Nota. Estudio de algunos quesos típicos españoles por microscopía electrónica de barrido. Principales modificaciones microestructurales causadas por la congelación / Note. Study of some typical Spanish cheeses by scanning electron microscopy. Main microstructural modifications caused by freezing

Abstract

The microstructure of some Spanish cheeses and the main microstructural modifications caused by freezing are studied by scanning electron microscopy (SEM). In cured and pressed cheeses such as Manchego and Mahón cheeses, the protein matrix constitutes a compact network in which fat glob ules, uniformly distributed, are immersed; frequently, these spherical globules are limited by an ap parent protein membrane. In the protein matrix, micellar bodies are identified in different aggrega tion grades; this is a characteristic of the enzymatic coagulation. In non-cured Herreño cheese (pressed paste) the compaction grade of the casein micelles is less than in cured and pressed cheeses. In fresh cheese, which is a fresh and non-cured cheese, proteins are distributed as micelle clusters more or less loose. Large fissures and small spherical voids, which would probably contain whey, air or fat, are observed. Cottage cheese, a non-pressed paste, is obtained fundamentally from whey protein coagulation; the protein bodies are distributed loose or in the form of clusters, and large voids are formed. Freezing at -25 °C affected the pressed and cured cheeses (Manchgeo and Mahón) and non- cured cheeses (Herreño); the spherical voids containing fat are deformed, the protector membranes are broken, and reticular structures and micellar bridges are found inside the protein matrix. In non- cured and soft paste cheeses such as fresh cheese, the protein matrix becomes hard with fissures, and the spherical voids appear destroyed and deformed. Freezing produces total destruction of the cot tage cheese structure. Texture studies of the cheeses (shear strength) agreed with microscopy results by SEM.