Meyve Dokusunun Spektroskopik İncelenmesi

Abstract

Gıda endüstrisinde, gıdanın güvenilirliği ve kalitesi, doğrudan insan sağlığını ilgilendirdiğinden önemli bir konudur. Son yıllarda gıda kalitesinin belirlenmesinde UV, Vis ve NIR Spektroskopisi kullanışlı, etkili ve hızlı bir teknik olarak önem kazanmıştır. Kemometrik ve bilişim teknolojisinin de ilerlemesiyle NIR spektroskopisinin kullanımı gıda kalitesi araştırmacıları tarafından sıklıkla tercih edilebilir duruma gelmiştir. UV spektroskopisinde 100 - 390 nm, Vis spektroskopisinde 390 – 700 nm NIR spektroskopisinde ise 750 – 2500 nm aralığı değerlendirilir ve moleküler yapısal bilgi sağlayan yansıma ( ve ince kesitlerinden geçirgenlik ) ölçümleri temel alınır. UV, Vis ve NIR spektroskopisi cihazı içerisinde birkaç ışık kaynağı ile yine en az 2 ışık detektörünün olduğu ve bu detektörlerden alınan sonuçların izlendiği bir cihazdır. Literatür araştırıldığında günlük tüketilen besinler süt, meyve, mısır, yağ, et, balık yağı, meyve suları, zeytinyağı ve daha birçok gıda ürünlerinde NIR spektroskopisi ile ölçümler yapıldığı görülmüştür. Bu çalışmaların incelenmesi ile birlikte yapılan ön çalışmalar sonucunda belirli dalga boylarında meyve dokusu ile ışık arasında etkileşim izlenmiş ve yansıma bantları görülmüştür. Genel olarak UV/Vis/NIR elektromagnetik dalgalar doku ile etkileşime girdiğinde, dokunun optik özelliklerine göre soğurulabilir, saçılabilir yada etkileşime girmeden dokudan geçebilir. Bu yüzden dokunun hücresel bileşenleri her bileşenin kendine özgü yapısından dolayı farklı dalga boylarıyla farklı biçimde etkileşir. Yani optik dokuları belirleyici veya ayırt edici olur. Meyvenin olgunluğunun belirlenmesinde 3 özellik incelenir ; 1) Meyve kabuğundaki pigmentler, 2) Meyvenin hücre yapısı, 3) Meyvenin su içeriği. Bu çalışmada ölçümler sonucu belirlenmiş en fazla 6 farklı dalga boyunda ve her biri ortalama 10 mW gücünde elektromagnetik dalga kaynakları kullanılarak yapılan yansıma ölçümleri ile meyvelerin farklı olgunluk dönemlerinde alınacak veriler işlenerek incelenmiştir. Elde edilen sonuçlar meyvelerin pigment yapısı, meyve et kısmı ve sulu kısımlarında belirli dalga boylarında etkileşim olduğunu göstermiştir. Etkileşim dalga boylarının her meyvede birbirine yakın belirgin değerlerde olduğu gözlemlenmiştir. Bu doğrultuda her meyve için kullanabilecek ortalama dalga boyları hesaplanarak kullanılacak ışık kaynaklarının dalga boyları belirlenmiştir.

In food industry, reliability and quality of food is an important subject manner since it relates directly to the human health. In recent years, UV (Ultraviolet), Vis (Visible) and NIR (Near Infrared) spectroscopy have become popular since these are useful, effective and fast techniques. Spectroscopic measurements are preferred frequently since these measurements neither damage nor change the tissue on which they are applied. Due to advances in chemometric and informatics technology, the use of spectroscopy by food quality researchers have become very popular. By performing spectroscopic measurements in a wider range, one can obtain more information in a wider spectrum interval. The following intervals are considered in UV, Vis and NIR spectroscopy, respectively: 100-390 nm, 390-700 nm and 750- 2500 nm, and reflection measurements are considered to obtain information on molecular structure. There are two light sources as well as two light detectors in UV, Vis and NIR spectroscopy devices and in spectroscopy devices the results obtained from these two detectors are monitored. In this study, measurements were performed in 280-2500 nm interval. This 280-2500 nm intervals occupies UV/Vis/NIR regions. Two light sources were exploited in the aforementioned device, while for the spectrum interval corresponding to NIR and Vis regions an halogen lamb was used. On the other hand, for the spectrum interval corresponding to the UV region, a spectrophotometer having a doterium lamb was used. Integrating sphere reflection measurements assures that results are obtained accurately and reliablely from all parts of the tissue and from all angles. Calibration of the device was repeatly performed every time it was turned on and the lambs were replaced every six months. The data obtained after measurements was transferred to a computer. In order to evaluate the gathered data, Powerful UV Winlab software was used in the processing computers. In literature, researchers performed measurements using spectroscopic methods on daily consumed foods such as milk, fruit, corn, oil, meat, fish oil, fruit juice, olive oil and so on. By the review of the current works in the literature, we observed through first studies that there is an interaction between the fruit tissue and light at certain wavelengths and reflections bands were observed. Generally, when fruit tissues are exposed to UV/Vis/NIR electromagnetic waves, these waves can be absorbed, scatterred or penetrate through the tissue without interaction according to the optical properties of the tissue. Therefore, the cell structure of the tissue interact with different wavelenghts in a different ways due to the the distinctive structure of the tissue's cell structure. In other words, the cell structure determines optical properties and can be distinctive. The following three features were investigated to determine the fruit ripening 1) The pigments at the pericarp of the fruit 2) The cell structure of the fruit 3) The water content of the fruit In this study, using reflection measurements at six different wavelengths, the data obtained at different ripening stages were processed and investigated. These six different wavelengths were determined with measurements and in reflection measurements, electromagnetic sources of 10 mW power were considered. Reflection bands formed by the tissue were investigated in detail in three parts: color region of the tissue, the region contains the tissue pigments and the water region inside the tissue. During experiments, according to the studies performed at color pigment regions, we observed that different fruits show absorption percentage peak values at different wavelenghts in the provided figures. First, these peak values correspond to the visible region of the electromagnetic spectrum. Second, the observed region is the region of tissue pigments and cell structure. In spite of the fact that different fruits show different absorption percentage peak values, we also observed that the fruits of the same kind can show different peak values at different times or when they were kept for some time. Finally, it is observed that the water absorption bands of the fruit tissue were more intense at specific wavelengths of the absorption band (such as 980 nm, 1250 nm, 1480 nm ve 1950 nm); however, it is seen that the depth of the concavities at the graphics of this region varies according to the maturity of the fruit tissue. We observed that with the increasing maturity of the fruit tissue, the mentioned concavities at the graphics become more apparent. According to the collected results, there is an interaction at specific wavelengths for the pigment structure of the fruit, fleshy fruit and juicy fruit. We observed that interaction wavelengths were specific values, which were close to each other for different fruits. Considering this fact, the wavelength of the light sources were determined by the calculation of the average wavelength that can be used for each fruit. Contrary to the studies given in literature, water content and color changes of the fleshy part of ten different types of fruits (apple-granny smith, apple-starking, apple-golden, plum, pear, apricot, peach, kiwifruit, pomegranate, strawberry and quince) are investigated in this study. Additionally, absorption percentance differences which were obtained from gritty and non-gritty surfaces of the pericarp of different fruits and color and water content changes according to the inner or oute layers of the fruit pericarp were analyzed. Moreover, the measurement value differences in the peak values show the inner cell structure after purification of the fluffies as well as the percentange differences in the absorption band of the water content of the inner cell structure of the two different types of fruits at the same color were investigated. As using the results of this work a original handheld device was developed by my fellow graduate student friend Ali SARIKAŞ to analyze several harvesting time, the maturity of the inner structure and the water content of the fruits. Measurement results can be monitored over the LCD display which is installed on the developed hand-held device and the corresponding results can be obtained as percentage. Specific percentage intervals can be displayed shown on the display for three different states of the fruit. By considering the results of the measurements, it becomes possible to determine the maturity state of the fruit (immature, half-mature, mature) as well as the suitable harvesting time of the fruit according to its maturity. In such a device only using UV and NIR light sources degree of aging of human skin, wound / burn healing, can be measured. Also available for this device with the optical fiber probe design more precise measurements can be made from the tissue surface. Using specific wavelengths and powerful light sources can also be more thick-skinned fruits maturity analysis. By changing the light source mentioned in the introduction of the thesis can be made from fruits other qualitative measures. This device provides a record of the reference number of the desired flexible software architecture can be measured by the thousands of species of fruit (~150,000 fruit type) allows. Measuring period (~5 seconds) is too short a period of time in resolution consequently faster measurement provides more instances. Analysis of the material to the thin film coating of composite materials, as well as to improve the strength properties of the compounds employed in the qualitative analysis of the optical properties may also be undertaken.