Silvia Rovira

Hot topic: Microstructure quantification by scanning electron microscopy and image analysis of goat cheese curd

Five microstructural parameters of goat cheese curd (number of pores, their area and perimeter, strand thickness, and porosity) were studied by scanning electron microscopy and image analysis. Image analysis was used to characterize and quantify differences in all parameters and to provide a procedure for the measurement of strand thickness. The micrographs provided visual evidence of differences in the protein matrix and were quantified by image analysis at 3 production times: 34 ± 1 min (cutting), 154 ± 6 min (before molding), and 293 ± 35 min (after pressing). The data showed that this procedure is an adequate tool for quantifying differences in the parameters analyzed in industrial samples despite their natural heterogeneity. The procedure was reproducible and repetitive for the first 2 production times because no significant intragroup differences were observed. Significant differences were found when comparing the values of the microstructure parameters analyzed at 34 ± 1 min and those corresponding to 154 ± 6 min and 293 ± 35 min, but no significant differences between samples analyzed at 154 ± 6 min and 293 ± 35 min were found. All microstructure parameters analyzed were related at a significance level of at least 95%. This procedure enables the characterization of the microstructure of industrial goat cheese curd.

Influence of ripening on proteolysis and lipolysis of Murcia al Vino cheese

The aim of this study was to evaluate the influence of five different manufacturers and two ripening periods on the proteolysis and lipolysis patterns of Murcia al Vino goat cheese. The manufacturers significantly affected the water activity (aw), pH, dry matter and fat content, several nitrogen fractions: water soluble nitrogen (WSN), trichloroacetic acid (12% w/v) soluble nitrogen (TCASN) and phosphotungstic acid (5% w/v) soluble nitrogen (PTASN); also the free amino acid (FAA) and free fatty acid (FFA) contents, with the exception of C4:0, C16:0 and C18:0. Different ripening periods significantly affected the dry matter content, WSN and PTASN and all FAA, except serine.

Influence of lamb rennet paste on the lipolytic and sensory profile of Murcia al Vino cheese

The influence of lamb rennet paste (71.1% chymosin, 177 international milk-clotting units/mL, 4.57U/g of lipase activity) during the ripening of Murcia al Vino goat cheese was studied. The aim of this study was to improve the knowledge of the effect of lamb rennet paste on the lipolytic patterns in this type of cheese by reference to the evolution of total and free fatty acids. A sensory analysis was carried out to compare cheeses made with commercial and paste rennet. The rennet paste showed higher lipolytic activity, enhancing the production of short-chain free fatty acids. In addition, the cheese produced with lamb rennet paste had a slightly more bitter and piquant taste, making it an attractive commercial alternative that can be used to develop new varieties of goat cheese.

Effect of starters and ripening time on the physicochemical, nitrogen fraction and texture profile of goat's cheese coagulated with a vegetable coagulant (Cynara cardunculus)

BACKGROUND The increase in the demand for goats cheese throughout the world has encouraged research into the development of new related products with different textural characteristics. The aim of this work was to study the effect of three commercial starter cultures through the assessment of physicochemical and textural characteristics of goats milk cheeses made with vegetable coagulant (Cynara cardunculus) during ripening. RESULTS Use of the different starter cultures produced a significant effect (P < 0.05) on moisture, proteins, pH, nitrogen fractions and hardness of the cheeses. Results show that the addition of mesophilic starters ensures the correct acidification rate and produced cheeses with lower pH values and greater hardness. Use of thermophilic starter cultures produces cheeses with less instrumental hardness and the use of mixed cultures produced less proteolysis. CONCLUSION These results are found useful for selecting the most suitable starter for the development of new goats cheeses.

Effect of feeding goats with distilled and non-distilled thyme leaves (Thymus zygis subp. gracilis) on milk and cheese properties.

The aim of this study was to evaluate the effect of feeding goats with distilled and non-distilled thyme leaves (Thymus zygis subsp. gracilis) on the physicochemical composition and technological properties of pasteurised goat milk, and on the physicochemical composition, phenolic content, oxidative stability, microbiology, sensory and texture profile of Murcia al Vino goat cheese. One group of goats was fed the basal diet (control), the second and third groups were fed with different levels of distilled (10 and 20%) or non-distilled (3·75 and 7·5%) thyme leaves. Goat milk physicochemical composition was significantly affected by the substitution of 7·5% of basal goat diet with non-distilled thyme leaves (increase in fat, protein, dry matter and PUFA content), while goat milk clotting time was increased significantly by the introduction of 20% distilled thyme leaves, which reduces its technological suitability. Microbiology, sensory and texture profiles were not affected by the introduction of distilled thyme leaves. The introduction of distilled and non-distilled thyme leaves as an alternative feed to diet can lead to an inhibition of lipids oxidation. The introduction of distilled and non-distilled thyme leaves into goats diet can be successfully adopted as a strategy to reduce feeding costs and to take advantage of the waste from the production of essential oils, minimising waste removing costs and the environmental impact.

Usefulness of a large field of view sensor for physicochemical, textural, and yield predictions under industrial goat cheese (Murcia al Vino) manufacturing conditions

The applicability of a light backscatter sensor with a large field of view was tested for on-line monitoring of coagulation and syneresis in a goat cheese (Murcia al Vino) manufactured under industrial conditions. Cheesemaking was carried out concurrently in a 12-L pilot vat and a 10,000-L industrial vat following the normal cheesemaking protocol. Cheese moisture, whey fat content, hardness, springiness, and adhesiveness were measured during syneresis. The results obtained show that cutting time is best predicted by considering the coagulation ratio at the inflection point and the percentage increase in the ratio during coagulation, with no need for the first derivative. The large field of view reflectance ratio provided good results for the prediction of moisture content, yield, hardness, springiness, and adhesiveness of the final cheese.

Microstructure of industrially manufactured goat cheese Queso de Murcia al Vino during synaeresis

The microstructural parameters of an industrially manufactured goat cheese curd (pore number, area and perimeter, strand thickness and porosity) were analysed by scanning electron microscopy and image analysis during synaeresis. The water-holding capacity, whey fat, pH and moisture content were also determined to establish any relationship with the curd microstructure. The quantification of the different microstructural parameters made it possible to assign pitching and stirring as important processing steps because these steps impart different features to the curd microstructure. Higher pore number was related to reduced pore area, perimeter and strand thickness, but higher porosity and moisture.

Consumer acceptance of milk from goats fed a diet supplemented with aromatic plants

Although Spain is an important producer of goat milk, less than 2% of this milk is used for direct consumption. The aim of this study was to evaluate the consumer acceptance of milk obtained from goats fed a diet supplemented with aromatic plants as a source of natural antioxidants, in this case distilled thyme and rosemary leaves and nondistilled thyme leaves. A paired comparison test identified significant differences between the control milk and all those obtained from goats receiving supplemented diets.

Physicochemical, microbiological, textural and sensory changes during the ripening of pasteurised goat milk cheese made with plant coagulant (Cynara scolymus)

This study describes the changes that occur during the ripening of cheeses made with a plant coagulant derived from artichoke flowers (Cynara scolymus). The results indicate that the physicochemical composition during ripening evolves similarly to other cheeses. The texture and sensory features of the cheeses during ripening evolved differently from that observed for other goat cheeses. Although it is common for a bitter taste to develop during the ripening of cheeses elaborated with plant coagulants, bitterness was scored very low in the cheeses made with artichoke, so that these cheeses could be suitable for marketing.