## 3 Results and Discussion
### Evaluation of Stability of Some Important Quality Attributes during Storage under Frozen Conditions  
After having optimized the osmotic dehydration step through RSM principles and attempting to maximize this OD beneficial effect by adding a preliminary anti-browning impregnation, using the side streams of _Rosa damascena_ distillation, a stability study under frozen storage was conducted (third phase of our study). The main purpose of this part of our research was to assess the effectiveness of the pretreatment implemented on the quality retention of mushroom samples, which constitutes the main objective of this work. Color is the most important factor of mushrooms quality, especially during the detrimental subzero frozen storage. Color changes of mushroom samples during frozen storage are presented in Figures 8 and 9. It can be easily observed from Figure 8a that control samples, after being thawed, have a significant reduction in lightness that remains almost constant throughout storage. After thawing, the OD samples have no significant changes during storage under freezing conditions, and ODR samples present a small reduction on lightness during storage. However, there is no significant difference in L values between control and OD samples during storage, with final values being equal to 50.87 (Control) and 49.04 (OD), while ODR reached a value of 42.73. On the contrary, b*-parameter of the control samples increased during storage, while the values of OD and ODR samples remained constant. From a visual observation viewpoint, the control samples turn yellow, and the OD and ODR samples retain their initial color. As far as total color change is concerned, a large difference is observed between treated and untreated samples, with the control samples suffering from an important degradation compared to the OD and ODR samples (Figure 8c). During storage under freezing conditions, the control samples had an average \(\Delta\)E value of 19.29, while the OD and ODR samples had values of 5.27 and 9.00, respectively. The untreated samples have almost four times higher \(\Delta\)E values compared to the OD samples and two times higher compared to the ODR samples.  
The changes in the texture of the thawed mushroom samples are presented in Figure 9a,b. It can be observed that the control samples do not maintain their initial compact structure, showing over 60% reduction in their hardness from day 15 until the end of storage and about 28.50% drip loss from day 75. Drip loss after this day remains constant. OD and ODR samples more efficiently maintain their structure, showing a progressive increase in hardness values, which reach 92% and 57%, respectively, after 62 days of storage, a level that remains constant throughout storage. Moreover, OD and ODR samples have lower drip loss values compared to control samples, more specifically, 16.4% for OD and 16.6  
Figure 7: Impregnation of phenolic compounds from _Rosa damascena_ by-products during osmosis at optimum conditions, expressed as mg gallic acid equivalents (GAE/g Mushroom). Error bars represent the \(\pm\) standard deviation of measurements.  
for ODR from the 75 th day until the end of storage. Previous studies also reported that osmotic dehydration prior to freezing improved the hardness of the final product [9].  
Overall, OD and ODR samples preserve their initial visual appearance and texture/structure characteristics to a greater extent compared to untreated samples during frozen storage. Similar results were presented for bananas [61], pears, kiwis, strawberries and apples [20], strawberries [22], apples [62], and mangoes [63].