عنوان مقاله [English]
Fruits and vegetables contain many nutrients that are essential for humans and significantly protect human health. Increasing consumption of fruits and vegetables has been suggested as an effective way to significantly improve public health in the world, and researchers believe that if per capita consumption of fruit increases, a large number of deaths before the age of 65 can be prevented. Consumption of fruits and vegetables is very high in the whole world, however, in different countries and regions, there is a big difference in terms of quantity and type of fruit. The World Health Organization and the Food and Agriculture Organization (FAO) advise people to consume these products as a priority to increase public health. One of the simplest operations in the post-harvest stages in a variety of fruits and vegetables is cutting the crop, which is known as sliced fruits and vegetables. In this process, the intact product is cut to different thicknesses after washing. This process is common in various products such as cucumbers, lettuce, cabbage, tomatoes, carrots, apples, peaches, citrus fruits, and watermelons and can facilitate their direct consumption for the consumer. However, one of the problems in the preparation of sliced products is the reduction of product shelf life, in which case the existence of a control and monitoring system for product safety and quality seems necessary. But at present, there is no standard method and system of tools to monitor the quality of these products.
Quality in healthy and uncut products is also usually done using techniques such as soluble solids content (SSC) or fruit texture properties by measuring hardness. The fruits selected as samples for evaluation of quality parameters are wasted because they can not be returned to the shipment after destruction. In addition, the fruits selected as a sample may not accurately reflect the actual condition of the consignment because it has been proven that fruits harvested from a tree branch may also have different quality characteristics. Therefore, it seems necessary to find non-destructive alternative techniques that can analyze the whole shipment without losing samples. In the last four decades, several methods for evaluating the quality of non-destructive products have been developed, only a few of which have been able to meet the favorable conditions technically and industrially and have economic justification. Optical, mechanical, chemical, and electromagnetic, and acoustic methods have played a major role in the development of non-destructive tests, but the methods used have the ability to explore the limited properties of fruits. Therefore, it is necessary to carefully review the prevailing conditions in these methods and to include them in the reporting or recording of test results. Among the mentioned methods, the application of electromagnetic waves, especially visible / near-infrared spectroscopy technology, has been commercialized due to its high accuracy and reproducibility and has had significant value for post-harvest industries.
Fresh cucumbers were prepared from the market with a uniform shape and color and without any signs of mechanical damage or fungal rot, and were immediately cut into rings with a thickness of 5 mm. A total of 48 slices of cucumber were prepared for data collection, of which 24 were uncoated and 24 were covered with light polyethylene film (cellophane) for 8 time periods. The samples were stored in a refrigerator at 5 ° C. In order to obtain the spectrum of the samples, a spectroradiometer model PS-100 (Apogee Instruments, INC., Logan, UT, USA) made in the USA was used. The soluble solids (SSC) of the samples were measured in Brix ° by a digital refractometer (PrismaTech BPTR50, Iran) by pouring a drop of fruit juice onto the refractometer glass plate. The titratable acidity (TA) was also determined using the 942.15 AOAC standard. For this purpose, gr5 of each sample was homogenized with 50 mL of distilled water using a home mixer. The mixture was filtered through a filter paper, then 5 mL of the homogeneous and filtered mixture and 1 mL of phenolphthalein (10 g / m) with distilled water were brought to a volume of 200 mL and the solution was stirred using 0.1 N NaOH (NaOH) to PH = 2.8 and the stable appearance of pink color was titrated. The amount of TA was expressed in terms of citric acid (fruit mold acid) and in percentage (grams of citric acid per 100 gr of cucumber). During spectral imaging, for some reason, some of the data obtained from the samples may be inadequate. In order to remove skewed samples, principal component analysis was used before any processing on the data. The application of non-destructive methods based on spectroscopy in the full range of wavelengths requires a lot of time and money, which makes the practical application of this method almost impossible. Therefore, one should look for a way to find the optimal wavelengths and limit the wavelengths to the minimum possible. The partial least squares (PLS) regression method seems ideal in this regard. In this study, in order to build the models, the data were randomly divided into two parts: 80% of the samples were used for cross-training and cross-validation and the rest of the data were used for independent validation. Models (PLS) were extracted for all predictions made on the data, and the statistical indices of correlation coefficient and root mean square error (RMSE) (Equations 1 and 2) were used to determine the best model to use.
The SSC and TA values of the chopped cucumber specimens in stages during the storage period for uncoated specimens and coated with lightweight polyethylene film are shown in Table 1. Based on the results, over time in each series of uncoated and coated samples, the amount of SSC increased and TA decreased in the samples. However, the present results show that the coverage of the samples has slowed down the process of these changes. Soluble solids are one of the most important factors determining the edible quality of fruits. The amount of SSC indicates the sweetness of the fruit and increases when reached by hydrolysis of starch by catabolic processes such as respiration to simple sugars. Mean absorption spectra Vis / NIR absorption spectra for different treatments in the range of 1000-500 nm are shown in Figure 2. Environmental factors (light and heat) as well as the expression quality of the spectrometer cause perturbations in the initial and final wavelengths of the spectra, so these wavelengths are removed from the data set. Based on the results of PCA analysis, the first principal component (PC-1) describes 93% and the second principal component (PC-3) describes 1% of the variance of the samples tested. As a result, the first two main components together represent 94% of the data. Due to the fact that the relationship between the properties of different samples during the experiments, for various reasons such as technical problems of equipment, data collection, incorrect sampling in some samples may be inappropriate or corrected.