FoodInfo Online Features -->12 May 2005
In the first part of a two-part series,
Ernest Mann rounds up the most recent literature relating to yoghurt. 
If proof was needed that there is increasing world-wide interest in yoghurt and related fermented milk products, this two part review of recent literature on the subject, covering reports from no less than 21 countries from all parts of the world, will surely provide it.
The proceedings of the International Dairy Federation (IDF) symposium on Aroma and Texture of Fermented Milk, held in Denmark in 2002 (1) provide an excellent starting point.
Following an introductory review of the applications of fermentation technology there were sessions on cultures, processing and product evaluation as well as nine poster presentations.
Among several reviews covering different aspects of yoghurt is a recent one published in this journal (2) dealing with the development of yoghurt and dairy dessert products with improved nutritional and health promoting properties.
The development of structure in fermented dairy products and ways of controlling their textural properties has been discussed and reviewed in a paper published in the International Journal of Dairy Technology (3).
The effects of different factors, including milk components, starters and manufacturing and handling processes on yoghurt texture, as well as methods for assessing texture, have been reviewed in the USA (4). A comparative assessment of the market for plain and fruit flavoured yoghurts in Europe (5) showed that, whereas the annual per capita consumption of plain yoghurt in 15 European countries averaged 3.7 kg (ranging from 0.30 kg in the UK to 13.95 kg in the Netherlands), that of fruit flavoured yoghurt averaged 8.86 kg (ranging from 3.10 kg in Hungary to 21.8 kg in Finland). Recent developments in the manufacture and properties of the Egyptian yoghurt, zabady, have been reviewed (6).
The first of several papers on microbiological aspects of yoghurt comes from France (7) and examines the interactions between Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus when they are co-cultured, as in the production of yoghurt.
Strains Belgian scientists (8) have examined the use of exopolysaccharide (EPS) producing strains of S. thermophilus as starter cultures in the production of products such as yoghurt. Italian workers (9) have compared the properties of 17 strains of S. thermophilus for the production of yoghurt.
The results indicate great differences in characteristics between different strains affecting the nature and quality of the yoghurt.
In Sweden (10) the functional properties of yoghurts produced with EPS producing strains and non-producing strains of S. thermophilus and L. delbrueckii subsp. bulgaricus have been screened and correlations between sensory and rheological properties investigated.
Chinese workers (11) have also studied the use of EPS producing yoghurt cultures with a view to improving the sensory and rheological properties of yoghurt. Three bacteriophage-sensitive strains of L. delbrueckii subsp. bulgaricus isolated from commercial yoghurt starters in Argentina (12a) and their indigenous bacteriophages, have been characterised with regard to the phage absorption process.
Scientists in Bulgaria (12b) have isolated strains of yoghurt cultures from home-made yoghurts in the mountain regions of Bulgaria, with a view to identifying new strains suitable for the production of improved quality yoghurts under industrial manufacturing conditions.
Several reports in the probiotic yoghurt sector are headed by one (13) on developments in the probiotic yoghurt market in Japan where, apart from the well-established Yakult, several new products have been launched in recent years.
Also reported (14) is the launch of a range of new probiotic yoghurt products in Slovenia using Bifidobacterium lactis HN019, a new culture produced by Danisco under the HOWARU name. Animal trials with this culture have demonstrated improved immune function response. Scientists in the Ukraine (15) have reported studies on the biotechnological parameters of yoghurt and kefir during which the probiotic properties of these products were confirmed in clinical trials.
Croatian researchers (16) have studied the aroma of probiotic yoghurts with and without supplements, with special reference to changes in aroma compounds occurring during storage as a function of time and temperature. Bifidobacterium lactis HN019, referred to above, has been described in greater detail (17) with regards to its immunity-enhancing properties and its inhibitory effects on gastrointestinal pathogens.
In Italy the production of probiotic yoghurt with increased levels of bioactive peptides has been investigated (18). Australian scientists (19) have reported studies on the effects of packaging materials and dissolved oxygen on the survival of probiotic bacteria in yoghurt.
The results suggest that, although the level of dissolved oxygen in yoghurt can be influenced by the type of packaging material, it is unlikely to affect the survival of probiotic bacteria in yoghurt. The effects of chicory fructooligosaccharides on the viability of yoghurt starter cultures and two strains of Bifidobacterium during refrigerated storage have been studied in Turkey (20). German dairy Onken has launched a new range of 1.5% fat functional yoghurts including flavours such as aloe vera and cherry, juniper and acerola mix (21). In Germany, Müller has introduced a coffee-flavoured yoghurt with a separate serving of amarettini biscuits in their dual compartment range. In Switzerland, Unilever has extended its pro.activ line of functional, cholesterol-lowering products with a mocca-flavoured yoghurt (22).
New yoghurts containing antioxidant ingredients have been introduced in Japan (23). Glico Dairy Products sells a probiotic yoghurt containing Bifidobacterium spp., whole blueberries (a source of antioxidant polyphenols) and a mixture of fruit juices. Ice cream yoghurt An ice cream yoghurt made with a live starter culture mixture capable of producing EPS during fermentation, gives improved texture and viscosity and (24) is covered by a European patent. Korean scientists (25) have reported that feeding ovariectomised rats with safflower seed yoghurt results in significant improvements in bone health, providing a protective effect against osteoporosis. The cholesterol-lowering ability of isolated soya proteins incorporated into yoghurt and fed to human subjects was confirmed in a Finnish study (26).
A Nigerian scientist (27) has reported good results from trials in which cashew apple was incorporated into yoghurt, with no adverse effects on composition or sensory quality.
A Chinese worker (28) has reported results from a trial in which Siraitia grosvenorii was added to yoghurt. The product satisfies consumer expectations for palatability, low sugar content and low energy value. Also reported from China (29) is a study on the optimum processing conditions for producing pollen yoghurt. Another Chinese team (30) has reported on the production of a blood sugar-reducing yoghurt for diabetics.
The production of salted yoghurt from set and torba yoghurts has been investigated in Turkey (31), with salted yoghurt produced by cooking for 30 minutes being the most preferable according to sensory tests. Among a number of enriched yoghurt products described are those enriched with rice starch (32) whose physical and sensory properties, together with a good low temperature stability, make it a very good texturiser for low-fat yoghurts.
Egyptian scientists have reported (33) that the replacement of up to 40% of dried skim-milk with a modified starch in yoghurt had no adverse effects on the sensory quality of the yoghurt. A PCT patent (34) covers a stirred type of yoghurt product incorporating chocolate or other confectionery pieces. Fortified milk A Turkish study (35) shows the effects on physicochemical properties, sensory properties and composition of methods used for the fortification of milk for yoghurt manufacture. Several of the additives had a significant effect on the sensory and other properties of the yoghurts.
The calcium fortification of yoghurt is covered in a US patent (36), as well as in work reported from Egypt (37) from which it was concluded that fortification of milk with calcium phosphate at levels of ≤90mg per 100ml leads to an acceptable product with high calcium content.
Product and process for magnesium enrichment of yoghurt to levels of up to 3 000mg per litre are covered in a European patent (38). An improved process for the production of a high viscosity stirred yoghurt is claimed in a PCT patent (39). A Croatian scientist (40) has described studies on the rheological properties of stirred yoghurt during long-term storage at 4 and 8ºC, using the dynamic oscillation method. Among the findings were that rheological properties were influenced by the addition of dried whole milk or whey protein.
Finally, the first of two reports from China (41) indicates that the addition of denatured starch in the manufacture of stirred yoghurt increased the viscosity as well as the stability of the yoghurt to heating, acidity and shearing stress. In the second study (42), different stabilisers were compared in the manufacture of stirred yoghurt in order to improve overall quality, texture and flavour.
(1) Internat Dairy Fed (2003) Proc Symp Fermented milks Kolding, Denmark 2002
(2) McKinley, M (2004) Dairy Inds Internat 69(4)32
(3) Lucey, J (2004) Internat J Dairy Technol 57(2-3)77
(4) Sodini, I et al (2004) Critic Rev Food Sci & Technol 44(2)113
(5) Anon (2003) Dte Milchwirtsch 54(22)958
(6) Abou-Donia, S A (2004) Egypt J Dairy Sci 32(1)1
(7) Courtin, P et al (2004) Lait 84(1-2)125
(8) De Vuyst, L et al (2003) Proc Symp Fermented Milks Kolding, Denmark 2002
(9) Lavezzari, D et al (2003) Proc Symp Fermented Milks Kolding, Denmark 2002
(10) Folkenberg, D M et al (2003) Proc Symp Fermented Milks Kolding, Denmark 2002
(11) Gu Rui Xia et al (2002) China Dairy Ind. 30(5)5
(12a) Quiberoni, A et al (2004) J Appl Microbiol 95(2)340
(12b) Minkova, S et al (2004) Khranitelno-vkusova Promishlenost No 2
(13) Hayes, D (2004) Dairy Inds Internat 69(7)14
(14) Anon (2004) Dairy Inds Internat 69(9)40
(15) Chagarovsky, V P et al (2003) Microbiol Zhurnal 65(6)67
(16) Hruskar, M et al (2003) Mljekarstvo 53(3)195
(17) Schmid, K et al (2003) Proc Symp Fermented Milks, Kolding Denmark 2002
(18) Chianese, L et al (2003) Proc Symp Fermented Milks, Kolding Denmark 2002
(19) Talwalkar, A et al (2004) Internat J Food Sci & Technol 39(6)605
(20) Alkalin, A S et al (2004) Internat J Food Sci & Technol 39(6)613
(21) Anon (2004) Dairy Inds Internat 69(5)8
(22) Anon (2004) Dairy Inds Internat 69(8)12
(23) Anon (2004) Dairy Inds Internat 69(6)13
(24) Yogurtal Sp A et al (2003) Europ Pat Appl 1,430 785
(25) Kim, K Y et al (2004) J Anim Sci & Technol 46(1)69
(26) Puska, P et al (2004) Brit J Nutrit 91(3)393
(27) Aroyeun, S O (2004) Nutrit & Food Sci 34(1)17
(28) Bu Chun Wen (2004) China Dairy Ind 32(1)35
(29) Zhao Hai Zhi et al (2003) China Dairy Ind 31(2)19
(30) Li Tao (2002) China Dairy Ind 30(5)106
(31) Sahan, N et al (2003) Gida 28(5)545
(32) Potts, A M (2004) Dairy Inds Internat 69(4)31
(33) Kebary, K M K et al (2004) Egypt J Dairy Sci 32(1)111
(34) General Mills. Inc (2003) PCT Pat Appl WO 2004/008867
(35) Guven, M et al (2003) Gida 28(4)429
(36) General Mills Inc et al (2000) US Pat 6 740 344
(37) El-Garawany, G A (2004) Egypt J Dairy Sci 32(1)59
(38) Roujanski, O (2002) Europ Pat Appl 1 385 386
(39) General Mills Inc et al (2003) PCT Pat Appl WO 03/096816
(40) Vilusic, M (2003) Mljekarstvo 53(3)211
(41) Wang Dan et al (2002) China Dairy Ind 30(3)14
(42) Shao Hong et al (2002) China Dairy Ind 30(4)10
This review was originally published in the March 2005 edition of Dairy Industries International
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