisfactorily monitored the hazelnut unshelling operation, pointed out possible improvements and necessary precaution to be taken both operation and as maintenance. The results indicate that it may be necessary to construct p-charts of damaged and recyclable hazelnut units for each diameter grades and for different percent kernel and production region.

Gıda Teknolojisi, (1997),  2 (10), 46-52.
 Critical Evaluation of Properties of Turkish Hazelnuts, Özdemir, M., (Türk Fındık Çeşitlerinin Özelliklerinin Kalite Açısından Değerlendirilmesi)

Özet: Dünyanın en büyük fındık üreticisi ve ihracatçısı olan Türkiye'nin yaklaşık 100 000 ton üretim fazlası bunulmaktadır. Fındık ve ürünlerinin kalitelerinin geliştirilmesi, yeni ürünlerle uygulama alanlarının genişletilmesi fındığa olan talebi artırabilir. Bu da ancak fındığın özelliklerinin ve işlemler sırasındaki davranışının iyi tanımlanmasıyla mümkün olabilir. Bu makalede, Türk fındık çeşitlerin fiziksel, kimyasal, besin özellikleri kalite açısından değerlendirilmiştir.
Abstract: Turkiye is the biggest hazelnut producer and exporter in the world, but it has hazelnut surplus of about 100 000 tons/year. Improvement of quality of the hazelnut and its products may extend the market. New applications or products of the hazelnut may also increase demand. Further studies are necessary to understand properties of Turkish hazelnut varieties and their behavior during storage and processing. In the article, current knowledge about properties of hazelnut is critically reviewed.

TÜBİTAK - TARP 2124, HAZİRAN 2000

 Kavrulmuş Fındıklarda Görülen İç Kararmasının Nedenlerinin Araştırılması ve Önleme Yöntemlerinin Saptanması, Murat Özdemir, Ferda G. Seyhan, Dr. Türcan Gürcan, Dr. Muammer Kaplan, Gül Biringen, Ayşe Kartal, Songün İlter, Hülya Ölmez, Aysun Aktaş

Özet: Bu projede kavrulmuş fındıklarda görülen iç kararmasının nedenleri ve önleme yöntemleri araştırılmıştır. Bulgular su aktivitesinin renk oluşumunu önemli ölçüde etkilediğini ve su aktivitesi arttıkça iç kararması da arttığını göstermiştir. Çalışmada koşullarında (0.29-0.83 su aktivitesi; 130oC'de 30 dak kavurma) iç kararması en az 0.29 su aktivitesinde kavrulmuş fındıklarda görülmüştür. İç kararmalı kavrulmuş fındıkların toplam şeker ve indirgen olmayan şeker içeriklerinin merkezi açık renkli kavrulmuş fındıklara göre daha fazla olduğu bulunmuştur. Ayrıca koyu renkli merkezin toplam şeker ve indirgen olmayan şeker içeriğinin, açık renkli çevresine göre daha yüksek olduğu saptanmıştır. Çiğ fındıkta da merkezdeki toplam şeker ve indirgen olmayan şeker içeriğinin çevresine göre %50 daha fazla olduğu bulunmuştur. Polifenoloksidaz aktivitesi de kavrulmuş fındıklarda saptanamamıştır. Bu nedenle iç kararması, fındıkların merkezinde subtratların, özellikle şekerin daha fazla olmasıyla ve ısı etkisiyle gerçekleşen enzimatik olmayan esmerleşme tepkimesinin fındıkların merkezinde daha hızlı seyretmesiyle ilgili olabilir. Foşa ve Çakıldak çeşitleri, Tombul ve Palaz'a göre iç kararmasına önemli ölçüde daha fazla maruz kalmışlardır. Endüstride sıkça kullanılan %5 nemdeki fındıklarda iç kararması önemli ölçüde daha fazla görülmüşken %2.5 neme kadar ön kurutma işlemi yapılmış fındıklarda iç kararması daha düşük seviyede gerçekleşmiţtir.
Kavrulmuţ fındıklarda 37oC'de bir ay depolama sonunda örneklerin peroksit değerleri 0.17-4.95 meq/kg arasında olmuştur. Kavurma sıcaklık ve/veya süresinin artması 37oC'de bir ay depolama sonundaki peroksit değerinin artmasına neden olmuştur. Elzem ve elzem olmayan amino asitler kavurmanın ön aşamalarında artmış ve ileri kavurma aşamalarında azalmıştır. Ancak yine de elzem amino asitler hemen hemen bütün kavurma koşullarında FAO'un belirttiği sınır değerlerinin üzerindedir. Daha koyu renkli olan kavrulmuş fındıkların genellikle daha düşük amino asit ve toplam şeker içerdiği tespit edilmiştir. Yepki yüzey yöntemi (Response Surface Methodology) kavurma sıcaklığını renk oluşumunu etkileyen temel etken olduğunu göstermiştir. Geliştirilen ikinci dereceden denklem kavrulmuş fındıkların dış-, un- ve iç-renklerinin L-, a-, b-değerlerini başarıyla tahmin etmiştir.
Abstract: Mechanism of internal browning of hazelnuts during roasting and its prevention were investigated in the project. The results indicated that water activity of hazelnuts significantly affects internal browning of roasted hazelnuts and the higher water activity caused more internal browning over the experimental range of the study (0.29-0.83 aw, 130oC-30min roasting). The lowest internal browning were observed in the hazelnuts having 0.29 water activity prior to roasting. Internally browned roasted hazelnuts contained more total sugar and non-reducing sugars compared to less internally browned hazelnuts. Moreover, center of internally browned roasted hazelnuts contained more total sugar and non-reducing sugars compared to its surroundings. In addition center of raw hazelnuts contained 50% more total sugar and non-reducing sugars compared to its surroundings. No activity of poliphenoloxsidase were determined in the roasted hazelnuts. Therefore, internal browning may be related to the concentration of sugars in the center of hazelnut and subsequently increased rate of browing due to non-enzymatic browning reactions during roasting. Foşa ve Çakıldak varities was more susceptible to internal browning compared to Tombul and Palaz. Hazelnuts with 5% initial moisture content were more susceptible to internal browning compared to hazelnuts predried 2.5% moisture prior to roasting.
Hazelnuts roasted at higher roasting temperature and/or longer roasting time obtained higher peorxide values after storage at 37oC for one month. Peroxide values ranged between 0.17-4.95 meq/kg at the end of storage. Essential and non-essential amino acids increased in the early stages of roasting and decreased during prolonged roasting. Nevertheless essential amino acids were above the reference values given by FAO in almost all the roasted samples. Samples having darker color contained lower amino acid and non-reducing sugar. Response Surface Methodology indicacted that roasting temperature was the main factor affecting color development. A second degree polynomial predicted L-, a- and b-values of roasted hazelnuts satisfactorily.
 

 

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