- Improving the nutritional quality of dairy products -
Nowadays, supplementation of food products with nutrients present at low level is a common industrial practice. Recently, we investigated the supplementation of yogurt, quark and semi-hard Ibérico cheese with edible seaweeds such as Himanthalia elongata (sea spaghetti), Laminaria ochroleuca (kombu), Porphyra umbilicalis (nori), Ulva lactuca (sea lettuce) or Undaria pinnatifida (wakame).
In Ibérico cheese with seaweeds, the microbiota was hardly affected during ripening, although we observed differences in dry matter and pH values. Antioxidant activity, correlated with total phenolic compounds, was higher in cheese supplemented with sea spaghetti than in control cheese. Color and texture parameters of cheeses varied with the added seaweed species. Cheeses made with sea spaghetti, kombu and wakame, associated with low seaweed odor and flavor scores, received from panelists odor and flavor quality scores which did not differ significantly until day 60 from those of control cheese.
At present, we are trying to develop dairy products with hypocholesterolemic properties, by adding plant extracts and probiotic microorganisms. We will also study the interactions between these plant extracts and the microorganisms present in dairy products and the manufacturing processes.
- Improving the sensory quality of dairy products -
We have a collection of lactic acid bacteria isolated from goat's milk of the Malagueña and Payoya indigenous breeds, as a result of a recent research. We have evaluated their technological properties, sensory characteristics and volatile compounds profile in some dairy products. These results could be useful to develop specific starter cultures for these varieties of goat's cheese, which might help to maintain their distinctive sensory characteristics.
- Preventing microbiological spoilage of dairy products -
Microbiological spoilage is one of the most common causes of dairy product deterioration, negatively affecting their quality, shelf life and acceptability, and causing important economic losses and food waste.
Late blowing is one of the most serious quality defects in hard and semi-hard cheeses, mainly caused by spore-forming Clostridium tyrobutyricum. This spoilage bacterium produces gas during the fermentation of the lactic acid present in cheese resulting in butyric and acetic acids, CO2 and H2. Due to the pressure of the gas, swelling and cracks appear in cheese, together with off-flavours.
The use of a nisin-producing Lactococcus lactis strain as starter in cheese making delayed the appearance of late blowing defect, although just one week. However, when we added Lactobacillus reuteri INIA P572, able to produce reuterin from glycerol, as adjunct to cheese, we achieved inhibition of C. tyrobutyricum growth and prevented late blowing during ripening, without compromising cheese sensory quality.
In addition, we inactivated C. tyrobutyricum vegetative cells, after germination of clostridial spores, by applying a high pressure treatment at 300 MPa, which avoided cheese blowing while maintaining its sensory characteristics.
Recently, we used an engineered Lactococcus lactis strain, expressing endolysin CTP1L (from bacteriophage CTP1 and active against C. tyrobutyricum), as cheese starter. The endolysin produced by L. lactis reduced the activity of C. tyrobutyricum, and delayed one month the development of cheese spoilage.
We are also characterizing a collection of 96 new bacteriophage isolates active against C. tyrobutyricum to prevent cheese late blowing defect.
Furthermore, we were able to visualize C. tyrobutyricum vegetative cells of cheese, by applying the cell wall binding domain of CTP1L endolysin marked with the green fluorescent protein.
- Improving the sensory quality of meat products -
High pressure treatments are widely used by the meat industry to ensure the microbiological safety of sliced and ready-to-eat meat products. Our research has shown that the chemical composition of dry-cured ham, the high pressure treatment and the refrigeration period affect volatile compounds profile of ham. Careful selection of dry-cured ham batches to be pressurized is important to safeguard the unique odor and aroma characteristics of Iberian and Serrano dry-cured ham.