# Physicochemical and Microbiological Changes Associated with Processing in Dry-Cured Tuna
## 3 Results and Discussion
### Physicochemical Parameters

Table 1: Physicochemical characteristics of fresh yellowfin tuna (_Thumus albacares_) and the respective dry-cured tuna (_mojama_), as affected by salting and salt-washing. Regarding the moisture content, the raw tuna presented a high content, with an average of 62.89%. This value did not significantly change for the samples analyzed after the salting and salt-washing steps. These results in yellowfin tuna agree with the literature [31; 32]. The final product samples (after drying) presented a significant decrease for this parameter (33.03%). This value was in accordance with the standards for this product, which ranged from 35 to 45% [33]. The WHC of fish products is an important quality parameter since it represents the capacity of flesh to retain its internal water [34]. The WHC values increased from 77.25% in the raw tuna samples to 97.29% in the final product. During processing, factors such as the type of salt used and the salting method may affect the WHC [35], which leads to decreased water content in the fish muscles due to alterations in the properties of proteins [36]. Most free water that can be easily released lies between the actin and myosin filaments of myofibrils in fresh tissue due to the structural change of muscle [37]. This can directly influence the consumers' perception of appearance and texture. Therefore, having a high WHC is one of the major aims of fish processing as it relates to the quality and sensory attributes of the product [38]. Another important factor is the pH. The method of preservation has an impact on this parameter since the salting and drying may alter the functionality of the proteins of flesh. [PERSON] et al. [35] reported that pH value was considered of major importance for the quality of salt-cured fish products. The pH of the raw tuna samples was in the range between 5.78-6.38, the values obtained for the samples analyzed during the different steps of the manufacturing process not changing significantly (Table 1). The results were consistent with those of the published studies regarding tuna species and their subsequent dry-cured products [8; 28; 39; 40]. Changes in the pH of fish depend on different factors, such as the state of the fish, the type and amount of salt used, and the type of salting process [41]. Furthermore, pH levels are correlated with lactic acid bacteria growth and lactic acid formation in fish muscles after the catch [42]. Lactic acid bacteria (LAB) are responsible for the production of lactic acid in the case of food contamination. LAB are Gram-positive and even though they are not considered a main microorganism group usually present in fish, some species as _Carnobacterium_, _Vagococcus_, _Lactobacillus_, _Enterococcus_, _Lactococcus_, have been found in aquatic environments [43]. The role of LAB in fish and fish products is complex and has not been established yet. In some cases, the presence of LAB can cause sensory degradation [43; 44]. In this study, the total acidity values measured as lactic acid did not show significant differences among the different stages of the processing (approximately 0.50%). Those values were in accordance with the values found for pH. This is evidence of the absence of microbial activity both in the raw fresh tuna and during the manufacturing process, assuring the integrity of the whole process.