TRADITIONAL DAIRY PRODUCTS

Lesson 29. APPLICATION OF MEMBRANE TECHNOLOGY

Module 12. Innovative processes for traditional dairy products

Lesson 29
APPLICATION OF MEMBRANE TECHNOLOGY

29.1 Introduction

Membrane technology is a pressure driven filtration process which discriminate the molecules primarily on the basis of size and to a lesser extent on shape and chemical composition. The main membrane systems widely used, in the ascending order of pore size, are reverse osmosis (RO), nano-filtration (NF), ultrafiltration (UF) and microfiltration (MF). In a broader sense, RO is essentially a dewatering technique, NF is a demineralization process, UF is a method for fractionation and MF is a clarification process. Membrane processes can be carried out at ambient temperature. Thus, thermal degradation problems common to evaporation processes can be avoided resulting in better nutritional and functional properties of milk constituents. The principles involved in the manufacture of some of the traditional dairy products, such as heat desiccation (Khoa, Rabri and Basundi), heat and acid coagulation (Chhana and Paneer) and fermentation and concentration (Dahi, Chakka and Shrikhand) are compatible with that of membrane processing. The membrane processes, therefore, may play a highly beneficial role in modernization and upgradation of the technologies of our traditional dairy products.

29.2 Application of Reverse Osmosis (RO)

RO is the most energy efficient dewatering process. RO membranes separate solutes with a molecular weight of approximately 150 Daltons and above. Hence fat, proteins, lactose and all undissociated minerals are retained and concentrated by the membrane and only water and some ionized minerals are allowed to pass through. Fluid milks and buttermilk can be partially concentrated economically using RO, particularly for the preparation of concentrated and dried products including indigenous dairy products like khoa, chakka, shrikhand, rabri, basundi and kheer. The economical levels of RO concentration for whole milk is up to 30% TS and for skim milk, 22% TS.

29.2.1 Production of khoa by RO process

Khoa, an important indigenous Indian milk product, is presently manufactured on a small scale by continuous boiling of whole milk until a desirable solids concentration (65-70% total solids) is obtained. In recent years, several attempts have been made to develop new methods including the use of scraped surface heat kettles or heat exchangers for commercial production of khoa. The use of concentrated milk having up to 30% TS has produced khoa of highly satisfactory quality. The reverse osmosis, being energy effective process for pre-concentration of milk prior to the manufacture of khoa, has great potential in India. Khoa has been prepared from cow milk as well as buffalo milk by atmospheric boiling of RO retentates in a steam kettle. The process is conveniently amenable to continuous production of khoa from RO milk retentate using SSHE. Such process offers attractive energy saving in the initial concentration of milk. The energy consumption in RO concentration was estimated to about 80 kcal/kg of milk for batch process and 25 kcal for continuous process, which brings about a net saving of 335 to 430 kcal/kg of milk.

29.2.2 Application of RO in other traditional desiccated dairy products

Rabri and basundi are partially concentrated and sweetened traditional milk products. Whereas rabri contains several layers of clotted cream (malai), basundi has either smooth consistency or small grains of coagulated milk solids. commercial method of preparing rabri using RO process involves pre concentration of standardized milk to about 24% total solids in a RO plant, addition of sugar to this concentrated milk and generation of characteristic cooked flavour by heating the mixture to about 95ºC followed by final desiccation to about 50% total solids in a scraped surface heat exchanger. The desired flaky texture of rabri is simulated by adding shredded (very thin slices) paneer to hot sweetened desiccated milk.

29.2.3 Preparation of dahi and chakka from RO process

Dahi is another important traditional fermented milk product where RO can play an important role. Dahi made from cow milk is weak and fragile in comparison with buffalo product. This problem is due to lower protein and calcium contents in cow milk, which are responsible for firmer curd. Partial concentration of cow milk to about 1.25 to 1.5 folds level by using RO system and preparing dahi from it adopting standard method has been found very useful in producing dahi similar to that buffalo dahi (Pal, et al., 2002).

Cow milk, standardized to fat: SNF ratio of 1:2.2 (12.5% TS), was pasteurized and concentrated (2.5 fold) using and RO plant equipped with tubular, polyamide membranes. A temperature of 50°C and a pressure of 30 kg/m2 were used for concentration. The concentrate was subjected to heat treatment of 90°C/5 min, cooled to 22°C, cultured at the rate of 2% with a mixed strain lactic culture and incubated for 18 hours. The coagulum then obtained was filtered and a minimal amount of whey (4.5 lit./40 lit. of coagulum) having 18% TS was removed from it to get the chakka. The yield of chakka produced by RO process was 35.5% as compared to 28.3% in case of conventional chakka.

29.3 Application of Nanofiltration (NF)

Nanofiltration falls between RO and UF as far as pore size of the membrane and operating pressure are concerned. The pore size of NF membrane ranges from 10 Å to 100 Å and operating pressure ranges between 25-30 bars. NF membrane allows water and small univalent ions (Na+, K+, Cl-) to pass through it whereas completely rejects lactose and other macromolecules. Most recently, the NF process has been tried for processing cow milk for improving the quality of traditional dairy products (Pal et al, 2002). The quality of traditional products, particularly khoa, paneer and dahi, is inferior to their counter part buffalo milk products, which is attributed to inherent compositional differences. Cow milk contains high chloride content, which imparts salty taste to these products, particularly khoa. The lower contents of fat, proteins and lactose in cow milk in comparison to buffalo milk are responsible for sandy texture in khoa, hard and very compact body in paneer and weak and fragile gel of dahi in addition to low yields of all products.

Cow milk heated to 72°C and concentrated to about 1.5 and 2.0 folds using NF membrane system at 50°C revealed that, NF reduced the salt content of cow milk up to 74% in 1.5 fold concentration without affecting other major constituents. Khoa prepared from this milk did not taste salty and the texture was comparable to buffalo khoa, thereby improved the acceptability of cow khoa. The organoleptic quality, particularly in respect of body and texture, of dahi also improved significantly when prepared from 1.5 folds NF concentrated cow milk.

29.4 Application of Ultrafiltration (UF)

From milk, UF produces a permeate containing water, lactose, soluble minerals, non-protein nitrogen and water-soluble vitamins. The process has been used for the manufacture of several fermented dairy products like Yoghurt and Srikhand. UF retentate seems to be a highly promising base for chhana, rasogolla mix powder, long-life paneer. UF technology has also been applied to upgrade khoa manufacture from cow and buffalo milks.

29.4.1 Preparation of chhana using UF process

Skim milk, heated to 95°C for 5 min., is ultrafiltered (26% TS). The retentate is diafiltered (23% TS) with equal amount of water to reduce lactose. For preparation of chhana, the retentate is mixed with plastic cream to a protein/fat ratio of 0.722. The mixture is heated to 85-90°C/5 min. and coagulated with dilute lactic acid to develop the characteristic grain. The granular mass is subsequently pressed to remove free moisture, yielding chhana. The process is reported to yield about 18-19 percent extra product and also no significant difference in flavour, body and texture and appearance compared to traditional method. High yield, easy automation and flexibility in operation are emphasized as advantages of this method for adoption for large-scale production.

29.4.2 Preparation of paneer using UF process

Paneer is a traditional heat-acid coagulated milk product and it is very popular all over India. Typically paneer is white in appearance with spongy body, close knit texture, possessing sweetish-acidic nutty flavour. Paneer manufacture essentially involves heat/acid coagulation of standardized milk followed by pressing of the coagulum. The existing batch manufacturing technique is labour and energy intensive and is susceptible to environmental contamination.

The process developed involves standardization and heating of milk followed by UF whereby lactose, water and some minerals are removed. UF of milk and the removal of permeate is synonymous to removal of whey by coagulation in conventional method. The concentrated mass, which has about 40 per cent total solids, is cold acidified to get the desired pH. Till this point, the product is flowable and can be easily dispensed into containers with automatic dispensing machines. The filled containers are then subjected to texturisation by microwave heating in a domestic microwave oven. This can also be achieved in a continuous process by using microwave tunnels. Such tunnels comprise of a series of magnetrons under which the product moves continuously on the conveyor belts. The resulting product has typical characteristics of normal paneer.

29.4.3 Preparation of shrikhand by UF process

Chakka and Shrikhand of good sensory quality and meeting PFA standards could be successfully prepared using ultrafiltration technology. In standardized ultrafiltration process, Skim milk is fermented with yogurt culture and it was heated to 60ºC for 5 minute with continuous agitation and ultrafiltered up to around 16.60% TS concentration. Whey is then removed from this concentrated coagulum by hanging it in a muslin cloth (eight layered) at room temperature followed by mild pressing to get chakka. Chakka then kneaded in a planetary mixer with 70% fat cream and sugar to prepare Shrikhand of smooth consistency. UF process resulted in nil fat loss in whey and 20.70% extra recovery of total solids in chakka.

29.5 Application of Microfiltration

Microfiltration (MF) is a low pressure membrane separation process for separating colloidal and suspended particles in the range of 0.05-10 microns. MF has been investigated as a competing technology to centrifugation for clarification and bacteria removal of milk and whey. Possible uses of MF include delipidizition of whey, shelf life extension of liquid milk, production of cheese with minimal risk of blowing and without nitrate addition, and several biotechnological applications. In case of traditional dairy products there appears to be no direct application of MF, but it can be used to improve the microbiological quality of milk intended for use in the manufacture of traditional dairy products.

Reference

Dharam pal, (2005). Role of Membrane Processing in Traditional Dairy Products, Souvenir, national seminar on value added dairy products, national dairy research institute, karnal.