Microstructure of cheese: Processing, technological and microbiological considerations Cla ´udia I. Pereira, Ana M.P. Gomes and F. Xavier Malcata CBQF/Escola Superior de Biotecnologia, Universidade Cato ´ lica Portuguesa, Rua Dr. Anto ´ nio Bernardino de Almeida, P-4200-072 Porto, Portugal (Tel.: D351 22 558 0004; fax: D351 22 509 0351; e-mail: fxmalcata@esb.ucp.pt) Cheese is a classical dairy product, which is strongly judged by its appearance and texture; hence, a renewed interest in its mi- crostructure has been on the rise, as sophisticated techniques of analysis become more and more informative and widely available. Processing parameters that affect microstructure play a dominant role upon the features exhibited by the final product as perceived by the consumer; rational relationships between microstructure (which includes biochemical and microbiological indicators), and quality and safety of the products are accordingly required. Subsequent to that extra fundamental knowledge, technological innovations may even- tually improve current cheesemaking processes, and permit mechanistic design of novel ones. This review thus focuses on recent advances pertaining to the microstructure of cheese, and discusses them in a logical and critical manner. Introduction Cheese is a highly regarded food in most human cultures, and has accordingly been present throughout ages in man- kind daily life. The variety of cheeses currently available is large, because a myriad of topical advances e encompassing manufacture and ripening, have cumulatively taken place over time. In addition to the somewhat intrinsic (and unpredictable) variability within each cheese type, tailor- made cheese matrices have been proposed based on specific microstructures e which have emerged side by side with introduction of alternative (or improved) methodologies in cheesemaking. Microstructure is not a static concept; it evolves instead along the food processing chain, and eventually leads to ma- jor transformations relative to the original microstructure of the milk feedstock itself. This realization thus encompasses specific molecular compositions and spatial arrangements. On the other hand, it should be emphasized that, besides the supporting proteinaceous/fatty matrix, microorganisms are also an integral part of cheese. Microbial activity pro- duces indeed major transformations of the cheese matrix, which will affect the final microstructure as well. Hence, it is also crucial to elucidate microorganismematrix interac- tions, in attempts to understand the whole picture. Consumer acceptance of a cheese product depends directly on its appearance, flavour and texture e which are in turn originated by a thorough combination of micro- biological, biochemical and technological parameters, that affect microstructure directly or indirectly. Note that the ultimate success of any food product relies on consumers’ reactions: in fact, human perception of organoleptic charac- teristics is closer to the consumer status at the moment of decision than data generated by any type of analytical instrumentation (Adhikari, Heymann, & Huff, 2003) e despite its constraints in repeatability and objectiveness. Texture is intrinsically related to the arrangement of various chemical components within distinct micro- and macrostructure levels e e.g. proteic network or fat fraction; it is the external manifestation of such structures that even- tually determines the uniqueness and distinctive character of a cheese product. However, cheeses are particularly complex systems, so full and meaningful assessment of the effects of microstructure (and texture) upon flavour and appearance is still incipient. This paper discusses a number of fundamental aspects pertaining to microstructure of cheese e and specifically focuses on issues associated with microstructural effects arising from technological and processing approaches. Manipulation of physical properties of milk A huge variety of dairy products exists at present, depending on the deliberate alterations of the original * Corresponding author. 0924-2244/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.tifs.2009.02.006