BY-PRODUCTS TECHNOLOGY

Module 1. Introductiom

Lesson 1
BY-PRODUCTS AND ISSUES INVOLVED IN THEIR UTILIZATION

1.1 Introduction

A dairy by-product may be defined as a product of commercial value produced during the manufacture of a main product. Skim milk, buttermilk, ghee residue and whey are the main dairy by-products as shown in Fig. 1.1. Utilization of dairy by-products improves plant economy, makes valuable nutrients available for humans and reduces environmental pollution originating from dairy waste. Conversion of edible substances into non-food items is not ordinarily justifiable, especially in countries, where there is an overall shortage of milk supplies. It has always been realized that economic disposal of by-products is an essential prerequisite to profitable dairying. Each and every component of milk must be judiciously processed into edible form for the obvious reason of its unique nutritional value. These by-products are, therefore, receiving increasing attention for their proper utilisation by the research workers all over the world. However, it should be recognized that just because it is technically feasible for any dairy by-product to be processed into interesting by-products, it does not mean that we can utilize it. Processing of by-products needs to be economically feasible, if one is to invest capital and resources into a programme to utilize them. Therefore, further emphasis needs to be put on cost effective processing and utilization technologies of dairy by-products.

In some countries like India, the most of problems associated with the production and utilization of dairy by-products are: a low per capita availability of milk, higher proportion of buffalo milk, poor quality of raw milk, lack of organized manufacture of products, lack of adequate technology, high cost of new technologies, lack of in-house R & D, lack of proper infrastructure, lack of indigenous equipments and plants etc. Before setting up a by-product factory, it is important to consider the economical aspects of the plant, because sometimes the cost of manufacture of the by-product may be more as compared to the by-product and, therefore, the setting up of the by-product plant is not economically feasible. But with advancement in science and technology as also the automation of plants, the economic feasibility of these can be improved.

1.2 Skim Milk and Its By-Products

Skim milk is produced by separation of cream from milk in dairy processing. Skim milk is rich in solid not fat (SNF) content and is used for standardization of milk, preparation of skim milk powder and coffee whitener. It is regarded as a by-product only when it is either not economically utilized or has to be utilized for the manufacture of derived by-products like casein in small quantities.

1.2.1 Casein and caseinates

These are prepared from skim milk and used in food preparations, specialized foods and manufacture of plastics etc. The technology of production of caseins from cow milk is well established. But when the milk is from buffalo or other animal origin, some technological modifications are required in the manufacture of casein from them. The R & D work on this aspect is very limited and is not available freely. This has been one of the limitations for production of edible casein from milk sourced from animals other than cow. Further, it is very difficult to control all the processing parameters when this product is manually prepared. For good quality product, large, mechanical and automatic plants have been developed. For using these plants economically, there has to be some minimum handling of milk of about 2 lakh litres per day. Also there should be facilities for proper utilization of whey that emerges in large quantity. Unless these conditions are met, casein production may not be techno-economically feasible. Additionally, in many countries, the technology and manufacturing plants need import that is costly and not all the time convenient.

The economic constraints for the production of spray dried caseinates are their high drying cost, low bulk density and high packaging, storage and transportation costs.

1.2.2 Co-precipitates

The technology of production of co-precipitates from skim milk is well established all over the world. However, their poor solubility especially of the high calcium co-precipitates, has been mainly responsible for their non-acceptability and so non-production on commercial scale.

1.2.3 Protein hydrolysates

Protein hydrolysates are the breakdown products of protein in the form of peptides and amino acids as a result of hydrolysis of protein either by acid, alkali or proteolytic enzymes. Acid and alkali hydrolysis of protein results in complete or partial destruction of some and racemisation of most of amino acids. These processes also pose problem of removing residual acid from hydrolysates. Bitterness, which is a natural consequence of enzymatic hydrolysis of protein, is the main hindrance in the production of an acceptable protein hydrolysate. Expert specialized knowledge of different available proteolytic enzymes is necessary for developing good quality protein hydrolysates through enzymatic hydrolysis.

1.3 Whey and Its By-Products

Whey, the greenish translucent liquid is obtained during the manufacture of cheese, casein, chhana, paneer, chakka and co-precipitates and has been viewed until recently as one of the major disposal problems of the dairy industry. Due to the presence of significant amount of organic matter (6-7% total solids) in the form of protein, lactose, fat, minerals and water-soluble vitamins, its disposal causes environmental pollution. The biological oxygen demand of whey is very high (40,000 mg/kg or more), constituting a major economical burden to be disposed of as a waste material.

The quantity of whey produced is sometimes not sufficient to utilize it economically. Hence, the utilization of whey is not taken up in a significant way in such circumstances. Further, in view of the low total solids content of whey, there has been a gross lack of interest in its utilisation compared to other fluid by-products of dairy industry. However, due to high cost of processing and handling, a large amount of whey is disposed off as raw whey.

However, whey being a source of precious nutrients like lactose, whey proteins, minerals and vitamins, some economical prepositions have been evolved to utilize it. Utilization of this by-product in the human food chain is now being predominantly favoured due to the economic opportunities provided by the milk nutrients contained in whey. It is the base material for manufacture of not only nutritional products like whey protein concentrates (WPC) and lactose, but also the base for manufacture of whey drinks and dietetic beverages.

Despite significant gains in the amount of whey being processed, a large amount of current whey production still is disposed of as raw whey. Much of this represents production of small plants, where the cost of purchasing, processing as well as the subsequent transportation and handling clearly exceeds the value of any whey product that might be produced. In small plants, the choice remains some form of disposal, be it municipal treatment, spreading raw whey on local farmlands for its nutrient value or feeding to local livestock. Further, acid whey, like cottage cheese whey, because of high mineral content and low pH, poses considerable difficulties in utilization and, therefore, mostly remains unutilized. Neutralization is possible; however, the process adds to the expense, changes the whey characteristics, and introduces more sodium ions. The high level of minerals (0.7-0.8%) present in whey also restricts their commercial utilization in many applications. A major problem with many whey-based products is their salty flavour owing to their high mineral content.

1.3.1 Whey drinks

A variety of whey based beverages consisting of plain, carbonated, alcoholic and fruit flavoured have been successfully developed and marketed all over the world, because they hold great potential for utilizing whey solids. The predominant types of new whey drinks are based on blends of fruit juices and whey. Other types of whey-containing beverages currently available on the market in various countries include products from deproteinated ‘milk serum’, fermented dairy-type beverages containing whey, and flavoured milk-type products containing whey or whey components. Manufacture of fermented whey beverages such as soft drinks, whey wine, beer like products and low alcoholic beverages appear to be most economical and viable process for returning the wasted milk nutrient into value added products among various innovative microbiological process of whey utilization. Although alcoholic whey beverages may still be available in certain local markets, products like whey beer and whey wine appear to be of limited importance. Whey-based liqueurs may become an important product in the near future.

Whey drinks contain valuable and nutritious whey proteins, but do not have large market value; they can be utilized only on small scales. Technological problems may be encountered also when the desired formulation contains additional components that interfere with processing or final product quality. Flavour losses with some fruit juices containing whey drinks may be encountered in UHT processing of the product, especially in the direct type machines employing a flash cooling vacuum chamber.

1.3.2 Concentrated and dried whey

Drying extends the shelf life of the whey, simultaneously reducing its weight and volume. This reduces the cost of transporting and storing the product. The advantage of processing whey into powder is that there are no by-product residues to be treated separately. Basic disadvantages include expensive equipment and energy, both of which requires a large processing capacity yet command relatively low prices for the final product when compared to other products such as whey protein concentrates. The evaporation of large quantity of water to convert the whey to dried form is found to be uneconomical with the conventional evaporators due to high evaporation cost. In the manufacture of dried whey more than 50% of energy consumed is required at evaporation stage therefore the cost of energy required for the evaporation of whey is a major factor determining the production of whey powder. Hence it is important for the economic production of whey powder to ensure that evaporators are operating at their maximum capacity and efficiency.

1.3.3 Ultra filtration processing of whey

Separation of whey proteins is typically achieved by ultrafiltration (UF)or diafiltration to produce whey protein concentrates (WPC), which have many applications in the food industry. By UF process, a highly functional WPC is produced as the primary end product for a wide variety of applications as a substitute for non-fat dry milk and other protein ingredients. Increased production of whey protein concentrate warrants its greater application in food products.

UF membrane technology is economically feasible only for large scale processing of whey, because the product yield is very low. Although UF of whey has been in commercial use since 1972, the industry has been slow to adopt it because the process generates a UF permeate as a by-product rich in lactose and minerals that creates a waste disposal problem, almost equal in magnitude to the disposal of whole raw whey.

1.3.4 Demineralized whey

Ion-exchange and electrodialysis processes are used to demineralize whey. These processes can be utilized only for large scale operation and their high capital cost, high running cost and the problem of resultant effluents are the main limitations of these processes. Economic feasibility of production of demineralized whey lies in its utilization in value added products only.

1.3.5 Lactose

Lactose production from whey can be economically feasible only when it is produced on large scale. Generally, sweet whey is preferred because of its high lactose and low ash content. In case of acid whey, neutralisation is necessary. This will change the whey characteristics and also increase the cost of manufacture. Lactose can be produced by using UF permeate as a raw material, but UF permeate, particularly the acid whey permeate, has a very high calcium content. Removal of approximately 50% calcium is necessary to avoid difficulties during evaporation, which makes the process costly.

1.3.6 Milk mineral products

These products are prepared by precipitation of calcium phosphate in whey UF permeate under suitable conditions of concentration, pH, time and temperature. The crystals that first precipitate quickly undergo solid state transitions depending on the conditions to which they are subjected. It is necessary to grow calcium phosphate particles to sufficient size to recover them in a good yield by centrifugation and filtration. Milk mineral products rich in natural calcium and phosphate are valuable nutritional supplements in today’s osteoporosis-sensitive world and are used as a natural calcium supplement in a growing range of food products including milks, yoghurts, canned milk powders and confectionary and health foods. However, their commercial production needs further boost.

1.4 Buttermilk

Buttermilk is the by-product of butter industry. Buttermilk is produced when butter is made by churning cream or whole milk curd. Buttermilk, as a by-product, has very important place in dairy industry and needs proper attention for its judicious utilization. The high nutritional value of buttermilk and increasing public awareness concerning the environmental pollution warrants for the economic utilization of this important by-product. Sweet cream buttermilk that is produced in organized sector is preferred for processing and utilization in different products. The spray dried buttermilk powder is less free flowing and dusty because of high fat content in comparison with skim milk powder. The high fat content reduces the shelf-life of the powder during storage. Desi buttermilk is an important domestic beverage, but it is mainly produced in unorganized sector in small and scattered quantities and is mostly utilized at domestic level.

1.5 Ghee-Residue

Ghee-residue is brownish sediment obtained by filtration of ghee after heat clarification. Major portion of ghee-residue in countries like India is obtained in small quantities, particularly from the scattered small scale household production of desi ghee in villages, which remains unutilized. Ghee-residue from ghee produced at organized sector or at commercial level can be utilized for the manufacture of chocolate burfi, samosa filling etc., but potentiality of its full utilization is yet to be explored.

Selected references

Goel, B.K. and Chouhdary, V.K 1996. Techno-economic aspects of production of salted spiced buttermilk: A promising profit making by-product utilisation. Indian Dairyman, 48 (5): 29-31.
Hoston, B. S. 1995. Whey processing and utilizing. Bulletin of IDF Document No. 308: 2-6.
Prasad, V. 2007. Whey processing. In: Dairy India-sixth edition, ed. P.R. Gupta and Sharad Gupta. Dairy India Yearbook: 244.