SummaryThe relationships between the composition, texture and microstructure of chhana (an Indian-style soft cottage cheese analogue) and rasogolla (a sweetened dairy product made from chhana) were analysed. Chhana contained a significantly higher proportion of fat, protein, lactose and minerals than did rasogolla. Cooking of chhana in 60% sucrose solution introduced sucrose and changed the texture and structure to that typical of rasogolla. As chhana was transformed to rasogolla, the Instron textural properties, hardness, gumminess and chewiness, fell significantly, whereas springiness increased dramatically. Market rasogolla had a slightly different composition from the laboratory-made samples, but both had similar Instron textural and sensory textural attributes. Scanning electron microscopy showed that chhana had a structure like cottage cheese or cream cheese, a compact, coalesced casein matrix with fat globules embedded in it. Rasogolla had a conglomerated, ragged and porous casein matrix with uneven surface and numerous large void spaces. The collapsed and ruptured fat globules were found embedded in the agglomerated protein particles of rasogolla. The textural attributes of both chhana and rasogolla could be explained by the microstructure.

Summary-The reddish-brown colour produced on heating protein-free filtrate of heated milks containing less than 1.0% lactose and free of ions in 6.4 N sulphuric acid was used for quantitative determination of lactulose. The absorptivity of the coloured solution of lactulose at 330 nm was 14-fold more than that obtained from 62.S-fold more concentration of lactose and other aldoses. By following the optimum conditions established in this method, a minimum of 10 mg/100 ml concentration of laetulose can be determined in high heated unsweetened milk and milk products. The method was found to be very useful and sufficiently sensitive under dairy industry conditions where the ion removed step can be omitted if raw milk filtrate is taken for blank preparation. This paper describes a simple and rapid spectrophotometric method which does not require separation of lactulose from lactose or other aldoses and can be conveniently applied for quantification of lactulose in unsweetened milk and milk products.

Scanning electron and Iight-microscopic studies were carried out to provide information on the micro-and macro-structural differences between cow, buffalo and mixed milk rasogolla (a local Indian milk product obtained via acid coaqulation followed by cooking in sugar syrup). Scanning electron microscopy of cow milk rasogolla revealed a loese, porous protein matrix with coa!esced casein micelles forming a thread-Iike structure,.while buffalo milk rasogolla had agglomerated casein micelles which were large and compact, and formed a scale-or layer-type structure. Casein micelles in mixed milk rasogolla formed a combination of thread-and scale-type structures. Fat globules collapsed and the membrane shrank noticeably in ail the 3 sampi es: Larger fat globules were~;'ost affected, while Iittle or no effect was observed in small fat globules. Ught microscopic investigation showed that cow milk rasogolla had smooth, small oval-shaped pores, whereas buffalo milk rasogolla had rough-edged. irregularly-shaped large pores. Mixed milk rasogolla had a heterogenous structure. The Instron and sensory texturai examination agreed weil with the composition and' structural characteristics of rasogolla. rasogolla 1electron microscopy llight microscopy 1 heat treatment 1texture 1microstructure Résumé-Microstructure et macrostructure de rasogolla de lait de vache, de lait de bufflesse et de lait de mélange. Des études au microscope électronique à balayage et au microscope optique ont été conduites pour déterminer les différences de micro-et macrostructure existant dans le rasogolla (produit laitier indien local obtenu par coagulation acide suivie d'une cuisson dans un sirop de sucre) obtenu à partir de lait de vache, de lait de bufflesse ou de mélange. La microscopie électronique à balayage du rasogolla de lait de vache révélait une matrice protéique lâche, poreuse, avec des micelles de caséine agglomérées en cneîneties filamenteuses. Au contraire, le rasogolla de lait de bufflesse présentait une structure compacte formée par de grosses micelles de caséine agglomérées en strates très denses. Le ra5Ogolla de lait de mélange avait quant à lui une microstructure intermédiaire comportant à la fois des oncnstnemems micellaires stratifiés et filamenteux. Les globules gras avaient une présentation plus ou moins dégonflée selon leur taille, la membrane des plus gros étant la plus rétractée sur elle-même. L'examen au microscope optique révélait que le rasogolla au lait de vache avait 476 AK Adhikari et al des pores petits, aux contours lisses, de forme ovale tandis que le rasogolla au lait de but/esse présentait des pores gros, aux contours et formes irréguliers. Le rasogolla de lait de mélange avait une structure hétérogène. Les résultats de l'étude de la texture du rasogolla par l'Instron ou par analyse sensorielle étaient en accord avec les caractéristiques de composition et de structure.

The influence of passing electric current in the acidic buffalo milk with a view to explore the possibility of retaining and utilizing such milk for the manufacture of dairy products was studied. Twelve trials were conducted on de-acidification of milk and the quality of milk was judged by the Heat Coaguldon time and the concentration of major minerals, namely, calcium, magnesium, phosphate and citrate in normal buffalo milk, its rennet whey, acidic milk whey and the de-acidified milk whey. The average HCT for normal milk, acidic milk and de-acidic milk was 42.66f1.40, 2.74fO. 03, 44.41 f 1.78 min, respectively. Ihe average pH of these milks were 6.72 f 0.19, 6.21 f 0.02 and 6.77f 0.03, respectively. Ihe soluble calcium, in diferent types of whey obtainedfrom whole milk, acidic milk and de-acidified milk were 24.03%, 33.11 % and 21.37%, respectively. Similarly, magnesium contents were 56.78 % , 66.58 % and 56.61 % and the phosphate contents were 43.87%, 60.74% and 42.24%; and citrate 67.93%. 81.48% and 62.16%.