## 3 Results and Discussions
### Evaluation of the Nutrient Content of the Analyzed Fish Dishes
#### 3.1.3 Evaluation of Water-Soluble and Fat-Soluble Vitamin Content  
Contrary to widespread opinions [49], which nevertheless led to a real \"trend\" in dietary nutrition--\"food without fire\"--most vitamins are not very sensitive to heat [50]. The vitamin content of a culinary dish can be ensured by efficiently associated raw materials but also optimized by the correct choice of culinary techniques and production systems that lead to superior vitamin retention. The heat treatment applied to culinary products is a decisive factor in preserving the native vitamin potential. From the data analysis, it results that the most protective production system for riboflavin, used in obtaining fine dining products from fish, is the sous vide (A1 \(-\) TR = 71.67%) and microwave cooking (A3 \(-\) TR = 59.20%). Riboflavin losses are influenced by the rapid cooling/freezing treatments and storage times. After convective cooking, in sample A2, a loss of vitamin B2 content of 45% was determined, and after 72 h under refrigeration and thermal regeneration conditions, the loss is 58.5%. In the case of frozen and regenerated products, after 20 days, the loss is approximately 65.3%. Although it is a relatively stable vitamin to thermal treatment, the literature indicates considerable losses of riboflavin during culinary preparation [51]. Thus, starting with the washing of raw materials, it was found that the first losses of riboflavin occur. By grinding raw materials, vitamin B2 losses can reach up to 7% of the existing content [52]. The type of heat treatment applied can influence riboflavin losses differently, the most unfavorable way of heat processing being frying, with losses of up to 30%. Baking at low temperatures, on the other hand, decreases the riboflavin content by very little. Riboflavin is photosensitive, so the processes that take place in light act negatively, transforming it into lumiflavin or lumichrome without vitamin activity. Significant losses occur during storage; even during short-term storage, the lack of adequate protection measures leads to its reduction [53]. [PERSON] et al. [54] and [PERSON] & [PERSON] [55] show in similar studies on microwaved products that a possible cause of the decrease in riboflavin content in microwaved products is the fat content of the raw materials. They show that there is a direct link between the fat content and the level of riboflavin retention: the higher the fat content of the product, the lower the riboflavin retention in the microwaved product than in the conventionally cooked product, since it is a water-soluble vitamin and the high fat content of a preparation is equivalent to a low water content in the product. Sterilization, the basic method used to preserve food products, due to the harshness of the heat treatment, causes multiple reductions in vitamin content, including riboflavin. For example, in a study conducted by [PERSON] et al. [56], when sterilizing canned vegetables in water, the losses of riboflavin are: in sweet corn 58.3%, mushrooms 45.6%, green beans 63.6%, and Parisian carrots 60%. These products are raw materials in the manufacturing process of catering products, raw materials that participate with a large deficit of riboflavin. Freezing is also a widely used method of food preservation, which, unlike sterilization, has the advantage of being associated with three times lower riboflavin losses. Some studies, such as the one of [PERSON] et al. [57] confirm that in the case of frozen meat, the reduction in vitamin B2 content during storage is relatively small, the losses depending on the fat content and the species. When defrosting meat, in addition to the losses of major nutrients, quantities of water-soluble vitamins are also lost, losses which are much more intense when defrosting is done in water than in air thawing.