Australasian Biotechnology (backfiles) AusBiotech ISSN: 1036-7128 Vol. 11, Num. 2, 2001, pp. 29-31

Australasian Biotechnology, Vol. 11 No. 2, 2001, pp. 29-31

BIOPROCESSING

Md Monwar Hossain* and Zaid Saleh

Natural Products Processing, Industrial Research Limited, P O Box 31-310, Lower Hutt, NEW ZEALAND
* Author to whom all correspondence should be addressed: Telephone: (64-4569000), Fax: (64-4-5690132); email: m.hossain@irl.cri.nz

Abstract

Application of a foam separation technique was evaluated in concentrating proteins from a whey permeate solution, which is considered a low-value effluent in the dairy industry. This was performed in a 75 mm diameter, 530 mm long glass column fitted with a stainless steel sparger that bubbled air through the system. It was possible to produce an enrichment protein fraction with a few times higher concentration and a residual solution with a significantly smaller concentration compared to that in the original feed. Concentration of proteins in whey permeate was performed with undiluted as well as diluted feed solution and it is shown that higher enrichment (about ten times) is achievable if the feed solution is diluted two times before foam separation. However, this resulted in an increase in residual protein concentration with reduced percentage recovery.

Introduction

Recovery of high-value components from natural sources or from industrial waste process solutions can be achieved by applying methods based on adsorptive bubble separations (Brown et al., 1990; Gehle and Schügerl, 1984; Okamoto and Chou, 1979; Sarkar et al, 1989;Wilson and Clark, 1987; Lemlich, 1968 and Halling, 1981). The attractiveness of foam-based processes, compared to other separation processes like adsorption, ion exchange, precipitation and ultrafiltration, is due to several technical and economic advantages. These are simplicity, ability to concentrate and separate, need for minimal additives (less contamination), low capital and operating costs, non-thermal nature; all these make it suitable for processing of food and dairy products.

The foam separation processes are still being investigated as waste process streams in many food and dairy industries contain small amounts of valuable components, which need to be recovered for economic and environmental reasons. Efficient recovery of these components not only reduces the waste stream BOD, but can also create a potential source of valuable products. One such waste stream is the whey permeate solution generated when whey protein concentrate (WPC) is ultrafiltered. This contains lactose, minerals, amino acids, peptides and low concentrations of small proteins, such as a-lactalbumin.

The treatment of this stream offers the opportunity to examine the ability of a foam-based technique to concentrate/ separate proteins (surface-active components) from an “industrial” sample. Foam separation concentrates the components of a solution by utilizing differences in their surface activities. A schematic diagram of a foam separation column is shown in Fig. 1. The process stream is introduced into the column and gas is forced into the solution through a sparger at the bottom of the column. The bubbles are formed and the liquid around them is enriched in the surface-active component. This enriched liquid is carried with the bubbles as they rise through the solution to form a layer of foam at the top of the liquid. As the foam rises above the foam-liquid interface, some of the entrained liquid drains off due to gravity. When the foam bubbles are collected and allowed to collapse, the liquid is concentrated.

In this paper, the results of a treatment process, using a foam column fitted with a stainless steel frit for bubble generation and operated in a semi-batch manner, with the whey permeate solution is presented. The performance of this separation is discussed in terms of the parameters: enrichment factor, percentage recovery, residual ratio and foam produced of a protein, a-lactalbumin, from the whey permeate solution.

Figure 1. Schematic of a batch foam fractionation column.

Performance Characteristics

To evaluate the performance of the separation the following criteria are considered. Enrichment (Ef) is defined as the ratio of foam concentration to that of initial feed.

On the other hand, recovery (PR) is the fraction of feed protein recovered in the foam. It determines the efficiency of the process and is given by

where Kd is the distribution coefficient, defined as the ratio of protein concentration in foam to that of the residual solution, Vr and Vf are the respective volumes of the residue and foam after separation.

The residual ratio (RR) is also considered as a measure of the residual concentration with respect to the original feed concentration:

RR =Concentration of protein in the residual solution Concentration of protein in the initial solution (3)

The volume of the foam produced is also a measure of the performance as this relates to the loss of liquid from the initial solution.

Experimental

Materials and Apparatus

Whey permeate solution: Puhoi Valley Cheese Co., North, Auckland, New Zealand

Proteins: (a−lactalbumin and ß-lactoglobulin, Sigma Chemical Co., USA

Foam Column: Glass column, 75 mm diameter and 530 mm height

Stainless steel Frit: Mean pore size 10µm, from Alphatec Systems Co. (USA)

pH Meter: PHM64 Research pH Meter, Copenhagen, Denmark

Pressure Regulator: Norgren (0 - 1.6 bar), Germany

Rotameters: Fisher 1100, Croydon, England

HPLC System: HPLC-Hewlett Packard 1050 Ti, USA.

Resource RPC column: Pharmacia Biotech AB, Sweden

Foaming Experiment

The feed solution was prepared batchwise in a container. Reverse osmosis (RO) water was used for dilution of the feed. The foaming experiment was conducted by introducing the feed and compressed air supply into the column. The temperature of air and the feed was kept at the desired temperature by circulating them through coils maintained at that temperature. The experiment was continued until no more bubbles were carried over.

Analysis of whey permeate samples

A HPLC (HPLC-Hewlett Packard 1050 Ti) system was used for the analysis of the whey permeate sample. A 1 ml resource RPC column (Pharmacia Biotech AB) was operated at room temperature (RT) and at a flow rate of 3 ml/min. The column was equilibrated in 80% solvent A (0.1% v/v TFA in Milli-Q water) and after sample injection a 1 min isocratic period was applied followed by series of linear gradients to 100% solvent B (0.09% v/v TFA, 90% v/v MeCN in Milli-Q water). Detection was by absorbance at 214 nm and total run time was 20 min.

Results and Discussion

Whey contains a dilute mixture of proteins and is concentrated into whey protein concentrate (WPC). The characteristics of the proteins and their concentrations are given in Table 1. Whey permeate solution is produced when whey protein concentrate is removed by ultrafiltration. The permeate contains lactose, minerals, amino acids, peptides and low concentrations of small proteins, such as a-lactalbumin.

The experimental conditions for the concentration of whey permeate are listed in Table 2. The effect of two airflow rates on the separation ß-lactalbumin from the undiluted whey permeate solution at a room temperature of 16ºC is presented in Table 3. Both enrichment and foam volume varied only slightly with the change in airflow rate. The percentage recovery and the residual ratio decreased with increasing airflow rate to the column. The effects of higher airflow are: increase in flow of foam and increase in bubble size (Zaid and Hossain, 2000). The larger bubble offers smaller amount of protein to be loaded at the bubble-liquid interface and less liquid to be drained. As a result, the residual concentration is increased yielding lower residual ratio and the foam concentration is decreased. This decrease in distribution ratio along with the larger foam volume significantly decreases the protein recovery at higher airflow rate (Hossain and Glenn, 1998).

The effect of the operating temperature on the process performance at an airflow rate of 1.2L/h is presented in Table 4. This is significant: the enrichment increased by more than 50%, the foam volume reduced by 4 times and the residual concentration decreased by about 2.8 times the original value. The percentage recovery decreased only slightly.

The process performance improved even further when the feed was diluted twice and the process was operated at 1.2 L/h. The enrichment increased by five times, the foam volume decreased and percentage recovery increased slightly; the residual concentration was increased by 3 times compared to the undiluted feed. The possible reasons of this dramatic improvement in enrichment could be attributed to (i) the higher protein adsorption, (ii) the considerable increase in drainage at lower concentration (Hossain and Glenn, 1998b) and (iii) less interference from the non-protein components. All these results suggest that there will be a compromise among the factors: dilution ratio (how many times to dilute the feed), the temperature and airflow rate to be used for processing to obtain the best performance.

Conclusions

It was possible to concentrate a-lactalbumin in whey permeate solution to a moderate degree with a residual fraction at significantly lower concentration than the original feed. The other useful attributes of the separation process are:

• the operating temperature plays a dominant role on the foaming process;
• volume loss in foam is smaller at lower temperatures;
• enrichment factor can be significantly enhanced by diluting the feed;
• the dilution of feed increases the residual concentration compared to the undiluted one;
• the percentage recovery in this process is modest.

References

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13. Saleh, Z. and Hossain, Md. M. (2000). “ Foam Separation of Proteins from Multicomponent Mixtures by a Batch Process”, Chem. Eng. & Proc. (in press).

Acknowledgement

This research was supported by the Foundation for Research, Science and Technology (FRST), New Zealand.

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