Rheology and Microstructure of Strained Yoghurt (Labneh) Made from Cow's Milk by Three Different Methods
Total Page：16
File Type：pdf, Size：1020Kb
Food Structure Volume 8 Number 1 Article 15 1989 Rheology and Microstructure of Strained Yoghurt (Labneh) Made From Cow's Milk by Three Different Methods A. Y. Tamime M. Kalab G. Davies Follow this and additional works at: https://digitalcommons.usu.edu/foodmicrostructure Part of the Food Science Commons Recommended Citation Tamime, A. Y.; Kalab, M.; and Davies, G. (1989) "Rheology and Microstructure of Strained Yoghurt (Labneh) Made From Cow's Milk by Three Different Methods," Food Structure: Vol. 8 : No. 1 , Article 15. Available at: https://digitalcommons.usu.edu/foodmicrostructure/vol8/iss1/15 This Article is brought to you for free and open access by the Western Dairy Center at DigitalCommons@USU. It has been accepted for inclusion in Food Structure by an authorized administrator of DigitalCommons@USU. For more information, please contact [email protected]. F OOD MICROSTRUCTURE, Vol. 8 (1989) , pp . 125-135 0730-5419/89$3. 00+. 00 Scanning Microscopy International, Chicago (AMF O'Ha r e). IL 60666 USA RHEOLOGY AND MI CRO STRU CTURE OF STRAINED YOGHURT (LABNEH ) MADE FROM COW'S MILK BY THREE DIFFERENT METHODS 1 2 1 A.Y . Tamime , M. Kalab and G. Davies 1 The West of Scotland College, Food Technology Department, Au chincruive, Ayr KA6 SHW Scotl and, U.K. 2 Food Research Centre, Research Branch, (Agriculture CanadaL Ottawa, Ontari o , Canada K1A OC 6. Ab stract Introduction labneh is the name for strained yoghurt, The origin of yoghurt- making in the Middle i.e., yoghurt made with an elevated sol ids East dates back several thousand years . The content, which has originated in the Middle East. nomads tending their herds prepared yoghurt in For this study, three types of Labneh were made earthenware vessels or in containers made from from cow' s milk: (a) "Traditional Labneh" was animal skins. The product was kept in these produced by straining yoghurt in a cloth bag, (b) containers until it was all consumed. It is "UF Labneh" was made by ultrafiltration of warm probable that during this time, the liquid phase yoghurt , and , (c) "UF Retentate Labneh" was (whey) seeped through the container or evaporated. obtained by culturing homogenised ultrafiltration The strained yo ghurt thus obtai ned , which has been (UF) milk retentate. A1 1 produ cts were passed call ed Labneh, wou l d keep for a l onger time t han t hrough a lactic curd homogen iser to smoothe n t he t he or igi nal yoghurt, partly du e t o an increased Labneh curd . Tota l sol ids contents of t he lactic acid concentration which preserved it . products were within the range of 21.0 to 24 . 2% , At present, modern manufacture of yoghurt is protein was 6 . 8 to B.?f:, and fat was 9.2 to 10.5%. carried out under controlled conditions using low Rhea 1og i cal properties such as consistency of fat or whole milk which is inoculated with mixed traditional Labneh and UF labneh were similar and starter cultures of screptococcus chcr:mophilus and no syneresis wa s observed after breaking the Lactobacillus delbrueckii subsp. bulgaricus (Rasic coagulum. The coagulum of the UF Retentate labneh and Kurmann , 1978; Tamime and Robinson, 1985, was very firm and its texture was crumbly . 1g88a, 1g88b; Marshall, 1g87). In the Middle Syneresis was noticeable after the coagulum had East, however , l abneh is still produced in the been broken. The best sensory attributes were tradition a 1 manner with the cloth bag used found with the UF Labneh followed by the universally for the straining of the yoghurt in traditional labneh whereas the UF Retentate Labneh spite of the centralized processing of milk in appeared not to be satisfactory. dairy plants. Electron microscopy revealed that the Similar cultured milk products have been microstructures of a 11 three labnehs were simi 1ar popular in various countries . Such products are and consisted of casein micelle chains and known as Tan or Than in Armenia, Torba, Kurut, or clusters. Minute fat particles which originated Tu 1urn in Turkey, Le ben Zeer in Egypt, and Labneh from the homogenisation of mi l k or retentate were or Lebneh in most Arab countries (Tamime and embedded in the casein mice lle c l usters. Robinson, 1978 ; El-Gendy, 1g83 ; Abou-Do nia , 1984 ) . Smoothening somew hat reduced t he di men sions of t he Ot her products c losely r elat ed to La bn e h ar e kno wn casein partic l e c hai ns a nd c lus t ers i n all as Chakka a nd Shirkhand i n I ndia, Skyr i n Ice l and, Labnehs. and Ymer in De nma r k (Tamime and Robinson, 1g88a}. The compositional standard of Labneh in Lebanon contains 26% total solids, 10% fat, and 1% Initial paper r eceived Februar y 10, 1989 saa, where as in Saudi Arabia, labneh contains Manuscr ipt received June 5, 1989 22% total solids and 7% fat (Tamime and Robinson, Di r ect inquiries t o A . Y. Tamime 1gssa). As a dish, Labneh is garnished with dried Telephon e nu mber: 44 -292-520 331 herbs and olive oil and is eaten with pita bread. The traditional manufacture of labneh is labour-intensive and unhygienic . Losses of the KEY WORDS : Casein micelles, Labneh , Lactobacillus product due to its adherence to the cloth bags are quite high . Over the past ten years , attempts delbcueckii SUbSp. bulgaricus, Streptococcus have been made to mechanize the process for ther:mophilus, Milk retentate , Scanning electron creamery-scale operations . Several systems of microscopy, Transmission electron microscopy, manufacturing have been developed . In one of Strained yoghurt , Ultrafiltration of milk , them, Labneh is produced from heated yoghurt by Ultrafiltraion of Yoghurt. centrifugation (Dagher and Ali-Ghariebeh , 1985). 125 A. Y. Tamime~ M. Kalab and G. Davies Sensory attributes of the product are similar to Process III (Traditional Labneh) -The the traditional labneh, i.e., labneh obtained by yoghurt (in bulk) was produced as described in draining yoghurt in a cloth bag. Alternatively, Process II above. The refrigerated yoghurt was labneh may be made by concentrating a mixture of mixed, emptied into a polyester cloth bag (Ets. yoghurt and brine (Kharrazi, 1984) using a Henri Bastien, 59157 Beauvois-en-Cambresis, centrifugal separator. In another method, warm France) and pressed overnight in a refrigerated skim-milk yoghurt is concentrated to the desired room (Fig. 2). For every 10-12 kg of yoghurt, 4.5 level of sol ids using a nozzle or quarg separator kg weight was used to press the product during the and cream is later blended with the product (Salji drainage period. It was observed that some Labneh et al.. 1983; Robinson and Tamime, 1986, Rasic, was lost, i.e. adhered to the bag, when collecting 1987). labneh may also be made from it. The labneh was then processed and packaged as ultrafiltration (UF) milk retentate by culturing described above. using a mixed strain yoghurt starter culture (Veinoglou et al., 1978; Abd El-Salam and El Ultrafiltration Plant Alamy, 1982; El-Samragy and Zall, 1988; Hofi, The mi 1 k and yoghurt were concentrated by 1988). In this study, the product thus obtained using the same Alfa-Laval UF pi lot scale plant is referred to as 11 UF Retentate Labneh". Finally, reported by Tamime et al. (1984), but it was warm yoghurt may be concentrated by slightly modified. The specifications of the ultrafiltration . This process is new in the membrane were: type PM - 50 series No. 6 PL 1256 2 production of Labneh and the product is referred S, surface area 1.3 m, fibre internal diameter to as "UF Labneh" (Tamime et al., 1989) in this 1.5 mm, membrane material polysulfone and study. molecular weight cut-off 50,000 dalton. Labneh is a smooth cultured milk product, the body of which may further be smoothened by passing Starter Culture it through a lactic curd homogeniser. A commercial mixed strain of concentrated The objective of this study was to examine freeze-dried yoghurt starter culture MYO - 87 the individual Labnehs by electron microscopy and (Eurozyme Ltd., london, UK) was used to ferment to assess their microstructures with respect to the milk. This starter (i.e., direct to vat the manufacturing procedures and rheological inoculation) was used at a rate of 16 units/100 L, properties of the products. and was incubated at 42°C. Material s and Methods Lactic Curd Homogeniser The homogeniser type ALM (Pierre Guerin S.A., Preparation of the mi 1 k Mauze, France) was used to smoothen the labneh at Whole cow's mllk was obtained from the West 7°C using a pressure of 8 MPa, and the homogeniser of Scotland College Farm in January and March, head employed was No. 0-170 (Tamime and Crawford, 1988. In each trial the milk was divided into two 1984). portions for the production of Labneh using three different methods. Rheological Analysis A Stevens lFRA Texture Analyser (C . Stevens & Product ion of Labneh Son ltd., Hertfordshire, UK) was used to assess Three different types of Labneh were the consistency of Labneh . The operating manufactured as described by Tamime et al. (1989), conditions were:- cone type TA3- TFE 105-504 (25 x and in brief they could be described as follows: 35 mm cylinder), penetration distance 15 mm, speed Process I {UF Retentate Labneh) -The milk of probe 0.5 mm/S and chart recorder {C. Stevens & was pre-warmed to 50°C before concentration by UF Son Ltd.) operating at 200 mV and 30 mm/min chart to 22% total solids (TS) using an Alfa-Laval pilot speed.