## 1 Introduction
Nonetheless, the reduction of moisture does not ensure the inhibition of microbial growth, and thus supplementary methods such as drying, refrigeration, freezing, or pasteurization are required [13; 16]. The application of OD followed by conventional freezing is called osmodehydrofreezing (ODF). The reduction of moisture and increase in solid content of products caused by the osmotic process will lead to an improvement in nutritional quality, reduction in drip loss, and better retention of color and texture in thawed fruits and vegetables. Moreover, a reduction in moisture content lowers the refrigeration load during freezing, the size of ice crystals, and the cost of packaging, distribution, and storage [9; 16; 17; 18]. Other advantages of the ODF process are the simplicity of the treatment, the reduced energy and cost as compared to common drying and freezing techniques (a savings of 27% for dehydrofreezing as compared with conventional freezing), the inhibition of enzymatic browning, and the minimum loss of natural flavor and color due to the mild temperatures that are usually used [11; 18; 19]. ODF has been successfully applied to apples [20; 21], strawberries [22], carrots [23], broccoli [18], mangoes [24], and pears [25], but there are only a few studies on mushrooms. During storage under freezing conditions, mushrooms can undergo enzymatic browning, a natural process that occurs due to the oxidation of phenolic compounds in their tissues, as well as damage of their structure [26], leading to a substantial reduction in their quality. The browning of mushrooms during freezing is among the greatest challenges for the frozen mushroom industry [27]. Besides post-harvest handling, browning of mushrooms is mainly related to the activity of enzymes known as polyphenol oxidase (PPO), which include mostly tyrosinase, catechol oxidase, and lactose. When mushrooms are exposed to low temperatures, the activity of polyphenol oxidase enzymes is not completely inhibited, leading to enzymatic browning. This enzymatic browning can result in undesirable changes in the appearance of mushrooms, with the development of darkened spots or discoloration on their surfaces. Although freezing effectively preserves the overall quality of mushrooms by slowing down other enzymatic and microbial reactions, precautions must be taken to minimize enzymatic browning during storage. Techniques like blanching, vacuum impregnation, or washing before freezing can help minimize the impact of enzymatic browning, ensuring that mushrooms retain their fresh appearance and quality for extended periods in frozen storage [27; 28; 29; 30]. In this context, the use of antioxidant treatments as a preliminary anti-browning process has been also investigated, especially by replacing metabisulfites with compounds that can be naturally retrieved from plants, which can also inhibit PPO activity and the resulting enzymatic browning. Among them, rose hydrosols (by-products produced by steam distillation of aromatic plant materials) have been found to reduce enzymatic browning of fresh-cut products, and this beneficial impact may be attributed to the main chemical compounds present, i.e., terpenoids [31; 32; 33]. In our study, the liquid side streams from _Rosa damascena_ distillation, rich in polyphenols and an acknowledged source of antioxidants [34; 35; 36], have been used to investigate their potential effect on the stability of dehydrofrozen mushrooms. If proven effective, this approach would assist in finding ways to rationalize the sustainable use of these by-products, which constitute a serious environmental issue regarding their management and disposal, by focusing on the exploitation of compounds of added value. Considering the increasing interest in the nutritional and pharmaceutical properties of mushrooms, the aim of this study was to investigate an optimized composite procedure, i.e., osmotic dehydration followed by commercial freezing, so to provide a final frozen product of improved quality and extended shelf life.