Studies of traditional cheese and fermented milks

[摘要] ENGLISH ABSTRACT:One of the curious facts about the food industry is that many of the processesin use today were being practised, in some form or other, by the Roman legions asthey marched across Europe and beyond. Certainly they were familiar with the basictechniques of fermentation, and much current research into fermented foods isconcerned with understanding the fundamental nature of these traditional processes,and how the individual stages in a particular fermentation can be better controlled.Recent developments in the dairy industry have tended to reflect this patternand, over the years, my research group has done much to support the expandingmarkets for yoghurt and similar fermented milks. Our evaluation of thepolysaccharide-producing characteristics of starter cultures, for example, encouragedyoghurt manufacturers to match physical properties to the perceived demands ofconsumers, and most culture suppliers followed this lead by labelling their productswith precise designations as to their potential for imparting viscosity to a retail item.Similarly, my group was the first to record the unique physical properties ofthe concentrated yoghurt, labneh, C 230 g 1-1 total solids) that had been made forhundreds of years by draining whey from natural yoghurt hanging in a cloth oranimal-skin bag. This detailed analysis of the product facilitated the application ofultra-filtration to natural yoghurt to generate a product with a quality that matchedtraditionallabneh and, today, factories in the Middle East, Greece and elsewhere areusing modern membrane-filtration plants to satisfy a growing market demand.Our success in publicising the attractive properties of concentrated yoghurtencouraged me to devote time to yet another 'historical' concept, namely the apparent'health benefits' derived by small communities in Eastern Europe from consumingkefir and koumiss. In the West, the flavour and texture of these latter products havenever been accepted, but employing similar cultures to produce 'health-promoting'bio-yoghurts opened an entirely new avenue for research. As clinical evidence insupport of the prophylactic and therapeutic properties of Lactobacillus acidophilus anda species of Bifidobacterium became available, so it became apparent that thetherapeutic advantage that accompanies the regular ingestion of 'bio-yoghurts'depended on the survival of these microfloras over the stipulated shelf-lives of theretail vehicles. However, no laboratory medium was immediately available for thesimultaneous enumeration of Lb. acidophilus and Bifidobacterium along with theyoghurt cultures, i.e. Streptococcus thermophilus and Lactobacillus delbrueckii sub-sp.bulgaricus. Designing such a medium became a priority for one of my students, and,even today, the procedures that he derived are being used by consumer groups thatmonitor the performance of the major dairy companies in England.If the improved quality of yoghurts and 'bio-yoghurts' had a major impact onconsumer perceptions of fermented milks, the food sector in England graduallybecame aware of an even more dramatic change in consumer attitudes. Thus twentyyears ago, cheese meant 'Cheddar' but, following a 'deluge' of television publicityabout the attractions of 'exotic' catering, housewives began demanding mozzarella andmascarpone for lavish desserts, Feta to sprinkle over salads and Halloumi to grill orfry. In turn, exporting countries like Italy, Greece and Cyprus came under intensepressure to increase supplies of top quality products. Local manufacturers soonrealised, however, that there was little information available concerning the scientificbasis to the procedures employed to make some of these traditional cheeses, and myresearch group was selected by Funding Agencies in Greece and Cyprus to act as afocus for a series of studies of Feta and Halloumi cheese.The need to eliminate pathogens from the storage brines of Feta cheese withoutkilling the yeasts and bacteria associated with maturation became an importantconsideration for exporters, and one of my students exploited a novel procedureemploying furocoumarins and long-wave ultra-violet light to achieve the desiredselective inactivation. At present, the economics of commercial application aresomewhat dubious but, as soon as cheap, synthetic, non-toxic furocoumarins becomemore readily available, the system may well merit re-evaluation. We did confirm,however, that the metabolic activities of the yeasts and bacteria typically isolated fromstorage brines are essential for flavour development in Feta cheese, and that similarmicrofloras are instrumental in the development of the important charactistics oftraditional Halloumi cheese. In particular, a new species of lactic acid bacterium,Lactobacillus cypricasei, was isolated from samples of the traditional ovine cheese,but whether or not the species has a unique role(s) in the maturation process remainsan open question.Clearly there is still much to learn but, if the activities of my reseach grouphave added just a little to the scientific background essential for future studies ofcheese and fermented milks, then their completion will have been worthwhile.

[发布机构] Stellenbosch University