CONDENSED AND DRIED MILKS

Module 4. Manufacturing techniques

Lesson 11
RECOMBINED CONCENTRATED MILKS - RAW MATERIALS

11.1 Introduction

Recombination process is applied for production of most dairy products and it has helped in creating new foods and formulations. Recombination is the process of recombining milk fat and milk solids-not fat (SNF) in one or more of their various forms with or without water. This recombination must be made so as to re-establish the product's specified fat-to-SNF ratio and solids-to-water ratio. The recombined process was first used widely during World War II and then onward spreaded worldwide. The main advantages derived are:

(1) It gives better opportunities for transfer of raw material from a surplus area via industrial manufacturing to fulfill demand in deficiency areas for local range of milk and milk products.

(2) It supplements and supports local milk and other products such as vegetable oils and sugars.

(3) It generates possible employment for local population at dairy as well as with related activities, and

(4) It creates goodwill and interest with authorities.

The mixing of milk solids and other ingredients such as sugar with water directly in the proportions normally required in the final product eliminates the costly evaporation step. However, the basic processes for manufacturing remain largely unchanged.

11.2 Raw Materials

Raw material selection is the main factor determining quality of the final product. Therefore, strictly quality criteria with respect to their usual physical, chemical and microbiological specifications along with the recommended standards for the skim milk powders, whole milk powder, butter milk powder and anhydrous milk fat for use in recombined milk and milk products are required to be maintained. In addition, they should have complete freedom from extraneous matter, scorched particles; have bland flavour and highest possible bacteriological qualities.

11.3 Skim Milk Powder (SMP)

The skim milk powder used has to comply with strict requirements. The suitability of SMP can be determined by pilot scale batch production of the product. The powder must have been made from skim milk that is heated so intensely (e.g., for 1 min at 130°C) that the recombined concentrated milk after its homogenization is sufficiently heat stable. The count of B . stearothermophilus spores should be so low that a moderate sterilization of the evaporated milk suffices. Skim milk powders of normal composition, in association with specific functional properties, generally ensure satisfactory performance and keeping quality. Depending on storage conditions, changes may occur in properties which influence manufacturing of recombined products even with well prepared powders. Hence, it is recommended that storage temperature should not exceed 28°C. Other requirements are

(1) Skim milk powder used should be medium and low heat type depending upon viscosity desired in end-product.

(2) Good reconstitutability is another required quality parameter.

(3) The factors like region and time of production of SMP are usually more important for recombined SCM.

(4) Other powder properties like fines content, bulk density, solubility index affecting dissolving properties are also important.

(5) Control of viscosity and poor solubility of powder is possible with less flexibility by blending different lots of powders. Higher viscosity can be obtained by using SMP which is made employing preheating temperature 85-125°C for >4 min. Also increased true protein content with preheating intensities results in higher apparent viscosities.

(6) Age thickening is a defect entirely determined by SMP used as raw material in sweetened condensed milk preparation. Hence a test giving idea about the behaviour of powder towards this defect which determines the Age Thickening Ratio (ATR) is suggested. Also the pyruvate content of SMP which indicates level of enzymes affecting shelf life of product should be checked.

(7) Viscosity of recombined concentrate used for preparing recombined WMP before spray drying is an important quality factor, which is largely due to properties of proteins and proportion of SMP added. Optimum choice is a low-heat or medium to low-heat SMP of uniform total protein content (~ 37 %).

11.4 Full Cream Milk Powder (WMP)

Use of full cream milk powder for reconstitution, possibly avoids need for further homogenization and offers other advantages including ease of handling, transport and storage of a single raw material.

Recent developments in spray drying techniques like agglomeration and instantization have enabled the industry to use WMP for reconstitution purposes, which was facing difficulty due to dispersion problem at high concentration, loss of solubility, foam formation and oxidized and stale flavour development during storage. Improved packaging materials and methods of gas packaging have demonstrated best stability during storage.

Full cream milk powders preheated to same level as non fat milk powders give higher viscosity in SCM and hence reduction in preheating conditions is required during preparation. Full cream milk powders having poor physical properties pose problems in dispersion and give sedimentation in SCM.

11.5 Buttermilk Powder (BMP)

In recombined products, only a part of SMP (10-15 %) can be replaced by BMP. It gives fuller, creamier taste due to its emulsifying properties. However >15% BMP added for recombined sweetened condensed milk may have a detrimental effect on flavour. In Evaporated milk, it improves heat stability. Looking to its susceptibility to oxidation, BMP should be stored at low temperature and be used within one year from production. Incorporation of butter milk powder improves flavour and stability after preheating of concentrate before spray drying of recombined whole milk powder.

Water activity of powder is the key factor in storage stability and hence moisture content >5 % and storage temperature >30°C should be avoided. For meeting the specifications and dietary needs of consumers, vitamin fortification with Vit. A in the powders is recommended. A safety margin up to 50% is kept in the addition.

11.6 Milk Fat Sources

A range of fat sources is available for recombination, but selection is decided by flavour quality required, ease of handling and cost. ‘Filled evaporated milk’ is also made. A fat different from milk fat is used.

11.6.1 Anhydrous Milk Fat (AMF)

It is a traditional source of fat because of its stability under ambient storage conditions. Keeping quality can be enhanced by protecting it from air (O₂) and packing under nitrogen. Greater peroxide formation in neutralized oils has been shown and hence a standard is to be fixed for maximum sodium concentration. Temperature < 40°C gives satisfactory storage period. Though restricted legally, antioxidants addition is suggested by some workers. However, their use is unnecessary if AMF is produced and packed correctly with low levels of dissolved head space oxygen. The copper and peroxide contents of the anhydrous milk fat should be low to avoid flavor deterioration.

It is found that the preparations containing ascorbyl palmitate, tocopherol and lecithin has a synergistic effect in controlling peroxide development. The AMF presents no problem provided it meets required specifications. Looking to the importance of AMF in influencing flavour of final product, low temperature (35-40°C) storage and immediate use of liquid AMF after opening the package is preferable.

11.6.2 Soft/Hard fraction

Soft fraction is prepared by fractional crystallization from melted fat. It contains higher proportion of low melting components and hence remains liquid at high temperature and retains dairy identity of recombined milk products but it is less stable. Use of high melting fraction of AMF for better quality recombined WMP is recommended.

11.6.3 Unsalted butter

It has a superior flavour and excellent shelf-life (2 yr.) at < -10°C. However high cost in transport, difficulty in storage, longer thawing period required, possible growth of mesophillic and thermophillic organisms causing protein precipitation (burn-on problem) in melted product and heat stable lipases and proteases limits its use.

11.6.4 Fresh frozen milk fat for recombining (FFMR)

Made solely from fresh cream by modified process to maximize buttery flavour, it combines best features of butter and AMF and is convenient in processing.

11.6.5 Emulsifiers

Carrageenan, lecithin, glycerol-monostearate and alginates in varying concentrations are used to stabilize fat emulsions.

11.6.6 Water

Good quality water, either natural or treated, is essential. High calcium and magnesium levels in water adversely affect protein stability of reconstituted skim milk. Sequestration of hardness of very hard waters is suggested as a method of avoiding protein coagulation.