D. hansenii shows lipolytic activity. In 1997 it was shown that a commercial starter of this yeast could hydrolyse a natural fatty substrate like pork fat and release fatty acids. In this case, lipolysis caused by D. hansenii was not affected by NaCl (most probably due to the salt-tolerant character of this yeast) and it was still significant at pH 4.7, indicating that this commercially available starter culture may hydrolyse pork fat during the processing of fermented meat products [69].

Later, our group has shown that the lipase activity of several strains isolated from Iberian dry-meat products greatly differed among strains, furthermore it was always higher than the corresponding activity in a control laboratory strain (CBS767) [29].

More recently, we used a selected terroir strain isolated from pork loin, D. hansenii Lr1, to inoculate different amounts of yeast either directly onto the meat surface or onto the collagen casing in which each loin piece was stuffed to make the product. Possible changes in the lipid profile of the loins were determined. In all cases, including control samples, loins contained a very low percentage of polyunsaturated fatty acids (PUFAs) and the most abundant were monounsaturated fatty acids (MUFAs). On the other hand, inoculation with the Lr1 strain did not significantly change the fatty acid profiles of any of the treatments applied. Within all the samples, oleic acid (C18:1) constituted around 50%, palmitic acid (C16:0) around 26%, and stearic acid (C18:0) around 10–12% of the total fatty acids. Clear differences could not be found related to the different treatments and only slight, although consistent, effects on the percentage of some fatty acids were observed as, for example, all the treatments showed a decrease in the percentage of t-oleic acid (elaidic acid, C18:1 n9t) when compared to the control samples. In summary, it was shown that inoculation with the D. hansenii Lr1 strain did not significantly change the global lipid profile of the loins. Only the amounts of some fatty acids were affected, however changes in the total amounts of saturated fatty acids (SFA), MUFAs, and PUFAs were not significant [58].

However, a different study showed that the generation of free fatty acids during sausage fermentation is affected by yeast inoculation. In this case, the D. hansenii P2 strain, previously isolated from naturally fermented sausages “salchichón de Requena [54,70], was inoculated in sausages manufactured with boar back fat or with gilt back fat. It was demonstrated that inoculated sausages had a higher degree of lipolysis and that this was strongly dependent on the ripening time and the conditions. After 63 days of ripening, an increase in the content of free MUFAs, PUFAs, and total free fatty acids was measured in the boar sausages while, in general, lower, or even no significant differences, were observed after 43 days of ripening or when the sausages were manufactured using gilt back fat instead of boar back fat. The authors concluded that environmental conditions affect lipase activity or lipase expression genes, potentially explaining differences between strains or products [66].

A generally accepted idea is that the generation of volatile compounds by D. hansenii is one of the most important contributions to the ripening process in dry-meat products. It is usually found that the introduction of D. hansenii as a starter culture affects volatile and aromatic compound generation. Among them, esters are essential contributors to the aroma of meat products due to their low detection threshold and sensory notes. The production of these compounds represents a complex scenario and it is strongly dependent on the different isolates and strains and even on the amount of yeast used [54,55]. In fact, production of volatile sulphur compounds from sulphur amino acids greatly varied among D. hansenii strains isolated from different food sources and the generation of, at least, some of these compounds could result from yeast metabolism [71].

Several groups have used starter cultures containing Debaryomyces in combination with other different microorganisms. For example, when dry-fermented sausages were inoculated with Debaryomyces spp. plus lactic acid bacteria and staphylococci, it was concluded that the use of this combination of microorganisms had a positive effect on the final flavour and sensory qualities of the product influenced by the generation of ethyl esters [72]. Importantly, the authors found that the amount of yeast used in the starter culture must be optimised, since too many yeasts may mask some positive effects. More recently, a similar approach was followed to study the effects of different starter cultures on volatile compounds of dry-cured foal sausages. In this case, three different starters were used and while two of them contained only bacteria, the third one was prepared with bacteria (Lactobacillus sakei, Staphylococcus carnosus, and Staphylococcus xylosus) and yeast (D. hansenii). Significantly different effects on the volatile compounds or acid taste were found among the different batches, with the batch containing D. hansenii showing a high flavour intensity and high levels of compounds derived from carbohydrate fermentation and amino acid catabolism [73]. The use of mixed starters containing only fungi has been less frequent. When Penicillium chrysogenum and D. hansenii were inoculated on dry-cured ham they did not remarkably alter the volatile compound profile. Only lower levels for some of the main odour-active volatile compounds were measured but they were not detected by a panel of experts [48].

Evidently, conclusions about the specific contributions of D. hansenii must be analysed from a global point of view, since all these experiments were performed with mixed starter cultures. Due to the difficulties surrounding the proper interpretation of the results obtained in these types of experiments, many other groups have focused on the use of pure D. hansenii starters [42,49,50,58].

One of the first realistic attempts to understand the specific effect of D. hansenii on aroma formation was performed by Olesen and Stahnke [42] in spiced fermented sausages. It was found that D. hansenii had very little effect with the analysis showing only a slight difference between the inoculated sausages and the control, possibly due to the fact that the yeast died out before the ripening process ended. The main reason was that sausages were spiced with garlic, and a fungistatic test of the garlic powder added to the sausages indicated that garlic inhibited the growth of the yeast starter cultures [42]. Later studies showed that D. hansenii contributes to the development of the characteristic flavour of some of these dry-meat products [49,50,58]. A research conducted on the dry-fermented sausage ‘‘salchichón” and performed with different D. hansenii strains indicated that the inoculation of selected isolates may have a positive contribution to the volatile compound generation involved in the flavour development of this meat product. In this study, yeasts were incorporated into the batches and the mixture of each batch was stuffed into regenerated collagen casings. The tested yeast strains promoted the generating of esters, alcohols, and aldehydes, and some volatile compounds derived from lipid oxidation [50]. In addition, when the effect of D. hansenii on dry-cured “lacon” and Iberian cured pork loin (“lomo ibérico”) was studied, similar approaches were followed: strains were selected from native products and used as starters. Yeasts were spread on the surface of the meat product and their capacity to generate volatile compounds was determined. Figure 1 shows the proliferation of inoculated D. hansenii on the surface of pork loin during the ripening period. As expected, quantitative differences were found when both studies were compared. This is not surprising, since both strains and meat products were different. Nonetheless, important qualitative similarities were found. In all cases, and in agreement with previous work in “salchichón”, D. hansenii modified the levels of volatile and aromatic compounds by increasing esters and alcohol metabolites in comparison to the non-inoculated samples [49,58]. However, and in contrast with what was reported in the case of “salchichón”, a significant decrease in aldehydes was reported in both “lacon” and “lomo ibérico”.

In some cases, a different approach was followed, since model minced meats which did not correspond to any specific commercial meat products were used. A first attempt by Olesen and Stahnke [42] indicated that the use of D. hansenii as a starter culture had very little effect on the production of volatile compounds in the model minces, although, as previously mentioned, the presence of garlic affected cell viability. More recently, the ability of several D. hansenii strains to generate aromas in a fermented sausage model system was evaluated. The performance of seven different strains previously selected on their ability to produce aromatic compounds in a defined culture media [70] were later studied in a meat model system. The presence of each inoculated strain was confirmed in the model system and an increase in volatile compound production was observed in all cases. However, significant differences were found among strains, especially in relation to ester production which was correlated to the lipolytic activity of the strains. Sulphur production was also strongly dependent on the inoculated strain. In summary, it was concluded that: (i) the inoculated D. hansenii strains affected the flavour development of the meat model system; (ii) wide differences do exist among strains, although in all cases volatile compounds increased; (iii) the meat model system is useful to show the ability of D. hansenii strains to produce aromatic compounds; and that (iiii) it is necessary to investigate the effects of specific strains in real dry-fermented sausages [54,55].