Study Of Lactose Recovery Processes From Whey Biology Essay

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The disposal of whey is a crucial problem for dairy industries because of strict environment regulations. Management of this waste stream is required implementation with the most economical alternative methods for disposal. At the same time, there is increasing demand of lactose present in the whey. The presence of lactose in whey is responsible for more than 90% BOD of whey. Recovery of this component from whey may solve the problem of whey BOD to some extent. In the present paper, we have described the different processes like; membrane separation, conventional crystallization, anti-solvent crystallization and anti-solvent sonocrystallization for the recovery of lactose from whey.

INTRODUCTION

The treatment of waste water usually coming from small and medium scale manufacturing plants is a very crucial problem because of strict environment regulations. The solution of this problem is a challenge for engineers to purify a process with combination of both economical and environmental acceptability (Giacomol et. al., 1996). One example of process industry is dairy industry, where numerous effluents are generated; out of which few effluents contain nutritionally valuable constituents such as proteins, lactose, fats, etc. One such effluent is whey. The dairy industry involves processing of raw milk into products such as consumer milk, butter, cheese, yogurt, condensed milk, dried milk (milk powder), and ice cream, using processes such as chilling, pasteurization, and homogenization. Typical by-products include buttermilk, whey, and their derivatives. Production of whey in the world appears to be in the order of 85 million metric tons with increasing rate of about 3% per year of cheese production (Guu and Zall, 1984). Among all nations of world, India is also one of the largest producers of milk and dairy products, hence, generates dairy based wastewaters. The production of milk crossed 85 million tones annually in the year 2002 and grows at the rate of 2.8% per annum (Ramasamy et. al., 2004). In India, the production of paneer has been increased substantially, resulting in an increased accessibility of whey. Production of paneer is estimated at 1, 50,000 tones per annum which produced 2 million tones of whey per annum (Goyal and Gandhi, 2009). In 2001, around 2.58 ï‚´ 106 tones of paneer whey was produced only in India (Bund and Pandit, 2007c). The study carried out in Serbia says that 11 big and medium scale dairies produces approximately 43,800 tone/year of whey or milk ultrafiltration permeate, out of which 3,212 tone/year is used for cheese production, 6,096 tone/year as animal food and 34,493 tone/year is discharge into a water bodies (Ostojic et. al., 2005). Whey contains 30,000 to 50,000 mg/liter biochemical oxygen demand (BOD) and a high chemical oxygen demand (COD) which are responsible for high polluting potential of whey and also waste treatment of whey is uneconomical (Bough and Landes, 1976, Kroyer, 1995). The large quantity of whey produced throughout the production of cheese and the increasing capacity of cheese plants make compulsory for dairy product manufacturers either to process whey or to dispose of it under environmental acceptability (Hobman, P.G., 1984). Whey has been considered as a waste for a long time since it has very low concentration of its components and unavailability of technically sound low-cost recovery process. It is estimated that 40-50% of the whey produced is disposed of as sewage or as fertilizer to be used for agricultural lands with the rest being used as animal feed. The main components of whey are 5-6% lactose, 0.8-1% protein, and 0.06% fat and mineral salts with varying concentration (Kargi and Ozmihci, 2006). Disposal of liquid whey is not economical because of high BOD and water content. It is reported that lactose content of whey is responsible for more than 90% whey BOD (Kisaalita et. al., 1990). The most economic way for industries to dispose of whey is to convert it into products which have commercial importance or to recover valuable components (lactose) from whey as lactose has good nutritional and functional properties and can be used in the food industry and in the cosmetic, pharmaceutical, and medical industries (Abolghasem et. al., 2005, Yebo et. al., 2006, Rossano et al., 2001). Therefore, the dairy industry must have to either decrease the lactose content from whey or recover huge amounts of lactose from whey before the disposal of it into the environment (Chollangi and Hossain, 2007). Progresses in market strategies and invention of new technology have made it possible for dairy industry to separate valuable components from whey. However, two trends are very clear. They may be based either on the recovery of valuable components like proteins and lactose, or on the degradation of substances which can change the environmental quality or the water resources negatively (Carta-Escobar et al., 2004). The aim of the present study is to review the process development on the recovery of lactose from whey.

Lactose is a major carbohydrate in the milk and whey. In the dairy industry, lactose is recovered from whey and whey permeates. The pure lactose recovery process generally involves concentration by evaporation, crystallization, separation, refining, drying and milling. Lactose (4-0--galactopyranosyl-D-glucopyranose, C12H22O11) is a disaccharide consist of one glucose molecule linked to a galactose molecule and in aqueous solutions lactose presents in  and  forms as shown in fig.1 (Ganzle et. al., 2008).

Fig.1.  and  configuration of lactose molecules (Ganzel et. al., 2008)

Lactose can exist as either amorphous lactose or crystalline lactose, as either -lactose or - lactose or as a mixture (Dincer et. al., 1999). The physical properties of lactose are shown in Table 1.

Table 1. The physical properties of lactose

Properties

-lactose

monohydrate

-lactose

ref.

Melting point

211

220

Drapier-Beche et al., 1997

solubility at 15 oC

7g/100g

50g/100g

Zadow, 1984

Density

1.540

1.589

Holsinger, V.H., 1999

Specific heat

0.299

0.2895

Holsinger, V.H., 1999

Heat of combustion (Cal/g)

3761.6

3932.7

Holsinger, V.H., 1999

Lactose recovery by membrane separation

Microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO) are the four major membrane processes which have become standard unit operations in the dairy industry. Nanofiltration and reverse osmosis are suitable operations for the treatment of dairy streams and to achieve the set targets like; to concentrate the milk constituents in non-food applications, to produce treated water which can be reused in the dairy industry (Balannec et. al., 2002). Nanofiltration and reverse osmosis are more efficient in terms of lactose recovery but higher operating pressures are required as compared to ultrafiltration which is one of most potential technology in dairy industry. This process has made it possible for dairy based product manufacturers to improve the quality of its traditional products, to create new food stuffs and to utilize the dairy by-product to be used in entire food industry. The application of UF in the dairy industry was started in the 1970s with the separation and concentration of whey proteins from cheese whey to get protein-rich retentate and lactose-containing permeate (Marcelo and Rizvi, 2008). In UF the constituents of whey are separated according to molecular sizes and depending on the retention characteristics of the membranes. The protein and fat fractions are retained well while the lactose, mineral and vitamins are separated in the permeate. When ultrafiltration process was studied for lactose recovery from pure lactose solution with three different size of membrane 3, 5 and 10 KDa made up of cellulose material with surface area of 0.1 m2, the recovery of lactose was found 70-80%, 90-95% and approximately 100%, respectively (Cholangi and Hossain, 2007). The yield of lactose may depend on the initially content of minerals which can influence lactose solubility in supernatant liquor during crystallization. These minerals, which decreased efficiency of recovery, can be removed by nanofiltration. Nanofiltration process was found effective for removal of mineral salts from whey (Cuartas-Uribe et. al., 2009). It was suggested that the combined application of ultrafiltration and nanofiltration may be useful in a recovery of lactose from whey (Guu and Zall, 1991). When the process combined of microfiltration (nominal pore size 0.2 μm), ultrafiltration UF3 (molecular weight cut off 5 kDa), ion exchange and reverse osmosis was studied for the recovery and purity of lactose from whey, overall lactose recoverey was obtained 74% with a lactose purity of 99.8%( Souza et. al., 2010). Also, the high product purity and desired yield can be achieved by combination of ultrafiltration with diafiltration (DF). This process includes three steps: (1) a pre-concentration stage, (2) a diafiltration stage to purify the retentate and permeate, and (3) a final concentration stage to maximize the concentration of high molecular weight solute in the retentate (Marcelo and Rizvi, 2008). Though membrane processes yields high lactose recovery, they are uneconomical process for the treatment of the whey in concern with small and medium scale dairy processors as membrane processes involve high capital and recurring costs due to limited membrane life and higher operating pressures (Bund and Pandit, 2007b). Despite the high removal of lactose, concentration of milk ions and COD level in permeate remained too high even with reverse osmosis membranes. Therefore, in a single membrane operation, it is difficult to produce water which can be reused in diary industry (Balannec et. al., 2002). Another disadvantage of the membrane separation process is that the retentate obtained is a mixture of whey proteins and lactose and other components which cannot be economically separated and exploited commercially to obtain pure components.

Lactose recovery by crystallization

Crystallization is a two-step process includes (1) nucleation and (2) growth of nucleus to a macro size. First step involves the activation of small and unstable particles with sufficient excess surface energy to form a new stable phase, which may occur in supersaturated solutions as a result of mechanical shock, the introduction of desired type of small crystals (seeding), or in the presence of certain impurities (Holsinger V.H, 1999). Factors which influences the crystallization processes are; solubility, supersaturation, seeding, crystal shape factor, agitation, growth rate kinetics, nucleation rate kinetics, agglomeration kinetics etc. (Nonoyama et al., 2006). Lactose is mostly obtained from whey for many years by crystallization. The commercial development of a continuous technique for crystallization of lactose from whey is require to offer more economic benefits to comparatively small scale processors (Zadow, 1984). The conventional lactose crystallization has three basic steps (i) Concentration of whey to 50 to 70% solids by evaporation, (ii) Initiation of crystallization, either spontaneously or by seeding with a small quantity of lactose crystals, and (iii) Separation of lactose crystals by centrifugation. The yield and the purity of crystals depend on the protein and mineral contained of whey, the highest purity and best yields can be obtained from deproteinized and demineralized whey (Holsinger V.H, 1999). There were two processes used in the recovery of lactose from cheese whey. One process was based on the assumption that the main constituent to be recovered was lactose, while in the other process the recovery of a whey protein was also assumed to be desirable (McGlasson and Boyd, 1951). During the seventeenth century in 1633, the first record of isolation of lactose was discovered by Bartolettus, using evaporation of whey. During the eighteenth century, lactose became a commercial commodity with the use of lactose principally in medicine (Holsinger V.H, 1999). Weisberg (1954) reviewed the conventional processes for the manufacture of lactose from whey. The process includes concentration of whey up to 40-65% of total solids by evaporation followed by cooling to give crude lactose. This is then re-dissolved, treated with activated charcoal and recrystalized. Yield of lactose by this method was found in the range of 50-60%. When the cheese whey was subjected to electro-dialysis using ion exchange membrane to reduce the salt content up to 60% and concentrated in evaporator to 60% solids, lactose was crystallized followed by the removal of lactose by centrifugation and recovery of lactose was obtained as high as 87.5% (Hull and Grange, 1965). McGlasson and Boyd(1951) studied the lactose recovery from cheddar cheese whey using ion exchange resins and found that the purity of lactose obtained was depend on the original content of whey. Lactose of a higher degree of purity about 97.0% was recovered when the original whey was not treated with ion exchange resins to remove protein. More improved conventional process for the higher recovery of lactose is described by Harju and Heikkila (1990). However, concentration of whey obtained by evaporation causes precipitation of calcium (complex) salts, which results in fouling or scaling on heat exchange surfaces. Furthermore, these insoluble calcium salts contaminates the lactose crystals during successive lactose crystallization operations. Also, due to low solubility of these salts, they are difficult to remove by washing with water. Hence, pretreatment of whey permeate must be done either before or during evaporation (Hobman, 1984). Also, this process is not only uneconomical because of the high evaporation costs but also takes longer crystallization time from 12 to 72 h. Additionally, the purity of the lactose is significantly influenced by the properties of the initial whey and its protein and mineral content. A few attempts have been done to develop processes for the lactose recovery, different from conventional cooling method (Bund and Pandit, 2007a).

Recovery of lactose by anti-solvent crystallization process

The crystallization process in which the organic products are separated from aqueous solution by adding non-solvent compounds which reduce the solute solubility without creating the new liquid phase is known as anti-solvent crystallization. The nucleation and the nature of the crystalline product depend on the conditions of crystallization process under which the material is crystallized. Hence, variations in yield of product can be observed by varying the operational parameters such as supersaturation, temperature, pH, and impurity content. The main problem associated with the lactose crystallization is a long induction time and large meta stable zone width (MZW). Raghvan et. al. (2001) has studied the bulk crystallization of lactose from aqueous solution with varied crystallization temperature (293-313 K) for total crystallization time (22-72 h) and found that the maximum possible yield of lactose was obtained 20-57 %. The long induction time (2-17 h) and extremely slow growth of lactose crystals was also observed. When sodium hydroxide was added to solutions containing lactose and manganese chloride, insoluble manganese hydroxide and lactose as a complex precipitated. Maximum lactose recovery was found to be 55% at molar ratios of sodium hydroxide to manganese chloride at 2.0 and manganese chloride to lactose at 4.0 (Yanaga and Bernhard, 1981). Cerbulis (1973) was applied Steffen process for the recovery of lactose from cheese whey and found that 81% of lactose was precipitated in a cold precipitation step at temperature 3-5 oC. When precipitant CaO was used in combination of FeCl3, lactose yield was improved to 87-95%. Addition of equal volumes of acetone or methanol gave almost complete precipitation of lactose from whey. Recovery of lactose explored with different anti-solvents is shown in Table 2. The solubility behavior of lactose explored in ethanol-water mixture (Machado et. al., 2000) and acetone-water mixture are shown in Fig.2 and Fig.3. In these studies, it was found that the lactose recovery was greatly influenced by anti-solvent (ethanol or acetone) concentrations. Higher recovery of lactose was attributed to the lactose solubility in solvent, which was substantially decreased with increase in anti-solvent concentration. Variation in the crystallization time and seeding was found to be affected the size distribution of lactose crystals. However, Conventional anti-solvent crystallization includes mechanical agitation, which introduces random fluctuations in the solution and cause heterogeneous distribution of local concentrations, leads to uneven growth of crystals and causes variation in the particle size and morphological features due to poor-mixing (Dhumal et. al., 2009).

Table 2. Recovery of lactose explored with different anti-solvents

Anti-solvent concentration

Sttiring

Speed

(RPM)

Initial lactose

solution

Crystallization

time

Temperature

Lactose recovery

References

Ethanol (85%)

750-1000

19.8% lactose in

concentrated whey

5 h

7 ± 2 oC

92.63 %

Bund and padit, 2007a

Acetone (85%)

500

10% lactose in

concentrated whey

3h

5± 1 oC

91.23%

Patel and Murthy, 2010

Acetone (65%)

-

18-20% lactose in

Concentrated whey

3.5 h

-

85%

Holsinger, V.H., 1999

Acetone

350

27.02g/100g of

solvent(Reconstituted

lactose solution )

2.9 h

20 oC

90.63%

Brito and Giulietti, 2007

Ethanol (80%)

-

30% concentrated permeate of a whey by ultrafiltration

3h

Room temperature

88%

Singh et. al., 1991

Fig. 2. Experimental ternary phase diagram for the system a-lactose/ethanol/water (Machado et. al., 2000).

Fig. 3. Lactose-water-acetone triangular diagram (Brito and Giulietti, 2007).

Recovery of lactose by anti-solvent sonocrystallization process

To develop an economical process of lactose recovery, recovery should be rapid from low initial lactose concentration of whey (less evaporation cost) and high purity of recovered lactose should be achieved in the first step of crystallization itself (Bund and Pandit, 2007b). The research and development in application of power ultrasound to chemical processes has progressed rapidly in the past few years. The interest arises in this field is due to the need of environmentally clean technology which can offer possibilities for cleaner chemical processes with improved product yield and quality. One such application is the use of ultrasound waves to control the process of crystallization known as sonocrystallization (Mansour and Takrouri, 2007). The main effect of ultrasound is used to influence the initial nucleation stage of crystallization, which is widely used now a day, at laboratory scale for an anti-solvent based crystallization process. Ultrasound irradiation induces acoustic streaming, micro streaming as well as highly localized temperature and pressure within the fluid. These ultrasonic effects have considerable benefits to crystallization process like; rapid induction of primary nucleation, reduction of crystal size, inhibition of agglomeration and manipulation of crystal size distribution(De Castro and Priego-Capote, 2007). When an ultrasound wave propagates in the liquid medium, cavitation phenomena occurs in it. On the collapse of cavitations, the shock wave and microjet produces from local high pressure of the cavitation, accelerates the motion of the liquid molecules and increase molecular impacts, which enhances the nucleation (Patel and Murthy, 2009). Some postulates suggest for the application of ultrasound wave in crystallization are; (i) rapid local cooling rates, 107 - 1010 Ks-1, play a important part to increase supersaturation; (ii) high localized pressure reduces the crystallization temperature, and (iii) the cavitation events overcomes the excitation energy barriers associated with nucleation (Ruecroft et. al., 2005). It was also reported that ultrasound has a significant effect in reducing induction time and narrowing the MZW when the mixing conditions are improved (Lyczko et. al., 2002). But a general phenomenon observed is that the crystal size in the presence of ultrasound is always decreased by shock waves and abrasion between crystals and the shape of crystals is changed by ultrasound (Guoa et. al., 2005). Typically, this occurs in anti-solvent based crystallizations process where the anti-solvent is added to the point of precipitation, which can lead to high supersaturation levels. For such a process, it has been shown that significantly less anti-solvent can be used in combination with ultrasound to induce crystallization for a number of molecules. The ultrasound induced crystal nucleation can be compare with seeding of crystallization as the main effect of seeding in crystallization is narrowing of the MZW, shortening of induction times, and control of particle size and distribution (Ruecroft et.al., 2005). For industrial crystallization processes, ultrasound can be used to induce the nucleation of materials which are difficult to nucleate spontaneously. Moreover, the use of ultrasound in crystallization avoids seeding, which avoids the introduction of foreign particles into the solution (Lyczko et. al., 2002). The advantage of sonocrystallization is that it needs only lower cost apparatus with relatively small and simple shaped crystallizer which are easily cleaned after usage. This advantage is important to fulfill the hygienic requirements of the preparation of pharmaceutical crystallization products (Li et. al., 2003). Recently, the recovery of lactose with the help of ultrasonic wave using different anti-solvent ethanol (Bund and Pandit, 2007b) and acetone (Patel and Murthy, 2009, 2010) has been studied either in reconstituted lactose solution or whey. The different parameters like initial lactose concentration, pH of samples, anti-solvent concentration and protein content of solution were analyzed. Bund and Pandit (2007b) have studied the lactose recovery from 17.5% w/v reconstituted lactose solution in an ultrasonic bath (22 kHz) with 85% v/v ethanol as an anti-solvent and found that sonication led to early crystallization (91.48 % w/w recovery) of lactose as compared to 14.63% w/w recovery for unsonicated (mechanically stirred samples) at the end of 5 min (Fig.4). Another study of lactose recovery from the 16% v/v reconstituted lactose solution in 80% v/v acetone as an anti-solvent (Fig.5) found that 83.01% w/w of lactose recovery obtained in sonicated samples as compared to non sonicated samples only 38.96 % w/w at the end of 4 min of crystallization time (Patel and Murthy, 2009). Based on these studies, the process parameters for the recovery of lactose from whey obtained from small scale dairy processors were optimized using Taguchi methods in ultrasound assisted crystallization. Bund and Pandit (2007c) were studied various process parameter for optimization using L12-orthogonal array in 85% v/v ethanol as an anti-solvent for the recovery of lactose from concentrated paneer whey (15-15.5 % w/v) in an ultrasound bath. The responses (Lactose recovery %) were analyzed for higher is better mean values as a option in MINITAB Software. The optimum process parameters were found deproteination (in presence of CaCl2 ) at level 2, crystallization time (20 min) at level 2, crystallization temperature (7±2 -C) at level 1, initial pH(pH 4.2±0.2) at level 2, end pH(pH 2.8±0.2) at level 1, stirring(250-300 rpm) at level 2 and seeding (1%, w/w). At these operating parameters the lactose recovery was found 90.3%. The rank of process parameters, which influenced the lactose recovery was found in order as seeding>deproteination step>stirring>initial pH>sonication time>crystallization temperature>end pH. The parameter seeding influenced the lactose recovery most and end pH had the least effect. In other study, the optimization of various parameters was carried out using L9-orthogonal array for the maximum recovery of lactose from whey in an anti-solvent acetone using sonocrystallization, the optimum parameters were found initial pH of sample (6.5) at level 3, initial lactose concentration (15 %w/w) at level 3, acetone concentration (75 %v/v) at level 2 (75 %v/v) and sonication time (15 min) at level 3. The maximum recovery obtained at the optimum conditions was 89.03%. The percentage contribution of various parameters towards the maximum recovery of lactose was found in order as: solvent concentration > sonication time > initial pH of samples > initial lactose concentration (Patel and Murthy, 2010).

Fig. 4. Effect of time on lactose recovery in sonicated and non-sonicated samples (Bund and Pandit, 2007b).

Fig. 5. Effect of time on sonicated and non- sonicated samples.

The rapid crystallization proposed in the presence of ultrasonic waves was due to rapid mixing of the anti- solvent with the lactose solution lead to rapid precipitation of lactose. Cavitation events such as micro streaming and acoustic streaming and high localized temperature and pressure within the mixture of anti-solvent and lactose solution caused early nucleation which was responsible for higher recovery of lactose. Also, cavitation bubbles themselves acting as crystal nucleation sites. The size and shape characteristics of the lactose crystals were improved. Crystal size distribution was influenced and narrow CSD was observed (Bund and Pandit, 2007b, Patel and Murthy, 2009, Patel and Murthy, 2010, Dhumal et. al., 2008). The morphology of the recovered lactose sample was observed rod shaped crystals as shown Fig.6.

Fig. 6. SEM photomicrograph of seed crystals harvested after sonication for 45 s (Dhumal et. al., 2008).

Advantage of ultrasound assisted crystallization is that the process completed rapidly with aid of ultrasound at the ambient condition. However, the capability of ultrasound penetration in the fluid is very less about 10 cm and the effective sonication volume is approximately 500 ml for a single probe with 1000W electric power. Yet, there is a prediction that the rapid sonocrystallization can be used at industrial scale also for batch and continuous processes which can be achieved by increasing the number of ultrasonic probes or by making the fluid flow over probes in a tube (Li et. al., 2003).

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