摘要：Coagulation of pasteurized (63 C for 30 min) milk and blending of the resulting curd with high-fat cream followed by heat treatment (44 to 80 C for 10 min) of the blend in preparation of a hot-pack cheese spread led to the formation of a gritty product. Microscopic examination of hard particles causing the grittiness indicated that they consisted of compacted protein. Staining for calcium failed to detect any elevated concentration of this element in the particles. They were amorphous and contained no crystalline structures. Encapsulation of the gritty curd in agar gel tubes made it possible to freeze-fracture the small hard particles and to examine their internal structure by scanning electron microscopy. The hard or gritty particles consisted of compacted protein. This was confirmed by transmission electron microscopy of thin sections of the product embedded in a resin. The unpasteurized (unheated) cold-pack cheese spread prepared from the same ingredients was smooth with no grittiness defect. Based on the findings, grittiness was avoided in the hot-pack product by using curd obtained by coagulating milk which had previously been heated to 90 C for 10 min.
关键词：Cheese spread; Curd; Electron microscopy; Fluorescence microscopy; Grittiness; Heating of milk; Milk coagulation
